50^th Anniversary Article: Seeing Stresses through the Thermoelastic Lens—A Retrospective and Prospective from an Australian Viewpoint

Abstract

Thermoelastic stress analysis (TSA) has been around for the past 30 years, but to date, it is still a very much underrated and under‐utilised experimental technique. Although there are devoted groups of practitioners in some industries, this technology is not well known within the aerospace sector. In contrast, the Aerospace Division of the Defence Science and Technology Organisation (DSTO) in Australia has been in the forefront of this technology for some time, achieving many pioneering feats. This paper gives a brief introduction to the development of this technology from a historical perspective, then focuses on a number of innovations that have stemmed from DSTO, including the development and application of the world's first focal plane array based TSA system and, more recently, the development of small and robust microbolometer based systems. For the latter, it is shown that despite nominally poorer temperature sensitivities, they make ideal TSA devices and can in some cases outperform their much more expensive photon detector counterparts. Because of this, together with the enormous practical advantages of microbolometers, the future of TSA is shown to be brighter than ever. Specifically, it is argued that such TSA systems can play a major role in the pervasive and persistent surveillance of full scale fatigue testing of aircraft structures. By detecting both design and developing faults early, it can effectively relieve cost and schedule penalties that are often associated with unanticipated failures. To realise this capability, integration of this technology with autonomous systems will be important, and some preliminary but promising results from a technology demonstrator program are presented.

The Transverse Crack Tension test revisited: An experimental and numerical study

“…A TSA setup is implemented to acquire the thermoelastic signal over the thickness face of TCT samples [27]. This technique is here chosen for a number of potential outcomes of particular interest for the evaluation of a TCT configura- The temperature variation ∆T at the loading frequency is referred to as the thermoelastic signal [28,29]. For a generic orthotropic material, with principal material directions indicated by subscripts 1 and 3, it is described by the following linear stress function [30,31]:…”

The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future

“…The first stage will involve a global testing of the component using for example, high-frequency modal analysis, in order to check for any deviations from the reference state [47,48]. Assuming there is an indication of anomalous response, the component will be further interrogated and inspected by more advanced and thorough techniques such as (lock-in) thermography and/or thermoelastic stress analysis [49][50][51], active shearography [51] and laser Doppler vibrometry [52]. These techniques actually provide a semi-quantitative view of the structural health of the component, and will identify "hotspots" that may deserve further attention.…”

Autonomous stress imaging cores: from concept to reality

“…At the Australian Defence Science and Technology (DST) Group low-cost automation-grade microbolometers are now used routinely in full-scale airframe structural test programs. Experience has shown that these devices enable TSA to be applied more easily, extensively and effectively in support of full scale structural fatigue testing of airframe components [5]. The reasons are manifold.…”