PSI - Issue 57

Yann Chevalon et al. / Procedia Structural Integrity 57 (2024) 633–641 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Curvature variation - ∆ k [1/m]

Fig. 7 – Curvature variation vs. their occurrences. The red dot is marking the 90 th percentile of all load cases.

2.5. Establishment of the design curve Independently of the global analysis, tests have been conducted with samples of extruded material in order to measure the fatigue material performance. This has been done through cyclic tensile testing and cyclic 4-points bending testing on samples having surface irregularities but also on machined samples with different strain ranges. Testing on samples with different surface finishing is a means to evaluate manufacturing effects and their impact on fatigue performance, and testing cyclically in tension/tension or bending is a way to mitigate specific testing issues such as jaw adherence on samples tested in tension or incertitude on curvature deformation in 4 points bending test. Because the Young modulus increases at low temperatures, testing has been done at negative temperature, while other tests were done at room temperature. The testing frequency was set to 1Hz to avoid hysteresis bias on mechanical properties of the polymers, but also because it is close to service conditions. An overview of the test results is given in the figure hereunder:

Fig. 8 Test results for HDPE for different temperatures. Round symbols are for machined samples, and crosses are for full thickness sample tests, while each color corresponds to a testing temperature.