Comparison of two micromechanical models for predicting elasto-plastic response of wood–plastic composites

The mechanical response of wood- and cellulose-filled polymers and its comparison to analytical models is studied in this article. To model the elasto-plastic response of the wood–plastic composite (WPC), two explicit semi-analytical micromechanical methods were used: Mori–Tanaka Method (MTM) and Generalised Method of Cells (GMC). For experimental purpose, several test specimens composed of matrix polypropylene (PP) or polystyrene (PS) and filled with wood or cellulose short fibres of different length to width aspect ratio and various volume fractions were injection moulded. Tensile testing was then used to gain experimental data, which were then compared to the calculated prediction of proposed micromechanical models to test their applicability. The comparison of results show that both methods can accurately predict the response of the composite in the elastic area; however Mori–Tanaka Method can achieve better results when forecasting plastic deformations of wood–plastic composites.     

Influence of Die Lubricants on Pickling and Conversion Treatment of High‐Pressure Die‐Cast AM30 Magnesium Alloy

The pre‐treatment of magnesium‐based components plays an important role in surface engineering technology to guarantee good adhesion of the final coating system to the magnesium substrate in order to achieve good corrosion resistance. This paper focuses on the influence of two different die lubricants—one based on mineral oil, the other on siloxane—on the pickling and conversion treatment of an AM30 alloy. The surface conditions after casting, pickling, and conversion treatment were determined by X‐ray‐induced photoelectron spectroscopy, spark erosion, optical emission spectroscopy, IR spectroscopy, and scanning electron microscopy (including EDX). The influence of the different die lubricants on the result of the pickling treatment in terms of surface morphology and composition was significant. The mineral–oil‐based lubricant was found to be removed more easily and uniformly from the surface. Only sufficient removal of the die lubricants can guarantee homogeneous and uniform formation of the conversion coating.     

Lamb waves for non-contact fatigue state evaluation of composites under various mechanical loading conditions

Methodologies for non-destructive evaluation of mechanically induced fatigue in fibre reinforced polymers are discussed. Specimens made of non-crimp glass fabric are fatigued using three different load ratios (tension–tension, tension–compression, and compression–compression). The investigation involves two loading directions (0° and 90°) of the quasi–orthotropic composite. Based on mode conversion of air-coupled ultrasound to Lamb waves, variation in a₀-mode velocity is measured in a non-contact and single-sided access configuration. The velocity measurements are performed within and outside the servo-hydraulic test rig used for inducing fatigue damage. Formation of cracks monitored in the transparent composite results in degradation of stiffness observed by the test rig. Decrease in a₀-mode velocity caused by fatigue is shown to correlate closely with stiffness degradation for all loading ratios and directions. The correlation is studied by calculating a₀-mode velocities from single-ply properties whose stiffness degradation was determined using the observed crack densities and a finite element based model.     

Fabrication and High Temperature Creep Behaviour of Interpenetrated Nickel–Chromium/Alumina Composites

A method to manufacture unique interpenetrating 50 vol% nickel–chromium/alumina composites, namely NiCr8020/Al₂O₃/50_pp, is reported. Key process is a high temperature squeeze casting procedure at temperatures above 1500 °C used to infiltrate alloy NiCr8020 into porous alumina preforms exhibiting a bimodal pore structure. Microstructure and mechanical properties of this new composite material are presented. Bending creep tests at 1000 and 1150 °C are performed. The obtained results are discussed in comparison to a nickel based superalloy. It is shown, that particle preform reinforcement is a promising method to improve creep resistance of nickel based alloys significantly. Due to its outstanding creep resistance, the composite material has a high potential for structural and tribological applications at high temperatures in oxidizing atmospheres.     

Human-like external function of the foot,and fully upright gait,confirmed in the 3.66 million year old Laetoli hominin footprints by topographic statistics,experimental footprint-formation and computer simulation

It is commonly held that the major functional features of the human foot (e.g. a functional longitudinal medial arch, lateral to medial force transfer and hallucal (big-toe) push-off) appear only in the last 2 Myr, but functional interpretations of footbones and footprints of early human ancestors (hominins) prior to 2 million years ago (Mya) remain contradictory. Pixel-wise topographical statistical analysis of Laetoli footprint morphology, compared with results from experimental studies of footprint formation; foot-pressure measurements in bipedalism of humans and non-human great apes; and computer simulation techniques, indicate that most of these functional features were already present, albeit less strongly expressed than in ourselves, in the maker of the Laetoli G-1 footprint trail, 3.66 Mya. This finding provides strong support to those previous studies which have interpreted the G-1 prints as generally modern in aspect.     

Desorption kinetics for field-aged polycyclic aromatic hydrocarbons from sediments

This study considers desorption kinetics for 12 field-aged polycyclic aromatic hydrocarbons (PAHs) desorbing from size- and density-fractionated sediments collected from two locations in the New York/New Jersey Harbor Estuary. Desorption kinetics for PAHs with a log octanol-water partition coefficient greater than 6 were well-described by a one-domain diffusion model that assumes that PAHs are initially uniformly distributed throughout spherical sediment aggregates. PAH hydrophobicity and sediment specific surface area were the parameters most strongly correlated with the magnitude of the observed diffusivity for the one-domain model. For less hydrophobic PAHs, a two-domain desorption model was used also, and the results suggest that a substantial fraction of these field-aged PAHs desorb via a relatively fast macro-mesopore diffusion mechanism. The model-predicted fraction of PAHs in the fast-diffusion regime by compound and sediment was highly correlated with the measured percent PAH desorption in 24 h. The fast-domain diffusivity was 100 times greater than the slow-domain diffusivity, was correlated with both PAH properties and sediment physical and chemical properties, and could be estimated by readily obtainable physical and chemical parameters. In contrast, the slow-domain diffusivity was not significantly correlated with PAH properties. Our results suggest that macro-mesopore diffusion may control mass transport of less-hydrophobic PAHs in estuarine sediments.     

Effect of substitution with Cr and addition of Ni on the physical and electrochemical properties of Ce0.9Sr0.1VO3 as a H2S-active anode for solid oxide fuel cells

Whereas Ce_0.9Sr_0.1Cr_0.5V_0.5O₃ is an active fuel cell anode catalyst for conversion of only the H₂S content of 0.5% H₂S-CH₄ at 850 °C, inclusion of 5 wt% NiO to form a composite catalyst enabled concurrent electrochemical conversion of CH₄. A fuel cell with a 0.3 mm thick YSZ membrane and Ce_0.9Sr_0.1Cr_0.5V_0.5O₃ as anode catalyst had a maximum power density of 85 mW cm⁻² in 0.5% H₂S-CH₄ at 850 °C, arising only from the electro-oxidation of H₂S. Using a same thick membrane, promotion of the anode with 5 wt% NiO increased the total anode electro-oxidation activity to afford maximum power density of 100 mW cm⁻² in 0.5% H₂S-CH₄. The same membrane provided 30 mW cm⁻² in pure CH₄, showing that the incremental improvement arose substantially from CH₄ conversion. Performance of each anode was stable for over 12 h at maximum power output. XPS and XRD analyses showed that an increase in conductivity of Ce_0.9Sr_0.1Cr_0.5V_0.5O₃ in H₂S-containing environments resulted from a change in composition and structure from the tetragonal oxide to monoclinic Ce_0.9Sr_0.1Cr_0.5V_0.5(O,S)₃.