Metallic thermal protection systems are used to protect the airframe and pay load from aerodynamic and aerothermal heating in hypersonic cruise vehicles that are powered with advanced scramjet engines. Metallic thermal protection systems is a composite structure that contains honeycomb sandwich panels at the top and bottom and a variety of thermal insulating materials placed in between them. Several design factors influence the structural and thermal performance of the honeycomb sandwich panels. Panel bending stiffness is one important structural property that is generally estimated using a destructive 3-point or 4-point bending test. In this study, a numerical model based on the impulse excitation nondestructive evaluation technique has been developed to estimate the effect of various design parameters that affect the bending stiffness of the honeycomb sandwich panels. The results obtained are analyzed using standard statistical procedures. A major advantage of this method lies in evaluating the panel stiffness at the design stage without resorting to actual fabrication of the panels for destructive testing.
Surface roughness is one of the important quality characteristic of a micromachined component. This paper presents a model to predict surface roughness of micro-EDmachined surfaces. The model is based on the configuration of a single-spark cavity formed as a function of process parameters. Assuming the normal distribution of surface heights, the μ and σ(Rq) of the surface profile are evaluated after every spark. The model was further extended to capture the role of debris in micro-EDM in changing electric potential at the micropeaks on the cathode surfaces. The chemical kinetics approach was used to evaluate the change in plasma enthalpy and composition as a result of debris inclusion in the dielectric. The corresponding energy distribution between the electrodes was used to predict configuration of the single-spark cavity and the consequent surface roughness using the earlier surface roughness model. The modeling results were found to agree well with the micro-EDM validation experiments performed without and with the inclusion of artificial debris (iron particles) in the dielectric.
In the present research, an experimental and numerical study on the crush response of square tube is presented. The explicit Finite Element Analysis (FEA) in LS-DYNA software is carried out to simulate crash behaviour under the quasi-static test conditions. Compression load is applied quasi-statically in an experimental study on the square tube specimens using Universal Testing Machine (UTM). In quasi-static test the bottom platen speed used is 1 mm/min. From experimental testing symmetric collapse mode is observed in all deformed specimens. The development of the symmetric collapse mode in a Finite Element (FE) model is also observed. Thus fold formation and crush response predicted by FE analysis are observed to be in very good correlation with the results obtained from experimental testing. Furthermore, the effect of the thickness of tube on crashworthiness parameters is investigated. From the FE analysis, it is found that the thickness of the square tube influences significantly the crashworthiness parameters.
This work presents a formulation for the free vibrations of isotropic homogeneous rectangular Mindlin plates with variable thickness. These plates are subjected to general boundary supports in present study. To obtain arbitrarily supported boundary conditions, new form of trigonometric series expansion functions is used as the admissible functions for transverse deflection and rotation due to bending. In order to account the constant shear stress assumption, a shear stress correction factor is taken into consideration. The Rayleigh-Ritz Method is employed in this formulation. The boundaries are assumed to have three set of springs to achieve required boundary condition. Thus the changes in boundary conditions can be easily obtained by varying the stiffness of these springs, without actually making any changes in the shape functions. In this study, FEA (Finite Element Analysis) has been carried out for the Mindlin plates, for simply supported and constrained on two opposite sides.
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