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Ductile fracture has been extensively studied in metals with weak mechanical anisotropy such as copper and aluminum. The fracture of more anisotropic metals, especially those with a hexagonal crystal structure (e.g. titanium), remains far less understood. This paper investigates the ductile fracture process in commercially pure titanium (CP-Ti) with particular emphasis on the influence of grain orientation and local state of strain on void growth. An experimental approach was developed to directly relate the growth of a void in three dimensions to its underlying grain orientation. Grain orientation was obtained by electron back scattered diffraction on void-containing CP-Ti sheets prior to their diffusion bonding. Changes in void dimensions were measured during in-situ straining within an x-ray tomography system. The strong influence of the embedded grain orientation and that of its neighbors on void growth rate and coalescence has been experimentally quantified. Finite element crystal plasticity simulations that take into account both grain orientation and the local strain state were found to predict the experimental void growth. Grains where basal slip dominates show the largest void growth rates because they are closer to a plane strain condition that favors void growth and coalescence. [ABSTRACT FROM AUTHOR]

The microstructural evolution during solution treatment at 500 °C of a cast AlSi12Cu4Ni2 piston alloy is evaluated by two dimensional and three dimensional imaging methods aiming at identifying the microstructural features affecting the processes of damage formation and accumulation under tensile deformation. Highly interconnected networks of aluminides and Si undergo a local loss of connecting branches within these networks owing to the partial dissolution of Cu-rich aluminides and a slight Si spheroidisation. The damage by tensile deformation is studied using synchrotron tomography during in situ tensile tests. In both studied heat treatment conditions (0 h and 4 h solution treated) damage initiates in the form of micro-cracks in clusters of primary Si particles and debonding at the interface between Si and the matrix. These micro-cracks grow through intermetallic phases in the last stages of deformation. Final failure occurs by coalescence of these cracks mainly through the rigid phases. The loss of connectedness of the Si-intermetallics network during solution treatment allows the alloy to accommodate more damage and plastic strain resulting in an increase of ductility with respect to the as cast condition. [ABSTRACT FROM AUTHOR]

In situ vacuum-assisted infiltration experiments were carried out using synchrotron X-ray computed tomography (SXCT) to study the mechanisms of microfluid flow within a fiber tow. A single tow of E glass fibers was infused with a water and syrup blend using an apparatus designed and built for this purpose. The high resolution of the SXCT images allows the detailed reconstruction of individual fibers within the tow while the contrast between the different phases (air, fluid and fibers) was enough to track the fluid front position and shape as well as the void transport during infiltration. The ability of this technique to provide detailed information of microfluid flow and void transport in composite materials is clearly established. The fluid propagation at the microscopic level as well as the mechanisms of void transport within the tow were related to the wetting between the fluid and the fibers, the rheological properties of the fluid and the local microstructural details (fiber volume fraction, fiber orientation) of the fiber tow. [ABSTRACT FROM AUTHOR]

Because of their widely generalized use in many industries, composites are the subject of many research campaigns. More particularly, the development of both accurate and flexible numerical models able to capture their intrinsically multiscale modes of failure is still a challenge. The standard finite element method typically requires intensive remeshing to adequately capture the geometry of the cracks and high accuracy is thus often sacrificed in favor of scalability, and vice versa. In an effort to preserve both properties, we present here an extended finite element method (XFEM) for large scale composite fracture simulations. In this formulation, the standard FEM formulation is partially enriched by use of shifted Heaviside functions with special attention paid to the scalability of the scheme. This enrichment technique offers several benefits since the interpolation property of the standard shape function still holds at the nodes. Those benefits include (i) no extra boundary condition for the enrichment degree of freedom, and (ii) no need for transition/blending regions; both of which contribute to maintaining the scalability of the code. Two different cohesive zone models (CZM) are then adopted to capture the physics of the crack propagation mechanisms. At the intralaminar level, an extrinsic CZM embedded in the XFEM formulation is used. At the interlaminar level, an intrinsic CZM is adopted for predicting the failure. The overall framework is implemented in ALYA, a mechanics code specifically developed for large scale, massively parallel simulations of coupled multi-physics problems. The implementation of both intrinsic and extrinsic CZM models within the code is such that it conserves the extremely efficient scalability of ALYA while providing accurate physical simulations of computationally expensive phenomena. The strong scalability provided by the proposed implementation is demonstrated. The model is ultimately validated against a full experimental campaign of loading tests and X-ray tomography analyzes. [ABSTRACT FROM AUTHOR]

Two Ti–6Al–6V–2Sn alloys, with globular and lamellar microstructures, are deformed at 750 °C during tensile and compression tests. The lamellar microstructure shows softening and higher peak stress values than the globular microstructure as a consequence of the Hall–Petch effect. In-situ high energy synchrotron diffraction experiments allow characterization of the load partition between α- and β-phases, plastic deformation mechanisms and texture evolution. The α-phase deforms mainly by rotation while the β-phase deforms by misorientation formation, acting merely as load transfer agent. The Taylor factor evolution of the α-phase and the annihilation of dislocations are analyzed qualitatively and quantitatively. The Taylor factor is connected to both the softening observed in the alloy with the lamellar microstructure and the texture development. [ABSTRACT FROM AUTHOR]

• Z-yarns enhance energy dissipation and improve impact performance of composite materials. • The amount of energy absorbed improves when ductile fibres are located at the back. • Maximum stress failure criteria provide good correlation for low-velocity impact. This study investigates the low velocity impact behaviour and the energy absorption capability of a hybrid 3D woven composite made from S2-glass (GF), T700 carbon (CF) and Dyneema fibres. The laminate was asymmetric, having a high concentration of CF on one side and GF on the other. Experimental results revealed a pseudo-ductile behaviour of the material and a higher capability to absorb impact energy when glass plies are located at the back face of the laminate. A detailed fractographic analysis by means of X-ray microCT and a FE model was included to explain such differences. [ABSTRACT FROM AUTHOR]

Background: The development of technological routes to convert lignocellulosic biomass to liquid fuels requires an in-depth understanding of the cell wall architecture of substrates. Essential pretreatment processes are conducted to reduce biomass recalcitrance and usually increase the reactive surface area. Quantitative three-dimensional information about both bulk and surface structural features of substrates needs to be obtained to expand our knowledge of substrates. In this work, phase-contrast tomography (PCT) was used to gather information about the structure of a model lignocellulosic biomass (piassava fibers). Results: The three-dimensional cellular organization of piassava fibers was characterized by PCT using synchrotron radiation. This technique enabled important physical features that describe the substrate piassava fibers to be visualized and quantified. The external surface area of a fiber and internal surface area of the pores in a fiber could be determined separately. More than 96% of the overall surface area available to enzymes was in the bulk substrate. The pore surface area and length exhibited a positive linear relationship, where the slope of this relationship depended on the plant tissue. Conclusions: We demonstrated that PCT is a powerful tool for the three-dimensional characterization of the cell wall features related to biomass recalcitrance. Original and relevant quantitative information about the structural features of the analyzed material were obtained. The data obtained by PCT can be used to improve processing routes to efficiently convert biomass feedstock into sugars. [ABSTRACT FROM AUTHOR]

Alternative and renewable fuels derived from lignocellulosic biomass offer a potential alternative to conventional energy sources. Biorefinery feedstocks are usually pretreated with acid, alkali, or high temperature/pressure treatments before enzyme hydrolysis to yield glucose and other useful sugars for fermentation to ethanol. If plant cell walls are to be efficiently deconstructed by conversion technologies, then a detailed understanding of their structural organization in different length scales is required. Here, a novel imaging technique provided an opportunity to probe the deconstruction of the biomass structure by alkali pretreatments under mild operation condition. High-resolution phase-contrast tomography (PCT) provided unique aspects on the recalcitrance-related changes of physical structures spanning macro and micrometer length scales. This approach revealed that the thickness of the plant cell walls was considerable reduced on the whole particle. However, long cracks could be particularly observed crossing over the thin-walled parenchyma cells, making each the fibrovascular bundles totally or partially unattached and independent. Such particle fragmentation was responsible for increasing its external specific surface area about 10 times, while the total surface area of the inner porous structure only doubled in value. The PCT and imaging processing techniques can be applied to different processing routes for ethanol conversion, providing new insights into the underlying mechanisms of biomass deconstruction. [ABSTRACT FROM AUTHOR]

Pre-alloyed powders of near-eutectic Ti 66 Fe 27 Nb 3 Sn 4 (at.%) were produced by two standardised gas atomisation methods, named as Crucible-based Gas atomisation (CGA) and Crucible-Free atomisation (CFA), for powder bed fusion (PBF) techniques. PBF seems the ideal (and largely unexplored) processing route for bulk ultrafine eutectics because of their strict solidification criteria requiring fast and uniform cooling rates. CFA produced more desirable physical properties in powders, although the alloy's high oxygen affinity resulted in a dendritic oxide Fe 2 Ti 4 O. Electron Microscopy, X-ray Diffraction, image analysis and nanoindentation were used to understand the solidification behaviour in powder particles across different sizes, thus, different crystallisation kinetics. The alloy is quite sensitive to compositional fluctuations and solidified via different pathways in the two methods resulting in different microstructures. Presence of meta-stable phase and ultrafine inter-lamellar spacing (< 190 μm) of the eutectic matrix, which increases with powder particle size, highlight the potential of gas atomisation as a method to study rapid solidification. [Display omitted] • New pre-alloyed ultrafine eutectic powders for SLM. • Crucible-based and Crucible-Free gas atomisation produce different results. • Solidified microstructures in powders vary with particle size. • Inter-lamellar spacing of ultrafine eutectic increases with powder particle size. • Gas atomisation has high solidification rates similar to SLM. [ABSTRACT FROM AUTHOR]

The physicochemical properties of porous Ti 2 AlC and Ti 3 SiC 2 MAX phase compounds with controlled porosity and grain size obtained by powder metallurgy techniques was studied in depth in order to access their suitability of applications such as catalytic devices on vehicles, heat exchangers or impact resistant structures. The study was performed on isostatic consolidated samples with different amount (20–60 vol%) and size of space holder (250–1000 µm) and in samples without space holder. Oxidation tests were performed at different temperatures for each material depending on their maximum service temperature. In order to understand the oxidation mechanism, oxidation kinetics were analysed to determine the influence of size and amount of porosity in each case. In addition, the microstructure and composition of the oxide layers formed after the tests were analysed by scanning electron microscopy (SEM). Electrical and thermal conductivity where studied at room temperature and at temperature up to 1000 °C. The effect of pore size and cell wall thickness is discussed. Permeability of foams was also measured. The effect of micro porosity and macro porosity on permeability is discussed. The coefficient of thermal expiation was also measured for all foams produced. It is established that these porous MAX phases have suitable properties for their use as catalytic substrates, heat exchanges, high temperature filters or volumetric solar receivers. • In-spite of high exposed surface area MAX phase foams show good oxidation resistance. • Increase in pore size increases thermal and electrical conductivity due to wall thickness effect. • Effect of decrease in electrical conductivity with temperature is greater with bigger pore size. • Good gas permeability for Ti 3 SiC 2 and Ti 2 AlC foams with interconnected porosity. • CTE increases with pore size and increase in porosity decreases the CTE. [ABSTRACT FROM AUTHOR]

The 3D microstructure and its effect on damage formation and accumulation during tensile deformation at 300 °C for cast, near eutectic AlSi12Cu4Ni2Mg and AlSi12Cu4Ni3Mg alloys has been investigated using in-situ synchrotron micro-tomography, complemented by conventional 2D characterization methods. An increase of Ni from 2 to 3 wt.% leads to a higher local connectivity, quantified by the Euler number χ, at constant global interconnectivity of rigid 3D networks formed by primary and eutectic Si and intermetallics owing to the formation of the plate-like Al-Ni-Cu-rich δ-phase. Damage initiates as micro-cracks through primary Si particles agglomerated in clusters and as voids at matrix/rigid phase interfaces. Coalescence of voids leads to final fracture with the main crack propagating along damaged rigid particles as well as through the matrix. The lower local connectivity of the rigid 3D network in the alloy with 2 wt.% Ni permits localized plastification of the matrix and helps accommodating more damage resulting in an increase of ductility with respect to AlSi12Cu4Ni3Mg. A simple load partition approach that considers the evolution of local connectivity of rigid networks as a function of strain is proposed based on in-situ experimental data. [ABSTRACT FROM AUTHOR]