Journal of Engineering Mechanics

In this paper, an innovative procedure is introduced for the identification of the mechanical properties of orthotropic membranes based on load-displacement data. To this end, novel functional forms of the displacement components for rectangular membranes are appropriately introduced. Unknown coefficients of these displacement functions are determined, minimizing the total potential energy of the membrane. The energy method is then combined with an optimization procedure to estimate the elastic constants of the membranes in a straightforward manner. Specifically, a genetic algorithm is used to minimize a properly defined objective function directly related to the sought mechanical properties and computed based on known load-displacement data of the membrane under uniformly distributed load. Numerous applications are reported to demonstrate the efficiency and accuracy of the proposed identification procedure in capturing properties of the membranes. Further, several numerical applications are presented to show the reliability of the proposed displacement field functions by comparing results with finite-element model data, as well as analytical solutions when available. Notably, considering the increasing use of membrane elements in many engineering applications, results suggest that the proposed procedure may represent an accurate and appealing alternative approach for determining membrane mechanical properties, whose characteristics are still difficult to estimate using commonly employed techniques.

The inverse dynamic analysis of vehicle-bridge (VB) systems provides a superior scheme for track irregularity identification using the onboard measurement data of vehicle dynamic responses. However, available algorithms face a great challenge when applied to high-speed railway bridges because of the increase in the number of unknown inputs, resulting in a degradation of identification accuracy. Here, we propose a condensation procedure to reduce the unknown inputs of the VB system, and then propose a novel algorithm for track irregularity identification using the augmented Kalman filter. A numerical simulation of a real continuous three-span simply supported railway bridge was conducted to validate the estimation accuracy of the proposed algorithm. Numerical results illustrate that the proposed algorithm can accurately estimate the track irregularities by using the vertical acceleration responses of the vehicle body only, thanks to the unknown input condensation. A comparative study demonstrates that the proposed algorithm outperforms the conventional track irregularity identification methods in terms of estimation accuracy. To evaluate the actual performance of the proposed algorithm, a set of onboard measurement data recorded by a typical high-speed train when running on the Hangzhou–Changsha high-speed railway in China was employed to identify the track irregularities of the railway line, and the results suggest that the proposed algorithm is highly efficient and low in cost. This study may help develop highly efficient real-time track irregularity monitoring in the years ahead.

While laboratory evidence suggests that particle crushing generates nonnegligible rate-dependence in granular materials, few constitutive laws reproduce such effects in light of grain-scale fracture mechanisms. This paper presents a continuum breakage model with adaptive fluidity aimed at simulating seamlessly the compression of crushable sands across loading regimes spanning both quasi-static and dynamic conditions. For this purpose, the macroscopic fluidity of the material is modeled through concepts inspired by dynamic fracture mechanics and granular solid hydrodynamics. Specifically, the relationship between dynamic grain-scale processes and bulk dissipation relies on the evolution of a state variable linked to microscale entropy fluctuations, here referred to as breakage temperature. The model performance is assessed by reproducing the results of Split-Hopkinson bar compression tests conducted at different strain rates. It is shown that, compared to a correspondent viscous-breakage model characterized by stationary fluidity, the incorporation of adaptive rate-dependence leads to an improved model performance, in that it enables the compression/breakage response to be captured accurately without ad hoc adjustments of the viscous properties.

Both time- and frequency-domain solution techniques are developed for determining the response of linear multi-degree-of-freedom systems exhibiting singular parameter matrices and endowed with derivative terms of noninteger orders modeled as rational numbers. This is done based on the Moore-Penrose matrix inverse theory, in conjunction with a state variable formulation and with a complex modal analysis treatment. It is worth noting that, for the class of systems considered herein, this treatment also yields decoupled governing equations, thus facilitating further their numerical solution. Next, a generalization of the standard frequency-domain input-output (excitation-response) relationship is derived based on an appropriately defined frequency response function. This spectral relationship is further extended to account also for stochastic excitation vector processes described by power spectral density matrices. Two illustrative examples are considered for demonstrating the validity of the herein developed technique and of the derived input-output relationships.

We conducted a series of numerical simulations to understand the effect of the shape of a partially confined geometry on blast wave strength, including its scaling method. We referred to an explosion of a high explosive in an underground magazine, and the underground magazine model had two sections: a chamber and a passageway. The internal diameter ratio between the chamber and the passageway was the parameter, and a smaller internal diameter ratio led to more impactful mitigation of the blast wave outside. Moreover, we adopted the shock tube theory with a large-area contraction to better understand the blast wave characteristics at the exit. The physical quantities at the exit agreed well with the analytical values applying the shock tube theory. The total energy release rate at the exit is an important factor for determining the blast wave strength, and we validated that the cube root of the total energy release rate of the shocked air at the exit, estimated by the shock tube theory, could scale the blast wave strength outside.

Defects, such as holes and flaws, greatly affect the mechanical behavior, failure mechanism, and stress wave propagation of frozen soil. To completely characterize the relationship between the dynamic strength and deformation of frozen silty soil containing prefabricated cracks, frozen silty soil specimens with different numbers of prefabricated cracks (zero, one, two, and three cracks) were developed, and dynamic uniaxial compression experiments were performed using the split Hopkinson pressure bar (SHPB) system. The effects of the strain rate and prefabricated crack number on dynamic stress–strain curve characteristics were analyzed. The compound damage variable, which can consider comprehensively the coupling effects of macro- and mesodefects, was calculated based on Lemaitre equivalent strain theory. Two dynamic damage constitutive models were developed and verified based on the conventional Taylor–Chen–Kuszmaul (TCK) and Zhu–Wang–Tang (ZWT) models, and their applicability, advantages, and disadvantages were compared. Strain rate enhancement and prefabricated crack weakening effects were detected for the dynamic compressive strengths of frozen silty soil. It was observed that the two constitutive models essentially could predict the dynamic curves trend under different strain rates and prefabricated crack numbers through a comparison of the theoretical and experimental results. The ZWT model could well reflect the increasing stage compared with the TCK model.