RMZ – MATERIALI IN GEOOKOLJE

Calculation of stress-strain dependence from tensile tests at high temperatures using ...345curves, as by definition flow curvesare stress-strain curves at a constantstrain rate.2. In the present work two functionsfor description of evolution of thepart of the contour which is in givenmoment in the plastic state, weretested, i.e. constant (approximationwith cylinder) and catenary. Basedon the comparison of the predictedevolution of contour and contoursobtained by measurements withfilm camera it was found that bothfunctions are capable of descriptionof evolution of minimal radiusof the rod in the neck with accuracywithin the measurement error.3. The main problem of applying thesimplest function, i.e. the constant,is that it is not possible to determinethe evolution of radius of curvatureof the couture at the minimalcross-section and consequentlyBridgman stress correction due tothree-axiality of the stress cannotbe applied since for constant thiscurvature is infinite. On the otherhand using catenary this problem isavoided and true stress – true straincurves including Bridgman correctioncan be determined.4. It could be possible to predeterminethe movements of jaws during thetests in such a way that constant truestrain rate would be maintained duringthe entire test or at least up tothe true strains up to the value of 1.0,but this will require many more testsfor different materials and at differentthermo-mechanical conditions.References[1]Bridgman, P. W. (1952): Studies inLarge Plastic Flow and Fracture,McGraw-Hill, NY.[2]Press, W. H. et. al. (1988): Numericalrecipes in C, Cambridge UnivrsityPress, Cambridge.[3]Kugler, G. (2004): Prediction of hotworkability of metals by use ofcellularautomata, Univrsity of Ljubljana,NTF, Ljubljana.[4]Turk, R. (1982):Postavitev modela zaoceno tople preoblikovalnosti kovin,Univerza v Ljubljani, FNT, Ljubljana.RMZ-M&G 2012, 59