International Journal of Damage Mechanics

The 2D extended homogenization model based on molecular chain network theory is employed to investigate the micro-to macroscopic mechanical behavior of polymer with randomly distributed voids under macroscopic compaction. A parametric study is performed to quantify the effect of the volume fraction of voids and the macroscopic stress triaxiality of loading conditions on the compaction behavior of porous polymer. The results suggest that the onset of localized shear band at the ligament between voids leads to the macroscopic yield of porous polymer. Furthermore, the microscopic localized shear deformation behavior is promoted in the polymer with high-volume fraction of voids under high macroscopic stress triaxiality loading condition, which results in the early appearance of the macroscopic yield. After the macroscopic yield, a remarkable strain hardening is shown in the macroscopic response of porous polymer under high macroscopic stress triaxiality loading condition, which is due to the onset and propagation of a large number of shear bands at the ligaments between voids. On the other hand, microscopic buckling develops at the narrowest ligament in the polymer with high-volume fraction of voids under high macroscopic stress triaxiality loading condition, which leads to the relative low macroscopic deformation resistance. Furthermore, to develop the macroscopic constitutive model of polymer with high-volume fraction of voids under high macroscopic stress triaxiality loading condition, a modified Gurson model is proposed which takes account of microscopic buckling and gives a good agreement with the unit cell computational results.

This article discusses the delayed fracture and localized polarization switching near a crack tip in three-point bending piezoceramics under electromechanical loading. We have used finite element analysis to study delayed fracture experiments with single-edge precracked-beam method. A nonlinear finite element analysis was employed to calculate the fracture mechanics parameters such as energy release rate for the permeable, impermeable, and open crack face boundary conditions. Recent proposed energetically consistent boundary conditions were also considered. The effects of applied electric field and localized polarization switching on the fracture mechanics parameters were then examined.

A crack initiates at an interface edge between submicron thick films and leads to the malfunction of microelectronic devices. In this study, the cohesive zone model method with a cohesive law based on the damage mechanics concept is developed to simulate the creep crack initiation at an interface edge between tin and silicon films. Experiments on delamination at the Sn/Si interface using a micro-cantilever bend specimen were conducted. The cohesive law is applied to the elements in the UEL user subroutine in the finite element code ABAQUS. The parameters characterizing the cohesive law are calibrated by fitting displacement-time curves obtained by experiments and FEM simulations. It is revealed that the order of stress singularity increases with time and has a significant jump in its value at the crack initiation.

The coupled computational procedure of the induction heating, the thermal conduction, the thermal elasto-viscoplastic damage, and the phase transformation analysis has been developed for the induction hardening analysis of steel machine parts. The validity of the proposed computational procedure has been illustrated by conducting the induction hardening analysis of a circular bar and a notched circular bar.

Numerical simulation by finite element analysis was used to investigate the relationship between the strength of glass fiber reinforced plastic (GFRP) and fiber length. Load speed dependability was also investigated, since thermoplastic resin used for GFRP exhibits much nonlinear stress—strain behavior and strong dependency on load speed. For this purpose, we conducted a periodic-cell simulation to address the effect of composite microstructure, matrix viscoplasticity, and microscopic damage (fiber break and matrix crack). When the fiber length was varied, the damage pattern was divided into two patterns: fiber-avoiding propagation and fiber-breaking modes of the matrix crack from fiber ends. When the matrix crack easily propagated in a fiber-avoiding way for shorter fiber lengths, the rate-dependent effect of the matrix was significant. Moreover, we considered the length at which the fracture mode changed based on this analysis, and compared it with the conventional critical length given by Kelly. Since the conventional critical length does not ensure improved composite strength, the consideration of the damage mode transition is essential for selecting the appropriate fiber length for strength improvement.

In order to clarify the elasto-viscoplastic deformation behavior and strength of rubber blended semi-crystalline polymer, micro- to mesoscopic mechanical behavior was modeled by using large deformation finite element homogenization method. In this model, dimension of mesostructure is identified by the volume fraction of interface region around the rubber particles. The effects of strain rate and the size of rubber particles on the mesoscopic true stress—strain relation, strain rate distribution in mesoscopic area, and change in mesoscopic morphology with deformation are investigated by numerical simulation of uniaxial tensile deformation of semi-crystalline polymer with nonuniformly distributed rubber particles. A series of computational simulations clarified that mechanical behavior of blend polymer is strongly affected by the size of rubber particles. Mesoscopic true stress—strain relationship shows softening for blend polymer with large rubber particles, which is closely related to the distribution of strain rate on mesoscopic scale. When the rubber particles are large, local strain rate is highly concentrated in the ligament area between adjacent rubber particles, while it distributes in larger area of semi-crystalline polymer matrix in case of small rubber particles. The difference in these localized deformation leads to characteristic change in the size and shape of rubber particles with straining. Nonuniform deformation in mesoscopic area caused by heterogeneous rubber particle distribution is emphasized by high strain rate and large rubber particles. Furthermore, maximum mean stress generated in semi-crystalline polymer matrix is very high when the size of rubber particles is smaller than or ligament thickness is larger than a specific value. The specific thickness corresponds to the critical value for brittle-ductile transition of rubber blended semi-crystalline polymer obtained by impact test.

In the present article, columnar specimens of lead zirconate titanate (PZT) were subjected to static compressive stress, and the characteristics of fracture under compression were clarified. The fracture tests were interrupted at certain intervals, and resonance and anti-resonance frequencies and electrostatic capacity were measured by means of an impedance analyzer with the compressive stress unloaded. The interruption and measurement were repeated with the maximum stress increased up to the fracture. The material properties of the specimens such as the electromechanical coupling coefficient, the dielectric constant, the elastic coefficient, and the piezoelectric constant were evaluated based on the resonant properties, and the variation of the material properties in the process of the fracture were clarified experimentally. An elastic coefficient was also evaluated from stress— strain relations during the compression fracture tests, and the difference in the elastic coefficient depending on the method of evaluation was discussed. Furthermore, internal damage developed in the specimens during the compression fracture tests was evaluated based on the variation of the elastic coefficients indirectly as a scalar damage variable on the basis of the continuum damage mechanics. Features of the damage development and the dependence of the quantitative value of the damage variables on the evaluation method of the elastic coefficient were discussed. SEM micrographs of the fracture surface were observed and the causes of the damage were investigated.