Large Range Of Strain Rates Research Articles

Response of Various Metals to Large Torsional Strains Over a Large Range of Strain Rates—Part 1: Ductile Metals

This paper presents torsional test results for six ductile metals subjected to large shear strains and high strain rates. Included are OFHC copper, Cartridge brass, Nickel 200, Armco IF iron, Carpenter electrical iron, and 1006 steel. Torsional shear strains as high as 700 percent are achieved and strain rates vary from quasi-static to over 300 s−1. At the lower strain rates all of the materials exhibit positive strain hardening and strain rate hardening under essentially isothermal conditions. At the higher strain rates there is significant adiabatic thermal softening and strong evidence for shear instabilities and localizations. Constitutive relationships are derived from the test data and finite element computations of the tests are performed.

Response of Various Metals to Large Torsional Strains Over a Large Range of Strain Rates—Part 2: Less Ductile Metals

This paper presents torsional test results for six metals subjected to large shear strains and high strain rates. Included are 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, tungsten alloy and DU-.75Ti (Depleted Uranium). The specimens are strained to fracture at strain rates from quasi-static to over 100 s−1. All of the materials exhibit strain hardening and strain rate hardening. At the higher strain rates some of the materials develop shear instabilities and localizations. Constitutive relationships are derived from the test data and finite element computations of the tests are performed.

The relationship between the effect of thermal pre-treatment and the viscoelastic behaviour of polycarbonate in the glassy state

The viscoelastic behaviour of three different samples of polycarbonate, with differing pre-treatment, is described here by a generalized non-linear Maxwell system, proposed previously. This model gives the variation of the tensile yield stress related to each sample as a function of temperature and strain rate. The response is checked over a large range of strain rates, at temperatures from 20 to 80° C. The model allows the determination of the damping peak arising from the molecular movements which it expresses. A correspondence is found with the intermediate loss peak location, which occurs for each sample just below the α transition. Results obtained from dynamic mechanical tests and differential scanning calorimetry show that the structure of the samples changes in the range of temperatures where the intermediate loss peak arises at 1 Hz.

Stress relaxation and mechanical behavior of metals

Stress relaxation tests have been made in the temperature range 200° to 400°C on two materials, the Mg-Al eutectic alloy and commercial purity zirconium. The materials represent respectively high and low homologous temperature regimes. The novel features of the tests are the use of high speed, high sensitivity digital measurement techniques and the direct reduction of the data to stress-strain rate curves. It was possible in this way to obtain phenomenological information on the material behavior over a very large range of strain rate with very few specimens. Comparison was made with results obtained by more conventional differential strain rate tests. The test lends itself well to establishing the phenomenology of mechanical behavior of metals.