The use of plasticine to simulate the dynamic compression of prismatic blocks of hot metal

Abstract

White plasticine was used as a model material at room temperature to study the dynamic compression of hot metals. Specimens of 1 in. nominal height having circular, square, rectangular, triangular and annular sections were subjected to dynamic compression at mean strain-rates up to 200 sec −1 between smooth platens at room temperature using a model drop-hammer. Rough platens were used in the cases of the triangular prisms and hollow cylinders. The quasi-static true stress-natural strain curve for the material exhibited little strain hardening up to a natural strain of about 1·0. The relation between the mean dynamic yield stress, Y m, and the mean strain-rate, ▪, is shown to be of the form Y m = B ▪ for different sections at room temperature. Following the manner in which the authors analyse their results, an increase in the falling mass appears to cause an increase in the mean dynamic yield stress at constant strain-rate. An increase in the mean dynamic normal pressure was apparent with increase in the coefficient of friction between a specimen and rough platens for equilateral triangular prismatic blocks and hollow cylinders. The relation between deformation energy/unit volume, E V , and natural strain, ε, is shown to be a power law of the form E V = C εm . Greater deformation for a given energy/unit volume is obtained with increase in mass. Upset axi-symmetrical specimens remain more or less axi-symmetric for all reductions, but the holes of the hollow cylinders do not close even with height reductions exceeding 70 per cent, regardless of whether or not the specimens are well lubricated. Non-uniform lateral spread is observed in the case of the cubes, rectangular and triangular prisms, but the change in shape of the squares and rectangles is not appreciable even for reductions up to 70 per cent. The prisms of the triangular section tend to become circular for reductions greater than 70 per cent. At a reduction of 87 per cent the triangular section becomes almost a complete circle of 2 in. diameter. Further qualitative experiments indicate that significant inhomogeneous deformation is encountered during dynamic compression of well lubricated specimens at fractional reductions exceeding about 0.5, even though axi-symmetric specimens remain approximately axi-symmetric.