Page 351 - Mechanics Analysis Composite Materials

336 Mechanics and analysis of composite materials

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0 15 30 45 60 75 90 f
Fig. 7.23. Calculated (lines) and experimental (circles) dependencies of dissipation factor on the ply
orientation for glass-epoxy (- 0) and carbon-epoxy (- --- o) unidirectional composites.

Dependence of an aramid-epoxy composite material temperature on the number of
cycles under tensile and compressive loading with frequency IO3 cycles per minute is
shown in Fig. 7.24 (Tamuzh and Protasov, 1986).
Under cyclic loading, structural materials experience a fatigue fracture caused by
material damage accumulation. As was already noted in Section 3.2.4, heteroge-
neous structure of composite materials provides relatively high resistance of these
materials to crack propagation resulting in their specific behavior under cyclic
loading. As follows from Fig. 7.25 showing experimental results obtained by
V.F. Kutinov, stress concentration in aluminum specimens practically does not
affect material static strength due to plasticity of aluminum but dramatically reduces
its fatigue strength. Conversely, static strength of carbon-poxy composites that

T "C
r

1.10 2 .10

Fig. 7.24. Temperature of an aramidxpoxy composite as a function of the number of cycles under
tension (1) and compression (2).