Design and Analysis of the Crack Rail Shear Specimen for Mode III Interlaminar Fracture 

 -  Composites Science and Technology, 31, p.143-157, 1988 .
<br/><br/> The crack rail shear (CRS)specimen ts a proposed test method to characterize the Mode III interlammar fracture toughness of contmuous- fiber-remforced composite materials. The spectmen utdtzes the two-rail shear test fixture, and contams embedded Kapton film placed symmetrtcally about the midplane to provide starter cracks for subsequent characterizatton. Otherwise, spectmen length and width are identical to the ASTM shear test specimen geometry. An analytical expresston for the strata energy release rate ts developed based on a strength of materials approach The model tllustrates the tmportant material and geometric parameters of the test, and provtdes a simple data reduction scheme for expertments. A quasi three- dtmensional, linear elastic fimte element code, CCMQ3D, ts employed to verify the pure Mode III fracture state and to determine admtssible crack lengths. Deformatton of the model shows that only the out-of-plane dtsplacement is non-zero, indicating that a pure Mode III fracture state does indeed exist within the constraints of the Q3D assumption Comphance and strain energy release rate predwttons are m good agreement with the strength of materials model over the range of crack lengths, 0"15 < a/w < 0"85. A fully three-dimensional, linear elasttc fimte element analysis of the CRS is employed to quanttfy the effect of finite length on the fracture state Only mtermediate crack lengths are investigated. Crack closure techniques are utdlzed to determine the components of the strata energy release rate present Results mdicate that a small boundary layer of mtxed mode behavtor exists at the free edges that dimtmshes to a pure Mode III fracture state Compliance and stram energy release rate predictzons by the 3D model show good agreement with the Q3D and strength of materials models.