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Dynamic Mechanical Analysis part 11

Tham khảo tài liệu 'dynamic mechanical analysis part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Another point of this test is that any mechanical or environmental noise in the vicinity will be seen in the test. This allows US to find and remove sources of error thathave nothing to do with the test. A lot of the oddities in data are caused by environmental effects including mechanical vibration impure gases poorly controlled gas rates improper cooling or noisy power. All of these sources of error must be eliminated before a test can be considered valid. As mentioned above creep-recovery testing is also done to see how time affects tOe polymer. This is done to determine the linear region for creep-recovery curves and to measure relaxation times. One first applies creep stresses to the sample in mcreasmg amounts and plots this as compliance J versus time. In the linear region J becomes independent of the stress so the curves overlay. A fast way to check this ia to start at a very low stress and increase it by doubling the stress for each run. When the strain stops doubling we are out of the linear region. 8.9 CHECKING THE TEMPERATURE RESPONSE Using the information from above we now check the response of the material to temperature by running a temperature scan. One normally scans the widest range pvsiiaie within instrumental limits. The end of the linear region from the static test-strain curve tells US the maximum total force and the maximum from the dynamic stress-strain run tells US the maximum dynamic force. Then we pick a dynamic force strong enough Io give US a strain between 2-12 pm. If we are running a tolid sample we adjust the static or clamping force to keep the specimen in good epataot with the probe. For a hard glassy sample this is normally 110 of the dynamic force. As the sample becomes soft and more rubbery this increases as eeaessary. For fluid samples in a torsional rheometer we set the gap to where the aample is able to keep a smooth edge. Obviously for some geometries such as the eone-and-plate the fixture is designed to run at a fixed gap. .