Development of Drop-Hammer Compression Apparatus with Controlled Stopping Device and Its Application to Bonding Test.

Abstract

A Drop-hammer compression apparatus with a controlled stopping device is developed. A check test for the stopping device is carried out by compression of a short circular bar. The accuracy of the device is confirmed to be satisfactory for practical use. It works well without redundant jumping motion of the drop-hammer. Application of the apparatus is performed to the bonding test, in which two rectangular blocks piled-up with a sawtoothed interface are compressed under plane strain condition. Soft pure aluminum(A1050-O), soft and a quarter hard aluminum alloy (A5056-O, 1/4H)and pure copper(C1100-O, H) are used. The initial hammer velocity is set to be 10 m/s in the high rate test. The corresponding low speed test is also carried out. The sawtoothed interface is degreased by liquid acetone and the naturally oxidized surface layer is removed by use of a dilute sulfuric acid solution before the test. The bondability in low speed compression is generally better than that in high rate compression in the cases of A1050-O and C1100-H. Shear-band type strain localization followed by shear fracture occurs in high rate compression of A5056-O and -1/4H specimens, and their bondability is rather low in low speed compression. Moreover, with respect to the hard pure copper, it is also tested for the case where the sawtoothed interface is scratched by a steel wire brush after removal of the oxidized surface layer. The remarkable improvement of bondability in low speed is attained by the scratching operation. Furthermore, the strain-rate sensitivity exponent(m-value) for the high strain-rate(∼500/s) of the tested materials is estimated by compressing a short circular bar, in which the method of direct comparison between the load-time curves by experiment and theory is used. The m-value of A1050-O is found 0.34, which is much higher than that for low speed compression. A5056 shows a tendency such that its m-value decreases rapidly as the strain increases. The shear fracture of A5056 mentioned above may be due to this characteristics of its m-value.