Local Energy Approach to Steel Fatigue

Abstract

This paper presents an experimental protocol developed to locally estimate different terms of the energy balance associated with the fatigue of DP600 steel. The method involves two quantitative imaging techniques. First, digital image correlation provides displacement fields and, after derivation, strain and strain-rate fields. A variational method, associated with an energy functional, is used to simultaneously identify elastic parameter and stress fields. The deformation energy rate distribution can then be determined on the basis of the stress and strain data. Secondly, infrared thermography provides thermal images which are used to separately estimate the thermoelastic source amplitude and mean dissipation per cycle distributions. The image processing uses a local form of the heat diffusion equation and a special set of approximation functions that take the frequency spectra of the sought sources into account.

Infrared thermography applied to the analysis of material behavior: a brief overview

“…Readers interested in the use of quantitative infrared imaging techniques applied to the analysis of fatigue mechanisms can refer to [31,32] where the IR image processing developed to process fatigue tests is detailed. Results of applications to steel and aluminum can be found in [33,34] and more recently in [32] where energy balance distributions were constructed using DIC and IRT techniques.…”

“…Results of applications to steel and aluminum can be found in [33,34] and more recently in [32] where energy balance distributions were constructed using DIC and IRT techniques. To briefly illustrate the potential of IR image analysis, Figure 7 shows the mean dissipation pattern per cycle The contour plots in Figure 7 also show that areas where the dissipation is high (respectively low) remain approximately the same from one block to another, even though the dissipation naturally increases with the stress range.…”

Determination of Local Thermophysical Properties and Heat of Transition from Thermal Fields Measurement During Drop Calorimetric Experiment

“…As explained in the first section, a 'reference' specimen is used to evaluate 218 heat losses functions in equations (9), (12), (15), (18 Figure 4 shows the DSC of the NiTi SMA selected for the study (section 237 3.5). This DSC was performed using a DSC TA Q200, with a 10…”

“…These estimations were used to study several mechanical coupled problems 22 such as Lüders bands and necking in steels [12,14], fatigue of materials 23 [15,16,17,18], plasticity in Al olygocrystal [19], thermomechanical behaviour 24 of NiTi Shape Memory Alloys (SMA) [13,20,21,22,23], etc.…”

“…Equation 18 and experimental data for the reference specimen is used 178 to estimate f (x, T ). At the temperature T = T s = T r and at the position 179 x = x s = x r , heat sources released by the 'studied' material are:…”