I. Stress terms
1.Proportional Limit
• It is the maximum stress up to which, the stress is linearly proportional to strain. Point A
• A material with high value of proportional limit can withstand greater stress without permanent deformation.
2. Elastic Limit
• Maximum stress a material can withstand without undergoing permanent deformation.
• It describes the elastic behavior of the material. (fig.6)Point B
x The elastic and proportional limits have nearly the same values, as they represent the same phenomena.
3. Yield Stress or Proof stress
• It is the stress at which materials start to show permanent deformation.(fig.6) Point
4. Ultimate(Tensile or compressive) Strength or stress
• Maximum stress that the material can withstand before failure (fracture) under tension or compression respectively.
• The material could not withstand any more stresses, as it will fracture. (fig.6) Point D
.The yield strength is often of greater importance than ultimate strength in design and material selection because it is an estimation of when a material will start to deform permanently.
5. Fracture strength or stress
• It is the strength at which the material fractures. (fig.6) Point F
