A Novel Approach for Mechanical Characterization of Angle-Ply Composite Laminates

​Composites made of continuous fibers generally have higher strength-to-weight ratios in fiber directions as compared to those made of discontinuous fibers. However, the latter tend to display quasi-isotropic properties which can be of advantage when directions of mechanical loading can vary. For many real-world applications such as robust design of vehicle body components for crashworthiness, impact loads are stochastic in nature both in terms of magnitude and direction. Hence, in order to realize the true potential of laminated composites with continuous fibers, instead of orthotropic laminates which are most common due to the ease of design and manufacturing, angle-ply laminates are necessary. The latter category of laminates introduce a high degree of flexibility in design options but are also simultaneously challenging in terms of mechanical characterization due to the presence of a larger number of material parameters, as compared to orthotropic laminates, with coupled normal and shear behaviors. A computationally attractive approach in large-scale numerical analysis of laminated composite structures lies in the modeling of laminates with equivalent homogeneous anisotropic properties. A practical strategy in published literature appears to be lacking on the determination of various elastic stiffness or compliance coupling coefficients for a generally-anisotropic angle-ply laminate. In the current exposition, a novel approach is demonstrated whereby using coupon specimens for tensile tests extracted at different directions with respect to a global x-direction for a square angle-ply laminate and one simple in-plane shear test, the membrane normal-shear coupling compliance parameters are determined by solving a set of linear simultaneous equations derived based on transformation of stresses and strains from global to off-axis directions. The current methodology obviates the necessity of using lateral strain gages traditionally deployed in uniaxial tests thereby making material characterization of anisotropic angle-ply laminates less time-consuming and more cost-effective.