Ability to interpret raw data separates those who understand what they did to those who just blindly accept results given by the machine. It a skill that require meticulousness and resourcefulness.
If this is really raw data, then while calculating the Young's Modulus, why has the deformation of the machine which will also be incorporated in the obtained displacement data removed before calculation?
Because we only test low modulus sample (A4 paper), the machine itself does not deform. At atomic level, the metal jaw does experience some deformation during pulling, but for practical purpose we can safely ignore it) So the machine do not deform, but the jaw is indeed move away (displace) when testing. in this experiment, part of original displacement data can be safely deleted because its does not represent the displacement that occur during positive force. Positive force here is a pulling force that experienced by the specimen when the specimen is stretched. the A4 paper sample is thin. and the tensile machine that we use rely on pneumatic grip. The pneumatic valve is connected to top jaw and also bottom jaw of tensile machine. The compressed air (which create a pneumatic grip) can be applied only one after the another , but not simultaneously. Depending on which jaw we first supply with compressed air, it can grip with some positive force ( the paper streched) or negative force ( the paper kinked). we test with the paper kinked at the initial position. (refer timestamp 2:07). so the paper only start streched when the force start increasing from 0N upward. whatever displacement that occur prior to stretching can be safely removed as the concept of stress-strain curve is to relate the strain (originated from dusplacement) with the stress ( tension experienced by the specimen).
