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To receive exact results when performing a tensile test at first you need a perfect prepared tensile specimen. This specimen has to meet the standard (ASTM, GHOST, EN, ISO, DIN, AFNOR, BS, JIS …) as well as the mechanical requirements. If the specimen has a bad quality the results of your test are wrong and not reliable. What for you invest in a HQ tensile test machine when your specimens do not allow correct results?
Tensile specimens those do not have a perfect edge / flank never will give you the high elongation the material is able to do. Often you loose 1/8 – 1/3 of the possible total elongation
At a tensile specimen that is blanked only (sheet metal tensile specimens from 0,05 – 8.0 mm thickness; imperial thickness 0.002 - 0.3 inch) the results of elongation, yield point, Rp0.2, Rto.5 are mostly wrong and total elongation is missing.
Even at weak material the edges will be deformed by deep drawing effect (see the side of matrix. If you don’t remove this damage of the edge your results of Rp0.2 / Rt 0.5 / yield point will be higher (up to 20 %) because this cold deforming process at blanking will effect a cold hardening effect into the edges and material.
Additional this cold hardened zone will content micro cracks and this will finally bring the effect that this cracks will be the initial marks of rupture. This will influence the total elongation up to 1/8 – 1/3.
With each coil you process wrong (and wasting) you loose money for the investment for a HQ specimen preparation system.
And also every national and international standard say: A cold hardened edge / damaged edge from punching / blanking has to be removed…
… not to influence the mechanic / technologic results of the performed tensile tests.
But at least:
This biggest problem is to loose a customer because of wrong quality … | |
