Values Of Dynamic Elastic Modulus Research Articles

The Effect of Andreasen ́s Packing Distribution Modulus on the Physical and Mechanical Properties of a Low Cement Refractory Castable

Among modern refractory concretes (MRC), those with low cement content (LCC) where CAC = 4-6wt%, are widely commercialized, considering that their properties approximate those of burned bricks of the same class. In this work, the effect of the modulus q of Andreasen ́s particle size distribution, on the physical (porosity, bulk density) and mechanical (flexural strength and dynamic elastic modulus) properties, of either pre-fired or simply dried specimens of a ≥85% Al2O3 LCC ́s, was investigated. The different LCC ́s samples were formulated according to the Andreasen ́s model, using several distribution modulus (q = 0.22, 0.26, 0.30, 0.33 and 0.42). Measurements of the Dynamic Elastic Modulus (DEM) as a function of temperature (25 to 1500°C), using the Impulse Excitation Technique (IET), were taken as a key indicator of the microstructure dynamic behavior. For the sake of just a punctual comparative term, the physical and mechanical properties of a conventional type refractory concrete (CRC) with a higher CAC percentage (15%) formulated with q = 0.26 was also evaluated. The results indicated that distribution modulus values of; q =0.22, 0,26, 0.30 and 0.33 lead to higher DEM values. While q=0.42 lead to the smallest value in the LCC series. Also, higher DEM values ​​were obtained for LCC ́s (CAC = 5%) than for conventional concrete with CAC = 15% under the same value of q for pre-fired samples. In addition, by observing the occurrence of damping effects in specific temperature ranges, the loss of crystallization water from the calcium aluminate hydrates, as well as the development of pyroplastic behavior could be inferred. The gathered information is relevant to predict the behavior of LCC ́s and CRC ́s when put into service for the first time.

Effect of foliation orientation on the P- and S-wave velocity anisotropies and dynamic elastic constants of the quartz-micaschists metamorphic rocks, Angouran mine, Iran

Laboratory measurements are required to study geophysical properties of the subsurface because of lacking direct observation of Earth’s crust. In this research, compressional (P) and shear (S) wave velocity measurements have been conducted on cylindrical specimens of Quartz-micaschist cored using rock blocks taken from the zinc and lead Angouran mine, Zanjan, northwest of Iran. Cylindrical rock specimens were prepared from the blocks by coring in 0°, 30°, 45°, 60°, and 90° into the foliation direction. P- and S-wave velocities were measured along the cylindrical specimens with different foliation orientations. Percent variations of the P- and S-wave velocities (Thomsen’s anisotropic parameters e and γ) and constant dynamic modulus of test results have been determined. Percent variations of the P-wave velocity (e) increase with an increase of the foliation angle with respect to the propagating waves direction by a parabolic function as it shows P-wave velocity differences up to a maximum value of 50 %. Thomsen’s anisotropic parameter of γ has also the same function with the foliation angle. Meanwhile, foliation orientation has a much greater influence on e than γ for foliation angle from 45° to 90° as $$ \frac{\varepsilon }{\gamma } $$ ratio increases with an increase of foliation angle. Values of dynamic elastic modulus (E), Poisson’s ratio (ν), shear modulus (μ), bulk modulus (K), and Lame’s constant (λ) increase with the increase of foliation angle with the parabolic function. The results show that dynamic elastic modulus, Poisson’s ratio, shear modulus, bulk modulus, and Lame’s constant have anisotropic behavior in relation with the foliation orientation.

Chitosan molecular weight effect on starch-composite film properties

The aim of this work was to prepare and characterize composite films based on chitosan (CH) and corn starch (CS), analyzing the influence of the chitosan molecular weight (MW) on film structure and functional properties. Three chitosan products were characterized and classified as low (LMW), medium (MMW) and high (HMW) according to its MW. Rheological behavior of filmogenic solutions depend on CH-MW from Newtonian to pseudoplastic one. Chitosan based film physicochemical properties were strongly affected by its molecular weight: the lower the MW the higher the color differences and film solubility. SEM observations demonstrated that plasticized chitosan films exhibited homogeneous structures, the higher the MW the more compact is the structure and the lower is the water vapor permeability (WVP, 4.55 ± 0.6 × 10−11 g/m s Pa.). Likewise, CH and CS were compatible polymers which led to the development of homogeneous blend films. Polymer interactions were evidenced in FTIR spectra by the shifts observed within the region of 1500–1700 cm−1, which reduce the hydrophilic groups’ availability of chitosan matrices, leading to a reduction in WVP of composite films. Mechanical properties of the developed films were performed through different complementary tests. Chitosan MW affects both the type and number of interactions, which determine the matrix structure and characteristics. In HMW-CH matrix polymer–polymer interactions are favored, leading to strong and resistant matrices with high dynamic elastic modulus values. Meanwhile, in LMW-CH one, polymer-plasticizer and polymer–solvent interactions became important and the development of high extensible and soluble materials is privileged.

Freezing and Thawing Durability of Ultra High Strength Concrete

Resistance to freezing and thawing of two UHSC (ultra high strength concrete) mixtures was evaluated in accordance with ASTM C 666 Procedure A. The two mixtures (plain and fiber reinforced) were developed using materials local to southern New Mexico, USA. Three different curing regimens were investigated for the mixture with fibers and one curing regimen was studied for the mixture without fibers. All curing regimens included 24 h of ambient curing followed by four days of wet curing at 50 o C, and then two days dry curing at 200 o C. At an age of seven days, one batch of fiber reinforced specimens was air cured at ambient conditions for the following six days and then placed in a water bath at 4.4 o C for 24 h prior to initiating freezing and thawing cycles. The second batch was air cured from day seven to day 12, and then wet cured for one day at 23 o C prior to being placed in the 4.4 o C water bath. The final batch was wet cured at 23 o C from the seventh day to an age of 13 days and then placed in the 4.4 o C water bath. The mixture with no fibers was air cured from the seventh day to an age of 12 days and then wet cured for one day at 23 o C prior to being placed in the 4.4 o C water bath. Higher moisture levels during curing produced greater initial dynamic elastic modulus values and durability factors at the end of the freezing and thawing tests, with the greatest durability factor being 87.5. Steel fibers were observed to improve both compressive strength and durability factor for UHSC.

Determination of dynamic elastic moduli and shear moduli of aged wood by means of ultrasonic devices

Due to ecological and environmental factors, re-using aged wood is becoming more and more important, also in applications where mechanical strength plays a central role. The aim of this study was to examine specific mechanical parameters of naturally aged and dried wood and to better understand the influence of aging on the elastic behaviour of wood. To this aim, measurements on boards and on small, clear wood specimens were carried out. Ultrasound velocities of longitudinal and, in some cases, of transversal waves were measured to determine dynamic elastic moduli and shear moduli. The measurements were performed on structural timber of aged Norway spruce (aged wood) and compared with specimens of recently cut and kiln dried timber of the same species (recent wood) as a reference with comparable density properties and average annual ring width. The measurements revealed higher values of dynamic elastic modulus for aged wood in the longitudinal and radial directions, but no significant difference was found in the tangential direction or in the shear moduli. It is supposed that the difference is more likely a consequence of variability in densities and the structure parameters (annual ring structure, microfibril angle, growth conditions) rather than a consequence of the wood age. The relation between the dynamic elastic modulus in the longitudinal direction and wood density was nearly the same for aged and recent wood specimens, so with increased prudence, grading methods developed for recent wood can also be applied for aged wood.

Synthesis and study of physical properties of dental light-cured nanocomposites using different amounts of a urethane dimethacrylate trialkoxysilane coupling agent

Objective The purpose of this work was the study of the effect of the amount of a urethane dimethacrylate silane (UDMS) coupling agent on physical properties of dental light-cured resin nanocomposites based on Bis-GMA/TEGDMA (50/50 wt/wt) matrix and Aerosil OX50 as filler. Methods Silica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of UDMS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Measurements were taken in samples stored, immediately after curing, in water at 37 °C for 24 h. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water of 75 vol% for 30 days. Thermogravimetric analysis of composites was performed in nitrogen atmosphere from 50 to 800 °C. Results Almost all of used amount of silane remained chemically bounded on the surface of silica particles, forming a layer around them, which have dense accumulation of methacrylate groups. No significant statistic difference was found to exist between the degree of conversion values of composites with different silane contents. The composite with the lowest amount of UDMS (1.0 wt%) showed the lower flexural strength value, the higher static and dynamic elastic modulus values and the higher sorbed liquid value and solubility. Significance The optimum concentration of UDMS seems to be that of 2.5 wt%. Higher concentrations of UDMS did not improve the properties of composites.

Effect of marble particle size and gamma irradiation on mechanical properties of polymer concrete

AbstractEffects of gamma radiation and the marble particle size on compressive properties and the dynamic elastic modulus of polymer concretes (PCs) were studied. The PCs had a composition of 30 % of unsaturated polyester resin and 70 wt. % of marble as aggregate. Different types of PC were developed with the combination of one, two or three marble-particle sizes. The materials were submitted to 5, 10, 50, 100 and 150 kGy of radiation doses. Both the compressive properties and the dynamic elastic modulus values depend on the combination of the marble-particle sizes and the applied radiation dose. Higher numbers of dispersed particles per unit volume provide more resistance to crack propagation. On the other hand, longer particles give more reinforcement. As a result of these two competing effects, medium size marble particles provide the highest compression modulus

A Novel AFM-MEA Platform for Studying the Real Time Mechano-Electrical Behavior of Cardiac Myocytes

AbstractWe present a novel experimental platform based on a combined Atomic Force Microscopy (AFM) and Micro-Electrode Array (MEA) set-up. We have used it to measure minimal changes in the morphological/mechanical properties of electrically active cell cultures as well as to measure the changes in the extracellular electrical activity when a single cell is stimulated by means of the AFM tip. In particular, we studied the dynamical changes in cell elasticity of embryonic rat cardiac myocytes along the contraction-relaxation cycle. Applying high load indentations, we also recorded the effects of mechanical stimulations on the cell electrophysiology. The dynamic elastic modulus of the cell related to the contraction-relaxation cycle reveals a temporal behavior that closely follows the changes in cell height. Observed values of dynamic elastic modulus at a maximum indentation depth of 1500nm varied between 8.93 ± 0.78 kPa during systolic (contraction) phase and 4.26 ± 0.47 kPa during diastolic (relaxation) phase. Induced electrophysiological responses were observed when applying loads in the range 40-150 nN. The probability P of recording an induced electrical response (P = 0.16 for a maximum load of 100nN) increased with the maximum applied load. Pulling-like stimulations due to the tip-cell adhesion could also evocate electrical responses.

Influence of Periodic Freezing on the Value of the Elastic Modulus of Light-weight Fibre Concrete

This paper deals with the influence of periodic freezing on light-weight concrete characteristics. Three different sets of light-weight concrete specimens were periodically freezing and non-destructively tested over time. Another three comparative sets of light-weight concrete specimens were tested at the same time and these sets were placed in water. The main aim was to determine and compare the dynamic elastic modulus values during and after 200 freeze-thaw cycles. The methods for this non-destructive testing were the ultrasonic impulse method and the resonance method.

Dynamic mechanical properties of particle‐reinforced EPDM composites

AbstractThe dynamic mechanical property of particle‐reinforced ethylene–propylene–diene monomer (EPDM) matrix composites has been studied by using a dynamic mechanical thermal analyzer (DMTA). The individual composite has been reinforced with the various reinforcing particles as follows: silicon carbide particles (SiCps) of 60 μm in average diameter with various volume fractions (i.e., 10–40%); copper (Cu) and aluminum (Al) particles with 20 vol %; and SiCps with 6 and 36 μm in different average diameters with 20 vol % over the total composite volume. It is shown from the experimental results that the dynamic elastic modulus values increase and the composites with 40 vol % SiCps exhibit higher tan δ values through the entire rubbery phase after the glass transition region compared with the composites with lower particle volume percentages. This shows that the composites with 20 vol % Cu particles have the higher dynamic elastic modulus but the lower peak tan δ value than the composites with other particles of 20 vol % do. Scanning electron microscopy results show that the effective particle volume in the composite with Cu particles is higher than the other composites, although the same particle volume fraction of 20% has been used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1595–1601, 2003

An experimental study on the replacement of the anterior cruciate ligament of the rabbit's knee using an augmented substitute

The mechanical properties of a reconstruction of the anterior cruciate ligament (ACL) using an augmented substitute were investigated in rabbits' knees. After total resection of the ACL, 25 knees were reconstructed with a patellar tendon alone (nonaugmented group) and 25 with a patella tendon augmented by a Leeds-Keio artificial ligament (augmented group). The rabbits were sacrificed for biomechanical testing at 0, 4, 8, 12 and 24 weeks, respectively, after operation. In the augmented group, the mean ultimate load was 48.8% of the original ACL load at 4 weeks, and this gradually increased to 65.6% at 8 weeks. That of the twenty-four-week specimens was restored to 71% of the original ACL load. In the nonaugmented group, the mean ultimate load decreased to 9.3% at 8 weeks, but increased to 37.5% at 24 weeks. The mean static stiffness in the augmented group was higher than in the nonaugmented group at all time periods. The differences between the augmented and nonaugmented groups were statistically significant in the 8 to 12 week period (p < 0.01). Tan delta values, exhibiting the magnitude of viscosity in a viscoelastic material, in the augmented group were significantly higher than those in the nonaugmented group at 8 weeks (p < 0.05) and 12 weeks (p < 0.01). The mean tan delta in the augmented group decreased to 0.08 +/- 0.04 at 24 weeks, but the values were higher than those of the original ACL. The mean dynamic elastic modulus in the augmented group was higher than in the nonaugmented group at all time periods. The difference between the augmented and nonaugmented groups was statistically significant in the 8th week (p < 0.05). The values of dynamic elastic modulus in both groups were increased at 24 weeks: 96.4 MPa in the augmented group, and 77.5 MPa in the nonaugmented group. It was demonstrated that the augmented ligaments used for anterior cruciate ligament reconstruction had greater strength and static stiffness than the patellar tendon autograft. As for dynamic properties, the augmented group showed higher viscosity group than ACL.

Cross-hole acoustic surveying in basalt

The purpose of this technical note is to present preliminary results of a series of cross-hole acoustic measurements performed in a tunnel situated in a basaltic rock mass. The tunnel, at a sub-surface depth of 46 m, was excavated by conventional drill-and-blast techniques. Located well above the water table, the rock mass is characterized as dense basalt with a jointing structure of 0.15-0.36 m thick vertical columns cut by low-angle cross joints. The objectives of the test program were: first, to evaluate in situ dynamic elastic properties, and to assess their spatial variation around the opening; second, to evaluate the extent of blast damage around the opening; and third, to assess the spatial variation of jointing and fracturing around the opening. Analysis of the data included an evaluation of the velocities and frequency spectra of compressional and shear waves transmitted through the rock. The authors found that (1) the acoustic velocity and attenuation data are clearly indicative of an anisotropic, jointed rock mass, with a greater intensity of jointing in the horizontal than the vertical direction. (2) low acoustic velocities are indicative of blast damage, and of zones of intense jointing or fracturing. The same trend is seen also in the values of dynamic elastic modulus. The dynamic Poisson's ratio, however, appears to be relatively insensitive to the degree of jointing or fracturing. (3) preliminary analyses of the frequency data show that the attenuation of elastic waves is also indicative of blast damage and the intensity of jointing and fracturing. Further analyses of the frequency data are clearly required. (TRRL)

A New Apparatus for Measuring Dynamic Viscoelastic Properties of Polymers

The film-shaped specimen is subjected to a longitudinal forced vibration by an electromagnetic transducer. The displacement and force are detected electrically by two strain gauges connected to the clamped ends of specimen. These voltages are introduced to a specially devised circuit by which the values of dynamic elastic modulus and loss factor can be measured directly from the reading of dial in potentiometer and of output meter. The time required for measurement is only a few seconds. The observation of Lissajous' figure is also utilized at frequencies below 5c/s. The applicability of apparatus covers frequencies from 0.01 to 20c/s, temperatures from 20 to 180°C and magnitudes of elastic modulus from about 107 to 1011 dyne/cm2. The experimental results on some graft copolymers are exemplified.

3—The Propagation of Longitudinal Stress Pulses in Textile Fibres—Part 1

A knowledge of the elastic properties of textile fibres, measured under dynamic conditions, is becoming of increasing importance for the elucidation of their visco-elastic properties and rheological behaviour. A study of previous work on the subject, however, reveals serious gaps in present knowledge, particularly in regard to measurements on single fibres at frequencies greater than about 20 kc/s ; also, determinations of the dynamic and static elastic moduli of the same samples, over a range of materials, are lacking. The present contribution describes in Part I an experimental method for the determination of Young's modulus for single textile fibres at a frequency of 100 kc/s, using a direct pulse-velocity method of measurement , and compares in Part II some values of dynamic elastic modulus obtained in this way with the static values measured on the same specimens, for a limited range of textile materials. The significance of the results as they affect the interpretation of the rheological characteristics of the fibres is briefly discussed.