Behaviour of photopolymerized silicate glass fibre-reinforced dimethacrylate composites subjected to hydrothermal ageing Part II Hydrolytic stability of mechanical properties

The flexural properties and failure morphologies of dimethacrylate-copolymer composites reinforced with either S2-glass® or quartz fibres (33–66 vol%) were examined after hydrothermal ageing (0–3 mon at 37 °C). Initially the S2-glass® composites were generally stiffer and stronger than comparably reinforced quartz composites, but within 1 wk the properties of S2-glass® composites decreased by 12%–26%. The properties ofquartz composites were relatively stable, except for those of composites with the least reinforcement (35 vol%), which decreased by roughly 15%. Scanning electron microscopy revealed that in all composites buckling had occurred at the site of load application. Evidence of good fibre–matrix adhesion was observed for both types of composites under all conditions. Modelling of degradation between 1 wk and 3 mon revealed that: (1) the only temporal change was a slight increase in the stiffness of S2-glass® composites; and (2) higher reinforcement levels reduced the retention of strength in S2-glass® composites but had the opposite effect (on both properties) for quartz composites (p<0.05). For the most highly reinforced S2-glass® composites, susceptibility to degradation was offset by high initial properties; and after ageing (elastic modulus 50 GPa, strength 1.2 GPa), these composites were still, on average, approximately 25% stiffer and 50% stronger than the more hydrostable quartz counterparts. © 1998 Kluwer Academic Publishers     

Continuous fiber reinforced mullite matrix composites by sol–gel processing: Part II Properties and fracture behaviour

The mechanical and interfacial properties of the mullite matrix and alumina–silica matrix composites reported in a previous publication [1], are related to the processing parameters. The flexural strengths were in the range of 428–737 MPa, flexural moduli from 82–214 GPa, work of fracture values from 293–482 KJ m^-2 and ultimate failure strains from 0.16–0.45%. The interfacial strengths were determined by the fibre push-in test and compared with fracture behaviour. The formation of different interfaces in the composites and the influence of the density of thermally-induced cracks and porosity on flexural modulus is discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiN_x) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiN_x thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiN_x films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiN_x thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiN_x thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiN_x layer during SiO₂ removal.     

Elastic moduli and damage evolution of three-axis woven fabric composites

Three-axis orthogonal woven fabric composites composed of carbon fibres and epoxy resin have been fabricated. Examined from micrographs, the fabric weaving yarns were found to be very slender with aspect ratios ranging from 11–13.6. Based upon the observed geometry, the composite has been modelled by a unit cell comprising wavy yarns. Both elliptical and lenticular cross-sections were adopted to simulate the slender weaving yarns. Taking into account one-dimensional stress concentration and yarn undulation, an iso-phase approach has been developed to analyse the composite elastic moduli. A higher weaving yarn aspect ratio was found to result in a lower modulus. Modulus reduction due to yarn undulation was more significant in weaving directions. Material characterization has been conducted based upon monotonic tensile and three-point flexural tests, and detailed damage mechanisms for both loadings have been examined. The onset of damage under tensile loading was found to be z-axis yarn debonding, followed by debonding and splitting in y-axis yarns. When subjected to flexural loading, yarn debonding, transverse cracking, and interyarn matrix cracking were the dominant damage mechanisms which appeared on specimen tensile sides. Stress transfer among yarns and how it relates to the composite damage have been discussed in detail. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of HF treatments on tensile strength of Hi-Nicalon fibres

Tensile strengths of as-received Hi-Nicalon fibres and those having a dual BN–SiC surface coating, deposited by chemical vapour deposition, have been measured at room temperature. These fibres were also treated with HF for 24 h followed by tensile strength measurements. Strengths of uncoated and BN–SiC coated Hi-Nicalon fibres extracted from celsian matrix composites, by dissolving away the matrix in HF for 24 h, were also determined. The average tensile strength of uncoated Hi-Nicalon was 3.19±0.73 GPa with a Weibull modulus of 5.41. The Hi-Nicalon–BN–SiC fibres showed an average strength of 3.04±0.53 GPa and Weibull modulus of 6.66. After HF treatment, the average strengths of the uncoated and BN–SiC coated Hi-Nicalon fibres were 2.69±0.67 and 2.80±0.53 GPa and the Weibull moduli were 4.93 and 5.96, respectively. The BN–SiC coated fibres extracted from the celsian matrix composite exhibited a strength of 2.38±0.40 GPa and a Weibull modulus of 7.15. The strength of the uncoated Hi-Nicalon fibres in the composite was so severely degraded that they disintegrated into small fragments during extraction with HF. The uncoated fibres probably undergo mechanical surface damage during hot pressing of the composites. Also, the BN layer on the coated fibres acts as a compliant layer, which protects the fibres from mechanical damage during composite processing. The elemental composition and thickness of the fibre coatings were determined using scanning Auger analysis. Microstructural analyses of the fibres and the coatings were done by scanning electron microscopy and transmission electron microscopy. Stengths of fibres calculated using average and measured fibre diameters were in good agreement. Thus, the strengths of fibres can be evaluated using an average fibre diameter instead of the measured diameter of each filament. © 1998 Kluwer Academic Publishers     

Magnesium oxychloride cement concrete

The scope of magnesium oxychloride (MOC) cement in concrete works has been evaluated. MOC cement concrete compositions of varying strengths having good placing and finishing characteristics were prepared and investigated for their compressive and flexural strengths, E-values, abrasion resistance etc. The durability of MOC concrete compositions against extreme environmental conditions viz. heating-cooling, freezing-thawing, wetting-drying and penetration and deposition of salts etc were investigated. The results reveal that MOC concrete has high compressive strength associated with high flexural strength and the ratio of compressive to flexural strength varies between 6 and 8. The elastic moduli of the compositions studied are found to be 23–85 GPa and the abrasion losses between 0·11 and 0·20%. While alternate heating-cooling cycles have no adverse effect on MOC concrete, it can be made durable against freezing-thawing and the excessive exposure to water and salt attack by replacing 10% magnesium chloride solution by magnesium sulphate solution of the same concentration.     

Mechanical and thermal characterization of epoxy composites reinforced with random and quasi-unidirectional untreated Phormium tenax leaf fibers

The present work investigates tensile and flexural behavior of untreated New Zealand flax (Phormium tenax) fiber reinforced epoxy composites. Two series of laminates were produced using the same reinforcement content (20 wt%), arranged either as short fibers or quasi-unidirectional ones. Composites reinforced using quasi-unidirectional fibers showed higher modulus and strength both in tensile and flexural loading, when compared to neat epoxy resin. Short fiber composites, although still superior to epoxy resin both for tensile and flexural moduli, proved inferior in strength, especially as concerns tensile strength. These results have been supported by scanning electron microscopy (SEM), which allowed characterizing fiber–matrix interface, and by acoustic emission (AE) analysis, which enabled investigating failure mechanisms. In addition, thermal behavior of both untreated phormium fibers and composites has been studied by thermogravimetric analysis (TGA), revealing the thermal stability of composites to be higher than for phormium fibers and epoxy matrix alone.     

Mechanism of cement paste reinforced by ultra-high molecular weight polyethylene powder and thermotropic liquid crystalline copolyester fiber with enhanced mechanical properties

In this study, a series of cementitious composites with high toughness and flexural strength was obtained by melt-dispersing ultra-high molecular weight polyethylene (UHMWPE) into a cement matrix followed by water immersion. The structure and chemical composition of the composites were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Three point bending tests showed that the flexural strengths of the composites were improved from 5.5 MPa to 18.2 MPa with the presence of 25 wt% UHMWPE, and could be further enhanced to 28.1 MPa with the addition of only 0.1 vol% oriented thermotropic liquid crystalline copolyester (TLCP) fibers. An adhesive test revealed that the interfacial binding force between polymer and fiber was much stronger than that between cement and fiber. Our findings provide a simple way for utilizing polymer to improve the interface between the fibers and cement matrix, consequently achieving a dramatic increase in the flexural strength and toughness.     

A Study on flexural properties of wildcane grass fiber-reinforced polyester composites

The main objective of this study is to introduce a new natural fiber as reinforcement in polymers for making composites. Wildcane grass stalk fibers were extracted from its stem using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were intentionally reinforced in a polyester matrix unidirectionally, and the flexural properties of the composite were determined. The fibers extracted by retting process have a tensile strength of 159 MPa, modulus of 11.84 GPa, and an effective density of 0.844 g/cm³. The composites were formulated up to a maximum fiber volume fraction of 0.39, resulting in a flexural strength of 99.17 MPa and flexural modulus of 3.96 GPa for wildcane grass fibers extracted by retting. The flexural strength and the modulus of chemically extracted wildcane grass fiber composites have increased by approximately, 7 and 17%, respectively compared to those of composites made from fibers extracted by retting process. The flexural strength and the modulus of KMnO₄-treated fiber composites have increased by 12 and 76% over those of composites made from fibers extracted by retting process and decreased by 3 and 48% over those of composites made from fibers extracted by chemical process, respectively. The results of this study indicate that wildcane grass fibers have potential as reinforcing fillers in plastics in order to produce inexpensive materials with high toughness.     

Comparison of the deformation and failure characteristics of morphologically distinct metal-glass interpenetrating phase composites

Deformation and failure characteristics of two metal-glass interpenetrating phase composite (IPC) systems were compared against a single-phase glass control. The first system (Captek-P) comprised an interleaved arrangement of flake-shaped Au/Pt/Pd particles, the second (Captek-G) comprised loosely packed spherical Au particles. Both materials contained a fully interconnected network of porosity, formed by thermal fusion of particles at contact points. Glass was infiltrated into the porous networks by capillary action at high temperature. Mechanical properties were evaluated using three-point bend tests and compared to data from the glass control. The strength of the glass control (123.47 MPa) was not significantly different to that of either IPC, however both Captek-P and Captek-G IPCs displayed significantly reduced elastic moduli (55.2 ± 10.6 GPa and 48.4 ± 12.4 GPa respectively) compared with the glass (91.5 ± 9.6 GPa). In addition to significantly higher relative toughness than the glass control the IPC materials exhibit plastic deformation prior to failure. Mixed fracture modes were evident on fracture surfaces. Corresponding stress-strain profiles for the materials show well-defined linear elastic regions that make a gradual transition into plastic behaviour. Strength of the glass control decreased by 28% upon exposure to moisture, a feature echoed by the Captek-G IPC system, however not by the Captek-P IPC, indicating that the morphology of the interpenetrating reinforcement can significantly affect the mechanical properties of IPCs.     

Fabrication and mechanical properties of glass fibre–carbon fibre polypropylene functionally gradient materials

Hybrid fibre mat reinforced polypropylene (PP) composites with carbon(CF) and glass fibre (GF) were prepared and four kinds of functionally gradient materials (FGM) were fabricated by changing the spatial distribution of GF and CF. To measure the mechanical properties of FGMs and hybrid composites, flexural tests and instrumented impact tests were performed. The flexural strengths and the flexural moduli of hybrid composites increased following the rule of mixture as the relative volume content of CF increased. On the other hand, the total impact absorption energy of hybrid composites decreased with the increment of CF relative volume content. Compared with GF–CF PP isotropic hybrid composite, the composites with compositional gradient showed similar flexural strengths, but characteristic flexural moduli. Especially, sandwich-type FGMs with a CF-rich outer layer and a GF-rich inner layer exhibited higherflexural moduli than others. Total impact absorption energies of four FGMs were also similar, but the ratios of crack initiation energy,Ei, to crack propagation energy, Ep, or ductility index, were quite different.     

Improvement of Mechanical Properties of Oligomer-modified Acrylic Bone Cement with Glass-fibers

Some mechanical properties of oligomer-modified acrylic bone cement with glass-fibers were studied. Under wet environments, oligomer-filler forms a porous structure in the acrylic bone cement. Test specimens were manufactured using commercial bone cement (Palacos^® R) with different quantities of an experimental oligomer-filler (0–20 wt%), and included continuous unidirectional E-glass fibers (l=65 mm) or chopped E-glass fibers (l=2 mm). The specimens were either tested dry, or after being immersed under wet environments for one week. The three-point bending test was used to measure the flexural strength and modulus of the acrylic bone cement composites (analysis with ANOVA). A scanning electron microscope (SEM) was used to examine the surface structure of the acrylic bone cement composites. Using continuous glass-fiber reinforcement, the dry flexural strength was 145 MPa and modulus was 4.6 GPa for the plain bone cement. For the test specimens with 20 wt% of oligomer-filler and continuous unidirectional glass-fibers, the dry flexural strength was 118 MPa and modulus was 4.2 GPa, whereas the wet flexural strength was 66 MPa and modulus was 3.0 GPa. The results suggest that the reduced flexural properties caused by the porosity of oligomer-modified bone cement can be compensated with glass-fiber reinforcement.     

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.     

Fabrication and characterization of fully biodegradable natural fiber-reinforced poly(lactic acid) composites

Polymer composites were fabricated with poly(lactic acid) (PLA) and cellulosic natural fibers combining the wet-laid fiber sheet forming method with the film stacking composite-making process. The natural fibers studied included hardwood high yield pulp, softwood high yield pulp, and bleached kraft softwood pulp fibers. Composite mechanical and thermal properties were characterized. The incorporation of pulp fibers significantly increased the composite storage moduli and elasticity, promoted the cold crystallization and recrystallization of PLA, and dramatically improved composite tensile moduli and strengths. The highest composite tensile strength achieved was 121 MPa, nearly one fold higher than that of the neat PLA. The overall fiber efficiency factors for composite tensile strengths derived from the micromechanics models were found to be much higher than that of conventional random short fiber-reinforced composites, suggesting the fiber–fiber bond also positively contributed to the composites’ strengths.     

Characterisation of mechanical and thermal properties of epoxy grouts for composite repair of steel pipelines

The mechanical and thermal properties of the grouts are critical to their potential application as infill materials in structural repair. In this paper, the mechanical and thermal behaviour of five epoxy based grouts were investigated to identify their prospects as a component of the composite repair for steel pipelines. The compressive strength and stiffness of the grouts are found to be 52–120 MPa and 1.7–11 GPa, respectively. The tensile, flexural and shear strengths of the grouts are found to be within the ranges of 11–32, 27–53, and 13–30 MPa, respectively. The tensile and flexural moduli range within 3–17, and 4–13 GPa, respectively. Thermal analysis of the grouts suggests that the glass transition temperature (T_g) within 60 and 90 °C which also provide the thermal applicability limits for the grouts in the composite repair of steel pipes. The development of compressive properties of three selected grouts over 28 days period was also investigated as well as the effect of the addition of coarse fillers.     

Rate dependence of the tensile and flexural strengths of glass–ceramic Macor

Understanding of the tensile and flexural strengths of the glass–ceramic Macor bears important applications in materials science, aerospace, defense, and other engineering disciplines. In this article, we systematically investigate the rate dependence of the tensile strength and the flexural strength of Macor utilizing two methods: the Brazilian disk (BD) test and semi-circular bend (SCB) test. Both static tests and dynamic tests are conducted to explore the rate dependence of tensile and flexural strengths of Macor. The static measurement is conducted with a servo-controlled material testing machine, and the dynamic experiment is carried out with a 6.35-mm diameter split Hopkinson pressure bar (SHPB) system. The pulse-shaping technique is used to achieve dynamic force balance, and thus eliminates the loading inertial effect and enables quasi-static stress analysis. The experimental results show that both the tensile strength and the flexural strength of Macor are loading rate dependent. The flexural strength is observed to be consistently higher than the tensile strength.     

Influence of filler/reinforcing agent and post-curing on the flexural properties of woven and unidirectional glass fiber-reinforced composites

The aim of this study is to investigate the reinforcing effect of woven and unidirectional glass fibers and the effect of post-curing on the flexural strength and flexural modulus of glass fiber-reinforced composites. A series of composites containing 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane and triethyleneglycol dimethacrylate matrices and different reinforcements of unidirectional or woven glass fibers were prepared. The samples, 25 × 2 × 2 mm, were cured with a halogen curing lamp, followed by additional curing by thermal treatment at 135 ± 5 °C temperature and 60 psi pressure. Samples were tested before and after post-curing in order to determine the flexural strength and flexural modulus. The degree of reinforcement with glass fibers was varied between 14 and 57 wt% or 7.64 and 38.44 vol% by changing the number of unidirectional bundles or woven glass fiber bands in the composites, respectively. The obtained flexural strength values were in the range of 95.20–552.31 Mpa; the flexural modulus ranged between 2.17 and 14.7 GPa. The highest flexural strength and flexural modulus values were recorded for samples with unidirectional glass fibers. The mechanical qualities of the glass fibers-reinforced composites increased after post-curing treatment. Increasing of the glass fiber amount in the experimental composites improves both flexural strength and modulus. SEM micrographs of fractured composites indicate a strong interfacial interaction between the glass fibers and the polymer matrix.     

Manufacture of High Performance Carbon Fibers from Precursors of Various Diameters

The effects of fiber diameter on the mechanical properties of PAN-based carbon fibers have been investigated in a series of processing experiments on fibers with different starting filament diameters. The fiber tows, with similar initial mechanical performance, were stretched at high temperatures to produce a large number of fiber types with a wide range of filament diameters. The three starting carbon fibers tows had nominal filament diameters of 5 μm, 6·5 μm, and 10 μm and contained 12000, 6000, and 3000 filaments respectively. These tows were stretched for 5 minutes at 2600^°C with a series of loads of up to 6 kg. For all fiber types and all stretching conditions, substantial increases in Young's moduli were induced, the increases being closely related to the induced extensions. However, it was found that tensile strengths generally decreased if fibers were subjected to high temperatures without significant stretching. On the other hand, the tensile strengths were restored to their original values when greater strains were induced by using higher stresses. Although fibers with a relatively large diameter of 8·3 μm were produced with a modulus of -470GPa and strength of -3·7 GPa, greater improvements in mechanical properties were achieved with smaller diameter fibers. The loads and temperatures involved in these hot stretching experiments were not excessive, and the investigations showed that serious consideration should be given to the feasibility of commercial production of high performance PAN-based carbon fibers by this processing route.     

Bulk and porous metastable beta Ti-Nb-Zr(Ta) alloys for biomedical applications

In this work, metastable beta Ti-Nb-Zr(Ta) ingots were manufactured by vacuum arc melting. The ingots thus obtained were divided into two batches: the first subjected to cold rolling (CR) from 30 to 85% of thickness reduction and subsequent annealing in the 450 to 900 °C temperature region, and the second atomized to produce 100 μm size powders. This powder was used to manufacture open-cell porous material. Regardless of the CR intensity, Ti-(18…20)Nb-(5…6)Zr (at.%) samples subjected to 600 °C (1 h) annealing showed a significant material softening due to the stress-induced martensitic transformation. The Young's modulus of these alloys varied between 45 and 55 GPa, and the yield stress, between 300 and 500 MPa. The obtained Young's moduli, which are comparable to 55-66 GPa of concurrent beta-titanium alloys and 45-50 GPa of superelastic Ti-Ni alloys, come close to those of cortical bones. Compression testing of the porous material as a function of porosity (from ~ 45 to 66%) and interconnected cell size (d₅₀ from 300 to 760 μm) showed the following properties: Young's modulus from 7.5 to 3.7 GPa, which comes close to that of trabecular bones, and ultimate compression strength, of from 225 to 70 MPa.     

Nanomechanical properties of FePtPd ternary alloy thin films

Presented in this study are crystalline structure and mechanical properties of FePt_0.75Pd_0.25 ternary alloy thin films deposited under the various annealing temperatures, obtained by means of transmission electron microscopy (TEM) and nanoindentation techniques. FePtPd ternary alloy thin films are deposited on Si substrates using a multi-target DC magnetron sputtering system. Results indicate that the grain size increase from 40 to 135 nm as the annealing temperature increases from 400 to 600 °C. From nanoindentation measurements, the hardness of FePtPd ternary alloy thin films are 11.6 ± 0.4, 10.4 ± 0.1 and 8.8 ± 0.3 GPa for the annealed temperatures of 400, 500 and 600 °C, respectively. And, the corresponding Young's moduli are 175.4, 152.2 and 142.6 GPa, respectively. Hardness for FePtPd ternary alloy thin films decreased slightly in accordance with the increase of the grain size. By fitting experimental results with the Hall-Petch equation, a probable lattice friction stress of 5.15 ± 0.05 GPa and Hall-Petch constant of 44.25 ± 2.55 GPa nm^1/2 are obtained.