Impact tests are used to determine the toughness of materials, i.e., the ability of a material to absorb energy during sudden or shock loading.

The Izod impact test measures the energy absorbed by a material during fracture when it is subjected to a sudden blow by a pendulum hammer.

This test is commonly used to evaluate the impact strength of metals and plastics.

Definition

Izod Impact Test

A test used to determine the impact strength of a material by measuring the energy absorbed when a notched specimen is broken by a pendulum hammer.

Impact Strength

The amount of energy absorbed by a material before fracture under sudden loading.

Core Concept Explanation

In the Izod test:

1. A notched specimen is prepared.

2. The specimen is clamped vertically in a vice.

3. A pendulum hammer is raised to a known height.

4. The hammer is released to strike the specimen.

5. The specimen fractures due to the sudden impact.

6. The energy absorbed during fracture is measured from the pendulum swing.

Higher energy absorption indicates higher toughness.

Test Arrangement

Key components of the Izod impact testing machine:

• Pendulum hammer

• Specimen holder

• Notched specimen

• Energy measuring dial

Specimen Details

Typical Izod specimen features:

The notch acts as a stress concentration point, helping initiate fracture.

Working Principle

The pendulum hammer has potential energy when raised to a height.

$$PE = mgh$$

When the hammer strikes the specimen:

• Some energy is used to break the specimen

• Remaining energy moves the hammer upward

The difference in energy gives the impact energy absorbed by the specimen.

Characteristics of Izod Test

• Specimen is held vertically

• Notch faces towards the hammer

• Measures energy absorbed during fracture

• Used mainly for metals and plastics

Applications in Engineering

Izod test is used for:

• Determining toughness of materials

• Quality control of metals

• Testing plastics and polymers

• Evaluating brittle fracture behavior

It is widely used in material testing laboratories and manufacturing industries.

Exam-Focused Points

Important for JE/AE mechanical exams:

• Specimen position → Vertical

• Notch direction → Facing hammer

• Impact load applied by → Pendulum hammer

• Property measured → Impact strength / toughness

Common Exam Traps

Confusion

Students often confuse the specimen position in Izod and Charpy tests.

Correct concept:

• Izod → Vertical specimen

• Charpy → Horizontal specimen

Example Competitive Exam Questions

Question: In the Izod impact test, how is the specimen positioned?
Answer: Vertically.

Question: What property is measured in the Izod test?
Answer: Impact strength (toughness).

Question: What type of notch is used in the Izod test specimen?
Answer: V-notch.

Quick Revision Summary

• Izod test measures impact strength of materials.

• Specimen is mounted vertically.

• Notch faces the hammer.

• Uses pendulum hammer to fracture specimen.

• Measures energy absorbed during fracture.