Class 4 (4th Engineer) MEKG 📅 Jun 2023

Exam Question

(a) Draw the stress vs strain curve showing the different phases of change that occurs when an elastic material is subjected to load. (5)

(b) What is plastic deformation of material and how it is caused? Explain yield stress & how strain hardening is caused? where is this phenomenon successfully used? (6)

(c) Explain fatigue and how fatigue failure occurs? Suggest means in practice as to how fatigue failure can be avoided. (5)

Reference Answer

### (a) Stress vs. Strain Curve for a Ductile Material
The relationship between stress and strain for a ductile material (such as mild steel) subjected to a tensile load can be graphically represented by a Stress-Strain Curve. The curve illustrates the material's behavior as it transitions from elastic deformation to plastic deformation and finally to fracture.
**Key Points and Regions on the Curve:**
* **Stress (σ)**: The applied force per unit of the original cross-sectional area ($$\sigma = \frac{F}{A_0}$$).

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