Papers by Keyword: Micro-Mechanical Model

Abstract: Most important macroscopic inelastic phenomena of filled elastomers are due to microscopic damage processes inside the rubber network. For example, the Mullins effect can be explained by debonding of polymer chains from the carbon black aggregates. In turn, the damage and following recovery of aggregates are responsible for the hysteresis. All these effects also induce anisotropy of an initially isotropic material. In the present contribution, we show how these effects can be quantified experimentally and simulated by a micro-mechanical model. The model is based on the decomposition of the rubber matrix into a purely elastic polymer, a polymer-filler and a filler cell network. The polymer-filler network model takes into account the debonding of polymer chains from filler aggregates and is thus able to predict the strain induced damage and the permanent set. The filler cell network model describes breakage and recovery of filler aggregates and is responsible for the hysteresis. The presented model is in accord with a broad range of experimental observations.

Abstract: The use of advanced composite materials reinforced with fibers is expanded in these years. The main reason for the increased use of these materials is their high strength and hardness coefficient, their density and low prices. So, the fiber-reinforced composite materials can be used in the design of structures that require high strength to weight ratio and hardness coefficient. In order to replace these materials and new applications, many research programs to study the mechanical behavior of these materials has shifted. In this paper Finite element model presented in which the fibers and matrix are modeled separately and to show a full description of the properties of the constituent components, the interface between matrix and fiber discontinuity is presented in the model With using modeling and analysis after great determination of mechanical properties of unidirectional fibrous composite single and compared with experimental results, the elastic modulus changes depending on the angle of the fibers is received . The results of this method are compared with available mathematical models.

Abstract: This study provides an engineering application of a continuum damage model to analyze the ductile tearing of axial surface cracks in X80 pipelines. Compact tension experiments were conducted to examine the behavior of large crack extension of X80 pipeline steel. The test results were used to verify the optimized parameter set of the proposed damage model. In the numerical model, progressive damage was restricted within a predetermined fracture process zone (FPZ). The material’s damage behavior in FPZ was described in terms of the Gurson–Tvergaard-Needleman (GTN) micro-mechanical damage model. The measured load versus load line displacement curve of CT specimens was numerically predicted using the damage model developed. T* integral was calculated to determine the limiting crack size in X80 pipelines. The damage model was then used to analyze the axial subcritical crack extension. It can help Leak-Before-Break (LBB) assessment.

Abstract: A continuum model for composite materials made of short, stiff and tough fibres embedded in a more deformable matrix with distributed microflaws is proposed. Based on the kinematics of a lattice system made of fibres, perceived as rigid inclusions, and of microflaws, represented by slit microcracks, the stress-strain relations of an equivalent multifield continuum is obtained. These relations account for the shape and the orientation of the internal phases and include internal scale parameters, which allow taking into account size effects. Some numerical analyses effected on a sample fibre-reinforced composite pointed out the influence of the size and orientation of the fibres on the gross behaviour of the material.

Abstract: In-situ SEM shearing tests were performed on samples from the heavily cold rolled (Extrahard) aluminium alloys, where the parallelepiped test sample was cut as to let shear direction (SD) have an angle α with the rolling direction (RD). This shear angle ranges from 0o to 165o with an interval of 15o. These include three heavily cold rolled non heat-treatable aluminium alloys AA1200, AA3004 and AA5182. During these tests, strain localization (macro-shearbands) was bserved. This phenomenon is found to be anisotropic and depends on the angle α. The strain localization or macro-shearbands are believed to be related with strain softening, where the flow stress decreases with strain. According to the crystal plastic theory, the strain softening is considered as resulting from the joint effects of texture and evolution of microstructure, in particular the dislocation patterns. Focusing on texture softening, simple and advanced Taylor type micro-mechanical simulations (Full-constraint Taylor (FC Taylor) and Advanced Lamel models (Alamel)) are performed to calculate the texture and average Taylor factor evolution with the increment of shear strain, on the basis of the measured rolling textures. After the simulations, the shear strain at which texture softening happens is recorded for each alloy and each shear angle. For alloys AA3004 and AA5182, it is found the texture-softening trend is similar to the experimental observations, which showed that the strain localization starts at smaller strains at shear angles of around 30-60o and 120-150o, finally leading to early failure. On the contrary, for alloy AA1200, the calculated average Taylor factor evolution does not resemble the flow behaviour. Furthermore the conclusions for alloys AA3004 and AA5182 are only qualitative, as the value of texture-softening strains predicted by simulation seems different from the observations. This shows that the importance of other effects such as possible microstructural softening mechanisms, especially the one due to the change of strain path (rolling/shear). Then for future models, it will be necessary to incorporate both the texture effects and microstructural effects comprehensively in order to precisely predict the strain localization behaviour of materials.