Punch shear damage of unidirectional (UD) composite is an important damagemode during the penetration and perforation of fiber-reinforced composites. A ratedependent progressive composite continuum damage model MAT162 in LS-Dyna?requires the punch shear strength and progressive damage softening parameters asinput. A micro punch shear experimental test method has been developed for UDcomposite at sub-millimeter length scale for determining the punch shear propertiesand parameters. S Glass/DER353 epoxy UD composite ribbon specimens have beenfabricated using the VARTM process. The samples have an nominal cross-sectionaldimensions of 1000 × 57~70 , with about six (6) through-thickness fibers. TheUD ribbon is adhesively bonded onto the specimen holder and a transverse load isapplied across the width of the sample. Localized transverse shear loading is createdwithin a narrow gap (153 ) between the punch and fixture support. Punch shearload-displacement data is reduced to engineering punch shear stress-strain. A largenumber of replicates are tested to quantify the stochastic non-linear progressivedamage behavior. In order to identify the micromechanical damage mechanisms andquantify the fiber-matrix debonding length, fracture surfaces of micro punch shear specimens have been thoroughly investigated using SEM and confocal microscopy.SEM micrographs clearly shows the initiation and propagation of mode Ⅱ dominatedfiber fracture, fiber-matrix debonding and matrix cracking. Confocal microscopy hasbeen used to quantify the probability distribution functions associated with fibermatrixdebonding and pull-out. The experimental methodology using the micro punchshear test developed in this study can be used to study the effects of compositeconstituents (fiber, resin and interphase properties and FVF) on the non-linearprogressive punch shear behavior of unidirectional composite punch shear strength.The statistical results and failure modes can also be used to validate micromechanicalmodels of punch shear strength.
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