Features of Inelastic Behavior of a Composite Under Cyclic Loading. Experimental and Theoretical Investigations
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FEATURES OF INELASTIC BEHAVIOR OF A COMPOSITE UNDER CYCLIC LOADING. EXPERIMENTAL AND THEORETICAL INVESTIGATIONS
V. N. Paimushin,* R. A. Kayumov, and S. A. Kholmogorov
Keywords: fiber-reinforced plastic, cross-ply lay-up, cyclic tension, experimental investigation, strain components, viscoelastic strain, irreversible creep strain For a carbon-fiber-reinforced plastic made of an ELUR-P unidirectional tape and an ХТ-118 cold-cure binder, specimens with a ±45° stacking sequence were tested for cyclic tension. The total axial strain was considered as the sum of nonlinearly elastic, viscoelastic, and irreversible creep strains. Using the Abel creep kernel, it was found that, at instants of time shifted by values multiples of the loading period, the ratios between the viscoelastic strain components depended neither on the period of cyclic loading, nor the loading amplitude, nor the parameter determining the degree of viscosity of the material, but only on the parameter determining the decrease in the rate of the viscoelastic strain. To find parameters of the creep kernel, an identification method based on the use of a hypothesis that allows one to separate reversible and irreversible creep strains, as well as on the properties of Abel creep kernel was developed. The method is illustrated by an example of processing experimental results.
Introduction Thus far, a great number of papers devoted to studying the mechanical properties of fibrous composites under cyclic loadings in the presence of creep have accumulated (see, for example, [1-16]). The greater part of them deal with investigating their residual rigidity and strength in multicyclic loadings by comparing the elastic modulus and strength after some A. N. Tupolev Kazan National Research Technical University, 420111, Russia Kazan (Volga region) Federal University, 420008, Russia 3 Kazan State Architectural–Engineering University, 420043, Russia * Corresponding author; e-mail: [email protected] 1 2
Translated from Mekhanika Kompozitnykh Materialov, Vol. 56, No. 4, pp. 611-630, July-August, 2020. Original article submitted December 27, 2019; revision submitted June 4, 2020. 0191-5665/20/5604-0411 © 2020 Springer Science+Business Media, LLC
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number of loading cycles with their values found in the first cycle. On the basis of experimental data, as a rule, a relation between the current elastic modulus of the composite and the number of cycles is constructed. Results of such experiments for a cantilever beam of a fibrous composite can be found, e.g., in [12]. A review of various models describing the residual rigidity of composites is given, e.g., in work [13]. For fibrous composites on the basis carbon fibers and an epoxy binder, models describing their decreasing elastic modulus during repeated loadings are constructed in [14]. A differential relation for the decrease rate of the elastic modulus of a material as a function of the number of loading cycles is offered, which, integrated over the number of cycles, results in a final formula. On the basis of experi
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