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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]

Abstract: Coherent stress-free (CSF) microstructures with specific morphologies are favored in shape memory alloys (SMAs) when special relations are satisfied by the lattice parameters. Experimentally observed microstructures are, however, also formed at non-exact CSF conditions. Here we propose a framework for the investigation of almost compatible (i.e. non-perfectly CSF) twinned wedges in SMAs, and make a systematic study of these microstructures for two types of symmetry-breaking martensitic transformations. We determine the domains in lattice-parameter space wherein there exist, and coexist, different families of almost compatible wedges with low overall stress. We find these to be wide regions largely unrelated to the existence of special CSF relations, if any even exist, giving stress-free configurations. We propose SMA improvement can be obtained by targeting domains in lattice-parameter space wherein, besides satisfying other suitable properties, a maximum number of almost compatible microstructures can also form in the material. We develop this approach for wedges in SMAs undergoing the cubic-to-orthorhombic transformation. [Copyright &y& Elsevier]

Abstract: The paper deals with the lifetime prediction of aluminium structures reinforced with composite patches. Load-controlled fatigue tests have been carried out on 2024-T3 aluminium specimens. First the scatter of aluminium fatigue properties is analysed. Damaged holed structures are then patched and their experimental fatigue behaviour is compared to the fatigue response of unpatched specimens. It is shown that the adhesive governs the fatigue response of the reinforced specimens for high load levels. A lifetime prediction method is then developed to assess the residual lifetime of damaged reinforced structures. The method is based on the intrinsic material fatigue properties and on the damage level attained when the aluminium specimens are reinforced with composite patches. Finally a comparison between experimental and theoretical results is performed. It is observed that the Mesmacque sequential law gives the most accurate lifetime prediction of the reinforced aluminium specimens. [Copyright &y& Elsevier]

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: This paper deals with the calorimetric analysis of deformation processes in natural rubber. Infrared thermography is first used to measure the temperature evolution of specimens under quasi-static uniaxial loading at ambient temperature (see Part 1). Then the heat sources produced or absorbed by the material due to deformation processes are deduced from the temperature variations by using the heat diffusion equation. Different main results are obtained from cyclic and relaxation tests. First, no mechanical dissipation (intrinsic dissipation) is detected during the material deformation. Second, strain-induced crystallization leads to significant heat production, whereas the melting of crystallites absorbs the same heat quantity with different kinetics. This difference in kinetics explains the mechanical hysteresis. Finally, relaxation tests show that crystallite melting does not systematically occur instantaneously. [Copyright &y& Elsevier]

Abstract: This paper investigates the mechanisms of deformation in rubber, especially stress-induced crystallization, using infrared thermography. Temperature variations are measured during cyclic uniaxial mechanical tests at ambient temperature. Results show that natural rubber mainly exhibits entropic behaviour: the material produces (resp. absorbs) heat during loading (resp. unloading). The crystallization of the polymer chains under tension leads to a temperature increase of the order of several degrees Celsius. If crystallization and crystallite melting occur over one mechanical cycle, a hysteresis loop is observed in terms of the strain–stress relationship. Stress relaxation tests show that the thermal signatures of crystallization and of crystallite melting are different. Indeed, if the strain is maintained fixed during loading, the temperature continues to increase for a few seconds before returning to the ambient temperature. This reveals that crystallization continues during relaxation. On the contrary, if the strain is maintained fixed during unloading, the specimen returns instantaneously to the ambient temperature. [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: The aim of this paper is to provide some solutions for the stress distribution in rectangular composite patches under in-plane loading. Two different cases are considered: normal stresses and shear stresses. The stress distributions in the patch, the adhesive and the substrate show evidence of some bidirectional effects, which are not accounted for by usual unidirectional solutions available in the literature. [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]

Abstract: This paper deals with the identification of constitutive parameters of a Mooney model suitable for hyperelastic materials. These parameters are retrieved from a multiaxial mechanical test that gives rise to heterogeneous stress/ strain fields. Since no analytical relationship is available between measurements and unknown parameters, a suitable tool, namely the virtual fields method, is developed in case of large deformations and used to identify these unknowns. Several results obtained with numerical simulations and experiments performed on rubber specimens illustrate the approach. [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]