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The aim of this study was to determine the interest in and relevance of the use of infrared thermography, which is a non-invasive full-field surface temperature measurement technique, to characterize the heterogeneous heating caused by ultrasound in biological tissue. Thermal effects of shear wave elastography, pulse Doppler and B-mode were evidenced in porcine tissue. Experiments were performed using a high-frequency echography Aixplorer system (Supersonic Imagine, Aix-en-Provence, France). For all three modes, ultrasound was applied continuously for 360 s while the temperature at the sample surface was recorded with a Cedip Jade III-MWIR infrared camera (Flir, Torcy, France). Temperature changes were detected for the three modes. In particular, "heat tunnels" crossing the sample were visualized from the early stages of the experiment. Heat conduction from the transducer was also involved in the global warming of the sample. The study widens the prospects for studies on tolerability, potentially in addition to classic approaches such as those using thermocouples., (Copyright © 2019 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Infrared (IR) thermography was used to analyze the thermomechanical response of a two-dimensional non-cohesive granular assembly. Two constitutive materials with different types of thermoelasticity were chosen: thermoplastic polyurethane (TPU) and polyoxymethylene (POM), which feature entropic and isentropic elasticity respectively. Cylinders of each material were mixed together. Analysis was performed under confined compression at two observation scales. Thermoelastic couplings and interparticle friction were separately evidenced. First, the strong thermal effect of entropic coupling was revealed at the contacts, in the stress concentration zones. Second, image processing enabled us to clearly extract the thermal signature of the interparticle friction zone, a quantity that cannot be identified by the other full-field measurement techniques available today. It can thus be claimed that IR thermography provides two distinct routes for the analysis of granular materials by distinguishing the reversible and irreversible parts from the global thermomechanical response. The study also opens prospects for the experimental analysis of “soft” granular media. [ABSTRACT FROM AUTHOR]

This paper presents a post-processing technique for noisy temperature maps based on a gradient anisotropic diffusion (GAD) filter in the context of heat source reconstruction. The aim is to reconstruct heat source maps from temperature maps measured using infrared (IR) thermography. Synthetic temperature fields corrupted by added noise are first considered. The GAD filter, which relies on a diffusion process, is optimized to retrieve as well as possible a heat source concentration in a two-dimensional plate. The influence of the dimensions and the intensity of the heat source concentration are discussed. The results obtained are also compared with two other types of filters: averaging filter and Gaussian derivative filter. The second part of this study presents an application for experimental temperature maps measured with an IR camera. The results demonstrate the relevancy of the GAD filter in extracting heat sources from noisy temperature fields. [ABSTRACT FROM AUTHOR]

This paper provides the first characterization of heat source field in the crack tip zone in carbon black filled natural rubber (NR). It focuses more especially on the calorific effects of strain induced crystallization (SIC). For this purpose, full thermal and kinematic fields are measured simultaneously. Initial image processing based on motion compensation enables us to track the temperature of any material point at the specimen surface. A second image processing stage, based on the heat diffusion equation, enables us to obtain the fields of heat sources produced and absorbed by the material during the test. The heterogeneity of the stretch states is analyzed from the kinematic measurements. In terms of heat production, crystallization acts in two opposite ways in the crack tip zone: the crystallization process produces additional heat, but crystallites act as fillers, which increases material stiffness in the crack tip zone. Moreover, the heat sources in the crack tip zone remain positive and small during unloading. This phenomenon is due to the production of mechanical dissipation and probably a continuation of the crystallization process. The results attained are compared with those recently obtained in non-crystallizing carbon black filled styrene butadiene rubber (SBR50). [ABSTRACT FROM AUTHOR]

The high reversibility of the martensitic transformation occurring in shape-memory alloys (SMAs) is at the origin of the mechanical performance of these materials. Infrared thermography is employed in this study to measure the mechanical dissipation produced by Cu–Zn–Al SMA specimens during stress-induced phase transformation. In practice, temperature change is first measured on the surface of a specimen subjected to cyclic mechanical loading at constant ambient temperature. The heat produced by the material can then be deduced from the temperature change by using the heat diffusion equation. The heat associated to mechanical irreversibility is expected to be very low compared to the other heat quantities produced by the material (such as the latent heat due to phase change and the heat due to thermoelastic coupling), so measuring this quantity requires special attention, as emphasized in this paper. The procedure which enables us to extract the mechanical dissipation from the measured heat source is first presented. The technique is then applied to two types of specimens: martensitic and austenitic. Different values of mechanical dissipation were measured, thus revealing different levels of mechanical irreversibility. [ABSTRACT FROM AUTHOR]

Abstract: This study aims at revealing martensitic microstructures that exist in a shape-memory alloy. Infrared thermography was used for this purpose. Experiments were performed on a Cu–Al–Be single crystal which features a pseudoelastic response at ambient temperature. The specimen was first partially transformed to martensite by mechanical loading. Then a small cyclic loading was applied while the temperature evolution on the specimen surface was captured by an infrared camera. Thermal images obtained were then processed to extract two types of quantities: the maps of heat sources produced by the material and the maps of temperature oscillation amplitudes. Two thermomechanical couplings are revealed: the thermoelastic coupling and the latent heat due to the small cyclic movement of austenite–martensite interfaces, thus highlighting the martensitic microstructure distribution in the specimen. [Copyright &y& Elsevier]

The aim of this work is to observe and to analyze various phenomena that exist in a multiphase ceramic material subjected to cyclic compressive loads. An infrared camera is used for this purpose. The material under study is an andalusite-based low-cement castable, which exhibits a pre-existing diffused damage (microcracks and debonded interfaces) before mechanical testing. The temperature variation in the specimen during the tests is investigated both at a macroscopic scale and a mesoscopic scale. In the first case, the material compaction, the thermoelastic coupling and the temperature increase due to mechanical dissipation are clearly evidenced. In the second case, local temperature variations related to microcracks are observed. The technique used and the results obtained are described and discussed in the paper. [ABSTRACT FROM AUTHOR]

This paper deals with the determination of the thermal response of elastomeric materials subjected to cyclic loading. In this case, the material undergoes large deformations, so a suitable motion compensation technique has been developed to track the material points and their temperature during the test. Special attention is paid to the Narcissus effect and to the detector matrix of the infrared camera used in the study. Heat sources are then derived from the temperature maps. The thermoelastic inversion phenomenon has been experimentally evidenced during a cyclic test performed on an elastomeric notched specimen. The heat source distribution close to the crack tip has also been deduced from the temperature maps, thus highlighting the relevance of the approach. [ABSTRACT FROM AUTHOR]

Abstract: The low cycle fatigue behaviour of the 2024-T3 aluminium alloy is examined in this paper in terms of both thermal measurements provided by an infrared camera and an energetic analysis performed with a suitable data processing. Oscillating variations of temperature are mainly due to the thermoelastic coupling. During the transient loading leading to the maximum stress value (higher than the yield stress of the material), sudden increases in temperature are observed. The heat sources produced by the material are assessed using the heat diffusion equation after an in-house filtering method. The mechanical dissipation attributed mainly to plastic strain is then estimated and the cumulative plastic damage is calculated by the temporal integral of it. Plastic damage fields are analysed for two geometries of specimens in order to underline structural effects and to study the initial damage state of the specimen before the steady-state cyclic loading. [Copyright &y& Elsevier]

Abstract: The objective of the study is to analyze the martensitic microstructure evolution in a shape-memory alloy during a stress-induced transformation. Two full-field measurement techniques are used for this purpose: the grid method to obtain strain maps and infrared thermography to measure temperature variation maps at the same time. The specimen is a monocrystalline Cu–Al–Be alloy which is austenitic at ambient temperature. Austenite progressively transforms into martensite during the mechanical loading and the impact of this transformation in terms of strain and temperature is analyzed in this paper. The spatial resolution of the strain maps obtained enables us to distinguish some typical martensitic microstructures such as martensite needles, habit planes and X-shaped microstructures, so the evolution of these microstructures during the test is presented and discussed with strain maps obtained at some points regularly spaced on the stress–strain curve. Infrared thermography provides some additional information to analyze the transformation phenomena. Maps of latent heat are calculated from temperature maps thanks to a specific post-processing procedure. Interestingly, the microstructure evolution during the loading phase is found to be different of the evolution during the unloading phase although the specimen precisely returns to zero strains at the end of the cycle. In the last part of the paper, the values of the measured in-plane strain components are used to identify the martensite variants that likely appear in the specimen during the loading phase of the test. This identification is based on some crystallographic compatibility calculations. [Copyright &y& Elsevier]

Abstract: Two different full-field measurement techniques were used in this study to investigate the mechanical response of an aluminium multicrystal specimen subjected to a tensile test. The experimental setups corresponding to each of the two techniques are first described. Strain fields were obtained with the grid method, to which a recent image treatment procedure was applied. This procedure leads to a high spatial resolution in strain and provides an accurate description of the plasticity that occurs in grains. Heat sources were derived from temperature maps captured with an infrared camera. Some typical strain maps are shown and significant heterogeneities clearly appear. These strain maps are also compared with their numerical counterparts, obtained using a finite element package suitable for crystal plasticity. The calculation of the heat source distributions from the raw temperature maps is then addressed. The strain, displacement and heat source maps were then processed together to estimate the fraction of anelastic power converted into dissipated power. This quantity was determined over the whole gauge section of the specimen and also for three individual grains. [Copyright &y& Elsevier]

Shape memory alloys (SMAs) are promising mechanocaloric materials for the creation of innovative heating/cooling systems. The present paper proposes a simple concept of "porous" SMA material in the form of a two-dimensional (2D) "granular" system. The basic idea is to place SMA cylinders in parallel and in contact, thus creating a 2D granular material, with fluid circulation in the third dimension (i.e. in the longitudinal direction of the cylinders). The study is dedicated to the validation of the mechanocaloric character of such a material system subjected to confined compression. First, experiments were conducted using superelastic nickel-titanium rods of various diameters, enabling us to create different bidispersity levels for the granular medium. Infrared thermography was used to analyze the temperature changes within the cylinders. Second, air was used as the circulating fluid for the sake of concept validation. Comparison between different levels of bidispersity of the granular system showed that a nearly-monodisperse configuration could be advantageous to optimize the concept. • Superelastic SMA cylinders were placed in parallel to create a 2D granular system. • Ni–Ti rods of varying diameters were used to create bidisperse configurations. • Mechanocaloric response under confined compression was validated by IR thermography. • Air was used as a fluid circulating in the longitudinal direction of the SMA rods. • A nearly-monodisperse configuration appears to be a relevant compromise. [ABSTRACT FROM AUTHOR]