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In any branch of science dealing with materials and their behaviour, strain is the geometrical expression of deformation caused by the action of stress on a physical body. Strain therefore expresses itself as a change in size and/or shape. In the case of geological action of the earth, if the release of stress through strain in rocks is sufficiently large, earthquakes may occur. Figure 1 Stress tensor In physics, stress is a measure of the internal distribution of force per unit area within a body that balances and reacts to the loads applied to it. ...
Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ...
Global earthquake epicenters, 1963–1998 An earthquake is a sudden and sometimes catastrophic movement of a part of the Earths surface. ...
If strain is equal over all parts of a body, it is referred to as homogeneous strain; otherwise, it is inhomogeneous strain.
Quantifying strain
Given that strain results in the deformation of a body, it can be measured by calculating the change in length of a line or by the change in angle between two lines (where these lines are theoretical constructs within the deformed body). The change in length of a line is termed the stretch or absolute strain, and may be written as . Then the (relative) strain, , is given by This article is about angles in geometry. ...
where is the original length of the material and is the extension. The extension is positive if the material has gained length (in tension), and negative if it has reduced length (in compression). The sign of the stretch is then passed on to the strain. Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ...
Compression in material science, physics or structural engineering, is the stress state of materials where the volume tends to decrease (compaction). ...
Strain has no units of measure because in the formula the units of length are cancelled. Dimensions of metres/metre or inches/inch are sometimes used for convenience, but generally units are left off and the strain sometimes is given as a percentage. The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ...
Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ...
A percentage is a way of expressing a proportion, a ratio or a fraction as a whole number, by using 100 as the denominator. ...
Engineering strain vs. true strain The above definition (known technically as engineering strain) is not linear, in that strains cannot be totalled. Imagine that a body is deformed twice, first by and then by (cumulative deformation). The final strain is slightly different from the sum of the strains: and As long as , it is possible to write: and thus True strain, however, can be totalled. This is defined by: and thus The engineering strain formula is the series expansion of the true strain formula. As the degree of the taylor series rises, it approaches the correct function. ...
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