Low Crack Growth Rates Research Articles

The effect of load ratio on the threshold stresses for fatigue crack growth in medium carbon steels

A study of the effect of load ratio, R, on the low crack growth rates and the threshold stress conditions exhibited by five medium carbon steels has been conducted. It was found that decreased values of R retarded crack growth to an increasing degree as a defined threshold for crack growth was approached, such that this threshold showed a marked dependence on K max rather than ΔK. Comparisons of the five materials showed that the threshold increased as yield strength increased for a given R, but this effect could be normalised in terms of a constant value of the maximum plastic zone size at the crack tip.

An Elevated Temperature Torsional Fatigue Testing Fixture

A simple fixture that can be used with any closed-loop tensile testing system for torsional cyclic testing is described. This fixture was successfully used for low cycle fatigue and crack growth rate studies of high-strength steels both at ambient and elevated temperatures. The unique design of this fixture is that by using the output of the torque cell as the feedback to the servocontroller of the hydraulic tensile testing machine, the applied torque remains independent of all machine variables and the tests can be programmed to follow any torque/time profile.