An experimental study on anisotropic mechanical properties of porcine thoracic aorta

Objective: To study the anisotropic mechanical properties of the thoracic aorta in porcine. Methods: Twenty-one porcine thoracic aortas were collected and categorized into three groups. The aortas were then cut through in their axial directions and expanded into two-dimensional planes. Then, by setting the length direction of the planar aortas (i.e., axial directions of the aortas) as 0°, each planar aorta was counterclockwisely cut into 8 samples with orientation of 30°, 45°, 60°, 90°, 120°, 135°, 150° and 180°, respectively. Finally, the uniaxial tensile tests were applied on three groups of samples at the loading rates of 1, 5 and 10 mm/min, respectively, to obtain the elastic modulus and ultimate stress of the aorta in different directions and at different loading rates. Results: The stress-strain curves exhibited different viscoelastic behaviors. With the increase of sample orientations, the elastic modulus gradually increased from 30°, reached the maximum value at 90°, and then gradually decreased till 180°. The variation trend of ultimate stress was similar to that of elastic modulus. Moreover, different loading rates showed a significant influence on the results of elastic modulus and ultimate stress, but a weak influence on the anisotropic degree. Conclusions: The porcine thoracic aorta is highly anisotropic. This research finding provides parameter references for assignment of material properties in finite element modeling, and is significant for understanding biomechanical properties of the arteries.

A multiscale study on the structural and mechanical properties of the luffa sponge from Luffa cylindrica plant

Cellular materials that are often observed in biological systems exhibit excellent mechanical properties at remarkably low densities. Luffa sponge is one of such materials with a complex interconnecting porous structure. In this paper, we studied the relationship between its structural and mechanical properties at different levels of its hierarchical organization from a single fiber to a segment of whole sponge. The tensile mechanical behaviors of three single fibers were examined by an Instron testing machine and the ultrastructure of a fractured single fiber was observed in a scanning electronic microscope. Moreover, the compressive mechanical behaviors of the foam-like blocks from different locations of the sponge were examined. The difference of the compressive stress-strain responses of four sets of segmental samples were also compared. The result shows that the single fiber is a porous composite material mainly consisting of cellulose fibrils and lignin/hemicellulose matrix, and its Young's modulus and strength are comparable to wood. The mechanical behavior of the block samples from the hoop wall is superior to that from the core part. Furthermore, it shows that the influence of the inner surface on the mechanical property of the segmental sample is stronger than that of the core part; in particular, the former's Young's modulus, strength and strain energy absorbed are about 1.6 times higher. The present work can improve our understanding of the structure-function relationship of the natural material, which may inspire fabrication of new biomimetic foams with desirable mechanical efficiency for further applications in anti-crushing devices and super-light sandwich panels.

Effect of microstructure and mechanical properties on the seizure resistance of cast aluminium alloys

Seizure resistance of several cast aluminium base alloys has been examined using a standard Hohman Wear Tester. Disks of aluminium base alloys were run against a standard aluminium 12% silicon base alloy. The seizure resistance of the alloys (as measured by the lowest bearing parameter reached before seizure) increased with hardness, yield and tensile strength. In Al-Si-Ni alloys where silicon and nickel have little solid solubility in α-aluminium and Si and Ni Al3 hard phases are formed, the minimum bearing parameter decreased with the parameter V (The product of vol. % of hard phases in the disk and the shoe). Apparently the silicon and NiAl3 particles provided discontinuities in the matrix and reduced the probability (1 − V) of the α-aluminium phase in the disk coming into contact with the α-aluminium phase in the shoe. The copper and magnesium containing Al-Si-Ni alloys with lesser volumes of hard phases exhibit considerably better seizure resistance indicating that a slight increase in the solute content or the hardness of the primary α-phase leads to a considerable increase in seizure resistance. Deformation during wear and seizure leads to fragmentation of the original hard particles into considerably smaller particles uniformly dispersed in the deformed α-aluminium matrix.

Influence of Joint Thickness and Mortar-Block Elastic Properties on the Strength and Stresses Developed in Soil-Cement Block Masonry

Soil-cement blocks are employed for load bearing masonry buildings. This paper deals with the study on the influence of bed joint thickness and elastic properties of the soil-cement blocks, and the mortar on the strength and behavior of soil-cement block masonry prisms. Influence of joint thickness on compressive strength has been examined through an experimental program. The nature of stresses developed and their distribution, in the block and the mortar of the soil-cement block masonry prism under compression, has been analyzed by an elastic analysis using FEM. Influence of various parameters like joint thickness, ratio of block to mortar modulus, and Poisson's ratio of the block and the mortar are considered in FEM analysis. Some of the major conclusions of the study are: (1) masonry compressive strength is sensitive to the ratio of modulus of block to that of the mortar (Eb/Em) and masonry compressive strength decreases as the mortar joint thickness is increased for the case where the ratio of block to mortar modulus is more than 1; (2) the lateral tensile stresses developed in the masonry unit are sensitive to the Eb/Em ratio and the Poisson's ratio of mortar and the masonry unit; and (3) lateral stresses developed in the masonry unit are more sensitive to the Poisson's ratio of the mortar than the Poisson's ratio of the masonry unit.

Microstructure and mechanical properties of unidirectionally solidified Al-Si-Ni ternary eutectic

Al-10.98 pct Si-4.9 pct Ni ternary eutectic alloy was unidirectionally solidified at growth rates from 1.39μm/sec to 6.95μm/sec. Binary Al-Ni and Al-Si eutectics prepared from the same purity metals were also solidified under similar conditions to characterize the growth conditions under the conditions of present study. NiAl3 phase appeared as fibers in the binary Al-Ni eutectic and silicon appeared as irregular plates in the binary Al-Si eutectic. However, in the ternary Al-Si-Ni eutectic alloy both NiAl3 and silicon phases appeared as irregular plates dispersed in α-Al phase, without any regular repctitive arrangement. The size and spacing of NiAl3 and Si platelets in cone shaped colonies decreased with an increase in the growth rate of the ternary eutectic. Examination of specimen quenched during unidirectional solidification indicated that the ternary eutectic grows with a non-planar interface with both Si and NiAl3 phases protruding into the liquid. It is concluded that it will be difficult to grow regular ternary eutectic structures even if only one phase has a high entropy of melting. The tensile strength and modulus of unidirectionally solidified Al-Si-Ni eutectic was lower than the chill cast alloys of the same composition, and decreased with a decrease in growth rate. Tensile modulus and strength of ternary Al-Si-Ni eutectic alloys was greater than binary Al-Si eutectic alloy under similar growth conditions, both in the chill cast and in unidirectionally solidified conditions.

Effect of recrystallization and grain growth on the mechanical properties of an extruded AZ21 Mg alloy

An experimental investigation into the effect of microstructural changes, which occur during post-extrusion annealing of a Mg based AZ21 alloy, on tensile and fatigue properties is conducted. Mechanical properties in the as-cast, as-extruded, and microstructural states that correspond to recovery, recrystallization and grain growth stages of annealing are compared. Results show that these microstructural changes do not alter the yield strength of the alloy markedly whereas significant differences were noted in the ultimate tensile strength as well as ductility. The initiation of abnormal grain growth (or secondary recrystallization) renders the tensile stress-strain response elastic perfectly plastic and results in a large drop in ductility, as high as similar to 60% during intermediate stages of abnormal grain growth, vis-A-vis the ductility of the as-extruded alloy. While the fatigue performance of all the wrought alloys is far superior to as expected, abnormal grain growth leads to a marked decrease in the endurance that of the as-cast alloy, limit. Possible microscopic origins of these are discussed. (C) 2009 Elsevier B.V. All rights reserved.

Elastic Properties of Boron Nitride Nanotubes and Their Comparison with Carbon Nanotubes

Boron Nitride Nanotubes (BNNTs) have alternating boron and nitrogen atoms in graphite like network and are strongly polar in nature due to a large charge on boron and nitrogen atoms. Hence electrostatic interactions are expected to play an important role in determining the elastic properties of BNNTs. In the absence of specific partial atomic charge information for boron and nitrogen, we have studied the elastic properties BNNTs varying the partial atomic charges on boron and nitrogen. We have computed Young modulus (Y) and Shear modulus (G) of BNNT as a function of the tube radius and number of walls using molecular mechanics calculation. Our calculation shows that Young modulus of BNNTs increases with increase in magnitude of the partial atomic charge on B and N and can be larger than the Young modulus of CNTs of same radius. This is in contrast to the earlier finding that CNTs has the largest tensile strength (PRL, 80, 4502, 1998). Shear modulus, on the other hand depends weakly on the magnitude of partial atomic charge and is less than the shear modulus of the CNT. The values obtained for Young modulus and Shear modulus are in excellent agreement with the available experimental results.

Effect of compatibilization on mechanical and thermal properties of polypropylene–soy flour composites

A new biobased composite was developed by adding soy flour (SF) to polypropylene (PP). This composite shows an enhanced tensile strength and modulus but decrease in elongation at break. The compatibilizer (coupling agent) appears to have a synergistic effect on tensile strength. The presence of the compatibilizer improves the dispersion of SF in the PP matrix. The addition of glycerol plasticizer to the composite improves the processability resulting in improved performance, as compared to composites without glycerol plasticizer. The optimal compatibilizer content appears to be 6%.

Studies on the Cell Wall Structure and on the Mechanical Properties of Norway Spruce

The structure and the mechanical properties of wood of Norway spruce (Picea abies [L.] Karst.) were studied using small samples from Finland and Sweden. X-ray diffraction (XRD) was used to determine the orientation of cellulose microfibrils (microfibril angle, MFA), the dimensions of cellulose crystallites and the average shape of the cell cross-section. X-ray attenuation and x-ray fluorescence measurements were used to study the chemical composition and the trace element content. Tensile testing with in situ XRD was used to characterise the mechanical properties of wood and the deformation of crystalline cellulose within the wood cell walls. Cellulose crystallites were found to be 192 284 Å long and 28.9 33.4 Å wide in chemically untreated wood and they were longer and wider in mature wood than in juvenile wood. The MFA distribution of individual Norway spruce tracheids and larger samples was asymmetric. In individual cell walls, the mean MFA was 19 30 degrees, while the mode of the MFA distribution was 7 21 degrees. Both the mean MFA and the mode of the MFA distribution decreased as a function of the annual ring. Tangential cell walls exhibited smaller mean MFA and mode of the MFA distribution than radial cell walls. Maceration of wood material caused narrowing of the MFA distribution and removed contributions observed at around 90 degrees. In wood of both untreated and fertilised trees, the average shape of the cell cross-section changed from circular via ambiguous to rectangular as the cambial age increased. The average shape of the cell cross-section and the MFA distribution did not change as a result of fertilisation. The mass absorption coefficient for x-rays was higher in wood of fertilised trees than in that of untreated trees and wood of fertilised trees contained more of the elements S, Cl, and K, but a smaller amount of Mn. Cellulose crystallites were longer in wood of fertilised trees than in that of untreated trees. Kraft cooking caused widening and shortening of the cellulose crystallites. Tensile tests parallel to the cells showed that if the mean MFA is initially around 10 degrees or smaller, no systematic changes occur in the MFA distribution due to strain. The role of mean MFA in defining the tensile strength or the modulus of elasticity of wood was not as dominant as that reported earlier. Crystalline cellulose elongated much less than the entire samples. The Poisson ratio νca of crystalline cellulose in Norway spruce wood was shown to be largely dependent on the surroundings of crystalline cellulose in the cell wall, varying between -1.2 and 0.8. The Poisson ratio was negative in kraft cooked wood and positive in chemically untreated wood. In chemically untreated wood, νca was larger in mature wood and in latewood compared to juvenile wood and earlywood.

Influence of finite size effect on magnetic and magnetotransport properties of La0.5Sr0.5CoO3 thin films

We present a comprehensive study of the thickness dependent structural, magnetic and magnetotransport properties of oriented La0.5Sr0.5CoO3 thin films grown on LaAlO3 by Pulsed Laser Deposition. We observe that these films undergo a reduction in Curie temperature (T-c) with a decrease in film thickness, and it is found to be primarily caused by the finite size effect since the finite scaling law [T-c(infinity) T-c(t)/T-c(infinity) = (c/t)lambda holds good over the studied thickness range. We rule out the contribution from the strain induced suppression of Curie temperature with decreasing film thickness since all the films exhibit a constant out of plane tensile strain (0.5%) irrespective of their varying thickness. However, we observe that the coercivity of the films is an order of magnitude higher than that of the bulk due to the tensile strain. In addition, we also observe an increase in the magneto resistance peak and a decrease in coercivity and electrical resistivity with an increase in film thickness. (C) 2010 Elsevier Ltd. All rights reserved.

Mechanical and Thermal Properties of Eva Blended with Biodegradable Ethyl Cellulose

In this study, biodegradable blend of Poly (Ethylene-co-Vinyl Acetate) (EVA) and Ethyl Cellulose (EC) were prepared. Ethylene vinyl alcohol (EVOH) copolymer was used as an interfacial compatibilizer to enhance adhesion between EVA and EC. The melt blended compatibilized biocomposites were examined for mechanical and thermal properties as per the ASTM standards. It has been found that the EC has a reinforcing effect on EVA leading to enhanced tensile strength and also impart biodegradability. Thus, a high loading of 50% EC could be added without compromising Much on the mechanical properties. Analysis of the tensile data using predictive theories showed an enhanced interaction of the dispersed phase (EC) and the matrix (EVA). The compatibilizing effects of EVOH on these blends were confirmed by the significant improvement in the mechanical properties comparable with neat EVA as also observed by SEM microscopy. The TGA thermograms exhibits two-stage degradation and as EC content increases, the onset temperature for thermal degradation reduces. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1044-1056, 2010

High temperature mechanical properties of thermal barrier coated superalloy applied to combustor liner of aero engines

High temperature load controlled fatigue, hot tensile and accelerated creep properties of thermal barrier coated (TBC) Superni C263 alloy used as a candidate material in combustor liner of aero engines are highlighted in this paper. Acoustic emission technique has been utilised to characterise the ductile-brittle transition teperature the bond coat. Results revealed that the DBTT (ductile to brittle transition temperature) of this bond coat is around 923 K, which is in close proximity to the value reported for CoCrAlY type of bond coat. Finite element technique, used for analysing the equivalent stresses in the bond coat well within the elastic limit, revealed the highest order of equivalent stress at 1073 K as the bond coat is ductile above 923 K. The endurance limit in fatigue and the life of TBC coated composite under accelerated creep conditions are substantially higher than those of the substrate material. Fractographic features at high stresses under fatigue showed intergranular cleavage whereas those at low stresses were transgranular and ductile in nature. Delamination of the bond coat and spallation of the TBC at high stresses during fatigue was evident. Unlike in the case of fatigue, the mode of fracture in the substrate at very high stresses was transgranular whereas that at low stresses was intergranular in creep.

Microstructure and Properties of the Spray-Formed and Extruded 7075 Al Alloy

In the present investigation, a very good combination of strength and ductility, 630MPa 0.2% proof stress and 14.8% elongation to fracture in tensile test, has been obtained for the 7075 Al alloy after optimizing the processing parameters for spray forming, hot extruding the spray deposit, and peak aging the samples taken from the extruded rod. The spray deposits contained some porosity but it was almost eliminated on hot extrusion. Electron probe microanalysis revealed that even though spray forming was carried out in an open atmosphere, it did not affect the oxygen content and its distribution in the material on spray forming, because the atomizing argon gas provided a protective cover to molten droplets and prevented their oxidation. The chemical composition of the spray-formed material was found to be almost the same as the raw material, and the major alloying elements were found to be uniformly distributed in the extruded rod.

Mechanical Properties of Al-Mica Particulate Composite Material

Cast aluminium alloy mica particle composites of varying mica content were tested in tension, compression, and impact. With 2.2 percent mica (size range 40µm – 120µm) the tensile and compression strengths of aluminium alloy decreased by 56 and 22 percent, respectively. The corresponding decreases in percent elongation and percent reduction are 49 and 39 percent. Previous work [2] shows that despite this decrease in strength the composite with 2.5 percent mica and having an UTS of 15 kg/mm2 and compression strength of 28 kg/mm2 performs well as a bearing material under severe running conditions. The differences in strength characteristics of cast aluminium-mica particle composites between tension and compression suggests that, as in cast iron, expansion of voids at the matrix particle interface may be the guiding mechanism of the deformation. SEM studies show that on the tensile fractured specimen surface, there are large voids at the particle matrix interface.

Effects of thermal annealing on the properties of zirconia films prepared by ion-assisted deposition

The effect of thermal annealing in the range 300–800 °C on the properties of zirconia films prepared by ion assisted deposition was studied. It was found that at low temperature the cubic phase is formed. This phase is stable up to 700 °C. All the films exhibit a monophasic monoclinic structure at 800 °C. The stress, estimated from X-ray patterns, shows a transition from tensile to compressive with increasing ion fluence. The refractive index and extinction coefficient do not seem to change appreciably up to 700 °C, showing a marked degradation thereafter. Single step annealing to the highest temperature was found to result in better stability than multistep annealing.