Mechanical properties of some glass-reinforced plastics at low temperature

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1. The elasticity modulus of unidirectional GRPs VIII and X decreases by 15%, on the average, with decreasing temperature from room to 4.2 °K. In this temperature range the Young's modulus of unreinforced bonding agent EDT-10 increases by a factor of three. 2. The ultimate strength of GRPs I-XI in tension, compression, and bending increases with decreasing temperature in the range 300-77 °K. With temperature reduced to 4.2 °K the behavior of all test GRPs with different straining methods is unstable, i.e., both an increase and a decrease in ultimate strength are observed; however, for practically all of the GRPs σf at 4.2 °K is higher than at room temperature. 3. With increasing fiber disorientation angle in relation to the loading direction, the strength of GRPs decreases over the whole temperature range. The temperature dependence of ultimate strength for specimens in the glass cloth weft direction is less defined, and their strength over the whole temperature range is much lower than for specimens cut in the glass cloth warp direction. 4. Of all the materials considered, the most stable is GRP IX. 5. In view of the nature of GRP failure at cryogenic temperatures, and in fact the breakup of material in the failure area into individual threads, it is possible to assume that specimen failure is facilitated by fracture of the matrix in the composite. 6. In the temperature range 300-4.2 °K the strength of GRPs I and III under tension is less sensitive to the effect of stress concentrators (a round hole in the specimen gauge length).