Fu yFnF22112

Failure tensor polynomial in fatigue (FTPF) assumes the same functional form as Eq. (1.10):

However, the components of failure tensors Ftj, Ft are functions of the number of cycles N, the stress ratio R, and the frequency v, of the loading:

Experimental evidence gained so far for any type of continuous fiber-reinforced polymers, at least, strongly suggests the form of functional dependence of failure tensor components shown in relation (1.14). This implies an increased complexity of experimental strength characterization with respect to static loading since it is not sufficient anymore to discriminate just between tension or compression, but also between the same type of loading, for example, tension, at different R values or loading frequency v. Therefore, fatigue strength of an orthotropic material, in-plane stressed, is characterized by three S-N curves [20]:

Failure tensor components are defined by:

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