Impact Strength Degradation of Adhesive Joints Under Heat and Moisture Environmental Conditions

The effects of environmental degradations on the deformation behavior of an epoxy resin for structural adhesive are experimentally examined using an INSTRON-type material testing machine. The effects of environmental degradations on the shear strength of adhesive joints are also examined using an INSTRON-type material testing machine and a split Hopkinson pressure bar apparatus. The results of quasi-static tensile tests for an epoxy resin for structural adhesive shows that the effect of the resistant to heat degradations tests is small on the deformation behavior, while it seems that the yield stress decreases and the elongation after the rupture increases as the degradations day increases in the resistant to moisture degradation tests. The results of quasi-static and impact shear tests for the adhesive joints shows that the effect of the resistant to heat degradations tests is small on the joint strength, while the shear strength decreases as the degradations day increases at any strain rate in the resistant to moisture degradation tests. In addition, the stress distributions at the adhesive interface of adhesive joints are examined using finite element stress analysis. From the numerical results, it is assumed that the joint strength increases as Young’s modulus of the adhesive decreases and the adhesive thickness is 0.25 mm. For verification of the FEA, the loading responses between the experimental and the numerical results are compared. A fairly good agreement is found between the experimental and the numerical results.