A methodology to measure the interface shear strength by means of the fiber push-in test

A methodology is presented to measure the fiber/matrix interface shear strength in composites. The strategy is based on performing a fiber push-in test at the central fiber of highly-packed fiber clusters with hexagonal symmetry which are often found in unidirectional composites with a high volume fraction of fibers. The mechanics of this test was analyzed in detail by means of three-dimensional finite element simulations. In particular, the influence of different parameters (interface shear strength, toughness and friction as well as fiber longitudinal elastic modulus and curing stresses) on the critical load at the onset of debonding was established. From the results of the numerical simulations, a simple relationship between the critical load and the interface shear strength is proposed. The methodology was validated in an unidirectional C/epoxy composite and the advantages and limitations of the proposed methodology are indicated

An experimental and numerical study of the influence of local effects on the application of the fibre push-in tests

Accelerated corrosion tests, Cohesive crack, Finite Elements simulations Several methods have been developed to test interfacial adhesion in composite materials such as pull-out, microbond and push-in/push-out tests. Some of them can only be applied to single fibre matrix composites and others are difficult to perform on brittle fibres due to premature fracture of the fibre. Push-in tests, consisting on pushing the fibre with a micro or nanoindenter on a bulk specimen, constitute a powerful technique that can be applied directly on composite laminates. However, the interfacial adhesion values obtained from different tests (microbond, push in) often differ and even are subjected to a large scatter. This might be due to the fact that the existing analytical solutions that are typically used to interpret the experimental data take into account the constrain effect of the surrounding fibres on a simplified manner. To study this, we have carried out a careful micromechanical modelling of the push-in test, coupled with experimental adhesion testing in a glass fibre reinforced epoxy matrix composite. The model takes into account the interfacial fracture process by means of interface cohesive elements at the fibre–matrix interface and focuses on the study of the constrain effects due to the local configuration of the surrounding fibre

An experimental and Numerical Study of the Influence of local Effects on the applications of the fibre push-in test

Several methods, such as pull-out, microbond and push-in/push-out tests, have been developed to test interfacial adhesion in composite materials. Some of them can only be applied to single-fibre matrix composites, like the microbond test, and others are difficult to perform on brittle fibres due to premature fracture of the fibre. Push-in tests, consisting of pushing the fibre with a micro- or nanoindenter on a bulk specimen, constitute a powerful technique that can be applied directly to composite laminates. However, the interfacial adhesion values obtained from different tests (microbond, push-in) often differ and even the results from one type of test are subjected to a large scatter. This might be due to the fact that the existing analytical solutions that are typically used to interpret the experimental data take into account the constraining effect of the surrounding fibres on a simplified manner. To study interfacial adhesion and the effect of the constraint of the neighbouring fibres, a micromechanical model of the push-in test was developed, coupled with experimental adhesion testing in a glass fibre-reinforced epoxy matrix composite. The model takes into account the interfacial fracture process by means of interface cohesive elements at the fibre–matrix interface and focusses on the study of the constraining effects due to the local configuration of the surrounding fibres

High temperature nanoindentation behavior of Al/SiC multilayers

Nanoscale Al/SiC composite laminates have unique properties, such as high strength, high toughness, and damage tolerance. In this article, the high-temperature nanoindentation response of Al/SiC nanolaminates is explored from room temperature up to 300_C. Selected nanoindentations were analyzed postmortem using focused ion beam and transmission electron microscopy to ascertain the microstructural changes and the deformation mechanisms operating at high temperature

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

The reliability of Pb-free solder joints is controlled by their microstructural constituents. Therefore, knowledge of the solder microconstituents’ mechanical properties as a function of temperature is required. Sn-Ag-Cu lead-free solder alloy contains three phases: a Sn-rich phase, and the intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. Typically, the Sn-rich phase is surrounded by a eutectic mixture of β-Sn, Cu6Sn5, and Ag3Sn. In this paper, we report on the Young’s modulus and hardness of the Cu6Sn5 and Cu3Sn IMCs, the β-Sn phase, and the eutectic compound, as measured by nanoindentation at elevated temperatures. For both the β-Sn phase and the eutectic compound, the hardness and Young’s modulus exhibited strong temperature dependence. In the case of the intermetallics, this temperature dependence is observed for Cu6Sn5, but the mechanical properties of Cu3Sn are more stable up to 200°C

High temperature micropillar compression of Al/SiC nanolaminates

The effect of the temperature on the compressive stress–strain behavior of Al/SiC nanoscale multilayers was studied by means of micropillar compression tests at 23 °C and 100 °C. The multilayers (composed of alternating layers of 60 nm in thickness of nanocrystalline Al and amorphous SiC) showed a very large hardening rate at 23 °C, which led to a flow stress of 3.1 ± 0.2 GPa at 8% strain. However, the flow stress (and the hardening rate) was reduced by 50% at 100 °C. Plastic deformation of the Al layers was the dominant deformation mechanism at both temperatures, but the Al layers were extruded out of the micropillar at 100 °C, while Al plastic flow was constrained by the SiC elastic layers at 23 °C. Finite element simulations of the micropillar compression test indicated the role played by different factors (flow stress of Al, interface strength and friction coefficient) on the mechanical behavior and were able to rationalize the differences in the stress–strain curves between 23 °C and 100 °C

Multiscale Modeling of Composites: Toward Virtual Testing ... and Beyond

Recent developments in the area of multiscale modeling of fiber-reinforced polymers are presented. The overall strategy takes advantage of the separa-tion of length scales between different entities (ply, laminate, and component) found in composite structures. This allows us to carry out multiscale modeling by computing the properties of one entity (e.g., individual plies) at the relevant length scale, homogenizing the results into a constitutive model, and passing this information to the next length scale to determine the mechanical behavior of the larger entity (e.g., laminate). As a result, high-fidelity numerical sim-ulations of the mechanical behavior of composite coupons and small compo-nents are nowadays feasible starting from the matrix, fiber, and interface properties and spatial distribution. Finally, the roadmap is outlined for extending the current strategy to include functional properties and processing into the simulation scheme

Micropillar compression of LiF [111] single crystals: effect of size, ion irradiation and misorientation

The mechanical response under compression of LiF single crystal micropillars oriented in the [111] direction was studied. Micropillars of different diameter (in the range 1–5 lm) were obtained by etching the matrix in directionally-solidified NaCl–LiF and KCl–LiF eutectic compounds. Selected micropillars were exposed to high-energy Ga+ ions to ascertain the effect of ion irradiation on the mechanical response. Ion irradiation led to an increase of approximately 30% in the yield strength and the maximum compressive strength but no effect of the micropillar diameter on flow stress was found in either the as-grown or the ion irradiated pillars. The dominant deformation micromechanisms were analyzed by means of crystal plasticity finite element simulations of the compression test, which explained the strong effect of micropillar misorientation on the mechanical response. Finally, the lack of size effect on the flow stress was discussed to the light of previous studies in LiF and other materials which show high lattice resistance to dislocation motion

Mecanismos de Deformación en laminados de matriz polimérica correlación digital de imágenes y micromecánica computacional

Se ha realizado un estudio micromecánico experimental del comportamiento de laminados unidireccionales sometidos a compresión en la dirección perpendicular a las fibras. Se ha empleado la técnica de correlación digital de imágenes para observar la evolución de los campos de desplazamientos y deformaciones en la microestructura del material compuesto. En los contornos de deformación obtenidos experimentalmente se ha comprobado como las fibras tienen una deformación muy pequeña, mientras que las mayores deformaciones se concentran en las zonas de matriz de menor fracción volumétrica de fibras. Simulando por elementos finitos la microestructura estudiada se han reproducido los resultados experimentales, obteniendo distribuciones de campos de desplazamientos y deformaciones muy similares a las observadas experimentalmente