Effect of low-cycle loading on the mechanical characteristics and structure of unidirectional organoplastic
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Low-cycle loading causes significant variations in the mechanical properties of unidirectional organoplastic — a variation in the character of the σ — ε relationship and corresponding variations in the elastic modulus, the area of the hysteresis loop, and the accumulation of residual strain.
Variations in the structure of the reinforcing fibers — the appearance of residual microstrains, a fact that we can associate with conformal transitions in the macromolecules — a variation in the intensity of diffraction reflections, which suggest variations in the degree of mesomorphicity and the appearance of flaws in the structure of the fibers are established by radiographic examinations.
The low-cycle loading of organoplastic by stresses σ∼⩽0.88σf gives rise to an increase in the elastic modulus. The elastic modulus also increases for stresses σ∼>0.88σf in the initial interval, but does not attain the level observed for lower stresses, and it begins to decrease after a certain number of cycles. The character of the variation in the elastic modulus can be explained by the effect of two factors: the increase is associated with conformai transitions in chains of macromolecules and by ordering of the structure, and the decrease with damage accumulation.
The magnitude of the residual strain during fatigue loading increases with increasing cyclic stress and may reach 1.5% prior to failure.
The area of the hysteresis loop decreases under cyclic loading. The area of the loop increases prior to failure. The total energy dissipation increases with decreasing cyclic stress.
Preliminary cyclic loading on a base N=103 cycles does not have a pronounced effect on the strength of unidirectional organoplastic.
KeywordsFatigue Elastic Modulus Macromolecule Hysteresis Loop Energy Dissipation
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