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International audience; Until now, the coupled stress and energy criterion has mainly been used in 2D applications, but it is possible to extend it to a 3D case. Herein the crack initiation in epoxy/aluminum bimaterial specimens under four point bending is predicted through a 3D numerical application of the coupled criterion. The stress and the energy conditions are computed by means of 3D finite element modeling of both undamaged and cracked specimens. The crack initiates at the epoxy/aluminum interface, meshes of the cracked specimens take into account the crack topology which is determined using the interface normal stress isocontours. By indirect confrontation to experimental tests on aluminum/epoxy bimaterial specimens of different width, the proposed approach allows determining the interface strength and fracture energy. The blind application of the proposed method to a crack initiation in aluminum/epoxy/aluminum specimens of different epoxy layer thickness under four point bending leads to a reasonable agreement with experimental data.

The paper presents the exact solution of the antiplane problem for an inhomogeneous bimaterial with the interface crack exposed to the normal load and cyclic loading by a concentrated force in the longitudinal direction. Using discontinuity function method the problem is reduced to the solution of singular integral equations for the displacement and stress discontinuities at the domains with sliding friction. The paper provides the analysis of the effect of friction and loading parameters on the size of these zones. Hysteretic behaviour of the stress and displacement discontinuities in these domains is observed.

The paper presents the exact analytic solution to the antiplane problem for a non-homogeneous bimaterial medium containing closed interfacial cracks, which faces can move relatively to each other with dry friction. The medium is subjected to the action of normal and arbitrary single loading in a longitudinal direction. Based on the discontinuity function method the problem is reduced to the solution of the system of singular integral-differential equations for stress and displacement discontinuities at the possible slippage zones. Influence of loading parameters and the effects of friction on the sizes of these zones is analyzed. The stress intensity factors, stress and displacement discontinuities, energy dissipation are determined for several characteristic types of external loading.

This work develops a series of Green’s functions for multi-phase Kirchhoff isotropic laminated plates. First, we derive the Green’s functions for a composite laminated plate composed of two bonded dissimilar isotropic laminated semi-infinite plates. Second, the obtained results for bimaterials are judiciously applied to obtain the Green’s function solution for a circular elastic inclusion embedded in an infinite isotropic laminated plate. Third, Green’s functions for a composite space composed of an arbitrary number of wedges of different isotropic laminated plates are derived. Finally, we derive Green’s functions for a laminated plate with an elliptical and a parabolic boundary, respectively. ASTAR (Agency for Sci., Tech. and Research, S’pore)

A novel method combining the experimental data at only two different mixed mode fractures and an empirical interface toughness function has been proposed to establish the interfacial toughness function of a bimaterial in submicron scale. The modified four-point bend specimen was used in experiment to evaluate the first type of mixed mode fracture, while the sandwiched cantilever specimen was employed to get the second one. An empirical interface toughness function reflecting quite accurately the delamination behavior was adopted as a typical one. The obtained results investigated that the proposed method could be used to calibrate not only the interfacial fracture criteria at pure modes but also at any mixed mode fracture of bimaterials in submicron scale.

A bimaterial resonant sensor(BRS) array consisting of 6 × 6 cells for uncooled infrared (IR) imaging was fabricated and tested. The resonance frequency of the BRS was found sensitive to temperature change due to IR radiation absorbed by the BRS. For comparison, four types of BRS cells with different configurations have been designed and fabricated. These BRSs exhibit a monotonic frequency response trend, approaching the theoretical prediction with Finite element method (FEM). The resonant frequency sensitivity was better than 181 Hz/K by electrical measurement.

The effect of thermal residual stresses in bimaterial structure with initial crack located near a sharp interface is discussed in this paper. Bimaterial compact tension (CT) specimen is used in the analysis, and the residual stresses are introduced by cooling of the specimen. The residual stresses affect the stress and strain fields near the crack tip, and the crack-driving force is different compared with that in the homogeneous material without residual stresses. This difference can be quantitatively expressed through an additional crack-driving force term—the material inhomogeneity term, Cinh. In this paper, it is evaluated using the post-processing procedure based on the concept of configurational forces, following a finite-element analysis. The results indicate that accurate numerical analysis of pre-cracked bimaterials should include the effect of thermally induced residual stresses. This effect cannot be neglected, even for bimaterials with homogeneous mechanical properties and inhomogeneity in thermal properties only (e.g. welded joints of ferritic and austenitic steel). Based on the obtained results, data from this study can be used in engineering practice to improve integrity and work safety of various inhomogeneous structures.

Green’s functions for transversely isotropic thermoelastic biomaterials are established in the paper. We first express the compact general solutions of transversely isotropic thermoelastic material in terms of harmonic functions and introduce six new harmonic functions. The three-dimensional Green’s function having a concentrated heat source in steady state is completely solved using these new harmonic functions. The analytical results show some new phenomena of temperature and stress distributions at the interface. The temperature contours are normal to the interface for the isotropic material but not for the orthotropic one. The normal stress contours are parallel to the interface at the boundary in the isotropic region only and shear failure is most likely at the heat source due to the highly degenerated direction of shear stress contours.

The transient motion of an anisotropic elastic bimaterial due to a line force or a line dislocation is studied. The bimaterial is assumed to be at rest and stress-free for t0. A formulation which is an extension to Stroh’s formalism for anisotropic elastostatics is employed. The general solution is expressed in terms of the eigenvalues and eigenvectors of a related eigenvalue problem. The method is used to obtain the analytic solutions without the need of performing integral transforms. Numerical examples of the GaAs bimaterial due to a line force or dislocation are presented for illustration.

The article of record as published may be found at http://dx.doi.org/10 .1117/1.OE.53.9.097103 One attractive option to achieve real-time terahertz (THz) imaging is a microelectromechanical systems (MEMS) bimaterial sensor with embedded metamaterial absorbers. We have demonstrated that metamaterial films can be designed using standard MEMS materials such as silicon oxide (SiOx ), silicon oxinitrate (SiOx Ny ), and aluminum (Al) to achieve nearly 100% resonant absorption matched to the illumination source, providing structural support, desired thermomechanical properties and access to external optical readout. The metamaterial structure absorbs the incident THz radiation and transfers the heat to bimaterial microcantilevers that are connected to the substrate, which acts as a heat sink via thermal insulating legs, allowing the overall structure to deform proportionally to the absorbed power. The amount of deformation can be probed by measuring the displacement of a laser beam reflected from the sensor’s metallic ground plane. Several sensor configurations have been designed, fabricated, and characterized to optimize responsivity and speed of operation and to minimize structural residual stress. Measured responsivity values as high as 1.2 deg ∕μW and time constants as low as 20 ms with detectable power on the order of 10 nW were obtained, indicating that the THz MEMS sensors have a great potential for real-time imaging. NCMR

In this study, based on multipole expansion method an analytical treatment is presented for the anti-plane scattering of SH-waves by an arbitrarily oriented elliptic cavity/crack which is embedded near the interface between exponentially graded and homogeneous half-spaces. The cavity is embedded within the inhomogeneous half-space. The boundary value problem of interest is solved by constructing an appropriate set of multipole functions which satisfy (i) the governing equation in each half-space, (ii) the continuity conditions across the interface between the two half-spaces, and (iii) the far-field radiation and regularity conditions. The analytical expressions for the scattered elastodynamic fields are derived and the dynamic stress concentration factor associated with the elliptic cavity as well as the dynamic stress intensity factor relevant to the case of a crack are calculated. In the given numerical examples, the effects of such parameters as the incident wave number, angle of the incident waves, the distance of the cavity to the bimaterial interface, and the aspect ratio and the orientation of the elliptic cavity/crack on the scattered field are addressed in detail. It is seen that such parameters have significant effect on the dynamic response of the medium. (C) 2018 Elsevier Ltd. All rights reserved.

Novel thermo-mechanical detector arrays with integrated diffraction grating for optical readout were designed and fabricated. Parylene was used as the structural material due to its high thermal isolation and mismatch properties. Calculations reveal that the NETD performance of a thermo-mechanical array using Parylene can be significantly better than SiNx based designs and offer a theoretical NETD value, Aselsan Inc; Scientific and Technological Research Council of Turkey (TÜBİTAK); Turkish Academy of Sciences (TÜBA) - GEBİP Distinguished Young Scientist Award

A stable numerical algorithm is presented for an elastostatic problem involving a crack close to and in front of an inclusion interface. The algorithm is adaptive and based on an integral equation of Fredholm’s second kind. This enables accurate analysis also of rather difficult situations. Comparison with stress intensity factors of cracks close to straight infinite bimaterial interfaces are made.

Following a review of the processing of functionally graded metals and metal-ceramic composites in Part 1; this Part 2 of the two part series focuses on the thermomechanical behaviour. The paper begins with an overview of the fundamentals of thermoelastic and thermoplastic deformation in metal-ceramic composites. Various approaches, including the rule of mixture approximations, mean field theories, crystal plasticity models, discrete dislocation models, and continuum finite element formulations of the constitutive phases of the composites, are discussed, and the significance and limitations of these approaches are highlighted. Issues specific to the thermomechanical analyses of graded materials are then addressed. It is reasoned that the introduction of a new length scale to the problem due to compositional gradients inevitably calls for detailed micromechanical analyses of the size, shape, continuity, and spatial dispersions of the constituent phases of graded metal-ceramic composites. Models for the thermal, elastic, and plastic deformation of graded multilayers are then presented within the context of classic beam and plate theories, in conjunction with strategies for developing 'design diagrams' for thermomechanical performance. Methods to identify the conditions governing the onset of instability and abrupt shape changes due to large deformation in graded multilayers are also provided. The macroscopic continuum analyses are followed by discussions of micromechanics simulations of the real microstructural dispersions by recourse to computational models which invoke von Mises type and crystal plasticity theories. Experimental methods to assess the validity of such models are then examined, along with typical results of processing induced internal stresses and thermal stresses arising from temperature excursions in model systems with gradients in metal-ceramic concentrations. It is demonstrated that stepwise or continuously graded metal-ceramic composites can be designed to improve interfacial bonding between dissimilar solids, to minimise and optimally distribute thermal stresses, to suppress the onset of plastic yielding, to mitigate the deleterious effects of singular fields at free edges of multilayers where interfaces intersect free surfaces, to reduce the effective driving force for fracture, and to arrest cracks.