Specimens Of Different Lengths Research Articles

Determining longitudinal- and shear-wave velocities in Japanese radish, watermelon and potato

Longitudinal- and shear-wave velocities were determined for Japanese radish, watermelon and potato. Pulsed waves propagating in cylindrically shaped specimens were detected, and their phase differences obtained in specimens of different lengths yielded phase velocities in the frequency range 0.4–8 kHz at 27 kHz. The Pochhammer–Chree dispersion relation was applied to analyze the fundamental and second modes of the measured velocities, which provided the longitudinal- and shear-wave velocities in an infinite medium. Longitudinal-wave velocities of 202, 82 and 571 m s−1 and shear-wave velocities of 61, 36 and 80 m s–1 for Japanese radish, watermelon and potato, respectively, were obtained. Furthermore, the Young’s modulus and Poisson’s ratio were determined. The drying effect of the velocities obtained in the Japanese radish suggested that gas porosity substantially influenced the velocities, resulting in smaller values of the longitudinal-wave velocity compared with that in water.

Structure Formation and Mechanical Properties of Wire Arc Additively Manufactured Al4043 (AlSi5) Components

In the current paper, the correlation between the physical size of additively built wire arc specimens and their structure and properties is studied. For the purpose of this work, two oval shaped specimens of different lengths were manufactured under the same technological conditions. The specimens have a length of 200 mm and 400 mm and will be referred to as L200 and L400. The microstructure of the samples was studied using X-ray diffraction analysis (XRD), optical microscopy, and scanning electron microscopy (SEM). The microhardness, yield strength (YS), and ultimate tensile strength (UTS) were determined and their correlation with the technological conditions of specimen build-up was clarified. The results of the carried out experiments indicated that the crystallographic structure of both specimens is similar. The scanning electron microscopy images show a higher concentration of irregularly shaped micro-pores formed near the edge of the αAl grains in the structure of the L400 specimen compared to the L200 one. An increase in the size of the αAl solid solution grains in the case of the L200 specimen towards its top section was noticed using optical microscopy. A slightly lower magnitude change was noticed concerning the L400 specimen. The increase in the size of the aluminum crystals was determined to be the increasing interpass temperature. Due to the much smaller thermal dissipation capacity of the smaller specimen, the interpass temperature of the same increased faster compared to the larger specimen. All of the above-mentioned factors led to a decrease in the microhardness of the specimens at higher stages of build-up. Since the specimens were deposited using similar layer deposition conditions, the resultant YS and UTS data are also highly comparable.

Experimental investigations on rolled angle sections reinforced with CFRP plates

AbstractTelecommunication or power transmission lattice towers may be in need of strengthening due to enhanced operational requirements of 5G systems or extension and upgrading of existing power lines. The members of such towers are mostly angle sections that are conventionally strengthened by a second profile to become a built‐up member. As an alternative, hybrid strengthening of tower angle members with carbon fiber reinforced polymers (CFRP) plates may be employed. The present paper provides experimental tests on hybrid angles that include bending tests and compression tests carried out in the frame of the RFCS research project ANGELHY. In 3‐point bending tests the specimens were subjected to loading along the principal and the geometric axes. They allow the definition of the bending capacity and the development of appropriate design rules for hybrid cross‐sections. The compression tests were performed on specimens of different length and loading eccentricity, with FRPs attached to one or both sides of the legs. Important parameters influencing the buckling capacity were detected.

Experimental investigation of mesoscale variability of clear spruce mechanical properties in the radial direction

The aim of this work is the investigation of mesoscale/local variability in mechanical properties of clear timber in the radial direction. Clear Norway spruce wood, Picea abies, was used for cutting specimens of different lengths with a small cross-sectional area of 4 × 4 mm2, in the radial direction of timber boards, and tested under tensile loading. In some boards, specimens were positioned regularly and, in some others, randomly, and local deformations in each specimen were measured during the tests. The results indicate a significant variability in the specimens’ elastic moduli and strengths. A correlation between the mesostructure of clear timber and mesoscale/local variability of the transverse elastic modulus in the specimens was observed. Specimens’ failures were classified and a reasonable correlation with the corresponding strength values was observed.

Trophic level and heavy metal pollution of Sardinella albella in Liusha Bay, Beibu Gulf of the South China Sea

To elucidate the trophic pathways and bioaccumulation characteristics of heavy metals in marine fish, 20 Sardinella albella specimens of different lengths were collected from Liusha Bay in Beibu Gulf of South China Sea and aimed to study their trophic level and heavy metal pollution. The results showed that their δ13C values ranged from −17.61 to −15.99‰ with an average of −16.59 ± 0.54‰, which was comparable with that of zooplankton. The δ15N values ranged from 12.73to 15.26‰ with an average of 14.03 ± 0.71‰, which was 3.47‰ greater than zooplankton. No trend in δ13C and δ15N values was observed with increasing body length. The trophic level, consisting with their feeding diet, ranges from 2.24 to 3.25 with an average of 2.76. Heavy metal content of Sardinella albella in Liusha Bay was in order of As > Pb > Zn > Hg > Cu, Cd, and most of these metals were below the pollution thresholds. The Pi index suggested that Sardinella albella were slightly polluted by Pb and As.

Physical Characterization of Fibre Optic Cable using Simple Laboratory Stress Tests

Most learning institutions in Zimbabwe use fibre optic cable for internet connectivity and the heavy human and vehicular traffic at these places may pose a threat to maintenance of the cable particularly on semi-rigid ground. Physical stress in form of pressure exerted on the cable by the said traffic need to be investigated and compared in relation to tensile strength of the cable. The cables are made of polymers which provide a good operating temperature, chemical resistance, bio compatibility and prevention to mechanical and chemical damage. Simple Physics lab tests offer an opportunity to investigate the stress and strain parameters of the cable. The study sought to determine the Young modulus of the fibre optic cable at Great Zimbabwe University using two methods namely : the centre span deflection method and the strain gauge method. The first method was based on adding standard weights to cable tied on horizontally on two ends and observing deflections from the equilibrium position, the second method involved adding standard weights to a vertically suspended fibre optic and observing extensions from original length. Results of the two methods were processed in linear equations which estimated a Young modulus constant for the cable which is a stress parameter that indicated the strength of the cable. The values for Young modulus for center span deflection method using three specimens of different lengths were 8.67 × 1010 N/m2, 2.34 × 1011 N/m2 and 1.78 × 1011 N/m2 with 0.003% error. For the strain gauge method readings obtained from two specimens of different lengths were 6.48 × 106 N/m2, 9.47 × 106 N/m2 with 0.3% error. Method 1 however gave values that are close to the literature figures and can be relied on to provide stress indicator values.

Experimental characterization of longitudinal mechanical properties of clear timber: Random spatial variability and size effects

In this study, an experimental campaign was conducted to characterize the length effect on the elasticity and tensile strength of clear spruce wood parallel to the grain direction. Four groups of specimens of different lengths, cut from the same log, were tested under the same conditions under longitudinal tensile loading. The cross-sectional area of the specimens was selected as being constant and sufficiently small to exclude the effect of variations of the properties in the transverse direction. Local deformations along the lengths of the specimens were recorded during the tests in order to characterize the spatial variability of the elastic modulus. A connection between the mesostructure of the clear wood and its local elastic modulus was observed. Statistics concerning the elastic modulus, strength and strain to failure and the effect of length change on these properties were extracted. The strength statistics were also used to examine the accuracy of the classical Weibull size effect law. The correlations between the strength, the elasticity and the density were obtained. The results show a variability of approximately 20% in the local elastic modulus. Also, the variability of the effective elastic modulus decreases with increasing length. The mean value of the strength has an upper bound when the length approaches zero, in contrast to the Weibull law, while its variability remains virtually unchanged for different lengths.

Investigation on the fatigue performance of Ni-Ti thin wires

The fatigue performance of shape memory alloys is one of the main features to assess their potential in most applications (i.e., in vibration mitigation). As experimental results showed, the hysteretic properties of shape memory alloys highly depend on chemical composition, manufacturing process, and loading strain rate. In this paper, commercial wires of Nickel-Titanium (of diameter 0.2 mm) are investigated. Specimens of different length are tested under cycles of loading-unloading either on a shaking table or on an MTS Systems Corporation hydraulic testing apparatus (MiniBionix II). The fatigue results of the research campaign are then synthesized in an interpolating model. Copyright © 2016 John Wiley & Sons, Ltd.

Time-of-Flight Adjustment Procedure for Acoustic Measurements in Structural Timber

The effect of timber length on time-of-flight acoustic longitudinal measurements was investigated on the structural timber of four Spanish species: radiata pine (Pinus radiata D. Don), Scots pine (Pinus sylvestris L.), laricio pine (Pinus nigra Arn.), and maritime pine (Pinus pinaster Ait.). Time-of-flight longitudinal measurements were conducted on 120 specimens of dimensions 90 × 140 mm using three commercially available acoustic instruments (Sylvatest Duo, USLab, and Microsecond Timer). Time-of-flight data were initially obtained from the full-length (4 m) specimens, and then from the specimens cut to 3, 2, and 1 meter in length by successively cutting off 0.5 m from each end. The acoustic longitudinal velocity of the timber specimens of different lengths was also measured using a resonance-based acoustic method. The apparent acoustic longitudinal velocity for all species increased linearly as the timber length decreased from 4 to 1 meter. Acoustic velocity determined from time-of-flight data was significantly higher than the acoustic velocity determined using the resonance method, indicating systematic measurement errors associated with the time-of-flight instruments. Empirical models were developed for the relationships between time-of-flight measurements on timber specimens and timber lengths in the range of 1 to 4 m. Finally, a procedure was proposed to correct the time-of-flight data.

Film boiling heat transfer and vapour film collapse on spheres, cylinders and plane surfaces

An experimental study of transient film boiling was conducted, with different coolant velocities, on two spheres with different diameters, two cylindrical specimens of different lengths in parallel flow, a cylinder in cross flow and two flat plates with different lengths. A frame by frame photographic study on the nature of the vapour/liquid interface and the collapse modes has revealed a new mode for film collapse, in which an explosive liquid–solid contact is followed by film re-formation and the motion of a quench front over the hot surface. Steady state tests were carried out on a plate similar to the short plate used in the transient experiments and the heat transfer, film stability and collapse results are compared with those of the transient investigation. Heat transfer coefficients and heat fluxes during film boiling were found essentially to depend on specimen temperature and water subcooling. In contrast, the influences on heat transfer of specimen size and water velocity were relatively small for the ranges studied. A theoretical model predicted heat transfer coefficients to within 10% of experimental values for water subcoolings above 10 K and within 30% in all cases.

Prediction of debonding strength of tensile steel/CFRP joints using fracture mechanics and stress based criteria

In this paper, the debonding strength of axially loaded double shear lap specimens between steel plates and carbon fibre reinforced plastic plates is investigated from the analytical, numerical and experimental point of view. Two steel plates were joined together by two carbon fibre reinforced plastic (CFRP) plates and epoxy adhesive in order to realize double shear lap specimens of different length. Failure of the steel–adhesive interface was identified as the dominant failure mode and fracture mechanics and stress based approach are presented in order to estimate the relevant failure load. A good agreement between the analytical–numerical results and experimental data is achieved.

Specimen size effects in the off-axis compression test of unidirectional carbon fiber tow composites

Specimen size effects in the off-axis compression test for unidirectional carbon fiber tow composites were studied by subjecting coupon specimens of different lengths and widths to off-axis compression under static and low velocity impact loading. Specimens were cut such that the fibers are at angles of 15, 30, 45 and 60° to the direction of loading. A modified compression fixture with anti-buckling side supports was used to carry out the tests. Static tests were carried out on a hydraulically activated MTS loading frame, where specimens were subjected to displacement controlled loading. Low velocity impact tests were conducted on a drop tower facility. A three strain gage rosette was used to measure global strains. Load was measured using a load cell. Due to the unique microstructure of the specimens, a modified three parameter orthotropic plasticity characterization of the plastic response was used and the constants associated with this characterization were determined uniquely. It is shown that the orthotropic plastic response of the material is affected by specimen size primarily due to the mechanism of load introduction in the off-axis test and load transfer through the fiber tow/matrix interface that is prevalent in the material.

Inverse estimation of the acoustic impedance of a porous woven hose from measured transmission coefficients.

A porous tube, comprised of a resin-coated woven fabric has recently been used as an effective component for use in intake systems of internal combustion engines to reduce the intake noise. For the prediction of the acoustic performance of an engine intake system with a porous woven hose, the acoustic wall impedance of the hose must be known. However, the accurate measurement of the wall impedance of a porous woven hose is not easy because of its peculiar acoustical and structural characteristics. A new measurement technique is proposed herein, that is valid over the low to mid frequency ranges. The acoustics impedance is inversely estimated from an overdetermined set of measured pressure transmission coefficients for specimens of different lengths and the reflection coefficient of end termination. The method involves only one measurement setup, and, as a result, it is very simple. A variation of the proposed method, an inverse estimation method using one of the four-pole parameters is also proposed. An error sensitivity analysis was performed to investigate the effect of measurement error on the accuracy of the final result. The measured TL for samples with arbitrary lengths and arbitrary porous frequency are in reasonably good agreement with values predicted from curve-fitted impedance data.

Necking and softening as a consequence of latent continuum damage

Necking and softening in ductile polycrystalline metals are modeled as consequences of continuum damage (CD) that consists in braking through of barriers resisting plastic deformation. Our model describes these materials as two-phase continua consisting of microdomains with easy glide and barriers with decreasing continuity in the course of deformation. Macroscopic homogeneity and increase of macroscopic stress with increasing deformation are conditioned by sufficient continuity of these barriers. Our model describes the whole course of engineering stress–strain diagrams up to rupture and the differences in the diagrams for test specimens of different length. The model is compared to experimental data measured on two materials − sorbitic steel and an AlMg3 alloy.

Using Impedance Spectroscopy to Assess the Viability of the Rapid Chloride Test for Determining Concrete Conductivity.

The suitability of using the initial current from the rapid chloride test (ASTM C 1202) to determine specimen conductivity is tested using impedance spectroscopy with a frequency spectrum of 10 Hz to 1 MHz. The specimen conductivity has an analytical relationship to specimen diffusivity and so is a useful quantity in service life prediction. Measurements made on specimens of different lengths indicate that the total charge passed during the six hour conduction test carried out according to ASTM C 1202 is not a direct measure of specimen conductivity. Further, ohmic heating during the 6 hour test makes it nearly impossible to directly measure any specimen transport property from the results. The total charge passed during the 6 hour conduction test is, therefore, not a reliable quantity for service life prediction. Results indicate that the direct current (dc) measurement of resistance using a voltage of 60 V is sufficient to overwhelm polarization effects, thereby yielding an accurate estimate of the true specimen conductivity. Impedance spectroscopy measurements also indicate that corrosion may form on the brass electrodes, adding bias to a conductivity estimate based upon a dc measurement.

Fluoride ion diffusion from a glass-ionomer cement.

The aims of this study were to observe the release of fluoride ions (F-) from GC-Fuji Lining-LC(R) glass-ionomer cement, to assess the diffusion process, and to measure fluoride diffusivity (D) in the set cement. Specimens of various dimensions and shapes, ranging from discs to cylindrical rods, were fabricated for both open and embedded modes of testing. In the open mode studies, specimens with different surface to volume ratios were selected and immersed in 37 degrees C distilled water. In the embedded mode studies, only one diametral surface of the rod-shaped specimens of different lengths and diameters was exposed. F- concentration was measured using a fluoride electrode. The storage solution was analysed at predetermined intervals hourly, daily, and weekly (up to 10 weeks). Immediately after each sampling, the old storage solution was discarded and replaced with new distilled water. F- release from the set cements was detectable (0.4-3.8 ppm, varied with sample geometry), even after a 10-week sampling interval. F- release was greater in ground set cements (0.37 ppm/mg powder) than in control samples of unmixed powder (0.01 ppm/mg powder) immersed for 1 h. Two mechanisms for F- release were proposed. One was short-term and involved rapid dissolution from the cement surface. The other was more gradual and resulted in the sustained diffusion of ions through the bulk cement, which can be modelled by applying a mathematical technique known as separation of variables to Fick's Second Law of Diffusion. The mean D of F- in embedded set cements of glass-ionomer was (1.4+/-0.5)x10-11 cm2/s, with higher apparent D observed in open mode samples [(7.6+/-1.4)x10-11 cm2/s].

Hydrogen permeability in (CeO 2) 0.9(CaO) 0.1 at high temperatures

It was found that hydrogen permeated the bulk of the fluorite-type (CeO 2) 0.9(CaO) 0.1 at 1075–1800 K. Two tube shaped specimens of different lengths were prepared. The hydrogen source gas was H 2(7.8%)+N 2 which was humidified at 293 K and supplied to the outside of specimens. Ar gas was let flow to the inside of specimens and the permeated hydrogen in the outlet Ar gas was analyzed by a gas chromatograph. Measurements were made at the same conditions on the specimens to eliminate the hydrogen permeated through Pt rings, which were used to fix the specimen, the alumina tube and disk, and the alumina supporting materials. The permeability, J H, in log( J H/mol h −1 cm −1) was almost proportional to 1/ T ( T: temperature). The gradient of the line changes at 1525 K. The activation energy, E, of conductive protons or electrons was estimated from the Arrhenius' relation, log J H= A− E/2.303 kT. A is constant and E is the activation energy, which is 1.07±0.03 eV above 1525 K and 0.73±0.06 eV below 1525 K, respectively. The electronic activation energies, which were determined from the oxygen permeability, were higher than the above values, and they might be the activation energy of protons. There is a possibility that (CeO 2) 0.9(CaO) 0.1 is an electron–proton mixed conductor under H 2–H 2O atmosphere at high temperature.

Softening of concrete in compression — Localization and size effects

This paper presents a constitutive macromechanical model for concrete in compression. The model, named the Compressive Damage Zone (CDZ) model, is based on the hypothesis of compressive failure within a zone of limited length. In this damage zone, the failure mode is a combination of distributed axíal splitting and localized deformation. Within the damage zone the post-peak behaviour is described by means of two curves, one related to the distributed splitting cracking and one to the localized deformation. The compressive strain caused by the axial splitting cracks is assumed to be proportional to the tensile fracture energy G F. It is shown through compressive tests of specimens of different length and width that the proposed failure hypothesis is realistic.

Finite element modeling of the three-point bend impact test

A dynamic finite element program has been applied to the analysis of the three-point bend impact specimen. First, the behavior of an unsupported specimen struck at its center was modeled. From this it was predicted that the best striker force response in an impact test would be obtained with an overhang at each end of 22% of the total length. This prediction was tested by modeling supported specimens of different lengths and by comparison with experiment. Reference curves of dynamic stress intensity for different material properties and impact speeds can be prepared from the numerical analysis. Providing the test geometry has been carefully chosen, a static displacement based stress intensity calculation appears valid even when pronounced oscillations are seen in the striker force.

Relationship between strength variability and size effect in unidirectional carbon fibre/epoxy

Abstract Unidirectional carbon fibre/epoxy exhibits a size effect which is not necessarily consistent with the variability of specimen strengths predicted on the basis of classical Weibull theory. In some cases the variability is higher than expected and this may be due to other sources of variability in the tests apart from the material. However, in bending tests consistently lower variability than expected has been measured. This is explained qualitatively in terms of the splitting that occurs during failure which means that the composite behaves between the extremes of a brittle solid and a loose fibre bundle. This also implies that the size effect should be more strongly dependent on specimen length than indicated by Weibull theory. Three-point bending tests on specimens of different lengths but the same cross-section have been carried out which support this.