PSI - Issue 75

Sixin Liu et al. / Procedia Structural Integrity 75 (2025) 200–204 Sixin Liu/ Structural Integrity Procedia (2025)

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Figure 3.2: Magnified view of the localized stress concentration

As depicted in Figure 3.2, a high-stress concentration zone emerges near the V-notch tip, with the peak von Mises stress ranging between 12 – 15 MPa. This stress localisation is the primary driver of crack initiation. The strain-life based fatigue analysis, using calibrated material parameters for polypropylene, predicted failure onset at approximately 30,000 loading cycles. This corresponds closely with the mid-life point of a reference aluminium structure designed for 60,000 cycles, validating the sensor’s ability to signal fatigue halfway through the monitored structure’s service life. The simulation framework was further validated by mesh refinement and load magnitude variation, both of which yielded consistent deformation and fatigue predictions, thus confirming the robustness and reliability of the finite element approach for sensor performance forecasting. 4. Experimental Verification The mechanical properties of PP under cyclic loading have been previously characterised in the literature [6]. A series of experimental tests were carried out to validate the sensor’s performance under real -world loading conditions. Substrate specimens were machined from aluminium alloy AA1050, selected for its high ductility and consistent fatigue response. Key mechanical properties include: tensile strength of 120 MPa, elongation at break of 10%, and density of 2.71 g/cm³. The fatigue sensor was fabricated from isotactic polypropylene, with properties measured as follows: density = 900 kg/m³, Young’s modulus = 1.5 GPa, Poisson’s ratio = 0.42, and fatigue strength = 299 MPa under R = 0.5 conditions.

Figure 4.1: Experimental setup using an Instron E3000