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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. [ABSTRACT FROM AUTHOR]

In the traditional formulation of the stress field near a crack tip, the presence of the T-stress is generally considered only under mode I or mixed mode I and II conditions. In this paper its presence in almost pure Mode II is experimentally investigated by mean of photoelasticity and its effects on the isochromatic fringe patterns are discussed. The test specimens are Brazilian discs containing sharp central cracks. After crack generation, all residual stresses are removed with thermal treatment of the specimens. Then, a compressive load is applied in a specific angle to induce mode II deformation. The observed isochromatic fringes show very good consistency with theoretical predictions. Experimental results indicate that this specimen has a negative T-stress in mode II condition. The results calculated for K and T from photoelastic experiments agree well with numerical results available from finite element method. [ABSTRACT FROM AUTHOR]

The use of damage models require a number of material parameters the identification of which should be made, when possible, based on direct measures of the damage that develops in the material. Among the possible experimental techniques to measure the occurrence of ductile damage in metals, the measure of the damage through the degradation of the material Young's modulus has been indicated as one of the more effective technique and used by several authors. In this paper, this technique is critically reviewed highlighting the number of issues that may affect the measure of damage. In particular, the attention is focused in the case where damage process initiates at the onset necking and develops in the post-necking regime where stress, strain and damage are no longer uniform in the gauged section. Since geometry variations alter the reference base length for both stress and strain definition, a procedure based on the use of finite element simulation is proposed in order to account for this effect on the measure of the stiffness loss. The procedure has been applied to two class of metals: a high strength steel and high purity copper. [ABSTRACT FROM AUTHOR]

Presents news briefs related to the field of strain analysis compiled as of November 2003. David Mitchell and Geoff Mordan's accomplishments in the field; Highlights of the Engineering Integrity Society's 2003 Fatigue 2003 Conference; Discussions on simulation technology at the 9th NAFEMS World Congress in Orlando, Florida.

On the basis of direct measurement of the opening displacement of the notch contour the procedure of the evaluation of local elastoplastic strains range, Δε*, is developed. The experimental values of Δε* are compared with the calculational data using known equations by Neuber. Glinka, etc. It is shown that for Δε* < 2% the experimental and calculational values are in good agreement but only in the case when the gradient of strains near the notch tip is taken into account. The proposed experimental method is used for the prediction of period N[sub i] to fatigue macrocrack initiation in specimens of a complicated shape. [ABSTRACT FROM AUTHOR]