Charpy Impact Steel Testing: Part One

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Introduction to Charpy Impact Testing

The Charpy V-notch impact test stands as a fundamental method in materials testing, providing critical data about material behavior under impact loading conditions. This standardized procedure measures the energy absorbed during material fracture, offering insights into material toughness and durability.

Test Methodology and Standards

The test follows specific international standards, primarily BS EN ISO 148-1:2009 (British Standard) and ASTM E23 (American Standard). These standards differ mainly in striker specifications but maintain consistent specimen dimensions: 55 mm length, 10 mm square cross-section, with a 2 mm deep notch featuring a 0.25 mm tip radius.

Figure 1: Standard Charpy-V notch specimen

Test Procedure and Equipment

The testing process involves mounting a standardized specimen on an anvil support system, with the notched face positioned away from the striking pendulum. The pendulum's impact fractures the specimen, and the final swing height indicates the energy absorbed during fracture.

Figure 2: The Charpy testing machine

Variables and Result Interpretation

Several factors influence test results, including:

• Specimen characteristics (notch geometry, grain structure, chemical composition)
• System parameters (machine calibration, friction)
• Environmental conditions (temperature control)
• Procedural aspects (operator technique)

Temperature Effects and Transition Behavior

A distinctive feature of carbon and low alloy steels is their temperature-dependent fracture behavior. When tested across various temperatures, these materials exhibit a characteristic 'S' curve showing the transition from ductile to brittle fracture.

Figure 3: Schematic Charpy-V energy and % age crystallinity curves