How can you test for material fatigue in quality control?

1 Fatigue testing methods

Various fatigue testing methods can be used to simulate the service conditions of a material and measure its response to stress cycles. For example, the tension-tension fatigue test applies a sinusoidal or constant amplitude load between a minimum and maximum stress level and is suitable for materials mainly subjected to tensile stresses, such as wires, cables, and ropes. The tension-compression fatigue test applies a sinusoidal or constant amplitude load between a positive and negative stress level, creating alternating tension and compression and is ideal for materials subjected to bending or torsion stresses, such as beams, shafts, and springs. Lastly, the rotating-bending fatigue test applies a constant bending moment to a rotating specimen, creating cyclic stress distribution along its cross-section and is suitable for materials subjected to rotating or vibratory stresses like axles, gears, and turbines.

3 Fatigue testing data

The main output of a fatigue test is the number of cycles to failure (Nf) for a given stress level (S). By plotting these data points on a log-log scale, you can obtain a fatigue curve or a S-N curve, which shows the relationship between the stress amplitude and the fatigue life of the material. The S-N curve can have different shapes and slopes, depending on the material type, microstructure, and loading mode. Some materials have a fatigue limit, which is the stress level below which they can withstand an infinite number of cycles without failing. Other materials have an endurance limit, which is the stress level below which they can withstand a very large number of cycles (usually 10^7 or more) without failing.

4 Fatigue testing standards

To ensure the consistency and accuracy of fatigue testing, you need to adhere to certain standards and guidelines that outline the procedures, equipment, and criteria for the test. There are several national and international standards that cover different aspects of fatigue testing, such as ASTM, ISO, DIN, and JIS. For example, ASTM E466 covers tension-tension fatigue testing of metallic materials at room temperature, ASTM E468 covers the presentation and analysis of S-N data for metallic materials, ASTM E606 covers tension-compression fatigue testing of metallic materials at room temperature, and ISO 12106 covers axial load fatigue testing of metallic materials at room or elevated temperatures. These are some of the most widely used standards.

5 Fatigue testing applications

Fatigue testing is used across a variety of industries and fields, such as aerospace, automotive, biomedical, civil, and energy. It can be used to evaluate the fatigue performance and durability of materials, components, and structures under different loading and environmental conditions. Additionally, it can be used to compare the fatigue properties and behavior of different materials or designs. It is also useful for identifying the factors and mechanisms that influence the fatigue resistance and failure of materials. Moreover, it can help develop and validate fatigue models and theories that can predict the fatigue life and damage of materials as well as optimize and improve the fatigue design and maintenance of materials, components, and structures.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?