Fatigue crack growth properties of a two-part acrylic-based adhesive in an adhesive bonded joint: Double cantilever-beam tests under Mode I loading

Fatigue lifetime is one of the most important factors that need to be considered when determining a material's design. This study deals with fatigue behaviors in adhesive bonded joints. Fatigue tests were conducted using double cantilever beam specimens to measure the fatigue crack growth properties of the DP8005 acrylic-based adhesive under Mode I loading on aluminum alloy, glass fiber-reinforced polypropylene matrix composite (GF/PP), and carbon fiber-reinforced epoxy matrix composite (CF/EP) adherends. The fracture surfaces were examined using a microscope to verify the fracture behaviors. The experimental results show that the slope (2.85) and intercept (2.14 × 10−10), as defined by the Paris law, expressed a relationship between the energy release rate range (ΔGI) and the crack growth rate (da/dN) for the three specimens were the same, in scenarios where the cohesive failures were dominant. The aluminum alloy specimens were found to have another slope and intercept at 1.36 and 6.00 × 10−7, respectively, when interfacial failures occurred. The threshold energy release rate range (ΔGI.th) for the GF/PP and CF/EP specimens were 69.3 and 72.5 J m−2, respectively. ΔGI.th for the aluminum alloy specimens were 46.5 (denoted as ΔGI.th1st) and 5.4 (denoted as ΔGI.th2nd) J m−2. ΔGI.th (fracture morphology) can be ranked as aluminum alloy (ΔGI.th2nd, interfacial failure) < aluminum alloy (ΔGI.th1st, mixture of cohesive and interfacial failures) < GF/PP (mixture of cohesive and adherend failures) < CF/EP (cohesive failure).