Papers by Keyword: Plasticity

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.

Abstract: This paper conducts three-dimensional, nonlinear finite element analysis to investigate the results of using different solution methods and the influence of initial imperfections and material plasticity on failure modes and maximum load of various Z-shaped column lengths; it also compares the column buckling responses between various lengths, each with different initial imperfections. Further analyses include investigating the element suitability and computational costs. Results showed that both displacement control method and Riks method are fully capable of receiving promising results from this analysis. In terms of the effects of initial imperfection and material plasticity on the maximum load that column could carry, the imperfection is the major contributing factor when the column is long whereas the plasticity is the major contributing factor when the column is short.

Abstract: Honeycomb shaped monolithic Fe-β zeolite catalyst for N₂O decomposition prepared by direct extrusion method was investigated. In this paper, we optimized the parameters of the molding process and studied the decomposition properties of the honeycomb catalysts. Monolithic materials could be extruded successfully only with the plasticity ranging from 0.177 to 0.473. The content of SB powder, nitrate and water was shown to have a significant influence on the mechanical strength of the extruded materials. The monolithic samples were characterized by using XRD. Catalytic performances of various monolithic zeolites with diverse density (49 cells/in.2, 81cells/in.2, 169 cells/in.2) were thereafter studied. As shown from the result, catalyst activity increased significantly with the increase of monolithic catalyst density.

Abstract: Residual Stress measurement has gained interests among researchers for many years. Slitting method is one of the destructive techniques that relies on the introduction of an increasing cut to a part containing residual stresses. Similar to all other mechanical strain relief techniques, slitting suffers from the level of plasticity occurs within the sample while cutting. In the present research, slitting method was simulated using finite element analysis. The correct performance of the slitting method procedure was explored using known residual stress fields. Then, simulations of the quenching process of beam samples were performed for three different temperature levels; 400°C, 600°C and 850°C. The experimental procedures of the slitting method on the quenched samples at these temperatures were then carried out. The influence of three stress levels on the ability of the slitting method was discussed. Interesting results were observed.

Abstract: This paper presents a coupled model of damage and plasticity to describe the complex behavior of concrete subjected to shock loading. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete.

Abstract: The dynamic property of carbon filled rubber materials is related to pre-load, excitation frequency and amplitude etc. A model by superimposing an elastic model, a viscoelastic model and an elastic-plastic model is presented to model the dynamic property of a rubber isolator. In this paper, this approach is adopted to calculate the dynamic property of a rubber isolator. It is shown that the presented model can predict the amplitude and frequency dependency of a rubber isolator with small relative errors. The validity of this model is verified by experiment. The approach described in this paper can be used in the design and calculation for rubber isolators.

Abstract: The fretting wear behavior of Ti-6Al-4V is studied with the focus on cyclic plasticity effect under gross sliding condition. The analysis is simulated using finite element based method with a new surface profile model represently a given number of cycles using a cylinder-on-flat geometry. The effect of cyclic plasticity on the stresses and plastic strain distribution is studied. The maximum tangential stress is predicted at the trailing edge while the maximum compressive tangential stress is predicted at the leading edge of contact area. Plasticity in shear component is significant compare to tangential component and predicted at 0^th and 3000^th cycles only. It is found that important to include plasticity that remains from previous cycle for better prediction of fretting wear.

Abstract: A detailed analysis of the expansion process will not only provide proper estimates for processing accuracy, but will also provide critical information needed to properly design the driving force required to perform the expansion process. Furthermore, accurate analysis of the contact of the threaded connection is necessary for estimating the sealing capacity of an expandable casing section after expansion. The 3D Finite Element Method has been used to numerically simulate the expansion process fora given expandable casing section. The principal results obtained from this numerical analysis include: 1) maximum value and distribution of equivalent plastic strain after expansion within the casing, 2) deformed casing shape, 3) maximum value and distribution of contact force at contact surface between pin thread and box thread, and 4) variation in values of the driving force of the mandrel cone during the expansion process.

Abstract: The paper describes and compares selected failure and plasticity conditions of concrete. The CEB-FIB condition, the von Mises plasticity condition with modification for concrete and the Chen-Chen condition are studied. The conditions are compared in 2D and two of these conditions are also used for numerical analysis of a deep beam. The software BSA is chosen for the analysis in the paper. The software BSA is based on the finite element method.

Abstract: Based on relationship between elastic and plastic strain, a new basic equation system of plasticity mechanics was established. In this paper, modification is made to the new basic equation system, and another form of basic equation system is presented based on stress strain constitutive relation, which also makes it possible to apply the results from elasticity mechanics directly to plasticity mechanics and decreases the solving difficulty of plastic problem. Finally, a simple application example is given, which shows that the new form of basic equation system is correct and practicable.