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Fatigue tests induce stress to determine material failure points, important for applications like bridges. Tests involve monitoring stress and recording when fatigue occurs. Results may need to be filed with government agencies.
A fatigue test is a type of material test where the goal is to determine where the material will fail. Fatigue is a problem for all materials, caused by wear and tear during use. In a fatigue test, fatigue is deliberately induced to find the stress limits of the material. Materials for certain applications may need to meet specific fatigue requirements. For example, the metals used in a bridge must be able to withstand very high stress loads.
Fatigue is caused by things like motion, oscillation, vibration, pressure, wear and load. To take the example of a bridge, bridges are subjected to stresses as they move in the wind, stresses during seismic events, and the daily vibration and loading of thousands of automobiles. Over time, fatigue leads to material failure and will eventually cause failure; either the material will break away, or the cracks will cause structural components to fracture, leading to collapse.
Whether it’s a bed frame or bridge, fatigue is an issue. In a fatigue test, the materials used are subjected to vibration and other types of stress and carefully monitored. As soon as signs of fatigue begin to appear, they are noted and monitored, recording how long it takes for fatigue to occur and any failure. The point at which fatigue begins to occur is the lower stress limit. Fatigue tests are sometimes referred to as dynamic tests, because they involve a variety of techniques for hitting and essentially assaulting the material to find its stress limits.
With something like a piece of furniture, the piece of furniture itself can undergo a fatigue test. With a chair, for example, a machine could simulate someone repeatedly plopping into the chair, or it could create the torsional stresses that occur when the chair is dragged across the floor, with or without an occupant. In the case of large equipment, individual machine components are fatigue tested, as the entire equipment may not fit within the test area.
Fatigue test results are kept on file and, in some cases, may need to be filed with a government agency. For example, people who work in a high-rise building need to demonstrate that a component fatigue test was performed and that the components passed. This information can be useful if an error occurs, creating a paper trail that can be used to figure out when things started to go wrong.
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