Modulus

Modulus

Young’s Modulus ( E ) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis. It is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus.

Importance

Elastomers are widely used for sound and vibration control, and are usually bonded and compressed between rigid plates. In order to predict the vibration transferred through the elastomer it is essential to have knowledge of the material properties, such as the Young’s modulus, the damping factor, and the Poisson’s ratio. Modulus tests are used for controlling product quality, and for determining the effect of chemical or thermal exposure on an elastomer/rubber. It is the retention of these physical properties, rather than the absolute values of the tensile stress, elongation, or modulus, that is significant.

Measurement

The modulus is described as the stress required to elongate the sample. In elastomers and rubbers the stress is not linear with strain. Therefore the modulus is neither a ratio nor a constant slope, but rather denotes a point on the stress strain curve.

Calculating Results/Reporting

The bulk modulus is a property of a material which defines its resistance to volume change when compressed. It can be expressed as:

K = p/ev

Here p is the hydrostatic pressure, ev is the volumetric strain, and K is the bulk modulus. In practice, a positive volumetric strain is defined as a decrease in volume.

As stated above, response is not linear. Therefore, a stress vs strain curve is plotted, and the slope of the linear portion is taken as the Young’s modulus, E. Relationships exists between Young’s modulus E, the shear modulus G, and Poisson’s ratio v.

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