Effect Of Damage Evolution Research Articles

Effect of damage evolution on the auxetic behavior of 2D and 3D re-entrant type geometries

In this work, a mathematical formulation based on variational asymptotic method (VAM) has been proposed to determine the effect of damage on the auxetic properties of two-dimensional (2D) and three-dimensional (3D) re-entrant geometries. The influence of damage progression on the auxetic behavior was captured using a geometrically exact one-dimensional beam theory and an isotropic damage law, implemented in a nonlinear finite element framework. The effect of material degradation on the macroscale effective elastic properties such as the elastic modulus and Poisson’s ratio for the two-dimensional and three-dimensional re-entrant auxetic geometries was quantified. The mechanical behavior as predicted by the in-house Python-based implementation of the proposed VAM-based formulation is verified with the results from the commercial finite element solver Abaqus, wherein the user material subroutine was used to capture damage evolution. The numerical examples presented in this paper reveal that the macroscale auxetic behavior of the geometries was affected significantly by damage progression. The results of this research will provide insights into the design and analysis of auxetic materials for applications that warrant consideration of damage evolution.

Effects of damage evolution on tensile strength measurement of nuclear graphite material by ring compression test

• Effects of damage evolution on tensile strength measurements were studied. • Damage evolution should be considered if an indirect method is used for strength measurement. • Uniaxial tensile strength can be measured via the diametrical ring compression test. Because of the limitations of the direct tension method, indirect methods such as Brazil tests or ring compression tests are widely applied to measure the tensile strength of brittle materials. However, in most cases of indirect method application, empirical equations that have been derived based on the assumption of a linear elastic material are used, and the effects of damage on the tensile strength measurements are ignored. Thus, in this study, ring-shaped nuclear graphite IG-11 specimens were subjected to diametrical compression tests to study the effects of damage evolution on tensile strength measurements. By analysing the experimental results and the damage evolution law obtained via an inverse method and finite element analysis, the true uniaxial tensile strength of IG-11 was accurately obtained. The results indicate that damage plays an important role in the tensile strength measurement of the nuclear graphite material when an indirect method is used. This study is also useful as a reference for obtaining accurate tensile strength predictions for other types of brittle materials.

Characterizing three-dimensional creep of Beishan granite by the variable-coefficient Abel dashpot

Accurate description of creep behavior is of great significance to the safety evaluation of high-level radioactive waste disposal in granite. In this study, a fractional derivative constitutive model is proposed to depict the creep process of Beishan granite, based on the conformable derivative. A variable-coefficient Abel dashpot considering the effect of damage evolution on creep properties is introduced to describe the nonlinear dilatancy strain in the accelerating stage. A new model is proposed and further generalized to three-dimensional creep equations by adopting Drucker–Prager criterion, and the analytic solutions are given employing the Laplace transform. The parameters of new creep model are determined based on experimental data and fitting results are compared. The fitting curves present a good agreement with experimental data, indicating that the conformable derivative creep model achieves a good performance in describing all three creep stages. The proposed model is validated by the comparison of different experiments and degradation of fractional derivative model. In addition, a sensitivity analysis is carried out to show the effects of stress level, fractional derivative order, damage exponent, and other parameters.

Creep Damage and Fracture in Advanced Tungsten Modified 9%Cr Ferritic Steel

Advanced tungsten modified 9%Cr ferritic steel (ASTM Grade P92) is a promising material for the next generation of fossil and nuclear power plants. Unfortunately, there are rather few published reports on damage processes in P92 steel during high temperature creep and the effect of damage evolution on the creep strength is not fully understood. In this work, the creep behaviour of P92 steel in as-received condition and after long-term isothermal ageing was investigated at 600 and 650°C using uniaxial tension creep tests. To quantify the effect of each damage process on the loss of creep strength, most of creep tests were followed by microstructural and fractographic investigations. It was found that the large Laves phase particles, which coarsened during creep exposure, served as preferential sites for creep cavity nucleation.

Elasto-plastic postbuckling of damaged orthotropic plates

Based on the elasto-plastic mechanics and continuum damage theory, a yield criterion related to spherical tensor of stress is proposed to describe the mixed hardening of damaged orthotropic materials. Its dimensionless form is isomorphic with the Mises criterion for isotropic materials. Furthermore, the incremental elasto-plastic damage constitutive equations and damage evolution equations are established. Based on the classical nonlinear plate theory, the incremental nonlinear equilibrium equations of orthotropic thin plates considering damage effect are obtained, and solved with the finite difference and iteration methods. In the numerical examples, the effects of damage evolution and initial deflection on the elasto-plastic postbuckling of orthotropic plates are discussed in detail.

Nonlinear dynamic response of piezoelectric elasto-plastic laminated plates with damage

Based on the elasto-plastic mechanics and continuum damage theory, a yield criterion that is related to the spherical stress tensor is proposed to describe the mixed hardening of damaged orthotropic materials, and the dimensionless form of which is isomorphic with the Mises criterion for isotropic materials. Then, the incremental elasto-plastic damage constitutive equations and damage evolution equations of orthotropic materials are established. By using the classical nonlinear plate theory, the incremental nonlinear dynamic governing equations of the piezoelectric elasto-plastic laminated plates with damage are obtained, and the equations are solved by finite difference method and iteration method. In the numerical examples, the effect of damage evolution, piezoelectric effect and external loads on the nonlinear dynamic response of elasto-plastic laminated plates are discussed detailed. The numerical results show that the mechanical properties of the structures change remarkably when considering the damage, damage evolution and piezoelectric effects.