PSI - Issue 47

Artur Mugatarov et al. / Procedia Structural Integrity 47 (2023) 654–659 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

656

3

Fig. 1. The order of experimental tests procedure: 1 – quasi-static tension tests; 2 – fatigue tests; 3 – preliminary cyclic loading; 4 – quasi-static tension after preliminary cyclic loading

2.2. Experimental data approximation Using experimentally obtained ultimate strength σ u after N preloading cycles fatigue sensitivity coefficients K B and preliminary cyclic exposure n are calculated as: (1) Dependence of K B on n is approximated using three models: Weibull-law based (WL), beta distribution based (BD) and proposed by Mao and Mahadevan (MM): ( ) ( ) ( ) ( ) ( ) 1 2 1 , 1 ln 1 ; 1 ; 1 1 . , n m m B B B B K n K K qn q n B       = − − − = − = − − − (2) The damage value derivatives corresponding to these approximations are calculated by the formulas: ( ) ( ) ( ) ( ) ( ) 1 2 1 1 1 1 1 1 1 2 1 1 ' ln 1 ; ' ; ' 1 . 1 , m m B B B n n n qmn q m n n B           − − − − − − = − − = = + − − (3) Model parameters were obtained numerically. Boundaries for fatigue damage accumulation stages are defined using the points where damage value derivative is equal to 0.3. 3. Results and discussion 3.1. Quasi-static and fatigue tests results Table 1 represents the results of quasi-static and cyclic testing of GFRP under various loading conditions. The increase in the stress maximum value during the cycle leads to a significant decrease in durability. The increase in temperature leads to the durability growth and reduced tensile strength. If temperatures and load levels are equal, [±45] n layout has the lowest strength, but the greatest durability, the [0/90] n layout has the highest strength and the lowest durability. 0 0 , . u B u N K n N  = = 

Table 1. Quasi-static and fatigue tests results. Group number Layout

σ u 0 , MPa σ max / σ u 0 Temperature, ° C N 0 , cyc

1 2 3 4 5 6

[0/90] n [0/90] n [0/90] n [0/90] n [±45] n

381 381 381 269 198

0.5 0.4 0.6 0.5 0.5 0.5

22 22 22

213448 1468979

20616

120

1199760 929300 397697

22 22

[0/±30/90/±60] n 294