Papers by Keyword: Damage Criterion

Abstract: Cold flowforming is a chipless forming process that deforms tubular parts by reducing theirouter diameter and thickness while increasing their length. It consists of a rotating mandrel and oneor more rollers that are translated along the tube axis, thus plastically deforming it. Flowforming ofTi-6Al-4V (also known as Ti64) is of great interest for improving the mechanical properties of thematerial, such as yield stress and fatigue strength. However this alloy is known to have poor ductilityat room temperature. Therefore, flowforming of Ti64 without failure or crack is a great challenge. Inthis present paper, the authors have attempted to predict the different failure modes occurring duringflowforming. An experimental machine has been built at the Center forMaterial Forming (CEMEF) inorder to monitor the force on the single roller, the torque on the mandrel and the actual rotation speedof the roller as well. Numerous flowforming tests have been performed using different processingparameters, such as working depth, roller feed and initial geometry, in order to investigate the criticalvalues which lead to the failure of the flowformed tube. In addition, numerical simulations of theprocess have been performed using the FORGE FEM solver. The results of the simulations have beenused to evaluate the relevance of usual failure criteria (Crockford-Latham, Rice-Tracey and Oyane).

Abstract: In order to simulate the rupture process of Cartridge Case, material failure constitutive model is researched. Johnson-Cook plasticity model is given as an analytical function of equivalent plastic strain, strain rate, stress triaxiality. Johnson-Cook plasticity model and Johnson-Cook Damage initiation criterion are used to describe the plastic deformation and fracture of case for the pressure of power gas. Using the implementation of this stress-displacement and characteristic length, problem of the relationship between fracture energy and the characteristic length in finite element model is solved. Finally, the simulated model which includes barrel, case, bolt and locking rigidity spring is built. Comparing the fracture shape and position in simulated test and physical experiment, the results are very similar. It proves that the rupture process of Cartridge Case can be simulated by the constitutive model which is introduced in this paper.

Abstract: In this paper, a new three dimensional FEM model was elucidated on arch dam cracking analysis. Based on the least potential energy method, the stiffness of the interface between two types of mesh is coupled into the whole stiff matrix in this model. By this means, the FEM mesh of local area of arch dam can be easily changed from a coarse mesh to a fine mesh. By changing the density of mesh, the consideration of heterogeneity for the calculating elements is achieved by assigned to the elements random strength and elastic modulus according to a Weibull distribution. This model allows to densify the mesh of a local area and to trace the cracking of this area undertake damage criterion. By applying this new model, the mechanism of vertical cracks opening along the downstream surface of Shuanghe Arch Dam after two years of operation was briefly analyzed. The numerical result is basically agreed with the field investigation.