Variation of transverse and shear stiffness properties of wood in a tree

In this work, the application of the unnotched Iosipescu test for the evaluation of the radial variability of longitudinal–radial stiffness parameters of maritime pine wood was investigated. Rectangular specimens with grain at 45° were tested using the Iosipescu fixture. For this configuration both the transverse (Q₂₂) and the shear (Q₆₆) stiffness parameters can be simultaneously identified by the virtual fields method. Displacement fields were measured by the grid method. The strain fields were reconstructed from the raw displacement fields using a polynomial approximation scheme. For the tested wood material, it was found that both parameters decrease from the centre to about the middle radius of the stem and increase afterwards to the outermost positions. Moreover, a relatively good correlation was obtained between the patterns of radial variability of Q₂₂ and Q₆₆.     

Fatigue properties of wood in tension,compression and shear

The fatigue properties of wood laminates have been investigated in tension, compression and shear. Fatigue lives in compression are significantly less than in tension, and S-N data at five R ratios has yielded a set of constant-life lines, the form of which is related to the failure mode of the wood observed by scanning electron microscopy. A point of inflection in the constant-life lines at the transition between all compressive and partially tensile fatigue loading is a new observation. S-N curves for wood laminates have been produced for shear across the radial-longitudinal and tangential-longitudinal planes, and the latter plane is observed to be more resistant to fatigue loads. Samples with four times the cross-sectional area of standard-sized samples have been fatigued at R=−1 and no significant difference in fatigue life is apparent. It appears that the absence of a size effect in tension-compression results from the orthotropic structure of wood which is insensitive to variations in the density of surface flaws.     

Piezoelectric behaviour of PZT doped with calcium: a combined experimental and theoretical study

An experimental and theoretical study on the piezoelectric behaviour of PZT doped with a range of calcium ion concentrations is presented. A systematic study of the effect on the piezoelectric properties of PZT doped with various concentrations of CaO at constant sintering temperature and sintering time was carried out. The remanent polarization, planar coupling factor and frequency–thickness constant increase with calcium concentration. Ab initio perturbed ion calculations show that the lattice energy decreases with calcium addition for both tetragonal and rhombohedral phases of PZT. This revised version was published online in November 2006 with corrections to the Cover Date.     

Assessment of viscous and elastic properties of sub-wavelength layered soft tissues using shear wave spectroscopy: theoretical framework and in vitro experimental validation

In elastography, quantitative imaging of soft tissue elastic properties is provided by local shear wave speed estimation. Shear wave imaging in a homogeneous medium thicker than the shear wavelength is eased by a simple relationship between shear wave speed and local shear modulus. In thin layered organs, the shear wave is guided and thus undergoes dispersive effects. This case is encountered in medical applications such as elastography of skin layers, corneas, or arterial walls. In this work, we proposed and validated shear wave spectroscopy as a method for elastic modulus quantification in such layered tissues. Shear wave dispersion curves in thin layers were obtained by finite-difference simulations and numerical solving of the boundary conditions. In addition, an analytical approximation of the dispersion equation was derived from the leaky Lamb wave theory. In vitro dispersion curves obtained from phantoms were consistent with numerical studies (deviation <1.4%). The least-mean-squares fitting of the dispersion curves enables a quantitative and accurate (error < 5% of the transverse speed) assessment of the elasticity. Dispersion curves were also found to be poorly influenced by shear viscosity. This phenomenon allows independent recovery of the shear modulus and the viscosity, using, respectively, the dispersion curve and the attenuation estimation along the propagation axis.     

Numerical and experimental failure analysis of screwed single shear joints in wood plastic composite

In this research, effects of end distances and thicknesses of side and main members on failure loads and also modes of failure of single shear plane joint, made on wood plastic composite (WPC) were studied, both experimentally and numerically as well. Yamada-Sun failure criterion was used to determine failure loads of this kind of joints fabricated on WPC and results were compared with that of experimental observations. Numerical analysis was made by making use of ABAQUS finite element (FE) software. Experiments were conducted according to ASTM D-1037. Predicted failure loads by numerical models were in good agreement with those observed experimentally. Results have indicated that failure load of tested joint is dependent on end distance and thickness of corresponding members as well. Failure modes were determined both by numerical models and tested joints. FE models were used to perform stress analysis.     

CVD growth of cubic boron nitride: A theoretical/experimental approach

Similarities and dissimilarities in the growth of diamond vs. c-BN, in the present series of investigations, have been studied using quantum mechanical calculations. Hydrogen species have been observed to be very effective in stabilising both types of compounds. Very large similarities have also been observed when considering the adsorption of various growth species to these materials. However, it was found necessary to avoid mixtures of B- and N-containing species in the gas phase during c-BN growth, since they should most probably result in a mixture of these species also on the (111) and (110) surfaces. In addition, a careful gas phase design was found necessary in order to avoid a preferential initial growth of h-BN. These theoretical results can be used as guide lines in striving towards a thin film deposition of cubic boron nitride using gentle CVD methods like atomic layer deposition.     

A powerful approach to develop nitrogen-doped graphene sheets: theoretical and experimental framework

Journal of Materials Science - We have reported a novel route to develop highly conductive graphene sheets using camphor as a natural precursor followed by nitrogen doping via low-temperature...     

Controlled drug delivery from porous hydroxyapatite grafts: An experimental and theoretical approach

Cylindrical hydroxyapatitic grafts at two different degree of porosity (60% and 40%) were tested as controlled drug delivery devices in order to evaluate the fundamental parameters which control release kinetics. The effect of device porosity, drug steric hindrance and drug loading on kinetics release has been appreciated using Ibuprofen-lysine and Hydrocortisone Na-succinate as non-steroidal and steroidal anti-inflammatory drug-models, respectively. The data put in evidence the difficulty for the more sterically hindered molecules to move throughout the microporosity of the ceramic graft. Furthermore, the results show how the higher drug load produces an initial higher release and how the less porous is the ceramic graft, the more evident is the initial burst release.A numerical approach, based on the use of the Finite Element Method, was adopted to describe the drug release kinetics from the porous ceramic graft. Numerical results on drug release in phosphate buffer saline solution were compared with experimental data and a good agreement was found. The importance of FEM modelling emerges as a predictive tool to study HA graft drug release performances in an efficient way, also in complex set-ups like the one here selected.     

Topology evolution of graphene in chemical vapor deposition, a combined theoretical/experimental approach toward shape control of graphene domains

Morphology control of thin film relies on understanding multiple ongoing processes during deposition and growth. To reveal the shape evolution of graphene domains on copper surfaces in chemical vapor deposition (CVD), a combinative study is performed on the CVD growth of graphene on copper surfaces. To identify the factors that influence the adsorption and diffusion of carbon atoms and further determine the domain shape, simulations based on kinetic Monte Carlo techniques are carried out. The results reveal the dependence of the graphene domain shapes on the crystalline orientation of the underlying copper substrate surfaces.     

Nonlinear shear properties of spruce softwood: Numerical analyses of experimental results

Determination of material parameters from experimental tests often rely on simplifying assumptions like the existence of uniform stress and strain fields within the considered part of the test specimen. However, more detailed analyses usually show that the stress and strain fields differ from the assumed (nominal) uniform distributions. In order to utilize the potential of numerical analyses of wooden structures by the FEM method, the nominal material parameters measured directly from tests need to be re-evaluated in order to make them more useful for FEM models and to make FEM models more reliable.Experimental data from shear testing of clear wood from Norway spruce was analysed numerically with a bilinear material law in shear. The inherent material parameters were fitted to the experimental behaviour by means of optimization methods in conjunction with FEM analyses. The study included six Arcan test configurations comprising the three orthotropic material planes of wood, and covered the whole loading range until failure. Compared to numerical results, it was found that stiffness values measured were too high, and that downward adjustments in the range of 5–30% were required. Linear limit stresses between 40% and 60% of the nominal shear strengths were found, whilst the tangent moduli ranged between 30% and 70% of the linear elastic shear moduli. The rolling shear plane RT showed most nonlinearity and the LT plane least. Analyses with modified bilinear parameters showed good correspondence with experimental findings. The parameters were found to be relatively well adapted by Weibull distributions.     

Determination of the high strain rate fracture properties of ductile materials using a combined experimental/numerical approach

The ‘flying wedge’ is a dynamic tensile test rig for determining the fracture properties of ductile materials over a range of strain rates from 10²–10⁴ s⁻¹. To accurately interpret the results from these tests, finite element simulations of the complete experiment as well as detailed models of the specimen subjected to different loading conditions are conducted using advanced materials constitutive relations. A new technique to carry out interrupted tensile testing at high strain rates on the flying wedge has been developed. Some typical results of the combined experimental and numerical technique are used to compare the predictions of different numerical ductile failure models which are also briefly reviewed in this paper.     

Analysis of the diffractional properties of dual-period apodizing gratings: theoretical and experimental results

We present an analysis of the diffractional properties of dual-period apodizing gratings. In a previous paper we used these components to obtain single-lateral-mode and dual-longitudinal-mode emission from a broad-area diode laser. We now calculate the diffracted field for a monochromatic beam incident on the grating by using an analytical model. Predictions of the model are compared with experimental measurements made with several dual-period gratings. We also discuss the situation in which a dual-period grating is used as an external coupler of a diode laser in a two-wavelength emission regime.     

Effects of conjugation on the properties of alkynylcarbazole compounds: experimental and theoretical study

Four novel dyes containing alkynylcarbazole, namely, 2-((9H-carbazol-3-yl)ethynyl)-9-ethyl-9H-carbazole, 3,6-bis((9-ethyl-9H-carbazol-2-yl)ethynyl)-9H-carbazole, 3-(phenylethynyl)-9H-carbazole and 3,6-bis(phenylethynyl)-9H-carbazole, were synthesized on the basis of single and double substitutes by following the Sonogashira coupling method. The synthesized dyes were then assessed as novel photosensitizers in visible-light photopolymerization to evaluate the effects of conjugation on the properties of aromatic compounds. A comparison between UV–vis and TD/DFT electron transition spectra shows that \(\lambda _{\mathrm{max}}\) in theoretical ultraviolet spectra matched well with the experimental spectra; every conjugated alkynylcarbazole dye exhibits a wide absorption band in the range of 300–400 mm. Moreover, conjugation enhancement by switching carbazoleacetylene moieties caused a red shift in the absorption bands. The theoretical study showed that the maxima \(\lambda \) of these molecules ranged from \(\sim \)330 to 370 mm, corresponding to \(\pi {\rightarrow }\pi ^{*}\) and \({n}{\rightarrow }\pi ^{*}\) electron transitions. Fluorescence spectroscopic data show that the strongest emission peaks exhibit a red shift because of the addition of conjugated acetylene groups. A combination of alkynyl dyes and iodonium under a halogen lamp atmosphere by visible-light photopolymerization displayed a positive response to the cationic polymerization of bisphenol-A epoxy resin A and free-radical polymerization of tripropylene glycol diacrylate.     

The role of ECL2 in CGRP receptor activation: a combined modelling and experimental approach

The calcitonin gene-related peptide (CGRP) receptor is a complex of a calcitonin receptor-like receptor (CLR), which is a family B G-protein-coupled receptor (GPCR) and receptor activity modifying protein 1. The role of the second extracellular loop (ECL2) of CLR in binding CGRP and coupling to Gs was investigated using a combination of mutagenesis and modelling. An alanine scan of residues 271–294 of CLR showed that the ability of CGRP to produce cAMP was impaired by point mutations at 13 residues; most of these also impaired the response to adrenomedullin (AM). These data were used to select probable ECL2-modelled conformations that are involved in agonist binding, allowing the identification of the likely contacts between the peptide and receptor. The implications of the most likely structures for receptor activation are discussed.     

A combined theoretical and experimental investigation of the valorization of mechanical and thermal properties of the fly ash-reinforced polypropylene hybrid composites

Journal of Materials Science - Fly ash (FA) particles were surface modified with cetyltrimethylammonium bromide (Ctab) and hybridized with graphene oxide (GO) and carboxymethyl cellulose (CMC)...     

Fatigue properties of wood and wood composites

An overview of the state of fatigue research for wood and wood products is presented. The extreme lack of a satisfactory data base and the persistent neglect of fatigue characteristics in wood material design is emphasized. Some theoretical considerations are presented to point out the difficulties met when attempting to model the behavior of wood products exposed to cyclic loading phenomena.A major conclusion of the work is the need for the entire materials science community to consider wood as a valuable and rewarding material upon which to focus research efforts. As wood is the world's primary renewable structural resource, a concerted effort must be made to understand its fatigue performance and the degree of accuracy in predicting life expectancy.

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Résumé On présente une revue générale des recherches dans le domaine de la fatigue du bois et des produits à base de bois. On fait remarques l'extrème pauvreté de bases de données satisfaisantes et la négligence persistante avec laquelle les caractéristiques de fatigue sont prises en considération dans la conception à partir de matériaux en bois. On présente quelques considérations théoriques exprimant les difficultés rencontrées lorsqu'il s'agit de modéliser le comportement des produits ligneux exposés au phénomène de mise en charge cyclique.Une conclusion importante du travail vise à sensibiliser la communauté des sciences des matériaux à considérer le bois comme un matériau valable et prometteur sur lequel un effort de recherche doit être concentré. Comme le bois est la ressource structurelle première entièrement renouvelable de ce monde, un effort concerté doit être entrepris afin de comprendre ses performances à la fatigue et le degré d'exactitude des prévisions de vie.

     

The dynamic properties of carbon-glass fibre sandwich-laminated composites: theoretical,experimental and economic considerations

Mathematical predictions of the dynamic properties of carbon-glass fibre sandwich hybrid laminated composites from the properties of the constituent materials have been developed. The energy method was used for predicting the dynamic properties of hybrid beams, while a finite element analysis technique was used for predicting the mode shape, resonant frequency and damping of the hybrid plates. Good agreement was obtained between the theoretical and experimental results for both beams and plates. It has been shown that by adding a small amount of cfrp to the surface of a grp composite, sandwich hybrid composites can be produced which have a much higher flexural modulus than the original grp. Thus, hybrid composites can be used economically for structural components, which carry mainly flexural loads.     

Investigations of Al:CdS/PVA nanocomposites: A joint theoretical and experimental approach

In the present work we investigate the aluminium doped cadmium sulphide (Al:CdS) nanoparticles embedded in polyvinyl alcohol (PVA) matrix by chemical route and density functional theory (DFT) based simulations. Supertetrahedron (T_n) cluster models are considered for the simulation of CdS nanoparticles. Using DFT simulations on T_n clusters, we observe that band gap of ligated clusters is slightly more as compare to bare clusters. This indicates the ability of organic ligands (PVA) to open the band gap of inorganic CdS nanoclusters. Negative value of binding energy indicates the stability of the inorganic–organic hybrid system. Frontier molecular orbitals (FMOs) indicate the charge transfer between organic and inorganic moieties which provides stability and longevity to nanoparticles, a prime function of ligands in nanocomposites. Absorption spectra of pure and doped clusters are calculated using time dependent density functional theory (TDDFT). CdS/PVA and Al:CdS/PVA samples are synthesized at room temperature by chemical method. Their structure, size and band gap is characterized by XRD, TEM, FTIR and UV spectroscopy. Optical band gap values as observed experimentally are in agreement with simulated TDDFT results.