Measurement Of Elastic Modulus Research Articles

Dynamic and quantitative assessment of blood coagulation using optical coherence elastography.

Reliable clot diagnostic systems are needed for directing treatment in a broad spectrum of cardiovascular diseases and coagulopathy. Here, we report on non-contact measurement of elastic modulus for dynamic and quantitative assessment of whole blood coagulation using acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE). In this system, acoustic radiation force (ARF) is produced by a remote ultrasonic transducer, and a shear wave induced by ARF excitation is detected by the optical coherence tomography (OCT) system. During porcine whole blood coagulation, changes in the elastic property of the clots increase the shear modulus of the sample, altering the propagating velocity of the shear wave. Consequently, dynamic blood coagulation status can be measured quantitatively by relating the velocity of the shear wave with clinically relevant coagulation metrics, including reaction time, clot formation kinetics and maximum shear modulus. The results show that the ARFOE-OCE is sensitive to the clot formation kinetics and can differentiate the elastic properties of the recalcified porcine whole blood, blood added with kaolin as an activator, and blood spiked with fibrinogen.

Mechanical properties of natural chitosan/hydroxyapatite/magnetite nanocomposites for tissue engineering applications

Chitosan (CS), hydroxyapatite (HA), and magnetite (Fe3O4) have been broadly employed for bone treatment applications. Having a hybrid biomaterial composed of the aforementioned constituents not only accumulates the useful characteristics of each component, but also provides outstanding composite properties. In the present research, mechanical properties of pure CS, CS/HA, CS/HA/magnetite, and CS/magnetite were evaluated by the measurements of bending strength, elastic modulus, compressive strength and hardness values. Moreover, the morphology of the bending fracture surfaces were characterized using a scanning electron microscope (SEM) and an image analyzer. Studies were also conducted to examine the biological response of the human Mesenchymal Stem Cells (hMSCs) on different composites. We conclude that, although all of these composites possess in-vitro biocompatibility, adding hydroxyapatite and magnetite to the chitosan matrix can noticeably enhance the mechanical properties of the pure chitosan.

Advantages of a 3-parameter reduced constitutive model for the measurement of polymers elastic modulus using tensile tests

Exact measurements of the rheological parameters of time-dependent materials are crucial to improve our understanding of their intimate relation to the internal bulk microstructure. Concerning solid polymers and the apparently simple determination of Young’s modulus in tensile tests, international standards rely on basic protocols that are known to lead to erroneous values. This paper describes an approach allowing a correct measurement of the instantaneous elastic modulus of polymers by a tensile test. It is based on the use of an appropriate reduced model to describe the behavior of the material up to great strains, together with well-established principles of parameter estimation in engineering science. These principles are objective tools that are used to determine which parameters of a model can be correctly identified according to the informational content of a given data set. The assessment of the methodology and of the measurements is accomplished by comparing the results with those obtained from two other physical experiments, probing the material response at small temporal and length scales, namely, ultrasound measurements with excitation at 5 MHz and modulated nanoindentation tests over a few nanometers of amplitude.

Shear elastic modulus is a reproducible index reflecting the passive mechanical properties of medial gastrocnemius muscle belly.

BackgroundPassive mechanical properties are important in muscle function because they are related to the muscle extensibility. Recently, the assessment of muscle shear elastic modulus using shear-wave elastographic (SWE) imaging was developed. However, reliability and validity of shear elastic modulus measurements during passive stretching remain undefined.PurposeTo investigate the reproducibility and validity of the shear elastic modulus measured by SWE imaging during passive stretching.Material and MethodsTen healthy men volunteered for this study. The shear elastic modulus of medial gastrocnemius (MG) muscle belly was measured using ultrasonic SWE imaging during passive dorsiflexion. To assess the intra-session and inter-day reliabilities, the protocol was performed twice by the same investigator with a 5-min rest period between measurement sessions and twice on two different days by the same investigator with a 1–2-week interval between the two sessions. To assess the inter-investigator reliability, the protocol was performed on the same day by two investigators with a 5-min rest between measurement sessions. In addition, B-mode ultrasonography was used to determine the displacement of myotendinous junction (MTJ) of MG during passive ankle dorsiflexion.ResultsThe intra-session, inter-day, and inter-investigator reliabilities of the method was confirmed on the basis of acceptably low coefficient of variations and substantially high intraclass correlation coefficients. In addition, a significant correlation was found between MTJ displacement and shear elastic modulus.ConclusionThese results suggested that shear elastic modulus measured using SWE imaging is a reproducible index reflecting the passive mechanical properties.

Effect of kerogen on rock physics of immature organic-rich chalks

We study the rock physics of organic-rich chalk from the Shefela basin, central Israel, based on laboratory measurements of core material from the Zoharim well. This deposit is an immature source rock that includes the Late Cretaceous Ghareb and Mishash formations. The studied rock is composed of three dominating phases: minerals, kerogen, and pores. We investigate how porosity and kerogen influence the physical behavior of the rock, based on measurements of porosity, density, acoustic velocities, elastic moduli, tensile strength and compressive strength. We find that the dynamic bulk modulus and the static Young’s modulus decrease with increasing kerogen content as well as with increasing porosity. To describe the stiffness of the solid skeleton we use two different poroelasticity models for fluid substitution assuming material isotropy: Biot-Gassmann model and Marion’s BAM model. The obtained poroelasticity coefficients indicate a soft matrix composed of kerogen-micrite mixture, characterized by a low BAM normalized stiffness factor (w ∼ 0.2) and a high Biot coefficient (β ∼ 0.9). These values appear to vary with changes in kerogen content, grain size and degree of cementation. Porosity, which typically decreases with depth in the studied basin, does not show a clear correlation with kerogen content. Moreover, both compressive and tensile strengths decrease linearly with increasing porosity, regardless of kerogen content. We use a density–kerogen relationship to create a porosity depth profile, by combining data from continuous cores and density well logs. By comparing sonic logs with laboratory measurements of P-wave velocities on fully-saturated cores, we are able to detect a gas zone in the shallow interval of the sequence in the studied well.

In situ hot elastic modulus evolution of MgO–C refractories containing Al, Si or Al–Mg antioxidants

Metals and alloys (such as Al, Si, Al–Mg and Al–Si) are commonly added to MgO–C refractory bricks as antioxidants due to their effectiveness to prevent carbon oxidation (in the 600–1400°C range) and their low cost. These additives act at different temperatures and react with refractory components and gases in the environment, inducing significant changes in the resultant microstructure and affecting the overall thermo-mechanical performance of these products. This work addresses the evaluation of physical properties, cold and hot mechanical resistance, as well as in situ hot elastic modulus (E) measurements in the temperature range of 30–1400°C for MgO–C bricks containing antioxidants (Al, Si or Al–Mg alloy) in a reducing atmosphere. Cured and fired samples of the designed formulations were evaluated throughout 1 or 2 heating-cooling cycles. Despite the improved mechanical behavior (higher cold crushing strength and hot modulus of rupture) of the antioxidant-containing formulations, compared to the additive-free MgO–C sample, the interaction of the selected additives with the refractory components and CO(g) led to a generation of phases (i.e., Al4C3, Al2O3, SiC, SiO2, MgAl2O4) that could not be well accommodated in the microstructure. Consequently, the in situ E drop was observed during cooling (mainly below 600°C) of the antioxidant-containing sample due to crack and flaw formations. Si and Al–Mg were the most promising antioxidants, whereas the Al-containing composition showed the highest E damage level after two heating/cooling cycles up to 1400°C for cured samples. Based on the elastic modulus profiles with the temperature, the results also indicated the best working conditions for these ceramic materials.

Nanomechanical probing of soft matter through hydrophobic AFM tips fabricated by two-photon polymerization

Atomic force microscopy (AFM) nanoindentation of soft materials is a powerful tool for probing mechanical properties of biomaterials. Though many results have been reported in this field over the last decade, adhesion forces between the tip and the sample hinder the elastic modulus measurement when hydrophilic soft samples are investigated. Here, two-photon polymerization (2PP) technology was used to fabricate hydrophobic perfluoropolyether-based AFM tips. The hydrophobic 2PP tips allowed us to overcome the limitations of commercial and functionalized tips as well as to successfully measure the elastic modulus of medically relevant soft materials in air. Our results obtained in the characterization of poly(dimethyl siloxane) and polyethylene glycol hydrogels showed lower adhesion forces over a larger measurement range when compared to measurements performed with commercial tips. The elastic moduli measured by means of hydrophobic 2PP AFM tips were also found to be comparable to those obtained using conventional techniques for macroscopic samples. We successfully showed that the hydrophobic AFM tips developed by this highly versatile technology enable the study of mechanical properties of soft matter, benefiting from reduced sample–tip interactions, and a custom-made shape and dimension of the tips.

Monitoring the setting process of eco-binders by ultrasonic P-wave and S-wave transmission velocity measurement: Mortar vs concrete

Current environmental imperatives have motivated much research on the possibilities of substitution of clinker, responsible for substantial emissions of CO2, by by-products of various industries.The concretes investigated are designed as to limit the early age cracking risk despite a massive substitution of up to 75% of clinker. In this framework, interest has been shown to mix designs combining the benefits of ground granulated blast-furnace slag and limestone microfiller. The aim of this study is to evaluate the impact of environmentally friendly cement-based binders on the initial and final setting time of mortars and concretes by means of a standard method (ASTM C403), early age compressive strength, elastic modulus, and ultrasonic transmission velocity measurements of P-waves and S-waves. This last method was observed to be a relevant setting indicator for both mortar and concrete samples. Critical influence of both the binder’s composition and the aggregate content has been observed on the setting process.

Compressive Mechanics of Collagen-Fibrin Composites and Their Structural Alterations

Collagen, fibrin and fibrin-collagen composite biomaterials play an important role in tissue regeneration and are widely used in surgery as sealants or fleeces and in bioengineering as scaffolds. Previous studies demonstrated that collagen-fibrin composite scaffolds possess improved tensile mechanical properties compared to matrices of either component alone. In this work, we showed that compressed collagen-fibrin composites have synergistic shear viscoelastic properties relative to either protein scaffold alone. Combined measurements of viscoelastic and structural properties of the composite and individual protein scaffolds using rotational rheometry, confocal and scanning electron microscopy indicated that these mechanical enhancements originated from structural alterations of the network. Measurements of elastic and loss moduli of collagen-fibrin constructs along with their individual components displayed a dual softening-stiffening transition occurring along the course of matrix compression from low to high compression degrees. Fibrin-collagen composite produced a biopolymer that was initially stiffer than its individual components and was more responsive to compression than fibrin or collagen alone. Improved stiffness of the collagen-fibrin biocomposite was attributed to the increase of fibrin network node density in the presence of collagen and formation of criss-crossing nodes between intersecting fibrin and collagen fibers as well as bundling of fibers of two interpenetrating networks. Composite collagen-fibrin materials revealed more complex network structure of higher apparent branching degree than collagen or fibrin alone. We demonstrated that changing protein density in collagen and fibrin constructs could drastically alter the stress-strain relationship by shifting the onset of stiffening to low compressive strains as the protein density increased. Correlations of the mechanical alterations and changes of the scaffold topology indicated the structural origin of the mechanical response of pure and composite materials. The results obtained can be useful for designing biomaterials of modulated mechanical characteristics.

Measurement of Elastic Modulus of Collagen Type I Single Fiber

Collagen fibers are the main components of the extra cellular matrix and the primary contributors to the mechanical properties of tissues. Here we report a novel approach to measure the longitudinal component of the elastic moduli of biological fibers under conditions close to those found in vivo and apply it to type I collagen from rat tail tendon. This approach combines optical tweezers, atomic force microscopy, and exploits Euler-Bernoulli elasticity theory for data analysis. This approach also avoids drying for measurements or visualization, since samples are freshly extracted. Importantly, strains are kept below 0.5%, which appear consistent with the linear elastic regime. We find, surprisingly, that the longitudinal elastic modulus of type I collagen cannot be represented by a single quantity but rather is a distribution that is broader than the uncertainty of our experimental technique. The longitudinal component of the single-fiber elastic modulus is between 100 MPa and 360 MPa for samples extracted from different rats and/or different parts of a single tail. Variations are also observed in the fibril-bundle / fibril diameter with an average of 325±40 nm. Since bending forces depend on the diameter to the fourth power, this variation in diameter is important for estimating the range of elastic moduli. The remaining variations in the modulus may be due to differences in composition of the fibril-bundles, or the extent of the proteoglycans constituting fibril-bundles, or that some single fibrils may be of fibril-bundle size.

A Retrospective View of EMM-ARM: Application to Quality Control in Soil-improvement and Complementary Developments

The EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) is a technique that allows the continuous measurement of the E-modulus of a given material under test, since the instant in which it is cast into the testing mould. The technique has been initially developed in 2008-2009 and it is particularly useful to monitor the hardening process of cement-based materials or any similar materials that can be cast into a mould and endure significant stiffness changes since early ages. EMM-ARM is based on the identification of the resonant frequency of the testing mould, which evolves along time due to the hardening process of the tested material, and then the E-modulus of the tested material can be inferred with basis on the dynamic equations of motion of the testing system. Even though the method has been originally devised to test concrete, it has quickly been extended to other materials such as mortar, cement paste, stabilised soils and even epoxy resins. In the particular case of stabilised soils, the method has been successfully applied to both cement-based stabilization and lime-based stabilization. This paper intends to provide a wide perspective of the several evolutions that EMM-ARM has endured throughout its applications to stabilised soils, namely in regard to: (i) mould geometry and material; (ii) sampling procedures for in-situ application; (iii) excitation and modal identification techniques; (iv) systematic application to several mix formulations and comparative evaluation of hardening kinetics. Indeed, one of the foremost applications of EMM-ARM in the context of soil stabilization is the capability to provide real-time data about the stiffness of the material, allowing the users to take early decisions in regard to the expectable stiffness that a recently improved soil will predictably attain. This readily available information can have strong economic impacts in the case of rejection of a given stabilised layer.

A generic "micro-Stoney" method for the measurement of internal stress and elastic modulus of ultrathin films.

Accurate measurement of the mechanical properties of ultra-thin films with thicknesses typically below 100 nm is a challenging issue with an interest in many fields involving coating technologies, microelectronics, and MEMS. A bilayer curvature based method is developed for the simultaneous determination of the elastic mismatch strain and Young's modulus of ultra-thin films. The idea is to deposit the film or coating on very thin cantilevers in order to amplify the curvature compared to a traditional "Stoney" wafer curvature test, hence the terminology "micro-Stoney." The data reduction is based on the comparison of the curvatures obtained for different supporting layer thicknesses. The elastic mismatch strain and Young's modulus are obtained from curvature measurements of cantilevers before and after the film deposition. The data reduction scheme relies on both analytical and finite element calculations, depending on the magnitude of the curvature. The experimental validation has been performed on ultra-thin low pressure chemical vapor deposited silicon nitride films with thickness ranging between 54 and 133 nm deposited on silicon cantilevers. The technique is sensitive to the cantilever geometry, in particular, to the thickness ratio and width/thickness ratio. Therefore, the precision in the determination of the latter quantities determines the accuracy on the extracted elastic mismatch strain and elastic modulus. The method can be potentially applied to films as thin as a few nanometers.

Interpreting measurements of small strain elastic shear modulus under unsaturated conditions

Bender element testing of unsaturated isotropically compacted speswhite kaolin samples was used to investigate the variation of small strain elastic shear modulus G under unsaturated conditions. Testing was performed in a suction-controlled triaxial cell and involved combinations of isotropic loading and unloading stages and wetting and drying stages. Analysis of the experimental results indicated that the variation of G could be represented by a simple expression involving only mean Bishop’s stress p* and specific volume v , with the only significant mismatches between measured and predicted values of G occuring at the end of final unloading. No significant improvement of fit was achieved by incorporating additional dependency on degree of saturation Sr or a bonding parameter ζ . The proposed expression for G reverts to a well-established form for saturated soils as Sr tends to 1.

Ultrasonic Measurement of Elastic Modulus of Kelvin Foam

Elastic modulus of 3D-printed Kelvin foam plate is investigated by measuring the acoustic wave velocity of 1 MHz ultrasound. An isotropic tetrakaidecahedron foam of 3 mm unit cell is designed and printed layer upon layer to fablicate a Kelvin foam plate of 14mm thickness by 3D CAD/printer using ABS plastic. The Kelvin foam plate is filled completely with paraffin wax for impedance matching, so that acoustic wave may propagate through the porous foam plate. The acoustic wave velocity of the foam plate is measured using the time-of-flight (TOF) method to calculate the elastic modulus of the Kelvin foam plate based on acousto-elasticity.

Development of novel beta Ti-Mo-Zr alloys for biomedical applications

Event Abstract Back to Event Development of novel beta Ti-Mo-Zr alloys for biomedical applications Raul O. Araújo1, 2, Pedro A. Kuroda1, 2, Mariana L. Lourenço1, 2, Gabriela P. Suarez1, 2, Fernanda F. Quadros1, 2, Diego R. Correa1, 2, Fábio B. Vicente1, 2 and Carlos R. Grandini1, 2 1 UNESP - Univ Estadual Paulista, Brazil 2 IBTN - Institute of Biomaterials, Tribocorrosion and Nanomedicine - Brazilian Branch, Brazil Titanium alloys include a series of advantageous properties for biomedical applications, such as density, high mechanical strength, wear and corrosion resistance, hardness and modulus of elasticity[1]. In addition, studies have shown that titanium favors the integration with bone tissues (osseointegration)[2]. Many alloys used in the aerospace industry were used as biomaterials, for example, the Ti-6Al-4V alloy (Ti-64), who possesses excellent mechanical properties. However the evidence of allergenic reactions and neurological problems related to the aluminum and vanadium ions, made necessary the development of alloys specifically for biomedical use[3]. The alloys with predominance of body centered cubic structure (β phase) have been reason to search for biomedical applications because in general have lower elastic modulus than other structures as the hexagonal compact (α phase), preventing stress shielding effect[4]. The addition of substitutional elements in titanium alloys can significantly change its structure/microstructure and its mechanical properties[5]. In this study Ti-Mo-Zr alloys were prepared by arc-melting, heat treated for homogenization by 24 hours at 1000° C, hot rolled and heat treated for stress relief by 6 hours at 1000° C. The structure and microstructure of alloys were evaluated by x-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM), whose results indicated the presence of α’, α’’ and β phase, depending of substitutional element quantity (Fig. 1). Fig. 1 – X-ray diffractograms for Ti-10Mo-Zr (a), Ti-15Mo-Zr (b), Ti-15Zr-Mo (d) and Ti-20Zr-Mo (d) alloys, after homogenization heat treatment. It can be observed the action β-stabilizer of zirconium in titanium alloys that have another β stabilizer element[6],[7]. The SEM results corroborated XRD measurements, showing the β-stabilizer effect of zirconium in the presence of another β-stabilizer element, in this case, molybdenum. The mechanical characterization of the produced alloys was made by microhardness and dynamical elastic modulus measurements. The results of Vickers microhardness (Fig. 2) and elastic modulus (Fig. 3) suffered strong influence regarding the processing and the substitutional element content[6]. Fig. 2 – Microhardness for Ti-10Mo-Zr (a), Ti-15Mo-Zr (b), Ti-15Zr-Mo (d) and Ti-20Zr-Mo (d) alloys, after homogenization heat treatment. Fig. 3 – Dynamic elastic modulus for Ti-10Mo-Zr (a), Ti-15Mo-Zr (b), Ti-15Zr-Mo (d) and Ti-20Zr-Mo (d) alloys, after homogenization heat treatment. The reduction of α’ phase in the alloys increases dislocations mobility, decreasing the hardness. The increase in the hardness for the alloys of the Ti-15Zr-Mo and Ti-20Zr-Mo systems was attributed to solid state hardening or precipitation of ω phase[8]. The addition of zirconium decreases the elastic modulus of the Ti-10Mo-Zr and Ti-15Mo-Zr alloys, due, mainly the increase of β phase. The addition of molybdenum in Ti-15Zr-Mo and Ti-20Mo-Zr alloys, increases the elastic modulus of the alloy, due the precipitation of ω phase[8]. Ti-Mo-Zr alloys were produced by arc-melting with good homogeneity and stoichiometry, with predominance of β phase. The microhardness have higher values than that of pure titanium The addition of zirconium decreases the elastic modulus of the alloys, showing that although neutral, in the presence of another β stabilizer element, this element has β stabilizing effect. No cytotoxic effects were observed in all studied alloys, showing that these alloys have potential to be used in orthopedic applications. The authors would like the brazilian agencies Capes, CNPq and FAPESP for the financial support.

Применение метода динамического индентирования для оценки механических характеристик композиционных материалов

Introduction. Dynamic indentation method is considered promising in testing mechanical properties of composite materials. Today, composite materials are widely used in the aviation and aerospace industries. That’s why, testing of mechanical properties of composite materials is so vital.
 Method. To register the current velocity of the indenter penetration into the tested composite material, use is made of a device that enables a contactless measurement of the indenter penetration velocity after the indenter strikes the tested product. 
 The data obtained is digitized and sent to a PC for further processing.
 Results. The experiment produced "contact force – penetration depth" diagrams for three test zones in the prepared samples. The analysis showed that the non-uniformity of mechanical properties in the rod’s butt end and side surface is stipulated by pores and microcracks, and this is confirmed by computer tomography. It is shown that dilaminations, microcracks and local non-uniformity zones in the structure tell on the elasticity modulus measurements.
 Conclusions. The dynamic indentation method allows one to test composites at the micro- and macrostructural level, as well as compute their integral mechanical properties.

Volume elastic modulus of the brachial artery and coronary artery stenosis in patients with suspected stable coronary artery disease.

This study aimed to examine the association between the non-invasive measurement of the brachial artery volume elastic modulus (V E), an index of arterial stiffness, and the presence of coronary artery stenosis in patients with suspected stable coronary artery disease (CAD). A total of 135 patients with suspected stable CAD (87 men, mean age, 64±12years) underwent oscillometric measurement of the brachial artery to obtain V E. Coronary angiography was thereafter carried out to diagnose CAD, defined as having≥75% stenosis in the epicardial coronary arteries. V E was significantly higher in patients with CAD (1.94±0.34mmHg/%) than in those without CAD (1.71±0.35mmHg/%, P<0.001). In multiple logistic regression analysis, V E was an independent predictor for the presence of CAD (odds ratio 1.19 per 0.1mmHg/% increase, 95% CI 1.04-1.51) even after adjusting for multiple potential confounders including the Framingham risk score (FRS). The area under the curve of the receiver operating characteristic curve analysis for discriminating CAD increased significantly after the addition of V E to the FRS (from 0.75 to 0.81, P=0.034). The category-free net reclassification improvement and the integrated discrimination improvement by adding V E to the FRS were 0.476 (95% CI 0.146-0.806) and 0.086 (95% CI 0.041-0.132), respectively. In conclusion, the brachial V E was significantly associated with the presence of coronary artery stenosis. The additional measurement of V E to the FRS improved the ability to identify patients with coronary artery stenosis among those with suspected stable CAD.

Mg(OH)2 Nucleation and Growth Parameters Applicable for the Development of MgO‐Based Refractory Castables

MgO is a very attractive raw material for refractory applications. However, its use has been mainly aimed at developing high‐magnesia and magnesia–carbon bricks due to the marked hydration likelihood of this oxide and the related drawbacks (volumetric expansion, crack formation) associated with this transformation. This work aims to evaluate some critical aspects that affect the MgO reaction with water (magnesia source, particle size, concentration of available sites for brucite nucleation, influence of a hydrating additive – acetic acid, and others) during the curing and drying steps of Al2O3–MgO binder‐free refractory castables. The attained experimental results were associated with the boundary nucleation and growth model proposed in the literature. According to the in situ elastic modulus measurements carried out at 110°C, the MgO particle size and reactivity present an important effect on the nucleation and growth of brucite crystals, highlighting that a proper site activation should be induced during the castables' curing process in order to effectively allow the use of magnesia as a binder source for refractories. Faster Mg(OH)2 nuclei generation also helps to minimize further growth of these crystals, leading to a decrease in the samples' porosity and, consequently, a continuous increase in the overall refractory stiffness (E values).

Influence of recycled sand and gravel on the rheological and mechanical characteristic of concrete

The objective of this paper is to investigate the influence of type and dosage of recycled sand (RS) and gravel on the fresh and mechanical properties of concrete. Experimental program was conducted on concretes made with different ratio of substitutions (15, 30, 70, and 100%) of natural sand and gravel with RS and gravel. At the fresh state, slump, air content, and density were measured at the exit of the mixer, and then at 30, 60, and 90 min after mixing. Tests were also performed for compressive strength at the age of 1, 7, and 28 days, whereas elastic modulus measurements were done at 28 days. The results indicated that maintaining the workability of recycled aggregate concrete depends on sand or gravel substitution and their rates. Up to 30 min, slump values were decreased, but after that, no substantial change in slump values was observed. Air content increased and density decreased, with increasing recycled aggregate content (sand or gravel). Mechanical properties, such as compressive strength and modulus of elasticity, were lower than those of reference concrete.

Measurement of CFRP elastic modulus based on FBG reflectance spectrum analysis

Based on fiber Bragg grating (FBG) reflectance spectrum analysis, one novel method to measure the elastic modulus of carbon fiber reinforced plastics (CFRP) is proposed. Basic theory of the novel method is that CFRP uniform cantilever beam produces linear gradient strain which leads to FBG reflectance spectrum broadening under external loadings. Calculation model of the basic theory is put forward and validated by finite element method (FEM) simulation. In order to obtain actual data about the relationship between elastic modulus and FBG reflectance spectrum, experiment of CFRP uniform cantilever beam under external loadings is implemented. The experiment spectrum corresponding to external weight 20g is chosen as the specimen to explain data processing procedure by self-adaptive method. 3dB bandwidth and center wavelength of FBG are selected as the reference indexes in the procedure. Elastic modulus of CFRP which is used in the experiment is extracted and its value is 6.617GPa. To validate the correctness of the elastic modulus, contrastive analyses between transmission matrix theory calculation and experiment spectrums with external weights 5g and 10g are also carried out. Absolute errors of 3dB bandwidth and center wavelength in the comparison are all less than 5pm which prove the feasibility and correctness of this novel elastic modulus measurement method.