An Experimental and Numerical Study of Ballistic Impacts on a Turbine Casing Material at Varying Temperatures

An experimental and numerical study of ballistic impacts on steel plates at various temperatures (700ºC, 400ºC and room temperature) has been carried out. The motivation for this work is the blade‐off event that may occur inside a jet engine turbine. However, as a first attempt to understand this complex loading process, a somewhat simpler approach is carried out in the present work. The material used in this study is the FV535 martensitic stainless steel, which is one of the most commonly used materials for turbine casings. Based on material test data, a Modified Johnson‐Cook (MJC) model was calibrated for numerical simulations using the LS‐DYNA explicit finite element code (see Figure 1). To check the mesh size sensitivity, 2D axisymmetric finite element models with three different mesh sizes and configurations were used for the various temperatures. Two fixed meshes with 64 and 128 elements over the 2mm thick plate and one mesh with 32 elements over the thickness with adaptive remeshing were used in the simulations. The formation of adiabatic shear bands in the perforation process has been found critical in order to achieve good results. Adiabatic shear bands are formed by the temperature rise due to the accumulation of plastic strain during impact (see Figure 2). The influence of the thermal softening in the plastic model has hence been analyzed for the room temperature impact tests, where the temperature gradient is highest

Demonstration of the operation principles of intermediate band solar cells at room temperature

In this work we report, for the first time at room temperature, experimental results that prove, simultaneously in the same device, the two main physical principles involved in the operation of intermediate band solar cells: (1) the production of sub-bandgap photocurrent by two optical transitions through the intermediate band; (2) the generation of an output voltage which is not limited by the photon energy absorption threshold. These principles, which had always required cryogenic temperatures to be evidenced all together, are now demonstrated at room temperature on an intermediate band solar cell based on InAs quantum dots with Al0.3Ga0.7As barriers.