Charpy Impact Test: Working Principle, Testing Procedure & Applications

1. Working Principle of Charpy Impact Test

The Charpy Impact Test is used to determine the toughness and impact resistance of a material by measuring the energy absorbed during fracture. It helps classify materials as brittle or ductile and is widely used in quality control and material selection.

Key Aspects of the Principle:

• A notched specimen is placed horizontally on two supports.

• A pendulum hammer is released from a fixed height to strike the specimen at its center.

• The energy absorbed in breaking the specimen is measured by the difference in the pendulum's height before and after impact.

• Higher absorbed energy indicates ductile behavior, while lower energy suggests brittle fracture.

• The test is often conducted at different temperatures to determine the ductile-to-brittle transition temperature (DBTT).

2. Testing Procedure for Charpy Impact Test

Step 1: Specimen Preparation

• The specimen is rectangular with a standard size (e.g., 55 mm × 10 mm × 10 mm as per ASTM E23 or ISO 148 standards).

• A V-notch (45° angle, 2 mm depth) or U-notch is machined at the center to concentrate stress and promote fracture.

• The material and notch type are selected based on the application.

Step 2: Mounting the Specimen

• The specimen is placed horizontally on the Charpy test machine’s supports.

• The notch faces away from the hammer (to maximize stress concentration).

Step 3: Releasing the Pendulum Hammer

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

• It is released, striking the specimen at its center with a controlled force.

• The specimen fractures, absorbing some of the hammer’s kinetic energy.

Step 4: Measuring Absorbed Energy

• The hammer swings to a reduced height after breaking the specimen.

• The difference in initial and final height is used to calculate the absorbed impact energy (in Joules).

• A higher energy value indicates a tougher material, while a lower value suggests brittleness.

Step 5: Analyzing Fracture Surface

• The fracture surface is examined:

  • Ductile fracture → Rough surface, large plastic deformation.

  • Brittle fracture → Clean, flat surface with minimal deformation.

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

3. Specific Applications of Charpy Impact Test

(A) Structural and Construction Industry

• Evaluates the toughness of steel beams, bridge materials, and pressure vessels.

• Helps in selecting materials that can withstand extreme weather conditions.

(B) Automotive and Transportation

• Used in testing car body panels, chassis, and bumpers for crash resistance.

• Ensures train and railway track materials can handle dynamic impact loads.

(C) Aerospace Industry

• Determines impact resistance of aircraft fuselage and turbine blades.

• Ensures safety and reliability in high-speed environments.

(D) Oil & Gas Industry

• Tests pipeline materials and pressure vessels for fracture resistance.

• Ensures materials used in low-temperature environments do not become brittle.

(E) Nuclear Industry

• Evaluates reactor vessel materials that must withstand radiation and temperature changes.

• Prevents catastrophic failure in nuclear power plants.

(F) Defense and Ballistics

• Assesses armor plates, helmets, and military-grade materials for shock resistance.