Journal of Engineering Mechanics

The extended finite-element method (XFEM) was proposed to simulate the problem of crack growth without any remeshing. In this paper, the penalty function method is introduced to deal with the contact constraints, and the trial-and-error method is employed to investigate the converged contact state. The monitoring points seed on the interface to detect the contact states of the cracks and to interpolate the displacement of the grid node. The formulations of the dynamic frictional contact problem for crack slip are established based on the multidimensional space method. In this proposed method, the implicit Newmark time integration scheme is applied to deal with the problems of dynamic frictional contact. Moreover, a numerical case is illustrated to verify the precision and robustness of the proposed method. It is found that the numerical results obtained from proposed method agree well with those obtained from the standard finite-element method.

Rutting performance of airfield pavements is predicted using mechanistic-based constitutive relationships for both asphalt and granular layers. Pavement analysis using nonlinear damage approach-airfield pavements (PANDA-AP) is used that encompasses a coupled viscoelastic–viscoplastic constitutive relationship to model the rutting distress in the asphalt layer and a modified extended Drucker-Prager-Cap (D-P-Cap) is used to predict permanent deformation induced in granular layers due to aircraft traffic. The D-P-Cap model captures the permanent deformation due to both shearing and densification of granular layers. Experimental test results from resilient modulus, cyclic triaxial, dynamic modulus, and flow number tests are used to fully calibrate the constitutive relationships. The calibrated constitutive relationship is then validated against independent lab experiments. The calibrated model is used to predict the performance of airfield pavement sections tested at the National Airfield Pavement Test Facility (NAPTF) of the Federal Administration Aviation (FAA). It is shown that the presented mechanistic-based constitutive relationships can be effectively used to predict the rutting performance of airfield pavements when subjected to high aircraft tire pressure.

Although spatially varying quantities in real life (e.g., mechanical properties of soils) often contain a linear or nonlinear trend, stationary random fields with zero trend are often used to model these quantities due to mathematical convenience. To model a random field with a linear or nonlinear trend through a stationary random field, removal of the trend, known as detrending, is often performed first on the available measurement data points to separate the random field into a deterministic trend component and a stationary random field, followed by characterization and simulation of the stationary random field. Detrending is a tricky process. Because the form of the trend function (e.g., linear or nonlinear) is often unknown in application, it is difficult to select the most appropriate form of trend function given the available measurements. Using different forms of trend function results not only in different deterministic trends, but also different parameters for the stationary random field (i.e., different random fields). The situation becomes even more challenging when the measurements are sparse and the difficulty in estimating parameters (e.g., correlation length) of the stationary random field from sparse data becomes significant. This paper proposes an innovative method to generate samples of random fields with a linear or nonlinear trend directly from sparse measurements without detrending. The proposed method is based on Bayesian compressive sampling and the Karhunen-Loève expansion. Because no detrending is needed in the proposed method, the difficulties associated with detrending in the simulation of random fields with a linear or nonlinear trend from sparse measurements are bypassed. The proposed method is illustrated and validated using numerical examples in this paper.

The solidification theory has been accepted as a thermodynamically sound way to describe creep reduction due to deposition of hydrated material in the pores of concrete. The concept of self-equilibrated nanoscale microprestress has been accepted as a viable model for the marked multidecade decline of creep viscosity after the hydration effect becomes too feeble, and for increases of creep viscosity after any sudden change of pore humidity or temperature. Recently, however, it appeared that the original microprestress-solidification theory (MPS) predicts incorrectly the diffusion size effect on drying creep and the delay of drying creep behind drying shrinkage. Presented here is an extension named XMPS that overcomes both problems and also improves a few other features of the model response. To this end, different nanoscale and macroscale viscosities are distinguished. The aforementioned incorrect predictions are overcome by dependence of the macroscale viscosity on the rate of pore humidity change, which is a new feature inspired by recent molecular dynamics (MD) simulations of a molecular layer of water moving between two parallel sliding calcium-silicate-hydrate (C-S-H) sheets. The part of aging that is not caused by microprestress relaxation is described as a function of the growth of hydration degree, and the temperature change effect on pore relative humidity is also taken into account. Empirical formulas for estimating the parameters of permeability dependence on pore humidity from concrete mix composition are also developed. Extensive validations by pertinent test data from the literature are demonstrated.

This study investigated the transport properties of cement mortar using microscale X-ray computed tomography (μCT) characterization techniques, the Permeability Solver computational program, and laboratory experiments. Lightweight aggregates (LWAs) were used as the internal curing agent in this study. Mortar samples with and without internal curing were prepared with a water-cement ratio of 0.45. The μCT techniques were applied to obtain digital data of the microstructure of the mortar samples at the resolution of 1 μm. The acquired images were processed to identify the pore structure. Three-dimensional (3D) digital pore structure samples were reconstructed, and the data were read by the Permeability Solver to analyze the porosity, pore conductivity, and permeability of the mortar mixtures. Pore connectivity was evaluated by the burning algorithm. Water transport was simulated by the finite-difference method combined with the compressibility relaxation algorithm. Darcy’s Law was then applied to calculate the permeability of the mixture. The transport properties of mortar with and without internal curing were simulated at 60 and 84 h. The results showed that the internally cured samples had lower permeability than the samples without internal curing. The permeability of the samples with internal curing decreased from 60 to 84 h. The results indicated that autogenous shrinkage cracks could be mitigated using internal curing.

Closed-form expressions for calculating stresses and displacements of partially restrained concrete pavement caused by a linear temperature gradient are presented. Translational and rotational linear elastic springs along the slab edges defined the partial restraint. In addition to plate theory behavior, the model assumes linear elastic concrete and an infinitely long slab resting on a Winkler foundation. The solutions of curling stresses and displacements were validated using the finite-element (FE) method and quantified the effect of semirigid connections, slab and foundation material properties, and slab thickness and width on them. Rotational and translational restraints, which can be related to joint condition in concrete pavement, had significant influence on the magnitude and location of maximum curling stresses and deflections. In addition, Westergaard analysis, a particular case of the proposed solution when there is no restriction along the slab’s edges, resulted into the largest deflections at the center of the slab and the lowest maximum curling stresses. Adjustment factors that convert the theoretical findings from an infinitely long slab to a square slab are proposed.

Stay cables are prone to vibrations due to their low inherent damping. This paper presents an approach for systematic identification of beneficial passive vibration absorber layouts consisting of a damper, a spring, or an inerter. With the proposed method, optimal configurations among all layouts with three elements or fewer are identified. The inerter is a two-port mechanical element with the property that the applied force is proportional to the relative acceleration between its terminals. In this work, a finite-element taut cable model, with a generic vibration absorber represented by its admittance function, is first established. Two performance measures, depending on the length of the cable and the forcing conditions, are introduced to assess the effect of candidate absorbers. Potential advantages of low-complexity inerter-based absorber layouts are then systematically investigated, with corresponding element values in these layouts identified. Building on this, the effect of series compliance is also examined for beneficial absorber layouts. It is shown that, up to a certain inertance, which depends on the stiffness of the series compliance, the performance advantages over a viscous damper can be maintained, or even increased in some cases, if the element values are properly tuned.

Predicting pore structure is of great importance in concrete because pore properties are essential factors in its durability and structural performance. In this study, a pore structure model, coupled with water migration and hydration of cement and water, was constructed. A diffusion model depending on the pore diameter was also constructed by introducing a different pattern of water movement for each pore size to water migration in a microscopic view. To evaluate the effectiveness of the proposed models, the analytical results were compared with experimental results of the pore size distribution measured by gas adsorption and mercury intrusion methods. Additionally, the experimental and analytical results of water migration were compared to confirm the applicability of the diffusion model. The experimental and simulated results were revealed to be in close agreement, with the simulated results characterizing the pore structures of cement hydrates and water migration.

The vibrations of ultrathin silicon cantilever microbeams are studied using consistent couple-stress theory to investigate size-dependent effects. The corresponding Euler-Bernoulli beam theory is used to estimate the couple-stress length scale parameter of single crystal silicon, based on measured experimental data for the resonant frequency of cantilever microbeams. The present work demonstrates that conventional use of classical beam theories, along with rigidly clamped cantilever boundary conditions, can lead to misinterpretation of experimental data, necessitating the introduction of nonphysical size-dependent effective material properties, such as an effective Young’s modulus. Alternatively, proper modeling of the cantilever boundary conditions combined with use of couple-stress theory can account for the observed mechanical scale dependence in silicon micro- and nanostructures from fundamental principles of continuum mechanics. Moreover, the modeling approach presented here can be generalized to other micro- and nanoscale structures and materials. As such, the developed approach may be useful for the rational design of additional novel applications of such structures, ranging from optomechanical transducers to ultrasensitive biochemical sensors.

An accurate and efficient numerical model is developed to calculate the earthquake-induced hydrodynamic pressure on uniform vertical cylinders with an arbitrary cross section surrounded by water. According to the boundary conditions and using the variables separation method, the three-dimensional Laplace equation governing the incompressible water is transformed into a two-dimensional (2D) Helmholtz equation. As a key element, a circular boundary surrounding the structures is introduced so that the computational domain is partitioned into unbounded and bounded domains. The unbounded domain is simulated by an exact artificial boundary condition, which is derived by using the separation variable method. The impedance matrix of the entire domain is obtained by the finite-element method. The hydrodynamic forces on rectangular and round-ended cylinders are calculated, which can be modeled as the product of an added mass of water and the acceleration of the cylinder. However, these complicated expressions of the hydrodynamic forces are not suitable for engineering application. Therefore, simplified formulas for the added mass of the round-ended and rectangular cylinders are obtained by the curve-fitting method. The results indicate that the precision of the present added mass formulas is enough for engineering applications.

A numerical time-delayed transfer entropy method combined with a surrogate data algorithm is proposed to identify the nonlinearities in the vibration data of structures with damages without the use of baseline data. Semianalytical methods based on the Galerkin method are used to precisely predict the linear and nonlinear response of structures. The proposed method can identify nonlinearities in vibration data well. A new nonlinearity index is also proposed. Computation results for different loads indicate that the nonlinearity index increases as load increases. Subsequently, a new discreteness degree index for transfer entropy is additionally proposed. The responses of a plate with different loads are calculated and linear relationships between the discreteness degree index and the nonlinearity index are obtained. Numerical examples with different geometries but similar nonlinearity indexes are also carried out. It is shown that the discreteness degree index for transfer entropy can quantitatively measure nonlinearity degree. As verified, the proposed methodology can be used for structure nonlinearity identification in areas such as civil engineering, mechanical engineering, and ocean engineering.