Analyses of Buckling and Stable Tearing in Thin-Sheet Materials

This paper was to verify the STAGS (general shell, geometric and material nonlinear) code and the critical crack-tip-opening angle (CTOA) fracture criterion for predicting stable tearing in cracked panels that fail with severe out-of-plane buckling. Materials considered ranged from brittle to ductile behavior. Test data used in this study are reported elsewhere. The STAGS code was used to model stable tearing using a critical CTOA value that was determined from a cracked panel that was “restrained” from buckling. The analysis methodology was then used to predict the influence of buckling on stable tearing and failure loads. Parameters like crack-length to-specimen-width ratio, crack configuration, thickness, and material tensile properties had a significant influence on the buckling behavior of cracked thin-sheet materials. Experimental and predicted results showed a varied buckling response for different crack-length-to-sheet-thickness ratios because different buckling modes were activated. Effects of material tensile properties and fracture toughness on buckling response were presented. The STAGS code and the CTOA fracture criterion were able to predict the influence of buckling on stable tearing behavior and failure loads on a variety of materials and crack configurations. NOMENCLATURE B Specimen thickness, mm ci Initial half-length of crack, mm d Minimum element size along crack line, mm E Young’s modulus, GPa ________________________________________________________________________ * National Research Council Resident Research Associate, NASA Langley Research Center, MS 188E, Hampton, VA 23681