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This study investigates the influence of cooling rate on the residual strain of the carbon fibre/polyphenylenesulfide unidirectional laminates. Three different cooling rates (−300℃/min, −100℃/min and −10℃/min) were applied to simulate a wide range of cooling conditions. The crystallisation behaviour which depends on the cooling rate was evaluated using differential scanning calorimetry. A process monitoring test was then conducted using embedded fibre Bragg grating sensors. In-plane transverse strain of carbon fibre/polyphenylenesulfide unidirectional laminates was measured and the results were presented based on the crystallisation behaviour determined by differential scanning calorimetry. Furthermore, residual strain change after subsequent annealing was examined. This study successfully demonstrates the effectiveness of in situ process monitoring using fibre Bragg grating sensors for evaluating material behaviour of thermoplastic composites during rapid heating and cooling under realistic processing conditions. [ABSTRACT FROM AUTHOR]

Vacuum-bag-only curing is an attractive out-of-autoclave method as an alternative to conventional autoclave curing. Previous extensive researches provided great insight into void formation during the vacuum-bag-only method and these findings are reflected in current vacuum-bag-only cure cycles to minimize void content. Cure process can be further improved by taking into consideration cure-induced residual stress/strain. The present paper proposed a residual stress/strain reduction method and evaluated its effectiveness using a commercially available vacuum-bag-only material by fiber-optic-based in-situ strain monitoring and tensile tests. First, cure process monitoring and tensile tests were conducted for the manufacturer’s recommended cure cycle. Cure process monitoring showed that the material vitrifies during post-cure temperature dwell. Furthermore, the tensile test revealed that the vacuum-bag-only material has lower strength than conventional autoclave materials, suggesting the importance of the effect of cure-induced residual stress/strain. Then, two cure cycles were proposed based on the findings from the manufacturer’s recommended cure cycle tests and a cure kinetics model. In the proposed cycles, resin vitrifies at a lower temperature than the manufacturer’s recommended cure cycle, leading to reduced residual stress/strain. Cure process monitoring and tensile test results for the new cycles showed that the residual strain was reduced by 12–18%, and the strength was increased by 26% in the best case. Moreover, void content was not significantly affected by changing the cure cycle. Although vacuum-bag-only material was used in this research, the proposed concept can be widely applied for autoclave cures and other types of vacuum-bag-only processes with slight modification. [ABSTRACT FROM AUTHOR]

The details of the time history of the elastic waves in ballistically im pacted composite laminates have been obtained by using surface and em bedded strain gages. Records show that a very low-amplitude in-plane tensile wave arrives first followed by a medium-amplitude flexural wave and then a high-amplitude flexural wave. Measured and calculated values of wave speeds agree well. [ABSTRACT FROM PUBLISHER]