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snowJT
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Is the only difference between these two impact tests how the specimen is held in position for the test? Charpy holds it like a simply supported beam, and Izod does it as if it was a cantilever?
This statement would indicate more resistance to fracture using the Izod test.HOWEVER, the numbers from those two test methods are not comparable. There is no accepted method of comparing CVN and IZOD numbers, but it is commonly known that the IZOD test produces higher numbers than a CVN test on an identical material sample, ie, CVN is more conservative.
Astronuc said:...
The issue we've had with tests of fracture toughness is how close the stress field in the test matches the stress field for in-service loading.
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The Charpy and Izod impact tests are both used to measure the impact strength of a material. The main difference between the two tests is the shape of the specimen and the type of impact. The Charpy test uses a notched square or V-shaped specimen and a pendulum impact, while the Izod test uses a notched bar specimen and a horizontal impact.
The Charpy test is more commonly used in industry due to its simplicity and the fact that it can be used to test a wide range of materials. However, the Izod test is still used in some specific applications, such as testing thin or brittle materials.
The Charpy test is able to generate higher impact energies, making it more suitable for testing materials that require higher impact energies. It also provides a more accurate measurement of the energy absorbed by the material, as the pendulum impact is less affected by friction and other external factors compared to the horizontal impact used in the Izod test.
The results of both tests are expressed in terms of the energy absorbed by the material during the impact. A higher energy absorption indicates a higher impact strength of the material. The results can also be used to compare the impact resistance of different materials or to determine the effects of temperature or other environmental factors on the material's impact strength.
Yes, there are limitations to both tests. The Charpy test may not be suitable for very soft or brittle materials, while the Izod test may not accurately measure the impact strength of materials with high ductility. Both tests also only provide a single data point and do not take into account the behavior of the material under repeated impacts or other types of loading.