Although thermo-stamping is one of the fastest and most cost-effective processes in the production of fabric-reinforced thermoplastic composite parts used in aerospace and automotive industries, it is quite prone to result in many defects. In particular, wrinkling is a frequently encountered defect in the production of doubly curved parts and is very sensitive to process parameters. Finite element analysis (FEA) is an effective tool for estimating defects that can occur during the thermo-stamping process. In this study, effects of spring configurations in spring-based holders and forming temperature on wrinkling and shear deformation are investigated experimentally and numerically by using two different spring configurations and three different forming temperatures. Non-isothermal and isothermal approaches used in thermo-stamping simulations are compared in terms of wrinkling estimation, and shear angle distribution. The results reveal that while the wrinkle predictions obtained by the non-isothermal approach are in good agreement with the experimental results, the isothermal approach cannot predict any of the wrinkles obtained in the experiment. Furthermore, the obtained results confirm that spring gripper configurations and forming temperature have a significant effect on wrinkling and shear angle distribution.
The anisotropic hyperelastic model (MAT_249) and Non-Orthogonal Model (MAT_293) are the material models developed recently to simulate the forming process of dry fabric and fabric-reinforced thermoplastic prepregs. In this study, the prediction capabilities of these two models in terms of shear angle distribution and boundary profile of the deformed fabric are compared over a hemispherical forming simulation of a plain weave E-glass fabric reinforcement. According to the results, in the simulation performed with MAT_293, it is seen that excessive distortions occur in the meshes at the advanced stages of the deformation in the fabric. In addition, after a certain punch stroke, the shear angle distribution obtained with MAT_293 starts to deviate rapidly from realistic results. MAT_249 produces consistent results even in large deformations.
The swage autofrettage process for a thick-walled cylinder was analyzed analytically and numerically. In order to get maximum benefit, optimized mandrel and thick wall cylinder inner diameter interference ratios were determined. Determined optimized interference ratios were used in production of a gun barrel. Autofrettage is the process of residual stress formation on the walls of the thick walled cylinders before their usage. These residual stresses help to increase the pressure bearing capacity of the thick walled cylinders by eliminating some stresses when service pressure is applied in the high pressure applications. In practice, there are two different autofrettage methods as hydraulic and swage. Swage autofrettage is a more economical method to form beneficial residual stresses in the thick walled cylinders when it is compared with the hydraulic autofrettage method. Figure A. Swage autofrettage operation was analyzed analytically and numerically in theory and applied in reality Purpose: In the current study, swage autofrettage process, applied on to two thick walled cylinders which have gained different material properties by heat treatment process is investigated. The main objective of the study is to determine the optimum mandrel-inner diameter interference ratios that results in maximum benefit. In accordance with this purpose, it is determined equivalent stresses on elastic-plastic junction, which is the most critical region of autofrettaged cylinder, being assumed to be used in max. 400 MPa service pressure. At first, maximum Tresca and Von Mises equivalent stresses on the elastic-plastic junction are obtained analytically for the autofrettaged thick walled cylinders exposing to the internal pressure of 400 MPa. Then, the verification of the analytical model is performed by making use of an ABAQUS software which uses the finite element method. Swage autofrettage is applied in the factory considering optimum values and permanent expansion of inner and outer diameter is measured. It is also calculated making use of ABAQUS software and results are compared. Theory and Methods: Analytical and numerical models were proposed and model calculation results were compared to each other. Autofrettage process were scheduled and performed in factory environment. Measured inner and outer diameters were compared to calculated values. Results: Internal and external diameter expansion quantities measured after the autofrettage process and the internal and external diameter expansion amounts obtained from the numerical calculation are compatible with the intersection value determined within the framework of the optimization calculation. Internal diameter expansion measurement and calculation results are 95%, and external diameter expansion measurement and calculation results are 87% close to each other. Conclusion: All stages of swage autofrettage process for a certain application was theoretically and experimentally enlightened and optimized by using proper methods.
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