Du Shanyi

Mixed-mode fatigue crack growth prediction in biaxially stretched sheets

Abstract Mixed-mode fatigue crack growth in biaxially stretched sheets is investigated. The modified fracture criterion proposed by Wang and Du is extended to the case of cyclic loading to predict the mixed-mode fatigue crack growth. The analysis of the mixed-mode fatigue crack growth process is very complex. Software developed recently by the authors can be used to more precisely predict the mixed-mode fatigue crack growth process. The software in which the fatigue crack growth criterion presented here is combined with the displacement discontinuity method, a boundary element method, is described in detail from a number of aspects. The analysis of the fatigue growth process of an inclined crack in biaxially stretched sheets is performed.

Mixed-mode fracture criteria for the materials with different yield strengths in tension and compression

Abstract The Nadai elastic-plastic boundary is introduced to define the core region, instead of a core region with a constant distance r from the crack tip and a core region with the Mises elastic-plastic boundary. Taking into account fracture parameters along the Nadai elastic-plastic boundary, two improved fracture criteria are presented for the two commonly used fracture criteria, the maximum tangential-stress criterion and the minimum strain-energy-density criterion. Using the two improved fracture criteria, the effect of properties of the material with different yield strengths in tension and compression on the mixed-mode crack fracture can be revealed. It is shown by analysis that the fracture of the mixed-mode crack is affected by this kind of property of the material. Many results are given by using the two improved fracture criteria, and they are compared with those obtained by using the commonly used mixed-mode fracture criteria.

Effects of Contact Resistance on Heat Transfer Behaviors of Fibrous Insulation

Abstract In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte Carlo method is utilized to determine the modified radiative properties with experimentally measured transient external temperature as high as 1 000 K. It is found that the estimated radiative properties become time-independent after about t = 3 000 s. By comparing the predicted to the measured results in transient state, the contact resistance exerts significant influences upon the temperature distribution in the specimen. Results show that the averaged absolute deviation is 3.25% when contact resistance is neglected in heat transfer model, while 1.82% with no contact resistance.

On anti-plane shear behavior of a Griffith permeable crack in piezoelectric materials by use of the non-local theory

In this paper, the non-local theory of elasticity is applied to obtain the behavior of a Griffith crack in the piezoelectric materials under anti-plane shear loading for permeable crack surface conditions. By means of the Fourier transform the problem can be solved with the help of a pair of dual integral equations with the unknown variable being the jump of the displacement across the crack surfaces. These equations are solved by the Schmidt method. Numerical examples are provided. Unlike the classical elasticity solutions, it is found that no stress and electric displacement singularity is present at the crack tip. The non-local elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum stress hypothesis. The finite hoop stress at the crack tip depends on the crack length and the lattice parameter of the materials, respectively.

Manufacturing and Characteristics of Glass Reinforced PTFE

A study on reinforced Polytetrafluoroethylene (PTFE) with chopped glass fiber or glass cloth was described. This study included manufacturing process of fibrous PTFE, the effects of the content of chopped glass fiber or glass cloth on the tensile strength and dielectric properties of the reinforced PTFE and the effect of filling particles on tensile strength and morphology of PTFE composites, etc. Our results showed that about 11% chopped fiber or 37% glass cloth reinforcing PTFE had the highest tensile strength and acceptable dielectric properties. Crystallizing phenomenon of PTFE was readily observed with the adding of particles. Finally, predicting of dielectric properties was discussed.

Two-dimensional electroelastic fundamental solutions for general anisotropic piezoelectric media

Explicit fomulas for 2-D electroelastic fundamental solutions in general anisotropic piezoelectric media subjected to a line force and a line charge are obtained by using the plane wave decomposition method and a subsequent application of the residue calculus. “Anisotropic” means that any material symmetry restrictions are not assumed. “Two dimensional” includes not only in-plane problems but also anti-plane problems and problems in which in-plane and anti-plane deformations couple each other. As a special case, the solutions for transversely isotropic piezoelectric media are given.

An effective method and its application in assembling the structural stiffness matrix in material-nonlinear finite element analysis

Abstract A very effective technique for assembling the structural stiffness matrix in material-nonlinear finite element analysis is presented. Its application to the stable crack growth analysis is described in detail. A finite element analysis of the process of slow crack growth for a center-cracked specimen subjected to monotonically and slowly increased load until the point of fast fracture is reached is made by means of a material-nonlinear and quasi-three-dimensional finite element program developed by the technique, as an example to illustrate that the technique has been successfully applied to a practical problem.

Electro-elastic green's functions for a piezoelectric half-space and their application

In this paper, as is studied are the electro-elastic solutions for a piezoelectric halfspace subjected to a line force, a line charge and a line dislocation, i. e., Greens functions on the basis of Stroh formalism and the concept of analytical continuation, explicit expressions for Greens functions are derived. As a direct application of the results obtained, an infinite piezoelectric solid containing a semi-infinite crack is examined. Attention if focused on the stress and electric displacement fields of a crack tip. The stress and electric displacement intensity factors are given explicitly.

General coupled solution of anisotropic piezoelectric materials with an elliptic inclusion

In this investigation, the Stroh formalism is used to develop a general solution for an infinite, anisotropic piezoelectric medium with an elliptic inclusion. The coupled elastic and electric fields both inside the inclusion and on the interface of the inclusion and matrix are given.

The stiffness and strength of transformation toughening ceramics with misoriented microcracks

Theoretical studies on misoriented transformation particles and microcracks in transformation toughening ceramics are presented using the Eshelby equivalent inclusion method. The stress field, stiffness and strength were calculated. Experiments were done by the three-point bend method using Al2O3/ZrO2 ceramics and the stiffness and strength were also measured. Comparison between theoretical and test results confirmed the important role of microcracks.