Ductile Instability Considerations And The Prediction Of Driving Force Curves For Six Test Geometries

TWI Industrial Member Report Summary 89/1979

By O L Towers and S J Garwood

Background

The use of resistance curve theory for elastic and elastic-plastic behaviour is discussed from an energy balance consideration to establish a criterion for the description of ductile instability behaviour which occurs in aluminium alloys, austenitic steels, and ferritic steels above the transition region.

This approach uses material resistance curves determined experimentally with calculated driving force curves to assess the stability of cracking. In the present report driving force curves and their first order derivatives have been determined for six specimen geometries, and the effect of machine compliance is discussed.

A comparison of the effects of the following variables on the driving force curves and derivatives, and therefore instability, is made:

(i) accuracy of analysis
(ii) elastic and elastic-plastic behaviour
(iii) displacement and load control and
(iv) the various test geometries.