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The Hopkinson pressure bar was first suggested by Bertram Hopkinson in 1914 [1] as a way to measure stress pulse propagation in a metal bar. Later, in 1949 Herbert Kolsky [2] refined Hopkinson's technique by using two Hopkinson bars in series, now known as the split-Hopkinson bar, to measure stress and strain, incorporating advancements in the cathode ray oscilloscope in conjunction with ...
An unmounted resistive foil strain gauge. A strain gauge takes advantage of the physical property of electrical conductance and its dependence on the conductor's geometry. . When an electrical conductor is stretched within the limits of its elasticity such that it does not break or permanently deform, it will become narrower and longer, which increases its electrical resistance end-to-
The strain measurements are most commonly measured with an extensometer, but strain gauges are also frequently used on small test specimen or when Poisson's ratio is being measured. [6] Newer test machines have digital time, force, and elongation measurement systems consisting of electronic sensors connected to a data collection device (often a ...
The original residual stress in the material is then evaluated based on the measured deformations and using the so-called calibration coefficients. The hole is made by a cylindrical end mill or by alternative techniques. Deformations are most often measured using strain gauges (strain gauge rosettes).
Slow strain rate testing (SSRT), also called constant extension rate tensile testing (CERT), is a popular test used by research scientists to study stress corrosion cracking. It involves a slow (compared to conventional tensile tests) dynamic strain applied at a constant extension rate in the environment of interest.
Distortion seismometer. A strainmeter is an instrument used by geophysicists to measure the deformation of the Earth. Linear strainmeters measure the changes in the distance between two points, using either a solid piece of material (over a short distance) or a laser interferometer (over a long distance, up to several hundred meters).
Camera image of a video extensometer measuring two line markers A video extensometer is a device that is capable of performing stress/strain measurements of certain materials, by capturing continuous images of the specimen during test, using a frame grabber or a digital video camera attached to a PC. [ 2 ]
An example of an electrical force gauge is an "electronic scale". One or more electrical load cells (commonly referred to as "weigh bars") are used to support a vertical or horizontal "live load" and are solid-state potentiometers which have variable internal resistance proportional to the load they are subjected to and deflected by. As the ...