Elastic Modulus

Depth sensing indentation is a powerful experimental technique for determining mechanical properties of materials. In this work a computational routine was developed based on Oliver-Pharr method for measuring a more precise values of elastic modulus using a Fischerscope H100-depth sensing indentation apparatus, with a Vickers indenter. This computational routine aims also to measure Vickers hardness, as the equipment does not have software for this purpose. From indentation data it was possible to determine initial unloading stiffness, contact depth, projected contact area, reduced modulus, elastic modulus and Vickers hardness of materials. The validity of the routine was verified analyzing two coatings and nine bulk specimens with different elastic-plastic behaviors. It was verified that the elastic moduli determined through the software of the equipment resulted in great discrepancies when low loads were applied. A good estimate of the elastic moduli of the tested materials is given by the developed routine. For several testing loads, the diagonals determined by means of analytical procedure were compared with the same diagonals measured by image analysis. A good estimate of the Vickers hardness of the above-mentioned materials is given by the developed routine using different testing loads.

Milling and baking tests were carried out on three transgenic wheat lines and their parental varieties grown in the field at two UK sites. The transgenic and control lines were essentially similar in their milling properties but the subunit 1Ax1 and 1Dx5 transgenes had different effects on breadmaking. The subunit 1Dx5 transgene resulted in a low loaf volume and poor crumb structure when expressed in lines with two or five endogenous HMW subunits, and this was accompanied by a greatly increased elastic modulus of the gel protein fraction. In contrast, the 1Ax1 transgene resulted in improved breadmaking quality and a more modest increase in the gel protein elastic modulus when expressed in the two subunit background. Blending of flour from a line expressing the 1Dx5 transgene with flour from a normal breadmaking wheat variety resulted in decreased breadmaking quality, even at a ratio of 1:9. The difference in the results obtained with the 1Ax1 and 1Dx5 transgenes may relate to the presence of an additional cysteine residue in the protein encoded by the latter, which promotes a more highly cross-linked glutenin network.

The technological effect of wheat fibre, as a healthy ingredient in which consumers are interested, was studied in surimi gel products. Three and six per cent wheat fibre with different particle sizes was added. Functional properties of wheat fibre, such as water retention capacity (WRC), swelling (SW) and fat adsorption capacity (FAC), were determined. Elastic modulus (G′) of surimi with 6% wheat fibre was lower throughout thermal gelling. Under scanning electronic microscopy (SEM), gel samples with added fibre presented uneven distribution of fibre. This induced the formation of a non-homogeneous protein net associated with lower gel strength, cohesiveness and water binding capacity (WBC). The sensory panel found no differences in appearance but differences in texture among samples containing different proportions and types of fibre. Fibre with large particle sizes protected surimi from loss of gel strength and hardness during freezing. There were very few variations during frozen storage of different samples.

Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's modulus of below 100 kPa to adhere well to substrates. Such a low effective Young's modulus allows the adhesive organs to make almost direct contact with the substrate and results in van der Waals forces along with capillary forces. In previous studies, the effective Young's moduli of adhesive organs were determined using indentation tests, revealing their structure to be very soft. However, adhesive organs show a layered structure, thus the measured values comprise the effective Young's moduli of several layers of the adhesive organs. In this study, a new approach is illustrated to measure the Young's modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus. As a result of the epicuti...

Biological vessels are characterized by their substantial compliance and low friction that present a major challenge for crawling robots for minimally invasive medical procedures. Quite a number of studies considered the design and construction of crawling robots; however, very few focused on the interaction between the robots and the flexible environment. In a previous study, we derived the analytical efficiency of worm locomotion as a function of the number of cells, friction coefficients, normal forces, and local (contact) tangential compliance. In this paper, we introduce the structural effects of environment compliance, generalize our previous analysis to include dynamic and static coefficients of friction, determine the conditions of locomotion as function of the external resisting forces, and experimentally validate our previous and newly obtained theoretical results. Our experimental setup consists of worm robot prototypes, flexible interfaces with known compliance and a Vicon motion capture system to measure the robot positioning. Separate experiments were conducted to measure the tangential compliance of the contact interface that is required for computing the analytical efficiency. The validation experiments were performed for both types of compliant conditions, local and structural, and the results are shown to be in clear match with the theoretical predictions. Specifically, the convergence of the tangential deflections to an arithmetic series and the partial and overall loss of locomotion verify the theoretical predictions.

Dry abrasive wear performance of five plain weave carbon fabric (CF) reinforced Polyetherimide (PEI) composites, developed with increasing CF contents (in the step of C10 vol%) is reported in this paper. It was observed that composite reinforced with 65 vol% CF (IP 65) exhibited the best tensile and shear strength and closely followed the leader (IP 75) in flexural strength. IP 65 when abraded against silicon carbide paper showed highest wear resistance (W R) and lowest friction coefficient (m) among all composites. The composites IP 85 and IP 40 containing highest and lowest amount of CF respectively showed least enhancement in strength properties and poorest wear performance. Parallel studies on the influence of fabric orientation with respect to the sliding plane and direction, on W R showed that when CF was oriented parallel to the sliding plane, it had poorest wear resistance. The performance improved for the composites when fabric was oriented normal to the plane. The parallel or anti-parallel orientation of warp or weft fibers with respect to sliding direction showed marginal changes in friction and wear performance. Wear mechanisms were suggested and strongly supported by worn surface analysis using SEM. Efforts were also done to investigate the wear-property correlation. It was observed that the W R was directly proportional to the product of interlaminar shear strength (I s) and elastic modulus (E). Fairly good linearity was shown for specific wear rate (K 0) as a function of factor (mP/I s E) where m is coefficient of friction and P is the normal pressure (N/mm 2).

Fibrin fibers, which are~100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of a-a cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of individual, uncross-linked, exclusively a-a cross-linked (gQ398N/Q399N/K406R fibrinogen variant), and completely cross-linked fibrin fibers. Exclusive a-a cross-linking results in 2.5Â stiffer and 1.5Â more elastic fibers, whereas full cross-linking results in 3.75Â stiffer, 1.2Â more elastic, but 1.2Â less extensible fibers, as compared to uncross-linked fibers. On the basis of these results and data from the literature, we propose a model in which the a-C region plays a significant role in inter-and intralinking of fibrin molecules and protofibrils, endowing fibrin fibers with increased stiffness and elasticity.

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.

The conductance and electrostriction of bilayer lipid membranes (sBLM) supported on stainless steel and on conducting polymer polypyrrole (PPY) were studied. We showed that an increase in ammonia concentration resulted in an increase in d.c. current flow across the PPY layer adjacent to the metal surface and that covered by the lipid bilayer. The elasticity modulus in the direction perpendicular to the sBLM surface (E) and the electrical capacitance (C) were characterized by a complicated dependence on the application of an external d.c. voltage. In the case of sBLM formed on the PPY layer and that modified by avidin-urease, higher values of E were observed and in addition the latter system was characterized by a less expressed hysteresis of E and C than the metal supported sBLM. This is evidence that sBLM formed on PPY layers is smoother and more homogeneous than that formed on a metal support. We developed a urea minisensor based on sBLM supported on a PPY layer. Avidin-biotin tec...

Human lung undergoes breathing-induced deformation in the form of inhalation and exhalation. Modeling the dynamics is numerically complicated by the lack of information on lung elastic behavior and fluid–structure interactions between air and the tissue. A mathematical method is developed to integrate deformation results from a deformable image registration (DIR) and physics-based modeling approaches in order to represent consistent volumetric lung dynamics. The computational fluid dynamics (CFD) simulation assumes the lung is a poro-elastic medium with spatially distributed elastic property. Simulation is performed on a 3D lung geometry reconstructed from four-dimensional computed tomography (4DCT) dataset of a human subject. The heterogeneous Young’s modulus (YM) is estimated from a linear elastic deformation model with the same lung geometry and 4D lung DIR. The deformation obtained from the CFD is then coupled with the displacement obtained from the 4D lung DIR by means of the T...

The material properties of a tendon affect its ability to store and return elastic energy, resist damage, provide mechanical feedback and amplify or attenuate muscle power. While the structural properties of a tendon are known to respond to a variety of stimuli, the extent to which material properties vary among individual muscles remains unclear. We studied the tendons of six different muscles in the hindlimb of Eastern wild turkeys to determine whether there was variation in elastic modulus, ultimate tensile strength and resilience. A hydraulic testing machine was used to measure tendon force during quasi-static lengthening, and a stress-strain curve was constructed. There was substantial variation in tendon material properties among different muscles. Average elastic modulus differed significantly between some tendons, and values for the six different tendons varied nearly twofold, from 829±140 to 1479±106MPa. Tendons were stretched to failure, and the stress at failure, or ultimate tensile stress, was taken as a lower-limit estimate of tendon strength. Breaking tests for four of the tendons revealed significant variation in ultimate tensile stress, ranging from 66.83±14.34 to 112.37±9.39MPa. Resilience, or the fraction of energy returned in cyclic length changes was generally high, and one of the four tendons tested was significantly different in resilience from the other tendons (range: 90.65±0.83 to 94.02±0.71%). An analysis of correlation between material properties revealed a positive relationship between ultimate tensile strength and elastic modulus (r 2 0.79). Specifically, stiffer tendons were stronger, and we suggest that this correlation results from a constrained value of breaking strain, which did not vary significantly among tendons. This finding suggests an interdependence of material properties that may have a structural basis and may explain some adaptive responses observed in studies of tendon plasticity.

Introduction: The aims of this study were to develop a method for constructing a 3-dimensional finite-element model (FEM) of the maxilla and to evaluate the effects of transverse expansion on the status of various midpalatal sutures. Methods: A 3-dimensional FEM of the craniofacial complex was developed by using computed-tomography images and Bionix modeling software (version 3.0, CANTIBio, Suwon, Korea). To evaluate the differences between transverse expansion forces in the solid model (maxilla without a midpalatal suture), the fused model (maxilla with suture elements), and the patent model (maxilla without suture elements), transverse expansion forces of 100 g were applied bilaterally to the maxillary first premolars and the first molars. Results: The fused model expressed a stress pattern similar to that of the solid model, except for the decreased first principal stress concentration in the incisive foramen area. The patent model, however, had a unique stress pattern, with the stress translated superiorly to the nasal area. The anterior nasal spine and the central incisors moved downward and backward in both solid and fused models but moved primarily downward with a slight backward movement of the anterior nasal spine in the patent model. Conclusions: Clinical observations of maxillary expansion can be explained by different suture statuses. This efficient and customized FEM model can be used to predict craniofacial responses to biomechanics in patients. (Am J Orthod Dentofacial Orthop 2009;136:367-74)

In the prediction of bone remodelling processes after total hip replacement (THR), modelling of the subject-specific geometry is now state-of-the-art. In this study, we demonstrate that inclusion of subject-specific loading conditions drastically influences the calculated stress distribution, and hence influences the correlation between calculated stress distributions and changes in bone mineral density (BMD) after THR.For two patients who received cementless THR, personalized finite element (FE) models of the proximal femur were generated representing the pre- and post-operative geometry. FE analyses were performed by imposing subject-specific three-dimensional hip joint contact forces as well as muscle forces calculated based on gait analysis data. Average values of the von Mises stress were calculated for relevant zones of the proximal femur. Subsequently, the load cases were interchanged and the effect on the stress distribution was evaluated. Finally, the subject-specific stress distribution was correlated to the changes in BMD at 3 and 6 months after THR.We found subject-specific differences in the stress distribution induced by specific loading conditions, as interchanging of the loading also interchanged the patterns of the stress distribution. The correlation between the calculated stress distribution and the changes in BMD were affected by the two-dimensional nature of the BMD measurement.Our results confirm the hypothesis that inclusion of subject-specific hip contact forces and muscle forces drastically influences the stress distribution in the proximal femur. In addition to patient-specific geometry, inclusion of patient-specific loading is, therefore, essential to obtain accurate input for the analysis of stress distribution after THR.

Continuous silicon carbide fibre yarn has been used as a reinforcement for borosilicate and 96% silica glass matrices. The resultant composites exhibit excellent levels of strength and elastic modulus up to temperatures of 600 ~ C and 1100 ~ C, respectively. At higher temperatures excessive matrix softening causes a significant reduction in composite flexural strength.

As the introduction of piezoelectric materials into micro electromechanical systems increases, there is a correlating requirement for understanding the mechanical properties of these films. We have investigated the mechanical properties of unpoled PZT [Pb(Zr,Ti)O 3 ] and PMNT [Pb(Mg 1/3 Nb 2/3 ) 1−x Ti x O 3 ] thin films deposited by sputtering. In this study, nano-indentation, a technique which allows determination of the transverse mechanical properties, is used. It is the easiest method for assessing the biaxial elastic modulus and the hardness of thin films. It was confirmed that neither cracks, nor pile-ups, were observed for indentation depths below 20% of the film's thickness.

Nanopaper is a transparent film made of network-forming nanocellulose fibers. These fibers are several micrometers long with a diameter of 4-50 nm. The reported elastic modulus of nanopaper often falls short of even conservative theoretical predictions based on the modulus of crystalline cellulose, although such predictions usually perform well for other fiber composite materials. We investigate this inconsistency and suggest explanations by identifying the critical factors affecting the stiffness of nanopaper. A similar inconsistency is found when predicting the stiffness of conventional paper, and it is usually explained by the effects introduced during drying. We found that the effect of the drying cannot solely explain the relatively low elastic modulus of nanopaper. Among the factors that showed the most influence are the presence of non-crystalline regions along the length of the nanofibers, initial strains and the threedimensional structure of individual bonds.

For some twenty years the marine coatings industry has been intrigued by polymer surfaces with low adhesion to other materials, especially to the biological glues used by marine organisms. Polymers with fouling release surfaces have been made from sundry materials, and their resistance to marine fouling in both static and dynamic tests has been evaluated in the world's oceans. Although the polymer surface property most frequently correlated with bioadhesion is its critical surface tension (), resistance to fouling is also influenced by other bulk and surface properties of the polymer. This paper reviews the types of bonding associated with polymeric materials used in fouling resistant coatings, describes the removal process in terms of fracture mechanics, and discusses the importance of surface energy, elastic modulus and coating thickness in the release of biofoulants.

The conversion of wood-based fiberboard materials into crack-free, monolithic, porous hard carbons is of significant interest due to their ability to perform in a multifunctional capacity. Three varieties of carbonized medium-density fiberboard (c-MDF) were studied for electrical, mechanical, and structural properties. X-ray diffraction data suggested that the volume fraction of large turbostratic crystallites increased with carbonization temperature (T). The volume fraction of large carb turbostratic crystallites had a positive correlation with elastic modulus and electrical conductivity. The c-MDF materials were approximately isotropic with respect to elastic modulus and exhibited increasing stiffness with increasing T (up to 4.5 carb GPa). Between 600 and 1400 8C, the electrical resistivity of c-MDF varied by seven orders of magnitude. The electrical resistivity of the hard carbon material in c-MDF 1400 8C was found to be within about an order of magnitude of polycrystalline graphite.

The properties of concrete containing fine recycled aggregate are investigated. Recycled aggregate consisted of crushed concrete (CC) or crushed brick (CB) with particles less than 5 mm in diameter. The free water/cement ratio was kept constant for all mixes. The fine aggregate in concrete was replaced with 0%, 25%, 50% and 100% CC or CB. Generally, there is strength reduction of 15 -30% for concrete containing CC. However, concrete incorporating up to 50% CB exhibits similar long-term strength to that of the control. Even at 100% replacement of fine aggregate with CB, the reduction in strength is only 10%. Beyond 28 days of curing, the rate of strength development in concrete containing either CC or CB is higher than that of the control indicating further cementing action in the presence of fine recycled aggregate. More shrinkage and expansion occur in concrete containing CC or CB. D

This paper described about design, fabrication and characterization of conductivity sensor using printed circuit board (PCB). The main objective is to sense the conductivity of aqua agriculture. A sensor was design by using interdigital capacitor concept where the term interdigital refers to pattern of fingers that is resembled by the shape and relative position of the electrodes. This sensor was fabricated by using PCB in order to minimize the cost than the existing conductivity sensor. Sensor performance was characterized by various test setups to check ability and accuracy of the sensor. From the result, it shown that the sensor has very good sensitivity with correlation coefficient R 2 of 0.969.

In this study, structure and biomechanical properties of freeze-dried decellularized porcine pulmonary heart valves were investigated. Heart valves were dissected from porcine hearts. The tissues were decellularized and separated in three groups: (1) without lyoprotectant, (2) with 5% sucrose, and (3) with a mixture of 2.5% sucrose and 2.5% hydroxyl ethylene starch (HES), and then underwent freeze-drying. Freeze-drying in the absence of lyoprotectants caused an overall more disintegrated appearance of the histological architecture of the porcine valves, especially between the fibrosa and the ventricularis layers. Freeze-dried tissues with lyoprotectants have a looser network of collagen and elastic fibers with bigger pore sizes. Tissue freeze-dried in the absence of lyoprotecants had the largest pore sizes, whereas the tissue freeze-dried in the presence of protectants showed pores of intermediate sizes between the decellularized tissue and the unprotected freeze-dried samples. Tissue freeze-dried with sucrose alone displayed less porosity than tissue freeze-dried with the sucrose/HES mixture, whereas no significant differences in biomechanical properties were observed. Decellularization decreased the elastic modulus of artery tissue. The elastic modulus of freeze-dried tissue without protectants resembled that of decellularized tissue. The elastic modulus values of freeze-dried tissue stabilized by lyoprotectants were greater than those of decellularized tissue, but similar to those of native tissue.

The treatment of humeral shaft fractures ranges from conservative modalities to operative fixation, including plate osteosynthesis and intramedullary fixation. Nonunion is a complication of conservative and operative interventions but is more often associated with elastic nailing. This article discusses elucidates the successful outcomes achieved with flexible nailing of humeral shaft fractures.

Objectives. The purpose of this study was to investigate the effect of light-curing protocol on degree of conversion (DC), volume contraction (C), elastic modulus (E), and glass transition temperature (T g) as measured on a model polymer. It was a further aim to correlate the measured values with each other. Methods. Different light-curing protocols were used in order to investigate the influence of energy density (ED), power density (PD), and mode of cure on the properties. The modes of cure were continuous, pulse-delay, and stepped irradiation. DC was measured by Raman micro-spectroscopy. C was determined by pycnometry and a density column. E was measured by a dynamic mechanical analyzer (DMA), and T g was measured by differential scanning calorimetry (DSC). Data were submitted to two-and three-way ANOVA, and linear regression analyses.

The elastic modulus and the internal friction of Sn and the g-In-Sn phase are measured with a two-component piezoelectric oscillator 26 at 50 kHz in the temperature range from 296 to 390 K. For both materials the viscoelastic responses at strains below 10 are described in terms of a Debye peak characterized by an effective activation enthalpy of 54.8 and 20.4 kJ / mol, for Sn and the g-In-Sn phase, respectively. Due to their higher damping, the dynamic mechanical responses of In and the eutectic In-Sn were measured with a three-components piezoelectric resonator between 296 and 390 K at 50 kHz. The temperature dependence of the internal friction of the eutectic can be well described in terms of a single relaxation time with an effective activation enthalpy of 38 kJ / mol. Indium is not only amplitude dependent but also exhibits thermal hysteresis.

An ultrasound examination was used to noninvasively determine the changes in mechanical properties associated with age for the common carotid, braehial, popliteal, femoral, and tibial arteries. Forty-two normal male subjects, ranging in age from 8 to 60 years of age, were examined. The subjects were placed in one of three age groups: <29 years of age, 29 to 38, and >38. Mechanical properties including percentage variation in diameter, pressure-strain, and circumferential elastic modulus were determined from changes in wall thickness and pulse pressure. Percentage variation in diameter (PVD) was seen to decrease with age for all arteries except the brachial, which remained relatively constant. Pressure-strain (Ep) and circumferential elastic moduli (Eo) were seen to increase with age in all arteries except the brachial, which remained relatively constant. Values of Ep and Eo were normalized into a stiffness index by dividing by the value found for the brachial artery. Stiffness indexes for the common carotM and femoral arteries were observed to increase more rapidly with age than the indexes obtained for the popliteal and tibial arteries. It is proposed that the stiffness index and changes in this parameter that occur with age may be useful in noninvasively assessing the progression of atherosclerosis.

A simply supported bridge is modelled to investigate the effect of a strain rate dependent modulus of elasticity on the dynamic response of the structure to a moving load. The bridge is modelled as a one-dimensional discretized finite element beam and the moving load is represented by a point force. A constant modulus of elasticity is traditionally employed when simulating the dynamic response of structures under moving loads. In this paper, a time-variant modulus is used to calculate strains and displacements and compare them to the traditional approach for different speeds and bridge spans. The time-variant modulus is obtained from the strain rate of the structure which is used in turn to update the strain. The results show significant changes in the modulus and in the resulting load effect as load magnitude and speed increase.

Ca 3 ZrSi 2 O 9 (baghdadite) has become a major research focus within the biomaterial community due to its remarkable in-vitro and in-vivo bioactivity. Although baghdadite seems to exhibit interesting biological properties, as yet there has been no data published concerning its mechanical properties. This lack of knowledge hinders targeting this novel bioactive material towards potential applications. In this study we prepare dense Ca 3 ZrSi 2 O 9 bulk ceramics for the first time, allowing the evaluation of its mechanical properties including hardness, bending strength, Young's modulus, and fracture toughness. The preparation of baghdadite has been accomplished by a direct solid-state synthesis in combination with conventional sintering at 1350-1450 1C for 3 h. Our results show that samples sintered at 1400 1C exhibit the best mechanical properties, resulting in a bending strength, fracture toughness, and hardness of 98716 MPa, 1.370.1 MPa m 0.5 , and 7.970.2 GPa. With a comparable mechanical strength to hydroxyapatite, but with an increased fracture toughness by 30% and hardness by 13% baghdadite is highly suitable for potential applications in non-load bearing areas (e.g. coatings or filler materials).

We explore the compliance approach for K I evaluation of a cracked three point beam (TPB) of functionally graded material (FGM). We suggest an equivalent beam of variable height for cracked FGM beams which includes the homogeneous beam for the linear, quadratic and cubic variations in elastic modulus along the beam span. The efficacy of equivalent beams is demonstrated numerically on a 250 × 41 × 6 mm FGM beam with modulus varying from 210 – 315 GPa under 5000 N load.

The physico-chemical aspects of three native Andean starches from Arracacha xanthorriza, Canna edulis and Oxalis tuberosa were investigated. Scanning electron microscopy-investigations showed that granules of A. xanthorriza were the smallest with irregular shape and sizes between 7 and 23 mm, whereas granules of O. tuberosa and C. edulis were both ovally shaped with granular sizes between 20 and 55 mm and 35±101 mm, respectively. All three starches revealed a B-type X-ray diffraction pattern. The gelatinisation behaviour was investigated using differential scanning calorimetry (DSC). The gelatinisation enthalpy was 14.6 J/g of starch for O. tuberosa, 15.7 J/g for C. edulis and 17.6 J/g for A. xanthorriza, and the peak temperature of the endothermic DSC-transition was 55.9, 61.2 and 60.18C, respectively. The amylose content determined by gel permeation chromatography after debranching with isoamylase was 4% for A. xanthorriza, 18.4% for O. tuberosa, and 23.8% for C. edulis. The amylopectin showed different structures among the three starches with a b-amylolysis limit of 67.6% for C. edulis, 64.5% for O. tuberosa and 56.6% for A. xanthorriza. The average chain length of the amylopectin was highest for A. xanthorriza (22.6), followed by O. tuberosa with 22.4, and lowest for C. edulis (21.9). The complexation ability of the three starches was investigated by adding sodium dodecyl sulphate (SDS), and the amylose content was positively correlated with the enthalpy of the amylose±SDS complex. q

CN x /ZrN multilayers were prepared by a dual-cathode unbalanced DC magnetron sputtering system. The results showed that under proper deposition conditions, the multilayer coatings were dense and fully crystalline with hardness exceeding 40 GPa and elastic modulus over 400 GPa. X-ray diffraction studies showed that there is a strong correlation between coating hardness and the occurrence of (111) texture of ZrN. Some crystalline regions going through the multilayers were clearly observed from the cross-sectional high resolution transmission electron microscopy image. Two extra d-spacings were obtained from the diffraction pattern that do not belong to any known d-spacing for ZrN, but match with two calculated d-spacings for b-C 3 N 4 . © 1997 Elsevier Science S.A.

In this study, CrTiAlN coatings were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The coating morphology and properties including surface roughness, adhesion, hardness/elastic modulus (H/E) ratio, and friction behavior were analyzed to evaluate the impact of the substrate bias voltage on the coating microstructure and properties. The results suggest that for an optimized value of the substrate bias voltage, i.e. − 150 V, the CrTiAlN coatings showed increased Cr content and improved properties, such as higher adhesion strength, hardness, and elastic modulus in comparison to the coatings deposited by other substrate bias voltage. Moreover, the optimum coatings achieved a remarkable reduction in the steel friction coefficient from 0.65 to 0.45.

Strain rate effects on surface deformation behavior of exfoliated nylon 66 (PA66)/organoclay nanocomposites have been explored by nanoindentation in present study. Sharp indenter (Berkovich) has been used to indent on the surfaces of polymer/clay nanocomposite with different strain rates. Significant strain-rate hardening has been found consistently existing in both neat PA66 and its nanocomposite systems from surface to subsurface (a few micron deep into the bulk). However, strain rate shows almost no effect on the elastic moduli of the neat system and the nanocomposites. The elastic modulus and hardness increase with the indentation depth due to inhomogeneous distributions of the crystalline morphology as well as clay concentration for the case of the nanocomposites along the indentation direction. The mechanical properties observed are correlated with the inhomogeneous microstructures of the studied systems. The plastic index of PA66 and the nanocomposites have been evaluated as a function of strain rate. q

Background Currently, most of mitral valve annuloplasty surgeries are performed by using open heart surgery. However, if such operation would be performed by using minimally invasive surgery via catheter-based techniques (CBT), it offers various advantages for both surgeons and patients.

The capacity of bone for post-yield energy dissipation decreases with age. To gain information on the cause of such changes, we examined the mechanical behavior of human cadaveric bone as a function of progressive deformation. In this study, tensile specimens from tibiae of 9 middle aged and 8 elderly donors were loaded till failure in an incremental and cyclic (load-dwell-unload-dwellreload) scheme. The elastic modulus, maximum stress, permanent strain, stress relaxation, viscoelastic time constant, plastic strain energy, elastic release strain energy, and hysteresis energy were determined at incremental strains of each loading cycle. Experimental results showed that elderly bone failed at much lower strains compared to middle aged bone, but little age-related differences were observed in the mechanical behavior of bone until the premature failure of elderly bone. Energy dissipation and permanent strain appeared to linearly increase with increasing strain, while non-linear changes occurred in the modulus loss and stress relaxation/time constant with increasing strain. Such changes suggest that two distinct stages may exist in the progressive deformation of bone. In Stage I, rapid damage accumulation and increased involvement of collagen in load bearing appeared to dominate the mechanical behavior of bone with limited energy dissipation (<20% of total energy dissipated), whereas Stage II is dominated by continuous plastic deformation, accompanied by major energy dissipation through all three pathways till failure. This study suggests that damaging mechanisms in bone vary with deformation and age affects the post-yield mechanisms causing a significant decline in the capacity of aged bone to dissipate energy.

Purpose: The objective of this study was to theoretically model, based on the Hertz contact theory, the impact force and contact time, as well as the linear and angular head accelerations during heading in children using two neck stiffness conditions (infinite and negligible stiffness). Methods: The following mathematical model inputs were obtained: elastic modulus and mass of size three, four, and five balls at inflation pressures of 10, 12, and 14 psi, head modulus, head mass, head length, head and trunk moment of inertia, and the precontact ball velocity. The model outputs consisted of linear and angular head acceleration, impact force, contact time between the ball and head, and head impact criteria (HIC) all at the point of impact. Head mass and length were obtained as a percentage of body weight and height, respectively, based on age. Results: With an increase in head mass, there is a decrease in the linear and angular head acceleration. With an increase in ball size, for the same head mass, there is an increase in the contact time between the head and the ball. Changing ball inflation pressure has little effect on the impact characteristics. Infinite neck stiffness decreased linear and angular head acceleration and HIC. Conclusion: Head mass and ball size have an effect on linear and angular head acceleration and contact time, respectively, whereas ball inflation pressure has a minimal effect on the impact characteristics. These results indicate that children should be restricted to using the appropriate ball for their age. Smaller head size within an age group is an underemphasized though important identifier of a player's injury risk.