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Stress-strain curves for Unfilled polymers

Posted by admin on July 23rd, 2012

below shows a typical stress-strain curve for short-term loading of a typical unfilled thermoplastic material. Figure 6 depicts the same curve as shown in Figure 5, except it is stretched horizontally to show the details within the elastic region. Several important material properties, such as Young’s modulus, proportional limit, elastic limit, yield point, ductility, ultimate strength, and elongation at failure, can be obtained from the stress-strain curve, as shown in Figures 5 and 6.  Young’s modulus  Young’s modulus is derived from the initial, straight-line portion of the curve as the ratio of stress to strain for that portion of the curve (see Figure 6).

Although it is occasionally referenced as a measure of material strength, Young’s modulus is actually more of an indicator of the rigidity of a material than the strength. It is the basis for simple linear engineering calculations, for example, in determining the stiffness of a plastic part.  Proportional limit  The Proportional limit, marked as point “P” in Figure 6, is the strain at which the slope of thestress-strain curve starts to deviate from linear behavior.  Elastic limit  The Elastic limit, point “I” on Figure 6, is the greatest strain the material can absorb and still recover. As strain continues to increase, the plastic will either draw, without recovery, or fail by rupturing (as shown in Figure 5).

FIGURE 5. Stress-strain curve for a typical thermoplastic.

FIGURE 6. The same stress-strain curve as shown in Figure 5, except it is stretched horizontally to show the details within the elastic region. Point P is the proportional limit, most often used as the design strain limit. Point I is the Elastic limit, beyond which the plastic part will not recover its original shape.


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