Abstract
Ti-6Al-4V has been extensively used in structural applications in various engineering fields, from naval to automotive and from aerospace to biomedical. Structural applications are characterized by geometrical discontinuities such as notches, which are widely known to harmfully affect their tensile strength. In recent years, many attempts have been done to define solid criteria with which to reliably predict the tensile strength of materials. Among these criteria, two local approaches are worth mentioning due to the accuracy of their predictions, i.e., the strain energy density (SED) approach and the theory of critical distance (TCD) method. In this manuscript, the robustness of these two methods in predicting the tensile behavior of notched Ti-6Al-4V specimens has been compared. To this aim, two very dissimilar notch geometries have been tested, i.e., semi-circular and blunt V-notch with a notch root radius equal to 1 mm, and the experimental results have been compared with those predicted by the two models. The experimental values have been estimated with low discrepancies by either the SED approach and the TCD method, but the former results in better predictions. The deviations for the SED are in fact lower than 1.3%, while the TCD provides predictions with errors almost up to 8.5%. Finally, the weaknesses and the strengths of the two models have been reported.
Highlights
The results obtained from the tensile tests have been analysed both in terms of strain energy density (SED) and theory of critical distance (TCD) to assess the reliability of the methods as an engineering tool for predicting the tensile behaviour of notched Ti-6Al-4V
The tensile strength of semi-circular and blunt V-notched Ti-6Al-4V components have been predicted using two of the most affirmed criteria available in literature, i.e., the strain energy density approach and the line method. Both the methods provide predictions that are in good agreement with the experimental results, but the SED approach provides predictions with lower discrepancies
The discrepancies on the tensile strength using the SED are lower than 1.3%, whereas with the TCD method the error for the semi-circular notched specimens is far higher, i.e., almost 8.5%
Summary
The adoption of Ti-6Al-4V alloy is widespread in advanced engineering fields, such as military, aerospace, automotive, and naval applications, due to its very good static and fatigue properties, high strength-to-mass ratio, and excellent wear resistance, including at high temperatures [1,2].Ti readily forms a titanium dioxide (TiO2 ) outer layer that assures its passivity in an oxidizing environment, determining a high corrosion resistance and guaranteeing a great reliability ofTi-6Al-4V in applications in which corrosion is one of the main issues, such as biomedical devices [3].In all these applications, geometrical discontinuities (notches) negatively affect the fracture and fatigue strength [4,5,6,7]. Approach, failure of aparameters componenttoisbe governed by a local parameter approach has been extensively used in the assessment of the tensile and fatigue behavior of different as the total strain energy density; when its value, averaged over a circular control volume of critical materials weakened by several notch geometries [31,40,41], and the results reported excellent radius Rc ahead of a crack or a notch tip, reaches the critical value Wc , the failure occurs [17]. [17], critical parameters can be Lazzarin [4] reported these critical parameters to be only material-dependent This approach has been analytically obtained with only few material properties: the ultimate tensile strength of the extensively used in the assessment the tensile and fatigue behavior of different materials un-notched material σUTS, the offracture toughness
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