---
title: "Tensile properties and effect of temperature"
subject: "Material Science"
chapter: 3
key: "semester_3/material_science:properties-from-tensile-test-and-temperature"
source: https://www.bctengineer.com/q/semester_3/material_science/properties-from-tensile-test-and-temperature
site: BCT Engineering
---

# Tensile properties and effect of temperature

Material Science · Chapter 3: Mechanical Properties and their tests

- Asked in: year not given, 5 marks
- Video: [Lab 3:  Effect of Temperature on Mechanical properties through Tensile Testing](https://www.youtube.com/watch?v=WBe0bfCF8s0) — Mechanical Engineering with Dr. Sanei
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/material_science/properties-from-tensile-test-and-temperature
- Whole chapter: https://www.bctengineer.com/md/semester_3/material_science/chapter-3

## Question

Write short notes on the properties obtained from a tensile test, and explain how temperature affects the tensile properties of metals.

## Short answer

Tensile test yields Young’s modulus (stiffness), yield strength, UTS, ductility (% elongation, % area reduction), resilience (σ_y²/2E), and toughness (area under curve). As temperature rises, yield strength, UTS and modulus decrease, while ductility and toughness increase; BCC metals may undergo a ductile-to-brittle transition at low temperatures.

## Answer

#### Properties from the tensile test
- **Young's modulus $E$**: slope of the elastic line, a measure of stiffness.
- **Yield strength $\sigma_y$**: stress at which plastic deformation begins (0.2% offset if no clear yield).
- **Ultimate tensile strength**: maximum engineering stress, $P_{max}/A_0$.
- **Ductility**: percentage elongation and percentage reduction in area.
- **Resilience**: energy absorbed elastically, $U_r = \sigma_y^2/2E$ (area under the elastic part).
- **Toughness**: total energy absorbed per unit volume up to fracture (total area under the curve).
- **Poisson's ratio**: ratio of lateral to axial strain (about 0.3 for steel).

#### Effect of temperature
As temperature rises:
1. Yield strength, UTS and modulus **decrease**, because thermal energy helps dislocations to move.
2. Ductility (elongation, reduction in area) **increases**.
3. Toughness generally increases, and the yield point of mild steel becomes less sharp.

```text
 strength / ductility
  |\  strength
  | \_______
  |         \___
  |  ductility  /
  |      _____/
  +-------------------> temperature
```

At low temperature BCC metals (carbon steel) show a **ductile-to-brittle transition**: yield strength rises, but fracture becomes brittle. FCC metals (Cu, Al, austenitic steel) stay ductile. At high temperature, time-dependent deformation (**creep**) also appears under constant load.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is modulus of resilience?
   A. sigma_y^2 / 2E, elastic energy per volume
   B. Total area under the curve
   C. The slope of elastic line
   D. UTS times strain
   Answer: A. Resilience = area under the elastic part = sigma_y^2/2E. (Key point: Resilience)

2. What is toughness?
   A. Elastic energy only
   B. Yield strength
   C. Poisson's ratio
   D. Total energy per volume up to fracture
   Answer: D. Toughness is the total area under the stress-strain curve. (Key point: Toughness)

3. How does rising temperature affect tensile properties?
   A. Strength falls and ductility rises
   B. Strength and ductility both rise
   C. Strength rises and ductility falls
   D. No change
   Answer: A. Thermal energy helps dislocations move: lower strength, higher ductility. (Key point: Rising temperature)

4. What happens to BCC steels at low temperature?
   A. They stay ductile
   B. They creep
   C. Ductile-to-brittle transition
   D. Yield strength falls
   Answer: C. BCC metals become brittle at low temperature; FCC metals stay ductile. (Key point: Low temperature)

## Related in Material Science

- [Tensile test and stress-strain diagram](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Atensile-test-engineering-stress-strain) — Material Science, chapter 3
- [Tensile test data of a steel bar](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Atensile-test-numerical-steel-bar) — Material Science, chapter 3
- [Annealing of cold-worked metals](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aannealing-recovery-recrystallization-grain-growth) — Material Science, chapter 4

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