Modulus of Elasticity also referred to as Elastic Modulus or just Modulus is the quantification of the ratio of a material's elasticity. Modulus of elasticity measures the resistance of a material to non-permanent or elastic deformation when a ratio of the stress is applied to its body. When under stress, materials will primarily expose their elastic properties. The stress induces them to deform, but the material will resume to its earlier state after the stress is eliminated. After undergoing the elastic region and through their production point, materials enter a plastic region, where they reveal everlasting deformation even after the tensile stress is removed.
Graphically, a Modulus is described as being the slope of the straight-line part of stress, denoted by (σ), and strain, denoted by (ε), curve. Focusing on the elastic region, if the slope is between two stress-strain points, the modulus will be the change in stress divided by the change in strain. Thus, Modulus =[σ2 - σ1] / [ε2 - ε1].
In this, the stress (σ) is force divided by the specimen's cross-sectional region and strain (ε) is the alteration in the length of the material divided by the material's original measure length. Seeing that both stress and strain are normalized quantifications, modulus exhibits a consistent material property that can be differentiated between specimens of different sizes. A huge steel specimen will have a similar modulus as a small steel specimen, though the large specimen would need a greater maximum force to deform the material.
Note: Brittle materials such as plastics, aluminium, copper and composites will reveal a steeper slope and higher modulus value than ductile materials such as iron, rubber, steel, etc.
Refer below for the Strain-Stress curve.
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In contrast to brittle materials like metals and plastics, elastomeric materials do not display a yield point and continue to deform the material body elastically until they break. In the case of synthetic polymers having elastic properties like rubber, the modulus is simply expressed as a measure of the force at a given elongation. For example, in the graph below, the modulus is reported as stress at different levels for various materials.
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The modulus of elasticity of a material is the quantification of its stiffness and for most materials remains consistent over a range of stress. Following are the different types of modulus of elasticity:
1. Young's Modulus
The ratio proportion of the longitudinal strain to the longitudinal stress is known as Young's modulus.
2. Bulk Modulus
The ratio of the stress applied to the body on the body's fractional decrease in volume is called the bulk modulus. Thus, when a body is subjected to three mutually perpendicular stresses of the same intensity, the ratio of direct stress to the corresponding volumetric strain is what we call the Bulk Modulus. Bulk Modulus is generally denoted with the letter K.
3. Shear Modulus
Also known as Rigidity Modulus, the ratio of the tangential force applied per unit area to the angular deformation in radians is called the shear modulus. Shear Modulus is generally denoted with a letter C.
There are different types of modulus of elasticity and specific ways of calculating types of modulus of elasticity which we will be discussing below.
Calculating Different Types of Modulus of Elasticity
Calculating modulus of elasticity is generally required by users recording modulus. Hence, they should be well acquainted that there are various ways to measure the slope of the initial linear portion of a stress/strain curve. Remember that, when comparing outcomes of modulus for a given material between different laboratories, it is crucial to know which type of modulus calculation has been selected.
Thus, slopes are measured on the initial linear portion of the curve by employing least-squares fit on test data. The steepest slope is concluded as the modulus.
Let’s see below how to calculate different types of modulus of elasticity:
Young’s Modulus, usually denoted by (Y) = Longitudinal Stress ÷ Longitudinal Strain Nm-² or pascals.
Bulk Modulus of material is easily calculated in the following manner.
Bulk Modulus (K) = (F÷A) ÷ (v÷V) = FV÷vA
Thus, we get
K=PV ÷ v Nm-²
F ÷ A = volume stress or bulk stress
v ÷ V = volume strain or bulk strain
P = F ÷ A
We determine the Shear Modulus in the following way.
Shear Modulus (n) = tangential stress ÷ Shearing strain
=F ÷ AøNm-²
To determine the chord modulus, we have to choose a beginning strain point and an end strain point. A line segment is needed to be drawn between the two points and the slope of that line is reported as the modulus.
Elastic modulus is identified using a standard linear regression strategy. The part of the curve to be used for the computation is chosen automatically and does not include the initial and final parts of the elastic deformation at the position where the stress-strain curve is non-linear.
Modulus is identified easily by a hysteresis loop produced by a portion of loading and reloading.
Using the zero stress/strain point as the beginning value and a user-selected strain point as the end value, we can determine this type of modulus. A segment is constructed between the two points, and the slope of that line is reported as the modulus.
We need to choose a start strain point and an end strain point. Using the least-squares fit on all points between the start and the endpoints, a line segment is drawn. The slope of the best fit line is thus recorded as the modulus.
Choosing a tangent point on the stress/strain curve, we can calculate the tangent type of modulus. The slope of the tangent line is thus recorded as the modulus.