Strain Calculator
Strain is how much a material deforms relative to its size. Work out normal (stretch) strain, thermal strain from a temperature change, lateral strain via Poisson’s ratio, or shear strain — with microstrain and true-strain output.
What Strain Means
Strain is deformation relative to size — how much something stretches, squashes or skews compared to its original dimension. Because it is a length divided by a length, strain has no units. The numbers are usually tiny, so engineers often quote microstrain (strain times one million), the unit strain gauges report. A strain of 0.001 is 0.1 percent, or 1000 microstrain.
Four Kinds of Strain
Normal strain is stretch or compression along the load: change in length over original length. Thermal strain comes from a temperature change, equal to the expansion coefficient times the temperature change — restrain it and you get thermal stress instead. Lateral strain is the sideways response to axial loading: pull a bar and it narrows, by Poisson’s ratio times the axial strain. Shear strain is angular distortion — the sideways displacement divided by the height, the tangent of the skew angle.
Engineering vs True Strain
Engineering strain divides by the original length and is fine for small deformations. True strain integrates over the changing length and equals the natural log of one plus engineering strain. The two agree to four decimals up to a percent or so, but diverge once a material is stretched substantially, as in metal forming.
Frequently Asked Questions
How do you calculate strain?
Divide the change in length by the original length. The result is dimensionless; multiply by one million for microstrain or by 100 for percent.
What is microstrain?
Strain multiplied by 1,000,000. It is the practical unit for strain-gauge readings, where values are usually a few hundred to a few thousand.
What is thermal strain?
The strain caused by a temperature change, equal to the thermal expansion coefficient times the temperature change. If the part cannot expand freely, that strain turns into stress.
What is lateral strain and Poisson’s ratio?
Lateral strain is the transverse change when a material is loaded axially. Poisson’s ratio is the negative of lateral strain over axial strain – about 0.3 for steel.
Related calculators
- Young’s Modulus Calculator — stress over strain, the stiffness link.
- Stress Calculator — the force side of the stress-strain pair.
- Thermal Expansion Calculator — turn thermal strain into length change.
- Shear Stress Calculator — the stress that drives shear strain.