Energetic analysis of fatigue hysteresis by thermographic and digital image correlation methodologies

Abstract

A hysteresis cycle can define the variation in mechanical characteristics of fatigue life and failure response. Traditional analysis is performed using forcedisplacement signals derived from the testing equipment, but this approach is prone to large errors due to clearances and slips in the measuring chain. For this reason, the authors here propose a novel setup able to assess accurately the strain status of specimens by digital image correlation (DIC) and a procedure to calculate the hysteresis energy by thermographic analysis in order to measure the damping energy with precision. The results obtained by an experimental investigation on a common austenitic steel (AISI 304) highlight that the hysteresis areas defined by the DIC displacements, and those found by the testing machine outputs have substantial differences in value. The thermal variations and the areas of the hysteresis loops, both linked to the plastic energy, were also compared, showing a reliable correlation.

On the relationship between mechanical energy rate and heat dissipated rate during fatigue for a C45 steel depending on stress ratio

“…The higher Δ T 2 ω values at R = −1 than at R = 0.1 can be explained by the major intrinsic dissipations in agreement with the results presented in literature 20,33 …”

“… function must be integrated over a period ( T = 1/ f ) in order to obtain the area under hysteresis loop: The W p value depends on stress ratio when the stored energy E s is negligible, Figure 1B, and can be obtained by estimating the heat converted energy ( E d ) that in turns can be assessed by analyzing the surface temperature of the sample 20,32,40 …”

Combined experimental methods to assess the fatigue limit

“…Digital Image Correlation (DIC) is widely used to assess the correct displacements in specimens under static or dynamic loading and can be usefully exploit to define the area of hysteresis, linked to the state of damage of the specimen [23,[26][27][28][29][30][31][32][33][34][35][36].…”

“…Following some studies assessing fatigue parameters by coupling different methodologies [23,[34][35][36][37][38][39][40], the aim of the present paper is the comparison about the results found by coupling TH, DIC and AE to define the fatigue parameters and the crack growing in static and dynamic testing. In particular, the 1214 (2022) 012014 IOP Publishing doi:10.1088/1757-899X/1214/1/012014 2 paper describes the evaluation of the fatigue limit using the three methodologies and the comparison among them.…”

A Comparative Study of Fatigue Energy Dissipation of Additive Manufactured and Cast AlSi10Mg Alloy

“…With the rapid development of infrared detector technology, the surface temperature variation can be recorded with high accuracy. This temperature variation is linked to a fatigue hysteresis cycle, which can be accurately assessed by Digital Image Correlation (DIC) [7]. A thermographic methodology was first used to rapidly determine the fatigue limit for steels [8][9][10].…”