Search

This study aimed at evaluating the effects of different surface conditionings on the microshear bond strength (µSBS) of a self-adhesive resin cement to VITA Suprinity (ZLS) and IPS e.max CAD (LD). Three surface conditioning protocols were performed on ZLS and LD before luting with a self-adhesive resin cement (RelyX Unicem 2, RXU): hydrofluoric acid (HF), HF + silane (HF + S), or Monobond Etch &amp, Prime (EP). In each group, 15 cylindrical buildups of RXU were prepared on five milled bars and submitted to a µSBS test. Data were statistically analyzed with two-way ANOVA and Tukey’s post hoc test (p &lt, 0.05). Failure modes were recorded and classified as adhesive, mixed, cohesive in resin, or ceramic, and statistically analyzed with Fisher’s exact test (p = 0.05). One additional bar per group was used for the morphological characterization of the conditioned surface by means of SEM. The material per se did not significantly influence adhesion (p = 0.744). Conditioning protocol was a significant factor: EP yielded significantly higher μSBS than HF (p = 0.005), while no significant differences emerged between EP and HF + S (p = 0.107), or HF + S and HF (p = 0.387). The material-conditioning protocol interaction was not statistically significant (p = 0.109). Significant intergroup differences were found in distribution of failure modes: mixed failures were predominant in the ZLS/EP group, while the other groups showed a prevalence of adhesive failures. The self-etching primer showed promising results in terms of immediate bond strength of a self-adhesive resin cement to lithium-silica-based glass ceramics, suggesting its alternative use to hydrofluoric acid and silane conditioning protocols.

In the present work, Crack-Free pure copper parts with relative densities exceeding 98% are processed by selective laser melting (SLM) using a high-power fiber laser. The influence of different laser scan parameters such as hatch spacing, laser power and scan speed on the texture evolution in the manufactured parts is determined. On the top surfaces, a clear interrelationship between laser scan parameters and crystallographic texture is established. This shows that the texture at the top surface can be very strong especially when a high laser power and a low scanning speed is used. However, a random texture exists in the core of the sample due to successive re-melting and altered heat gradients induced by the application of a 90° scan rotation between subsequent layers. A maximum electrical conductivity of 88% of the International Annealed Copper Standard (IACS) is achieved in the as-built state. Damage to the optical mirror of the SLM machine is observed and recommendations for sustainable up-scalability are proposed. ispartof: JOURNAL OF MATERIALS PROCESSING TECHNOLOGY vol:270 issue:August 2019 pages:47-58 status: published

OBJECTIVE To investigate the influence of opacity and color of luting cements on the final shade of metal-free restorations. MATERIALS AND METHODS Five resin cement colors in combination with four different thicknesses of CAD/CAM ceramic materials were tested, and a composite substrate was used as dentin color reference (n = 3). Specimen color was measured with a spectrophotometer equipped with an integrating sphere before and after cementation (CIELAB). Cement and ceramic color and opacity (TP) were assessed by measuring the tested ceramic thickness as a 1-mm thick disk for each of the cement shades. The differences in color were evaluated (ΔE00 ). Data were statistically analyzed by a Two-Way ANOVA followed by the Tukey Test for post-hoc comparison (P 0.6) in case of mismatch between color and translucency of cement and ceramic. Only the clear shade in combination with the thickest ceramic, resulted in an imperceptible color change (ΔE00 = 0.69 ± 0.54). CONCLUSIONS The final shade of ceramic restorations can be influenced by resin cements; the magnitude of influence is related to the cement optical properties. CLINICAL SIGNIFICANCE In order to influence the final shade of a ceramic restoration, a cement more opaque than the restorative material should be used. Conversely, in the case of a fitting shade of the restoration, a cement more translucent than the restoration should be used to avoid undesired changes.

The properties of RbBi$_2$, a 4.15 K superconductor, were investigated using magnetic field, pressure and neutron diffraction. Under hydrostatic pressure, an almost 50 % reduction of T$_c$ is observed, linked to a low Debye temperature estimated at 165 K. The resistivity and magnetic susceptibility were measured on quenched and slow-cooled polycrystalline samples. The resistivity follows a low temperature power-law dependence in both types of samples, while the diamagnetic susceptibility, $\chi$, is dependent on the sample cooling history. Slow-cooled samples have a $\chi= -1$ while quenched samples have $\chi< -1$ due to grain size differences. Evidence of the effects of the cooling rate is also discerned from the local structure, obtained by neutron diffraction and the pair density function analysis. Slow-cooled samples have structurally symmetric Bi hexagons, in contrast to quenched samples in which disorder is manifested in periodic distortions of the Bi hexagonal rings of the kagome sublattice. Disorder may lead to flux pinning that reduces vortex mobility, but T$_c$ remains unaffected by the cooling rate., Comment: 6 pages including References, 3 figures

Ductile isotropic materials are widely used in protective systems against transient pulse pressure loads, such as those of localised blasts. This is due to the combined elastic-plastic response which contributes to dissipation of total impulse from extensive loading as the energy stored elastically limits deformation while the energy expended plastically limits the level of transferred forces in the structure. In the case of thin, modern armour graded steel plates, the tailored metallurgy helps the structure store energy within the bounds of elastic region, which may be dissipated at a later stage as damping kills it off in subsequent cycles. On the other hand, the plastic work is almost entirely converted to heat and dissipates. The present work focuses on the elastic and plastic energies in the membrane and aims at deducing, from the minimization of Föppl-Von-Kármán (FVK) energy functional combined with enforcing the constitutive relations of limit analysis, the dynamic elastic-plastic response of localised blast loaded square membranes undergoing large deformations. The presumed blast load function is a multiplicative decomposition of a prescribed continuous piecewise smooth spatial function and an arbitrary temporal function which may assume various temporal shapes (e.g. rectangular, linear, exponential). Considering the elastic response, a single-degree-of-freedom model was developed from the prescribed displacement field and associated stress tensor having clamped and simply supported boundary conditions. The explicit closed form solutions were sought by using the Ritz-Galerkin’s variational method as well as the Poincaré-Lindstedt perturbation method. The theoretical solutions of rigid-perfectly plastic square membranes subjected to the same blast scenarios were then discussed. From the combined effects we deduce the load displacement curves representing the trajectory of the nonlinear elastic-perfectly plastic structure.

In this article, the laser-based powder bed fusion (L-PBF) processing behavior of pure copper powder is evaluated by employing a conventional infrared fiber laser with a wavelength of 1080 nm, a small focal spot diameter of 37.5 µm, and power levels up to 500 W. It is shown that bulk solid copper parts with near full density (ρ Archimedes = 99.3 ± 0.2%, ρ Optical = 99.8 ± 0.1%) can be produced using a laser power of 500 W for the chosen combination of powder particle size, L-PBF settings, and pure copper baseplate. Moreover, at 500 W, parts with a relative density exceeding 99% are manufactured within a volumetric energy density window of 230–310 J/mm3, while laser power levels below 500 W did not produce parts with a relative density above 99%. An analytical model is used to elucidate the L-PBF processing behavior, wherein both conduction and keyhole regimes corresponding to the employed L-PBF settings are identified. The analytical model-based results predict that the bulk solid copper parts with near full density are produced in a keyhole regime prior to the onset of keyhole-induced porosity, which is in accordance with the porosity types observed in the parts. The L-PBF fabricated copper parts exhibit an electrical conductivity of 94 ± 1% compared to the international annealed copper standard (IACS) and demonstrate a tensile strength of 211 ± 4 MPa, a yield strength of 122 ± 1 MPa, and an elongation at break of 43 ± 3% in the as-built condition. ispartof: Additive Manufacturing vol:42 pages:1-15 status: Published online

Understanding the deformation mechanisms of hexagonal close-packed (HCP) polycrystals at the grain scale is crucial for developing both macro and micro scale predictive models. Slip and twinning are the two main deformation mechanisms of HCP polycrystals at room temperature. In this paper, the development of grain-level stress tensors during nucleation and growth of twins is investigated. A pure zirconium specimen with HCP crystals is deformed in-situ while the centre-of-mass, orientation, elastic strain, and stress of individual grains are measured by three-dimensional synchrotron X-ray diffraction (3D-XRD). The observed microstructure is subsequently imported into a crystal plasticity finite element (CPFE) model to simulate the deformation of the polycrystal. The evolution of stress in twin-parent pairs at the early stages of plasticity, further into plasticity zone, and unload is studied. It is shown that twins do not relax very much at the nucleation step, but the difference between the measured stress in the twin and parent increases further into plastic zone where twins relax. While at the early stages of plasticity all six twin variants are active, a slightly better estimation of active variants is obtained using the measured grain-resolved stress tensors. Discovery Grant from the Natural Sciences and Engineering Research Council of Canada (NSERC).

In the present study, the synthesis of superparamagnetic collagen-based nanocomposite hydrogels with tunable swelling, mechanical and magnetic properties is reported. The fabrication strategy involved the preparation of pristine collagen type-I hydrogels followed by their immersion in highly stable aqueous solutions containing pre-formed double-layer oleic acid-coated hydrophilic magnetite nanoparticles (OA.OA.Fe3O4) at different concentrations, to interrogate nanoparticles' deposition within the 3D fibrous collagen matrix. Besides the investigation of the morphology, composition and magnetic properties of the produced materials, their mechanical properties were experimentally evaluated under confined compressive loading conditions while an exponential constitutive equation was employed to describe their mechanical response. Moreover, the deposition of the nanoparticles in the collagenous matrix was modeled mathematically with respect to the swelling of the gel and the effective stiffness of the matrix. The model recapitulated nanoparticle diffusion and deposition as well as hydrogel swelling, in terms of nanoparticles' size and concentration of OA.OA.Fe3O4 aqueous solution.

Extensive shock and highly localised blast waves generated by detonation of near field explosives (such as improvised explosive devices (IEDs)) are catastrophic to structures and humans, resulting in injury or death, progressive damage, or perforation through the structure and collapse. Mitigating the effects of such waves is paramount in various aspects of design engineering. A theoretical model is presented here to predict the large inelastic deformation of ductile thin square membranes induced by a generic, short pulse pressure load, comprising a piecewise function of spatial and temporal parts. Using the constitutive framework of limit analysis and incorporating the influence of finite displacements, two patterns of kinematically admissible, time dependent velocity profiles were investigated. These patterns included stationery and moving plastic hinges. The results were investigated in two cases: once with the interaction between bending moment and membrane forces retained in the analyses, and then when the response was solely governed by membrane forces. For blast loads of high magnitude, the pressure was replaced by an impulsive velocity and the results were expressed in terms of dimensionless form of initial kinetic energy. The effects of boundary conditions and visco-plasticity have also been investigated. The theoretical results corroborated well with various experimental results in the literature, on ductile metallic plates such as high strength ARMOX steel and mild steel.

The local atomic structure of the non-magnetic layered superconductor Bi4O4S3 was investigated using neutron diffraction and pair density function (PDF) analysis. Although on average, the crystal structure is well ordered, evidence for local, out–of–plane sulfur distortions is provided, which may act as a conduit for charge transfer from the SO4 blocks into the superconducting BiS2 planes. In contrast with LaO1−xFxBiS2, no sulfur distortions were detected in the planes, which indicates that charge density wave fluctuations are not supported in Bi4O4S3.

The Fe vacancy and its ordering pattern is a unique property of the A x Fe2−y Se2 (A = K, Rb, Cs) superconductors. Below the structural transition temperature T S ∼ 550 K, the system phase separates into the I4/mmm phase with no Fe vacancy and the I4/m phase with the $\sqrt 5\times \sqrt 5\times 1$ vacancy order. In this work, an Ising-like Hamiltonian defined on the Fe-sublattice is constructed and employed in a Metropolis Monte Carlo simulation to study the Fe vacancy order and the domain distribution under different thermal treatments. A third phase with randomly distributed Fe vacancies and space group I4/mmm is observed in the simulation. The response of the volume fraction of this simulated phase under thermal treatment shows a direct connection to the change of the superconducting shielding fraction under annealing and quenching processes, indicating a close relation between the vacancy disordered I4/mmm phase and the superconducting phase.

Four point bending end notched flexure (4ENF) tests were used to evaluate the mode II fracture toughness ( G IIC ) of glass fibre reinforced vinyl-ester (GFRP) specimens in order to expose the sensitivity of G IIC to loading rate. Tests were carried out at load displacement rates ranging from 1 to 6000 mm/min. Finite element models were used to evaluate the correction factors that are required during data reduction in order to compensate for geometrical non-linearity in the test. A high speed video camera was used in conjunction with the digital image correlation technique to measure crack propagation during the tests. It was found that, for short crack lengths, G IIC tended to increase as loading rate was increased.

Objectives: To assess shear bond strength and failure mode (Adhesive Remnant Index, ARI) of orthodontic brackets bonded to polymethylmethacrylate (PMMA) blocks for CAD-CAM fabrication of temporary restorations, following substrate chemical or mechanical treatment. Methods: Two types of PMMA blocks were tested: CAD-Temp® (VITA) and Telio® CAD (Ivoclar-Vivadent). The substrate was roughened with 320-grit sandpaper, simulating a fine-grit diamond bur. Two universal adhesives, Scotchbond Universal Adhesive (3M ESPE, SU) and Assure Plus (Reliance, AP), and a conventional adhesive, Transbond XT Primer (3M Unitek, XTP, control), were used in combination with Transbond XT Paste (3M Unitek) to bond the brackets. Six experimental groups were formed: 1) CAD-Temp®/SU; 2) CAD-Temp®/AP; 3) CAD-Temp®/XTP; 4) Telio® CAD/SU; 5) Telio® CAD/AP; 6) Telio® CAD/XTP. Shear bond strength and ARI were assessed. On 1 extra block for each PMMA-based material surfaces were roughened with 180-grit sandpaper, simulating a normal/medium-grit (100 μm) diamond bur, and brackets were bonded. Shear bond strengths and ARI scores were compared with those of groups 3, 6. Results: On CAD-Temp® significantly higher bracket bond strengths than on Telio® CAD were recorded. With XTP significantly lower levels of adhesion were reached than using SU or AP. Roughening with a more coarse bur resulted in a significant increase in adhesion. Conclusions: Bracket bonding to CAD-CAM PMMA can be promoted by grinding the substrate with a normal/medium-grit bur or by coating the intact surface with universal adhesives. With appropriate pretreatments, bracket adhesion to CAD-CAM PMMA temporary restorations can be enhanced to clinically satisfactory levels.

The occurrence of keyhole porosity in selective laser melting (SLM) has so far not been quantified systematically using X-ray computed tomography (X-CT). In this study, keyhole porosity in selective laser molten Ti-6Al-4V grade 23 parts was analyzed using post-process characterizations. Single tracks were produced with optimum, high volumetric energy density and low volumetric energy density parameters on the top of SLM substrate. High volumetric energy density was achieved by either (i) high laser power and optimum scan speed to study the effect of laser power or (ii) optimum laser power and low scan speed to study the effect of scan speed. Keyhole porosity is sensitive to the SLM process parameters. It was observed by using X-CT that a high amount of keyhole porosity was formed below the line scan produced with a high volumetric energy density achieved by optimum laser power and low scan speed; however, a line scan produced with same volumetric energy density but achieved by high laser power and optimum scan speed resulted in less or no voids. The X-CT porosity analysis helped to understand the size, shape, location, and number of keyhole pores that were formed.

Localised blast loads due to proximal charges are encountered in a variety of circumstances. This paper proposes an analytical solution for the dynamic plastic response of a rigid-perfectly plastic thick square plate subject to a localised explosion. The proposed model is an extension of the analytical model proposed by Micallef et al [1] to study circular plates which is adopted and modified in order to study impulsively loaded square plates where the effect of shear deformation is included. A piecewise continuous blast load function was assumed with axisymmetric spatial distribution of constant pressure in the central zone and exponentially decaying beyond it. Using the constitutive framework of limit analysis and incorporating the interactions between bending moment and transverse shear forces in the analyses, transverse displacement and response duration were examined on three classes of plates, classified according to the length to thickness ratio parameter ν. The results were furnished in terms of the impulsive velocity, which is a function of the localised blast load parameters. A theoretical solution for plates with ν > 2 was sought for the non-impulsive blast loads. Parametric studies were performed to elucidate the effect of loading parameters and plate thickness on the permanent deformation. The theoretical solutions have been found generic and can predict, by the correct choice of the load parameters, the dynamic response of most blast load scenarios brought about by proximal or distal charges. It was found that, for proximal impulsive blasts, the effect of transverse shear becomes irrelevant for even moderate values of ν, which effect is inconsequential on both central and endpoint displacements at discontinuous interface in the range of ν > 5 . Since the short duration pulse is of concern, localised pressure loads affect only a small area of the plated structures. Thus, whilst the theoretical treatments also examine the fully clamped plates, the boundary conditions in such loads do not influence the overall response of the structure compared to the static or global blast loads.

Metal parts produced by Laser Powder Bed Fusion (L-PBF) are frequently used for demanding applications. To meet stringent safety and certification requirements, a better understanding of melt-pool behavior and stability during processing is desired. This work presents a novel, fast and economically feasible virtual sensing approach for accurate estimation of melt-pool depth and width during L-PBF of metals. In a first step, the melt-pool width is determined by GPU-based processing of images from a high-speed coaxial camera monitoring system. In a second step, a physics-based analytical model is used to calculate the melt-pool depth-to-width ratio from the processing conditions and material properties. In a third and last step, the results from the first two steps are combined to estimate the melt-pool depth. Experimental validation of these predicted melt-pool dimensions is performed on 316L SS single layer strips that are consecutively produced, cross-sectioned, polished and etched to reveal the actual melt-pool boundaries. The results indicate an average relative error on the predicted melt-pool depth of 9.9% and 2.8% for the full L-PBF parameter range and for the optimal parameter range respectively. This gives confidence in the predictive capabilities of a virtual sensing approach using coaxial camera images for the assessment of the melt-pool depth and process stability. ispartof: Additive Manufacturing vol:40 status: Published online

The characterization of elastic strain and stress at the grain level is becoming an important route for validating meso- and nano-scale numerical models. The response of a grain to a mechanical load depends not only on the elastic and plastic properties of the single crystal, but also on the interaction of the grain with its local neighborhood. In this paper, an in-situ three-dimensional synchrotron X-ray diffraction experiment is conducted on a polycrystalline zirconium specimen. The data obtained from the experiment are used to develop methods to reconstruct three-dimensional grain maps by adding the grain layers measured by a planar X-ray beam, and to track individual grains across loading steps. The measured center-of-the-mass and volume of each grain are subsequently used to reconstruct 3D grain boundaries using the weighted Voronoi technique, and to determine grain neighborhoods. The results from the developed post-processing methods are compared against those measured using electron backscatter diffraction (EBSD) technique. It is shown that with the use of the developed methods, both small and big grains are accurately determined with 3D-XRD. It is further shown that the accuracy of the implemented Voronoi technique in determining the right grain neighborhood is more than 80%.

The mechanical response of polycrystalline materials to an externally applied load and their in-service performance depend on the local load partitioning among the constituent crystals. In hexagonal close-packed polycrystals such load partitioning is significantly affected by deformation twinning. Here we report in-situ compression-tension experiments conducted on magnesium specimens to measure the evolution of grain resolved tensorial stresses and formation and annihilation of twins. More than 13000 grains and 1300 twin-parent pairs are studied individually using three-dimensional synchrotron X-ray diffraction. It is shown that at the early stages of plasticity, the axial stress in twins is higher than that of parents, yet twins relax with further loading. While a sign reversal is observed for the resolved shear stress (RSS) acting on the twin habit plane in the parent, the sign of RSS within the majority of twins stays unchanged until twin annihilation during the load reversal. The variations of measured average stresses across parents and twins are also investigated. Load partitioning to grains during deformation of a polycrystalline material is affected by the presence of twins. Here, synchrotron diffraction is used to study 1300 twin-parent grains, revealing that stress is higher in twins than in the parent grain during the early stages of plastic deformation.

Permanent plastic deformation is expected when close-in blasts due to e.g. detonation of Improvised Explosive Devices (IED's) hit thin metallic targets. A circular thin steel plate i.e. a membrane is studied in the present work subject to a general form of a localised blast loading. The spatial shape of the pulse is fixed and different temporal shapes are investigated. Dynamic analyses are conducted and the permanent transverse displacements are found for each case. For high amplitude pulse loads of short duration, it was found that the permanent transverse displacement can be found by replacing the load by an impulse without the loss of accuracy. Excellent correlation with numerical simulations obtained from ABAQUS/Explicit is achieved. The predicted final displacements for different pulse shapes are also found to be similar, thus where membrane action is dominant, the response is insensitive to pulse shape.

In spite of its frustrated lattice, the multiferroic Lu0.5Sc0.5FeO3 exhibits two consecutive magnetic transitions at T N1 ≈ 175 K and T N2 ≈ 70 K determined from neutron diffraction. In the ordered state, magnetic fluctuations are present, most likely arising from the in-plane frustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover of the magnetic intensity is observed from elastic to inelastic upon warming, indicating that magnetic fluctuations persist well above T N1 , a common feature in hexagonal multiferroics.

A new quasi-two-dimensional oxyfluoride, Sr1-δFeO2-xFx, has been successfully synthesized by combining topotactic fluoridation and CaH2 reduction. The introduction of F through this synthesis provides a new route to introducing charge carriers into the square layered lattice through the formation of Fe(1+) ions. While the average crystal symmetry and magnetic structure remain the same as in the parent compound, the addition of F results in an enhanced buckling of the Fe(O/F)2 square plaquettes that is most likely topologically driven.

Ge2Sb2Te5 (GST-225), a phase change material (PCM) with vast differences in the electrical and optical characteristics between its amorphous and crystalline phases, is revisited to explore its properties with Se doping. GST crystallizes in a layered hexagonal ground state, while the precursor to the amorphous state is a distorted rock salt like structure with vacancies at the Ge/Sb sites. Upon doping, liquid nitrogen quenched Ge 2 Sb 2 Se 5 x Te 5 − 5 x (GSST-225) exhibits a direct hexagonal-to-amorphous phase change above x > 0.8, whereas the rock salt like structure appears as a second phase with a volume fraction that does not change as a function of the doping. The phase change is accompanied by a metal-to-insulator transition (MIT), with a several orders of magnitude increase in the resistivity on approaching the amorphous state. A similar MIT is observed even without the phase change in hexagonal crystals with doping levels above x > 0.8. On warming amorphous GSST (x = 0.9) above room temperature, a reversal to the hexagonal phase occurs with a re-crystallization onset temperature (Tc) above 300 °C, much higher than the Tc (∼ 170 °C) of amorphous GST and an activation energy of 1.47 eV, which is comparable to good glass formers.

Amalgamated 3D fiber/hydrogel composites were successfully synthesized based on double-hydrophilic semi-interpenetrating (semi-IPN) hydrogel matrices consisting of 1,2-bis-(2-iodoethoxy)ethane (BIEE)-crosslinked poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) chains and linear polyvinylpyrrolidone (PVP), and prefabricated PVP/Ag nanocomposite electrospun fibrous mats. The latter were incorporated within the semi-IPN hydrogels by following 2 unique ways of dispersion, i.e. the “laminated” and the “homogeneous” dispersion mode. In the “laminated” dispersion mode, the prefabricated electrospun fibrous mat was placed in the circumference of the fiber/hydrogel composite, while in the “homogeneous” dispersion mode, 2D circular fibrous mats were homogeneously encapsulated within the 3D hydrogel matrix. Among others, the effect of fiber inclusion as well as of the fiber dispersion mode within the hydrogel matrix on the materials’ mechanical properties was investigated. The obtained results clearly demonstrated that the dispersion mode of electrospun fibrous mats within the hydrogel influences significantly the mechanical performance of the resulting composites. Moreover, the influence of the presented structure-defined 3D fiber/hydrogel composites on the viability of human pancreatic fibroblasts was investigated in vitro. Consequently, these fiber/hydrogel composites exhibiting enhanced mechanical performance and biocompatibility could be potentially used as tissue engineering scaffolds with controllable mechanical properties and multi-functionalities.

Published version, 6 months embargo. Source at: https://doi.org/10.1177/2041419618807721 Localised blast loads give rise to high gradients of overpressure detrimental to structural elements as beams and plates. This article presents an analytical study on the dynamic plastic response of beams made of a ductile metallic material due to close-in pulse pressure loading. The close-in pressure load is characterised by a spatially varying function constant over a central region and exponentially decaying beyond it. The temporal pulse shape is assumed to take different forms. The exact static plastic collapse load was obtained for the characteristic load using the framework of plastic limit analysis, whereby the analysis was then extended to the dynamic case by considering the appropriate yield surface and inclusion of inertia forces. The yield surfaces considered were representative of pure bending, the interactions between the bending moment and transverse shear, and bending moment and membrane force, each corresponding to a special case depending on the geometry of the beam. A time-dependent, kinematically admissible velocity profile was assumed to treat the dynamic formulations in interaction of each phenomenon. A study on the strain-rate sensitivity was also presented, and existence of a critical pressure triggering the apparition of travelling plastic hinges was hence highlighted. For blast loads of high magnitude, the expressions for normalised deflection were furnished in terms of the impulsive velocity. The analytical models were validated by performing a parametric study on the two-dimensional representative of the beam model in commercial finite element software ABAQUS 6.14. The numerical results show a good correlation with the analytical results in each case.

The ferroelectric phase transition in RMnO3 breaks both Z3 and Z2 symmetries, giving rise to 6 structural domains. Topological protected vortices are formed at the junctions of all 6 domains, and the ferroelectric phase transition is closely related to these Z6 vortices. In this work, Monte-Carlo studies on both the ferroelectric and magnetic transition have been performed on RMnO3 system. The magnetic simulation results on lattices with different structural domain distributions induced by external electric field and simulated quenching show different magnetic transition temperature T s , indicating that the coupling of magnetism and ferroelectricity is through the Z6 structural domain. At extreme case, lattice quenched from above the ferroelectric transition results in high vortex density, which can drive the system into spin glass.

This paper presents the theoretical solution to the response of a square plate undergoing plastic deformation due to a generic localized blast pulse. A localized blast load function was assumed multiplicative of its spatial distribution and temporal pulse shape. The spatial distribution was representative of constant pressure over the central zone, while exponentially decaying outside that zone. Considering an appropriate moment function and ignoring the membrane, transverse shear, and rotary inertia effects, the static plastic collapse was found, whereby the analysis was extended to the dynamic case by assuming a kinematically admissible, time-dependent velocity profile. The analytical model, which was validated against the numerical results obtained through ABAQUS hydrocode, showed close correlation in terms of the permanent transverse deflection profile. In order to consider the effect of temporal pulse shape, the results were formulated for rectangular as well as exponentially and linearly decaying pulses. For blast loads of high magnitude, the pressure load was replaced by an impulsive velocity. The calculations were simplified by utilizing the dimensionless form, and the results were corroborated with theoretical and experimental results from the literature. The model showed improvements in predicting the final deformation of square plates over previous models of simplified loading function.

This paper presents a comparative study of numerical, experimental and empirical techniques on the effect of localised air blast loads on mild steel and armour steel plates. The blast load effects on monolithic plates have been accounted for by using different approaches provided in the Finite Element hydrocode ABAQUS 6.13, namely an Eulerian Lagrangian and a Coupled Eulerian Lagrangian model. In the first model, the air and the explosive were modelled using multi-material Eulerian grids while the plate was modelled using a rigid Lagrangian mesh, while in the second model the rigid target was replaced with deformable plate.\ud \ud \ud \ud The transient deformation of the plate, strain localisation, pressure distribution on the plate have been investigated in the FE models, which have been validated against small scale experimental data for a limited range of charge sizes for both the mild steel and armoured steel. Despite the lower deflection of armour steel compared to mild steel plates, both plates were shown to undergo rupture upon similar charge mass and stand-off. For this purpose, a non-dimensional analysis was carried out with consideration of stand-off distance and slenderness ratio to predict the rupture impulse.

Shear locking is a major issue emerging in the computational formulation of beam and plate finite elements of minimal number of degrees of freedom as it leads to artificial overstiffening. In this paper, discontinuous Timoshenko beam and Mindlin‐Reissner plate elements are developed by adopting the Hellinger‐Reissner functional with the displacements and through‐thickness shear strains as degrees of freedom. Heterogeneous beams and plates with weak discontinuity are considered, and the mixed formulation has been combined with the extended finite element method (FEM); thus, mixed enrichment functions are used. Both the displacement and the shear strain fields are enriched as opposed to the traditional extended FEM where only the displacement functions are enriched. The enrichment type is restricted to extrinsic mesh‐based topological local enrichment. The results from the proposed formulation correlate well with analytical solution in the case of the beam and in the case of the Mindlin‐Reissner plate with those of a finite element package (ABAQUS) and classical FEM and show higher rates of convergence. In all cases, the proposed method captures strain discontinuity accurately. Thus, the proposed method provides an accurate and a computationally more efficient way for the formulation of beam and plate finite elements of minimal number of degrees of freedom.

Electronic tunability in crystals with weakly-bound layers can be achieved through layer stacking order. One such example is MoTe$_2$, where the low-temperature orthorhombic T$_d$ phase is topological and host to Weyl quasiparticles. The transition mechanism to the non-trivial topology is elucidated by single crystal neutron diffraction. Upon cooling from the monoclinic 1T$\prime$ to the T$_d$ phase, diffuse scattering accompanies the transition, arising from random, in-plane layer displacements, and dissipates upon entering the T$_d$ phase. Diffuse scattering is observed only in the H0L plane due to irreversible layer shifts along the c-axis that break the centrosymmetry of the monoclinic lattice., Comment: This paper contains 8 pages including references and supplement materials. 3 figures and 1 table

Statement of problem The white color of zirconia limits the possibility of a natural-looking restoration. Industrially precolored blocks and green-stage coloring liquids are used to obtain shaded zirconia. Several authors have reported that pigments may negatively affect the mechanical characteristics of the material. Purpose The purpose of this in vitro study was to investigate the effect of a recently marketed coloring system on the flexural strength (σ), Weibull characteristic strength (σ 0 ), and Weibull modulus (m) of a zirconia for computer-aided design/computer-aided manufacturing (CAD/CAM) systems. Material and methods Noncolored white blocks (In-Ceram YZ), industrially precolored blocks (In-Ceram YZ col. LL1p), and green-stage infiltration-shaded blocks in 4 colors (In-Ceram YZ Coloring Liquids) were tested. Industrially precolored specimens (n=30) were assigned to the PREC group. Noncolored specimens were divided into 5 groups (n=30). Group CNTR was not treated (control). Groups INF-N, INF-L, INF-M, and INF-I were subject to green-stage infiltration (neutral, light, medium, and intense, respectively). Specimens were tested in a 3-point bending apparatus following ISO 6872:2008 specifications. Data were analyzed by 1-way ANOVA. Results The calculated flexural strengths (MPa) were CNTR 1232.56 ±103.91; PREC 1215.16 ±141.42; INF-N 1280.72 ±160.10; INF-L 1218.92 ±78.63; INF-M 1153.71 ±176.80; and INF-I 1248.46 ±111.73. No statistically significant differences were found among the tested groups ( P =.195). Conclusions Unlike what has been reported for other combinations of zirconia and coloring liquids, the coloring technique tested in the present study did not negatively influence the flexural characteristics of the tested zirconia.

Close-range blasts pose a threat through severe damage to structures and injury or death. In this work, the spatial and temporal descriptions of a localised blast load are presented using 6 non-dimensional parameters. These are found to be solely functions of the charge stand-off distance to diameter ratio for a cylindrically-shaped charge. Numerical simulations of a localised blast are performed using AUTODYN, where the pressure variation on a rigid barrier for various charge stand-off/diameter combinations is obtained. The least-square regression is then utilised to obtain the relationship between stand-off/diameter ratio and dimensionless loading parameters. The relevant expressions and dimensionless charts are presented. The proposed equations are verified by comparing experimental data with numerical results obtained by finite element analysis (FEA) of blast loaded steel plates (using the user-defined subroutine VDLOAD implemented in the FEA package ABAQUS/Explicit). Excellent correlation of the measured permanent displacement with numerically predicted results is obtained.

This article presents results from an experimental investigation into the influence of material properties on the response of plates subjected to air-blast loading. The failure of mild steel, armour steel, aluminium alloy and fibre reinforced polymer composite plates were investigated experimentally by detonating disks of plastic explosive at small stand-off distances. Permanent mid-point displacement increased linearly with increasing impulse for each material type, up to rupture. At higher charge masses, the mild steel plates exhibited ductile tensile rupture, while the armour steel plates (which ruptured at the same impulse) exhibited a more brittle type of failure. The aluminium alloy plates exhibited signs of melting and spraying radially outwards, resulting in material loss in the plate centre followed by rupture at higher impulses. The fibre reinforced polymer composite showed evidence of fibre fracture at lower impulses than the other equivalent mass materials. Non-dimensional rupture impulse was not found to correlate with tensile strength or material ductility, but was found to increase with increasing specific energy to tensile fracture (obtained from quasi-static tensile tests). Hence, the energy absorption capacity of the materials obtained from simple tensile tests could provide an approximate indication of their blast performance.

Neutron scattering measurements were carried out on polycrystalline samples of LaO1−x F x BiS2 to investigate the evolution of the crystal structure with the appearance of superconductivity. It is observed that the BiS2 layer gradually unbuckles as x increases to 0.3 and the orientation of the buckling reverses by x = 0.5. The Debye temperatures were estimated to be ∼319 and ∼224 K for the x = 0 and x = 0.5, respectively, indicating significant softening related to structural disorder.

Uniaxial tensile strain changes the magnetoresistance according to the direction it is applied on in MoTe2., Quasi–two-dimensional transition metal dichalcogenides exhibit dramatic properties that may transform electronic and photonic devices. We report on how the anomalously large magnetoresistance (MR) observed under high magnetic field in MoTe2, a type II Weyl semimetal, can be reversibly controlled under tensile strain. The MR is enhanced by as much as ~30% at low temperatures and high magnetic fields when uniaxial strain is applied along the a crystallographic direction and reduced by about the same amount when strain is applied along the b direction. We show that the large in-plane electric anisotropy is coupled with the structural transition from the 1T′ monoclinic to the Td orthorhombic Weyl phase. A shift of the Td-1T′ phase boundary is achieved by minimal tensile strain. The sensitivity of the MR to tensile strain suggests the possibility of a nontrivial spin-orbital texture of the electron and hole pockets in the vicinity of Weyl points. Our ab initio calculations show a significant orbital mixing on the Fermi surface, which is modified by the tensile strains.

Quasi-two dimensional transition metal dichalcogenides (TMD) exhibit dramatic properties that may transform electronic and photonic devices. We report on how the anomalously large magnetoresistance (MR) observed under high magnetic field in MoTe$_2$, a type II Weyl semimetal, can be reversibly controlled under tensile strain. The MR is enhanced by as much as ~ 30 % at low temperatures and high magnetic fields, when uniaxial strain is applied along the $a$-crystallographic direction and reduced by about the same amount when strain is applied along the $b$-direction. We show that the large in-plane electric anisotropy is coupled with the structural transition from the 1T' monoclinic to the Td orthorhombic Weyl phase. A shift of the Td - 1T' phase boundary is achieved by minimal tensile strain. The sensitivity of the MR to tensile strain suggests the possibility of a nontrivial spin-orbital texture of the electron and hole pockets in the vicinity of Weyl points. Our ab initio calculations indeed show a significant orbital mixing on the Fermi surface, which is modified by the tensile strains., Comment: 20 pages, 4+5 figures

We report on the results of dimensional analyses on the dynamic plastic response of square armour steel plates due to detonation of proximal cylindrical charges and ensued air blast loading. By assuming a generic function for the blast load, which is multiplicative comprising its spatial and temporal parts, a set of 14 dimensionless parameters, representative of the load and plate deformation, were identified and recast in the form of dimensionless functions of stand-off to charge diameter ratio. Parametric studies were performed using commercial code ABAQUS’s module of Finite Element hydrocode using MMALE and MMAE techniques, and combined with regression analyses to quantify the dimensional parameters and the expressions for dimensionless functions. A few numerical studies with various FE mesh types were also performed to validate the transient deflections against the small-scale experiments. For pulse loading due to proximal charges of small orders of stand-off/charge diameter ratio, the magnitude of the transverse deflection increased abruptly with incremental decrease in stand-off, in contradistinction to the plate deformations at higher stand-offs where variations in displacement are smooth. This confirmed the existence of a stand-off at which a transition in behaviour takes place. For stand-off values less than charge diameter, a dimensionless energy absorbing effectiveness factor was considered to investigate the prediction of rupture in the plate corresponding to different charge masses. This factor is measured as a baseline parameter to predict, using solely numerical means, the blast loads which ensue rupture on full-scale prototypes.

This paper reports on the dynamic response of a potential blast-resistant lightweight alternative to steel for military applications, namely ultra-high molecular weight polyethylene (UHMwPE) fibre composites known as Dyneema ® . The results of localised air-blast loading tests on Dyneema HB26 panels are reported and analysed. Various failure modes were observed, including permanent deformation, delamination, in-plane shear, buckling around the boundary, localised melting and matrix damage. Total penetration (rupture) at the highest charge masses was also exhibited by the Dyneema panels. The experimental results are compared to the numerically simulated responses of mild steel and armour steel plates of equal areal density and reasonable correlation was observed in most cases. Dimensional analysis was used to compare the responses and showed that there is a possibility of unifying all the results i.e. the responses for all materials once a newly proposed slenderness ratio was incorporated into the formulation. Simple dimensionless expressions are proposed to predict permanent midpoint transverse displacements, irrespective of the particular material type. It was also observed that armour steel and Dyneema HB26 offer potential displacement reductions of almost 50% and 30%, respectively for the range of impulses tested.

Near-field explosive charges, such as buried land mines, produce localised blast loadings which can potentially cause damage to property and/or loss of life in both military and civil structures. As the localised short duration blast pulse affects most severely a small area of a plated structure, boundary effects are not as significant as they are when a quasi-static or global blast loading is applied and full plate action may not be utilised. Many common structural forms are composed of individual plated elements and thus the investigation of localised blast loading effects on plates is a prerequisite to understanding the integral behaviour. Typically, plates are made of ductile materials such as steel, which exhibit considerable post-yield deformation capacity when subjected to such extreme dynamic loads. Analytical study of the dynamic plastic response of rigid-plastic plated structures is the aim of the present study. A circular plate is studied in the present work and a general form of a localised blast loading function with a spatial variation having a central radial zone with constant pressure and exponentially decaying profile outside the zone is assumed. Assuming that steel exhibits perfectly plastic behaviour and ignoring membrane action, transverse shear and rotatory inertia effects, the static plastic collapse pressure is initially found and the analysis is extended to take into account the inertial effects arising from dynamic loading. Results for the permanent transverse displacements are found for rectangular and linearly and exponentially decaying pulse loads. For high loads and/or loads of short duration, it was found that the permanent transverse displacement can be found by replacing the applied pulse load by means of an impulsive velocity without great loss of accuracy. Good correlation with numerical simulations obtained from ABAQUS/Explicit is achieved (within 15% accuracy) for plate geometries falling within the identified limits where membrane and shear effects are negligible. The predicted final transverse displacements are found to be dependent on the loading pulse shape, but the pulse-shape effects are eliminated by using the correlation parameters (effective impulse and pressure) advocated by Youngdahl (1971) [52] to give a single pulse shape-independent curve for the final plate deflection as a function of the effective pressure and effective impulse. © 2012 Elsevier Ltd.

The discovery of phonon-mediated superconductivity in the BiS2 class led to a renewed interest in compounds that exhibit a strong structure-property relationship due to its intrinsic disorder. The ...

The extended finite element method (XFEM) is found promising in approximating solutions to locally non-smooth features such as jumps, kinks, high gradients, inclusions, voids, shocks, boundary layers or cracks in solid or fluid mechanics problems. The XFEM uses the properties of the partition of unity finite element method (PUFEM) to represent the discontinuities without the corresponding finite element mesh requirements. In the present study numerical simulations of a dynamically loaded orthotropic viscoelastic cracked body are performed using XFEM and the J-integral and stress intensity factors (SIF’s) are calculated. This is achieved by fully (reproducing elements) or partially (blending elements) enriching the elements in the vicinity of the crack tip or body. The enrichment type is restricted to extrinsic mesh-based topological local enrichment in the current work. Thus two types of enrichment functions are adopted viz. the Heaviside step function replicating a jump across the crack and the asymptotic crack tip function particular to the element containing the crack tip or its immediately adjacent ones. A constitutive model for strain-rate dependent moduli and Poisson ratios (viscoelasticity) is formulated. A symmetric double cantilever beam (DCB) of a generic orthotropic material (mixed mode fracture) is studied using the developed XFEM code. The same problem is studied using the viscoelastic constitutive material model implemented in ABAQUS through an implicit user defined material subroutine (UMAT). The results from XFEM correlate well with those of the finite element method (FEM). Three cases viz. static, dynamic and viscoelastic dynamic are studied. It is shown that there is an increase in the value of maximum J-integral when the material exhibits strain rate sensitivity.

The aim of the current study is to develop a constitutive model which captures the full orthotropic behaviour of a laminated composite by employing nine material parameters and also taking into account strain-rate sensitivity to loading. The formulation is an extension of the work by Ogihara and Reifsnider (DOI: 10.1023/A:1016069220255), whose model considers 4 parameters, and with the inclusion of strain-rate effect considerations using the method employed by Thiruppukuzhi and Sun (DOI: 10.1016/S0266-3538(00)00133-0).A plastic potential function which can describe plasticity in all directions, including fibre plasticity, is chosen and using an associated flow rule, the plastic strain-rate components are derived. The plastic compliance matrix is assembled, using a rate-dependent visco-plastic modulus. The elastic compliance matrix is combined with its plastic counterpart to give a rate-form constitutive law. The proposed model accounts for strain-rate dependence and by correct choice of model parameters, the model can also be used for various composite architectures, including woven and uni-directional. The present study is limited to the investigation of the performance of uni-directional composites, where a parametric study is conducted to assess the influence of strain-rate and the off-axis angle of loading on the composite behaviour. A numerical study is conducted in ABAQUS/Explicit, with a user-defined material subroutine (VUMAT) to describe the visco-plastic constitutive behaviour. It is found that visco-plastic effects are particularly significant for high strain-rates (≈1000s-1), leading to increases in stress of 25-50% in some cases. Fibre alignment angle is observed to be less critical, except for the steepest angle (90°). It is also found that visco-plasticity does not significantly affect fibre performance whilst matrix and, in particular, shear failure is severely affected by the inclusion of visco-plastic effects. © 2012 Elsevier Ltd.

Dilute magnetic ion doping in LaCo1−y Ni y O3 with y≤1 % leads to the formation of isotropic magnetic clusters that exhibit intracluster interactions which are ferromagnetic in nature. The clusters are comprised of Ni ions surrounded by six magnetically polarized Co ions. The Ni spin is delocalized from the Ni3+ ion but is confined in the vicinity of the six Co coordinated environment forming small magneto-polarons. The cluster ground state is estimated from bulk magnetization to be about gS∼10, in contrast to LaCoO3, which is not magnetic. Using neutron spectroscopy, transitions are observed between the lowest energy levels indicating that the cluster ground state is split. Under a magnetic field of 1 Tesla, the transitions are suppressed while with increasing temperature, the intracluster transitions are overshadowed by the activation of the Co3+ ions to the intermediate spin state.

Debonding in adhesively-bonded lap joints is a detrimental failure mode contingent upon the level of stresses develped in the adhesive. In this work, an analytical model is developed to estimate the peel and shear stresses in an isotropic elastic adhesive in a single lap joint subjected to transverse pulse loads. The proposed analytical model is an extension of the mathematical models developed by He and Rao ( Journal of Sound and Vibration 152 (3), (1992) 405–416, 417–425) to study the coupled transverse and longitudinal vibrations of a bonded lap joint system. The adhesive, in this work, is modelled as an elastic isotropic material implemented in Abaqus 6.9−1. The interfacial stresses obtained by finite element simulations were used to validate the proposed analytical model. The maximum peel and shear stresses in the adhesive as predicted by the analytical model were found to correlate well with the maximum stresses predicted by the corresponding numerical models. The peel stresses in the adhesive were found to be higher than shear stresses, a result which is consistent with intuition for transversally loaded joints. The analytical model is able to predict the maxium stresses in the edges where debonding initiates due to the highly asymetrical stress distribution as observed in the finite element simulations and experiment. This phenomenon is consistent with observations made by Vaidya et al. ( International Journal of Adhesion & Adhesives 26 (2006) 184–198). The stress distribution under uniformily distributed transverse pulse loading was observed to be similarly asymetric.

Using neutron diffraction and the pair density function analysis, the effect of Sc alloying for Y on the local atomic structure of Y56-x Al24Ni10Co10 was investigated. The replacement of Y with Sc significantly changes the local atomic structure of amorphous Y56-x Al24Ni10Co10 as it promotes the formation of nanocrystalline particles. By comparing the structure function in reciprocal space of three alloys with x = 0, 0.1, and 0.2 (in atomic percent), small Bragg peaks are observed that increase in intensity proportionate with the amount of Sc. In real space, the substitution of Sc for Y leads to a drastic structural contraction most likely resulting from efficient cluster packing.

An integral part of a typical offshore module is the surrounding profiled blast walls that separate the potentially hazardous regions of the topside. Many of the blast walls in operation were designed to resist lower loads than those envisaged today [1] rendering them currently non-functional, thus it is desirable to upgrade their blast resistance in a cost-effective and non-intrusive manner. One proposal is to retrofit the existing blast walls partially with centrally located composite patches. This study presents the development of a rapid assessment tool which provides understanding of the effect of a composite patch on the blast resistance of profiled blast walls. The tool is based and is an improvement upon a previous analytical formulation for unstrengthened walls with realistic connection systems [2] . Numerical simulations of a proposed retrofitted wall are performed to gain insight into the failure progression of the wall. Damage in the composite patch is modelled using the Hashin damage model, and the numerical simulations showed that fibre fracture did not occur and that the small amounts of matrix failure occurring at the composite patch edges did not result in significant loss of in-plane stiffness and strength. Based on these observations the rapid assessment tool, analytically formulated to incorporate the effect of the composite patch which strengthens the wall and moves the plastic hinge locations away from the wall centre to the composite-steel edge, is deemed a suitable tool. The assessment tool and the numerical simulations are partially validated by the experimental results presented in [1] for unstrengthened blast walls. The tool runs quickly and provides reasonable predictions for the deformation response of the walls, and enables the user to quickly assess the effect of adding a composite patch. It allows for multiple deformation modes in the panels and the development of plastic hinges at the composite-steel edges and the wall connections, providing a significant advantage over conventional single-degree-of-freedom models. The numerical simulations and the rapid assessment tool give reasonable agreement for different loading regimes, given the anticipated use of the analytical approach.

The effect of fatigue on ZrCuAl amorphous metals induced by mechanical cyclic loading is investigated using inelastic neutron scattering and the pair density function analysis of neutron diffraction data. With cooling, the local atomic structure undergoes reorganization under fatigue that is directly related to the number of fatigue cycles. Also under fatigue, suppression in the atomic dynamics is observed as well. A structural restructuring occurs within a 4 Å radius and intensifies with increasing the compression cycles, whereas the vibrational density of states is attenuated as the intensity shifts towards the elastic, zero-energy transfer peak. The combined static and dynamic structural effects are a signature of the microscopic changes brought about by fatigue, and together may be the onset for subsequent behaviors following extended cyclic loading such as fracture. Even after the load is removed, the structural changes described here remain and increase with repeated cyclic loading which is an indication that the lattice deforms even before shear bands are formed.

Near-field explosive charges, such as buried land mines, produce localised blast loadings which can potentially cause damage to property and/or loss of life in both military and civil structures. As the localised short duration blast pulse affects most severely a small area of a plated structure, boundary effects are not as significant as they are when a quasi-static or global blast loading is applied and full plate action may not be utilised. Many common structural forms are composed of individual plated elements and thus the investigation of localised blast loading effects on plates is a prerequisite to understanding the integral behaviour. Typically, plates are made of ductile materials such as steel, which exhibit considerable post-yield deformation capacity when subjected to such extreme dynamic loads. Analytical study of the dynamic plastic response of rigid-plastic plated structures is the aim of the present study. A circular plate is studied in the present work and a general form of a localised blast loading function with a spatial variation having a central radial zone with constant pressure and exponentially decaying profile outside the zone is assumed. Assuming that steel exhibits perfectly plastic behaviour and ignoring membrane action, transverse shear and rotatory inertia effects, the static plastic collapse pressure is initially found and the analysis is extended to take into account the inertial effects arising from dynamic loading. Results for the permanent transverse displacements are found for rectangular and linearly and exponentially decaying pulse loads. For high loads and/or loads of short duration, it was found that the permanent transverse displacement can be found by replacing the applied pulse load by means of an impulsive velocity without great loss of accuracy. Good correlation with numerical simulations obtained from ABAQUS/Explicit is achieved (within 15% accuracy) for plate geometries falling within the identified limits where membrane and shear effects are negligible. The predicted final transverse displacements are found to be dependent on the loading pulse shape, but the pulse-shape effects are eliminated by using the correlation parameters (effective impulse and pressure) advocated by Youngdahl (1971) [52] to give a single pulse shape-independent curve for the final plate deflection as a function of the effective pressure and effective impulse.

Purpose: To evaluate the adhesion to CAD/CAM feldspathic blocks by failure analysis and shear bond strength test (SBSt) of different restorative systems and different surface treatments, for purpose of moderate chipping repair. Materials and methods: A self-adhering flowable composite (Vertise Flow, Kerr) containing bi-functional phosphate monomers and a conventional flowable resin composite (Premise Flow, Kerr) applied with and without adhesive system (Optibond Solo Plus, Kerr) were combined with three different surface treatments (Hydrofluoric Acid Etching, Sandblasting, combination of both) for repairing feldspathic ceramics. Two commercial systems for ceramic repairing were tested as controls (Porcelain Repair Kit, Ultradent, and CoJet System, 3M). SBSt was performed and failure mode was evaluated using a digital microscope. A One-Way ANOVA (Tukey test for post hoc) was applied to the SBSt data and the Fisher’s Exact Test was applied to the failure analysis data. Results: The use of resin systems containing bi-functional phosphate monomers combined with hydrofluoric acid etching of the ceramic surface gave the highest values in terms of bond strength and of more favorable failure modalities. Conclusion: The simplified repairing method based on self-adhering flowable resin combined with the use of hydrofluoric acid etching showed high bond strength values and a favorable failure mode. Repairing of ceramic chipping with a self-adhering flowable resin associated with hydrofluoric acid etching showed high bond strength with a less time consuming and technique-sensitive procedure compared to standard procedure.

Hybrid steel-to-composite joints are being used more commonly for load bearing applications. However, these hybrid joints usually entail geometry and material discontinuities which can induce stiffness mismatch and cause local stress concentrations. The shock impedance mismatch caused by the different wave propagation characteristics can also be crucial to the structural response of the hybrid joints under impulsive loads. Recent research at Imperial College London (ICL) and the U.S. Naval Academy (USNA) has focused on characterizing the behavior and ultimate load capacity of hybrid steel-to-composite joints with different configurations under various loading conditions. This paper presents results from tensile strength testing of steel-to-composite double lap joints, comparing pseudostatic strength with dynamic strength and comparing joints that exploit perforated steel plates with those manufactured with non-perforated steel plates. An intentional manufacturing flaw also was incorporated into half of the joints, both perforated and non-perforated joints, in order to assess the effect of this flaw type on joint strength. Finite Element Analysis (FEA) results are compared to experimental results for both perforated and non-perforated joints.

We have applied a MgO and a ZrO2 shell deposition method to control the interface between two indolenebased organic dyes in solid-state dye-sensitized solar cells. The shell deposition was carried out at less than 100 °C, and shell thickness was shown to be 2 nm for the ZrO2 and 6-10 nm for the MgO by transmission electron microscopy. X-ray photoelectron spectroscopy has shown the initial ZnO NWs and core-shell structures have little surface water contamination. The use of suitable dyes, D102 and D149, has led to power conversion efficiency for ZnO NW based hybrid solar cells of 0.71%. Transient absorption measurements indicate that enhancements in photoinduced charge generation with core-shell formation are the main factor leading to the improved device efficiency. © 2009 American Chemical Society.