Difference Between Stress and Strain

Main Difference – Stress vs. Strain

When deforming forces act on an object, they can change the object’s shape. The main difference between stress and strain is that stress measures the deforming force per unit area of the object, whereas strain measures the relative change in length caused by a deforming force.

What is Stress

Whenever a force attempts to deform an object, we say that the object is under stress. Stress is defined as the deforming force per unit area of the object. Since we can resolve any force on an object into directions parallel and perpendicular to the surface, we define normal stress to be equal to the force perpendicular to the surface per unit area. Similarly, we define shear stress as the force parallel to the surface  per unit area. If the force acting on a surface is F and the area of the surface is A, then the stress \sigma is given by:

\sigma=\frac{F}{A}

Stress has the same dimensions as pressure, so the units used for measuring stress are also N m-2 or Pa (1 Pa=1 N m-2). When forces act to lengthen the material, the stress is referred to as tensile stress. When the forces try to compress a material, the stress is referred to as compressive stress.

What is Strain

Strain measures the amount of relative deformation caused by a force acting on an object. For simplicity here, we will only consider the normal strain, created by normal stress. Suppose the original length of the object is l_0 and due to stress, the length changes to l_1. The change in length is \Delta l=l_1-l_0. The strain \epsilon is then given by,

\epsilon =\frac{\Delta l}{l_0}

Since strain is given by a fraction where the numerator and denominator both have units of length, the strain itself has no units. i.e. it is a “dimensionless quantity”. It is common to see strain expressed in terms of percentages.

Stress vs. Strain Curve

We can draw a graph of how the strain in a body changes as we vary the stress acting on the object (this can be done, for example, by adding weights). These graphs, called stress vs. strain curves, reveal lots of information about the nature of the material that the object is made of. The figure below shows the typical stress-strain curve for a ductile material (“ductile” means that the material can be stretched out well):

Difference Between Stress and Strain - Stress_vs_Strain_Curve_for_a_ductile_material

Stress-strain curve for a ductile material

The gradient of the elastic region of the curve is called the Young Modulus. This is a very important number for materials engineers, as it gives how much strain would be caused by a given stress in a material.

Difference Between Stress and Strain

What it Measures

Stress gives the force acting per unit area of an object.

Strain gives the relative change in length due to deforming forces.

Units

Stress is measured in pascals (Pa).

Strain has no units; it is simply a ratio.

Image Courtesy

“Typical Stress vs. Strain diagram for a ductile material (e.g. Steel).” by Breakdown (Own work) [], via  (Modified)

About the Author: Nipun


Related pages


arr calculatordifference between stepup and stepdown transformerdifference between diabetes insipidus and mellituscompare reflecting telescopes and refracting telescopespeak vs rmsare chinos khakisepinephrine and norepinephrine differencesunicameral vs bicameralwolf and coyote comparisonarchaebacteria vs eubacteriameristematic tissue structure and function907.18474 kilogramsmarginal costing systemdefine polyunsaturated fatty acidssociology vs cultural anthropologysteps in writing an expository essaydelusions hallucinationssulphate ioncondensation polymerization pdfindicative mood sentence exampleswhat is the difference between recessive and dominantwhat is sporophyte3 examples of pure substancespaneer and tofudefinition of antagonist literary termmodal verbs auxiliary verbswhat is a closed syllableheterochromatin and euchromatin differencesmeaning of acculturationdifference between normative and positive economicsdefinition of furniture and fixtures in accountingupthrust definitionsushi vs sashimiwhat is allomorphassimilation sociology definitiondifferentiate aerobic and anaerobic respirationwhat are some examples of a pure substancedefine snugglehow are sharks and dolphins alikewhat is assonance and examplesicing vs frostingexamples of protagonist and antagonistcharacteristics of omnivores animalsthe difference between accuracy and precision in chemistrypolar and nonpolar molecules examplescalculating equilibrium priceleast count of measuring instruments pdfwhat is the process of mitosiswhat is a protostomewhat is the difference between plant mitosis and animal mitosisexamples of alkaline earth metalsiupac name for formaldehydegst refund singapore eligibilitydefinition of a dicotexamples of conceit poemssn1 and sn2 mechanismwhat is the difference between benign and essential hypertensionamebiasis dysenterysepsis vs septic shockdifference in cyclone and tornadoexamples of synesthesiaconsulate and embassy differencedefine superegosardonic meaningdifference in alligator and crocodilewhat is the difference between uracil and thyminemetaphors and analogiesallude and eludechiral and achiral differenceare broccoli and cauliflower the same plantmetaphysical conceit examplesheterotrophs autotrophs