Issue 38

M. Lutovinov et alii, Frattura ed Integrità Strutturale, 38 (2016) 237-243; DOI: 10.3221/IGF-ESIS.38.32 241 Figure 2: Results of estimations carried out on the bar specimen loaded non-proportionally with subsequent tension and torsion [6]. Estimations were performed with the use of 6-linear approximation of cyclic stress–strain curve. Using the Ramberg–Osgood material model The predictions using the Ramberg–Osgood material model led to worse estimation quality in general. In case of stresses, all estimates are shifted to the conservative region, while strains are shifted to the non-conservative region. The estimate of the shear stress component by Buczynski’s method with the ESED rule changed more than all other predictions and led to a distinctly non-conservative result. C ONCLUSIONS  Quality of estimates of all methods is substantially dependent on used inputs. Therefore, further investigation is needed in order to determine the extent of this dependence. For the same reason, it is also desirable to apply the methods to other types of specimens and to experimental data. Proportional loading  For calculating maximum principal stresses and strains, Hoffmann–Seeger’s method should be used as the upper limit. As the lower limit, Moftakhar’s method with the ESED rule is the best option from those considered.  For calculating middle and minimum principal stress and strain components, both Moftakhar’s estimations can be successfully used as the lower and the upper limit. Non-proportional loading  Due to the high dependence of the estimates according to Buczynski’s method on settings of the solver function and based on the observation that predictions according to the Buczynski’s method and Singh’s method are very similar, it is proposed to use Singh’s method.