Proportional Limit (Hooke's Law)
   *From the origin O to the point called proportional limit, the stress-strain curve is a straight line. Hooke's Law that within the proportional limit, the stress is directly proportional to strain.
   *The constant of proportionality k is called the Modulus of Elasticity E or Young's Modulus and is equal to the slope of the stress-strain diagram from O to P. 
 

Elastic Limit
   *The elastic limit is the limit beyond which the material will no longer go back to its original shape when the load is removed, or it is the maximum stress that may be developed such that there is no permanent or residual deformation when the load is entirely removed.
 

Elastic and Plastic Ranges
   *The region in stress-strain diagram from O to P is called the elastic range. The region from P to R is called the plastic range.
 

Yield Point
   *Yield point is the point at which the material will have an appreciable elongation or yielding without any increase in load.
 

Ultimate Strength
   *The maximum ordinate in the stress-strain diagram is the ultimate strength or tensile strength.
 

Rapture Strength
   *Rapture strength is the strength of the material at rupture. This is also known as the breaking strength.
 

Modulus of Resilience
   *Modulus of resilience is the work done on a unit volume of material as the force is gradually increased from O to P, in N·m/m3. This may be calculated as the area under the stress-strain curve from the origin O to up to the elastic limit E (the shaded area in the figure). The resilience of the material is its ability to absorb energy without creating a permanent distortion.
 

Modulus of Toughness
   *Modulus of toughness is the work done on a unit volume of material as the force is gradually increased from O to R, in N·m/m3. This may be calculated as the area under the entire stress-strain curve (from O to R). The toughness of a material is its ability to absorb energy without causing it to break.
 

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