Strain rate-dependent deformation and failure process of adhesive joints

Rate-dependent deformation and failure process of adhesive joints are investigated in this study. For this purpose, acrylic foam pressure sensitive adhesive (PSA) was employed with aluminum adherents. Tensile and shear loading of the adhesive joint was applied at displacement rates ranging from 5 to 500 mm/min. Results show that the failure process under tensile loadings start with initiation of cavities, hardening through fibrillation process and final fracture of the fibrils. For shear loading the failure process is a combination of fibrillation processes, shear flow, and by interfacial sliding. Both modulus and strain energy density at fracture reach maximum value at a displacement rate of 100 mm/min under tension, while continuously increase with displacement rate under shear loading. Adhesive failure dominates at low loading rate (below 10 mm/min.), while mixed-mode and cohesive failure are common at faster loading rates above 250 mm/min. Finite element employing Yeoh constitutive model adequately predicts viscous shear deformation of the PSA joints

Moisture absorption effects on the mechanical properties of carbon/epoxy composites

Purpose: This paper investigates the influence of moisture absorption on the mechanical properties of carbon/epoxy composites. Design/methodology/approach: Three types of specimens are prepared, which are for longitudinal, transverse and shear tests. Specimens are immersed in distilled water at 70°C for 1, 3 and 9 months. These correspond to the moisture content of 2.2, 3.8 and 5.3%. Findings: Compared to the values at dry condition, the longitudinal modulus, shear modulus and Poisson's ratio are invariant with the moisture content. However, the transverse modulus, transverse strength and shear strength are sensitive to moisture attack. The maximum degradation is 33%, 76 and 33% for the three properties, respectively. It is also worth to note that the longitudinal tensile strength is stable at 1 and 9 months of immersion. However, at 3-months ageing period, there is only 67% of the longitudinal tensile strength retained. Originality/value: The experimental results are fitted with a residual property model. Results show comparatively good fit, with a difference within 16% except the longitudinal tensile strength at 9-months immersion. This highlights that the model is not suitable to fit the experimental data with a fluctuated trend