Material Properties

A thin fiber or sheet curled into a circular container has a detached region whose shape and force ratios are independent of material properties and container radius. We compute this shape and compare it with experiments. The discrete forces acting at either end of the detached region have a ratio that depends only on the length of the fiber or sheet relative to the circle radius. We calculate this force ratio in three regimes of circle radius.

Scaling Effects in Direct Shear Tests. [AIP Conference Proceedings 1145, 413 (2009)]. Andrés D. Orlando, Daniel M. Hanes, Hayley H. Shen. Abstract. Laboratory experiments of the direct shear test were performed on spherical particles of different materials and diameters. ...

It is generally recognized that proper quantification of microstructural behavior is necessary for the optimization of materials properties. In the specific case of polycrystalline thin films, transmission electron microscopy ͑TEM͒ is required for microstructural interrogation due to the small ͑nm-m͒ inherent length scales in these systems. While a meaningful study requires large grain populations, typical data sets are relatively small due to the need for human interpretation of the contrast in TEM micrographs. To overcome this limitation, a general methodology has been developed to fully automate the grain boundary identification procedure by using a combination of both conventional and newly developed image processing algorithms to extract and combine information from multiple, optimized TEM micrographs. This technique has been validated by systematically analyzing microstructures of thin Al films, as obtained from TEM micrographs, and comparing these results with those obtained by a conventional, manual approach. Indeed, a statistical analysis shows that the agreement between these two methods is quite good. We further show that based upon a large population ͑8185 grains͒ one can estimate the number of grains required to draw meaningful conclusions about this microstructure. While the emphasis of this work is on TEM image processing, the techniques developed here are expected to be sufficiently general and flexible so as to be applicable to other ͑e.g., focused-ion beam͒ microscopies.

A new condition for crack penetration into the aggregate phase in concrete materials is developed based on numerical simulations. The numerical simulation utilizes a newly developed micromechanical model which considers the concrete internal structure as a three-phase material, viz. matrix, aggregate and interfaces between them. The micromechanical model is capable of capturing the entire load-deformation response of a concrete specimen under monotonic loading including softening. The new condition for crack penetration is developed based on a simple specimen con®guration where a crack is driven towards an aggregate particle. Results from numerical simulations are implemented to relate the relative properties of both aggregate and matrix phases (represented by the characteristic length ratio) to their tensile strength ratio. It is shown that the tensile strength ratio between the aggregate and the matrix plays the dominant role in determining the penetration condition. Predictions based on this condition agree with direct tensile simulations using dierent specimen con®guration. Ó

LL-37 is a cationic, amphipathic R-helical antimicrobial peptide found in humans that kills cells by disrupting the cell membrane. To disrupt membranes, antimicrobial peptides such as LL-37 must alter the hydrophobic core of the bilayer. Differential scanning calorimetry and deuterium ( 2 H) NMR experiments on acyl chain perdeuterated lipids demonstrate that LL-37 inserts into the hydrophobic region of the bilayer and alters the chain packing and cooperativity. The results show that hydrophobic interactions between LL-37 and the hydrophobic acyl chains are as important for the ability of this peptide to disrupt lipid bilayers as its electrostatic interactions with the polar headgroups. The 2 H NMR data are consistent with the previously determined surface orientation of LL-37 (Henzler Wildman, K. A., et al. (2003) Biochemistry 42, 6545) with an estimated 5-6 Å depth of penetration of the hydrophobic face of the amphipathic helix into the hydrophobic interior of the bilayer. LL-37 also alters the material properties of lipid bilayers, including the area per lipid, hydrophobic thickness, and coefficient of thermal expansion in a manner that varies with lipid type and temperature. Comparison of the effect of LL-37 on 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC-d 31 ) and 1,2-dimyristoyl-phosphatidylcholine (DMPC-d 54 ) at different temperatures demonstrates the importance of bilayer order in determining the type and extent of disordering and disruption of the hydrophobic core by LL-37. One possible explanation, which accounts for both the 2 H NMR data presented here and the known surface orientation of LL-37 under identical conditions, is that bilayer order influences the depth of insertion of LL-37 into the hydrophobic/hydrophilic interface of the bilayer, altering the balance of electrostatic and hydrophobic interactions between the peptide and the lipids.

Drawing of the hollow all-polymer Bragg fibers based on PMMA/PS and PVDF/PC materials combinations are demonstrated. Hole collapse during drawing effects the uniformity of a photonic crystal reflector in the resultant fiber. We first investigate how the core collapse effects fiber transmission properties. We then present modelling of fluid dynamics of hollow multilayer polymer fiber drawing. Particularly, hole collapse during

The development of three-dimensional P-wave velocity models for the regions surrounding five large earthquakes in California has lead to the recognition of relations among fault behavior and the material properties of the rocks that contact the fault at seismogenic depths; regions of high moment release appear to correlate with high seismic velocities whereas rupture initiation or termination may be associated with lower seismic velocities. These relations point toward a physical understanding of why faults are divided into segments that can fail independently, an understanding that could improve our ability to predict earthquakes and strong ground motion.

It is proven that time-independent viscoelastic Poisson ratios (PR) can only exist under separation of variable solutions which severely limits the class of applicable problems to quasi-static ones with incompressible homogeneous materials and non-moving boundaries under separable stress or displacement boundary conditions without any thermal expansions. Therefore, composites which are inherently anisotropic and sandwich structures which are nonhomogeneous and anisotropic are generally precluded from having time-independent PRs. Equal time variations for material properties in all directions are shown to be another simultaneous requirement instead of the incompressibility condition for achieving time-independent PRs. However, such restricted models lead to physically unrealistic bulk moduli responses when compared to experimentally determined relaxation moduli and are not generally achievable in current real materials. Consequently, viscoelastic materials are best characterized in t...

A time-domain formulation for sound propagation in rigid-frame porous media, including waveform attenuation and dispersion, is developed. The new formulation is based on inversion of the relaxation functions from a previous model [Wilson DK, Ostashev VE, Collier SL. J Acoust Soc Am 2004;116:1889-92], thereby casting the convolution integrals in a form amenable to numerical implementation. Numerical techniques are developed that accurately implement the relaxational equations and transparently reduce to previous results in low-and high-frequency limits. The techniques are demonstrated on calculations of outdoor sound propagation involving hills, barriers, and ground surfaces with various material properties. We also compare the relaxation formulation to a widely applied phenomenological model developed by Zwikker and Kosten. The two models can be made equivalent if the resistance constant, structure constant, and compression modulus in the ZK model are allowed to be weakly frequency dependent. But if the ZK parameters are taken to be constant, as is typically the case, the relaxation model provides more accurate calculations of attenuation by acoustically soft porous materials such as snow, gravel, and forest litter.

Needles with asymmetric bevel tips naturally bend when they are inserted into soft tissue. In this study, we present an analytical model for the loads developed at the bevel tip during needle-tissue interaction. The model calculates the loads based on the geometry of the bevel edge and gel material properties. The modeled transverse force developed at the tip is compared to forces measured experimentally. The analytical model explains the trends observed in the experiments. In addition to macroscopic studies, we also present microscopic observations of needle-tissue interactions. These results contribute to a mechanics-based model of robotic needle steering, extending previous work on kinematic models.

This paper examines quasi-static magnetic processes such as those found in magnetic recording. We shall discuss the hysteresis in medium-hard magnetic materials of the type used in recording media, and the magnetizability of soft magnetic materials such as those used in recording heads. There are two general modeling techniques used to described these processes: physical modeling and phenomenological modeling. In physical modeling, the basic processes involved are simulated in order to be able to describe the basic magnetizing modes. On the other hand, in phenomenological models, the gross behavior of the material is described mathematically by Preisach-type models in order to couple the material properties to Maxwell's equations so as to obtain solutions of field problems. The latter models are computationally more efficient than the former, but they do not give any insight into the physical principles involved. Edward Della Torre (Fellow, IEEE) was born i n Milano, Italy, and received the B.E.E. degree from the Polytechnic Institute of Brooklyn, the M.Sc. (E.E.) degree from Princeton University, the M.Sc. (physics) from Rutgers University, and the D.Sc. degree from Columbia University.

Direct Metal Laser Re-Melting is a variant of the Selective Laser Sintering process, a Rapid Prototyping (RP) technology. This tool-less manufacturing technology has the potential of producing complex, high quality components from single-phase metal powders in short time scales. This is made possible by the production of consecutive two-dimensional layers. Unfortunately, finished components manufactured by this technique have their integrity

In this paper the results of experimental works pertaining to the crash behaviour, collapse modes and crashworthiness characteristics of carbon fibre reinforced plastic (CFRP) tubes that were subjected to static axial compressive loading are presented in detail. The tested specimens were featured by a material combination of carbon fibres in the form of reinforcing woven fabric in thermosetting epoxy resin, and they were cut at various lengths from three CFRP tubes of the same square cross-section but different thickness, laminate stacking sequence and fibre volume content. CFRP tubes were compressed in a hydraulic press of 1000 kN loading capacity at very low-strain rate typical for static testing. The influence of the most important specimen geometric features such as the tube axial length, aspect ratio and wall thickness on the compressive response and collapse modes of the tested tubes is thoroughly analysed. In addition, the effect of the laminate material properties such as the fibre volume content and stacking sequence on the energy absorbing capability of the thin-wall tubes is also examined. Particular attention is paid on the analysis of the mechanics of the tube axial collapse modes from macroscopic and microscopic point of view, emphasizing on the mechanisms related to the crash energy absorption during the compression of the composite tubes.

Sounds convey information about the materials composing an object. Stimuli were synthesized using a computer model of impacted plates that varied their material properties: viscoelastic and thermoelastic damping and wave velocity ͑related to elasticity and mass density͒. The range of damping properties represented a continuum between materials with predominant viscoelastic and thermoelastic damping ͑glass and aluminum, respectively͒. The perceptual structure of the sounds was inferred from multidimensional scaling of dissimilarity judgments and from their categorization as glass or aluminum. Dissimilarity ratings revealed dimensions that were closely related to mechanical properties: a wave-velocity-related dimension associated with pitch and a damping-related dimension associated with timbre and duration. When asked to categorize sounds, however, listeners ignored the cues related to wave velocity and focused on cues related to damping. In both dissimilarity-rating and identification experiments, the results were independent of the material of the mallet striking the plate ͑rubber or wood͒. Listeners thus appear to select acoustical information that is reliable for a given perceptual task. Because the frequency changes responsible for detecting changes in wave velocity can also be due to changes in geometry, they are not as reliable for material identification as are damping cues.

This paper discusses the informational requirements of rapid prototyping and layered manufacturing (RPLM). The study is motivated by the recent decision to embark on the development of a new Application Protocol for the international standard ISO 10303, speci®cally to handle layered manufacturing information.

Electrowetting is arguably the most flexible tool to control and vary the wettability of solid surfaces by an external control parameter. In this article we briefly discuss the physical origin of the electrowetting effect and subsequently present a number of approaches for selected novel applications. Specifically, we will discuss the use of EW as a tool to extract materials properties such as interfacial tensions and elastic properties of drops. We will describe some modifications of the EW equation that apply at finite AC voltage for low conductivity fluids when the electric field can partially penetrate into the drops. We will discuss two examples where finite conductivity effects have important consequences, namely electrowetting of topographically structured surfaces as well as the generation of drops in AC electric fields. Finally, we review recent attempts to incorporate electrowetting into conventional channel-based microfluidic devices in order to enhance the flexibility of controlling the generation of drops.

In this paper, atomic layer deposited (ALD) alumina (Al 2 O 3 ) has been demonstrated as the structural material for a micro-resonator for the first time. An electrostatically actuated micro-bridge made of chromium (Cr) coated ALD Al 2 O 3 was used as a resonator. The resonator was formed by simple wet-and dry-etching processes. The static displacement profile of the micro-resonator under electrostatic load was measured by an optical interferometer. A model of a pinned-pinned beam with axial stress of 250 MPa was used to fit the measured data. Two techniques based on scanning electron microscope (SEM) and atomic force microscope (AFM) were developed to characterize the resonant frequencies of different modes and quality factor of the resonator. The measured resonant frequencies match well with the calculated values with residual stress of 258 MPa, providing additional insight into resonator model and ALD alumina material properties. The developed techniques can be applied to further size reduction of devices made with ALD methods.

This paper presents applications in which Electron Beam Induced Deposition (EBID) is used to characterize, analyze, and fabricate, nanostructures and devices. High aspect ratio Cylindrical Ultra Sharp (CUS) Atomic Force Microscope (AFM) probe tips are grown on discarded AFM tips using EBID. AFM is done using these CUS probe tips and compared to standard commercially available AFM probes as a baseline. The use of EBID to deposit platinum nanodots on thin foils for use as a hard mask in the fabrication of Quantum Cellular Automata cell structures is also reported. Successful EDS analysis was performed on these nanodots in a conventional Scanning Electron Microscope (SEM) with a high spatial resolution normally found only in the Scanning Transmission Electron Microscope (STEM). These EDS results demonstrate the ability to capture pertinent material properties of nanostructures in a more manageable SEM, and therefore, forgo the necessary complexities associated with a standard STEM.

This novel research work is motivated by the fascinating climbing ability of geckos. Recent experiments on the attachment mechanism of gecko feet have confirmed that van der Waals forces dominate gecko adhesion. Images of gecko feet have revealed a very intricate hierarchical fiber structures. These fibers are primarily responsible for the important properties of the gecko feet including strong adhesion, easy detachment, rough surface adaptation, self-cleaning, and resistance to wear. This paper introduces a methodology for designing biomimetic dry adhesive pads inspired by the attachment mechanism of gecko feet. The research has enhanced the understanding of gecko adhesive properties and their dependence on the geometry and material properties of gecko feet nano-fibers. We model the fibers as an array of oriented cantilever beams. Mathematical relations between the adhesion properties and fiber properties are studied, and design guidelines are formulated for fabrication of the biomimetic synthetic adhesives.

Many components are subjected to repeated impacts, or in some cases these impacts can appear as additional loads. Repeated impacts define a fatigue phenomenon known under the name of Impact Fatigue. Because the strain rate changes the material characteristics it is to expect that the material properties at impact fatigue to be different in regard to those obtained at non-impact fatigue. This paper presents a classification of repeated impact tests, and starting from this a series of parameters used for durability estimation will be analyzed. The high number of parameters used by different authors creates difficulties in comparison the different laboratories results. The importance of the shape and dimensions of specimens, and the stiffness of supports are highlighted. In order to avoid these influences the authors proposed an experimental technique, based on testing of Charpy specimens, in similar conditions as single impact test. A new parameter η is proposed in order to correlate the durability at repeated impacts with the Charpy V Notch (CVN) impact energy.

Landslides at continental margins are natural hazards for submarine installations and coastal regions. The occurrence of gas hydrates at continental margins is thought to be one major cause for these slides. It is assumed that the decomposition of gas hydrates increases the water content of the host sediment and thus lowers the strength of the soil. In order to predict

This paper presents a comprehensive comparison of three state-of-the-art heterojunction bipolar transistors (HBTs); the AlGaAs/GaAs HBT, the Si/SiGe HBT and the InGaAs/InP HBT. Our aim in this paper is to find the potentials and limitations of these devices and analyze them under common Figure of Merit (FOM) definitions as well as to make a meaningful comparison which is necessary for a technology choice especially in RF-circuit and system level applications such as power amplifier, low noise amplifier circuits and transceiver/receiver systems. Simulation of an HBT device with an HBT model instead of traditional BJT models is also presented for the AlGaAs/GaAs HBT. To the best of our knowledge, this work covers the most extensive FOM analysis for these devices such as I-V behavior, stability, power gain analysis, characteristic frequencies and minimum noise figure. DC and bias point simulations of the devices are performed using Agilent's ADS design tool and a comparison is given for a wide range of FOM specifications. Based on our literature survey and simulation results, we have concluded that GaAs based HBTs are suitable for high-power applications due to their high-breakdown voltages, SiGe based HBTs are promising for low noise applications due to their low noise figures and InP will be the choice if very high-data rates is of primary importance since InP based HBT transistors have superior material properties leading to Terahertz frequency operation.

We perceive the shapes and material properties of objects quickly and reliably despite the complexity and objective ambiguities of natural images. Typical images are highly complex because they consist of many objects embedded in background clutter. Moreover, the image features of ...

Future developments in cellulosic materials are predicated by the need to understand the fundamental interactions that occur at cellulose fibre interfaces. These interfaces strongly influence the material properties of fibre networks and fibre reinforced composites. This study takes advantage of fluorescence resonance energy transfer (FRET) and fluorescence microscopy to image cellulose interfaces. Steady-state epi-fluorescence microscopy suggests that energy transfer from coumarin dyed fibres to fluorescein dyed fibres is occurring at the fibre-fibre interface. The FRET response for natural spruce fibre interfaces is distinctly different from that observed in synthetic viscose fibres. This approach constitutes a novel methodology for the characterization of soft material interfaces on the molecular scale, and represents a major opportunity for advancing the understanding of fibrous network structures.

In this paper a complete rheological characterisation of bread dough added with water-solvable pentosans is showed. In the literature several works are available showing the chemical and physical effect of pentosan addition but it is still matter of discussion of their effect on the mechanical properties of dough. Therefore, the main objective is to further study this point, evaluating the effect of pentosans on the rheological properties of dough, using fundamental measurements and rheological modelling. Small amplitude oscillations at different temperatures were performed to evaluate material properties and stress relaxation tests, either within or out of the linear range, were used to investigate the effect of large deformations on material structure. Results showed that the effect of the addition is variable, depending on the amount, type of pentosans and deformation amplitude. The obtained results, together with rheological modelling, allow either to design dough having controlled properties during critical manufacturing steps (e.g. leavening or baking) or to reduce mechanical properties variability as effect of natural variation in flour characteristics.

As well as acting as a moderator and reflector, graphite is used as a structural component in many gas-cooled fission nuclear reactors. Therefore the ability to predict the structural integrity of the many graphite components which make up a graphite reactor core is important in safety case assessments and reactor core life prediction. This involves the prediction of the service

Detailed descriptions of the structural features of bone abound in the literature; however, the mechanical properties of bone, in particular those at the micro-and nano-structural level, remain poorly understood. This paper surveys the mechanical data that are available, with an emphasis on the relationship between the complex hierarchical structure of bone and its mechanical properties. Attempts to predict the mechanical properties of bone by applying composite rule of mixtures formulae have been only moderately successful, making it clear that an accurate model should include the molecular interactions or physical mechanisms involved in transfer of load across the bone material subunits. Models of this sort cannot be constructed before more information is available about the interactions between the various organic and inorganic components. Therefore, further investigations of mechanical properties at the 'materials level', in addition to the studies at the 'structural level' are needed to fill the gap in our present knowledge and to achieve a complete understanding of the mechanical properties of bone.

The crystal structure of the intermetallic compound Nb6Sn5 has been determined. The space-group symmetry was found to be Immm (D22~), and lattice parameters were measured as a--5.656+ 0.002, b= 9.199 _+ 0.003, e= 16.843 + 0"004 A. The compound shows pronounced layering normal to the short axis.

Purpose. To evaluate important material properties of six experimental resin-based restorative materials (EXP) with systematically modified resin matrices using conventional and alternative monomers in comparison with an experimental standard (ST). Materials and methods Commercially available monomers were selected according to their molecular weight, functionality, viscosity, and polymerization shrinkage. ST, 71 wt% filler, matrix UDMA/Bis-GMA/TTEGDMA and six EXPs with modified organic matrices but the same filler content were manufactured. Flexural strength, flexural modulus, water sorption, solubility and polymerization shrinkage of all EXPs were measured and compared with the results of ST. Results. ANOVA (p < 0.05) revealed significant differences among the materials and all investigated properties. Bis-GMA and UDMA were substituted by alternative monomers without losing flexural strength or modulus. Replacing the diluting monomer TTEGDMA with alternative monomers resulted in increased flexural strength. None of the experimental products with modified matrices showed increased water sorption or solubility but some even performed better than ST. Increased hygroscopic expansion and reduced shrinkage were achieved using a very hydrophilic monomer but no significant differences of water sorption and solubility in comparison with ST were found. Conclusion. The results indicated that there are monomers commercially available providing the same or even better properties than conventional matrices.

Compact silicon carbide (SiC) power semiconductor device models for circuit simulation have been developed for power Schottky, merged-PiN-Schottky, PiN diodes, and MOSFETs. In these models, the static and dynamic performance of the power SiC devices requires specific attention to the low-doped, voltage blocking drift region; the channel transconductance in MOS devices; the relatively low-intrinsic carrier concentration; the incomplete ionization of dopants; and the temperature dependent material properties. The modeling techniques required to account for each of these characteristics are described.

Transient creep crack growth due to grain boundary cavitation, and under plane strain and small scale creep conditions, is investigated. Full account is taken of the finite geometry changes accompanying crack tip blunting and the material is characterized as an elastic-power law creeping solid with an additional contribution to the creep rate arising from a given density of cavitating grain boundary facets. All voids are assumed present from the outset, distributed on a given density of cavitating grain boundary facets. Our analyses show the competing effects of stress relaxation due to creep, diffusion and crack tip blunting, and the stress increase due to crack growth. Another outcome of our analyses is the crack growth rate under various conditions of loading and for various values of material properties and for various characterizations of the failure process. Prior to crack growth, Hutchinson-Rice-Rosengren type singular fields dominate over the crack tip region, outside of a finite strain zone that has dimensions of the order of the crack opening displacement. These singular fields scale with the path integral C(t), which to a good approximation decays as K~/t, with t being the elapsed time since load application and KI the imposed stress intensity factor. When the crack growth rate is faster than the growth rate of the creep zone, our finite element results show that Hui-Riedel singular fields dominate over the crack tip region and the magnitude of the Hui-Riedel fields scales with the crack growth rate. For a crack that grows more slowly than the creep zone, Hutchinson-Rice-Rosengren type fields dominate over the crack tip region. In these circumstances, the crack growth rate is found to scale as C(t) to a power. Regardless of which of the two singular fields dominates for the growing crack, finite strain effects are found to be significant over a size scale of the order of the crack opening displacement at crack growth initiation. The effect of increased mesh refinement is also considered and very little mesh dependence is found.

In the development of numerical schemes for compressible multifluids, the treatment of the interface is very important. In this paper, we proposed a numerical method based on interface interactions where the ghost cells of the ghost fluid method, GFM [J. Comput. Phys. 152 (1999) 457], are determined by solving the real interface interaction and the hypothetical ''ghost'' interaction. Extensive tests in 1D are carried out and with the 2D examples suggest that the present scheme is able to handle multifluids problems with large difference of states and material properties at interface while still keeping to the simplicity of the original GFM.

This paper describes a study of petiole structural morphology in which tissue materials, cross-sectional geometry, layer-architecture and hydrostatic condition are variables that affect the overall structural properties of the organ. Philodendron melinonii is selected as a model species for characterizing the mechanical properties of the petiole. The shape of the petiole is modeled through the polar parameterization of the Lame's curves, i.e. Gielis formulation. A multiscale model of bending stiffness is proposed to capture the impact of changing the constituent tissues and the cross-sectional geometry. Stiffness and density of different tissues are used to plot the domain bounded by the limiting curve of the respective tissue material. Shape parameters and the respective tissue properties are used to generate structural efficiency maps displaying property domains within which fall all possible combinations of tissues that are shaped into a certain geometry during growth. The turgor pressure is also taken into account to show how the domain of the effective material properties changes with water content. Finite element analysis besides experimental data is used to validate the theoretical results. The maps may offer a source of inspiration for biomimetic design, as they help to gain insight into the efficiency of biological beams described by different tissues properties, geometry and turgidity.

Ultrasonic spectroscopy is a promising measurement technique for the characterisation of emulsions and suspensions over a wide range of particle size and concentration. It appears highly suitable for on-line applications, in particular for dense nano-sized particle systems, where the system stability may be very sensitive to changes in the concentration. In the case of colloidal dispersions the particle sizes are usually smaller than the sound wavelength. Then dissipative processes rather than scattering govern the acoustic behaviour of such systems. The dissipative processes, however, are affected by several material properties, whose significance for the overall acoustic behaviour depends on the type of the material system, e.g. thermal properties are important in the case of emulsions and non-watery suspensions but not for watery suspensions. Often the information on these parameters is incomplete and not sufficiently accurate. In this paper the stability of ultrasonic particle size measurement against incorrect values of the relevant material properties is investigated. This was done firstly by analytical consideration. From this, the degree of influence of the respective material properties on the analysis of spectrometric measurements was derived for oil-water-emulsions, watery and non-watery suspensions. It could be shown that the single properties affect the analysis very differently. In a second step, the conclusions obtained analytically could be confirmed by analysing experimental attenuation spectra with slightly changed material property data. The paper is intended to give users of ultrasonic spectroscopy a practical guide for deciding which material properties have to be obtained with high accuracy and which can be estimated. : S 0 9 2 7 -7 7 5 7 ( 0 0 ) 0 0 5 7 1 -9

Since nearly all adult insects fly, the cuticle has to provide a very efficient and lightweight skeleton. Information is available about the mechanical properties of cuticle-Young's modulus of resilin is about 1 MPa, of soft cuticles about 1 kPa to 50 MPa, of sclerotised cuticles 1 -20 GPa; Vicker's Hardness of sclerotised cuticle ranges between 25 and 80 kgf mm 22 ; density is 1 -1.3 kg m 23 -and one of its components, chitin nanofibres, the Young's modulus of which is more than 150 GPa. Experiments based on fracture mechanics have not been performed although the layered structure probably provides some toughening. The structural performance of wings and legs has been measured, but our understanding of the importance of buckling is lacking: it can stiffen the structure (by elastic postbuckling in wings, for example) or be a failure mode. We know nothing offatigue properties (yet, for instance, the insect wing must undergo millions of cycles, flexing or buckling on each cycle). The remarkable mechanical performance and efficiency of cuticle can be analysed and compared with those of other materials using material property charts and material indices. Presented in this paper are four: Young's modulus-density (stiffness per unit weight), specific Young's modulus-specific strength (elastic hinges, elastic energy storage per unit weight), toughness-Young's modulus (fracture resistance under various loading conditions), and hardness (wear resistance). In conjunction with a structural analysis of cuticle these charts help to understand the relevance of microstructure (fibre orientation effects in tendons, joints and sense organs, for example) and shape (including surface structure) of this fibrous composite for a given function. With modern techniques for analysis of structure and material, and emphasis on nanocomposites and self-assembly, insect cuticle should be the archetype for composites at all levels of scale. q

Mechanical properties of concrete mixtures with AR glass fibers are studied. Two types of concrete mixtures representing a lean mixture and an HPC (High Performance Concrete) mixture are used. Two types of AR Glass fibers High dispe rsion (HD) and High Performance (HP) with different sizing formulations to help with distribution, bonding and durability were considered. High dispersion (HD) AR Glass fibers of several different lengths were used to evaluate the effect of fibers which disperse thoroughly throughout the mixture. These were compared with High Performance (HP) type AR Glass fibers which maintain the bundle characteristics throughout the mixing and casting and are designed to help with long term strength and ductility. Bot h mixtures were compared with control specimens without fibers.

Finite element (FE) models of long bones are widely used to analyze implant designs. Experimental validation has been used to examine the accuracy of FE models of cadaveric femurs; however, although convergence tests have been carried out, no FE models of an intact and implanted human cadaveric tibia have been validated using a range of experimental loading conditions. The aim of the current study was to create FE models of a human cadaveric tibia, both intact and implanted with a unicompartmental knee replacement, and to validate the models against results obtained from a comprehensive set of experiments. Seventeen strain rosettes were attached to a human cadaveric tibia. Surface strains and displacements were measured under 17 loading conditions, which consisted of axial, torsional, and bending loads. The tibia was tested both before and after implantation of the knee replacement. FE models were created based on computed tomography (CT) scans of the cadaveric tibia. The models consisted of ten-node tetrahedral elements and used 600 material properties derived from the CT scans. The experiments were simulated on the models and the results compared to experimental results. Experimental strain measurements were highly repeatable and the measured stiffnesses compared well to published results. For the intact tibia under axial loading, the regression line through a plot of strains predicted by the FE model versus experimentally measured strains had a slope of 1.15, an intercept of 5.5 microstrain, and an R 2 value of 0.98. For the implanted tibia, the comparable regression line had a slope of 1.25, an intercept of 12.3 microstrain, and an R 2 value of 0.97. The root mean square errors were 6.0% and 8.8% for the intact and implanted models under axial loads, respectively. The model produced by the current study provides a tool for simulating mechanical test conditions on a human tibia. This has considerable value in reducing the costs of physical testing by pre-selecting the most appropriate test conditions or most favorable prosthetic designs for final mechanical testing. It can also be used to gain insight into the results of physical testing, by allowing the prediction of those variables difficult or impossible to measure directly.

Catastrophic flank collapses have occurred at many stratovolcanoes worldwide. We present a three-dimensional (3-D) slope stability analysis for assessing and quantifying both the locations of minimum edifice stability and the expected volumes of potential failure. Our approach can search the materials underlying a topographic surface, represented as a digital elevation model (DEM), and determine the relative stability of all parts of the edifice. Our 3-D extension of Bishop's [1955] simplified limit-equilibrium analysis incorporates spherical failure surfaces, variable material properties, pore fluid pressures, and earthquake shaking. Although a variety of processes can trigger collapse, we focus here on gravitationally induced instability. Even homogeneous rock properties strongly influence the depth and volume of the least stable potential failure. For large failures in complex topography, patterns of potential instability do not mimic local ground surface slope alone. The May 18, 1980, catastrophic failure of the north flank of Mount St. Helens provides the best documented case history to test our method. Using the undeformed edifice topography of Mount St. Helens in an analysis of dry, static slope stability with homogeneous materials, as might be conducted in a precollapse hazard analysis, our method identified the northwest flank as the least stable region, although the north flank stability was within 5% of the minimum. Using estimates of the conditions that existed 2 days prior to collapse, including deformed topography with a north flank bulge and combined pore pressure and earthquake shaking effects, we obtained good estimates of the actual failure location and volume. Our method can provide estimates of initial failure volume and location to aid in assessing downslope or downstream hazards.

A model to simulate the dense flow of granular materials is presented. It is based on continuum, pseudofluid approximation. Balance equations and constitutive relations account for fluctuations in the velocity field, through the`granular temperature' concept. Partial wall slip is also allowed by means of a slip-length approach. The model is applied to an industrial silo geometry, though not limited in its formulation to any geometry or flow configuration. It predicts realistic flow patterns, requiring quantitative validation with detailed measurements. This work focuses on the prediction of the normal stress at the wall during discharge. Profiles closely match available correlations by Jannsen and Walker, including prediction of peak pressure where section changes. Connections with literature correlations together with a sensitivity analysis provide clues to link model parameters to intrinsic material properties.

 A differential quadrature element method (DQEM) based on first order shear deformation theory is developed for free vibration analysis of non-uniform beams on elastic foundations. By decomposing the system into a series of sub-domains or elements, any discontinuity in loading, geometry, material properties, and even elastic foundations can be considered conveniently. Using this method, the vibration analysis of general beam-like structures is to be studied. The governing equations of each element, natural compatibility conditions at the interface of two adjacent elements and the external boundary conditions are developed in a systematic manner, using Hamilton's principle. The present DQEM is to be implemented to Timoshenko beams resting on partially supported elastic foundations with various types of boundary conditions under the action of axial loading. The general versality, accuracy, and efficiency of the presented DQEM are demonstrated having solved different examples and compared to the exact or other numerical procedure solutions.