Papers by Keyword: Thermoelastic Stress Analysis

Abstract: The emergence recently of a thermoelastic stress analysis (TSA) capability exploiting low-cost, compact and rugged microbolometer detector technology provides a significant opportunity topromote a broader use of this powerful non-contact full-field stress analysis technique. An area whereit has considerable and hitherto unexplored potential is in in-situ structural health monitoring (SHM).The present paper outlines the case for a nexus between SHMand TSA in this new form. It is proposedthat the approach should yield diagnostic and prognostic capabilities surpassing those of some existingSHM modalities. An F/A-18 centre-fuselage full-scale structural fatigue test is employed as a casestudy to illustrate the practical feasibility of the approach and to underscore some of its potential.Although the case study focuses on an aircraft structure, the concept has potential application to awide variety of different engineering assets across the aerospace, civil and maritime sectors.

Abstract: Thermoelastic stress analysis and grey-field photoelasticity are combined with the Laplace and Beltrami-Michell equations to non-destructively evaluate the individual internal components of stress in a loaded 3-D aluminium member. Experimental results agree with those predicted numerically by the finite element and finite difference techniques.

Abstract: Crack tip plasticity has been investigated using thermoelastic stress analysis (TSA) and digital image correlation (DIC). The plastic zone size at the tip of a propagating fatigue crack was measured using both techniques. At longer crack lengths, the results compared well with Dugdale’s and Irwin’s models for crack tip yielding. The TSA methodology requires careful observation of the adiabatic assumption.

Abstract: This paper describes a theoretical and experimental analysis on full-filed stress distribution from thermoelastic measurements and its application to determination of stress concentration. The sum of the principle stress can be measured by Thermal Stress Analysis (TSA). Lock-in Thermography is very effective tool to measure the structure stress distribution by its high thermal resolving. In this study, the thermoelastic effect theory is described and the relationship between the temperature and the applied stress is developed in an elastic material. Experiments were carried out with 2A12 aluminium alloys plate and ones with hole structure under cyclic load. The thermoelastic effect coefficient is obtained for 2A12 aluminium alloys materials, and the effect law is analyzed that the stress value measured was affected by load frequencies. The optional load frequency is obtained, and that is, the load frequency is selected greater than 3.5Hz for 2Al12 materilas, and it was found that the structure stress can be evaluated with good accuracies by the lock in thermography. The experiment was carried out for aircraft components stress distribution measurement and structure stress analysis. The experimental results show the stress concentration position is easy found from stress distribution by lock-in thermography.

Abstract: This paper describes a theoretical and experimental analysis on full-filed stress distribution from thermoelastic measurements and its application to determination of stress concentration. The sum of the principal stress can be measured by Thermal Stress Analysis (TSA). Lock-in Thermography has been applied to measure the sum of principal stress distribution of component structure by its high thermal resolving. In this study, Finite element method is used to calculate the sum of principal stress distribution, and the thermoelastic effect model is developed to study the relationship between the temperature deviation and the applied stress in an elastic material. Experiments were carried out with ANSI 7071 high strength aluminum alloys ply and ones with a crack under cyclic load. The thermoelastic constant is obtained for ANSI 7071 high strength aluminum alloys materials. The stress concentration factor is calculated for a ply with modeling crack under the condition of different loads. The experiment was carried out with high strength aluminum alloys component structure with rivet joints. The experimental results show the stress distribution can be measured and analyzed the contact stress distribution between ply and rivet by using Lock-in thermography. It was found that the structure stress can be evaluated with good accuracies by the lock in thermography.

Abstract: Al-Li alloys are characterized by a strong anisotropy in mechanical properties and microstructure with respect to the rolling direction. Plates of 2198 Al-Li alloy were friction stir welded by employing maximum rotation speed: 1000 rev/min and welding speed of 80 mm/min, both in parallel and orthogonal directions with respect to the rolling one. The joints mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests performed with a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz loading, were conducted in axial control mode with R(σmin/σmax)=0.33, for all the welding and rotating speed conditions. The fatigue crack propagation experiments were performed by employing single edge notched specimens.With the aim to characterize the weld performances, both the microstructure evolution at jointed cross sections, related to the welding variables, and the fractured surfaces were respectively analyzed by means of optical and scanning electron microscopy.

Abstract: The paper presents background information and experimental results regarding the assessment of fatigue damage in welded steel structures by thermographic investigations of thermomechanical coupling effects. The results confirm the high potential of specialized thermographic methods for the experimental characterization of all stages of fatigue damage in welded and un-welded components. The technique provides a new experimental mean to investigate early inhomogeneous fatigue damage as mesoplasticity and cracks in the weld toe. The method has been successfully applied during fatigue testing of welded components and allows detecting localized damage as early as 10% to 20% of the total fatigue lifetime of the tested specimens.

Abstract: The current paper presents a new combined technique for damage detection, localisation and establishing damage severity. The technique is based on the use of two infrared detection approaches: Pulsed Phase Thermography (PPT) and Thermoelastic Stress Analysis (TSA). A methodology is described that allows the technique to be applied to fibre reinforced composites. The usefulness of the technique is demonstrated on delaminated glass epoxy laminates. A means of developing controlled delamination damage in such specimens is developed so that real sub surface damage is evaluated in the paper.

Abstract: Thermoelastic Stress Analysis (TSA) is a non-contacting technique that provides full field stress information and can record high-resolution measurements from small structures. The work presented in this paper summarises the application of TSA to two types of small medical devices that are used to treat diseased arteries; angioplasty balloons and vascular stents. The use of high resolution optics is described along with a calibration methodology that allows quantitative stress measurements to be taken from the balloon structure. A brief account of a study undertaken to characterise the thermoelastic response from Nitinol is also included and it is demonstrated that thermoelastic data can be obtained from a stent at high resolutions.

Abstract: This work presents a set of experimental results based on the measured thermoelastic signal from GRP composite coupons adopting different lay-ups. A comparison is made with the thermoelastic signal predicted by two different analytical models: one based on the classical law of the thermoelastic effect for orthotropic materials, and the other based on a novel theory accounting for the presence of a resin layer on the external surface of the composite structure. The composite coupons were designed such to determine a significant difference in the predictions made by the two theoretical models. Experimental results have shown a far better match with the predictions based on the novel theory accounting for the presence of a surface resin rich layer.