繰返し衝撃引張荷重を受けるガラス繊維強化プラスチックスの疲労の進行について (強化プラスチック特集号)

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Low cycle tensile impact fatigue properties of glass fiber reinforced plastics were investigated using a drop weight impact tesing machine with primary emphasis on the progressive failure during fatigue. The materials tested were plain woven glass cloth reinforced polyester resin (cloth GRP) and chopped strand glass mat reinforced polyester resin (mat GRP).<BR>With a drop weight impact testing machine, a free fall from a fixed height can not produce a constant impact load if the rigidity of a specimen changes during fatigue. Therefore, the impulsive load during impact fatigue tests was monitored every time by using a wave memory, and when the decrease in maximum impulsive load was noticed a proper compensation for the drop height was made.<BR>The tensile impact fatigue strength was equal to or higher than the static strength up to 100 cycles of impact loading. The damage caused by the impact loading was not concentrated but extended over the whole specimen. The decrease in longitudinal extension modulus during fatigue showed a regular pattern on cloth GRP but not on mat GRP. The variation of the modulus for cloth GRP could be divided into three stages. The first stage is the region where the cycle ratio is less than about 0.1 and the modulus decreases rapidly. The third stage is the region where the cycle ratio is larger than about 0.9 and the modulus decreases rapidly again. The second stage is between these two stages and the modulus decrease gradually. It was found that the decrease in modulus in the first and second stages was mainly caused by the matrix but not by the fibers since the residual static strength scarecely changed until the cycle ratio exceeded 0.9.<BR>A gradual failure model with two components, namely STRONG part and WEAK part, was introduced to analyze such a decrease in modulus with the assumption of stochastically accumulated damage of WEAK part. The theoretical predictions showed a good agreement with the experimental results until the failure of the main load-carrying element could not be ignored anymore. Furthermore, it was found that the probabilities for the applied stress and the number of cycles during the damaging process of WEAK part were stochastically independent.
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繰返し衝撃引張荷重を受けるガラス繊維強化プラスチックスの疲労の進行について (強化プラスチック特集号)

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