What Is a Shear Test?

Mary McMahon

A shear test determines the ability of a material to stand up against perpendicular, or upright, stresses. Such testing can be used for a variety of activities and may involve many different kinds of equipment. Two common applications are in geological evaluations of sites and materials testing for commercial products. Technicians can perform this test to exacting specifications when necessary for product control or forensic purposes, where a controlled testing environment is required for validity.

Shear tests are performed with soil samples that are placed under intense pressure.
Shear tests are performed with soil samples that are placed under intense pressure.

In geotechnical engineering, a shear test can be used to assess the properties of rock and soil at a site. The underlying substrate of a building can be subject to shear stress during earthquakes, heavy weather, and other events. Engineers need to know if it is strong enough to withstand the stress without failing. If it isn't, designs may require modifications, such as anchors to bedrock to keep a building stable. Knowledge about soil conditions can also be helpful for disaster planning.

Engineers can use lab or field techniques in a shear test. They work with samples of soil and rock taken from various places on the site and subject them to compressive forces to watch how they behave. The test equipment can record the amount of pressure used to allow the engineer to determine the failure point. Tests may be repeated to confirm results in cases where there are questions or concerns about the quality of the testing. Similar testing is used by people like rangers to assess avalanche risk.

Another type of shear test is used in materials testing with products like plastics and films. These may need to endure perpendicular forces and remain operational. Technicians can sandwich a test material between two plates, apply pressure, and determine when it ruptures or wrinkles. The point at which the material starts to deform is noted so technicians can develop accurate technical specifications. If a material fails at low pressures, it may not be suitable for some applications.

Regulatory agencies may set standards for shear test procedures. These ensure that companies use the same methods with all their testing, which makes it possible to compare tests from different facilities. Standardization also contributes to the development of universal technical specifications. Companies reviewing lists of material and their accompanying data can understand the shear test results because they can be generalized. Facilities preparing bids can review the listed tolerances to determine if they have or can make materials that will meet their needs.

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