Plastic impact properties refer to the ability of a polymer material to exhibit toughness or resistance to breakage under high-speed impact. Simply supported beam impact is an important means of testing the impact properties of materials. The important factors affecting the charpy impact test are as follows:
Since the sample is elastically deformed during the impact process, the elastic deformation accumulation is released when the sample is destroyed, so the energy of the pendulum impact on the sample is always greater than the energy required for the sample to break, so after the fracture The sample will fly out. The values read on the dial of the pendulum impact tester include not only the cracks in the sample, the expansion and cracking energy of the crack in the sample, but also the energy that flies out after the sample is broken. Gong. The flying work has nothing to do with the toughness of the sample, but it sometimes accounts for a large proportion, especially for brittle materials that absorb less energy.
When using the same formulation and plastic samples with different thicknesses of the same molding conditions for the impact test, the test results of the samples of different thicknesses on the same span and different spans and the impact of the specimens of the same thickness but on different spans can be found. As a result of the test, the obtained impact strength could not be compared and converted. The greater the thickness of the same sample, the higher the impact strength value; and at the same sample thickness, the greater the test span, the higher the impact strength value.
Generally, the impact velocity of the impact tester pendulum is 3 m/s to 5 m/s. In the impact test, the impact velocity value decreases as the impact velocity increases; the thermoplastic is more remarkable.
The impact strength decreases as the temperature decreases. This is because as the temperature decreases, the material changes from a tough state to a brittle state. This transformation occurs in a narrow temperature range, and the sample exhibits brittle fracture below the brittle temperature, and the impact strength is low; The toughness fracture higher than the brittle temperature has higher impact strength, so the influence of the test temperature on the test results in the impact test cannot be ignored. Generally, the test methods stipulate that the impact test should be carried out at a standard ambient temperature. When the temperature rises, the polymer chains and segments are easy to move, the polymer gradually changes from hard and brittle to soft and tough, and the impact strength and elongation at break increase, especially when the embrittlement temperature of the polymer is near. The change is more significant.
The correct installation of the test machine directly affects its accuracy. The offset or looseness of the installation position of the charpy impact device and the horizontal placement will have a great impact on the test results.
Through the above analysis, it can be found that there are many factors affecting the charpy impact test results. Therefore, in the actual testing work, some controllable factors should be excluded from the test. Control the temperature and humidity of the laboratory before the test, check the condition of the instrument, whether the level of the pedestal is in place, determine the size of the sample and the experimental method in strict accordance with the standard. Use the standard recommended machining method to process the sample gap, reduce the above factors. The impact of the results and improve the comparability of the test results.
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