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| Kováčová A., Kvačkaj T.,Kvačkaj M., Donič T., Martikán M., Besterci M. |
| STRESS-STRAIN CURVES PROGRESS ANALYSE OF UFG Cu DURING DYNAMIC LOADING AND ITS FRACTURE AREAS INVESTIGATION |
Abstract
In the present paper behavior of ultrafine-grained (UFG) oxygen free high purity (OFHP) copper prepared by severe plastic deformation (SPD) methods was investigated during dynamic loading. The initial Cu after zonal purification was subjected by 5 passes of equal-channel angular pressing (ECAP) via C route at room temperature. The 5 ECAP passes are sufficient by reason of mechanical properties stable state achievement and grain size below 1 ?m obtention. The dynamic tensile tests were conducted by high speed tensile machine at room temperature. The material characteristics of UFG Cu during tensile tests were investigated by various circumferential speeds namely 2.0, 2.5, 3.0, 4.0 m/s. Results, which were achieved during dynamic tests measuring clearly show atypical loading-elongation curves progress. The curves investigation and following available literature [1,2] it’s clear, that dynamic upper yield stress ReH,d, dynamic lower yield stress ReL,d (dynamic tensile properties) exist in dynamic loading UFG Cu and also oscillations were found in samples. The rapid yield stress Re increase and their rapid decrease it’s named in literature “peak”. The “peak” presents plastic deformation progress process [1]. The ReH,d, ReL,d investigations in different deformation rates suppose their increase with deformation rate increasing. The deformed area observations of dynamically fractured surface show a typical ductile fracture mode in every circumferential speed regime. The dimple size measurements indicate decrease of dimple size with circumferential speed increasing. The dimple size was determined based on 200 measuring file for every regime. Following dynamic tests reduction of area shows its increase with dimple size increasing.
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| Keywords: ECAP|UFG copper|dynamic tensile tests|dynamic tensile properties|fracture analyse| |
| No 2 (2009), p. 100-104 |
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