research mechanical engineer, Mechanics and Structures Branch, Army Materials Technology Laboratory, Watertown, MA
The effects of nonlinear intralaminar shear behavior on the modeling accuracy of pin-loaded [(0/90)3,0]s and [(+45/−45)]3s fiberglass epoxy composite laminates was quantitatively examined. The comparison of net, bearing, and shearout sectional strains from linear and nonlinear elastic three-dimensional finite-element approximations with similar front surface experimental geometric moire sectional strains formed the basis of this investigation.
Three-dimensional constitutive equations for the [(0/90)3,0]s laminate were developed from actual lamina properties and classical laminate plate theory. A material axes transformation of similar [(0/90)]3s constitutive equations was used to derive the [(+45/−45)]3s laminate constitutive equations. The validity of these equations and the effects of nonlinear intralaminar shear behavior were experimentally investigated by comparing them with laminate uniaxial tensile test data.
Nonlinear elastic [(+45/−45)]3s finite-element results exhibited a nonlinear material response in both the net and bearing sections. Similar results were observed in the [(0/90)3,0]s laminate shearout section. Both pin proximity and load level intensified these effects. Net section [(+45/−45)]3s experimental moire strains agreed well with nonlinear elastic finite-element results at low pin-load level, but surpassed them at higher pin-load levels near the pin. Similar trends were observed in the [(+45/−45)]3s bearing and [(0/90)3,0]s shearout sections, but were slightly skewed by unsymmetric experimental pin boundary conditions.
Variations in nonlinear elastic finite-element and experimental moire sectional strains were examined by a qualitative determination of material damage made with a backlit liquid penetrant experimental arrangement. Material failure was observed in those regions where experimental moire and nonlinear elastic finite-element sectional strains diverged, thus signifying the presence of a discontinuous stress-strain material behavior.
Paper ID: CTR10232J