Metal Fatigue Testing 101

Tensile testing fracture

Metal raw materials are often fabricated into parts or components designed to tolerate cyclical stresses throughout their service lives; This constant repeated exposure to stress can often result in deformation, cracks, or other damage to the metal over time.

To accurately estimate the tolerances and service life of a part, fatigue testing simulates the cyclical stresses that the part will experience in a given application. Using a method referred to as cyclic loading, metal fatigue tests apply repeated stresses to the part until its structural integrity is compromised.

Why Metal Fatigue Testing Matters

Using metal fatigue testing, manufacturers can reliably estimate the service life of new designs before applying them into real-world applications where fatigue failure can sometimes have unfortunate, if not catastrophic, consequences. Installing untested parts in applications where they will bear cyclical loads poses serious risks for both workers and equipment. Knowing how and when a part or material will display signs of fatigue – from initial cracks through critical failure – allows manufacturers to produce the safest, most durable product possible.

In addition to addressing safety concerns, fatigue testing is an efficient way for engineers to test the limitations of their designs. If specific areas of the part succumb to early fatigue, this indicates a design flaw or inappropriate material choice that must be corrected before the design can move forward into mass production.

Metal Fatigue Testing Options

Cyclical stresses come in multiple forms, such as:

  • Weight
  • Compression
  • Tension
  • Vibration
  • Bending
  • Torsion
  • Axial

A range of metal fatigue tests is commonly used to test finished metal parts and raw materials across a diverse set of industries. These tests include:

Temperature-based tests

High-temperature and cryogenic fatigue testing determines functional limits in materials that will be operating in extreme temperatures. Exposure to extreme hot or cold temperatures often causes materials to expand and contract, so analyzing this effect via cryogenic and high-temperature fatigue testing helps determine how harsh temperature environments will impact the material.

Mechanical tests

Cyclical displacement testing, fracture testing, high and low cycle fatigue tests, bend tests, and other mechanical tests evaluate the physical properties of the test sample to predict how it will tolerate the appropriate physical stresses. Physical stress tests are usually performed by applying the maximum level of the appropriate stress type predicted by the application for a set amount of cycles or until the material fails. Depending on the specific application, materials may be tested at different stresses as well.

Metallurgical tests

If a raw material has inherent weaknesses, those flaws will subsequently exist in the finished part. In tandem with cyclical stress tests, metallurgical analyses can identify potentially dangerous qualities in the metallic material at the microstructure level that might make it more susceptible to early fatigue. These types of tests are often conducted on parts slated for use in high stakes industries, such as aerospace, medical, or oil and gas.

The Importance of Metal Fatigue Testing

Metal fatigue testing is a crucial step in the design and manufacturing process that helps engineers determine the viability of designs and the quality of the materials they plan to use. Through these tests, manufacturers learn the limits of the materials they work with and the parts they produce, and can make important adjustments to improve durability and service life.

Fatigue testing is a highly complex process that should be conducted by experienced professionals to ensure that the results are accurate and productive. A well-equipped laboratory with state-of-the-art equipment and highly educated staff with years of experience is essential to ensuring the strength and safety of final products. 

 

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Image Credit: Kimtaro / Shutterstock.com 

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