Introduction to the Charpy V-Type Impact Test
Date:2025-08-12
I. Core Purpose of the Test
The core purpose of the Charpy V-Type impact test is to determine:
Notch Toughness/Impact Toughness: The ability of a material to withstand rapid impact loads without fracture in the presence of a sharp notch (a source of stress concentration). Materials with high toughness absorb more energy before breaking.
Ductile-Brittle Transition Temperature: For many materials (particularly metals with a body-centered cubic structure such as mild steel), their toughness decreases dramatically with decreasing temperature, transitioning from ductile to brittle fracture. CVN testing, by testing at different temperatures, can characterize the material's ductile-brittle transition curve and determine its transition temperature range. This is crucial for evaluating a material's suitability for low-temperature environments (such as those in extremely cold regions and cryogenic engineering).
Material Quality and Consistency: The effects of different batches of material, different heat treatment conditions, or different manufacturing processes on material toughness can be quickly compared.
II. Test Principle and Procedure
The test is based on a relatively simple but well-defined principle: measuring the energy required for a pendulum to break a specimen with a standard V-notch.
Specimen Preparation:
A standard rectangular specimen (typically 55mm x 10mm x 10mm) is used.
A V-shaped notch of specific dimensions is machined in the middle of one of the specimen's longitudinal faces. This is a key feature of the test:
Notch Angle: Typically 45°.
Notch Depth: Typically 2mm.
Notch Root Radius: Very small (typically 0.25mm) to ensure a sharp stress concentration. This sharp V-notch simulates a potential crack, defect, or stress concentration area in the material, making the test extremely sensitive to the material's embrittlement potential.
Testing Equipment:
Pendulum Impact Tester: The core equipment. It consists of a pendulum that rotates about a fixed axis and is initially raised to a predetermined height (with a defined potential energy).
Specimen Support: Two supporting anvils used to position the specimen horizontally (with the notch facing away from the pendulum's impact direction).
Energy Indicator: A dial or digital display indicates the height to which the pendulum rises after breaking the specimen, allowing calculation of the impact energy consumed to break the specimen.
Test Procedure:
Precisely place the specimen on the two supporting anvils of the testing machine, ensuring that the notch is centered between the anvils and facing away from the pendulum.
Release the pendulum, raised to the predetermined height.
The pendulum falls freely, striking the specimen directly opposite the notch at its lowest point.
The specimen breaks under the impact load.
The pendulum continues to swing upward, but reaches a height lower than the initial release height.
The testing machine measures and records the angle or height difference of the pendulum's rise after breaking the specimen.
Calculating Absorbed Impact Energy: The energy absorbed by the specimen at break is calculated from the difference between the initial potential energy of the pendulum and the residual potential energy after breaking the specimen. This energy is known as the Charpy V-Notch Impact Energy (usually represented by the symbols KV, CVN, or Akv, and expressed in joules). This energy value is a key indicator of a material's notch toughness.
