Earth and Space 2021: Materials, Structures, Dynamics, and Control in Extreme Environments

Persistent research effort has been devoted for decades in developing materials for the aerospace industry. Among the most crucial requirements in the new generation of aerospace, vehicles are optimizing their structural material stiffness, strength, and fuel-to-weight ratio. Accordingly, it has been established that lightweight polymer-based composite materials represent the ideal alternative to relatively heavy metallic structural alloys. Graphene/epoxy nanocomposites have been attracted much attention due to their exceptional mechanical properties. They have been used in fabricating carbon fiber/graphene/epoxy hybrid composites for improved properties relative to traditional carbon fiber/epoxy composites. This work addresses the interfacial interaction and adhesion in graphene/epoxy nanocomposite materials. This is necessary to investigate and maintain the material integrity at the nanoscale level by tailoring the molecular network structure. Molecular dynamics simulation with a reactive force field was used to quantify the interfacial interaction energy of the nanocomposite constituents, and graphene pull-out simulations were used to determine the interfacial shear strength. It has been shown that surface functionalization of graphene nanoplatelets can significantly increase their interfacial adhesion with the hosting epoxy matrix. The results show that there is a tremendous improvement in the functionalized graphene/epoxy interfacial interaction energy up to ∼570%. Furthermore, surface functionalization of graphene nanoplatelets can improve the interfacial shear strength by ∼750 times. This substantial improvement is from altering the noncovalent graphene-epoxy interfacial adhesion into strong covalent bonding utilizing the functional groups. Furthermore, the wrinkled and rough topology of functionalized graphene is found to improve the interlocking mechanism with the host matrix. These findings are important to the future of synthesizing next generation ultra-strength and lightweight polymer-based nanocomposite materials.

The authors are proposing a comprehensive research approach and terminology for providing a framework to utilize an ordinary portland cement (OPC) alternative class of materials for both extraterrestrial habitats and terrestrial 3D construction applications, where sand and clay can replace regolith. Magnesia-based binders (MBBs) have shown a great promise for use in different additive construction (AC) applications due to its superior properties such as high compressive strength, rapid setting time, and excellent durability, in addition to the possibility of harvesting these binders from lunar and Martian regolith. Our primary objective in this research is to prove the concept of utilizing magnesia phosphate cement (MPC) composites with different additives, including boric acid, graphene nanoplatelets (GnP), acetic acid, and potentially Martian and lunar regolith simulants as a potential construction material for the planetary habitation exploration missions. Before adjusting the mix design properties required to meet specific 3D construction printing needs, several aspects must be studied in depth to provide a better understanding of the MPC paste and composite behavior. This work aims to give more insight into the relative physical, mechanical, thermal, and chemical performance of the MPC pastes with varying additions of boric acid. The experimental results show that boric acid can change the phase compositions of the MPC paste and affect its performance. It can improve the initial setting time of the paste and alter the structure of its binding products. Finally, our proposed research creatively utilizes artificial neural networks (ANN) to investigate and subsequently optimize both the MPC pastes and composite formulation for real-time adjusting of 3D printing processes based on the desired material performance criteria.

The advent of the use of complex and hypercomplex algebras for arbitrary order sensitivity computations provide a new and perhaps more efficient approach to estimate uncertainty. The basic concept is to explore probabilistic moment approximations of multivariable structure and material models, using high order, below sensitivity results from the hypercomplex finite-element method. The utilization of hypercomplex derivatives allow probabilistic moments to be estimated in a single simulation run, compared to Monte Carlo sampling, which can be computationally expensive for complex models. These moment approximations, specifically expected value, variance, skewness, and kurtosis, are used to estimate the probability density function of structure and material models using the generalized lambda distribution. Criteria to determine optimal order of approximation and parameter importance will be proposed and examined. These moment approximations can also be an efficient proxy for variance based Sobol indices. Sobol indices provide an estimate to the individual contribution of each input parameter to the output variance and identify non-important variables that can be fixed at their nominal values to reduce model complexity. For high dimensional models, the direct application of traditional variance-based global sensitivity analysis measures can be time consuming and impractical, whereas a sensitivity-based estimation can provide a low-cost meaningful substitute. An uncertainty quantification analysis is conducted on a fracture mechanics related effective modulus application.

Establishing infrastructure on the lunar surface requires construction materials and methods that are appropriate for the Moon’s remote and austere environment. Construction approaches that maximize the use of the Moon’s in situ resources along with in-space manufacturing technologies provide benefits to long-duration exploration compared to other construction approaches that require greater material transport or prefabrication. These benefits include reduced launch mass, increased infrastructure flexibility, and greater potential for repair and reconfiguration. This paper evaluates a novel bio-composite material, biopolymer-bound soil composite (BSC) for additive construction (3D printing) applications. The use of the BSC’s rheological and strength properties to predict shape stability and rate of structural buildup are discussed. These material attributes dictate the building time and maximum size of the lunar projects, as well as the required capabilities of the automated construction systems used to build an autonomously constructed facility. Preliminary results of rheological and strength testing experiments are included in this paper as a first attempt to begin understanding the properties of the extruded BSC.

Provoked by recent advancements in additive manufacturing, 3D printable concrete has been explored as an alternative method to construct concrete structures. 3D printing of cementitious materials has the potential to address several major challenges faced by the current concrete industry: (i) it eliminates the use of formwork (mold) and vibration that are typically necessary for consolidating wet concrete, which can in turn significantly reduce material and labor costs involved in the formwork construction; (ii) the highly automated construction process can reduce the material waste, cut down construction time, and reduce human error; in addition, (iii) it allows a new approach for concrete design–the composition and property of printed material can be parametrically varied from one location to another, tuning to the optimal structural performance and functionalities. In the last decade, some showcase examples have became available–e.g., WinSun, XTree, TotalKustom, Smart Dynamic Concrete, as this new construction technology becomes more commercially and economically feasible.

Building infrastructure outside the known environment on Earth poses challenges that must be dealt with in order to safely protect the habitants and equipment. One of the issues that must be dealt with on the Moon and Mars, for example, is the influence of reduced gravity. For the first time, work is presented that helps understand the influence of reduced gravity on the hydration of a tricalcium silicate (C₃S) paste, an important component of cement. The C₃S samples were mixed in the microgravity environment on the International Space Station (ISS) and placed within a centrifuge to simulate the gravity of the Moon, Mars, and a statistical point at 70% of Earth’s gravity. In addition to the simulated gravity samples, identical samples were mixed in the microgravity environment on the ISS, as well as a control sample on Earth. Microstructural analysis shows that an increase in gravity level results in less trapped air, as well as smaller pore size distributions.

Assessment of the crashworthiness of the aircraft structure like the wing is important. Nowadays, the finite-element (FE) analysis is widely used in this area. Also, the numerical simulation can aid air crash investigation to exclude some unreasonable reasons. In this work, finite-element models of the wing and slat structures are generated including skin, spars, stringers, and ribs. In every scenario with various fidelity of the mesh of the wing, material model of the birch, and the impact location, the front spar of the wing cut through the tree and the upper part of the tree fell in the direction of the movement of the airplane. The damage to the wing is localized on the leading edge and front spar, while the structural integrality of the wing is maintained. The impact with the birch tree cannot cause significant damage to the wing. This paper exhibits the methodology of modeling and simulating the wing impact against the tree to assess its crashworthiness and explore the possible reason for the accident.

A material model which incorporates several key capabilities required for the predictive simulation of the impact response of composite materials has been developed. This model has been implemented into the commercial transient dynamic finite element code LS-DYNA as MAT 213. The deformation and damage modules of the material model utilize experimentally based tabulated input to define the evolution of plasticity and damage as opposed to specifying discrete input parameters (such as modulus and strength). The deformation module of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a plasticity model including a generalized yield function with a nonassociative flow rule. For the damage module, a strain equivalent formulation is utilized to allow for the uncoupling of the deformation and damage analyses. The terms in the damage tensor are semicoupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. For the failure module, a unique tabulated failure model has been developed which allows for arbitrarily shaped failure surfaces. A systematic series of validation and verification studies, at a variety of length scales ranging from single element simulations to simulations of a flat panel impact test, have been performed to fully exercise and evaluate the capabilities of the developed model.

In June 2019, a full-scale crash test of a Fokker F28 Fellowship aircraft was conducted as part of a joint National Aeronautics and Space Administration/Federal Aviation Administration (NASA/FAA) project to investigate the performance of transport aircraft under realistic crash conditions. The test objectives were to provide data for assessment of transport aircraft crashworthiness under realistic impact conditions and to generate test data for model validation. The test article was loaded with transport aircraft seats in a 3 + 2 configuration. A total of 24 instrumented ATDs were placed in the seats and restrained. The test article weighed 33,306-lb. (15,107.3-kg) and, during the crash test, impacted a 2-ft (0.61-m) high soil bed at 65.3-ft/s (19.9-m/s) forward and 31.8-ft/s (9.7-m/s) vertical velocity. The full-scale aircraft crash test was simulated using the commercial nonlinear explicit transient dynamic finite element code, LS-DYNA. This paper will provide a description of the test article and the crash test conditions, document the F28 full-scale model development, and present test-analysis comparisons. The test-analysis comparisons include inertial properties, kinematic responses, structural acceleration responses, and structural deformation and failure.

Thermoplastic matrix composites (TMCs) exhibit desirable characteristics applicable in the aerospace industry. For processing of TMCs, a wide range of elevated temperatures are typically applied to the material, leading to the formation of internal residual stresses during the final cool down step. These residual stresses may lead to net shape deformations or internal damage. Furthermore, volumetric shrinkage, and thus additional residual stresses, could be generated during crystallization of the thermoplastic matrix phase. This paper investigates the molecular modeling of a polyether ether ketone (PEEK), a high-performance semi-crystalline thermoplastic polymer, to predict the thermal-mechanical properties as a function of temperature and degree of crystallinity. This information is important in multiscale process modeling to establish ideal processing conditions to yield maximal material performance. In this study, the mass density for the amorphous phase of PEEK has been predicted and compared with experimental data from the literature. The PEEK crystallization kinetics have also been reviewed to provide a thorough understanding of the influence of temperature history on degree of crystallization. Finally, a theoretical framework for future work is presented.

This study is aimed at development and testing of concrete made using alkali-activated binders (AAB) and cured at ambient temperatures. Standard test specimens are prepared for evaluating compressive strength, flexural strength, and splitting tensile strength. Numerical models of AAB test specimen are developed in ABAQUS and are calibrated using the experimental results. The numerical models are used for reliability analysis of AAB concrete test specimen using Monte Carlo simulations. The performance functions for AAB concrete for failure in compression, flexure, and splitting tension are derived. The results of the reliability analysis elucidate that the trends in the AAB concrete failure are similar to that of Portland cement (PC) concrete failure, with flexural loading being the governing failure mode. These results instigate a further exploration of AAB concrete as a viable alternative of PC concrete.

China has the most abundant antimony, accounting for 84% of the world. Due to the large amount of antimony ore waste rock produced by perennial mining, the antimony ore waste rock is deposited in the open air and need high treatment cost. The goal of this study is to provide a possibility to utilize the antimony waste rock as a complete replacement for coarse aggregate in high strength concrete. The chemical composition of the antimony ore waste rock is investigated. Then, the C50 concrete mix ratio is designed. The construction performance, mechanical properties, and durability performance are systematically studied. It is found that all indexes meet the requirements of the current national industry standards of China. It is shown the antimony waste rock can be reused as a complete substitute of coarse aggregates for high strength concrete.

To quantify damage to a reinforced concrete (RC) column members after an earthquake, the maximum applied force generated by the earthquake is important information for an engineer. Therefore, in this study, the piezoceramic transducers are used to detect the applied force for an RC column member under dynamic loadings. To investigate the use of postembedded piezoceramic sensors in detecting the force that is applied to RC columns, eight full-size RC column specimens with various failure modes are tested under dynamic loadings that are induced by specified earthquakes. Postembedded piezoceramic sensors are installed at a range of depths (7,080 mm) beneath the surface of a column specimen to examine the relationship between the signals that are obtained from them and the force applied by the dynamic actuator. The signals of the postembedded piezoceramic sensors which correlate with the applied force are presented. These results indicate that the postembedded piezoceramic sensors have great potential as a tool for measuring the maximum applied force on an RC column under an earthquake. Restated, for an RC column in an earthquake, signals that are obtained from postembedded piezoceramic sensors can be used to identify the applied force and corresponding damage or residual seismic capacity.

In the following paper, general principles, methodology, and tools for crash analysis of the large aircraft are presented. Attention was focused on the crash of the Polish presidential airplane TU-154M on April 10, 2010, in Smolensk. The way of finite-element method (FEM) model developing that can be used in crash analysis using LS DYNA software was shown. A Tu-154M airplane geometry model was obtained using reverse engineering methods. Moreover, the parameters of a wingtip, especially a mass and the inertia tensor, have been reverse engineered using drawings and specialized tools for crash analysis. During analysis, the Johnson–Cook material model for structure strength elements and wood material model for a tree were used. In addition, aerodynamic forces were taken into account. An aerodynamic analysis was aimed to take into account the effect of ground proximity and influence of the flow around an aircraft, including tip vortices, to the flight of the unconstrained wingtip.

The objective of this study is (1) to validate the *MAT_224 model for Aluminum 2024 with complex impact conditions; (2) to evaluate its predictability of ballistic limit and residual velocities of a projectile under various impact conditions; and (3) to investigate the effects of oblique and attitude angle variations of a projectile on penetration to a target plate. The newly developed *MAT_224 model version 2.0 for Aluminum 2024 was utilized to simulate a series of ballistic impact tests conducted by NASA using a rectangular block projectile of Inconel 718 with sharp edges and corners, impacting Aluminum 2024 flat panels at oblique angles of incidence. A full ballistic impact simulation model was created with over twenty million solid elements and used to conduct approximately one hundred ballistic impact simulations. Overall, the ballistic impact simulations showed highly comparable results with the NASA tests in terms of projectile residual velocities, failure shapes of the target plates, and projectile penetration behavior. Based on a series of ballistic impact simulations, the ballistic limit velocities of the projectile were predicted.

The Federal Aviation Administration has regulations designed to protect aircraft occupants in the event of a crash. Two drop tests of barrel sections and a full-scale test of a Fokker 28 (F-28) small regional jet airframe performed by the National Aeronautics and Space Administration provided full-scale crash data on the performance of transport category aircraft seating systems. The crash pulse measured at the floor and the performance of the seats differed from the certification tests. To assess injuries, lumbar loads, neck loads, and head accelerations were collected for most anthropomorphic test devices (ATDs), and a range of occupants were included for comparison. Overall results were positive in that the seats were able to maintain their attachment to the aircraft with the ATDs measuring head accelerations that would be considered acceptable during certification testing; however, most had spinal loading above the lumbar load criteria. This testing demonstrated that seats dynamically qualified for lower impact severities (14 G) were able to maintain structural integrity but were not able to control injury risk in all seating configurations.

Vehicle operations in dynamic environments have inherent risks to the occupants. Whether these risks are associated to whole body injury from an emergency landing or to the neck for a passenger seated in a side-facing aircraft seat, mitigation techniques must be developed. This is also true when trying to assess the safety consequences of an unmanned aerial system (UAS) impact to a non-participating bystander. In 2016 the Federal Aviation Administration published the Part 107 rule covering the operations of small unmanned aircraft systems (sUAS). One of the limitations imposed was the prohibition without further considerations on the operations over people. The rule identified that research was needed to ensure safe operations. The first step to develop injury mitigations for these bystanders is to quantify the associated risks. Oftentimes, this is through the application of risk curves that relate the probability of injury of a specific body region to some quantifiable input that can be measured during a test. This test is to replicate the potential conditions; in this case, it would be for head and neck injury from blunt impacts. The end goal is then to develop a test methodology by which a UAS product can be evaluated. These risk curves then become directly connected to the injury criteria, and because of this, there is a process that is followed in their development. This rigorous process involves seven different steps: defining the injuries, defining the environment, specifying the input energy, conducting specific testing to generate injuries, regression analysis, development of test procedures, and verification. The resulting injury criteria can then be used to assess the safety of a system and used for conducting trade studies. How each of these steps applies to the development of a methodology for determining the effects of a UAS impact to a bystander will be explored to demonstrate the effectiveness of this methodology. Data from several research projects were collected, and a notice of proposed rule making was published. This rule identified the data necessary and from this, the proposed testing methodology was developed. It involves characterizing the types of injuries and using these to baseline a simplified test methodology using either a rigid flat plate or an instrumented anthropomorphic test device.

In this study, the capability of component fuselage testing and finite-element models (FEMs) to predict occupant injury risk in a full-scale aircraft crash test was evaluated. Component and full-scale crash tests of a Fokker-F28 aircraft were performed in conjunction with representative FEM simulations. Lumbar spine injury risk calculated through anthropomorphic test device (ATD) outputs measured in the full-scale test was compared with predictions made by component testing and simulation. A quantitative assessment of FEM prediction accuracy was made using the International Organization for Standardization (ISO) Technical Report (TR) 16250 curve comparison methodology. Lumbar load injury risk measured in the full-scale test configuration was found to be significantly higher than the component tests performed. The FEM was found to provide a closer prediction of occupant injury risk than component testing but exhibited limitations in the multi-axis load environment. This work will help inform the application of component testing and FEM simulation when used to evaluate aircraft crashworthiness.

Extraterrestrial construction presents many interesting and new challenges. Transporting large amounts of construction materials from Earth is cost prohibitive. Thus, to take advantage of limited in situ extraterrestrial resources, this work focuses on a novel class of biopolymer-bound soil composite (BSC) materials. These quasi-brittle composites are produced by desiccating a mixture of soil, water, and a biopolymer binder to create a versatile material with uniaxial compressive strength comparable to concrete. This paper expands upon a BSC design methodology for regolith soils. Previous work has been successful in reliably designing BSC materials with graded sands that exhibit compressive strengths above 20 MPa. Lunar regolith, JSC-1A simulant presents an additional challenge due to the broad ranges of the soil particle sizes. Nineteen BSC mixes using JSC-1A regolith were tested with varying biopolymer solution concentrations and biopolymer to soil ratios. A maximum compressive strength of 25 MPa was obtained at a biopolymer concentration of 48% and a biopolymer to soil ratio of 12.4%. A brief discussion on the effect of manufacturing variables on compressive strength and bulk density is presented. Finally, a design tool is introduced to design regolith BSC for desired compressive strength for future use in the structural design of structures on the Moon, Mars, or other extraterrestial bodies.

The Impact Dynamics Laboratory at NASA Glenn Research Center recently developed a pneumatically actuated crash sled for investigating the crush behavior of structural elements for vehicular applications. The apparatus includes an adjustable striker mass and specimen support mass, which are mounted on separate rails. This setup provides two advantages over crash sleds with so-called fixed specimen supports: (1) it allows for multiple independent measurements of the crush response using different instruments; and (2) the specimen support can be varied and its reaction can be explicitly measured. This paper describes the experimental setup and data analysis methodology and illustrates the capability of the sled for measuring the specific energy absorption (SEA) of triaxially braided carbon/epoxy composite C-channels and corrugated plates. The corrugated plate had a higher SEA than the C-channel, and the SEAs did not vary when the striker mass and velocity were changed so that incident energy was constant.

Failure modeling of composites is an ongoing challenge. In the current work, an orthotropic plasticity-based material model has been implemented into LS-DYNA as *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE or *MAT_213. The material model is driven by tabulated input data which can be generated either from experiments or virtual testing and is made up of three submodels that deal with deformation, damage, and failure. The focus of the current work is the implementation, verification, and validation of a modified version of an already existing failure submodel, with a brief introduction to the deformation and the damage sub-model. The suite of validation tests involves a unidirectional composite and includes a stacked-ply model loaded at a slow rate as well a high-velocity impact of a flat panel. Preliminary results are encouraging and show the versatility of the developed material model.

According to the aero-engine containment structure application and loads, the numerical simulation method of Kevlar fabric wrap structure under the impact of high-speed rotating blade was studied and compared with test results. The mechanical properties of Kevlar fabric were investigated firstly, including static and dynamic tension, shear, and friction. Some test methods and fixtures were developed. The response behavior of Kevlar fabric under different loads were obtained and analyzed. Then MAT-214 material model in LS-DYNA was studied to characterize the Kevlar fabric, and the data obtained by the mechanical properties tests were applied. The numerical simulation model of subscale casing and blade was established to simulate the impact process of casing and rotating blade. The casing is composed of an inner thin aluminum ring and outer wrapping Kevlar fabric. The fabric was modeled as continuum by using shell element. The effect of mesh size and shell element layers was discussed. The impact process was analyzed, and it matched well with the high-speed photography. The blade kinetic energy and fabric deformation of simulation and test results also matched well.

Thermoplastic composites have important applications in medical, electronics, automotive, and aerospace industries due to their good mechanical properties, easy for processing, recyclability, and low cost. In this work, the mechanical failure behavior of short carbon fiber reinforced PEEK composites is studied systemically using experimental technologies of quasi-static tests and dynamic Hopkinson bar tests. The experimental characterization covers different loading rate from 0.001 s to 1,000 s and temperature ranges from -30°C to 100°C, which provides detailed illustration for the effects of strain rate and temperature on the mechanical failure of short carbon fiber reinforced PEEK composites. The experimental results provide fundamental understandings on the failure mechanism of this material, especially in identifying the main factors affecting the rate-dependent and temperature-dependent behavior, which can facilitate the material design and model development. Based on the experimental data, this paper proposes an improved phenomenological constitutive model to describe the constitutive behavior of PEEK composites under different strain rates and different temperatures conditions.

The depth of the highway guardrail column is directly related to the safety of the driver’s life and property. The traditional method of pulling piles destroys the original roadbed and takes time and effort. As a nondestructive testing method, stress wave reflection method is widely used in structural size and structural integrity testing. However, for the traditional stress wave reflection method, the interpretation of the waveform mainly depends on the experience of the operator, and there is a larger error in the pile detection results. This paper proposed a reflection period extraction method based on image processing. Firstly, the time-frequency diagram obtained by wavelet denoising, multiple selfcorrelation, and short-time Fourier transform. Secondly, edge detection, binary filtering, and column pixel mean statistics are performed on the time-frequency diagram. Finally, the dominant frequency of the statistical signal is extracted by the fast Fourier transform, and the reflected wave period is obtained accordingly. Experiment proved that the algorithm can effectively extract the reflection period and accurately measure the length of the guardrail column.

The breaking of waves is a common phenomenon and threatens to the safety of offshore structures located in the ocean wave splash zone. In this paper, a series of experiments in the wave flume were conducted to investigate the action of breaking waves on bridge piers. The breaking waves were generated using focused wave theory. Three breaking wave conditions and three pier models with different cross sections, dimensions, and orientations were employed in the experiments. The breaking wave loads were recorded for each pier model located in different region of breaking waves. The main conclusions can be drawn as follows: (1) the breaking wave load varies with the distance between the breaking location and the pier and reaches the maximum while the waves break immediately in front of the pier and the breaker tongue hits the pier at wave crest level; (2) the breaking wave load is sensitive to the geometric shape; for example, the breaking wave load on the square pier is greater than that on the circular pier with the same projected dimension; and (3) the breaking wave load on the square pier with the orientation of 45° is the minimum. This study provides a valuable experimental reference for the study of breaking waves on the piers of sea-crossing bridges.

This paper studies the vibration control performance of a new type of superelastic shape memory alloy (SMA) helical spring braces to a frame structure under an earthquake. To explore the vibration control performance of the proposed braces, a steel frame model and four SMA springs were made in the laboratory. Based on a stress-strain relationship of the SMA material, a mathematical model was developed to determine the nonlinear force-displacement relationship of the SMA helical springs under general dynamic load, and the model agreed with the test results very well. Then, a numerical simulation model of the frame with the new SMA spring braces was set up to get the seismic responses of the frame. To check the validity of the simulation model, a number of vibration tests were conducted. The experimental results are in very good agreement with the numerical results, and the proposed braces can greatly suppress structural vibrations. Therefore, it is expected that the SMA spring braces have a great potential for the vibration control of practical frame structures.

Estimating the fatigue life of structures in challenging environment is an important factor for both design and maintenance of the asset. Much research has been completed to provide a better estimate of fatigue life of the structure under such extreme loading conditions. However, the uncertainties in the behavior of both the material and the structure have made impractical to provide a real estimate of the fatigue life of the asset. Using extensive field experiments in the Gulf of Mexico, this paper studies the fatigue assessment of structures under deep ocean current profiles. The real VAL stress-time history is used to study the fatigue life of the structure against those calculated based on various numerical fatigue models. It is illustrated that the application of simplified fatigue models that are based on CAL scenarios is nonconservative and has resulted in implementation of high safety factors in the industry.

In order to further understand the characteristics of longitudinal grouting compactness, this paper develops a stress wave based active sensing approach using piezoceramic transducers for monitoring the longitudinal grouting compactness of the curve tendon ducts. Experimental results show that in the no grouting, 50% grouting, 75% grouting, and 90% grouting conditions, the sensors cannot receive any stress wave. Only when the actuator and the transducers are grouted fully, the transducers can receive the stress wave propagated by the actuator. The wavelet packet-based energy analysis was adopted to compute the total signal energy received by PZT sensors in this research. With the change of the grouting compactness in the posttensioned tendon curve duct, the energy received by the sensor closer to the actuator changes more rapidly than that received by the sensor farther from the actuator. This is mainly due to the fact that these sensors are located in different longitudinal positions, which leads to their different degree of grouting compactness in the same time period. This paper shows that the grouting quality can be effectively evaluated by analyzing the difference between the signals received by the transducers in the curve tendon duct. So, the proposed method has potentials to be utilized to monitor the grouting quality of the curve tendon ducts.

A carbon nanofiber aggregate (CNFA) contains carbon nanofibers (CNFs) as an admixture of selfconsolidating mortar and produces an electrical response under stress. CNFA is a sensor that notifies the health status and provides a signal for the structural health monitoring system. It is necessary to understand the working principle and behavior of a CNFA and observe if CNFAs show consistency under various stress. In this research, three sets of test methods were tested under different loading methods to investigate the electrical impedance of CNFA under compressive stress, including the sweep-frequency test, the response from load removal, and the response from a car wheel. The behavior of CNFAs and their consistency under various loading conditions relies on the fact that they are conductive under stress. First, the sweep-frequency test compares the electrical impedance for various frequencies ranging from 1 to 500 kHz when the CNFA is scanned without the load and with a constant load. After reaching the targeted load, it is kept constant. Second, the impedance of CNFA is recorded for a constant load and a selected frequency. The electrical response of the CNFA under constant load is compared with the electrical response without any load. Third, the car wheel provides the load to the CNFA. The three methods demonstrated a positive correlation between impedance and compressive stress. The variables considered in the tests are various concentrations of CNFs and the age of samples. Irrespective of these variables, the test results from three methods show consistency in the behavior of CNFA. Therefore, the correlation between the electrical impedance and the stress is validated based on the experimental study.

This paper presents a complementary and synergistic material system that integrates superelastic shape memory alloy (SMA) with damage-tolerant engineered cementitious composites (ECC) to address the issues of yielding of steel bar and fragility of concrete. Reverse cyclic loading tests were done on four specimens to demonstrate the feasibility of this method, which consisted of conventional steel reinforced concrete shear wall (SW-R-C), steel reinforced ECC wall (SW-R-ECC), SMA reinforced concrete wall (SW-SMA-C), and SMA reinforced ECC wall (SW-SMA-ECC). The results showed that SW-SMA-C specimen exhibited remarkable self-centering capability, which can reach more than 85% even after large deformation compared to SW-R-C. Furthermore, superior reduced damage and better ductility were observed in the SW-SMA-ECC specimen, besides reduced residual displacement. The proposed approach indicated that it is more effective for SMA combined with ECC in improving the seismic performance of shear walls.

Low-ductility steel concentrically braced frame (CBF) buildings are considered to have reserve capacity after brace failure. This study proposes a series of shake table tests of a scaled two-bay, three-story, moment-resisting frame model with a pair of square hollow section braces placed in a chevron arrangement to examine its dynamic behavior. The model structure was repeatedly subjected to two earthquake records with successively increasing magnitudes. The failure mechanisms, reserve capacity, and overall collapse performance were investigated. The results show that the reserve system is sensitive to spectral characteristics of ground motions, especially for soft soil site ground motions.

Corrosion of metallic materials accounts for most of the structural failures across multiple industries. In this paper, a novel corrosion sensor was proposed based on the piezoelectric-metal transducer using electromechanical impedance (EMI). The corrosion sensor consisted of a metal plate with a lead-zirconate-titanate (PZT) patch of the same cross section attached to it. Due to the electromechanical coupling effect, under the alternating electric field excitation, the in-plate contraction and extension of the PZT patch induces bending vibration of the piezoelectric-metal transducer. Corrosion-induced thickness loss of the piezoelectric-metal transducer reduces its bending rigidity and thus the bending resonant frequencies, which are measured by the electromechanical impedance technique. Finite-element simulation and experimental investigation were performed to validate the proposed corrosion sensor. Results showed that the proposed corrosion sensor is able to determine the corrosion-induced thickness loss quantitatively, which shows promising application potential.

Leakage loss of urban water pipelines is a common problem, which causes tremendous waste of water resources and great economic loss. Due to the long distance and complicated pipeline network, the existing technologies cannot effectively realize the leakage detection and localization of the whole pipeline network. In this research, the feasibility of leakage detection and localization in water pipelines was demonstrated based on active thermal method and distributed fiber optic temperature-sensing technology. In the proposed method, the sensing element was a thermal cable that was fabricated by coupling the heating element with the distributed fiber optic temperature sensing element. The thermal cable was buried under the pipeline. On account of the different heat transfer characteristics of heated thermal cable in soil and water environments, the conduction in soil and convection in water, respectively, the leakage and nonleakage locations can be identified. Numerical simulations and experiments were conducted to verify the feasibility of the proposed method for leakage detection. Good agreement has been achieved.

This paper presents an enhanced base isolation system (BIS) by involving the tuned mass damper (TMD) in series with clutching inerter damper (CID), mounting in the isolation layer, which is similar to the conjunction use of the BIS and the tuned-mass-damper-inerter (TMDI); the difference is that the inerter in the TMDI is replaced by the CID. Compared with the TMD enhanced BIS, the proposed control strategy has better control for the displacement of the isolation layer and the superstructure. Comparing with the TMDI enhanced BIS, the proposed control strategy has better control for the TMD stroke because of the superiority of the CID over the inerter.

To investigate the influence of temperature on the longitudinal displacement of an asymmetric cable-stayed bridge with a hybrid girder, a finite-element system (FES) of the bridge and a simplified system of the girder and bearings in the pylon area were established. The systems were based on a cable-stayed bridge with a hybrid girder during the period after the closure of the midspan and before opening to traffic. The bearing reaction of the piers and the unbalanced force in the horizontal direction in the pylon area were calculated according to the displacement bearing data collected in the case of drastic temperature changes for 24 h. The results of the entire bridge system were substituted into the simplified system for calculation. The displacement bearing data were collected and compared with 24 h onsite results. The results indicate a linear relationship between the longitudinal displacement of the girder to the side span and the temperature of the girder. A hysteresis effect of longitudinal displacement of the concrete girder to the side span with a change in the temperature, which satisfies a bilinear model, was observed. A residual longitudinal displacement of the concrete girder displacement to the side span was observed when the temperature returned to the initial value after 24 h of continuous observation and could not be eliminated within the 24 h observation period. These results provide a sound research basis for the study of displacement bearing regularity under vehicle action; the “rump-up” of concrete side spans in which the residual value of bearing displacement accumulates for a long period within each temperature change period; and similar engineering problems of a cable-stayed bridge with a hybrid girder.

This paper presents a new closure method for closing the deck in the middle span of a cable-stayed bridge. It discusses the mechanism of the single joint method and develops a regression approach for fabrication dimensions of closure segment incorporating with temperature correction based on the field measurement. Following this, the authors propose the key erection procedures and the pulling system based on the erection of Jingyue Bridge in China. The application in this completed bridge demonstrates the proposed method, simple in operation and high in accuracy.

This paper constructed numerical analysis models of two typical low-rising RC building structure (a 2-floor and a 4-floor RC frame). To study the dynamic structural damage and the damage reduction effect of the extra devices, twenty ground motion records were selected from the Pacific Earthquake Engineering Research Center (PEER) database to perform nonlinear dynamic analysis; incremental dynamic analysis was used to perform nonlinear dynamic structural analyses to collect the data for estimating seismic collapse fragility, and the structural damage index is used to evaluate the damage level of each floor. The results indicate that a simple support scheme can have a significant improvement in structural seismic resistance, as it reduces the maximum seismic response and the collapse probability. However, the improvement of the 4-floor RC frame means that the support scheme works better on lower structures.

During extreme flooding events, submerged bridge components would encounter strong lateral fluid forces. With lateral flowing water, debris, such as sediments or tree branches can be transported along rivers and accumulate on submerged components. With debris accumulations, short span bridges are required to resist additional fluid pressure due to the increasing current-obstruction area. Besides, debris accumulations would accelerate bridge scour process, as well, due to increasing flow speeds. The floating debris can also directly impact bridge foundations and affect the dynamic behaviors. Many bridges collapse due to fluid forces and debris impacts during flooding events. Few studies have been conducted to investigate the structural behaviors of bridges considering the effects of debris. In the present study, the dynamic analysis for OSBs is conducted with the consideration of debris accumulations and debris impacts. Firstly, a short span OSB is simulated with foundation scour due to possible debris accumulations. Secondly, the fluid pressure applied to the OSB is updated considering an extra blocking area due to accumulated debris. The collision forces due to floating woody debris are also introduced into the analysis. Thirdly, the dynamic amplification factors with and without considering the effects of debris impacts are calculated and compared. Finally, some conclusions are drawn about how to simplify the effects of debris impacts on the dynamic responses of bridges.

Recently, the concrete-filled double-steel-plate composite walls (CFDSPCWs) have been widely applied in ultra-high-rise civil infrastructure due to their excellent mechanical properties. It is urgent to develop the nondestructive testing method for the debonding detection of CFDSPCWs to guarantee the mechanical performance and structural safety of civil structures. In this study, the feasibility of multichannel analysis of surface waves method (MASW)-based interfacial debonding defection for CFDSPCWs was investigated. The 2D and 3D finite-element models of CFDSPCWs were established, and the detailed wave propagation process in CFDSPCWs was numerically simulated. The influence of the dimension of CFDSPCWs and thickness of the steel plates on the wave fields in CFDSPCWs with and without debonding defects was discussed respectively. The relationship between the excitation signal frequency and the geometry variation of CFDSPCWs was analyzed in depth. The numerical finding indicates that the interfacial debonding defects in CFDSPCWs can be detected using the proposed method. The research findings can provide referential significance to the practical application of interfacial debonding defection for CFDSPCWs using the MASW method.

The purpose of this study is to understand how spatial ability differs under extreme environments and to provide implications on individually relevant training approaches by using VR technologies. Special jobs under extreme conditions (e.g., astronaut or scuba diver) demand higher spatial ability and effective spatial strategy. This paper examines how the conflicts between visual vertical and the body vertical may affect spatial ability. In addition, the study tested the relationship between an individual’s tendency to adopt a certain spatial strategy (egocentric vs. allocentric) and their use of a particular spatial reference frame (body vs. visual) under the extreme condition.

With the rapid development in megacities, useable lands for construction are in short supply. The upper space above the garage of subways is considered a potential land source for megacities. However, interference from the train-induced vibration has not been properly solved. The existing vibration controls have been applied to the railway fastener, floating slab, and sleeper, yet these facilities suffer from some drawbacks. This study mainly discusses the feasibility of a new type of material, i.e., periodic material, in reducing the train-induced vibration. The periodic material is a kind of material that has the characteristic of frequency band gaps. In other words, the train-induced vibration wave with a frequency falling into the frequency band gap of the designed periodic materials can be dramatically attenuated. The train-induced frequency of elastic stress waves affecting the super-structure is considered to be in the range of 30–80 Hz according to the reported acceleration spectrum obtained from the subway vibration experiments. The vibration reduction by using periodic materials in a variety of structural forms and material properties was evaluated through numerical simulation. It is found that the vibration in the considered frequency range can be effectively reduced by using periodical material, which is a better solution than the existing damping methods.

This study gives a comprehensive review on the smart rock technology to monitor local scour depth of bridge piers or abutments, which was originally proposed by our group in 2015. The smart rock is one or more stacked magnets encased in a concrete ball that can automatically roll to the deepest point of a scour hole around a bridge pier and provide its location through remote measurement over time. As of today, three types of spherical smart rocks designated as arbitrarily oriented system (AOS), automatically pointing south system (APSS), and automatically pointing upward system (APUS) have been developed. This study gives a comprehensive review on the smart rock technology for local scour monitoring of bridge piers, in terms of sensing principle, advantages and disadvantages, localization algorithm, effective monitoring range, as well as field test. The smart rock technology was also compared with other technology to monitor bridge scour such as optical fiber sensor, ground penetration radar, sonar, magnetic sliding collar, and so on.

The stability of the floating wind turbine against complex environmental loadings is one of the major challenges in the development of the floating wind turbine industry. Hydrostatics of floating wind turbine is one of the main sources of stability of the floating structure. The use of linear hydrostatic stiffness is very common in the analysis of floating wind. In this paper, nonlinear hydrostatic stiffness is obtained for a floating spar platform, taking into account the rotational displacement of the platform. The dynamic equation of motion of the floating wind turbine is formulated using Newton-Euler approach. The mooring lines are modeled using the elastic catenary cable element. The hydrodynamic forces on the floating platform are calculated using Morison’s equation. The effect of hydrostatic nonlinearity on the dynamic response of the floating offshore wind turbine through the analysis of OC3-Hywind model. The results show a significant effect of hydrostatic nonlinearity on the amplitude of heave displacement.

Regarding the inevitable self-destruction of the Earth, we may expect the potential of the Moon to work as an alternative for future survival. To achieve life on the Moon, we first need to establish permeant residence bases. While severe plans have attempted to construct infrastructure on the Moon, a severe problem that we face is how to accurately detect and ensure the integrity of the temporary structural connections (e.g., scaffolds), whose failures can induce terrible catastrophe that lead to severe impairment. Current structural health monitoring (SHM) methods for scaffolds on the Earth depend on constant sensor-deployment, which requires a continuous power supply and good durability, and thus they may be impractical in terms of harsh environments on the Moon. Therefore, in this paper, we attempt to propose a novel robotic-assisted active sensing method to detect the integrity of the cup-lock joint of scaffolding. Particularly, a pair of PZT-enabled smart gloves (SGs) is designed and worn on a robotic manipulator that can grasp the scaffolding, and integrity can be judged by analyzing signals via our new proposed damage index (DI) based on entropy. Compared to current SHM methods, the proposed method can avoid constant interaction between structures and transducers, thus improving maneuverability and survivability. Moreover, the proposed entropy-based DI can mitigate the saturation problem of current DI (i.e., signal energy) of active sensing method effectively, which dramatically enhances the practicability in future applications.

The unmanned vehicle can automatically evaluate the structural safety of the building by carrying a visual crack detection camera. However, the complexity of layout within the building requires that unmanned flaw detection robot has high obstacle avoidance performance. Aiming at the difficulty of obstacle avoidance in complex environment, the direction control method based on image sensor is adopted. The image is transmitted to the convolution neural network (CNN), and the direction instruction of the neural network is output to the motor driver to realize the autonomous obstacle avoidance of the wheeled robot. Data sets are automatically classified by arranging camera arrays. In this paper, the transfer neural network is used to reconstruct the neural network by discarding the last three layers and setting up new three layers. The accuracy of the neural network trained by the simulation results can reach 89.01%.

Through advances in wireless sensor networks and micro electro-mechanical systems over the past couple of decades, energy harvesting from the ambient environment as a self-sustaining energy source has attracted more and more attention worldwide. Piezoelectric materials are ideal sources for energy harvesting, since they can convert minor mechanical energy, which is often neglected or wasted, into electrical energy directly. The most commonly used piezoelectric energy harvesting structure is the cantilevered beam. Investigators around the world have made significant effort on the modeling of cantilevered piezoelectric energy harvesters. Throughout previous modeling of cantilevered piezoelectric energy harvesters, without exception, the electric field in the piezoelectric layer is considered as uniform as the potential difference between the electrodes divided by the thickness of the piezoelectric layer. However, based on the uniform electric field assumption, the divergence of the electric displacement, which represent the free charge density, in the piezoelectric layer is nonzero. This is against a basic physical law, i.e., the free charge in an insulator should be zero. By introducing the divergence of the electric displacement in the piezoelectric layer as zero, we found that the electric field in the piezoelectric layer is actually nonuniform. Using the electrical boundary conditions, the nonuniform electric field in the piezoelectric layer is derived and utilized in a distributed parameter model. Considering the present proposed nonuniform electric field, the theoretical performance of a cantilevered energy harvester is corrected. The proposed nonuniform electric field could also be applied to other bending piezoelectric components such as composite piezoelectric plates.

Large span steel pipe truss structure has complex space forms. Each bar interacts with each other. As an example of the gymnasium of Xining Haihu, the health monitoring technology of Fiber Bragg grating sensors and the vibrating wire sensors is introduced in the application of the gymnasium construction stage. This paper expounds on the arrangement of the health monitoring system, monitoring methods, measuring point arrangement, etc. Analysis of monitored data shows that in the construction phase, the stress in each primary bar changes stability, the internal force is much smaller than the yield strength of steel. Besides, the stress in each bar is always under the service limit state, which meets the design requirements. Each ring displacement monitoring data change stability, structural stiffness is rich in reserves. To Xining Haihu gymnasium in the process of using security is a critical evaluation index; at the same time, relevant experience and data provide a reference for similar health monitoring project.

The seismic performance and damage assessment of electrical substation involving dynamic interaction between main structure and electric equipments are studied systematically. Specimen of a real substation with the scale of 1:8 had been tested on the shake table to investigate the effect of seismic performance of structure and electrical equipments. After that, a simplified numerical method based on ABAQUS is proposed to determine the damage of the cracked specimen. From experimental and numerical investigations, it is found that (1) the interaction of structure and electrical equipments is obvious in electrical substation; (2) the horizontal acceleration of the electrical equipments are larger than the structure, which means dynamic effect caused by electrical equipments should not be ignored in the seismic design of substation; (3) the damage assessment model is proposed, which is effective to assess the damage of substation; and (4) the simplified numerical method is proven to determine the seismic performance of large substation rationally.

Stiffness degradation of high-performance steel (HPS) beams with local shear-span corrosion is studied by experimental investigation and numerical analysis. Six beams subjected to various level of local corrosion damage are designed. 3D scanning technology is employed to analyze the geometric features affected by the corrosion damage. Flexural tests are carried out, and the effect of the local corrosion on the stiffness degradation is analyzed. Numerical models considering corrosion characteristics are established. By using the FEA models, parametric analysis is carried out to investigate the impact of different damaged positions and thicknesses on the stiffness degradation. Results show that the local corrosion within the shear span has an obvious adverse effect on the stiffness of the beam, especially for the open-hole steel beam caused by heavy corrosion. The degradation caused by corrosion near the support is greater than that near the loading point. When the thickness decreases by 30%, the stiffness has an obvious degradation.

Strain measurement is an important part of structural health monitoring. Measuring the strain of different parts is of great significance to understand the safety performance and service state of the structure. This study utilized smartphone with an high popularity, cheap, and portable mobile phone microscope and corresponding devices to take small deformation images of objects, tracked local feature points in images, calculated the displacement, and got the average strain of the objects, so as to achieve a portable, low-cost strain measurement method. The results show that this method could measure the strain of the structure surface very well, and its errors are within 6 με. It meets the needs of structural health monitoring; in addition, it is simple to operate and easy to be popularized in a wide range.

In offshore reinforced concrete (RC) structures, the phenomenon of rebar corrosion is widespread, and how to monitor the early production and development of the rebar corrosion is of great significance. However, the rebar corrosion in RC structures is localized and develops along the interface, which brings great challenges to the evaluation of rebar corrosion level (especially in corrosion areas). In this paper, theoretical analysis, numerical calculation, and experiment validation are used to study the rebar local corrosion monitoring and evaluation of RC structures with piezoelectric ultrasonic guided waves (UGWs). For this purpose, a reasonable selection of piezoelectric guided wave excitation and reception method and corresponding setup is studied. Frequency dispersion curves of the selected guided waves under different corrosion conditions are obtained by analyzing the wave dispersion and multimodal characteristics. Based on echo signal energy values and their fractal dimension characteristic values for different corrosion levels, an evaluation index of rebar corrosion is proposed, and a corresponding evaluation equation is established. The effectiveness of the proposed algorithm is verified by a rebar corrosion monitoring test with the accelerated corrosion test and guided wave technology. A fitting relationship between the corrosion level (length and thickness) and the basic characteristics of the sensing signal is established. A corrosion evaluation method is established based on the corrosion index. The results show that the rebar corrosion has a certain effect on the energy and fractal characteristics of longitudinal guided waves. The larger corrosion length and the thicker corrosion layer result in the smaller energy value of echo signal, smaller fractal characteristic value, and the larger corrosion index value.

This paper presents state-of-art of a novel vibration control device, namely the pounding tuned mass damper (PTMD). The PTMD basically introduces a single side or double side delimiter covered with viscoelastic material to the classical tuned mass damper (TMD). The delimiter serves two purposes: (1) to restrain the stroke of the tuned mass; and (2) to enhance the energy dissipation. The so-called PTMD is also a integration of the traditional TMD and the impact damper (ID). Consequently, it has two vibration control mechanisms: (1) when the overall vibration amplitude of the main structure is relatively small, the tuned mass generates initial force to control the vibration of the main structure; and (2) when the excitation is large enough, the tuned mass will collide on the delimiters and dissipation energy via impacts. The two combined vibration control mechanisms have improved the effectiveness of the PTMD and its robustness against detuning effects. This paper summarizes recent investigations on this damping device. The schematics and the features of the PTMD are provided. Applications of PTMD in vibration control of a variety of structures are also presented. In the last part, suggestions for future works are provided.

The most important factor in restricting safe and efficient is the unfavorable geological conditions ahead of the tunnel face during tunnel construction in karst area. To avoid the occurrence of geological disasters, advanced geological forecast technology is widely used to detect the development of unfavorable geological bodies. In order to better explain the time-frequency characteristics of GPR signals of tunnel cavern fillings, the Gaussian window function is selected according to the uncertainty principle, and the short-time Fourier transform is used to analyze and process the GPR signals of cavern fillings with different properties based on forward simulation. The results show that the time-frequency spectrum based on short-time Fourier transform can meticulously describe the process of change that takes places in time and frequency plane of GPR signals, which is beneficial to accurately extract the time-frequency characteristic parameters in GPR signals. When the electromagnetic wave wavelength of the GPR transmitting antenna is shorter than the detection depth of cavern fillings, two target reflectors which reflect the upper and lower reflecting interfaces of the fillings will appear in the spectrum of forward simulation signal. The relative errors of recognition results obtained according to the reflection time interval are all less than 5%, which provides a reference for the quantitative interpretation of GPR signals of tunnel cavern fillings.

Joint failure, which causes leakage in bridge decks as well as deterioration in girders and substructures, is one of the most common concerns in highway bridges in the United States. Therefore, closure pours or link slabs have been considered as a solution to eliminate these joints. The link slab system in this study is designed for an overpass bridge in the state of Maryland to improve its durability and reduce maintenance costs. However, traditional link slab design requires the replacement of current bearings to elastomeric bearings with one fixed condition, while others use expansion bearings, to minimize the thermal stress generated in the superstructure. Theoretically, this action will increase the longitudinal movement of the deck while releasing the stress caused by thermal expansion or contraction in the material. This paper proposes a more economical method of replacing bearings by revising the sliding plate to match the designed boundary condition. Firstly, some background information and the finite element analysis of the overpass highway bridge with link slab under thermal loading would be described, which shows the general idea of this project. Then, the sensor validation and installation of the bridge were introduced, and finally, the monitoring system is established. Finally, the long-term monitoring system for the pilot bridge is introduced, and results from finite element analysis are validated by the measurement.

The security problems of pipeline networks have received considerable attentions in the academia and engineering field. The successful application for piezoelectric smart material provides a development opportunity for damage detection of the pipeline structures. In this paper, the electromechanical impedance method for damage detection of the pipeline structure was studied. The electromechanical impedance model for the pipeline structure was developed, based on which a new damage sensitive feature factor is proposed. And the electromechanical admittance equation was derived. Based on the admittance equation, the mechanical impedance was extracted. Then, the new damage sensitive feature factor can be defined. The achievements of this paper provided a theoretical basis and an analysis method for damage identification and safety evaluation of the pipeline structures.