To ensure that manufactured cartridges is safe to use, a tensile test is performed. The frictional force between the bullet and the case is required according to Normas standard to be between 15 – 75 Kg. Variations of the frictional force, with values outside of the standard had been noted by Norma Precision without understanding the cause. The aim of this report was to investigate and evaluate possible causes of the variations measured by tensile tests, difference between extreme values and to find a solution to what can be done to prevent the variations. Two different cases and three different bullets were used by request from Norma in the scope of this report. Different combinations of the bullets and cases was tested by alternating process parameter, surfaces and loading procedures. The loaded cartridges went through tensile tests to investigate differences. Bullets and cases with extreme values from the measured frictional force were chosen for further investigation in SEM and profilometer. To be able to draw further conclusions four different simulation models was created in Abaqus and different parameters was calculated. The dimensions and shape of the bullet resulted as the cause of changes of the tensile test curves. The smallest frictional force was found to differ from the largest by a change in wear mechanism from mainly abrasive ploughing to cutting and adhesion that caused transfer of material from the bullet to the case. The change in wear mechanism was found to be caused by an increased bullet diameter. The loading procedure was found to cause variations in plastic deformation on the neck of the case and damage the bottom of the bullet. The loading procedure was assumed to have the largest impact on the variations in frictional force. To minimize the variations the central axis of the case was suggested to be in line with the central axis of the bullet.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kau-68653 |
| Date | January 2018 |
| Creators | Hahlin, Mattias |
| Publisher | Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013) |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf, application/pdf |
| Rights | info:eu-repo/semantics/openAccess, info:eu-repo/semantics/openAccess |
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