AN ANALYTICAL AND EXPERIMENTAL EVALUATION OF 0 90 LAMINATE TESTS FOR COMPRESSION CHARACTERIZATION/

For materials development and specification, accurate compressive prop erty measurement with low variability is important, especially if the accuracy is improved by elimination of premature failure by buckling. Existing compression test methods do not satisfy these needs. For this reason the effectiveness of using 0/90 laminates for the determinatio n of unidirectional (0-degrees) compressive strength of composites was evaluated. The concept of using 0/90 laminates to evaluate lamina com pressive strength exploits the transverse constraint provided by the 9 0-degrees plies in combination with increased buckling stability obtai ned by positioning the 0-degrees plies away from the neutral axis. The studies were conducted using the SACMA SRM-1 compression tests for se veral material types that represent a broad range of fiber and matrix performance combinations. Laminate configuration and stacking sequence effects were evaluated over a range of temperatures up to 120-degrees -C. Additionally, load introduction factors, including tab type, tab d esign, and adhesive, were examined for effects on strength. Under all conditions evaluated, the [90/0/0/90], configuration was found to meas ure higher compressive strengths in the 0-degrees plies than that dete rmined for the same material using 0-degrees coupons. The experimental findings could be explained by a numerical simulation of the SACMA ty pe compression test. The simulation was based on a specially developed materials model designated COMPO-D which was implemented in the finit e element code of DYNA-3D. The FEM analysis of the [90/0/0/90], config uration explains the suppression of stress concentrations resulting in a more homogeneous distribution at the point of failure within the ga ge area.