Study on fracture mechanisms of CFRTP composites by AE technique (Japanese text)

The purpose of this study is to clarify the fracture mechanism of carbon fiber reinforced thermoplastic composites (CFRTP) by using the acoustic emission (AE) technique. Micro- and macro-fractures in a deformation process were monitored in real-time, and the relationships between failure modes, such as fiber break, matrix cracking, and debonding etc., and AE parameters were investigated in CFRTP composites. This in turn was used to distinguish failure modes and to evaluate the material life. To identify the fracture sources and failure modes, the experiments of single-fiber-composites or unidirectional composites were conducted under in situ observation. The acoustic emission signals measured in the fracture process were characterized by the parameters in the waveform of signals and by the power spectrum analysis.; The dissertation comprises (1) an overview of the AE technique in evaluation of material science and the flow of this research project; (2) failure modes and AE parameters in single-fiber-composites; (3) failure modes and AE parameters in unidirectional composites; (4) an application of the relationships between failure modes and AE parameters to engineering materials for evaluation of damage and elucidation of fracture mechanisms; (5) a description of stress intensity factor K and AE energy and their application to CFRTP composites with high fiber content; (6) proposition of the formulae for describing the relations of the J integral and AE parameters, and their application to CFRTP composites with lower fiber content.; The conclusions drawn from this study are (1) the relationships between the failure modes and AE parameters is made clear, and this verified effectiveness of AE technique for identifying the micro fractures sources and failure modes; (2) the formulae between AE parameters and the stress intensity factor or the J integral are obtained, which are useful for evaluating damage of material and the behavior of crack propagation quantitatively; and (3) the experimental results from both model and practical composites provides an possibility of AE technique for engineering use in healthy monitoring of material system.