ASTM E606 / E606M Test for Strain-Controlled Fatigue Testing

Scope:

ASTM E606 / E606M test method provides information on the fatigue properties of a material. They determine the ability of a material to withstand repeated strain (deformation). They determine fatigue life and crack growth data, identify critical locations or demonstrate the safety of a structure that may be susceptible to fatigue.

Strain-controlled fatigue testing is an important element in the designing of the structure to prevent failure by fatigue. It is also used in research and development, process and quality control, product performance, and failure analysis.

This ASTM E606 / E606M test is not used to test full-scale structures, for instance, an airplane wing. Rather, it tests coupons. A coupon is a small sample of the material under test that has been prepared in such a way that its failure mechanism will be representative of the larger production pieces.

Test Procedure:

In the ASTM E606 / E606M test, a load is applied, removed, and reapplied again and again to a coupon until the coupon cracks and breaks. The data gathered during the test is used to calculate fatigue life and the rate of crack growth. The fatigue life of a coupon is the number of cycles it takes to break the coupon. The rate of crack growth in a coupon can also be measured, either during the test or after by fractography.

This data is also used in the ASTM E606 / E606M test to create stress-life or strain-life curves, identify critical locations, and demonstrate the safety of a structure that may be susceptible to fatigue. Fatigue tests on coupons are typically conducted using servo-hydraulic test machines capable of applying large variable amplitude cyclic loads. Constant amplitude testing can also be applied by simpler oscillating machines. Testing of coupons can also be carried out inside environmental chambers where the temperature, humidity, and environment that may affect the rate of crack growth can be controlled.

Video 01: An introduction to fatigue testing

Specimen size:

The test specimens in the ASTM E606 / E606M test method are usually hourglass in shape. A minimum of ten specimens should be used to generate a fatigue strain-life curve. 

Data:

ASTM E606 / E606M strain fatigue testing is done to gather the following information: 

1. The rate of crack growth and fatigue life of components such as a coupon or a full-scale test article. 
2. Location of critical regions. 
3. Degree of fail-safety when part of the structure fails. 
4. The origin and cause of the crack initiating defect from fractographic examination of the crack.

Conclusion:

ASTM E606 / E606M test method provides information on the fatigue properties of a material.