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[Display omitted] • Descriptors for cross-section shape of ligaments allow comparing features in np-Au. • Computer generated and experimental network structures show significant differences. • Ligament shape distribution of artificial structures changes during coarsening. Nanoporous gold (np-Au) exhibits a bi-continuous network structure of nanoscale pores and solid ligaments, which form a random 3D network. Geometrical descriptors are developed that allow for characterization, statistical analysis and comparison of a large number of ligaments in real and computer generated np-Au structures. In addition to the voxel resolution and ligament length, the cross-sections of the ligaments are described by roundness, circularity, and compactness. The structures are analyzed in initial and coarsened conditions for various solid fractions. Although the structures do not change topologically, the results confirm significant changes in the geometry during coarsening. It is found that after coarsening the computer-generated structures compare much better to tomographic reconstructions of annealed np-Au structures, although there are still differences in the free ligament length. Therefore, in addition to the topological similarity, similarity of geometrical descriptors is found to be equally important for deriving predictive models based on computer-generated structures. [ABSTRACT FROM AUTHOR]

Dental enamel is a highly anisotropic and heterogeneous material, which exhibits an optimal reliability with respect to the various loads occurring over years. In this work, enamel’s microstructure of parallel aligned rods of mineral fibers is modeled and mechanical properties are evaluated in terms of strength and toughness with the help of a multiscale modeling method. The established model is validated by comparing it with the stress–strain curves identified by microcantilever beam experiments extracted from these rods. Moreover, in order to gain further insight in the damage-tolerant behavior of enamel, the size of crystallites below which the structure becomes insensitive to flaws is studied by a microstructural finite element model. The assumption regarding the fiber strength is verified by a numerical study leading to accordance of fiber size and flaw tolerance size, and the debonding strength is estimated by optimizing the failure behavior of the microstructure on the hierarchical level above the individual fibers. Based on these well-grounded properties, the material behavior is predicted well by homogenization of a representative unit cell including damage, taking imperfections (like microcracks in the present case) into account. [ABSTRACT FROM AUTHOR]

Highlights: [•] Systematic study of microstructure on failure mode, strength, fracture energy for FRC. [•] Several different failure modes have been included. [•] Effect of length and radius of fibres, and effect of precrack was studied. [•] Investigation of fibre matrix bonding properties on microstructure response. [•] Simulations identified microstructures with optimized fracture properties. [Copyright &y& Elsevier]

Abstract: Here we present an in situ scanning electron microscopy (SEM) investigation of the compressive failure of unidirectional (UD) carbon fibre reinforced polymer (CFRP) composites with varying pre-existing void content. The experiments were carried out within a dual beam microscope, which couples a SEM with a focused ion beam (FIB), allowing sub-surface investigations of damage. In these tests, the specimen is monitored during the entire loading history, allowing the correlation of microstructural changes and the evolving load–displacement behaviour. Therefore, loading characteristics can be linked directly to failure events. Observations of the sequence of events leading to failure showed direct fibre deflection into a kinked shape eventually followed by fibre fracture. Failure of void-containing CFRP was shown to depend on the void shape as well as the proximity of the void to the kink band. In some cases voids stopped the propagation of kink bands, while in other cases the void caused the kink to deflect in a new direction. The failure structure was observed to change with time, both during hold-load segments as well as after unloading. Through cross-sectional ion beam milling in the unloaded state, the sub-surface damage was observed and shown to be similar to that observed at the surface. [Copyright &y& Elsevier]

Friction Stir Welding (FSW) imparts both heat and deformation to the metal being joined, producing profound microstructural changes that determine the weld properties. In the case of welding of aerospace aluminium alloys, the most important change is the modification of the size, nature, and fraction of strengthening precipitates. To understand these changes requires the ability to measure the microstructural evolution during the welding process. This paper describes a new tool, the FlexiStir system, a portable friction stir unit designed for use in a high-energy synchrotron beamline that enables in-situ studies of microstructural evolution during FSW. FlexiStir has been used to measure precipitate evolution during FSW of aluminium alloy 7449-TAF and provide time-resolved measurement of precipitate size and volume fraction via small angle X-ray scattering (SAXS). These measurements have been interpreted with the aid of a previously developed microstructural model. The model predictions and SAXS measurements are in good qualitative agreement and demonstrate the complex precipitate transformation, dissolution, and reprecipitation events that occur during welding. [ABSTRACT FROM AUTHOR]

Highlights: [•] High speed FSP was performed on Mg AZ31 at processing speeds between 1 and 10m/min. [•] Process zone EBSD analysis revealed deformation prone microstructure and texture. [•] The TMAZ featured low aspect ratio grains, with high mounts of HAB. [•] Formability tests revealed increases of up to 100% over the base material. [•] Local anisotropy was most present in the tensile regime of the FLD. [Copyright &y& Elsevier]

Abstract: Refill friction stir spot welding (FSSW-Refill) was used to produce solid-state joints in an automotive 5042 aluminium alloy. The influence of plunge depth, rotational speed, plunge rate and time on the microstructure and shear strength was investigated. The Statistica software package was used to correlate process parameters with the mechanical properties of the joints. The most significant variables are plunge depth and tool rotational speed, while volumetric defects have a small influence on the mechanical performance of the welds. Reducing the rotational speed from 1900rpm to 900rpm increased the bonding ligament length. For joints produced at a higher tool rotational speed (1900rpm) the material flow was more vertical, i.e., towards the surface of the joint, the bonding ligament length was reduced and the shear strength was impaired. [Copyright &y& Elsevier]

Abstract: The asymmetric material flow, severe plastic deformation and thermal cycle imposed on the base material during friction stir welding (FSW) result in unique microstructural development, which causes a gradient in local mechanical properties in the weld region. Micro-tensile and indentation testing were applied to determine the local mechanical properties in a friction stir welded joint. The local stress–strain curves exhibited a drastic change at the advancing side (AS) due to a steep gradient of mechanical properties. Finite Element Model (FEM) predictions of the tensile performance of the welded joints, based on the local mechanical properties measured by micro-tensile testing, were in very good agreement with the macro-tensile test data. [Copyright &y& Elsevier]

Abstract: The present paper is concerned with the analysis of size effects in short fibre reinforced composites. The microstructure of such composites often represents the first hierarchy level of a bioinspired material. For modelling fibre cracking as well as debonding between fibre and matrix material, a fully three-dimensional cohesive zone model is applied. It is shown that this model indeed captures the size effect associated with material failure of a single fibre. Furthermore, this scaling effect strongly depends on the shape and orientation of the assumed pre-existing crack. For this reason, a two-dimensional description can usually only predict the size effect qualitatively. Based on the aforementioned findings, a representative volume element (RVE) containing ceramic fibres embedded within a polymer matrix is considered. Similar to the single fibre, the RVE also shows a pronounced size effect. However, the underlying physical process is significantly more complex. More explicitly, the size effect of the RVE is a superposition of that related to the isolated fibres as well as of that induced by debonding of the fibres from the matrix material. For estimating the different effects, a perfect bond is also modelled. [Copyright &y& Elsevier]