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Vehicle–track coupling vibrations, primarily induced by track irregularities and vehicle speed, have a profound influence on the service life of fastening systems. However, the failure mechanism and damage evolution of elastic fasteners under such vibration coupling have remained elusive. In this research, tensile tests on 60Si2Mn steel and quasi-static as well as fatigue tests on e-type clips were conducted. A finite element model of the fastening system and a vehicle–track coupling dynamics model for a metro vehicle were developed to conduct a comprehensive analysis of the fatigue life of the e-type clip, considering the combined effects of track irregularity, vehicle speed and initial clamping force. Additionally, a modified mean stress correction model was employed to predict the clip’s fatigue life, and a novel two-parameter nonlinear fatigue cumulative damage model was proposed to describe the clip’s damage evolution. These innovative approaches and models provide valuable insights for guiding the installation and maintenance of track infrastructure.

This paper is concerned with development of a process map for sequential compression-backward extrusion of bulk AZ31 Mg alloy at the warm temperatures. In experiments, metal flows and crack initiations are carefully investigated and formability is examined systematically for various forming conditions such as forming temperature, punch speed, and a gap between a specimen and die. Then, a process map for the sequential compression-backward extrusion of bulk AZ31 Mg alloy at the warm temperature is proposed. In order to further understand deformation behaviors and damage evolution during warm forming process, thermo mechanical finite element analyses coupled with damage evolutions are carried out. In general, finite element predictions support experimental observation. Finally, it is concluded that the process map, proposed for the sequential compression-backward extrusion of AZ31 Mg alloy, is valid.

The tensile responses and the associated damage evolutions of a 3D C/SiC composite with and without heat treatment on the fiber preforms were compared. The results show that the composite without heat treatment exhibits a largely non-linear stress-strain behavior up to rupture as well as a lower strength and a strain-to-failure. The damage evolution characterized by acoustic emission indicates the composite failures in the region of matrix cracking multiplication. However, the composite with heat treatment has a larger strength and a strain-to-failure, and the damage evolution indicates that the composite had experienced the region of matrix cracking saturation and then fiber bundle pull-out just prior to final failure. Microstructural observations on the fractured specimens revealed the interfacial bonding between fibers and matrix becomes weaker after heat treatment.

At high strain rates, the dynamic response of cement mortar, a heterogeneous material with damage, was experimentally studied under three different stress states: (1) one-dimensional stress state by using the SHPB technique, (2) one-dimensional strain state at high pressures from 1 to 5 GPa by using a one-stage gas gun, and (3) quasi one-dimensional strain state by using an improved passive confining SHPB technique. The experimental results indicate that cement mortar is a kind of nonlinear rate-dependent material with internal damage evolution, and that the confining pressure greatly influences its ductility and strength. The main results are given and discussed.

The aim of this paper is that the precise description of damage behavior is crucial to well catch the mechanical behavior of structures in the dynamic numerical simulation, and address the issue on the coupled plastic-damage constitutive model for circular steel tubes of reticulated shells under severe earthquake. Continuum Damage Mechanics (CDM) constitutive model established by Lemaitre is reviewed at the beginning. Then, an improved damage model for circular steel tubes of reticulated shells is developed based on Lemaitre’s model by replacing the original damage evolution law with a new one suitable for circular steel tubes. In addition, we introduce the stress update process. In this procedure, the well-known operator split strategy, which leads to the standard elastic predictor/return mapping algorithm, is adopted to solve the evolution problem of the improved model. Exploiting user-defined material subroutine, the implementation of the model is achieved within software ANSYS using BEAM189 element. Finally, the dynamic response of reticulated shells under severe earthquake are numerically simulated with the proposed model and with the conventional Prandtl-Reuss model, respectively. The comparison results show that the consideration of material damage accumulation, on the one hand, may change the failure mode of reticulated shells from dynamic instability to strength failure; on the other, may reduce the dynamic ultimate load obviously. This consideration should be taken into account when conducting nonlinear dynamic analysis of reticulated shells.

A nonclassical multiscale "morphological approach" devoted to highly-filled particulate composites was proposed by Nadot et al.¹ It is extended by developing complementary ingredients in order to describe the evolution of damage by decohesion of grain/matrix interfaces. A defect nucleation criterion allows the evolution of the number of defects to be followed, and a closure criterion monitors the respective proportions of open and closed defects. The nucleation criterion is associated with a critical value of the current distance between two points located on both sides of the interface considered, whereas the closure criterion is based on the normal component of the displacement jump across the interface. The "morphological approach" is tested at macroscopic and local scales for a random particulate microstructure under loading paths involving tension and compression. The corresponding results are a specific contribution of this work. At global scale, the numerical results presented show the effects of damage induced anisotropy and recovery of mechanical properties by defects closure. Thanks to explicit schematization of the microstructure, the discrete model provides, at microscale, the characteristics of damage (chronology of events, position and morphology of defects) as well as its effects on local strains.

An experimental campaign is underway in order to understand the behavior of rectangular columns under uniaxial and biaxial flexure. The present paper addresses the initial part of that campaign, by reporting on two columns tested under uniaxial bending in one horizontal direction and then submitted to another uniaxial test in the other direction. The test result analysis focuses on the contributions of flexure, shear and slip components to the global deformation. The experimental results were compared with a simplified method for column response. The Park and Ang damage index is calculated and compared with the physical damage observed.

A new rate-dependent stochastic damage model for the dynamic modeling of concrete is presented in the paper. This model is formulated on the basis of the stochastic damage model, from which, the static stochastic evolution of damage is strictly derived. Then, rate dependency of concrete is included by means of viscous-damage mechanism. The model predictions are tested against experimental results on concrete specimens that cover different strain rates. The results demonstrate the proposed model may predict dynamic failure behavior of concrete quite well.

Slip or debonding of bonding interface is the key cause of the performance degradation or failure of the reinforced concrete (RC) member. In this paper, based on Monte Carlo method, a mesoscopic finite element model composed of mortar, coarse aggregate and steel rebar was established to consider the mesoscopic damage on the bonding interface and its influence on macroscopic performance deterioration of RC specimen. The results show that the simulation results fit well with experimental data. Higher initial interfacial damage results in lower bonding strength and smaller final displacement. Higher mortar modulus could greatly improve the initial bonding property and bonding strength, but slightly increase the final damage. Compared with the RC specimen model with plain steel bar, the model with deformed steel bar shows a longer duration of nonlinear increase for drawing force and lower bonding strength. When confinement is applied, the coalescence of damage zones is prevented due to the effect of thread. Therefore, the application of confinement could increase the bonding strength and the initial bonding property.

In order to reveal the underlying mechanism governing the failure of solids subjected to impact loading, this paper presents a closed trans-scale formulation and numerical simulation of damage evolution to macroscopic failure, in particular to spallation. The trans-scale formulation consists of equations of continuum, momentum, and microdamage evolution, in which there are several time scales and length scales on meso- and macroscopic levels. With this formulation, numerical simulation on spallation is performed. The effects of several predominate dimensionless parameters, such as imposed and intrinsic Deborah numbers, on spallation are discussed.

The impact behavior of cement mortar, a heterogeneous material with damage, were experimentally studied under three different stress states: (1) one-dimensional-stress state by using the SHPB technique, (2) one-dimensional strain state at high pressures from 1 to 5 GPa by using an one stage gas gun and (3) quasi one-dimensional strain state by using an improved passive confining SHPB technique. The experimental results show that cement mortar is a kind of nonlinear rate-dependent material with internal damage evolution, and the confining pressure greatly influence its ductility and strength. The main results are given and discussed.

This paper is concerned with development of a process map for sequential compression-backward extrusion of bulk AZ31 Mg alloy at the warm temperatures. In experiments, metal flows and crack initiations are carefully investigated and formability is examined systematically for various forming conditions such as forming temperature, punch speed, and a gap between a specimen and die. Then, a process map for the sequential compression-backward extrusion of bulk AZ31 Mg alloy at the warm temperature is proposed. In order to further understand deformation behaviors and damage evolution during warm forming process, thermo mechanical finite element analyses coupled with damage evolutions are carried out. In general, finite element predictions support experimental observation. Finally, it is concluded that the process map, proposed for the sequential compression-backward extrusion of AZ31 Mg alloy, is valid.