Narrow Results

We study the stability of anisotropic fluid configuration using a relation between density and pressure. For this purpose, we formulate the corresponding field equations, generalized Tolman-Oppenheimer-Volkoff equation and mass equation which are necessary to discuss the structure of compact stars and solve them through numerical technique. The stability of the compact object is analyzed through cracking and formulate the force distribution function after perturbing the matter quantities. Further, we plot the resulting force function and examine the occurrence of cracking/overturning.

In order to know the impact behavior of turbine blade-grade monolithic silicon nitride ceramic, particle impact tests have been carried out at room and elevated temperatures with and without tensile load, which simulates the centrifugal force of blade rotation. In the experiments, a 1 mm diameter samarium-cobalt particle is impacted at velocities up to 900 ms^-1. The main results are : 1) Degradation of impact strength was clearly observed at elevated temperature and under tensile stress. 2) The critical stresses for the ring cracking were evaluated from both dynamic and static loading tests and were compared with each other. For a candidate material the reasonable stress value was supposed to be 14 GPa or less. 3) Moreover, X-ray inspection revealed that the radial cracks were prevailing in impacts at elevated temperatures.

Ceramic injection moulding is a well established processing technique, but is still limited to thin section components. This paper gives an overview of a variety of defects which appear preferentially in thick moulding sections. The generation of porosity and voidage during packing and solidification are discussed and related to the conditions prevailing during solidification. The use of an insulated sprue extended gate solidification and eliminated voids in thick sections and the use of a polyoxymethylene binder system enabled the progressive removal of binder from large 35 mm sections. Low hold pressure, applied by using a modified injection moulding machine reduced residual stress-induced cracking. Pronounced differential sintering was traced to particle alignment during mould filling and could be eliminated by using equiaxed powders.

This paper introduces the research work of “High Performance Sheet Metal Forming Team” from Huazhong University of Science & Technology, in hot stamping technology and application. Aiming at the basic theory and engineering application of hot stamping, the team has begun comprehensive study in materials, process and equipment for hot stamping of high strength steel since 2008. The representative achievements in many aspects of the team are illustrated, including microstructure control, heating, simulation of phase transition, frictional behavior between materials and die, and simulation and experiments of tailored tempering process. In addition, the CAD/CAE software and non-destructive testing instrument for hot stamping were developed to meet the industrial requirements.

Hot stamping of high strength steel (HSS) can significantly improve overall mechanical properties of part and thus meet the increasing demands for weight reduction and safety standards in vehicles. However, cracking prediction using traditional forming limit curve (FLC) in hot stamping is challenging. In this paper, to predict HSS cracking in hot stamping a temperature-dependent forming limit surface (FLS) is developed by simulations combined with experiments. Different from the FLC the newly developed FLS, where temperature and phase transformation are included, suits the hot stamping of HSS. A finite element (FE) thermo-mechanical coupled numerical model of the hot stamping process is developed and implemented under ABAQUS/Explicit platform. Finally the developed FLS is used to predict crack initiation in a hot stamping. Results show that effectiveness of the developed FLS is verified in cracking prediction for hot stamping of HSS.