Thermoelastic stress analysis with a compact low-cost microbolometer system

Abstract

This article describes the development and validation of a novel thermoelastic stress analysis (TSA) system based on a low-cost microbolometer device. The use of a microbolometer for a highly synchronous and delicate temperature measurement breaks a longstanding and exclusive reliance on high performance, cooled photon detectors for thermoelastic applications. It is shown that despite markedly inferior noise equivalent temperature detectivity and dynamic response specifications, microbolometers are capable of achieving comparable levels of stress measurement performance. The practical implications for experimental stress analysis are significant. Microbolometers are relatively low in capital cost, small in size, have good tolerance to shock and vibration and consume less power than their photon counterparts, attributes that confer enormous practical advantages. It is argued that the emergence of TSA systems that are more affordable and better suited to in-service application could help to promote a much broader use of this powerful technique in applications across the life cycle of high value civil, maritime and aerospace assets, from the validation of finite element modelling for design to in-service structural integrity assessment. A full-scale fatigue test of a flight-critical aircraft structural component is employed as a case study to demonstrate important aspects of the capability. Future directions in the development and application of low-cost miniaturised systems are also discussed.

Autonomous stress imaging cores: from concept to reality

“…Although much less costly and more practical, thermal detectors have a relatively slow dynamic response and a poor sensitivity compared to cooled photon detectors, factors that were assumed to militate against their use for TSA which entails the measurement of rapidly fluctuating temperature variations of around 1 mK in amplitude. This view began to change in 2005 when experimental testing of the first TSA system developed using a thermal detector demonstrated levels of stress-measurement performance that were far better than what might have been expected [3]. Indeed, given sufficient "observation" time the thermal detector was able to consistently outperform a significantly more sensitive 1 cooled detector applied under the same circumstances.…”

“…This board provides a more readily accessible hardware interface and includes a 3.3V regulated voltage supply to power the core. The LVDS signal was converted to a Gigabit Ethernet (GigE) stream using a Pleora iPORT PT1000LV frame grabber and then fed into a standard notebook computer where it was de-serialized and then cross-correlated against a reference signal using the MiTE (Microbolometer Thermoelastic Evaluation) software [3]. The process is shown schematically in Figure 4.…”

Quantitative analysis and image processing techniques of large-scale industrialsize fire tests using infrared thermography

“…By comparison, an InSb photon detector has a time constant in the order of micro or even nano seconds. In addition, the Noise Equivalent Temperature Difference (NETD) can be up to three times higher [6].…”

“…In many practical cases the dominant frequency is on the order of 1 Hz. Therefore, studying fire phenomena using infrared themography allows for slower IR systems as opposed to, for instance, thermoelastic stress analysis (TSA) [6]. While Eq.…”

Detection and characterisation of delamination damage propagation in Woven Glass Fibre Reinforced Polymer Composite using thermoelastic response mapping

“…The high capital-cost disadvantage of TSA no longer applies following a recent finding that low-cost automation grade thermal detectors can provide comparable stress sensitivities to cryogenically cooled photon detectors (Nick Rajic & Rowlands 2013;Rajic N., Weinberg S. & D. 2007). Thermal detectors are generally far less expensive, much smaller, have better tolerance to shock and vibration and consume less power than their photon-detector counterparts.…”