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For the fabrication of structures in complex environments and to improve device performance, this paper presents a thermoelastic topology optimization formulation for the design of support structures in layer-by-layer printed additive manufacturing. The formulation is written in the form of structural compliance minimization with two competing constraint functions, one related to mechanical performance (stress) considering mechanical stress and thermal stress and one related to thermal performance (temperature). The optimization problem is solved by applying the p-norm function to handle global stress constraints and overall temperature constraints, separately. The sensitivity information of the objective function and constraints is derived using the adjoint variable method. The design variables are updated using the Method of Moving Asymptotes (MMA). We present several examples that explore the ability of the formulation to obtain optimized support structures for additive manufacturing under different volume constraints, various performance constraints, and print orientations, which addresses the issues of mechanical and thermal stress concentration when considering thermoelastic coupled effect, thus validating the effectiveness of the proposed method. In comparison with previous works, thermal performance-related constraints are introduced in this study, which effectively solves the optimization problem under thermoelastic coupling effect. [ABSTRACT FROM AUTHOR]

A small, novel, integrated SHM system has been deployed during full-scale testing of a wing fatigue test for several weeks and a fuselage pressurisation test for several months. Complementary NDE measurement techniques were combined, with inputs from visible and infrared optical sensors, as well as resistance strain gauges. Sensor units were deployed at regions of interest and integrated board computers permitted near real-time data processing. The outputs were full-field measurement datasets from digital image correlation and thermoelastic stress analysis systems. Changes in these datasets in the regions of interest were successfully quantified using orthogonal decomposition and were indicative of changes in the condition of the structure. The results from these case studies demonstrate that this system can be successfully deployed in spatially restricted areas within airframe structures to monitor crack growth. The low cost and small footprint of the system presents the opportunity for installation of arrays of similar sensors for both test and in-service data collection. Near real-time data processing would allow timely reporting to service engineers, informing maintenance or operational decisions. [ABSTRACT FROM AUTHOR]

The conventional approach to temperature evolution in cyclic loading is explained by a hysteresis curve with three phases. However, it has not been matched with experimental data except in the beginning of the cyclic loading. Thus, this study suggests a new approach to temperature evolution with three phases in cyclic loading by plastic deformation using the thermoelastic effect. The sample was fabricated following ASTM D638 standard for cyclic loading, and the temperature was measured during the cyclic loading by an infrared camera. Thermography was used to observe partial heating caused by cracks. The results were evaluated with the correlation (R2) coefficient between temperature and the derived equation as 0.96 in phases 1 and 2. Also, the partial heating was observed showing the effect of cracks for the temperature evolution in phases 2 and 3. Based on these results, a new approach to temperature evolution in cyclic loading is suggested. [ABSTRACT FROM AUTHOR]

The potentials of CuZnAlNi shape memory alloys to serve as viable reinforcement in Aluminium matrix composites (AMCs) was investigated. The AMCs were double stir cast developed, containing 4, 6, and 8 wt% CuZnAlNi particles; and their structural characteristics and mechanical properties were compared with that of the unreinforced Al alloy and AMC containing 8 wt% SiC. Scanning electron microscopy and X-ray diffraction results show that the CuZnAlNi refined the grain size, and increase in the CuZnAlNi wt% resulted in the formation of varied AlCu-based intermetallics, apart from the primary Al rich phase. The strength indicators – hardness, ultimate tensile strength, and specific strength largely improved with increase in the CuZnAlNi wt% and were comparatively higher than that of the unreinforced Al alloy and AMC reinforced with 8 wt% SiC for the 6 and 8 wt% CuZnAlNi reinforced AMC (specific strength being the only exception). The percentage elongation and fracture toughness values of the AMCs reinforced with CuZnAlNi (12–14.5% and 10.5–12.3 MPa m1/2) were equally superior to the SiC reinforced AMC (9% and 6.5 MPa m1/2, respectively). However, a partial reduction in the % elongation was observed with the increase in the CuZnAlNi wt%. Improved matrix/particle interface bonding, matrix refinements, thermoelastic-induced compressive residual stresses, inherent ductile, and tough nature of the SMA were advanced as mechanisms responsible for the improvements in properties.

• The effect of temperature on non-slipping adhesive contact behavior is investigated. • The full analytical solutions of the anisothermal oscillatory stress fields are derived. • Both the temperature and inclined angle of the external force have significant influences on adhesion behaviors. • The non-oscillatory solutions can not always serve as a good approximation for the oscillatory solutions. The temperature difference always exists between contacting objects in various thermal bonding technologies, where the adhesion strength is found to be very sensitive to the temperature. In this paper, the anisothermal adhesive contact between an elastic cylinder subjected to the external force with an inclined angle and an elastic substrate is investigated based on the non-slipping JKR model, where the coupling effect between the normal and tangential tractions within the contact region is taken into consideration. The stated problem is reduced to a system of coupled singular integral equations, which can be solved with the analytical function theory. The full analytical solutions of the oscillatory stress fields are obtained for the first time by taking the series expansion of the integrand induced by the thermoelastic effect, which is of substantial significance. The relationship between the contact size and the external loadings is established by virtue of the Griffith energy balance criterion. The difference between the oscillatory and non-oscillatory solutions of stress fields is discussed in detail. Numerical results demonstrate that the oscillatory solution cannot be well approximated by the corresponding non-oscillatory solution for the cases of large Dundurs' index and external compressive force. Furthermore, it is found that both the thermoelastic effect and the inclined angle of the applied force have significant influences on the adhesive contact behaviors. The presence of temperature difference between contacting objects can either enhance or weaken the adhesion effect, which is related to the inclined angle of the external force. The results obtained from this paper may provide a new insight into the influence mechanism of the temperature on adhesion behaviors. [ABSTRACT FROM AUTHOR]

A novel optical arrangement to generate a laser array line source of laser-generated ultrasound based on two-beam interference is proposed. The arrangement simplifies the adjustment of the laser array source period by changing the intersection angle of two interference beams. The performance of the arrangement is illustrated through measurements of the surface acoustic wave generated by the nanosecond laser array line source in aluminum metal. The surface acoustic wave generated by the laser line array source has stronger directivity parallel to the direction of the line source. The intensity of the measured surface acoustic wave is higher than that generated by a laser spot source with the same incident energy. The optical arrangement generating the laser array line source will be particularly advantageous in laser-generated ultrasound systems used for chemical corrosion detection.

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In the paper, the general decay of energy solutions for a type III thermoelastic coupled system with distributed delay is studied. The coupling is via the acoustic boundary conditions. Our result is obtained under a class of generality of the relaxation function g: R+ --> R+ satisfying the inequality W) < for all t > 0, where £ and 'ri are functions satisfying some specific properties. This work extends previous works with thermoelasticity of type III and improves earlier results in the literature. [ABSTRACT FROM AUTHOR]

Thermoelastic stress analysis using arrays of small, low-cost detectors has the potential to be used in structural health monitoring. However, evaluation of the collected data is challenging using traditional methods, due to the lower resolution of these sensors, and the complex loading conditions experienced. An alternative method has been developed, using image decomposition to generate feature vectors which characterize the uncalibrated map of the magnitude of the thermoelastic effect. Thermal data have been collected using a state-of-the-art photovoltaic effect detector and lower cost, lower thermal resolution microbolometer detectors, during crack propagation induced by both constant amplitude and frequency loading, and by idealized flight cycles. The Euclidean distance calculated between the feature vectors of the initial and current state can be used to indicate the presence of damage. Cracks of the order of 1 mm in length can be detected and tracked, with an increase in the rate of change of the Euclidean distance indicating the onset of critical crack propagation. The differential feature vector method therefore represents a substantial advance in technology for monitoring the initiation and propagation of cracks in structures, both in structural testing and in-service using low-cost sensors.

Tensile deformation behavior of nuclear grade Austenitic Stainless Steel (SS) and its weld joints fabricated by Gas Tungsten Arc Welding (GTAW) and Activated flux Gas Tungsten Arc Welding (AGTAW) processes were studied and correlated with relevant microstructural morphologies using Infrared Thermography (IRT) technique. The microstructure of base metal showed a complete austenite phase. GTAW Fusion Zone (FZ) exhibited both primary ferrite and primary austenite mode of solidification. Meantime, AGTAW FZ exhibited only primary austenite mode of solidification A strain rate of 4.4x10-4 s-1 was used during the tensile test of the base metal and weld samples. The failure locations of the base metal, GTAW and AGTAW samples were noticed at the center of the gauge portion, the base metal side away from Fusion Line (FL) and Heat Affected Zone (HAZ) respectively. Temperature variations of the base metal and weld zones were recorded in the form of thermograms using the IR camera at the different stages of the tensile deformation. During deformation study, peak temperatures of 39.2 oC, 38.8 oC and 34 oC were observed at the base metal, GTAW and AGTAW samples respectively. The lesser peak temperature of the AGTAW sample compared to the base metal and GTAW samples indicated that the AGTAW sample undergone lesser deformation. Moreover, tensile deformation behaviors of the base metal and weld samples were correlated with their microstructural morphologies using corresponding temperature curves.

This research was performed to study the influence of the 3D printing technique on the thermoelastic effect. Specimens were made by following Standard ASTM D 638 Type 4 for tensile properties of plastics because the method of research was a tensile test using the universal tensile test machine (UTM). In 3D printing, raster angle which was the main factor was studied as factor which can affect to thermoelastic effect; and annealing was also studied because annealing can increase crystallinity and relieve residual stress and then, these can make change on thermoelastic effect. While this research was carried out, mechanical properties simultaneously were measured and it is utilized when fractography was performed using filmed scanning electron microscope (SEM) image. The main method was by filming infrared thermography for detecting temperature change. Using these methods, influence of 3D printing technique on thermoelastic effect was researched. [ABSTRACT FROM AUTHOR]

We report on the further development of our previously described spectroscopic imaging technique based on time-resolved interferometric measurements of laser-induced thermoelastic expansion (POISe: Pulsed Optoelastic Interferometric Spectroscopy and Imaging). We show the capability of POISe to form tomographic images of tissue phantoms and live animal tissues. By performing image reconstruction on data sets acquired from several tissue-like phantoms we demonstrate the ability of POISe to provide better than 200 μm spatial resolution in a strongly scattering medium (μ′ s=1.5/ mm). Additionally we demonstrate the ability of POISe to image chicken chorio-allantoic membrane (CAM) blood vessels through a 6-10 mm layer of Intralipid with μ′ s=0.75/mm.

We report on the further development of our previously described spectroscopic imaging technique based on time-resolved interferometric measurements of laser-induced thermoelastic expansion (POISe: Pulsed Optoelastic Interferometric Spectroscopy and Imaging). We show the capability of POISe to form tomographic images of tissue phantoms and live animal tissues. By performing image reconstruction on data sets acquired from several tissue-like phantoms we demonstrate the ability of POISe to provide better than 200 μm spatial resolution in a strongly scattering medium (μ′ s=1.5/ mm). Additionally we demonstrate the ability of POISe to image chicken chorio-allantoic membrane (CAM) blood vessels through a 6-10 mm layer of Intralipid with μ′ s=0.75/mm.

POISe is a spectroscopic imaging technique based on the measurement of surface motion resulting from thermoelastic stress waves produced by short pulse laser irradiation of optically heterogeneous turbid samples. Here we show the capability of POISe to form tomographic images of tissue phantoms using surface displacement measurements taken at several locations following irradiation of a sample with a λ- switched Nd:YAG laser A=1064 nm. The principal component of POISe is a modified Mach-Zehnder interferometer that provides surface displacement measurements with a temporal resolution of 4 ns and a displacement sensitivity of 0.2 nm. By performing simple image reconstructions on data sets acquired from several tissue-like phantoms, we demonstrate the ability of POISe to provide better than 250 μm spatial resolution at depths of 6 to 8 mm in a strongly scattering medium (μ s′=1/mm). This technique shows great promise for high-resolution non-invasive imaging of superficial (< 1 cm) tissue structures.

POISe is a spectroscopic imaging technique based on the measurement of surface motion resulting from thermoelastic stress waves produced by short pulse laser irradiation of optically heterogeneous turbid samples. Here we show the capability of POISe to form tomographic images of tissue phantoms using surface displacement measurements taken at several locations following irradiation of a sample with a λ- switched Nd:YAG laser A=1064 nm. The principal component of POISe is a modified Mach-Zehnder interferometer that provides surface displacement measurements with a temporal resolution of 4 ns and a displacement sensitivity of 0.2 nm. By performing simple image reconstructions on data sets acquired from several tissue-like phantoms, we demonstrate the ability of POISe to provide better than 250 μm spatial resolution at depths of 6 to 8 mm in a strongly scattering medium (μ s′=1/mm). This technique shows great promise for high-resolution non-invasive imaging of superficial (< 1 cm) tissue structures.

An optical method of registration of optical anisotropy (birefringence) in glasses is offered. The research of heat transfer processes was based on the occurrence and registration of the thermoelastic effect. This effect arises in the sample during radiative cooling. Change of heat balance and loss of internal energy are due to the thermal radiation. This leads to the formation of an inhomogeneous radiation, temperature, and deformation fields in the sample. The measurement method is based on the modulation of polarization of laser radiation transmitted through the anisotropic area and the definition of its anisotropy parameters by means of this modulation. Phase differences between orthogonal components of linearly polarized light are linearly dependent on a mechanical stress magnitude. The method allows obtaining several desired material parameters by measuring one stress σ(t) value. Detectability of the modulation polarimetry technique was high and ensured the registration of the mechanical stresses during radiative cooling by a fraction of a degree. The mechanical stresses induced by the heat flow also have small values and are nonlinearly related to the temperature function. Time dependence of the stress σ(t) in various coordinates of the sample demonstrates a complicated and variable dependence during the measurement. Components related to radiation, conductive and convective heat transfer mechanisms are obtained from the σ(t) dependence. Relaxation parameters of these components are determined. The technique allows simulating high-temperature heating-cooling processes during the manufacture of materials and their technological application [ABSTRACT FROM AUTHOR]

The paper discusses an acoustoelastic study of residual stresses and related structural changes in thin-walled austenitic steel pipes. A probing ultrasonic (US) beam is formed owing to the thermoelastic effect by absorption of a laser pulse in an optoacoustic transducer. Normal and oblique incidence (at an angle close to critical) of the US beam was used on the studied. Distribution maps of US velocity variations over the object's surface and the volume structural inhomogeneities inside the metal were plotted. Estimates are presented for the residual stresses in the sample under nonstationary thermal loading. The coincidence between the residual stress distribution, structural inhomogeneities of the metal, and distribution of thermal loading sources is established. The possibility of estimating the residual life and finding of macrocrack nucleation centers is discussed. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical results of a polyurethane shape memory polymer (SMP) subjected to cyclic tensile loading. The goal was to investigate the polymer yielding phenomena based on the effects of thermomechanical coupling. Mechanical characteristics were obtained with a testing machine, whereas the SMP temperature accompanying its deformation process was simultaneously measured in a contactless manner with an infrared camera. The SMP glass transition temperature was approximately 45 °C; therefore, when tested at room temperature, the polymer is rigid and behaves as solid material. The stress and related temperature changes at various strain rates showed how the SMP yield limit evolved in subsequent loading-unloading cycles under various strain rates. A two-phase model of the SMP was applied to describe its mechanical response in cyclic tension. The 3D Finite Element model of a tested specimen was used in simulations. Good agreement between the model predictions and experimental results was observed for the first tension cycle. [ABSTRACT FROM AUTHOR]

The three-phase-lag model of heat conduction has been proposed for considering thermoelastic effect in medium. The bioheat transfer equations based on Taylor's series approximation of the three-phase-lag model were derived in conjunction with a modified energy conservation equation. For exploring the effect of non-linear expansion in the phase lag times, the Taylor's series of second-order expansion was applied. The resulting equation involves mixed derivative terms and higher-order derivatives of temperature with respect to time. The hybrid application of the Laplace transform method and a modified discretization technique was extended to solve the equations and explore the effect of thermoelasticity on the thermal behavior in living tissue with surface heat flux. The influence of thermoelastic parameters and phase lags on heat transfer in tissue has been investigated. The present results illustrate the thermal response oscillation is excited in medium for the thermoelastic effect, the phase lag times significantly affect the amplitude and frequency of the oscillation, and the expansion order of TPL model evidently affects the predicted temperature. • The non-linear expansion three-phase-lag model of bioheat transfer is solved. • The need for the heat flux boundary condition to include phase lag effect is discussed. • Nonlinear behavior of thermal lagging of the TPL model is investigated. • The thermal response oscillation is excited in medium for the thermoelastic effect. • The expansion order of TPL model evidently affects the predicted temperature. [ABSTRACT FROM AUTHOR]

This paper reports a type of detector based on the thermoelastic effect of a miniature quartz tuning fork (mQTF) for infrared spectroscopy applications. Instead of using a pyroelectric infrared detector, a mQTF with a resonant frequency of ∼45 kHz was adopted as a detector for infrared light signal collection. To explore the capabilities of this technique, measurement of infrared absorption spectra of samples was conducted, and the effect of scattered light on the sensitivity was investigated. The experimental results indicate that the mQTF detector is sensitive to infrared radiation within a wide range of wavelengths, and packaging the mQTF could increase the sensitivity and signal-to-noise ratio (SNR) by 2.54, and 2.87 times, respectively. The infrared transmission spectrum of polystyrene (PS), polyethylene (PE) have been measured by the mQTF detector, and the experimental data show that the infrared characteristic absorption peaks appears in the same position as commercial pyroelectric detector. Finally, mid-infrared spectroscopy of acetone gas was measured by the mQTF with high precision. It is worth noting that this is the first study of using the mQTF-based photodetector for gas phase infrared spectroscopy, the mQTF exhibits its cost-effectiveness, sensitivity, and broadband optical response advantages, could be used for qualitative analysis of components by the infrared spectrum. [ABSTRACT FROM AUTHOR]

Background: As the most abundant protein in human tissues, the use of collagen is essential in the fields of biological science and medicine.Objective: The aim of this study is to investigate the mechanical effect of pulsed laser irradiation on collagen tissue.Methods: With various laser parameters such as peak power, pulse width, and repetition rate, the induced stresses on samples were measured and analyzed. Monte Carlo simulation was performed to investigate the effect of laser parameters on the collagen sample.Results: The results indicated that the magnitude of mechanical stress could be controlled by various laser parameters.Conclusions: This study can be used in biostimulation for therapy and mechanoreceptor stimulation for tactile application. [ABSTRACT FROM AUTHOR]

The main objective of this study is to predict the temperature variation of a rubber ball under cyclic compression. The prediction scheme is composed of three parts: mechanical analysis, heat source identification and heat transfer analysis. In the mechanical analysis, a compressible hyper-viscoelastic model was employed to describe the mechanical behavior of rubber under cyclic compression, in which material constants were identified using experimental data. In the heat source identification, the heat sources caused by three effects, namely thermoelastic, entropic and viscous dissipation effects were evaluated based on a theoretical consideration. In the heat transfer analysis, the above-mentioned heat sources were used as input to calculate the time variation of the temperature field. The temperature variation inside and on the surface of the ball under both adiabatic and non-adiabatic conditions were discussed. In addition to that, the temperature amplitude and phase difference between temperature and displacement in the steady state were considered. [ABSTRACT FROM AUTHOR]

A novel optical arrangement to generate a laser array line source of laser-generated ultrasound based on two-beam interference is proposed. The arrangement simplifies the adjustment of the laser array source period by changing the intersection angle of two interference beams. The performance of the arrangement is illustrated through measurements of the surface acoustic wave generated by the nanosecond laser array line source in aluminum metal. The surface acoustic wave generated by the laser line array source has stronger directivity parallel to the direction of the line source. The intensity of the measured surface acoustic wave is higher than that generated by a laser spot source with the same incident energy. The optical arrangement generating the laser array line source will be particularly advantageous in laser-generated ultrasound systems used for chemical corrosion detection. [ABSTRACT FROM AUTHOR]

This paper presents general outlines of the research conducted in the applied mathematics field, − the theory of inverse problems, specifically utilized for the thermoelastic stress analysis model for exact estimation of thermo-elasticity parameters. We present formulation of the well posed direct mathematical model that depicts general interconnections between physically governed fields for thermally heated plate subjected to fixed constrains on the boundaries with small deformations from thermal expansion over the homogeneous multilayered medium domain. Applying elements of variational calculus, functional analysis and fractional order derivatives, we demonstrate the derivation of the conjugate problem and analytical expressions used for exact estimation of structural material thermoelastic properties. The novelty of proposed methodology lies in derivation of exact estimators that could be utilized for general homogenized thermoelastic model with finite amount of sampled temperature measurements on the domain outlets. It also opens curtains over the key issues and some important aspects aroused in the derivation procedures of exact estimators for general problem statement. There were posed and discussed necessary conditions in a form of a working hypothesizes. Results may be utilized as an experimental technique designed to obtain an essential information on the surface stress field along with the thermoelastic material properties. [ABSTRACT FROM AUTHOR]

Fatigue damage onset involves a transformation of mechanical energy. This is in part spent into work of plastic deformation and fracture and in part transformed into heat. Therefore, different thermomechanical heat sources are activated during a fatigue loading cycle, resulting in a temperature modulation that can be characterized by its frequency content. Several studies have monitored the temperature on samples undergoing high-cycle fatigue, measuring specific thermomechanical metrics which could serve as indicators of damage evolution. The present work evaluates the harmonic content of temperature, to investigate its correlation with the material dissipation. The harmonic terms investigated are the amplitude and phase of temperature at the loading frequency (First Harmonic) and at twice the loading frequency (Second Harmonic). The paper reviews the mechanisms linking the evolution of heat dissipation to changes in these four parameters. The theoretical analysis is supported by an experimental campaign carried out on C45 steel tensile specimen subject to R = − 1 and R = 0. 1 loading ratios. The harmonic metrics are evaluated analyzing both their spatially averaged value and their spatial dispersion, to check for the formation of localized heat dissipation zones in early fatigue life. The study shows that the phase of the Second Harmonic signal has a peculiar bimodal distribution that can be correlated to either a thermoelastic or dissipative prevailing effect. This behavior evolves towards a unimodal dissipative behavior when the load amplitude is increased, thus proposing the Second Harmonic phase parameter as an effective indicator for monitoring internal intrinsic dissipation in the material. • Heat dissipation at early fatigue stages is correlated to temperature harmonics. • Mechanisms correlating the First Harmonic to heat dissipation are highlighted. • Thermoelastic and dissipative heat sources induce different Second Harmonic phases. • The phase of the Second Harmonic has a bimodal distribution. • Early fatigue-induced intrinsic heat dissipation is a non-localized phenomenon. [ABSTRACT FROM AUTHOR]

Recently various nanomaterials, such as carbon nanotubes and graphene, have been added to rubbery elastomers, such as poly dimethyl siloxane (PDMS), to enable generation of stress and displacement in response to remote illumination. While the response is primarily due to heat-induced generation of stress; i.e., the thermoelastic effect in rubbers, illuminated samples have shown unexpected deviations between the transient waveforms of sample temperature and induced stress. In this report we have created a new and simple lumped element model to explain the stress behavior of these photomechanical nanocomposites. The model consists of two parameters that describe the spatially averaged steady state temperature rise due to optical absorption of the structure (typically a long strip of pre-strained elastomer) and the spatially averaged convective cooling rate of the strip, together with a time-varying function that effectively represents the temperature distribution and thermal convection along the length of the strip. The model is used to compare two actuators that each have a thin embedded layer of carbon nanotubes, in which the one film consists of randomly aligned nanotubes and the other has a much more ordered alignment. The model not only fits both transient responses, but the differences between the parameters suggests that the ordered film conducts heat across the strip more rapidly than the disordered film, leading to it more rapidly reaching the steady state level of maximum stress. This model should be helpful in future experimental studies that work to observe, delineate and identify possible nanoscale and molecular contributions to photomechanical stress.

Abstract: In order to assess the thermoelastic influence on the long-term performance of hot dry rock (HDR) reservoirs, a simple three-dimensional (3-D) thermoelastic model has been developed based on an assumption of a spherically symmetric volume of cooled rock within reservoir. This model has been incorporated into a 3-D stochastic network model, FRACSIM-3D, which incorporates a fracture network designed to mimic natural fracture distributions as well as stimulation and circulation. The model has been used to evaluate the possible long-term performance of the deep HDR reservoir at Hijiori, Japan. Simulation results showed that thermoelasticity could exert a significant influence on production temperature, injection pressure and water loss. For a multi-well geothermal system, thermoelasticity seemed to have a potential to cause the development of high flow rate/rapidly cooling flow paths (thermal short circuits). [Copyright &y& Elsevier]

Abstract: The temperature variation phenomenon during uniaxial deformation of materials with positive coefficient of linear thermal expansion is studied. The formula for a change in the specimen temperature during non-adiabatic tensile deformation is briefly derived. Thermomechanical behaviour of austenitic stainless steel, titanium and aluminium alloy during initial stage of tension at strain rates from 10−4 to 10−1 s−1 has been investigated. It was confirmed, that with increasing stress the temperature of each tested specimen first decreases linearly, reaches a minimum and then starts to rise. The decrease in the specimen temperature corresponds to elastic deformation whereas the temperature rise is related to the plastic one. Thus, the change in the specimen temperature can be used for study of elasto-plastic transition. From the viewpoint of strict theoretical analysis, the yield point will be defined as the stress corresponding to the lowest temperature, if tensile deformation process is adiabatic. The processes of deformation considered in this work are not adiabatic; there is a heat exchange between the specimen and the surroundings. The influence of this fact on the change in the specimen temperature vs. stress is discussed. The problem of yield point as the value of stress corresponding to minimum temperature of the specimen is considered. The influence of the strain rate on the yield point for tested materials is studied. Comparing of the obtained results with theoretical model, the limit above which the deformation process can be treated as the adiabatic one was determined. The values of the yield points determined on the basis of the thermoelastic effect were compared with the stress corresponding to the 0.2% of plastic strain. [Copyright &y& Elsevier]

Thermoelastic stress analysis (TSA) is now a well-known experimental technique providing information on the surface stress field in structures. Many studies have assessed the potential of the technique for a number of applications and some useful and detailed reviews of these investigations are available, focusing mainly on the experimental aspects related to the measurement of the thermoelastic signal. In this work, instead, a complete and detailed insight into the origins of the various forms of the equations describing the thermoelastic effect is given with reference to the concepts of the thermodynamic theory of a continuum. A discussion on the theory leading to the thermoelastic effect law is intended to give a useful overview of the applications and real limitations of TSA. [ABSTRACT FROM AUTHOR]

Light metals have high thermoelastic internal friction due to high coefficients of thermal expansion which has to be considered for various structural damping investigations. The thermoelastic effect of a powder metallurgically produced aluminium composite DISPAL™ and a magnesium casting alloy AZ91 (9 wt.% Al, 1 wt.% Zn) was investigated by measurements of the logarithmic decrement of free vibrations of bending beams. Because of inhomogenous stress distribution, a temperature gradient occurs between the compressed and the extended surface of the specimen, which leads to a transverse heat flow. This causes damping that is sensitive to the frequency of vibration. When the time of stress reversal equals the time necessary for heat flow from the compressed to the extended regions, a maximum of the logarithmic decrement occurs. The damping was measured as a function of the specimen thickness and the frequency of vibration ranging from 10 to 130 Hz. The frequency range was realised by both, a variation of the thickness and the mass at the end of the bending beams. By drawing the logarithmic decrement versus the product of the frequency and the quadratic thickness, a Debye peak is obtained which overlays all other damping mechanisms. The thermal diffusivity was calculated by determining the position of the maximum of the peak. The height of the peak, Young''s modulus and the specific heat of each sample were used to calculate the coefficient of thermal expansion of the specimens. The values agree, within the limits of scatter, with values measured by a dilatometer and taken from the literature, respectively. [Copyright &y& Elsevier]

[Display omitted] • A light-induced thermoelastic calibration method (TCM) was proposed. • The temperature effects on the resonance frequency of QEPAS was reported. • The proposed TCM improved the accuracy of resonance calibration by 2 orders. • TCM showed a shift of <0.3 ppm, with the temperature from 25.6 °C to 70.4 °C. • TCM can work with light intensity of only ~50 μW. A light-induced thermoelastic calibration method (TCM) was proposed for the temperature-compensated frequency calibration of quartz enhanced photoacoustic spectroscopy (QEPAS). The temperature effects on the resonance frequency of QEPAS was reported in traditional electrical calibration method (ECM) and TCM. With the temperature varying from 25.6 ℃ to 70.4 ℃, the resonance frequency calibrated by ECM shows a frequency shift of 36.6 ppm. The proposed TCM by using of light-induced thermoelastic wave to drive the resonance of quartz crystal tuning fork (QTF), improved the accuracy of resonance calibration by 2 orders, resulting in a frequency shift of ~ 0.3 ppm. Detailed research demonstrates the TCM is able to work with light intensity of only ~ 50 μW. It is indicated that TCM is a powerful tool for the temperature-compensation of resonance frequency of quartz tuning fork. [ABSTRACT FROM AUTHOR]

The thermoelastic behaviour of an unfractionated polystyrene was studied in the temperature interval 353–453 K in the regimes of isobaric cooling and of isothermal quasi-adiabatic loading, respectively. The main experimental results can be summarized as follows. 1. In the temperature interval far above the glass transition temperature Tg, both the temperature and volume relaxations of the polystyrene melt after sudden pressure jumps were completely reversible and proved to be simple exponential functions of the time. Therefore, by a straightforward application of Eqs (1) and (2) to the relevant thermoelastic data obtained in a single experimental run one can arrive at the reasonable values of the specific volume, specific heat capacity, thermal diffusivity and heat conductivity of the polymer in the equilibrium melt state. 2. In the temperature interval close to Tg, both the temperature and volume relations of the supercooled polystyrene melt in compression/expansion cycles became markedly asymmetric and non-exponential. The low values of the exponent β in the fractional-exponent Eq. (5) for the volume relaxation suggest a broad spectrum of relaxation times indicating the high degree of coupling between different mechanisms of the molecular motions involved. [ABSTRACT FROM AUTHOR]

A state-of-the-art thermographic system has been developed based on a 512×512 focal-plane array thermal imager. The system was primarily designed to perform stress analysis, but has applications in other areas where small cyclic temperature variations are encountered. A detailed analysis of its performance relative to an existing equipment (SPATE) revealed that, at least for low frequency applications, the proposed system out performs SPATE by some two to three orders of magnitude such that high-resolution area scans can now be achieved in minutes instead of hours. It is suggested that higher frequency applications (i.e., order of 10 Hz) can be achieved with more up-to-date imagers. [ABSTRACT FROM AUTHOR]

A state-of-the-art thermographic system has been developed based on a 512×512 focal-plane array thermal imager. The system, dubbed FAST (for focal-plane array for synchronous thermography) is able to deliver high-resolution full-field thermoelastic stress scans in minutes rather than hours. The paper itemizes the hardware components together with their functions. The digital signal processing required is described in detail as well as some of the problems encountered and how they were solved. Finally a thermoelastic image is displayed illustrating the capability of this system. [ABSTRACT FROM AUTHOR]