Numerical and Experimental Analysis of Thermo-Stamping Process Applied to Woven Fabric Reinforced Thermoplastic Composites
Tez Türü: Doktora
Tezin Yürütüldüğü Kurum: Ankara Yıldırım Beyazıt Üniversitesi, Mühendislik ve Doğa Bilimleri Fakültesi, Makine Mühendisliği, Türkiye
Tez Danışmanı: Fahrettin Öztürk
Tezin Onay Tarihi: 2022
Tezin Dili: İngilizce
Desteklendiği Program: Öğretim Üyesi Yetiştirme Programı (ÖYP)
Özet:
Lightweight structures are very critical in the aerospace industry. Different materials have been investigated to enhance the structure's lightness. Fabric reinforced thermoplastic composites have recently drawn significant attention due to their high specific strength and stiffness. Another reason for the interest in thermoplastic composites is that they require a shorter processing time than their thermoset counterparts. By using production methods such as thermo-stamping, processing time of thermoplastics can be reduced to around one minute. Although thermo-stamping is one of the fastest and most cost-effective processes in the production of fabric-reinforced thermoplastic composite parts, it is prone to several different processing 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 in estimating defects that occur during the thermo-stamping process. It is necessary to use the FEA method effectively and choose the appropriate simulation approach and material model to get results well trending with the real process. In addition, the parameters needed to be defined in the material model must be precisely determined by the characterization tests. This thesis aimed to simulate the thermo-stamping process of thermoplastics using the FEA method in line with these requirements. The validity of the simulations was confirmed by the experiments. In addition, the process parameters affecting the wrinkling were investigated both numerically and experimentally. Results revealed that among the evaluated material models, the strongest was the anisotropic hyperelastic model (MAT_249). Characterization test results indicated that the picture frame test results for the shear behavior of the fabric are more reliable than the bias extension test results since the yarn sliding problem was encountered after a certain shear angle in the bias extension test. In addition, the low forming temperature decreased the average and local maximum shear angles. The low forming temperature increased the wrinkle formation.It was observed that spring gripper configurations significantly affect shear deformations and wrinkle formation.