Papers by Keyword: Explicit Finite Element Method

Abstract: The heat treatment simulation based on the explicit finite element method was developed. The subloading surface model considering the phase transformation was implemented in VUMAT of commercial FE code Abaqus/explicit. It is expected that the error of explicit analysis decrease in the stress integration, since the subloading surface model has an ability of pulling back stress state automatically to the yield surface in the plastic loading process. The formulation of subloading surface model in metallo-thermo-mechanics is presented, and the verification of the presented model is shown by the finite element quenching simulation. The deviation from the yield surface is less than that of the conventional explicit analysis, and the computation time is considerably less than that of the implicit analysis.

Abstract: Phenomenological ductile fracture criteria represent, among others, one of powerful tools for prediction of ductile fracture. These criteria are based on evaluating damage throughout the solid body as a response to straining. The damage is influenced by plasticity but not vice versa. Therefore, these criteria are often called uncoupled as they do not mutually couple the damage and plasticity. One of immense advantages of such criteria is a possibility not only to predict the crack initiation but also to follow the propagation based on the damage. Moreover, it is not restricted for one specific locus but the damage is evaluated in the entire solid body and one or more cracks can be tracked simultaneously or sequentially. Ductile fracture criteria are calibrated on the basis of several independent calibration tests under various stress states. One way how to verify calibrated model is to simulate numerically an experimental tests and follow the crack initiation and propagation. In the present study, selected phenomenological criteria were calibrated using various calibration tests. Then, selected calibration tests were simulated together with implemented ductile fracture criteria. In our case, the verification is carried out on tensile cylindrical specimens. Finally, computationally obtained results were compared to the experimentally observed ones and the prediction ability and reliability of selected phenomenological criteria is discussed.

Abstract: According to the theory of collapse numerical simulation, the explicit finite element algorithm based on explicit dynamics was chose as the numerical calculation method. And combined with the plane RC frame collapse test and the example of ten layers frame structure, the wire frame model, integrated model and separate model were established and the alternate path method was adopted to study the simulate method of structural collapse. With the comparison of several aspects to the results, the rationality of the numerical simulation method and the applicability of the numerical models were verified respectively. At the same time, according to the complex pre-treatment process to the numerical simulation of structural collapse, an MFC program with the function of exporting APDL file which can generate wireframe models for structural collapse simulation in ANSYS/LS-DYNA was developed using VC++ language with the purpose of offering convenience to the numerical simulation process of structure collapse.

Abstract: Solid shell element models which possess only translational degrees of freedom and are applicable to thin structure analyses has drawn much attention in recent years and presented good prospect in sheet metal forming. In this study, a solid shell element model is introduced into the dynamic explicit elastic-plastic finite element method. The plane stress constitutive relation is assumed to relieve the thickness locking and the selected reduced integration method is used to overcome volumetric locking. The assumed natural strain method is adopted to resolve shear locking and trapezoidal locking problem. Two benchmark examples and a stage of roll forming process are calculated, and the calculating results are compared with those by solid element model, which demonstrates the effectiveness of the element.

Abstract: This study evaluates cracks in a ceramic ferrule. When an optical fiber is connected to machinery, a ferrule is used to precisely set the optical axes of an optical fiber. A ferrule is a cylinder of 10.5mm in length and 2.5mm in diameter. The crack size of a ferrule can range from 10.40
m to 32.35
m. An acceptable ferrule must have no cracks. In this paper, we predicted and examined defects by Resonant Ultrasound Spectroscopy (RUS). To verify the data obtained from the experiment, we carried out simulation by explicit finite elements method, and compared the experimental results with simulation results. The average error range is 1~2 percent between the experimental resonant frequency of the acceptable specimens and the simulated FEM resonant frequency. Also, we compared the resonant frequencies of specimens with a crack with those of acceptable specimens. The histogram drawn from these data and the available mode surveyed were used to classify the specimens in the plant as either cracked or non-cracked specimens.