Shear Modulus

The aim of this work is to propose a new method for determining both the in-plane shear modulus and the in-plane shear strength of composite materials by using three-point flexure tests on [AE45] angle-ply laminates. Symmetric and anti-symmetric configurations have been analysed by Classical Laminated Plate Theory. The anti-symmetric configuration has been considered more suitable than the symmetric one, due to the absence of bending/ twisting coupling effects. Three-point bending tests have been performed on [AE45] antisymmetric laminates of AS4/8552 carbon/epoxy material. Experimental results obtained by flexure tests in anti-symmetric laminates agree with the values attained by tensile tests on symmetric laminates, and with values reported in literature. Experimental conditions for determining in-plane shear properties by using the anti-symmetric three-point bending method are recommended.

This paper reviews the processing, properties, and structure of carbon fibers. Carbon fibers are derived from several precursors, with polyacrylonitrile being the predominant precursor used today. Carbon fibers have high strength (3–7 GPa), high modulus (200–500 GPa), compressive strength (1–3 GPa), shear modulus (10–15 GPa), and low density (1.75–2.00 g/cm3). Carbon fibers made from pitch can have modulus, thermal, and electrical conductivities as high as 900 GPa, 1,000 W/mK, and 106 S/m, respectively. These fibers have become a dominant material in the aerospace industry and their use in the automotive and other industries is growing as their cost continues to come down.

The selection of an adhesive for a particular application is not as easy as endeavour as it might originally appear. To achieve optimum performance when bonding two materials, one must carefully plan every stage of the bonding process. The selection of an adhesive is a critical factor that will influence each step. The adhesive selection will be dependent primarily on:

Centrifuge models of soft clay deposits were shaken with suites of earthquake ground motions to study site response over a wide strain range. The models were constructed in an innovative hinged-plate container to effectively reproduce one dimensional ground response boundary conditions. Dense sensor arrays facilitate back-calculation of modulus reduction and damping values that show modest misfits from empirical models. Low amplitude base motions produced nearly elastic response in which ground motions were amplified through the soil column and the fundamental site period was approximately 1.0s. High intensity base motions produced shear strains higher than 10%, mobilizing shear failure in clay at stresses larger than the undrained monotonic shear strength. We attribute these high mobilized stresses to rate effects, which should be considered in strength parameter selection for nonlinear analysis. This nonlinear response de-amplified short period spectral accelerations and lengthened the site period to 3.0s. The nonlinearity in spectral amplification is parameterized in a form used for site terms in ground motion prediction equations to provide empirical constraint unavailable from ground motion databases.

Hot compression testing of Mo-TZM (Mo-0.5Ti-0.1Zr-0.02C) alloy was carried out between 600 and 900°C employing strain rates from 0.001 s À1 to 1 s À1. Both the constant strain rate and strain rate change test results showed that Mo-TZM possesses low strain rate sensitivity in this temperature range. Activation energy calculated by using strain rate change data and plotting temperature compensated strain rate (Z) vs. shear modulus corrected flow stress (r/G) was found to be 290 kJ/mol. Electron back scattered diffraction (EBSD) and transmission electron microscopic (TEM) results obtained from the rapidly cooled deformed specimens revealed the formation of subgrains. Flow stress-plastic strain results and misorientation angles between subgrains showed an anomalous behavior at 800°C.

Mechanical and surface properties of paint films treated with organic solvents and water have been investigated using a range of thermomechanical and dielectric techniques together with Fourier transform infrared spectroscopy and scanning electron microscopy. Changes in the nature of the surface after treatment were observed. The effect of water, propan-2-ol and propanone (acetone) immersion for 24 hours, and swabbing for a few minutes, on naturally aged 12 years old samples of lead white/linseed oil and burnt sienna/linseed oil could be measured directly in terms of change in the shear modulus of the paint films together with the accompanying change in the ratio of viscous to elastic components present in each system. Generally, the solvent-treated films became harder and showed reduced viscous components, whereas the water-treated samples became softer. There was a change in the dielectric properties of the leached films which pointed to the polar nature of the leachings. FTIR diffuse reflectance spectra supported this conclusion. Mittels einer Reihe von thermomechanischen und dielektrischen Verfahren sowie FT-IR-Spektroskopie und Scanning-Elektronenmikroskopie wurden die mechanischen und OberflÄcheneigenschaften von mit organischen Lösungsmitteln und Wasser behandelten Anstrichfilmen untersucht. Nach der Behandlung konnte eine VerÄnderung der OberflÄchenbeschaffenheit beobachtet werden. Der Effekt von 24-stündigem Eintauchen in bzw. paar minütigem Abtupfen mit Wasser, Propan-2-ol und Propanon (Azeton) von natürlich gealterten, 12 Jahre alten Proben von Bleiwei\/Leinöl und gebrannter Sienaerde/Leinöl konnte als Funktion des Schubmodules des Anstrichfilmes gemessen werden, begleitet von einem übergang von viskosen zu elastischen Komponenten in jedem System. Im allgemeinen wurden die lösungsmittelbehandelten Proben hÄrter und wiesen weniger viskose Bestandteile auf, wÄhrend die wasserbehandelten Proben weicher wurden. Es trat auch eine Änderung der dielektrischen Eigenschaften der ausgelaugten Filme auf, was auf den polaren Charakter des Auslaugungsvorganges hinweist. FT-IR Remissionsspektren bekrÄftigten diese Schlu\folgerung.

The Osterberg cell (O-cell) type of bidirectional pile load testing is a modern full-scale proofing method in the realm of performance-based pile design. It is done at considerable cost, not possible on small-to medium-size projects. An economical approach of utilizing the flexible and approximate analytical solution proposed by Randolph has frequently been adopted in the past for evaluating pile settlements under static, unidirectional, top-down axial compression loading. To extend this solution for O-cell loadings, the following adaptations are warranted: (i) appropriate modifications to handle the loadings in two directions and (ii) development of a nonlinear stiffness reduction model, derived from the back-analysis of O-cell pile load tests. Accordingly, a modified analytical solution is presented for the two common cases of O-cell loading arrangements. Using these modified sets of solutions and a well-documented database of O-cell load tests on drilled shaft foundations from different sites, two stiffness reduction models have been developed. The shear wave velocity readings obtained from the hybrid geophysicalgeotechnical seismic piezocone tests afford the evaluation of fundamental shear stiffness modulus (G max) profiles. These profiles together with the rearranged modified solution were applied to the axial loads versus displacements (Q-w) from the database of load tests to back-calculate the applicable operational shear stiffness (G) values. Additional sensitivity analyses indicate that pile geometry and soil stiffness profile are the two most significant factors affecting the outcome of this solution. A comprehensive set of step-by-step example calculations is included to explain the procedure for implementing the solution.

This paper presents a novel self-gelling hydrogel potentially suitable for controlled drug delivery and tissue engineering. The macroscopic gels are obtained by mixing dispersions of oppositely charged crosslinked dextran microspheres. These microspheres in turn were prepared by crosslinking of dextran derivatized with hydroxyethyl methacrylate emulsified in an aqueous poly(ethylene glycol) solution. Negatively or positively charged microspheres were obtained by addition of methacrylic acid (MAA) or dimethylaminoethyl methacrylate (DMAEMA) to the polymerization mixture. Rheological analysis showed that instantaneous gelation occurred when equal volumes of oppositely charged microspheres, dispersed in buffer solutions of pH 7, were mixed. The shear modulus of the networks could be tailored from 30 to 6500 Pa by varying the water content of the system. Moreover, controlled strain and creep experiments showed that the formed networks were mainly elastic. Importantly for application of these systems, e.g. as controlled matrix of pharmaceutically active proteins, it was demonstrated that the hydrogel system has a reversible yield point, meaning that above a certain applied stress, the system starts to flow, whereas when the stress is removed, gel formation occurred. Further it was shown that the network structure could be broken by either a low pH or a high ionic strength of the medium. This demonstrates that the networks, formed at pH 7 and at low ionic strength, are held together by ionic interactions between the oppositely charged dextran microspheres. This system holds promise as injectable gels that are suitable for drug delivery and tissue engineering applications. r

The submission explores the mechanical behavior of a very porous chalk formation, in which a system of ancient caverns was excavated. Incidents of general and localized failure of these ancient caverns initiated a comprehensive laboratory testing program aimed at investigating the anisotropic nature of the stress-strain response and strength of the material. It was felt that these aspects could be of profound importance in the stability of the cavern systems. The effect of water content over a broad range from 1.5% to saturation, on the compressive and tensile strength was also studied. Testing was based on the hollow cylinder methodology and was supplemented with uniaxial compression of solid cylinders and diametric compression of Brazilian disks. Use of the hollow cylinder methodology was extended to failure conditions.

Acoustic radiation force impulse (ARFI) imaging involves the mechanical excitation of tissue using localized, impulsive radiation force. This results in shear-wave propagation away from the region of excitation. Using a single diagnostic transducer on a modified commercial ultrasound (US) scanner with conventional beam-forming architecture, repeated excitations with multiple look directions facilitate imaging shear-wave propagation. Direct inversion methods are then applied to estimate the associated Young's modulus. Shear-wave images are generated in tissue-mimicking phantoms, ex vivo human breast tissue and in vivo in the human abdomen. Mean Young's modulus values of between 3.8 and 5.6 kPa, 11.7 kPa and 14.0 kPa were estimated for fat, fibroadenoma and skin, respectively. Reasonable agreement is demonstrated between structures in matched B-mode and reconstructed modulus images. Although the relatively small magnitude of the displacement data presents some challenges, the reconstructions suggest the clinical feasibility of radiation force induced shear-wave imaging. (

The elastic moduli of single layer graphene sheet (SLGS) have been a subject of intensive research in recent years. Calculations of these effective properties range from molecular dynamic simulations to use of structural mechanical models. On the basis of mathematical models and calculation methods, several different results have been obtained and these are available in the literature. Existing mechanical models employ Euler-Bernoulli beams rigidly jointed to the lattice atoms. In this paper we propose truss-type analytical models and an approach based on cellular material mechanics theory to describe the in-plane linear elastic properties of the single layer graphene sheets. In the cellular material model, the C-C bonds are represented by equivalent mechanical beams having full stretching, hinging, bending and deep shear beam deformation mechanisms. Closed form expressions for Young's modulus, the shear modulus and Poisson's ratio for the graphene sheets are derived in terms of the equivalent mechanical C-C bond properties. The models presented provide not only quantitative information about the mechanical properties of SLGS, but also insight into the equivalent mechanical deformation mechanisms when the SLGS undergoes small strain uniaxial and pure shear loading. The analytical and numerical results from finite element simulations show good agreement with existing numerical values in the open literature. A peculiar marked auxetic behaviour for the C-C bonds is identified for single graphene sheets under pure shear loading.

The design of GFRP beams is often governed by deflection limits in service, hence it becomes crucial to evaluate accurately their flexural stiffness. In this work, the flexural stiffness of GFRP pultruded profiles is evaluated experimentally, numerically and analytically. A procedure that simultaneously yields the flexural and the shear modulus of GFRP pultruded profiles directly from 3-point bending tests is applied. Direct tension and 3-point bending tests on coupons extracted from these profiles were also conducted. The TBT and the FEM were applied to analyze the profiles under bending, using material properties estimated by CLT. Comparisons of numerical, analytical and experimental results are presented and discussed at the end.

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : https://oatao.univ-toulouse.fr/ Eprints ID : 4663 Colette ( 2011) Dynamic mechanical properties of oral mucosa: comparison with polymeric soft denture liners. Dynamic mechanical analysis Polyacrylic Polyisoprene Polysiloxane Oral mucosa Denture soft liner A B S T R A C T The purpose of this work was to characterize the viscoelastic behaviour of oral mucosa and compare it with the dynamic mechanical properties of different soft liners. For this purpose, a sample of pig oral mucosa and six commercialized soft liner samples have been investigated. A comparison was also carried with the first suitable hard rubber for dental prosthetics: vulcanite. Creep recovery (CR) and dynamic mechanical analysis (DMA) have been used to determine the mechanical modulus of oral mucosa and soft liners respectively. The Poisson ratio is used to compare mucosa bulk modulus and soft liner shear modulus. The biomechanical concept of conventional complete dentures needs a good adjustment of dynamic mechanical impedance between the base and oral mucosa. The viscoelastic mechanical property of the oral mucosa as a referent biopolymer has been confirmed in vitro. The modulus value, adjusted for old patients in physiological conditions, is in the order of 3 MPa. This study underlines the plasticization effect of absorbed water on the mechanical properties of the underlying tissue. This study allows us to define some characteristics of the most adapted biomaterial according to the clinical exigency. The required biomaterial must display the following properties: compatibility and chemical resistance with biological environment perpetuated mechanical properties during physiological conditions and clinical use, good adjustment of dynamic mechanical impedance with supporting mucosa and easy sample processing.

A micromechanics framework for the development of continuum-level constitutive models for the large-strain deformation of porous hyperelastic materials is presented. A kinematically admissible deformation field is assumed which enables the derivation of a strain energy density function for the porous material. The strain energy density function depends on the properties of the incompressible hyperelastic matrix material, the initial level of porosity, and the macroscopic deformation. Differentiation of the strain energy density function, with respect to deformation, provides an expression for the stress–strain behavior of the porous hyperelastic material. Example calculations are carried out for porous hyperelastic materials with a Neo–Hookean matrix. The constitutive model is used to predict the stress–strain behavior of the pore-containing matrix as a function of initial porosity and macroscopic loading conditions. Predictions of the dependence of the small-strain elastic response on porosity are compared to various estimates of effective elastic moduli for porous materials found in the literature. Constitutive model predictions of the small to large-strain deformation behavior compare well with results from numerical three-dimensional micromechanical multi-void cell models.

We have studied the mechanical properties of a new family of infrared transmitting glass-ceramics based on the GeS 2 -Sb 2 S 3 -CsCl system. Cs-based crystals have been generated inside the glass matrix and the crystal size is controlled to be less than 100 nm in order to keep the transparency of the composite materials. The presence of crystals leads to significant increase of the fracture toughness and the critical load for crack initiation. The increases depend on the type and on the size of crystals. Other mechanical properties such as Young's modulus, Shear modulus are much less sensitive to these crystals.

A new set of slope-deflection equations for Timoshenko beam-columns of symmetrical cross section with semi-rigid connections that include the combined effects of shear and bending deformations, and second-order axial load effects are developed in a classical manner. The proposed method that also includes the effects of the shear component of the applied axial force as the member deflects laterally (Haringx Model) has the following advantages: (1) it can be utilized in the stability and second-order analyses of framed structures made up of Timoshenko beam-columns with rigid, semi-rigid, and simple end connections; (2) the effects of semi-rigid connections are condensed into the slope-deflection equations for tension or compression axial loads without introducing additional degrees of freedom and equations; (3) it is more accurate than any other method available and capable of capturing the phenomena of buckling under axial tension forces; and (4) it is powerful, practical, versatile and easy to teach. Analytical studies indicate that shear deformations increase the lateral deflections and reduce the critical axial loads of framed structures made of members with low shear stiffness. The effects of shear deformations must be considered in the analysis of beam-columns with relatively low effective shear areas (like laced columns, columns with batten plates or with perforated cover plates, and columns with open webs) or with low shear stiffness (like elastomeric bearing and short columns made of laminated composites with low shear modulus G when compared to their elastic modulus E) making the shear stiffness GA s of the same order of magnitude as EI/L 2 . The shear effects are also of great importance in the static, stability and dynamic behavior of laminated elastomeric bearings used for seismic isolation of buildings. Four comprehensive examples are included that show the effectiveness of the proposed method and equations. . bending moment only and neglecting those caused by shear and axial forces. Basically, a number of simultaneous equations are formed with the unknowns taken as the angular rotations and displacements of each joint. Once these equations have been solved, the moments at all joints may be determined. The method is simple to explain and apply since it is based on the equilibrium of the joints and members. The classic slope-deflection method is generally taught in the introductory structural analysis courses (Norris and Wilbur [3], Kassimili [4]) and used in the structural design (Salmon and Johnson [5]) because it provides a clear perspective and a complete understanding of how the internal moments and the corresponding deformations are interrelated, both of which are essential in structural engineering. However, advances in composite materials of high resilience capacities and low shear stiffness as well as the need for lighter 0141-0296/$ -see front matter c Please cite this article in press as: Dario Aristizabal-Ochoa J. Slope-deflection equations for stability and second-order analysis of Timoshenho beam-column structures with semi-rigid connections. Engineering Structures (2008), Engineering Structures ( ) -3 J. Dario Aristizabal-Ochoa / Engineering Structures ( ) -7 J. Dario Aristizabal-Ochoa / Engineering Structures ( ) -9

In highway pavement management, the bearing capacity of the subgrade layers have significant influence on the performance of the overall pavement structure. Thus, the evaluation of subgrade quality is periodically needed for monitoring of the quality of the pavement so that it can be passed by moving vehicles without damage. The Spectral Analysis of Surface Wave-SASW, method is an in-situ non-destructive seismic testing method which is used for assessing the stiffness and the depth of road pavement structures including the subgrade layer in a fast and inexpensive manner. The objective of this paper is to present the capability of the SASW method in the assessment of the quality of pavement subgrade layer. The SASW method employed is based on the R-wave propagation. Using the phase difference data of Rwaves propagating in the surface of a pavement, the experimental dispersion curve of phase velocity is obtained. Consequently, inversion process is conducted to obtain the dynamic elastic and shear modulus of the pavement structure. The results showed that the SASW method was able to determine useful dynamic parameters for evaluation of the subgrade layer performance. Empirical models with good correlations were also derived from this study which can be easily used for in situ evaluation of the subgrade layer stiffness.

Seismic base isolation is now a days moving towards a very efficient tool in seismic design of structure. Increasing flexibility of structure is well achieved by the insertion of these additional elements between upper structure and foundation as they absorb larger part of seismic energy. However in Bangladesh, this research is still young for building structures. Therefore, this is a burning question to design isolation device in context of Bangladesh. Effort has been made in this study to establish an innovative simplified design procedure for isolators incorporated in multi-storey building structures. Isolation systems namely lead rubber bearing (LRB) and high damping rubber bearing (HDRB) have been selected for the present schoolwork. Numerical formulation and limiting criteria for design of each element have been engendered. The suitability to incorporate isolation device for seismic control has been sight seen in details. The study reveals simplified design procedures for LRB and HDRB for multi-storey buildings in Bangladesh. The detail design progression has been proposed to be included in Bangladesh National Building Code (BNBC).

This article is concerned with the so-called van Gurp-Palmenplot which charts the phase angles vs the absolute values of the complex shear modulus from a rheological experiment. Its basic characteristic features are elucidated for polymers having a simple, i.e., a linear structure. A subsequent manuscript will then address more complicated topologies as present in long chain branched polymers.

Dimensional changes between a pattern die and its corresponding investment cast part occur as a result of complex phenomena such as thermal expansion/contraction and hot deformation (elastic, plastic, and creep) during the processing of the pattern material (wax), mold material (shell), and solidifying alloy. In this study, wax pattern dimensions are determined using computer models that take into account the thermophysical and rheological behavior of the wax. Pattern dimensions are calculated using a three-dimensional finite element model for coupled thermal and mechanical analysis developed within the commercial software ABAQUS TM . Cerita TM 29-51, an industrial wax is considered in this study. The effects of restraint geometrical features by the metal die, and process parameters such as dwell time, die/platen temperature, injection pressure and injection temperature are also considered. The results of numerical simulation are compared with experimental measurements on test patterns. Measurements of the temperature at the injection port, pressure in the die cavity, and the results of numerical simulations provide several insights into the wax injection process. Viscoelastic models exhibit good potential for accurately capturing the details of wax pattern deformation. Conversely, pure elastic models are unsuitable for predicting deformation, as any distortion is completely relaxed once the pattern is removed from the die.

A comprehensive first principles study of structural, elastic, electronic, phonon and thermodynamical properties of novel metal carbide, platinum carbide (PtC) is reported within the density functional theory scheme. The ground state properties such as lattice constant, elastic constants, bulk modulus, shear modulus and finally the enthalpy of PtC in zinc blende (ZB) and rock-salt (RS) structures are determined. The energy band structure and electron density of states for the two phases of PtC are also presented. Of these phases zinc blende phase of PtC is found stable and phase transition from ZB to RS structure occurs at the pressure of about 37.58 GPa. The phonon dispersion curves and phonon DOS are also presented. All positive phonon modes in phonon dispersion curves of ZB-PtC phase indicate a stable phase for this structure. Within the GGA and harmonic approximation, thermodynamical properties are also investigated. All results reveal that the synthesized PtC would favor ZB phase. The compound is stiffer and ductile in nature.

Chalk develops as a result of diagenesis of pelagic calcareous ooze. In a newly deposited ooze sediment, porosity ranges from 60% to 80% but porosity reduces with burial. We studied how different porosity reduction mechanisms change the strength of these deep sea carbonate-rich sediments and effect Biot's coefficient, β. In calcareous ooze, β is one. Mechanical compaction reduces porosity, but only leads to a minor decrease in β. Recrystallization renders particles smoother, but does not lead to reduction in β unless it gives rise to pore stiffening cementation. Pore stiffening cementation causes β to fall, even when porosity remains constant. Biot's coefficient correlates with strength-indicating properties: compressional and shear modulus, oedometer modulus, yield strength, strain from direct loading and creep strain. Our data indicate that β may be used for predicting the diagenetic process involved in porosity reduction and strengthening of chalk during burial diagenesis.

The in-plane shear behaviour of URM wallettes strengthened using near surface mounted high strength twisted stainless steel reinforcement (TSNSM) was investigated and in particular, the effectiveness of the reinforcing schemes to restrain the diagonal cracking failure mode was studied. A total of 17 URM wallettes, each being 1.2 m  1.2 m in size, were structurally tested in induced diagonal compression. Of these, 3 wallettes were tested as-built and 14 wallettes were tested after being strengthened using different patterns of TSNSM bars. Several parameters pertaining to the in-plane shear behaviour of strengthened URM walls were investigated, including failure modes, shear strength, maximum drift, pseudoductility, and shear modulus. It was inferred from the results that as-built tested wallettes exhibited sudden post-peak strength degradation and failed along a stepped diagonal joint crack, whilst strengthened wallettes failed along distributed diagonal cracks in a more ductile fashion and exhibited a shear strength increment ranging from 114% to 189%.

The mechanical properties of fingernails are important because of their impact in preventing damage and in maintaining their appearance. In particular, knowing the effect of local environmental conditions can tell us how they might best be protected. In order to better understand this, tensile tests were carried out to characterise the properties of fingernails at different relative humidities. Cyclic tests were also conducted to investigate the ability of the structure to recover deformation at different moisture contents. Torsional tests were performed to determine the shear modulus of the keratinous matrix material which binds together the fibrous components of the fingernails. This enabled an analysis of how the material may resist bending, torsion and permanent deformation in a natural environment. In particular, it is shown that at low relative humidity the nails are more brittle, and at high moisture contents they are more flexible. Increasing relative humidity lowers torsional stiffness much more than tensile stiffness, suggesting that moisture plasticises the matrix rather than affecting the fibres. The twist to bend ratio is minimised at 55% RH, close to the natural condition of nails which should minimise susceptibility to torsional damage due to plasticisation and a disruption of the matrix material binding the keratin fibres.

We have studied the influence of the calcium ion concentration, [Ca 2þ ], and the pH on the storage (G 0 ) and loss (G 00 ) shear modulus at 1 Hz of low methoxyl pectin solutions and gels. Upon lowering the temperature in the presence of Ca 2þ , G 0 and G 00 increase immediately followed by a further slow logarithmic increase with time. The immediate response increases with increasing [Ca 2þ ] and decreasing temperature. The 'gel' temperature (T g ) where G 0 and G 00 cross increases with increasing [Ca 2þ ]. However, G 0 and G 00 have a universal temperature dependence at all [Ca 2þ ] if plotted as a function of T 2 T g .

Using unit load method, upper and lower bounds for the effective transverse shear moduli of a chevron folded core used in sandwich construction are analytically derived and compared to finite element computations. We found that these bounds are generally loose and that in some cases chevron folded cores are 40% stiffer than honeycomb-like cores.

Decay factor λ X , λ Y , λ Z X, Y and Z dimension length scale factors C 10 , C 01 Temperature dependent coefficients G 0 Short term shear modulus G ∞ Long term shear modulus t Time Abstract: A new 3 dimensional finite element representation of the human head complex has been constructed for simulating the transient occurrences of simple pedestrian accidents. This paper describes the development, features and validation of that model. When constructing the model, emphasis was placed on element quality and ease of mesh generation. As such, a number of variations of the model were created. The model was validated against a series of cadaveric impact tests. A parametric study (a High/Low study) was performed to investigate the effect of the bulk and shear modulus of the brain and cerebrospinal fluid (CSF). The influence of different mesh densities on the models and the use of different element formulations for the skull were also investigated. It was found that the short-term shear modulus of the neural tissue had the predominant effect on intracranial frontal pressure, and on the predicted Von-Mises response. The bulk modulus of the fluid had a significant effect on the contre-coup pressure when the CSF was modelled using a coupled node definition. Differences of intracranial pressure were reported that show the sensitivity of the method by which the skull is modelled. By simulating an identical impact scenario with a range of different finite element models it has been possible to investigate the influence of model topologies. We can conclude that careful modelling of the CSF (depth/volume) and skull thickness (including cortical/ trabecular ratio) is necessary if the correct intracranial pressure distribution is to be predicted, and so further forms of validation are required to improve the finite element models' injury prediction capabilities.

Low-frequency analytical solutions have been obtained for phase velocities of symmetrical fluid waves within both an infinite fracture and a pipe filled with a viscous fluid. Three different fluid wave regimes can exist in such objects, depending on the various combinations of parameters, such as fluid density, fluid viscosity, walls shear modulus, channel thickness, and frequency. Equations for velocities of all these regimes have explicit forms and are verified by comparisons with the exact solutions. The dominant role of fractures in rock permeability at field scales and the strong amplitude and frequency effects of Stoneley guided waves suggest the importance of including these wave effects into poroelastic theories.

Physical properties of chalcogenide glasses in the As x Se 1−x system have been measured as a function of composition including the Young's modulus E, shear modulus G, bulk modulus K, Poisson's ratio , the density , and the glass transition T g . All these properties exhibit a relatively sharp extremum at the average coordination number ͗r͘ = 2.4. The structural origin of this trend is investigated by Raman spectroscopy and nuclear magnetic resonance. It is shown that the reticulation of the glass structure increases continuously until x = 0.4 following the "chain crossing model" and then undergoes a transition toward a lower dimension pyramidal network containing an increasing number of molecular inclusions at x Ͼ 0.4. Simple theoretical estimates of the network bonding energy confirm a mismatch between the values of mechanical properties measured experimentally and the values predicted from a continuously reticulated structure, therefore corroborating the formation of a lower dimension network at high As content. The evolution of a wide range of physical properties is consistent with this sharp structural transition and suggests that there is no intermediate phase in these glasses at room temperature.

In a study on the properties of very soft clays, bender element testing was used to evaluate thixotropic hardening behavior; that is, to measure the stiffness with resting time under constant volume and water content. A laboratory vane test, which measures the undrained shear strength of the materials, was also carried out for comparison purposes. To investigate the mechanism of the thixotropic phenomenon, a consolidation test with very low pressure was also performed in a cell equipped with bender elements. The most important findings from this study are as follows: (1) regardless of soil types, the effect of thixotropy was significant around the liquid limit state and less remarkable at the lower and higher ranges; (2) the shear modulus at the liquid limit after 24 h resting is around 200 kPa; (3) the correlation between the shear modulus and the undrained shear strength of very soft clays is similar to that of cementtreated soil proposed by Seng and Tanaka (2011); (4) the increment of the shear modulus developed in the thixotropy process appears to be noticeably higher than that in the secondary consolidation process. It is believed that these findings are very useful to establish a new theory for the consolidation of ground filled by very soft clays or dredged soils with extremely high water content as well as to understand the effects of ageing on the consolidation properties of natural soils.

Displacement-length (D/L)scaling relations for normal and thrust faults from Mars, and thrust faults from Mercury, for which sufficiently accurate measurements are available, are consistently smaller than terrestrial D/L ratios by a factor of about 5, regardless of fault type (i.e. normal or thrust). We demonstrate that D/L ratios for faults scale, to first order, with planetary gravity. In particular, confining pressure modulates:

A common assumption in modeling soil-structure interaction is that the foundation is rigid. This reduces the complexity of the problem (i.e. the number of additional degrees of freedom for accounting for the interaction), and makes it possible to present general results that can be used for different structures (the substructure approach for linear models). In reality, building foundations are flexible. This paper presents an analysis of the consequences of this assumption, using a simple structural model: an elastic circular wedge supported by a flexible circular foundation embedded into a half-space and excited by incident pane SH-waves. The problem is solved by expansion of the motion in all three media (wedge, foundation and half-space) in cylindrical wave functions (Fourier-Bessel series). The structural model is simple, but accounts for both differential motions of the base and for the effects of soil-structure interaction. Usually, structural models in earthquake engineering consider either differential ground motion, but ignore soilstructure interaction, or consider soil-structure interaction, but for a rigid foundation, thus ignoring differential ground motion. This study attempts to find how stiff the foundation should be relative to the soil so that the rigid foundation assumption in soil-structure interaction models is valid. The shortest wavelength of the incident waves considered in this study is one equal to the width of the base of the wedge. It is concluded that, for this model, a foundation with same mass density as the soil but 50 times larger shear modulus behaves as "rigid". For ratio of shear moduli less than 16, the rigid foundation assumption is not valid. Considering differential motions is important because of additional stresses in structures that are not predicted by fixed-base and rigid foundation models.

We determine finite-frequency kernels for wave propagation in porous media based upon adjoint methods. These sensitivity kernels may be obtained based upon two numerical simulations for each source: one calculation for the current model and a second, 'adjoint', calculation that uses time-reversed signals at the receivers as simultaneous, fictitious sources. The adjoint equations for a porous medium are identical to the usual Biot equations, with the exception of the adjoint source term, which involves time-reversed measurements of the differences between simulations and data. Isotropic poroelastic wave propagation is governed by eight primary model parameters which appear in the original Biot equations. These parameters include four moduli: the shear modulus of the frame plus three bulk moduli. We consider two alternative parameterizations: one involving density-normalized moduli corresponding to squared wave speeds, and a second involving the poroelastic shear and compressional wave speeds. The alternative parameterizations lead to density-sensitivity kernels that are small, reflecting the fact that the traveltime of a poroelastic wave is governed by wave speed, not density. We systematically investigate and illustrate the sensitivity of the fast and slow compressional waves and the shear wave to the poroelastic model parameters using a 2-D spectral-element method. The poroelastic sensitivity kernels presented herein form the basis of tomographic imaging and inversion in porous media.

Three-directional orthogonal, 3-directional plain-woven and 4-directional in-plane composites are three architectures commonly used in components made of carbon/carbon composites. Homogenization and finite element analysis of a three-dimensional periodic unit cell characterizing the structure of the composite and periodic boundary conditions are used to compute the elastic moduli of carbon/carbon composites for different architectures. First, the mechanical properties of a fiber bundle are predicted assuming the fiber bundle to be a perfectly bonded uni-directional composite. Second, these properties are used to predict the mechanical properties of the multidirectional composite. Cohesive zone models are used to simulate the interfacial debonding at the fiber bundle/matrix interfaces. The application of cohesive zone model when there are debonds at the interface between the fiber bundle and the matrix results in a remarkable change in the values of shear modulus when compared to that obtained for perfectly bonded composites. The analysis predicts a significant effect of architecture on the properties of composite.

This paper reviews the processing, properties, and structure of carbon fibers. Carbon fibers are derived from several precursors, with polyacrylonitrile being the predominant precursor used today. Carbon fibers have high strength (3–7 GPa), high modulus (200–500 GPa), compressive strength (1–3 GPa), shear modulus (10–15 GPa), and low density (1.75–2.00 g/cm3). Carbon fibers made from pitch can have modulus, thermal, and

The strength of different wet granular materials is investigated as a function of the liquid volume fraction by measuring the elastic shear modulus, G ′ . We show that the optimum strength is achieved at a very low liquid volume fraction of 1-3%. Surprisingly we find that the macroscopic strength of different wet granular materials depends with a power of 2/3 on the microscopic elastic modulus of the individual grains, with a power of −1/3 on the radius, and with a power of 1/3 on the surface tension. This can be explained by assuming that the attractive capillary force between two grains deforms the grains elastically, yielding a "spring constant" for further deformation. Averaging over many grain-grain orientations allows us to predict the macroscopic shear modulus in excellent agreement with our experiments.

ABSTRACT This study investigates the effect of cement additive on some properties of asphalt binder using Superpave testing methods. Six cement-to-asphalt (C/A) ratios were considered in the study: 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 by volume of asphalt binder. The experimental tests that were conducted in the study included the Superpave rotational viscosity (RV) test and the dynamic shear rheometer (DSR) test. The RV test was conducted at the Superpave-specified high temperature of 135°C that represents the average mixing and laydown temperature, and at seven different rotational speeds of 5, 10, 20, 30, 50, 60, and 100rpm. On the other hand, the DSR test was conducted at four test temperatures of 58, 64, 70, and 76°C; one lower and two higher than the Superpave high performance grade (PG) temperature of the asphalt binder used in the study (PG 64). The loading frequency used in the DSR test was 10rad/s (1.59Hz) as specified by the Superpave system. Results of the study showed that the addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135°C and different rotational speeds. The C/A ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and the value of the DSR G*/sinδ rutting parameter of asphalt binders. The C/A ratio had insignificant effects on the Newtonian behavior, the phase angle (δ), and the elastic behavior of asphalt binders. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G*) value. The increase in the C/A ratio improved the rutting parameter, G*/sinδ value, at all temperatures. The increase in C/A ratio improved the Superpave high PG temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G*/sinδ value). It was also shown that the best function that described the relationship between each of RV, G*, and G*/sinδ and the C/A ratio was the exponential function with high coefficient of determination (R2).