，要求不少于2500 The Test Method of Low Temperature Charpy Impact Test for Metals
Low-temperature Charpy impact test is a kind of mechanical test which is usually used to measure the impact properties of metals. It is a test method used to measure the energy absorbed by a metal during fracture under the action of impact force. This test has been applied to obtain the effect of deformation behaviour and post-yield energy absorption at low temperatures.
Low temperature Charpy impact test is an important parameter for the design for various applications, such as pressure vessels and other structural components that are intended for operation in below ambient temperatures.
The main purpose of this test is to measure the brittle fracture behaviour of metals due to the decrease in impact energy absorption capacity at refrigerated or below ambient temperatures. This test is mainly used to check cracking tendency in low temperature.
The test consist of a test specimen which is clamped in a pendulum. Then the pendulum is released and the impact energy is absorbed by specimen due to the dynamic load. The impact force (pendulum) is determined by measuring the released pendulum energy before and after impact.
The specimen size normally used in the low temperature Charpy impact test is dependent on materials specifications. For steels, the specimen size should conform to ASTM A370. The test temperature should be according to the standards specified.
The procedure and interpretation of the results obtained from this test are discussed in ASTM E23. Generally, the result of the test is the difference between the total impact energy and the impact energy at a given temperature. The result of the test depends upon the material and the test temperature. The result is expressed as the impact energy absorption, impact velocities and the nature of the fracture.
For assessing the impact properties at low temperatures, test temperature between -20°c to -50°c is commonly used and the specimen shall be conditioned, upon the standards specified. The test equipment is a pendulum, which swings at a given angle to hit the specimen and measure the energy absorbed by the specimen.
Ideally the low temperature Charpy impact test shall be performed in the laboratory equipped with a refrigerator, where the specimen will be cooled in a circulating bath and then tested in the pendulum.
The test results should conform to the requirements of the applicable standard. The range of valid test results is based on the material in question and the test temperature. Any specimen which departs outside this range shall be considered as invalid, and the test shall be repeated.
In conclusion, the low temperature Charpy impact test is a very useful tool for engineering design and material selection. It gives designers information about the brittleness of a material at low temperatures which can be used to determine if the material can stand up to the required load and service temperatures. The result is also a parameter to determine whether the material is safe enough to be used.
