According to statistics, metal fatigue is responsible for more than 90% of mechanical failures. Fatigue can be defined as the piecemeal degradation and eventual failure of materials under cyclic loads. Because the applied load on the material is usually dynamic, the load amount can differ from the tensile strength of the material.
Stress concentrations, when repeated, will result in microcracks. The cracks will grow if the stresses continue. Because the cracks are so small, there may be no visible warning. As a result, metal fatigue failure can be unpredictable.
Metal fatigue can cause unexpected catastrophic failures, such as a fan blade separating from a jet engine, causing damage or even death.
Stresses That Lead to Metal Fatigue
Bending and radial stresses are some of the types of stresses that can cause metal fatigue. Also, there could be a flaw in the manufacturing process or within the material itself. Therefore, it’s advisable to always use the best materials (such as metals that are corrosion-resistant) and metal glue for long-lasting metal. In this case, epoxies will be more appropriate as they are specially formulated for metal-to-metal applications.
Metal fatigue can also occur due to temperature, part rotation, wear, or structural design. For instance, the edges of holes frequently exert stress the most; however, the hole could be placed in another section of the metal, making the part less prone to fatigue. The stresses that cause metal fatigue are typically lower than the ultimate tensile strength of the material.
Forms of Material Fatigue Failure
Metal fatigue failure can manifest itself in a variety of ways, which includes:
- Thermal Fatigue Failure: Changes in temperature cause this type of metal fatigue. It could also be due to environmental factors and temperature fluctuations caused by applications being turned on and off.
- Vibration Fatigue Failure: This is caused by vibrational damage that results in cracks and stresses when equipment operates at levels that exceed operational standards.
- Corrosion Fatigue Failure: Corrosive environments commonly cause metal damage. Corrosion can cause cracks, which can lead to mechanical fatigue.
- Mechanical Fatigue Failure: This type of metal fatigue is caused by cumulative stresses and includes vibration and corrosion fatigue failure.
How to Identify Metal Fatigue
Although fatigue is a natural property of metals, similar disasters caused by fatigue stresses are uncommon nowadays. There are several methods for determining when a metal is becoming fatigued:
- Noise analysis – Damaged metal makes a distinct rattling sound.
- Fluorescent dyes – They draw attention to cracks by making them visible.
- Visual inspection – Helps with the detection of cracks and other deformations.
- Ultrasonic and X-ray inspection – In this regard, steel structure and human body diagnostics share many similarities.
How to Prevent Metal Fatigue
Structures designed to resist fatigue include the boring of small radii, abrupt changes in sections, etc. Increasing the size of a part can frequently eliminate structural errors. This will relieve stress and keep the metal from exceeding the fatigue limit.
Technological anti-fatigue measures frequently boil down to proper part processing. For example, when it comes to high-strength steel parts, the focus is primarily on surface grinding. However, incorrect structure assembly can result in dangerous variable stresses. Foreign inclusions in a metal caused by contamination during casting can also cause fatigue cracks to form.
Metal fatigue can be greatly reduced with proper material and design selection. Also, polishing can help offset the effects of application wear and tear. It should be noted, however, that given current industry advancements, leading steel producers devote efforts to improving metal purity, heat treatment of products, and chemical composition.
As a result, engineers and builders are now dealing with fundamentally different, stronger steel grades. While fatigue occurs, critical failures of metal structures and parts due to fatigue stresses have been reduced.