Izod Impact Test: Working Principle, Testing Procedure & Specific Applications

1. Working Principle of Izod Impact Test

The Izod Impact Test is used to measure a material’s impact strength (toughness) under sudden loading conditions. It determines the energy absorbed by a notched specimen when struck by a pendulum hammer. This test is widely used for plastics, metals, and composites to evaluate their resistance to impact forces.

Key Aspects of the Principle:

• A notched specimen is held vertically in a clamping vise.

• A pendulum hammer is released from a fixed height and strikes the specimen above the notch.

• The energy absorbed in breaking the specimen is recorded.

• Higher absorbed energy indicates a ductile material, while lower absorbed energy suggests brittleness.

• The test can be conducted at different temperatures to study the ductile-to-brittle transition behavior of materials.

2. Testing Procedure for Izod Impact Test

Step 1: Specimen Preparation

• The test specimen is typically 75 mm × 10 mm × 10 mm as per ASTM D256 (for plastics) or ASTM E23 (for metals).

• A V-notch (45° angle, 2 mm depth) or U-notch is machined into the specimen.

• The notch is designed to create a stress concentration point to promote fracture.

Step 2: Mounting the Specimen

• The specimen is clamped vertically in the Izod testing machine.

• The notch faces toward the pendulum hammer to ensure maximum stress concentration.

Step 3: Releasing the Pendulum Hammer

• The hammer is raised to a fixed height, storing potential energy.

• It is released, striking the specimen above the notch with a controlled force.

• The impact fractures the specimen, and the pendulum swings forward with reduced energy.

Step 4: Measuring Absorbed Energy

• The difference between the initial and final height of the pendulum is used to calculate the absorbed impact energy (Joules or ft-lbf).

• A higher energy value means a more ductile material, while a lower energy value indicates brittleness.

Step 5: Analyzing Fracture Surface

• The fracture surface is inspected:

  • Ductile fracture → Rough surface, significant deformation.

  • Brittle fracture → Clean break, minimal deformation.

• If tested at different temperatures, a ductile-to-brittle transition curve can be plotted.

3. Specific Applications of Izod Impact Test

(A) Plastics and Polymers Industry

• Evaluates the impact resistance of plastic components in consumer products, pipes, and casings.

• Ensures plastics used in electrical enclosures and automotive parts can withstand shocks.

(B) Automotive Industry

• Tests bumpers, dashboards, and structural components for crash resistance.

• Helps select materials that absorb impact energy without failing.

(C) Aerospace Industry

• Determines the impact resistance of aircraft panels, turbine blades, and interior parts.

• Ensures materials can withstand high-speed impacts.

(D) Construction and Structural Materials

• Used to test metals and composites for building frames, bridges, and pipelines.

• Ensures materials maintain toughness at low temperatures.

(E) Sports and Safety Equipment

• Evaluates helmets, protective gear, and composite sports equipment for impact strength.

• Ensures safety standards are met for sports and industrial applications.

(F) Medical Industry

• Tests prosthetic limbs, surgical tools, and biomedical implants for impact durability.