Characterisation of dynamic behaviour of alumina ceramics: evaluation of stress uniformity

Accurate characterisation of dynamic behaviour of ceramics requires the reliable split-Hopkinson pressure bar (SHPB) technique and the condition of uniaxial homogeneous specimen deformation. In this study, an experimentally validated 3D finite element model of the full scale SHPB experiment was developed to quantitatively evaluate the wave propagation in the bars and the stress distribution/evolution in the alumina specimen. Wave signals in both the SHPB experiments and the finite element model were analysed to characterise the dynamic behaviour of alumina. It was found that the equilibrium of both stresses within the specimen and forces at the specimen ends can be established in the intermediate stage of deformation. The validity of stress uniformity in the alumina specimen supports the assumption of uniaxial homogeneous specimen deformation in the SHPB and validates the characterisation of dynamic behaviour of alumina ceramics

Voronoi cell finite element modelling of the intergranular fracture mechanism in polycrystalline alumina

The mechanisms of fracture in polycrystalline alumina were investigated at the grain level using both the micromechanical tests and finite element (FE) model. First, the bending experiments were performed on the alumina microcantilever beams with a controlled displacement rate of 10 nm s–1 at the free end; it was observed that the intergranular fracture dominates the failure process. The full scale 3D Voronoi cell FE model of the microcantilever bending tests was then developed and experimentally validated to provide the insight into the cracking mechanisms in the intergranular fracture. It was found that the crystalline morphology and orientation of grains have a significant impact on the localised stress in polycrystalline alumina. The interaction of adjacent grains as well as their different orientations determines the localised tensile and shear stress state in grain boundaries. In the intergranular fracture process, the crack formation and propagation are predominantly governed by tensile opening (mode I) and shear sliding (mode II) along grain boundaries. Additionally, the parametric FE predictions reveal that the bulk failure load of the alumina microcantilever increases with the cohesive strength and total fracture energy of grain boundaries

Novel Design And Synthesis Of Transition Metal Hydroxides And Oxides For Energy Storage Device Applications

Supercapacitors (SCs) and Li-ion batteries (LIBs) are two types of important electrical energy storage devices with high power density and high energy density respectively. However, to satisfy the increasing demand of high-performance energy storage devices, the energy density of SCs and power/energy densities of LIBs have to be further improved. The exploration, research, and development of electrode materials with high-performance for applications in SCs and LIBs are still needed to meet the ever-increasing demand on energy and power densities. Herein, the amorphous Ni-Co-Mo ternary hydroxides nanoflakes for SCs and oxides nanoflakes for LIBs with ultrathin stature, abundant open spaces, and interconnecting mesoporous were prepared via electrodeposition method and further annealing process, respectively. The as-obtained materials with unique hierarchical structures offer a large electrochemical active area, resulting in a fast ion transportation (OH- in SCs and Li+ in LIBs) electrolyte immersion, as well as provide effective pathways for electron transport. Thus, the as-prepared Ni-Mo-Co triple hydroxides and oxides electrodes exhibit a high specific capacitance /capacity (3074 F g-1 at 2 A g-1 in SCs and 1132.31 mA h g-1 at 0.2 A g-1 in LIBs), remarkable rate performance, as well as long-term cyclability in SCs and LIBs, respectively. Also, the effect of composition of trimetallic hydroxides on SCs performance have been studied, and the performance have been optimized by tuning the feeding ratio of Ni, Mo, and Co. It is found that supreme performance was achieved when feeding ratio Ni/Mo/Co (1/1/0.4)

The effect of slurry composition on the microstructure and mechanical properties of open-cell Inconel foams manufactured by the slurry coating technique

Open-cell nickel-based alloy foams are attractive materials for applications such as sound damping and heat exchange, especially those involving exposure to high temperature environments. This study demonstrated the potential of a developed slurry coating technique for manufacturing open-cell Inconel alloy foams, and then investigated the effect of slurry composition on the microstructure and mechanical properties of the foams. It was found that the compressive properties of the foam can be quantitatively related to its relative density using the empirical equations. The deformation behaviour of the foam is bending-dominated; and unit cell struts undergo brittle fracture after the elastic region. Increasing the slurry solid loading leads to a higher average bulk foam density and more non-uniform crush bands in the foam under compression. Compared to other fabrication processes, this slurry coating technique is able to produce open-cell Inconel foams with relatively higher strength-to-weight ratios. This study also revealed that the sound absorption capability of the foam increases when its unit cell size is reduced

Characterisation and constitutive model of tensile properties of selective laser melted Ti-6Al-4V struts for microlattice structures

Predicting the mechanical performance of selective laser melted (SLM) microlattice structures requires the constitutive data of the parent solid material in the struts. This work first characterised the cross-sectional features of individual SLM Ti-6Al-4V struts. The direct examination revealed the non-linear relation between the equivalent diameter and the Feret diameter of a strut, which was quantified by an empirical equation. The equation considering surface roughness effects allowed the non-destructive determination of the equivalent diameter using the directly measured Feret diameter prior to tension testing. Uniaxial tension experiments were then performed to accurately measure the constitutive behaviour of SLM Ti-6Al-4V struts, with the strain history tracked and recorded using high resolution imaging. It was found that the strut diameter ranging 300–1200 µm has a negligible effect on the stress–strain response. The strain hardening and fracture behaviour of the SLM Ti-6Al-4V can be quantitatively described using the Johnson–Cook models with damage. The constitutive models were finally validated by the 3D finite element model and experiments of uniaxial compression on an SLM microlattice structure. The methodology presented here can accurately characterise and formulate the constitutive behaviour of SLM metallic struts for microlattices

Quantification of flexural fatigue life and 3D damage in carbon fibre reinforced polymer laminates

Carbon fibre reinforced polymer (CFRP) laminated composites have become attractive in the application of wind turbine blade structures. The cyclic load in the blades necessitates the investigation on the flexural fatigue behaviour of CFRP laminates. In this study, the flexural fatigue life of the [+45/−45/0]2s CFRP laminates was determined and then analysed statistically. X-ray microtomography was conducted to quantitatively characterise the 3D fatigue damage. It was found that the fatigue life data can be well represented by the two-parameter Weibull distribution; the life can be reliably predicted as a function of applied deflections by the combined Weibull and Sigmodal models. The delamination at the interfaces in the 1st ply group is the major failure mode for the flexural fatigue damage in the CFRP laminate. The calculated delamination area is larger at the interfaces adjacent to the 0 ply. The delamination propagation mechanism is primarily matrix/fibre debonding and secondarily matrix cracking

CorefPrompt: Prompt-based Event Coreference Resolution by Measuring Event Type and Argument Compatibilities

Event coreference resolution (ECR) aims to group event mentions referring to the same real-world event into clusters. Most previous studies adopt the "encoding first, then scoring" framework, making the coreference judgment rely on event encoding. Furthermore, current methods struggle to leverage human-summarized ECR rules, e.g., coreferential events should have the same event type, to guide the model. To address these two issues, we propose a prompt-based approach, CorefPrompt, to transform ECR into a cloze-style MLM (masked language model) task. This allows for simultaneous event modeling and coreference discrimination within a single template, with a fully shared context. In addition, we introduce two auxiliary prompt tasks, event-type compatibility and argument compatibility, to explicitly demonstrate the reasoning process of ECR, which helps the model make final predictions. Experimental results show that our method CorefPrompt performs well in a state-of-the-art (SOTA) benchmark.Comment: Accepted by EMNLP202