Impulse loading

Shock-compression processes are encountered when material bodies are subjected to rapid impulsive loading, whose time of load application is short compared to the time for the body to respond inertially. The inertial responses are stress pulses propagating through the body to communicate the presence of loads to interior points. In our everyday experience, such loadings are the result of impact or explosion. To the untrained observer, such events evoke an image of utter chaos and confusion. Nevertheless, what is experienced by the human senses are the rigid-body effects the time and pressure resolution are not sufficient to sense the wave phenomena. 

Fowles, G.R. (1972), Experimental Technique and Instrumentation, in Dynamic Response of Materials to Intense Impulsive Loading (edited by P.C. Chou and A.K. Hopkins), pp. 405-480. 

We discuss, here, some examples of computational solutions to shock or impulsive loading problems. We consider, in turn, one-, two-, and three-dimensional simulations, and the role each typically plays in computational physics and mechanics investigations. 

Swift, H.F., Preonas, D.D., Dueweke, P.W., and Bertke, R.S., Response of Materials to Impulsive Loading, Air Force Materials Laboratory Technical Report No. AFML-TR-70-135, Wright-Paterson AFB, OH, 76 pp.. May 1970. 

Fig. 2.1. The traditional approach to the study of mechanical responses of shock-compressed solids is to apply a rapid impulsive loading to one surface of a diskshaped sample and measure the resulting wave propagating in the sample. As suggested in the figure, the wave shapes encountered in shock-loaded solids can be complex and may require measurements with time resolutions of a few nanoseconds.

However, we are increasingly confronted with practical problems that involve material response that is inelastic, hysteretic, and rate dependent combined with loading which is transient in nature. These problems include, for instance, structural response to moving or impulsive loads, all the areas of ballistics (internal, external, and terminal), contact stresses under high speed operations, high... 

Using plastics under impulse loading conditions requires a careful design approach. Test data taken with high-speed testing... 

In addition, it should exhibit a fairly high hysteresis level that would have the effect of dissipating the sharp mechanical impulse loads as heat. The material will develop heat due to the stress under cyclical load. Materials used are the elastomeric plastics used in the products or as a coating on products. 

From inspection of the three designs it is apparent that the main stress of the loading will be at the support point for the seat. This will be assumed to be sufficiently strengthened to prevent failure, either by excessive stress or bending at the support point. The analysis will be concerned with the fact that the seat itself will not break as a result of the load and will not sag excessively after continued use. For this example the impulse load caused by dropping into a chair will be ignored. 

Strength. Ability of each structural component of the building to withstand overpressure and impulse loads. 

Krauthammer 1990, "Response of Reinforced Concrete Elements to Severe Impulsive Loads , T. Krauthammer, S. Shahriar, and H. M. Shanaa, ASCE Structural Journal, Vol. 116, No. 4, American Society of Civil Engineers, New York, NY, April, 1990, pp 1061-1079... 

The technique was then changed to entrap a small mass of water under a molten aluminum surface and simultaneously to overpressure the system. In this manner it was hoped to collapse steam films around the water. The actual procedure employed a small glass sphere containing water. The sphere was moved beneath the aluminum surface and broken by impulsively loading the system from a falling steel cylinder which impacted on a graphite toroid immediately above the molten aluminum. About 0.7 g of water was released into I kg of aluminum at 1170 K and pressurized to about 8 MPa. No explosions were detected. 

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