Short-term Tensile Tests Research Articles

The long-term strength of substructure-strengthened and recrystallized aluminum

1. The long-term strength of polygonized aluminum at 100°C depends on the subgrain size and on the dislocation density within the subgrains, while that of the recrystallized metal depends on the grain size: The long-term strength of aluminum increases (at least for lives up to 1000h) with reduction in the grain or subgrain size and with increase in the density of internal dislocations. 2. The rate of loss of strength (the tangent of the angle of slope of the long-term strength curves) decreases with increase in the grain or subgrain size of aluminum; this leads to the convergence of the long-term strength curves of metal with different subgrains (or grains) at long lives. 3. An analogy has been found between the behavior of polygonized and recrystallized in long-term strength tests at relatively short times to failure and that in short-term tensile tests.

Effect of Relative Mean Strain in High-Temperature Low-Cycle Fatigue of a Stainless Steel

The effect of the relative mean strain in the low-cycle fatigue of a stainless steel (AISI 304) in air at 650°C and at a constant strain rate (4 × 10−3s−1) is studied. Two modes of strain measurement (axial and diametral) were used separately in nonzero mean strain experiments with controlled axial strain in real time. The effect of the relative mean strain on the fatigue life has been found to be negligible in the range of lives 200 ⩽ N ⩽ 10,000 cycles when the mean strain does not exceed 1.5 times the total range. This effect, however, becomes important when the mean strain is several times the total strain range. In addition, for N < 200 cycles at failure, the effect of even a small value of the mean strain appears to be significant. The extension of a method previously developed is presented for establishing the high-temperature fatigue behavior under isothermal conditions with positive mean strain. On the basis of the results of a short-term tensile test, the technique gives predictions in good agreement with experimental data.

High-temperature fatigue-life estimation: Extension of a unified theory

A procedure is presented for predicting the fatigue behavior at elevated temperature by extending the unified theory of fatigue damage previously proposed for room temperature. The method predicts the experimental results of high-temperature push-pull tests under isothermal conditions, using the total strain range. The analysis is based on parameters obtained from short-term tensile tests in which the temperature and the strain rate are the same as for the fatigue test. The procedure is applied for fatigue of a stainless steel at 650°C under cyclic axial strain. It has also been applied to published data for three austenitic stainless steels. In general, the present procedure gives estimates closer to experimental results than those obtained from other known methods.

A new approach to the prediction of low-cycle fatigue data

Low-cycle fatigue data for annealed AISI Type 304, 316, and 348 stainless steel to 816°C have been analyzed and a new relationship has been identified associating fatigue data with shortterm tensile behavior. A logarithmic plot of plastic strain range vs time to fracture was shown to be linear with a slope of minus unity. This line was also found to originate at the point corresponding to the tensile ductility. A similar analysis for elastic strain range data revealed a relationship with the strain-hardening exponent measured in a short-term tensile test at the same temperature and strain rate. These correlations have been combined to provide an equation for predicting the relationship between total strain range and cycles to fracture. This approach has been termed the Method of Characteristic Slopes.