Search

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]

Highlights: [•] We reconstruct heat sources from temperature fields using a derivative Gaussian filter. [•] Synthetic temperature fields corrupted by noise enabled us to optimise the filter. [•] The influence of both the dimension and the level of a localised heat source is discussed. [•] Experimental fields on aluminium plates heated by electric patches were processed. [•] The relevancy of the filter to reliably reconstruct heat source fields is demonstrated. [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]

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]

This paper presents a calorimetric approach to the measurement of mechanical dissipation in specimens subjected to cyclic tensile tests. Mechanical dissipation, that is, the heat power produced by the material due to mechanical irreversibility, can potentially be deduced from the temperature changes captured on the specimen surface by infrared thermography. However, a difficulty arises for long-term cyclic tests: Results are easily skewed by any change in the specimen's environment. The problem is amplified by the fact that mechanical dissipation is in general small compared to the heat sources associated with thermomechanical couplings, making its estimation difficult. The paper proposes a simple procedure to extract a well-resolved estimation of mechanical dissipation by solving two key points specific to long-term cyclic tests: (a) the reduction of the parasitic effects associated with changes in the specimen's environment by using a specific device based on two references samples and (b) the choice of relevant thermal data acquisition parameters. A test is performed on a copper-based shape-memory alloy whose calorific response comprises three origins of heat sources: thermoelastic coupling, phase transformation, and mechanical irreversibility. The results obtained demonstrate the relevancy of the approach in extracting mechanical dissipation from the thermal response of the specimen subjected to long-term tensile tests in fatigue. [ABSTRACT FROM AUTHOR]

This study aims at characterizing heat sources during the deformation of the crack tip zone in carbon black filled Styrene Butadiene Rubber (SBR). For this purpose, the thermomechanical response of cracked specimens was investigated using coupled full thermal and kinematic field measurements and a suitable motion compensation technique. The kinematic analysis enabled us to define the zone of influence of the crack and to measure the maximum stretch ratio level. The maximum stretch ratio level at the crack tip is higher than that measured at specimen failure during uniaxial tensile tests, which can be explained by considering the maximum chain extensibility. The calorimetric analysis shows that the high heat source gradient zone is very much more confined than the high temperature gradient zone. The heat sources at the crack tip remain positive and small during unloading, which indicates that mechanical dissipation is high and confined to the crack tip. This result highlights that the material behaves very differently in the crack tip zone compared to homogeneous tests. This proves that it not possible to predict the behavior of the crack tip zone from homogeneous tests. Moreover, it is observed that the mechanical dissipation decreases with the number of first cycles, which highlights the fact that the material is increasingly accommodated. This study provides the first accurate measurement of heat sources at the crack tip of rubber, constituting a new experimental tool in the fracture mechanics of rubber. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the calorimetric analysis of deformation processes in filled styrene-butadiene rubbers. More especially, the study focuses on the effects of the addition of carbon black fillers on the calorimetric response of “demullinized” SBR. Temperature variations are measured by infrared thermography during cyclic uniaxial tensile tests at ambient temperature. Heat sources 1 [1] The term heat source is used in this paper to mean the heat power being produced or absorbed. produced or absorbed by the material due to deformation processes are deduced from temperature fields by using the heat diffusion equation. First, the results show that no mechanical (intrinsic) dissipation is detected for weakly filled SBR, meaning that the heat produced and absorbed over one mechanical cycle is the same whatever the stretch ratio reached. Second, the mechanical dissipation in highly filled SBR is significant. The quantitative analysis carried out highlights the fact that it increases quasi-linearly with the stretch ratio. Finally, a simplified framework is proposed to discuss the identification of the heat sources, in particular the mechanical dissipation. [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]