Application of thermoelastic stress analysis for the experimental evaluation of the effective stress intensity factor

Abstract

In recent years, the advent of staring array detectors has made Thermoelastic Stress Analysis (TSA) a technique with considerable potential for fatigue and fracture mechanics applications. The technique is noncontacting and provides full field stress maps from the surface of cyclically loaded components. In addition, the technique appears to have a great potential in the evaluation of the effective stress intensity factor range during fatigue since fracture mechanics parameters are derived directly from the temperature changes in the vicinity of the crack tip rather than from remote data. In the current work TSA is presented as a novel methodology for measuring the effective stress intensity factor from the analysis of thermoelastic images. ΔK values inferred using TSA have been employed to estimate an equivalent opening/closing load at different R-ratios in a cracked aluminium 2024 CT specimen. Results have been compared with those obtained using the strain-offset technique showing a good level of agreement.

Mechanical Behaviour of Stainless Steels under Dynamic Loading: An Investigation with Thermal Methods

“…Fracture mechanics is actually supported by Infrared Technique [23][24][25][26][27][28][29][30][31][32] referring to the measurement of the crack propagation or the determination of the Stress Intensity Factor. However, it has been demonstrated [3,14,31], that a direct measurement of surface temperature can provide an overview of the crack tip region.…”

“…By taking this limitation of temperature measurements into account, the TSA technique has been proposed for detecting the position of the crack and SIF evaluation [24][25][26][27][28]. In particular, several authors [24,25,28] have studied the phase shift of TSA signal in order to localize the position of the crack. The phase changes of the signal are due to high stress gradients, which may be ascribed to non-adiabatic conditions and to plastic behaviour at the crack tip.…”

“…The potential of thermal analysis lies with the possibility of detecting and monitoring the position of the crack. In literature [24][25][26][27][28], it has been found that the crack tip occurs when phase value approaches zero. Referring to the second order parameter S2, by observing Figure 5, there are two maximum values: the first maximum is related to crack closure effect while the second is related to plasticization beyond the crack tip.…”

Linear Elastic Fracture Mechanics Analysis of Fatigue Crack Growth Under Complex Loading Using the Digital Image Correlation Technique

“…crack growth. Crack closure results obtained here agree with similar studies using DIC [86,87] and other studies using the TSA technique [88]. In addition, this pseudo-KI should be interpreted carefully as a sum of elastic and plastic SIF [86,89] SIF as non linear phenomena such crack closure and blunting are present [49].…”

“…On the contrary, if the selected reference image has a load different than zero, the measured SIF should be interpreted as a SIF range [87]. Moreover, in literature there are plenty of cases where the COD is used to quantify SIF and crack openening with different techniques [40,67,88,92,93]. Therefore, the measures reported here use widely accepted practices.…”