MECHANICAL TESTING

Low Cycle Fatigue - ASTM E 606

"ASTM E606 - Standard Test Method for " Strain-Controlled Fatigue Testing"
This Low Cycle Fatigue testing method covers the determination of low-cycle fatigue properties of nominally homogeneous metallic materials by the use of uniaxially loaded test specimens. It is intended as a guide for low-cycle fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis.

Although low-cycle fatigue is a phenomenon that is influenced by many of the same variables that influence high-cycle fatigue, the nature of low-cycle fatigue imposes distinctive requirements on fatigue testing methods.

In particular, the cyclic total strain should be measured and cyclic plastic strain should be determined. Furthermore, either of these strains typically are used to establish cyclic limits; total strain usually is controlled throughout the cycle. The uniqueness of this recommended practice and the results it yields is the determination of cyclic stresses and strains throughout the tests.

Low-cycle fatigue can be an important consideration in the design of industrial products. It is important for situations in which components or portions of components undergo either mechanically or thermally induced cyclic plastic strains that cause failure within relatively few cycles. Information obtained from low-cycle fatigue testing may be an important element in the establishment of design criteria to protect against component failure by fatigue.

Low-cycle fatigue test results are useful in the areas of mechanical design as well as materials research and development, process and quality control, product performance, and failure analysis. Results of a low-cycle fatigue test program may be used in the formulation of empirical relationships between the cyclic variables of stress, total strain, plastic strain, and fatigue life. They are commonly used in data correlations such as curves of cyclic stress or strain versus life and cyclic stress versus cyclic plastic strain. Examination of the cyclic stress-strain curve and its comparison with monotonic stress ­ strain curves gives useful information regarding the cyclic stability of a material, for example, whether the values of hardness, yield point, yield strength, and strain hardening exponent will increase or decrease (that is, whether a material will harden or soften) due to cyclic plastic straining. Results of the uniaxial tests on specimens of simple geometry can be applied to the design of components with notches or other complex shapes provided that the strains can be determined and multiaxial states of stress or strain and their gradients are correctly correlated with the uniaxial strain data.

Reference: ASTM E606 - Standard Practice for Strain-Controlled Fatigue Testing

Index of Mechanical Testing