For the purpose of clarifying the fracture toughness and microfracture mechanism of fiber reinforced plastics composites at cryogenic temperature 4K, fracture toughness tests were performed for a short glass fiber reinforced polyester composite. Acoustic emission signals were also detected during the fracture toughness tests to obtain a reasonable explanation of the microfracture mechanism. The results are summarized, as follows:
(1) The maximum load on the load-displacement curve at 4K increases by about three times that at room temperature 297K.
(2) The AE activity for the specimen at 4K is extremely higher than that at 297K.
(3) The fracture toughness K
AE, which is defined as the critical stress intensity factor corresponding to the abrupt increase of AE energy, becomes larger with decreasing temperature below room temperature.
(4) The fracture toughness obtained by the 5% offset procedure of ASTM standard does not agree with the fracture toughness K
AE.
(5) The AE signals were discriminated into two types by the spectrum analysis and the microfracture mechanism was discussed.
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