Papers by Keyword: Damage Evolution

Abstract: A coupled model of damage and plasticity is presented to describe the dynamic behaviors of TiC-particulate reinforced titanium matrix composites (TiCp/TMCs) subjected to shock loadings. The TiCp/TMCs are assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to TiCp/TMCs is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, the smashing destroy takes place. The model parameters for TiCp/TMCs are determined using plate impact experiments. Comparison with the test results shows that the proposed model can give consistent predictions of the dynamic behaviors of TiCp/TMCs subjected to impact loadings.

Abstract: The leaching behavior of hydraulic concrete can’t be neglected for its long-term exposure to surrounding water resulting in irreversible damage to durability, such as strength loss and porosity increase. Given that the coupling effect of leaching and freeze-thaw cycling on the durability of hydraulic concrete especially in severe cold regions is a big challenge. For the quite slow process of natural leaching, electrochemical accelerated leaching method (EALM) was proposed to investigate the damage evolution under two test schemes (scheme one is only leaching for 50 days and scheme two is first 100 rapid freeze-thaw cycles and then leaching for 50 days) designed in this work. The electrical resistivity and calcium oxide dissolution mass were measured through electrochemical impedance spectroscopy (EIS), namely two-probe method, and EDTA titration method, respectively. Based on electrical resistivity measurement, the measurable damage can be discussed during abovementioned singe and coupled tests. The results indicate that compared with single leaching test, the leaching coupled with the freeze-thaw cycling leads to over 50% electrical resistance loss.

Abstract: This work focuses on the application of a higher-order gradient-dependent plasticity-damage model for microstructural modeling of dual-phase (DP) steels. Damage evolution is governed by the evolution of a nonlocal plasticity measure which is a function of the local equivalent plastic strain rate and its corresponding first-order gradient. Different RVEs of DP microstructures are virtually generated and simulated in order to predict the macroscopic mechanical response. Size effects and additional hardening due to evolution of geometrically necessary dislocations are predicted.

Abstract: Superplastic instability and damage evolution of AZ31B magnesium alloy sheet were investigated in this paper. Maximum elongation of 216% and strain rate sensitivity of 0.36 were obtained at 723k and a strain rate of 1×10^-3s^-1, whose fracture was due to the growth and interlinkage of cavities that nucleated at grain boundary. After superplastic tensile tests and quantitative analysis of cavity volume fraction, A cavity growth model were established, and the damage evolution equation based on the law of the micro-damage evolution and statistical mechanics was derived out, and damage characteristic parameters as well as the critical value of damage variable were identified so as to provide a theoretical ground on which the plastic forming technology of magnesium alloy sheet can be optimized.

Abstract: Surface mechanical attrition treatment (SMAT) is an excellent method to get nanocrystalline and nanotwinned ultrafine crystalline steels from coarse-grained AISI 304 stainless steel. Due to their outstanding mechanical properties, they both appear to be relevant candidates for ballistic protection of marine engineering. Comparing their ballistic performance against coarse-grained steel, as well as identifying the effect of the hybridization with a carbon fiber–epoxy composite layer have been done by Jaime Frontan et al. Hybridization is proposed as a way to improve the nanocrystalline brittle properties in a similar way as is done with ceramics in other protection systems. Dur to the limit of experimental equipment, there are many results which are hardly got. In this paper, a numerical method with Johnson–Cook flow stress model, user material subroutine VUMAT and surface-based cohesive behaviour is presented.

Abstract: To study the failure process of metal structure with meso-defects, RVE (representative volume element) with various initial meso-defects were analyzed by using ABAQUS software, the parameter f (void volume fraction) of GTN damage model was regarded as the criterion of structural damage. The result shows that f increased more obvious with volume of defects for spherical defects with the same shape but different size. When the radius of defects is less than 0.15mm, the influence of defects’ volume on increases of f is clear enough. When the radius is greater than 0.15mm, the effects is diminishing. For ellipsoidal defects with the same volume but different aspect ratio, when the long axis perpendicular to the direction of load, the increased trend of f according to plastic deformation more obvious along with aspect ratio of defects. Apparently, as aspect ratio approaches infinity, f would have the fastest growth. Consequently, the bigger defect volume and aspect ratio, the more conducive for damage evolution of the metal structure.

Abstract: This paper presents an integrated creep-fatigue (ICF) theory to describe the non-linear creep-fatigue interaction during thermomechanical loading. The ICF theory recognizes the damage evolution as a holistic process consisting of nucleation and propagation of surface or subsurface cracks in coalescence with internally distributed damage, leading to final fracture. In a polycrystalline material under combined cyclic and dwell loading, crack nucleation and propagation occurs by fatigue or oxidation mechanisms, whereas internally distributed damage often occurs in the form of grain boundary cavities or microcracks due to creep or dwell effects, particularly at high temperatures. Based on the above mechanism, a damage evolution equation is mathematically derived, and the generality of the above physical mechanisms warrants the applicability of the ICF theory over a wide range of stresses and temperatures. This paper uses Mar-M 509, a cobalt base superalloy, as an example to illustrate how the ICF theory describes creep and low cycle fatigue (LCF).

Abstract: This paper aims to investigate the performance of a new three-parameter damage mechanics model which describes three basic damage mechanisms of quasi-brittle solids: tension, shear, and hydrostatic compression. The stress is first decomposed into its positive part and negative part, and then the latter is further decomposed into its deviatoric part and hydrostatic part, whereby a three-parameter damage description is formulated. Through matrix representation of the tensor formulation, specific forms of the three-parameter damage theory are illustrated in various stress states. It is found that the proposed framework of three-parameter damage theory can inherit the existing two-parameter models and extend them to a broader scope of application.

Abstract: To analyze the damage evolution characteristics of Liaoxi frost sand soil on dynamic load , firstly in the foundation of frozen soil damage theory,micro-strength and dynamic modulus are introduced to analyze the damage evolution characteristics of Liaoxi frost sandy soil .Then ,based on the dynamic triaxial test ,respectively analyze the influences made to dynamic modulus by confining pressure and initial water content . Some regular patterns are summarized .The greater the confining pressure, the greater the dynamic modulus of frost sand soil is ,and with the increase of dynamic strain the dynamic modulus under different confining pressure trend to be same .The bigger quantity of initial water content ,the greater the dynamic modulus is and the change rate of frost sand soil`s dynamic modulus with different initial water content are approximately equal .That initial water content has more significant effects on the dynamic modulus is found by the comparison of the effects caused by confining pressure and initial water content .

Abstract: A coupled model of damage and plasticity to describe the complex behavior of concrete subjected to impact loading is proposed in this paper. The concrete is assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to concrete is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. It induces a decrease of strength and stiffness of concrete. Compaction of concrete is physically a collapse of the material voids. It produces the plastic strain in the concrete and, at the same time, an increase of the bulk modulus. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, concrete takes place the smashing destroy. The model parameters for mortar are determined using plate impact experiment with uni-axial strain state. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete.