Walker-Wasley criterion

Firstly, a non-shock initiated detonation regime has been identified which cannot be described by the essentially shock-based Walker-Wasley criterion. Beyond this we must also recognise that impacts at lower velocities than those required to produce detonation can for many explosives nevertheless result in violent deflagrations. The description of such a complex phenomenon is unlikely to be possible in terms of single parameter. Finally, even when the Walker-Wasley criterion can be used, its value must be derived from experimental studies. We have no a priori methods for the estimation of the critical energy. 

Much effort is being invested on the development of computer programs for the prediction of initiation thresholds of expls and proplnts but none to date are satisfactory because of the lack of a clear threshold criterion. Shock induced mechanical failure (spall) has been correlated with stress and time by varying the thickness of the flyer plates. Likewise Walker and Wasley (Ref 15) have attempted to use a P t criterion (where P is the scalar shock pressure... 

Theoretical analysis of the data is based on the critical energy criterion for bare explosives postulated by Walker and Wasley (3) and developed by James (4) to cope with projectiles such as flat-ended cylindrical rods. It is assumed that the theory is valid for covered explosives providing that -... 

The work reported here indicates that a critical energy criterion as postulated by Walker and Wasley and modified by James can provide a useful model of prompt shock initiation in projectile impact experiments. However, it is important that the shocked volume is accurately estimated. It is at least likely that it is the failure to take into account rarefactions in the barrier material which account for the different critical energy values required to give the best fits to our data with metal and PMMA barriers. Figs 6-8. 

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