Papers by Author: Ya Zhi Li

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Authors: Ya Zhi Li, Jing He, Zi Peng Zhang
Abstract: The behavior of plasticity induced fatigue crack closure (PICC) in middle tension specimen was analyzed by the elastic-plastic finite element method. For the constant-K (CK) loading cases, the opening stress intensity factor are independent of crack length. The level of increases with the maximal applied stress intensity factor for given load ratio and increases with for fixed . The in plane strain state is much smaller than that in plane stress state. The results under CK loadings can be deduced to constant amplitude cyclic loading case during which the load ratio, maximal load level, crack length and specimen thickness are all the factors affecting the crack closure effect. The phenomena revealed in the analysis are beneficial in understanding the driving force mechanism of the fatigue crack growth.
Authors: Ya Zhi Li, Jing He, Zi Peng Zhang, Liang Wang
Abstract: The crack closure phenomenon has attracted great attention in the prediction of fatigue crack growth. The finite element analysis of fatigue crack growth has been conducted by many researchers mainly emphasized on the technique implementation of the simulation. In this paper the behavior of plasticity induced fatigue crack closure was analyzed by the elastic-plastic finite element method for middle crack tension (MT) specimen. The material was assumed as linear-kinematic hardening. The crack growth was simulated by releasing the “bonded” node pairs ahead of crack tip in stepwise. The calculations focused on the effects of load cases and crack length on crack opening/closure levels. For constant amplitude cyclic loadings with different load ratios, the crack opening/closure levels increases for a while and then decreases continuously, with the increase of crack length. For the loadings with invariable maximum stress intensity factors (briefly the constant-K loading), however, the crack tip plastic zone sizes at different crack lengths remain unchanged and the crack opening and closing load levels normalized by the maximum load levels keep constants as well. The results indicate that the crack length does not affect the relative opening and closure levels and numerical analysis for the constant-K loading case should play a key role in characterizing the fatigue crack growth behavior.
Authors: Wei Jiang, Ya Zhi Li, Yi Xiu Shu, Masanori Kikuchi
Abstract: Ductile fracture of 2024-T3 aluminum alloy has been investigated under tensile and shear loading conditions. In order to predict rupture, a void–based meso–damage constitutive relationship which can deal with both tensile and shear problems is developed and implemented in commercial software ABAQUS. The tensile and shear fracture behaviors including the load–displacement response and crack propagation path, of 2024–T3 aluminum alloy are analyzed using the proposed approach and compared with experimental data. It is shown that the proposed approach can be used to predict the failure of ductile materials under complex loading conditions.
Authors: Biao Li, Ya Zhi Li, Xi Li, Zhen Hua Yao
Abstract: The residual compressive strength of composite laminates subjected to low-velocity impact (CAI) was analyzed using the ABAQUS/Explicit package through a two-step calculation. The finite element model was composed of solid elements and interfacial cohesive elements. The out of plane low-velocity impact process was simulated in the first step and the results of which were taken as the input for the second step of the in-plane compression, until the collapse of the laminate. The usefulness of the explicit solution algorithm in dealing with the quasi-static procedure of the in-plane compression was investigated by examining the effect of different initial velocities of the compression loading on CAI values. The simulation results agree well with the experimental results.
Authors: Liang Wang, Ya Zhi Li, Hong Su
Abstract: The use of weight function technique in fatigue crack growth subjected to external cyclic loading and residual stress field has been questioned by several researchers in that the technique is unable to account for the residual stress redistribution during the crack growth. In this paper a center cracked tension specimen containing residual stresses was analyzed by finite element method. The crack growth was simulated by releasing the nodes ahead of crack tip in stepwise and the stress intensity factors induced by residual stresses at different crack lengths were estimated. The results from the numerical analysis are identical to the weight function solution, which demonstrates that the weight function technique can be used for the fatigue crack growth analysis in residual stress field, unless the residual stress distribution is disturbed by the plastic yield.
Authors: Ya Zhi Li, Kai Da Zhang, Bo Ping Zhang
Authors: Xiang Dong Liu, Ya Zhi Li, Zhen Hua Yao, Huai Shu
Abstract: The experiment and finite element analysis were made to determine the pin-load distribution of multiple countersunk bolted single-lap joints. In the experiment, the pin-load fractions were evaluated indirectly by the lap-sheet surface strains collected from a few rows of strain gages. The joint strains and pin-load distribution were also obtained directly in the finite element analysis. The calculated strains correlated well with the experiment. Nevertheless, the pin-load fraction results of the both techniques are quite different. The further analysis revealed that the procedure of transforming the measured strains into pin loads is not reliable, since the intrinsic additional bending had not been taken into account. Therefore the appropriate way to determine the pin-load distribution should be the numerical analysis validated by the strain measurement. The another attempt showed that the pin-load distribution can be evaluated by the finite element modeling of two-dimensional shells and beams as well with satisfied accuracy.
Authors: Jian Yin, Ya Zhi Li, Pei Xin Zhang, Kai Da Zhang
Abstract: A fatigue analysis method was developed to predict the fatigue behavior of the T300/QY8911 multidirectional laminated composites. The finite element analysis of the interlaminar stresses and the average of them localized to the free edges of the specimens were made for predicting the delamination onsets and lives. The residual lives to failure after delamination was estimated afterwards. The predicted fatigue lives agree well with the test results.
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