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Abstract

A method of analysis for characterizing non-linear crack propagation in thin plates under double torsion is presented. Quasistatic energy method is used to derive the fracture toughness and to study the stability conditions of crack propagation within the subcritical crack growth range.

Non-linear relationship between the torque and angular deflection of a thin rectangular bar is well known. A thin rectangular plate containing a central longitudinal crack and acted upon by a system of four-point loading (two opposite forces on each side of the crack) causes non-linear structural response to this loading mode.

The stability of crack propagation in thin plates under double torsion is examined for both the linear (thin plates) and non-linear (thick plates) cases. It is shown that improved stability can be attained if the specimen geometry and loading mode display a non-linear load-displacement relationship at constant crack area, as compared with the corresponding linear case.

A series of experiments is conducted to measure the fracture toughness of PMMA material of different thicknesses. It is observed that the fracture toughness values evaluated analytically using the quasi-static energy method compare favourably with those measured experimentally.

For the range of PMMA plate thicknesses considered, the effect of thickness on the fracture toughness of PMMA material is negligible. Finally, the validity of employing the double torsion specimen for fracture studies is examined by comparing the fracture toughness of thin plates of different thicknesses loaded separately by double torsion and by tension. No significant difference between the two sets of results is observed.

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Crack propagation in thin plates under double torsion

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Abstract

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