Longitudinal shock waves in solids: the piston shock analogue

Propagation of longitudinal deformation in hardening elastoplastic solids is investigated by the way of analogy with the shock tube pattern in fluid mechanics. Conditions for the appearance of a shock discontinuity are formulated and steady-state continuous and discontinuous solutions are derived. Field characteristics are then investigated for a representative family of hardening elastoplastic Mises solids accounting for finite strains. A critical limit value of the imposed velocity for the emergence of a shock wave is found and sensitivity to material parameters is assessed. Evaluation of dissipation effects is conducted and field response is compared with other uniaxial stress fields. In agreement with available experimental results, it is established that the field may consist of both an elastic precursor and a plastic shock separated by a continuous elastoplastic range. Or, alternatively, when the imposed velocity is higher, the plastic shock overtakes those regions allowing for a variety of resulting fields.

Stiffness and Fatigue Study for Surface Mounted Module/Lead/Card Systems

Modules attached to circuit cards by peripheral J- and gullwing leads were studied for their behavior under flexure. Three aspects of mechanical behavior were focused upon: the stiffness of the system, the forces arising in the leads, and the fatigue strength of the latter. The effective stiffness of a module-reinforced circuit card was measured experimentally in several configurations (load on card and load-on-module, double-sided and stacked). The leaded attachments were in two parallel rows. Analytical modeling of these tests were performed considering the leads as a continuous elastic foundation connecting the module and the card; test results were corroborated. Experiments were also conducted to establish the elastic and elastoplastic range of lead stiffness in three perpendicular directions: in two shearing planes and axially. The latter was the stiffest and most significant direction, motivating much of the present analysis. For lead force, the analytical procedure yielded values which were confirmed by finite element computation methods described previously by Engel (1990). Fatigue tests were performed on both J- and gullwing leads. Solder joints failed in the former, while lead failures occurred in the latter.

The Analysis of Ship Structures Subjected to Slamming Loads

This paper describes the results of a fundamental study of various phases of the ship structural design problem, as affected by slamming-type loads. By a slamming load, we mean a suddenly applied impact-type load such as is introduced for example, by: (a) The pitching and heaving motions induced by waves, which in turn cause the ship's bow to emerge and then reenter the seaway at a relatively high velocity. Upon reentering the sea, suddenly applied impact-type loads may be applied to the ship hull. These cause a sudden change in acceleration, generally felt as a shudder (or series of shudders or vibrations) which introduces the slam loading. (b) Berthing or docking of ships. If, for any reason the berthing introduces heavy impact loads due to sudden contact between the ship hull and the fender-dock system then we have a response very similar to that described in (a). The study[1]2 was concerned with several different facets of the over-all slam problem. Among the topics considered (and reported upon herein) are 1) time effect in ship-slamming problems; 2) damping of slam oscillations; 3) model scaling requirements for slam phenomena; 4) an approximate method of analysis for ship hulls (in the elastic range) subjected to slam loads; 5) comparisons between the method 4) and other methods; 6) extension of 4) to the elastoplastic range.