IntermediateTopic 45 of 106Engineering Mechanics
Stress-strain curve
Shows elastic region, yield, ultimate strength and fracture of a material.
In depth
A tensile test plots stress against strain: proportional limit, elastic limit, yield (often 0.2% offset), strain hardening, ultimate tensile strength, necking and fracture. Ductile materials show large plastic strain; brittle materials fracture with little.
Key points
- Area under curve is toughness
- Modulus is initial slope
- Engineering curve drops after necking
ExampleMild steel yields near 250 MPa and fails near 400 MPa.
The stress-strain curve is the basic test data for materials, and it defines yield, strength and ductility for design.
What is Stress-strain curve?
Shows elastic region, yield, ultimate strength and fracture of a material.
Why is it important to understand stress-strain curve?
The stress-strain curve is the basic test data for materials, and it defines yield, strength and ductility for design.
What is the yield strength?
The stress at which permanent deformation begins, often defined as the stress at 0.2 percent offset strain for materials without a clear yield point.
Why does the curve show a peak and then fall?
After necking begins, the cross-section reduces, so the engineering stress falls even though the material is still deforming.
How is Stress-strain curve used in practice?
Typical applications include selecting a steel grade by its yield strength, checking whether a plastic part will creep or crack under load and comparing the toughness of two alloys from the area under the curve.
What should I learn before Stress-strain curve?
Study "Strain" first (topic 44 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Stress-strain curve?
Area under curve is toughness. Modulus is initial slope. Engineering curve drops after necking.
Can you give an example of Stress-strain curve?
Mild steel yields near 250 MPa and fails near 400 MPa.
What comes after Stress-strain curve?
The next topic is "Hooke's law", which builds directly on this one.
How difficult is Stress-strain curve?
It is classed as Intermediate in Engineering Mechanics (topic 45 of 106). It is an intermediate topic. Work through the beginner topics in Engineering Mechanics first.