Discrete Stiffness Tailoring for Improved Buckling Performance

Continuously varying fibre angle across flat plates has analytically been shown to improve buckling performance by up to 60%. However, manufacture of such panels has so far used methods which have either high radius of curvature and low deposition rate (Continuous Tow Shearing) or low radius of curvature and medium deposition rate (Advanced Fibre Placement). Discrete Stiffness Tailoring (DST) is an alternative way of varying fibre angle to increase buckling performance that is compatible with current high rate deposition methods such as Advanced Tape Laying (ATL). DST uses discrete changes of angle within individual layers to effect variation in stiffness across a composite component at the cost of in-plane butt joints within layers. Two schemes of distribution are considered for tailoring stiffness across the width of a panel; (i) Half Seam; where half the layers in a laminate are subject to tailoring and (ii) Full Seam; where all layers are tailored. Compression testing of flat panels shows that DST can improve buckling stress for Full Seam by up to 16% for the simple example of redistributing material in a standard angle quasi-isotropic [±45/90/0]_2S laminate. Comparison of experimental results with standard buckling analyses (FEA, VICONOPT) indicates that DST results are predictable within the bounds of error introduced by experimental boundary conditions. Although no compression strength reductions were apparent in compression testing, tensile testing of seamed regions shows that improved buckling performance comes at the cost of reductions in transverse strength for Half Seam and Full Seam schemes. However, such reductions should be acceptable where loading is compression dominated and seams run parallel to the load.