The Charpy impact test assesses a material’s response to sudden stresses by striking it with a pendulum. A standard size sample with a machined notch is used, and the test determines if the material is ductile or brittle and its yield point.
The Charpy impact test is a procedure used to determine the response of a material to sudden stresses. The test procedure is performed by striking a stationary sample of material with a pendulum using a measured amount of force. The sample material has a machined notch located directly behind the point of impact. This notch is needed to provide a stress concentration area for testing. The primary objective of a Charpy impact test is to determine whether a material is ductile or brittle.
A Charpy impact test is performed by placing a sample of indented material in the path of a swinging pendulum. The specimen is fixed at each end so that the pendulum’s path is in its center and is directly behind the indented area. The distance the pendulum travels before impact produces a measurable force. The results of this test are then used to determine the material’s ability to withstand sudden stresses. Charpy impact testing is usually a simple and inexpensive way to assess the suitability of a material in a particular application.
Sample materials used in a Charpy impact test must be of standard sizes to provide accurate results. In addition, a standard depth notch should be made in the sample just behind the exact point of impact. The pendulum can only strike the sample once during the procedure. If the pendulum fails to fracture the material during the test, the procedure is run again using a new material sample. The pendulum force is increased with each successive trial until a fracture occurs.
The Charpy impact test is mainly used to determine if a material is more ductile or brittle. If the sample material breaks along a plane during testing, it is considered more brittle. Samples that fracture in a jagged manner are considered more ductile. Most materials tend to break in a mixture of both ways. When this occurs, the fracture is analyzed to determine the percentage of ductile or brittle properties.
This test also determines the yield point. The yield point of a material is the point at which plastic deformation begins. A material usually undergoes elastic deformation before reaching its yield point. Elastic deformation allows the material to regain its original shape after the stresses are removed. Plastic deformation causes permanent damage to the material.
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