Studies on pressure distribution in compression of block between parallel plates

Abstract

Compression tests of a block between parallel plates are usually applied to determine the stress-strain curves in compression under plane-strain condition such as in rolling, and to estimate the "reduction capacity" of lubricants.It is clear that these tests are based on the compression under plane-strain condition. However, it will be necessary to confirm whether the compressive deformation of a block between parallel plates occurs under the plane-strain condition.The pressure distribution in the contact area between the material and the parallel plates was studied by the method of "pressure pick-up pin" under various conditions of different thicknesses of specimens, lubricants, reduction percentages, and thickness ratios (b/t0).The results obtained were summarized as follows:(1) When the thickness ratio (b/t0) was a positive integer, the value of specific yielding point stress (po/2k) was approximate to 1.(2) The pattern of contact pressure distribution in the direction of die width did not much depend upon lubricant conditions, thickness ratio, and reduction percentage. However, high pressure appeared in the middle part and near the ends of the die width, and lower pressure appeared in the intermediate parts.(3) As for the contact pressure distribution in the direction of larger length of die, the pressure showed maximum in its center and gradually decreased toward ends (plotting a convex curve) under good lubrication. Whereas, in bad lubrication, the maximum pressure appeared at several mm apart from the center, which plotted a concave curve.(4) When a block, having the same width as the die, was compressed between parallel plates, the pressure distribution along the larger length of die was nearly constant, which was called "flat pattern".(5) The leading factor affecting the pressure distributions in the compression of a block between parallel plates was the non-contact deformed part on both sides of the contact part between the die and specimen. The above part constrained the flow of material in the directions of width and length, and produced various patterns of pressure distribution.