SHORT-WAVELENGTH BUCKLING AND SHEAR FAILURES FOR COMPRESSION-LOADED COMPOSITE LAMINATES (ANISOTROPIC, PLATES, STRUCTURES).

摘要

This investigation studies the short-wavelength buckling (or the microbuckling) and the interlaminar and inplane shear failures of multi-directional composite laminates loaded in uniaxial compression. A laminate model is presented that idealizes each lamina. The fibers in the lamina are modeled as a plate, and the matrix in the lamina is modeled as an elastic foundation. The out-of-plane w displacement for each plate is expressed as a trigonometric series in the half-wavelength of the mode shape for laminate short-wavelength buckling. Nonlinear strain-displacement relations are used. The model is applied to symmetric laminates having linear material behavior. The laminates are loaded in uniform end shortening and are simply supported.;A linear analysis is used to determine the laminate stress, strain, and mode shape when short-wavelength buckling occurs. The equations for the laminate compressive stress at short-wavelength buckling are dominated by matrix contributions. The effects of fiber volume fraction on the compressive stress at short-wavelength buckling is reported for a laminate with any stacking sequence and any thickness. The laminate mode shape at short-wavelength buckling is discussed.;A nonlinear analysis for laminae with initial imperfections is used to determine laminate stresses and interlaminar strains. Results are presented for imperfection-amplitude-to-lamina-thickness ratios of 0.1 and 0.5. The nonlinear behavior of 0(,2) (,s), 0/90 (,s), (+OR-)45 (,s) and +45/0/-45/90 (,s) laminates is discussed. Results are presented for laminate stress, end shortening, and w displacement. The w displacement gradients cause significant interlaminar shear strains (gamma)(,xz) at laminate stresses that are much lower than the laminate stress at short-wavelength buckling, and the distribution of these strains is described. The effect of fiber volume fraction on the nonlinear laminate response is presented for 0(,2) (,s) and +45 (,s) laminates.;A failure criterion for compression-loaded laminates is discussed. Laminate failure that is initiated by outer-lamina buckling, by interlaminar shear strains from lamina imperfections, or by inplane matrix shearing is considered. The laminate strength is calculated as a function of lamina orientation for (+OR-)(theta) (,s) laminates. A simple method referred to as the stiffness-ratio method is described for predicting the strength of 0(DEGREES)-dominated laminates.