Criteria on jet formation and jet cohesiveness are proposed for collapsing solid plates and shells. These criteria are also applicable to impinging fluid sheets from plane or annular nozzles. Under the high impact speeds treated here, the solid plates or shells behave as compressible fluids; for the impinging fluid sheets compressibility effects will also be assumed important. Jetting will occur if either the collision is subsonic or the impinging angle is large enough such that the shock in the flow is not attached at the collision point. Jets formed from subsonic collisions are coherent; those from supersonic collisions are not coherent. The criteria are shown to be in general agreement with available experimental evidence. Further, the proposed criteria are also verified by two-dimensional unsteady finite-difference computer calculations. In addition, these calculations indicate the mechanical reasons for the coherency or noncoherency of the jet under various impact conditions. The practical applications of these criteria include collapsing shaped-charge liners, the explosive welding of plates, and steady impinging fluid sheets from annular nozzles.

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