PSI - Issue 82

Celalettin Baykara et al. / Procedia Structural Integrity 82 (2026) 206–212 C. Baykara et al./ Structural Integrity Procedia 00 (2026) 000–000

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2. Material and methods This study investigates the influence of adhesive thickness on the fatigue performance of single-lap joints composed of DC01 steel and unprocessed aluminum. The DC01 steel plates were coated with cataphoresis to simulate industrial surface protection. Three adhesive thickness levels were selected: 1 mm, 2 mm, and 3 mm, applied under controlled bonding conditions using 1-component polyurethane base adhesive with moisture curing mechanism, no time- or temperature-related heat treatment was applied to accelerate cure (Baykara 2024). Adhesive joint thicknesses are jointed in specially prepared molds (Figure 1).

Fig. 1. Molds employed for the preparation of specimens.

The bonding surfaces were degreased using isopropyl alcohol prior to adhesive application. Bonding was conducted using a precision jig to maintain constant overlap (25 mm) and ensure uniform adhesive layer distribution. Fatigue tests were performed on a servo-hydraulic test machine under controlled conditions, that is constant amplitude loading at a frequency of 10 Hz with a stress ratio (R) of 0 as depicted in Figure 2. The testing environment was maintained at 23 °C and 50% humidity. Load levels were chosen to target low- to mid-cycle fatigue regimes. For each adhesive thickness, at least five specimens were tested to failure. All specimens share the same dimensions for the lap, width, and sheet length, as shown in Figure 2.

Fig. 2. Experimental setup and dimensional properties.