Fatigue Loading Of Material Or Mechanical Parts

Fatigue loading of mechanical parts or materials results from inconstant structural loads that change over time and can result in failures without warning. These loads can change slowly or very rapidly. As the loads vary, so does the stress level within the component. When considered during design, load variations are foreseeable and manageable. However, if fatigue loading is not considered during design, or if the part is used in an unexpected way or is defective, the part can fail.

Envista Forensics experts can determine how and why a part failed. Failure may be due to design, manufacturing, or the environment in which the part was used. The design may not have adequately considered all variable loads the part or material would encounter, it may have been manufactured with a virtually undetectable defect, or the environment it is used or stored could have compromised its properties.

Based on composition and manufacturing processes, some materials used for components hold up better over time to fatigue loading conditions. When considering material and part issues, one needs to consider:

• The static and dynamic loads experienced directly leading to fatigue failure
• Whether a defect within the component from the start led to the fatigue failure
• Whether the correct material or part was used, tracking this from design to the manufacturing and installation phase
• Whether the environment where it was stored or used conducive to the lifetime of the material or part

Fatigue Loading Analysis

The root cause of fatigue loading is investigated by physically examining the material or part to determine its properties (e.g. metallographic or grain structure) and signs of stress through microscopic and macroscopic means. Envista Forensics experts also review load history and fatigue lifetime and algorithms, which requires performing physical measurements and numerical calculations.

Most fatigue failure modes result from a combination of the following conditions:

• Simple fatigue, or loss of strength over multiple loading cycles, which often leads to other failure modes
• Fractures
• Yielding, or excess stress
• Deflection, where the material or a part of it is too flexible
• Buckling, where the material is not thick enough and the stress applied from both sides is too great
• Creep, where the body of the part of material deforms over time due to stress and/or heat

Though these issues may seem straightforward, rigorous analysis is needed to get to the true root of a fatigue issue. Our engineers and consultants have the tools and the expertise to identify what caused your unique fatigue loading incident and help you understand how to avoid these failures in the future.