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Strong bonds can be produced by the explosive welding process and usually the weld interface has a characteristic wavy form. In this paper the mechanism of explosive welding is discussed, the present theories of wave formation are critically examined and a new mechanism of wave formation is proposed. According to this mechanism the materials of the impacting plates in the region of collision behave in a similar manner to liquids of low viscosity. As a result the impacting or flyer plate divides into a re-entrant jet and a salient jet. Very high pressure is produced at the stagnation point of the divided jet. The parent plate deforms under the stagnation point and consequently a hump is formed in the parent plate ahead of the point of collision. The hump builds up and eventually traps the re-entrant jet. The stagnation point then transfers to the top of the hump and then descends it and starts forming a new hump, and in this manner successive waves are formed. The proposed mechanism of wave formation seems to explain the experimentally observed behaviour reasonably well. Furthermore, experiments are reported in which one of the surfaces to be bonded was copper plated and the second surface was nickel plated and by this means the movements of the surfaces being bonded were traced. These experiments gave strong support to the proposed theory of wave formation.

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The deformation occurring in the articular cartilage covering the human femoral head has been measured both when the femoral head is loaded in its natural acetabulum and when the cartilage is loaded with a small indentor. The results indicate that the material response is substantially different in these two situations. In the intact joint the cartilage deformation is substantially greater in older joints, but the response of cartilage to loading with an indentor does not change significantly with age. Theoretical elastic models of the cartilage behavior in these two situations were analyzed. For old cartilage which is idealized as an elastic material the increased deformation which is observed in the intact joint can be attributed to changes in Poisson's ratio, though in the real material increased fluid flux under load is the more probable cause.

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