ESDU Engineer

Endurance of High-Strength Steels

ESDU 04019, which will be issued in the autumn of 2004, presents endurance data for high-strength steels. The results of more than 10 000 constant-amplitude fatigue tests, on plain and notched specimens subjected to rotating-bending, plain-bending and axial loading, are presented in the form of curves of alternating stress versus endurance.

In the Data Item, a high-strength steel is defined as a steel having a room-temperature 0.2 per cent proof stress greater than 800 MN/m2 (116 × 103 lbf/in2). The data presented relate to the medium- and high-cycle regimes, that is endurances of greater than 10 000 cycles.

The data have been grouped according to type of steel based on the unified numbering system (UNS) codes and also according to alloy content, the tempering temperature applied to the specimen before testing, the test-piece shape, the surface condition of the specimen and the size of the notch, when present. Test temperature and mean stress are also considered.

The text of the Data Item includes discussion of the data presented and of the influence of various factors on fatigue strength; the effects of tempering temperature, mean stress, test temperature and frequency, loading type, surface roughness and notches, and surface treatment are all discussed in detail with reference to the data in the Item. Figures that illustrate explicitly the effects of some of these variables are also presented.

The figures in the Item contain data for materials covering 12 different UNS specifications subjected to a variety of heat treatments. They embrace the following:
• tempering temperatures between 420 and 850°C (790 and 1560°F)
• stress ratios of 0 and –1
• test temperatures between room temperature and 600°C (1110°F)
• test frequencies between 10 and 160 Hz
• tests performed using axial, rotating-bending or plain-bending loading
• specimen surface finishes including polished, as-machined and as-carburized
• stress concentration factors between 1 and 3
• specimen surface treatments including shot-peened, polished, carburized, nitrided and low-plasticity-burnished.

The plots of the data are accompanied by tables which give comprehensive details of the material: composition, yield strength, proof stress, tensile strength and heat treatment; and of the tests themselves: loading type, specimen geometry, test temperature and frequency, grain direction and surface finish.

The curves through the data have been derived using ESDUpac A9724, the program that accompanies Data Item No. 97024, “Derivation of endurance curves from fatigue test data, including run-outs”, and the equations of the derived curves are given on the figures. In addition, all the data points are available in the Microsoft Excel® file that accompanies the Data Item.

Queries regarding this article should be directed to the Strength Analysis Group via esdu@esdu.com or the ‘feedback’ form at www.esdu.com