Experimental determination of critical strain energy density of ductile materials
Date
2019-03-20
Journal Title
Journal ISSN
Volume Title
Publisher
Видавництво Львівської політехніки
Lviv Politechnic Publishing House
Lviv Politechnic Publishing House
Abstract
The method of experimental determination of strain energy density of plastic
materials is developed. The technique for complete true stress-strain curves plotting is formulated.
The standard hydraulic testing machine is equipped with specially designed experimental setup for
Bridgman specimens testing at strain controlled tension loading with digital camera and light source
for using digital image correlation method – a non-contact technique for strain and displacement
measurement. The digital image correlation method was used to determine the local strain at the onset
of fracture in the neck of Bridgman specimen. The technique takes into account the change of crosssection area in the neck of specimen due to internal crack propagation when calculating the true
stresses. The complete true stressstress-curve of 40Kh alloyed steel is plotted end criticalstrain energy
density of steel is determined from it. It is shown that the critical strain energy density of material,
determined from the curve obtained by developed technique is 1.8 times higher than determined from
the classical true stress-strain curve and is close to the value of the specific heat of fusion of steel. The
curves built using the proposed technique can be used for setting material properties in stress-strain
state calculations by finite element method at large scale yielding conditions, for instance at pressure
vessels critical pressure calculation. The critical strain energy density value can be considered as a
material property at fatigue life-time calculation using energy approach.
Description
Keywords
strain energy density, stress-strain curve, true stress, true strain, Bridgman specimen, digital image correlation, strain-controlled loading, alloyed steel
Citation
Experimental determination of critical strain energy density of ductile materials / Yuriy Molkov, Yaroslav Ivanyts’kyi, Taras Lenkovs’kyi, Andriy Trostianchyn, Volodymyr Kulyk, Roman Shyshkovskyy // Ukrainian Journal of Mechanical Engineering and Materials Science. — Lviv : Lviv Politechnic Publishing House, 2019. — Vol 5. — No 1. — P. 39–44.