I recently performed Repeatability experiment (Tensile expeiment) on my material and I found lot of variation in the nature of tensile curves. I performed uniaxial tensile test at cross head speed of 1 mm/min in rolling direction (RD). Total 18 tests have been performed and many of the curves largely deviated from each other. I have added a picture for better understanding. I tried to find papers regarding room temperature tensile behaviour of 17-4 PH stainless steel but only high temperature tensile behaviour data were available. Can anyone recommend some papers regarding tensile test data at room temperature ??
The scatter inherent in ALL experimental trials, due to machine compliance, operator error/bia, sample to sample variation, the list goes on.
I suppose x-axis is engineering strain (%). I would ask what the scatter is in yield strength. There seem to be little variation there. If so, some aspects of processing history, such as any heat treatment, and chemical composition can be ruled out. The UTS seems to vary between 1200 and 1600 MPa. I would look into the work hardening characteristics between YS and UTS. The part of the curve after UTS is localize deformation in the neck so unless you measured the specimen dimensions in situ, you cannot extract much information from there. However, I would also look into the reduction in area, which will give a good indication about how much plastic strain the material could absorb before fracture. The largest scatter would be there.You can do Weibull statistics with that data to characterize it. The scatter would be due to inclusions and defects in the metal. I hope this helps.
perhaps the specimens slip in the holder from about 600 MPa, because from there the curves drift apart
Dear R. Saxena, really, the scatter of your data is seemed too large and I agree with Murat Tiryakioḡlu that reason is closely related with defects of specimen.
We have similar problem during tests of beryllium bronze foils when noticeable tear-out on the edge of the specimen in form of double-sided trowel was reproduced owing to the little hangnail on blank die. After deleting of this defect by manual grinding of specimen edge we obtain good repeatability of tension strength and the rupture strain has increased essentially.
So, the tension strength and strain parameters of such enough hard materials as stainless steel and beryllium bronze are sensible to quality of specimen.
Because of high tensile strain, it shows its super natural variation. For surviving in nature ,it has to go down because it is required to survive.Otherwise the variation will be in infinite inertial state without not appropriate outcome.
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