PSI - Issue 18

Staroverov Oleg A. et al. / Procedia Structural Integrity 18 (2019) 757–764 Staroverov O.A., Wildemann V.E., Tretyakov M.P., Yankin A.S./ Structural Integrity Procedia 00 (2019) 000–000

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Fig. 2. Diagram of fatigue sensitivity of fiberglass specimens with different laying angles of reinforcing layers

Figure 3 shows photos of specimens after fatigue failure. For samples with layouting [±45] in the process of cyclic loading, there was a gradual stretching and destruction in the direction of laying reinforcing fibers according to the type in accordance with the classification of ASTM standard DGM. Samples with folding angles [0/90] and [0/30/0/60] destruction occurred according to the normal detachment pattern.

[0/90]

[0/30/0/60]

[±45]

Fig. 3. Photos of fiberglass specimens with various layouts

Thus, when analyzing the fatigue sensitivity diagrams, it was revealed that the phased nature of changes in the residual strength and deformation properties of glass-reinforced plastics is typical for samples that have reinforcement directions in the structure that coincide with the load application 4. Investigation of the fatigue sensitivity of glass-reinforced plastics with various parameters of cyclic load The research of the regularities of changes in the stiffness and strength properties of polymer composite materials in the process of fatigue damage accumulation during various preliminary cyclic loads (0.4–0.6∙σmax) was performed for samples with reinforcement angles [0/90]. The research method was similar to the method described earlier. Patterns of changes in the residual strength properties are reflected in the diagram of fatigue sensitivity (Fig. 4). Within the framework of the research, it was found that for the investigated fiberglass specimens tested under conditions of preliminary cyclic and subsequent quasi-static loads, with changing loading parameters, staging changes in residual strength remain. Also allocated areas of initial, stabilization and exacerbation of fatigue sensitivity. It should be noted that for samples tested at the maximum stress value in the cycle σ max =0.5∙σ B and σ max =0.6∙σ B , the transition between the initial fatigue sensitivity and stabilization areas occurred at approximately the same value n’=0.3. The values of the static strength retention coefficient were close to n’=0.5, where the curve σ max =0.5∙σ B showed a sharp decrease in K Bn ’, characteristic of the fatigue sensitivity exacerbation stage. The length of the stabilization section during cycling σ max =0.5∙σ B was 25% of the relative number of cycles of preliminary cycling and lay in the