Standard Damage Model Research Articles

Simplified Damage Assessment Tool for Rails and Crossings Based on Standard Wear and RCF Models

A numerical tool is proposed to simultaneously assess various damage mechanisms that are driven by contact loading. The tool transfers loads to the contact-patch level using three contact parameters: the maximum contact pressure (pmax), the creepage (c) and the contact length (2a). The local wear and RCF predictions are implemented based on existing models from the literature. The load input can originate from numerical vehicle–track simulations or manual input of the user. The assessment tool is applied for a finite element analysis of a fixed manganese crossing nose to prove its validity. The algorithm is implemented via an automated Python code, which, on the one hand enables damage prediction for track components based on standard damage models. On the other hand, knowledge of novel local contact damage models can be transferred to the scale of track components.

The Progressive Failure Analysis of Uni-Directional Fibre Reinforced Composite Laminates

ABSTRACTThe three dimensional standard damage model developed by Lavedeze et.al [9, 13] for uni-directional fibre reinforced ply is implemented into the nonlinear solution of NX Nastran within composite solid element to analyze the progressive damage process and ultimate failure of fibre reinforced composite laminates. This ply level meso-damage-constitutive-model takes into account main damage mechanisms including fibre breaking, matrix transverse cracking, and fibre/matrix de-bonding; also considers contributions like plasticity coupling, damage delay effects, and elastic nonlinearity in fibre compression. Dissipated energy and damage status are also introduced to reflect the damage condition on the macrostructural-level. Using the implemented code, simulation is carried out on the uniaxial tension of a [±45]2s laminate with IM6/914 material, wherein the predicted ply shear rupture stress matches the experimental results very well and better than the theoretical predictions in literature. Moreover, a [-45/0/45/90] holed laminate loaded in tension is simulated to show the complex behavior of subcritical damage evolution and failure process in the composite structure. The composite solid element with damage model supported in NX Nastran is shown to be a reliable tool to analyze the progressive failure of uni-directional fibre reinforced composite laminates.

The structure of steady shock waves in porous metals

The paper aims at developing an understanding of steady shock wave propagation in a ductile metallic material containing voids. Porosity is assumed to be less than 0.3 and voids are not connected (foams are not considered). As the shock wave is traveling in the porous medium, the voids are facing a rapid collapse. During this dynamic compaction process, material particles are subjected to very high acceleration in the vicinity of voids, thus generating acceleration forces at the microscale that influence the overall response of the porous material. Analyzing how stationary shocks are influenced by these micro-inertia effects is the main goal of this work. The focus is essentially on the shock structure, ignoring oscillatory motion of pores prevailing at the tail of the shock wave. Following the constitutive framework developed by Molinari and Ravichandran (2004) for the analysis of steady shock waves in dense metals, an analytical approach of steady state propagation of plastic shocks in porous metals is proposed. The initial void size appears as a characteristic internal length that scales the overall dynamic response, thereby contributing to the structuring of the shock front. This key feature is not captured by standard damage models where the porosity stands for the single damage parameter with no contribution of the void size. The results obtained in this work provide a new insight in the fundamental understanding of shock waves in porous media. In particular, a new scaling law relating the shock width to the initial void radius is obtained when micro-inertia effects are significant.

Calculation of Gamma Induced Displacement Cross-sections of Iron Considering Positron Contribution and Using Standard Damage Model

The displacement cross-section of iron was calculated for gamma-ray irradiation with the energy range of 1 to 15 MeV, which corresponds to radiation fields in fission reactors. Three gamma-material interactions, Compton scattering, pair production and photoelectric effect were considered. The displacements induced by both electrons and positrons were included. For damage function the modified Kinchin-Pease model with the displacement energy of 40 eV was applied, which are used as the standard damage model in neutron-induced displacement calculations. The standard damage model gave a lower cross-section by a factor of 1.3 compared to Kinchin-Pease model, and the exact treatment of positron contribution gave a lower cross-section by a factor 1.1 compared to an approximation treating positrons as electrons. The present cross-section was lower by a factor of 1.1–2.0 than the cross-sections previously proposed in the literatures.

Calculation of Gamma Induced Displacement Cross-sections of Iron Considering Positron Contribution and Using Standard Damage Model

Calculation of Gamma Induced Displacement Cross-sections of Iron Considering Positron Contribution and Using Standard Damage Model

GRADIENT ENHANCED DAMAGE FOR QUASI-BRITTLE MATERIALS

Conventional continuum damage descriptions of material degeneration suffer from loss of well-posedness beyond a certain level of accumulated damage. As a consequence, numerical solutions are obtained which are unacceptable from a physical point of view. The introduction of higher-order deformation gradients in the constitutive model is demonstrated to be an adequate remedy to this deficiency of standard damage models. A consistent numerical solution procedure of the governing partial differential equations is presented, which is shown to be capable of properly simulating localization phenomena.