Effect of microstructure on the modulus of PAN-based carbon fibers during high temperature treatment and hot stretching graphitization

The changes of microstructure and Young’s modulus of PAN-based carbon fibers during the high temperature treatment (2400–3000 °C, stretching 0%) and hot stretching graphitization (0–5%, 2400 °C) were compared. It was observed that although the Young’s modulus of the fibers could be increased by the two graphitization techniques, the microstructure parameters determined by X-ray diffraction were different for the same value of modulus. The relationship between microstructure and modulus showed that Young’s modulus not only depended on the preferred orientation, but also related to the crystallite size (L _c and L _a ) and shape (L _a /L _c ). On the other hand, it was found that crystallite size of the fibers was mainly affected by heat treatment temperature and the crystallite shape could be altered by hot stretching graphitization. Further investigation indicated that the fibers were composed of turbostratic carbon structure even after heat treated to 3000 °C, which could be detected from the absence of 101 and 112 peaks in X-ray diffraction pattern, and the interlayer spacing (d₀₀₂) and preferred orientation (Z) were only 0.3430 nm and 14.71°, respectively.     

Young’s modulus of cast HMS 2112-C f composite—prediction and ultrasonic evaluation

Various models for the prediction of strengthening mechanism of metal matrix composites (MMCs) containing either fibres or particulates are analysed. Assuming that the matrix strengthening by dislocations could be treated as equivalent to the effect of different volume fraction of dispersoids, as well as by considering the effect of morphology of reinforcement on the Young’s modulus, an expression for Young’s modulus for MMCs has been derived. The Young’s modulus values thus predicted, using this model, have been validated by ultrasonically-derived values of Young’s modulus of an Al-alloy matrix composite containing 5, 8 and 12 wt% chopped carbon fibre (C _f) dispersoids, in as cast and extruded conditions. Further, the theoretically- and ultrasonically-derived Young’s modulus of cast Al-alloy-C _f composites with 5 and 8 wt%C _f have been found to be comparable with the reported values of Young’s modulus for these weight fractions.     

Structure and properties of ultrafine silk fibers produced by <Emphasis Type="Italic">Theriodopteryx ephemeraeformis</Emphasis>

Theriodopteryx ephemeraeformis commonly known as bag worms produce ultrafine silk fibers that are remarkably different than the common domesticated (Bombyx mori) and wild (Saturniidae) silk fibers. Bag worms are considered as pests and commonly infect trees and shrubs. Although it has been known that the cocoons (bags) produced by bag worms are composed of silk, the structure and properties of the silk fibers in the bag worm cocoons have not been studied. In this research, the composition, morphology, physical structure, thermal stability, and tensile properties of silk fibers produced by bag worms were studied. Bag worm silk fibers have considerably different amino acid contents from those of the common silks. The physical structure of the bag worm silk fibers is also considerably different compared with B. mori and common wild silk fibers. Bag worm’s silk fibers have lower tensile strength (3.2 g/denier) and Young’s modulus (45 g/denier) but similar breaking elongation (15.3%) compared with B. mori silk. However, the tensile strength and Young’s modulus of bag worm fibers are similar to those of the common Saturniidae wild silk fibers. Bag worm silk fibers could be useful for some of the applications currently using the B. mori and wild silk fibers.     

The Effect of Crack Spacing Distribution on Stiffness Reduction of Cross-ply Laminates

The effect of transverse crack distribution on the effective mechanical properties of cross-ply laminates is considered. Young’s modulus and Poisson’s ratio dependence on the transverse ply crack density is obtained experimentally for glass fiber/epoxy laminates of lay-ups [0₂/90₂]_s, [0/90₂]_s, and [0/90₄]_s subjected to uniaxial tensile loading. Crack spacing distributions at the edge of the specimen are also measured at a predefined applied strain. Mechanical property reduction is evaluated for two crack spacing distributions: uniform spacing routinely considered in theoretical derivations and the experimental crack spacing distribution; the results are compared with test data.     

Preparation and properties of silicon oxycarbide fibers

Silicon oxycarbide fibers have been prepared from vinyl trimethoxysilane (VTMS) by a modified sol–gel method and with secondary cellulose acetate (SCA) as the fiber-forming aid. Its main advantage over a normal sol–gel fiber processing is that the spinning dope remains spinnable for a long period of time. The effect of the pre-hydrolysis of VTMS on the dope spinnability is studied. At H₂O/VTMS = 4, the resultant sol transforms into gel very quickly, unsuitable to obtain a spinnable dope; at H₂O/VTMS = 2, too much un-reacted VTMS exists in the sol, making the extruded fiber difficult to solidify; at H₂O/VTMS = 3, a dope with good spinnability and stability, and thus high ceramic yield is obtainable. Pyrolysis at 1,000 °C in argon/5% hydrogen results in silicon oxycarbide fibers with the maximum tensile strength (940.0 MPa), moderate Young’s modulus (63.2 GPa) and high carbon content (33.2%).     

The effect of temperature on fatigue damage of FRP composites

The present study intends to investigate the effect of temperature on cumulative fatigue damage (D) of laminated fibre-reinforced polymer (FRP) composites. The effect of temperature on fatigue damage is formulated based on Ramkrishnan–Jayaraman and Varvani-Farahani–Shirazi residual stiffness fatigue damage models. The models are further developed to assess the fatigue damage of FRP composites at various temperatures (T). This task is fulfilled by formulating the temperature dependency of Young’s modulus (E) and ultimate tensile strength (σ_ult) as the inputs of the models. Temperature-dependant parameters of Young’s modulus and ultimate tensile strength are found to be in good agreement with the experimentally obtained data when used for unidirectional, cross-ply and quasi-isotropic FRP laminates. The proposed fatigue damage model is evaluated using six sets of fatigue damage data. The proposed temperature-dependent model was also found promising to predict the fatigue damage of unidirectional (UD) and orthogonal woven FRP composites at different temperatures.     

Ab initio study on fracture toughness of Ti<Subscript>0.75</Subscript>X<Subscript>0.25</Subscript>C ceramics

Ab initio density functional theory calculations have been performed to evaluate the fracture toughness for selected Ti_0.75X_0.25C ceramics (X = Ta, W, Mo, Nb and V). The calculated Young’s modulus E, surface energy γ and fracture toughness K _IC of pure TiC are in a good agreement with experimental data and other theoretical calculations. The results for Ti_0.75X_0.25C system show that alloying additions increase Young’s modulus, and all but vanadium increase surface energy. It was observed that tungsten has the most significant effect on increasing Young’s modulus, while tantalum on increasing surface energy of the Ti_0.75X_0.25C system. Surface energy plays a dominated role in determining the trend of fracture toughness. Overall, tantalum and tungsten are the most effective alloying elements in increasing the fracture toughness of Ti_0.75X_0.25C ceramics.     

Mechanical studies on poly(vinyl chloride)–poly(methyl methacrylate)-based polymer electrolytes

The aim of the present work is to study the mechanical properties of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends based polymer electrolytes for lithium ion batteries. The introduction of PVC into PMMA is found to increase the Young’s modulus value from 5.19 MPa (in pure PMMA) to 6.05 MPa (in PVC:PMMA = 70:30). The different Young’s modulus values in PVC blends is due to the difference in the cross-linking density provided by PVC with different weight fraction values. The stress–strain analysis reveals that the mechanical strength of the polymer electrolyte system deteriorated with the incorporation of LiCF₃SO₃. The results show that the introduction of salt decreases the Young’s modulus and stress at peak values along with higher elongation at peak value. The addition of low molecular weight plasticizers to PVC–PMMA–LiCF₃SO₃ decreases the modulus and stress at peak of the complexes. To be applicable in practical applications, the mechanical strength of the plasticized films is found to improve with the addition of silica as nanocomposite filler.     

Processing, characterization and biological testing of porous titanium obtained by space-holder technique

The high Young’s modulus of titanium with respect to that one of the bone is the main cause of the stress-shielding phenomenon, which promotes bone resorption around implants. Development of implants with a low Young’s modulus has gained increased importance during the last decade, and the manufacturing of porous titanium is one of the routes to reduce this problem. In this work, porous samples of commercially pure titanium grade IV obtained by powder metallurgy with ammonium bicarbonate (NH₄HCO₃) as space-holder were studied. Evaluations of porosity and mechanical properties were used to determine the influence of compaction pressure for a fixed NH₄HCO₃ content. Measurements by ultrasound tests gave Young’s modulus results that were low enough to reduce stress shielding, whilst retaining suitable mechanical strength. Biological tests on porous cp Ti showed good adhesion of osteoblasts inside the pores, which is an indicator of potential improvement of osteointegration.     

Changes of wood properties treated with aqueous amine solution,bending tests and X-ray analysis of wood after amine treatment

Bending tests were conducted on oven-dried wood samples (Picea jezoensis Carr.) following treatment with various concentrations of aqueous ethylenediamine (EDA) to investigate the influence of amine treatment on the mechanical properties of wood. Under oven-drying conditions following EDA treatment and a methanol rinse, the densities of wood samples increased at concentrations above 50%, and the Young’s modulus decreased at concentrations above 60%. The specific Young’s modulus of wood samples decreased at concentrations above 60%, and stress- and strain-at-yield changed slightly at EDA concentrations in the range of 60–70%. X-ray analysis showed that the structures of cellulose changed at concentrations above 60% EDA and confirmed the transformation into cellulose III_I at 70% EDA. These results indicate the possibility that changes in the structure of the cell wall, accompanied by changes in the structures of cellulose microfibrils, contributed to changes in the specific Young’s modulus of the treated wood samples. In the same concentration range, changes in the Young’s modulus of wood samples increased with increasing relative humidity (RH). This also suggests that changes in the cell wall structure during the treatment contributed to changes in the Young’s modulus of wood at different RHs.     

High electrical conductivity and high corrosion resistance fibers with high modulus and high strength prepared by electroless plating of gold on the surface of poly (<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) (PBO)

In an attempt to produce glittering gold fibers with high modulus and high strength, gold plating on the surface of poly(p-phenylene benzobisoxazole) (PBO) fibers was carried out by using an electroless plating method. Due to the difficulty in plating gold directly on organic and inorganic fibers, gold plating was carried out on the surface of copper-plated and nickel-plated fibers; for the latter the nickel was plated on the copper-plated fibers. Namely, composite fibers, termed PBO/Cu/Au and PBO/Cu/Ni/Au, were prepared. The morphology of plated fibers was studied by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy and electrochemical polarization measurements. It was found that gold was uniformly plated on the PBO fiber, and the gold-plated fibers have good corrosion resistance. The electrical conductivities of the two kinds of gold-plated fibers were higher than 4 × 10⁴ S/cm, and their tensile strengths and Young’s moduli were greater than 1.9 GPa and 130 GPa, respectively, when estimated in terms of a single composite fiber.     

Computation of phonon dynamics of Mg<Subscript>70</Subscript>Zn<Subscript>30</Subscript> metallic glass

In the present paper, the computation of the phonon dynamics of binary Mg₇₀Zn₃₀ metallic glass is reported using the well-recognized model potential of Gajjar et al. The present study includes the phonon dispersion curves (PDC), elastic and thermodynamic properties such as longitudinal sound velocity υ_L, transverse sound velocity υ_T, Debye temperature θ_D, isothermal bulk modulus B _T, modulus of rigidity G, Poisson’s ratio σ and Young’s modulus Y and specific heat capacity C _V of the glass. Three theoretical models given by Hubbard–Beeby (HB), Takeno–Goda (TG) and Bhatia–Singh (BS) are used to compute the PDC. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are employed for the first time to study the effect of exchange and correlation in the aforesaid properties. The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard’s Law.     

Scaling functions in conical indentation of elastic-plastic solids

Summary The finite element method was used to simulate the conical indentation of elastic-plastic solids with work hardening. The ratio of the initial yield strength to the Young’s modulus Y/E ranged from 0 to 0.02. Based on the calculation results, two sets of scaling functions for non-dimensional hardness H/K and indenter penetration h are presented in the paper, which have closed simple mathematical form and can be used easily for engineering application. Using the present scaling functions, indentation hardness and indentation loading curves can be easily obtained for a given set of material properties. Meanwhile one can use these scaling functions to obtain material parameters by an instrumented indentation load-displacement curve for loading and unloading if Young’s modulus E and Poisson’s ratio ν are known.     

Crystal growth and elastic properties of In<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Perfect α-In₂Se₃ single crystals have been grown, and ultrasound velocities, v _i (i = 1–7), have been measured in single-crystal α-In₂Se₃ in various directions for different polarizations. We have determined the components of its elastic tensor (C _ij ) and calculated its elastic characteristics: elastic compliance, Young’s modulus, shear modulus, linear and volume compressibilities, bulk modulus, and Poisson’s ratio.     

Mechanical properties of very thin cover slip glass disk

The biaxial flexural strength, Young’s modulus, Vicker’s microhardness and fracture toughness data for very thin, commercial, soda-lime-silica cover slip glass (diameter, D-18 mm, thickness, T-0.3 mm; T/D ≈ 0.02) are reported here. The ball on ring biaxial flexure tests were conducted at room temperature as a function of the support ring diameter (≈ 10–20 mm) and cross head speed (0.1–10 mm min⁻¹). In addition, the Weibull modulus data were also determined. The Young’s modulus data was measured using a linear variable differential transformer (LVDT) from biaxial flexure tests and was checked out to be comparable to the data obtained independently from the ultrasonic time of flight measurement using a 15 MHz transducer. The microhardness data was obtained for the applied load range of 0.1–20 N. The fracture toughnessK _IC data was obtained by the indentation technique at an applied load of 20 N.     

纤维束分布对复合材料有效性能的影响

针对纤维束增强相在基体材料中的分布方式不同,建立了由固体基体和纤维束增强相两相介质组成的复合材料细观力学模型。假设该模型的细观结构呈周期性均匀分布,纤维束内的纤维接触是光滑的。采用二尺度展开法计算了复合材料的有效性能,得出了不同微结构分布的复合材料的刚度系数、横向弹性模量、泊松比和剪切模量随纤维束体分比的变化曲线,并将数值结果与实验数据进行了比较。研究表明,数值结果与实验数据有较好的吻合,增强相的分布直接影响到复合材料的力学性能。     

Fracture mechanisms in a stoichiometric 3Al2O32SiO2 mullite

The mechanical behaviour from room temperature up to 1400°C (strength, toughness, Young’s modulus) of a 3Al₂O₃·2SiO₂ dense mullite material containing 0.2 wt% alkali has been studied. Microstructure has been characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Toughness, bend strength and static Young’s modulus have been determined from room temperature up to 1400°C. The influence of strain rate on fracture behaviour has been investigated and a correlation of the mechanical parameters to fractographic observations by SEM has been stated. A strong influence of loading rate on microstructural modifications during fracture at 1300°C has been found. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties and apatite forming ability of TiO<Subscript>2</Subscript> nanoparticles/high density polyethylene composite: Effect of filler content

Composite materials consisting of TiO₂ nanoparticles and high-density polyethylene (HDPE), designated hereafter as TiO₂/HDPE, were prepared by a kneading and forming process. The effect of TiO₂ content on the mechanical properties and apatite forming ability of these materials was studied. Increased TiO₂ content resulted in an increase in bending strength, yield strength, Young’s modulus and compressive strength (bending strength = 68 MPa, yield strength = 54 MPa, Young’s modulus = 7 GPa, and compressive strength = 82 MPa) at 50 vol% TiO₂. The composite with 50 vol% TiO₂ shows a similar strength and Young’s modulus to human cortical bone. The TiO₂/HDPE composites with different TiO₂ contents were soaked at 36.5°C for up to 14 days in a simulated body fluid (SBF) whose ion concentrations were nearly equal to those of human blood plasma. The apatite forming ability, which is indicative of bioactivity, increased with TiO₂ content. Little apatite formation was observed for the TiO₂/HDPE composite with 20 vol% content. However, in the case of 40 vol% TiO₂ content and higher, the apatite layers were formed on the surface of the composites within 7 days. The most potent TiO₂ content for a bone-repairing material was 50 vol%, judging from the mechanical and biological results. This kind of bioactive material with similar mechanical properties to human cortical bone is expected to be useful as a load bearing bone substitute in areas such as the vertebra and cranium.     

Effect of deposition pressure on the adhesion and tribological properties of a-CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CN _x H films) was deposited on n-type single-crystal Si (100) by direct current radio frequency plasma-enhanced chemical vapor deposition (DC-RF-PECVD), under the working pressure of 5.0–17.0 Pa, using the CH₄ and N₂ as feedstock. The composition and surface morphology of the a-CN _x H films were characterized by means of Raman spectroscopy and atomic force microscopy, while the Young’s modulus, elastic recovery, adhesion strength, and tribological properties were evaluated using nano-indentation, scratch test and friction test system. It was found that the surface roughness and Raman spectra peak intensity ratio I _D/I _G of the films increased with the increase of working pressure, while the Young’s modulus, elastic recovery and adhesion strength of the films significantly decreased. Moreover, the tribological properties of the films also varied with the working pressure. The wear life sharply increased with the increase of working pressure from 5.0 Pa to 7.5 Pa, further, an increase in the deposition pressure led to a gradual decrease in the wear life, consequently, the a-CN _x H film deposited at 7.5 Pa exhibited the longest wear life. The deposition pressure seemed to have slight effect on the average friction coefficients, whereas the surface roughness and adhesion strength have deteriorated with increasing deposition pressure.     

Ultrasonic evaluation of polyether ether ketone and carbon fiber-reinforced PEEK

Polyether ether ketone (PEEK) and carbon fiber-reinforced (CFR) PEEK are commonly used in medical implants. This study evaluated the mechanical moduli of PEEK and CFR PEEK using nondestructive, ultrasonic tests. The Young’s modulus of CFR PEEK was determined in all the spatial directions. Ultrasonic attenuation has not been studied extensively in PEEK, and not at all in CFR PEEK. The broadband ultrasound attenuations (BUAs) were determined for PEEK and CFR PEEK. The average Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio of PEEK were 4.21, 1.52, 6.25, and 0.388 GPa, respectively. The maximum and minimum Young’s moduli of CFR PEEK were 15.1 and 5.1 GPa measured parallel and perpendicular to the fiber axis respectively. The longitudinal and transverse BUAs of PEEK were 1.33 and 4.37 dB/cm MHz, respectively. The longitudinal BUAs of CFR PEEK parallel and perpendicular to the fiber axis were 2.43 and 1.45 dB/cm MHz, respectively. Characterization of Young’s modulus of CFR PEEK in all the spatial directions is useful for stiffness matching in implant design. The BUA values are useful in modeling the interaction of ultrasound and the PEEK materials and can also be used for developing non-destructive tests to find structural defects in implants made from these materials.