Key Engineering Materials Vols. 462-463

Abstract: In the present paper, a concrete material is taken as a studying object, both the No. 16 and the JHC constitutive models in LS-DYNA commercial software are used because the parameters of both models are comparatively easy to obtain. The results show that, computational maximum value and the width of the overload curves are good agreement with experimental curves by using these two models in the Lagrange method. With increasing penetrating depth, the ramp and down slopes of the overload curves by computing is increasingly agreement with experimental curves. The JHC model is better to compute overload curves in the Lagrange method. The Lagrange method is also used to compute the penetration of multilayer concrete plate. It is found that, the peak value of acceleration goes down with increasing penetrating layers; this decreasing peak value depends on layer thickness and the strength. Acceleration value between layers will go to zero; this trend is agreement with experiments.

Abstract: Using numerical code RFPA2D (dynamic version), spallation processes of rock-like medium induced by reflection of stress wave with different rise time and decay time are simulated, and based on description and discussion on the failure area in the document [1], the influence of the rise time and decay time of stress wave on spalling process of rock-like material are numerically analyzed and discussed. Results indicate that the comminution zone is affected little by the duration of stress wave regardless of the rise time or decay time, and the fracture zone is affected to a greater extent by the rise time than the decay time, and the spalling zone is affected to some extent by the duration of stress wave regardless of the rise time or decay time, also, the stability of specimen is affected by the duration of stress wave regardless of the rise time or decay time, and the specimen loses stability at a certain decay time earlier than that at the same rise time. Furthermore, the effects of rise time and decay time on the number of failure elements are also investigated. Results show that a shorter rise and decay time increase the number of radial cracks. At longer rise time and decay time, the number of cracks is reduced and the cracks extend longer. In addition, the spalling increases to some extent as the rise time or decay time decreases.

Abstract: The Plasma transferred arc welding (PTAW) is widely used for hardfacing components exposed to severe conditions. Without post welding heat treatments, large tensile residual stresses remain in the hardfacing coating, which is detrimental. In this paper, a set of post welding heat treatments was evaluated for the heat-resistant steel substrate – Co-based alloy hardfacing coating system. Microstructural and mechanical properties, including the chemical phases of coating surface, the microstructure of coating surface, the Vickers hardness and the residual welding stress, were investigated before and after the heat treatments. Results revealed that during the heat treatments, some elements reprecipitated and the secondary carbide Cr23C6 was formed. After the treatments, a more regular structure and a higher Vickers hardness were obtained. Moreover, the tensile residual stresses in the coating decreased significantly. Therefore, it can be inferred that the post welding heat treatments employed in this paper were proper for this material system.

Abstract: Reflective crack is one of the major technical problems in highway with semi-rigid base, studying its formatting mechanism is of great significance. By means of a numerical analysis method named RFPA, formatting process of reflective crack such as initiation and expansion was studied in asphalt pavement with semi-rigid base. Two-dimensional model of asphalt pavement with cement-treated base was established based on mechanical parameters, thickness and homogeneity of commonly used structural layer in china, symmetrical and non-symmetrical load were both considered, and crack of cement-treated base was set before loaded. First, reasons for crack initiation were studied below the bottom layer subjected to different types of loads. The conclusion showed crack under symmetrical load mainly due to pull destruction while crack under non-symmetrical load mainly due to shear failure. Then, crack expansion in asphalt layer subjected to different load numbers with different homogeneity material was studied. The result showed that with the increase of the load numbers, the deformation in the same level deformation grows continuously. Different homogeneity level of layer material has an important influence on crack expansion; higher homogeneity has better regularity.

Abstract: To solve a large scale elasto-plastic dynamics analysis of a complicated structure, such as a seismic analysis of a nuclear power plant and a skyscraper, a new implementation strategy for a parallel finite element code, suitable on a parallel supercomputer with modern multi-core / many core scalar CPUs, has been required. In this work, we propose a new design and programming style to optimize the performance of a parallel finite element code based on the domain-decomposition method (DDM) on multi-core CPUs, considering their cache hierarchy. Instead of a traditional, memory access-intensive approach, DS (Direct solver-based matrix Storage), two new matrix storage-free approaches, DSF (Direct solver-based matrix Storage-Free) and ISF (Iterative solver-based matrix Storage-Free), are proposed. Our new DSF/ISF-based DDM solver is not only more efficient in memory usage but also comparable in computational time against existing DS-based DDM solvers on multi-core CPU architectures.

Abstract: The purpose of this study is to predict the stability of slope using adaptive neuro fuzzy inference system (ANFIS). Based on limit equilibrium theory, four different methods of analyses, i.e. Morgenstern-Price, Janbu, Bishop and Ordinary were used to calculate the overall safety factor of various slope designs. Neuro-fuzzy inference system was used to map from a given input to an output. Important parameters such as height of slope (H), unit weight of soil (γ), angle of slope (θ), coefficient of cohesion (c) and internal angle of friction (ф) were used as the input parameters while overall safety factor was the output. ANFIS model to predict the stability of the slopes was generated from the calculated data. Results showed that factors of safety predicted using ANFIS agreed well with factors of safety calculated using Limit Equilibrium Methods (LEM).

Abstract: Taking a double cantilever beam (DCB) as a representative of one dimensional fracture, a unique pair of pure fracture modes I and II are successfully found in the absence of axial forces, which are orthogonal to each other with respect to the coefficient matrix of the energy release rate. Although the pair are pure modes there still exist interactions between them. The interactions result in energy flow between the two modes and are successfully determined. With the presence of axial forces, there are two independent pure modes I and two independent pure modes II, which are orthogonal to each other as well. They are found and used to partition the total energy release rate.

Abstract: The thermal stress and thermal fatigue life for three different microgyroscope chip models were investigated in this paper. The deformation and stress distribution in chip, at interface between microgyroscope and chip, and in the spring of microgyroscope were obtained for three different microgyroscope chip models by the finite element method. The results show that for the simplified model, no obvious differences from linear or nonlinear analyses are obtained and the fatigue life of microgyroscope chip can be predicted with the properly simplified model. Also, the model having the same process in fabricating microgyroscope and carrier has better reliability. This paper provides an effective method for the reliability analysis of microgyroscope chip.

Abstract: The Enriched Free Mesh Method (EFMM) is a Mixed Method using the Hellinger-Reissner principle. A highly accurate stiffness matrix is computed for each local cluster. As a result, the EFMM can compute the high performance structural problem of low-order mode without an increase in the number of DOF. In this research, a large eigen frequency analysis of discrete model of the EFMM is performed using the Lanczos method on a PC cluster environment.

Abstract: It is evident that most rubber components in the automotive industry are subjected to repetitive loading. Vigorous research is needed towards improving the safety and reliability of the components. The study is conducted on an automotive rubber jounce bumper with a rubber hardness of 60 IRHD. The test is conducted in displacement controlled environment under compressive load. The existing models by Kim, Harbour, Woo and Li are adopted to predict the fatigue life. The experimental results show strong similarities with the predicted models.