| The compression failure properties of laminates are of increasing interest in structural applications of carbon fiber composites. As practical structures are typically made with multiple fiber orientations, it is necessary to be able to predict failure under these general conditions.; This is a study on the compressive behavior of advanced carbon fiber composite materials. The materials were AS4/3501-6, IM7/8551-7, and YLA/135-1 carbon/epoxy composite materials in laminate form. The layups tested for uniaxial compression loading were (90/0{dollar}sb6{dollar}/90/0{dollar}sb6{dollar}/90) {dollar}sb{lcub}rm t{rcub}{dollar}, ((0/90/{dollar}pm{dollar}45){dollar}sb2rbracksb{lcub}rm s{rcub}{dollar} or ((90/{dollar}pm{dollar}45/0){dollar}sb2rbracksb{lcub}rm s{rcub}{dollar}, and ((0{dollar}sb2{dollar}/{dollar}pm{dollar}45){dollar}sb2rbracksb{lcub}rm s{rcub}{dollar}. The tests utilized uniaxial compression loading of a 2.0-in diameter (50.8 mm) tube and a 3.8-in diameter (96.52 mm) tube. The test results for uniaxial compression loading showed systematic differences in the strain to failure depending on the lamination type.; Additionally, axial compression tests have been performed on 2.0-in (50.8 mm) tubular specimens of carbon/epoxy laminates under hydrostatic confining pressure, with the intent of determining the effects of multiaxial state of stress on compression failure properties. Pressures up to 52 MPa (7500 psi) were used, and tests were run on several laminate types of AS4/3501-6 and IM7/8551-7 carbon/epoxy. The results varied with both material and lamination type. Compression strengths increased significantly for quasi-isotropic laminates of both material types tested, with the AS4/3501-6 system showing the largest increase in strength. Increasing the confining pressure acted to suppress delamination in these specimens. Other lamination types showed less, or no, increase in compression strength with pressure. In general, the results show that the compression failure was sensitive to the lamination type and state of multiaxial stress.; These experimental findings were examined with the predicted results of a modified micromechanical model. This model led to good correlations with the experimental data. An approach to measure the waviness of layers was developed that can be applied to calculation of the analytical model. |
