Static Strength of Adhesively Bonded ARALL-1 Joints

Abstract

ARALL® Laminates are a family of structural composite materials which consist of thin aluminum alloy sheets alternating with aramid fiber/epoxy prepreg layers developed for fatigue-critical applications requiring light gage sheet. To obtain the benefits associated with ARALL Laminates, the joint regions must be designed to carry the required loads without incurring a substantial weight penalty. This paper considers the static strength of adhesively bonded ARALL-1 single and double lap joints. Single and double lap joints with various overlap lengths were fabricated using two standard ARALL thicknesses: 3/2 ARALL-1 (three layers of aluminum with 2 prepreg layers) and 5/4 ARALL-1 (five layers of aluminum with four prepreg layers). These joints were tested in uniaxial tension. A shear lag analysis based on failure of the adhesive was used to predict the failure load as a function of the joint configuration and overlap length. A finite element analysis was used to determine the interlaminar shear and tensile stresses within the laminate. The results of these two analysis techniques were compared to the experimental results. The results show that the maximum adhesive and adherend stresses calculated using the shear lag analysis agree with those calculated using finite element techniques. While the shear lag analysis gave accurate predicted failure loads for 312 ARALL-1 single and double lap joints, the predicted failure loads for 5/4 ARALL-1 single lap joints were generally higher than the experimental failure loads. For the 5/4 ARALL-1 specimens, the experimental failure loads were dependent on the observed failure mode. The premature failure can be attributed to interlaminar tensile and shear stresses in the prepreg layers closest to the bondline. The interlaminar failure observed in these joints can be predicted using the interlaminar shear and tensile properties and an appropriate interaction equation.