An experimental and finite element investigation into the nonlinear material behavior of pin-loaded composite laminates

The effect of crossply nonlinear intralaminar shear behavior on the modeling accuracy of pin-loaded ((0/90){dollar}sb{lcub}rm n{rcub}{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} and ((+45/-45){dollar}sb{lcub}rm n{rcub}{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} composite laminates was quantitatively investigated. Both linear and nonlinear elastic three dimensional finite element approximations that included pin elasticity and contact angle formation were generated. These approximations were compared to both front surface in-plane and out-of-plane experimental moire displacement contours generated from geometric and projection shadow moire techniques.; A modified three point bend test was used to obtain values of laminate transverse shear moduli while through thickness contraction measurements on laminate tension tests were employed to obtain estimates of the Poisson ratio values. Nonlinear crossply intralaminar shear behavior was determined from the ASTM D3518-76 specification.; Three dimensional constitutive equations for the ((0/90){dollar}sb{lcub}rm n{rcub}{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} laminate were developed from effective and actual lamina mechanical properties. A material axis transformation of these constitutive equations was employed to produce ((+45/-45){dollar}sb{lcub}rm n{rcub}{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} laminate constitutive equations. The validity of these constitutive equations and the effects of nonlinear intralaminar shear behavior were experimentally investigated by a comparison with uniaxial tension tests of both laminates. A sensitivity analysis of through thickness modulus was also done in this comparison in hope of providing insight into the selection of its magnitude.; Comparisons of linear and nonlinear elastic finite element results show significant stress level reductions and increased strain values in ((+45/-45){dollar}sb3{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} laminate net and bearing sections. Similar results were observed in the ((0/90){dollar}sb3{dollar},0) {dollar}sb{lcub}rm s{rcub}{dollar} laminate shearout section. Both pin proximity and load level intensified these effects. Net section ((+45/-45){dollar}sb3{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} experimental strains agreed well with nonlinear elastic finite element results at low pin load levels, but surpassed them at higher pin load levels. Closer pin proximity and increased load level intensified these results. Similar trends were observed in ((+45/-45){dollar}sb3{dollar}) {dollar}sb{lcub}rm s{rcub}{dollar} bearing and ((0/90){dollar}sb3{dollar},0) {dollar}sb{lcub}rm s{rcub}{dollar} shearout sections, but were affected by unsymmetric experimental pin boundary conditions.; A qualitative determination of material damage within the pin-loaded laminates indicated material failure in those regions where experimental and nonlinear elastic finite results diverged.