Rapid estimation of fatigue limit for C45 steel by thermography and digital image correlation

Abstract

Combining thermography and Digital Image Correlation (DIC) measurements, this paper aims to experimentally capture the fatigue damage phenomenon in steels, with a methodology allowing to rapidly estimate the fatigue limit. Surface temperatures and displacement fields are collected during fatigue tests performed with blocks of progressively increased stress amplitude, at different stress ratios. Results show that both thermography and DIC-based parameters have bilinear trends as a function of the stress amplitude. These changes in the thermal and mechanical behaviours, highly sensitive to the selected stress ratio, are related to damage initiation due to microplasticity and give a precise and rapid estimation of the fatigue limit.

On the correlation of temperature harmonic content with energy dissipation in C45 steel samples under fatigue loading

“…It is also observed that T o is not subject to steep increases, at least of the order of magnitude reported in other works [2,4,18], where the same material is tested. The absence of an abrupt increase of the curve is likely to be attributed to the lower loading frequencies of the higher stress amplitudes applied in this work (see tables 3, 4).…”

“…This is confirmed by the stabilised hysteresis loops acquired at different σ a and shown in Fig. 17, which also show a significantly smaller area and exhibit a marked ratcheting [2]. The average value of Φ E over the ROI is first considered and subtracted to the phase of the load FH signal (see also eq (15).…”

“…Amplitude of the load signal harmonics at the angular frequencies ω and 2ω R Amplitude of the harmonic of temperature at the angular fre- process. Traditional experimental characterization schemes to investigate the fatigue behavior require significant time and resources [1,2] and may act as a bottleneck in the continuous quest for better performing structural materials.…”

“…It is therefore useful to propose temperature metrics related with temperature changes at specific loading frequencies. A number of works, including the present one, have then propsed to investigate the influence of the heat sources on the temperature modulation by means of frequency domain signal processing strategies [2,6,7,9,10,16,18,[20][21][22][23][24][25][26][31][32][33].…”

Ratcheting assessment of corroded elbow pipes subjected to internal pressure and cyclic bending moment

“…Ratcheting: In this stage, some plastic strains in each cycle are added to the structure that is subjected to loading. 3,4…”