The influence of hydration on the tensile and compressive properties of avian keratinous tissues

Despite recent research exploring the elastic properties of avian keratins, data on failure properties are less common in the literature. In this paper we present data on the failure properties and moduli of both avian feather and claw keratin in tension and the modulus of claw keratin in compression. Increased water content acts to decrease stiffness and strength but to increase strain at failure. The modulus of claw did not differ significantly when tested under tension and compression.

Surface properties and locations of gluten proteins and lipids revealed using confocal scanning laser microscopy in bread dough

Surface properties of gluten proteins were measured in a dilation test and in compression and expansion tests. The results showed that monomeric gliadin was highly surface active, but polymer glutenin had almost no surface activity. The locations of those proteins in bread dough were investigated using confocal scanning laser microscopy and compared with polar and nonpolar lipids. Added gluten proteins participated in the formation of the film or the matrix, surrounding and separating individual gas cells in bread dough. Gliadin was found in the bulk of dough and gas 'cell walls'. Glutenin was found only in the bulk dough. Polar lipids were present in the protein matrix and in gas 'cell walls', as well as at the surface of some particles, which appeared to be starch granules. However, nonpolar lipid mainly occur-red on the surface of particles, which may be starch granules and small lipid droplets. It is suggested that the locations of gluten proteins in bread dough depends on their surface properties. Polar lipid participates the formation of gluten protein matrix and gas 'cell walls'. Nonpolar lipids may have an effect on the rheological properties by associating with starch granule surfaces and may form lipid droplets. (C) 2004 Published by Elsevier Ltd.

Interaction of heat-moisture conditions and physical properties in oat processing: I. Mechanical properties of steamed oat groats

Research interest in oats has focussed on their nutritional value, but there have been few studies of their food processing. Heat treatment is characteristic of oat processing, as it is needed to inactivate lipase and to facilitate flaking. A Texture Analyser was used to characterise the mechanical properties of unkilned and kilned oat groats after steaming and tempering in an oven for 30, 60 and 90 min at 80, 95 and 110 degrees C. Maximum force, number of peaks before maximum and final force after 5s hold were used to characterise the behaviour of the groats during compression. Kilned groats were larger and softer before steaming. After steaming and tempering, the moisture content of the kilned groats was higher than for unkilned groats. Hot, steamed oats were softer than cold, unsteamed groats, indicated by a decrease in maximum force from 59 to 55 N, and there was no significant difference between kilned and unkilned groats. However, higher temperatures during tempering increased maximum force. These results suggest that mild steam treatment yields softer oat groats, whereas cold or over-treated groats tend to be harder. (c) 2007 Elsevier Ltd. All rights reserved.

Measurement of the Viscoelastic Properties of the Vocal Folds

Objectives: Studies of the viscoelastic properties of the vocal folds are normally performed with rheometers that use parallel assigned a fixed value. In tissues subject to variation of thickness plates whose interplate space is usually at between samples, fixed gaps could result in different compressions, compromising the comparison among them. We performed,in experimental study to determine whether different compressions call lead to different results in measurements of dynamic viscosity (DV) of vocal fold samples. Methods: We Measured the DV of vocal fold samples of 10 larynges of cadavers under 3 different compression levels, corresponding to 0.2, 0.5, and 10 N on an 8-mm-diameter parallel-plate rheometer. Results: The DV directly varied with compression. We observed statistically significant differences between the results of 0.2 and 10 N (p = 0.0396) and 0.5 and 10 N (p = 0.0442). Conclusions: The study demonstrated that the level of compression influences the DV measure and Suggests that a defined compression level should be used in rheometric studies of biological tissues.

Influence of z-pinning on the buckling of composite laminates under edge-wise compression

Z-pinning is a newly developed technique to enhance the strength of composite laminates in the thickness direction. Recent experimental and theoretical studies have shown that z-pins significantly improve mode I and mode II fracture toughness. In practice, buckling accompanying delamination is a typical failure mode in laminated composite structures. For a complete understanding of the z-pinning technique towards improvements of the overall mechanical properties of laminated composites, a numerical model is developed in this paper to investigate the influence of z-pins on the buckling composite laminates with initial delaminations under edge-wise compression. The numerical results indicate that z-pinning can indeed effectively increase the compressive strength of the composite laminates provided that the initial imperfection is within a certain range. The magnitude of the improvement is consistent with available experimental data.

Processing and mechanical properties of porous titanium-niobium shape memory alloy for biomedical applications

Ti-26 at.%Nb (hereafter Ti-26Nb) alloy foams were fabricated by space-holder sintering process. The porous structures of the foams were characterized by scanning electron microscopy (SEM). The mechanical properties of the Ti-26Nb foam samples were investigated using compressive test. Results indicate that mechanical properties of Ti-26Nb foam samples are influenced by foam porosity. The plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 10~200 MPa and 0.4~5.0 GPa for the Ti-26Nb foam samples with porosities ranged from 80~50 %, respectively.

Nano- and macro-scale characterisation of the mechanical properties of bovine bone

In the present study, nano- and macro-scale characterisations on the mechanical properties of bovine cortical bones have been performed by using nanoindentation and conventional compressive tests. Nanoindentation results showed that the elastic modulus for the osteons and the interstitial lamellae in the longitude direction were 24.7 ± 2.5 GPa and 30.1 ± 2.4 GPa. As it’s difficult to distinguish osteons from interstitial lamellae in the transverse direction, the average elastic modulus for cortical bovine bone in the transverse direction was 19.8 ± 1.6 GPa. Significant differences were found in the modulus values between different microstructures of bone tissue and in different testing direction. It was found that the elastic modulus of bone bovine material in nano-level was higher than that in macro-level. The elastic modulus and
ultimate stress of large bone samples were 12.5 ± 1.9 GPa and 195 ± 19 MPa respectively from the compression test.

Mechanical properties and energy absorption of ceramic particulate and resin-impregnation reinforced aluminium foams

The mechanical properties of aluminium foams can be improved by matrix reinforcement and resin-impregnation methods. In the present study, aluminium foams were reinforced by both ceramic particulate reinforcing of the aluminium matrix and resin-impregnating pores. The mechanical properties and the energy absorption of the reinforced aluminium foams were investigated by dynamic and quasi-static compression. Results indicated that the ceramic particle additions of CBN, SiC and B4C in aluminium foams increase the peak stress, elastic modulus and energy absorption of the aluminium foams, under both conditions of dynamic and quasi-static compression. Moreover, the aluminium foams with and without ceramic particle additions exhibited obvious strain rate sensitivity during dynamic compression. Furthermore, the resin-impregnation improves the mechanic properties and energy absorption of aluminium foams significantly. However, aluminium foams with resin-impregnation showed negligible strain rate sensitivity under dynamic compression. It is reported that both the ceramic particle addition and resin-impregnation can be effective techniques to improve the mechanical and the energy absorption properties of aluminium foams.

Texture changes during uniaxial compression of Mg-3AI-1Zn

The mechanical anisotropy of wrought Mg alloys is very high. For example the yield stress of extruded Mg-3Al-1Zn tested in tension can be as high as twice that obtained in compression [1]. To solve the problems this creates for product design it is necessary to understand the sensitivity of texture to processing parameters. Uniaxial compression tests at different temperatures were performed on cylindrical samples of an extruded Mg-3Al-1Zn bar. The texture
during this deformation changes from a situation where all crystal c-axes are nearly perpendicular to the sample axis to one where the c-axes are all nearly parallel to this axis. Compression was stopped at different strains to examine the rate of this texture change. Textures were examined using EBSD measurements. It was found that different mechanisms operate depending on the temperature of deformation and that a variety of textures can be created. Also it was seen that an annealing treatment performed after compression has an influence on the texture. Afterwards the samples were subjected to another uniaxial compression test to examine the influence of texture on room temperature properties.

A comparative study of the mechanical properties of wool and alpaca fibres

This study reports the latest research into alpaca and wool fibres. In particular, those properties that have received little attention in research literature have been examined. They include single fibre abrasion and bending fatigue, single fibre tensile properties, as well as resistance to compression behaviour. These properties are important because they affect the softness and pilling propensity of these fibres and the resultant fabrics. Clean wool and alpaca fibres were used in this study. Fibre abrasion/bending fatigue measurements were carried out using a Textechno FIBRESTRESS instrument. The resistance to compression (RtC) tests were carried out according to Australian Standard AS3535-1988. The results indicate that wool and alpaca fibres behave quite differently, even though both fibre types are of animal origin. Wool fibre resistance to compression decreases as fibre diameter increases while the opposite appears to occur for alpaca fibres. For both wool and alpaca the number of abrasion/bending cycles at fibre break increases with an increase in fibre diameter, it takes longer to break the alpaca fibres. Reasons for these differences have been postulated based on differences in fibre surface and structure between alpaca and wool.

Properties of mechanically milled and spark plasma sintered Al–15 at.% MgB2 composite materials

Air-atomized pure aluminium powder with 15 at.% MgB₂ was mechanically milled (MMed) by using a vibrational ball mill, and MMed powders were consolidated by spark plasma sintering (SPS) to produce composite materials with high specific strength. Solid-state reactions of MMed powders have been examined by X-ray diffraction (XRD), and mechanical properties of the SPSed materials have been evaluated by hardness measurements and compression tests. Orientation images of microstructures were obtained via the electron backscatter diffraction (EBSD) technique.

The solid-state reactions in the Al–15 at.% MgB₂ composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction were a combination of AlB₂, Al₃BC and spinel MgAl₂O₄. Mechanical milling (MM) processing time and heating temperatures affect the characteristics of those intermetallic compounds. As the result of the solid-state reactions in MMed powders, a hardness increase was observed in MMed powders after heating at 573–873 K for 24 h. The full density was attained for the SPSed materials from 4 h or 8 h MMed powders in the Al–15 at.% MgB₂ composite materials under an applied pressure of 49 MPa at 873 K for 1 h. The microstructure of the SPSed materials fabricated from the MMed powders presented the bimodal aluminium matrix grain structure with the randomly distributions. The Al–15 at.% MgB₂SPSed material from powder MMed for 8 h exhibited the highest compressive 0.2% proof strength of 846 MPa at room temperature.

Mechanical properties of titanium foam for biomedical applications

Understanding the mechanical behaviour of pure titanium (Ti) foam is crucial for the design and development of Ti foam-based load-bearing implants. In this work, pure titanium foam is fabricated by a powder metallurgical process using the space-holder technique with a spacer size of 500 to 800 µm. Experimental data from static compression testing on the Ti foam are presented. The application of theoretical formulae to predict Young's modulus and yield strength of titanium foams is also discussed. A foam with 63% porosity, 87 ± 5 MPa yield strength, and 6.5 ± 1.3 GPa Young's modulus is found to be appropriate for a number of dental and orthopaedic applications.

Mechanical properties of porous Ti-26NB alloy for regenerative medicine

Porous titanium-26at.%niobium (hereafter, Ti-26Nb) alloys with different porosities were prepared by space-holder sintering. The porous structure of the alloys was characterized by scanning electron microscopy (SEM). Mechanical properties of the porous alloys were investigated using compression test. Results indicate that the porous alloys with 60, 70 and 80% porosities exhibit interconnected porous structure with pore sizes of 100-300 µm. The porous structure has the potential to provide new bone tissue ingrowth ability. The mechanical properties of these porous alloys decrease with the increase of porosity. The mechanical properties of the porous Ti-26Nb alloys can be tailored to match those of human bone.

Study of the effect of grain size on the dynamic mechanical properties of microalloyed steels

In the present paper the effect of grain refinement on the dynamic response of ultra fine-grained (UFG) structures for C–Mn and HSLA steels is investigated. A physically based flow stress model (Khan-Huang-Liang, KHL) was used to predict the mechanical response of steel structures over a wide range of strain rates and grain sizes. However, the comparison was restricted to the bcc ferrite structures. In previous work [K. Muszka, P.D. Hodgson, J. Majta, A physical based modeling approach for the dynamic behavior of ultra fine-grained structures, J. Mater. Process. Technol. 177 (2006) 456–460] it was shown that the KHL model has better accuracy for structures with a higher level of refinement (below 1 μm) compared to other flow stress models (e.g. Zerrili-Armstrong model). In the present paper, simulation results using the KHL model were compared with experiments. To provide a wide range of the experimental data, a complex thermomechanical processing was applied. The mechanical behavior of the steels was examined utilizing quasi-static tension and dynamic compression tests. The application of the different deformation histories enabled to obtain complex microstructure evolution that was reflected in the level of ferrite refinement.

Compression and extrusion of metals using rotating dies

Experimental and theoretical investigations of compression and extrusion of metals with steadily or cyclically rotating dies were carried out. Reasonably simple models were produced by classical plasticity theory and analytical equations were developed to establish a theoretical basis for the associated phenomena. Analytical solutions agreed well with the experimental results.