Determination of Fatigue Limit by Mono-Axial Tensile Specimens Using Thermal Analysis

Abstract

In this work is indicated how it could be possible to evaluate the limit stress of the thermo-elastic phase of deformation by thermo-analysing the surface of the specimen during a static traction test. Adding the temperature curve measured on a small area of the surface (the hottest) to the classic stress-strain curve, it is possible to evaluate a limit temperature T0 coincident with the beginning of the non linear trend of the curve. The corresponding stress value is coincident with the fatigue limit of the analyzed component. As an example, the results of traction tests performed on two notched specimens, where the change of linearity in the temperature curve during static traction test was evident, are reported.

Fatigue characterization of mechanical components in service

“…The Tab. 5 and 6 resume the results obtained during the static tests in agreement with [15][16][17][18][19]. In the tables with the caption "material without damage" it has been identified the resistance values provided by the tie rods building firm.…”

“…In the tables with the caption "material without damage" it has been identified the resistance values provided by the tie rods building firm. Specimen 2 of an old tie rod 420 Table 6: Results using the [15][16][17][18][19] theory.…”

“…During the last years, according to Risitano and his school experiments, different authors [6][7][8][9][10][11][12][13] have applied and confirmed the validity of this methodology, extending it to other materials different from the steels and for which this methodology was born. Risitano and the members of his staff have applied the methodology to mechanical components characterizing the fatigue of the components themselves [14], to verify the possibility of estimating a material's fatigue limit by studying the surface temperature evolution of a specimen loaded with a static axial force [15][16][17][18][19] and to propose a new linear damage model [20][21][22][23]. For years and according with the endless application of this methodology, the temperature has been adopted as a damage or a change index of the characteristics of the material.…”

Definition of the linearity loss of the surface temperature in static tensile tests

“…Since the first analyses of this type which date back to 1987, it has been noted that, using this approach, it was possible to determine the region (stress-strain) in which the material follows the laws of the Thermoelasticity [38,39]. The Thermal analysis applied to various steels during the static tensile test [29][30][31][32][33][34], showed that it was possible to define the "fatigue limit" by analyzing the temperature of the hottest point of the specimen surface and determining the point where the slope changes, in the temperature vs. stress curve. On the basis of the first results, other researchers [35,36] tested the procedure on other materials, different from the steels (composite materials).…”

Fatigue assessment by energy approach during tensile tests on AISI 304 steel

“…And in [15] have investigated experimentally on thermal and calorimetric effects induced by Luders band propagation during monotonic and quasi-static tensile tests. In previous papers, authors investigated the variation of temperature during static tensile tests of plastic [16] and metallic [17] materials to connect the variation of the slope of the stress strain versus temperature curve with the conventional fatigue limit of the material. In [18], authors suggested that during quasi-static tensile tests the area, where first irreversible plasticization occurred, is detectable on T vs curve by the variation of temperature (slope).…”