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Cure Cycle Optimization of Out-of-Autoclave Composites Based on In-Process Cure Strain Monitoring

Nobuo Takeda, Shinsaku Hisada, Kazunori Takagaki and Shu Minakuchi

Abstract


Aerospace-grade CFRPs are mainly manufactured under high pressure using an autoclave to achieve high quality. The method, however, has enormous costs during installation and operation, and it is also time-consuming. Therefore, out-of-autoclave (OOA) method is recently attracting considerable attention to overcome these disadvantages. There are several OOA methods such as filament winding and vacuum assisted resin transfer molding. Among them, prepreg based vacuum bag only (VBO) method is a promising one for aerospace applications due to high fiber volume fraction and the similarity to the autoclave method. Several studies on VBO were conducted and considerable insight into void formation was obtained. However, they focused on only void and did not investigate the internal states such as residual strain which significantly affects the mechanical properties after molding. Therefore, in this study we measured strain development during VBO cure processes using fiber Bragg grating (FBG) sensors. First, we proposed a novel cure cycle (Modified cycle) in which the cure temperature is controlled to be lower than Tg during the heating. Then, we measured internal strain for specimens fabricated using manufacturer’s recommendation cure cycle (MRCC) and modified cycle. In modified cycle, the residual strain was considerably reduced compared with that in MRCC. Finally, we conducted tensile tests to evaluate the validity of the modified cycle, showing that the higher strength can be achieved using the proposed cure cycle.

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