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Brittle
Terms modified by Brittle Selected AbstractsBrittle,ductile transition in the PETG/PC blends by adding PTW elastomerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2010Xinlan Zhang Abstract In this paper, an elastomer containing epoxy groups, ethylene-butylacrylate-glycidylmethacrylate (PTW), was used as toughening modifier for the poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) (PETG)/polycarbonate (PC) blends. A remarkable improvement of toughness was achieved by addition of only 5,wt% PTW. In particular, an obvious brittle,ductile (B,D) transition in impact toughness was found when the PTW content increased from 3 to 5,wt%. The toughening mechanism and observed B,D transition have been explored in detail, combining with electronic microscopy observation, melt rheological investigation and dynamic mechanical analysis (DMA). It is suggested that the B,D transition can be attributed to a better interfacial adhesion between different phases, and importantly, to a continuum percolation dispersed-phases network formed at appropriate PTW content, in which PC particles are connected with each other by PTW phase. Our present study offers new, profound insight on the toughening mechanism for the elastomer modified amorphous/amorphous plastic blends. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ab Initio Guided Design of bcc Ternary Mg,Li,X (X,=,Ca, Al, Si, Zn, Cu) Alloys for Ultra-Lightweight ApplicationsADVANCED ENGINEERING MATERIALS, Issue 7 2010William Art Counts Abstract Ab initio calculations are becoming increasingly important for designing new alloys as these calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis. In this paper, fundamental physical properties (like formation energies and elastic constants) of a set of bcc Mg,Li and Mg,Li-based compounds are calculated using density functional theory (DFT). These DFT-determined properties are in turn used to calculate engineering parameters such as (i) specific Young's modulus (Y/,) or (ii) shear over bulk modulus ratio (G/B) differentiating between brittle and ductile behavior. These parameters are then used to identify those alloys that have optimal mechanical properties for lightweight structural applications. First, in case of the binary Mg,Li system, an Ashby map containing Y/, versus G/B shows that it is not possible to increase Y/, without simultaneously increasing G/B (i.e., brittleness) by changing only the composition of a binary alloy. In an attempt to bypass such a fundamental materials-design limitation, a set of Mg,Li,X ternaries (X,=,Ca, Al, Si, Cu, Zn) based on stoichiometric Mg,Li with CsCl structure was studied. It is shown that none of the studied ternary solutes is able to simultaneously improve both specific Young's modulus and ductility. [source] Removal of the , -Case Layer from Precision-Cast Cellular TiAl6Nb7 to be Used for Biomedical Applications,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Teodolito Guillén The present work deals with the chemical removal of the ,-case layer formed during precision casting of cellular TiAl6Nb7 sponges for biomedical applications. The major part of the brittle ,-case layer can be attributed to chemical reaction between titanium and the investment mold components. To improve the ductility of the cell struts by eliminating the brittle surface, a pickling-vibration treatment was developed by which the ,-case layer is chemically removed. [source] A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007M. ONO ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source] Near-lithostatic pore pressure at seismogenic depths: a thermoporoelastic modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Francesca Zencher SUMMARY A model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure. This configuration is thought to be pertinent to the South Iceland seismic zone (SISZ) and to other tectonically active regions of recent volcanism, where volatiles are continuously released by ascending magma below the brittle,ductile transition. Poroelastic parameters are computed for basaltic rock. The model is 1-D, the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium. Environment conditions are considered, pertinent to basalt saturated with water at shallow depth (case I) and at mid-crustal depth (case II). If the intrinsic permeability of the rock is high, no significant effects are observed in the pressure field but advective heat transfer shifts the brittle,ductile transition to shallower depths. If the intrinsic permeability is low, the pressure-dependent permeability can propagate near-lithostatic pore pressures throughout most of the transition layer, while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition. Geometrical parameters characterizing the fracture distribution are important in determining the effective permeability: in particular, if an interconnected system of fractures develops within the transition layer, the effective permeability may increase by several orders of magnitude and near-lithostatic pore pressure propagates upwards. These modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the SISZ, in connection with the two 2000 June M= 6.5 earthquakes, including: (i) fluid pressure pulses in deep wells, (ii) low resistivity at the base of the seismogenic layer, (iii) low VP/VS ratio and time-dependent seismic tomography, (iv) heterogeneity of focal mechanisms, (v) shear wave splitting, (vi) high b -value of deep foreshocks, (vii) triggered seismicity and (viii) Radon anomalies. [source] Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology of the lithosphereGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Jacques Déverchère Summary The correspondence between the predicted brittle,plastic transition within the crust and the maximum depth of earthquakes is examined in the case of the Baikal rift, Siberia. Although little accurate information on depths is available through large- and moderate-size earthquakes, there are frequent indications of foci at 20 km depth and more. We have relocated 632 events recorded at nearby stations that occurred between 1971 and 1997, with depth and epicentral uncertainties less than 5 km, over the eastern and southern parts of the Baikal rift. We have compared these results with other depth distributions obtained in previous studies from background seismicity in the NE rift (1365 events in the Kalar-Chara zone and 704 events in the Muya region). The relative abundance of earthquakes is generally low at depths between 0 and 10 km (7,15 per cent) and high between 15 and 25 km (,50 per cent). Earthquake activity is still significant between 25 and 30 km (9,15 per cent) and persists between 30 and 40 km (7,13 per cent). Very few earthquakes are below the Moho. We use empirical constitutive laws to obtain the yield-stress limits of several layers made of dominant lithologies and to examine whether the observed distribution of earthquakes at depth (519 events controlled by a close station and located within the extensional domain of the Baikal rift system) can match the predicted crustal strength proportion with depth and the deeper brittle,ductile transition in the crust. A good fit is obtained by using a quartz rheology at 0,10 km depth and a diabase rheology at 10,45 km depth with a moderate temperature field which corresponds to a ,100 Myr thermal lithosphere. No dioritic composition of the crust is found necessary. In any case, earthquakes occur at deep crustal levels, where the crust is supposed to be ductile, in a way very similar to what is found in the East African Rift System. From these results we conclude that the seismogenic thickness is ,35,40 km in the Baikal rift system and that the depth distribution of earthquakes is at first order proportional to the strength profile found in a rheologically layered crust dominated by a mafic composition in the ,10,45 km depth range. An upper mantle core with high strength, however, generally prevents it from reaching stress failure at greater depth. [source] Micromechanical models of the strength of a sandstoneINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2010L. Dormieux Abstract In this paper, the strength of a sandstone is determined from a micromechanical approach. The microstructure of the rock is described as a porous polycrystal. A von Mises criterion is used for the strength of the solid grains. The grains are surrounded by Mohr,Coulomb interfaces describing the cement phase. The macroscopic strength of the polycrystal is determined by means of nonlinear homogenization techniques. The failure mechanism of the grains is assumed to be ductile. It is combined with a failure mechanism of the interfaces, which is successively assumed to be ductile and brittle. The theoretical predictions are then compared with the experimental data. Copyright © 2009 John Wiley & Sons, Ltd. [source] A constitutive model for bonded geomaterials subject to mechanical and/or chemical degradationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2003R. Nova Abstract The mechanical behaviour of bonded geomaterials is described by means of an elastoplastic strain-hardening model. The internal variables, taking into account the ,history' of the material, depend on the plastic strains experienced and on a conveniently defined scalar measure of damage induced by weathering and/or chemical degradation. For the sake of simplicity, it is assumed that only internal variables are affected by mechanical and chemical history of the material. Despite this simplifying assumption, it can be shown that many interesting phenomena exhibited by weathered bonded geomaterials can be successfully described. For instance, (i) the transition from brittle to ductile behaviour with increasing pressure of a calcarenite with collapsing internal structure, (ii) the complex behaviour of chalk and other calcareous materials in oedometric tests, (iii) the chemically induced variation of the stress and strain state of such kind of materials, are all phenomena that can be qualitatively reproduced. Several comparisons with experimental data show that the model can capture the observed behaviour also quantitatively. Copyright © 2003 John Wiley & Sons, Ltd. [source] Mechanical behavior of carbon nanofibre-reinforced epoxy compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Sohel Rana Abstract Epoxy resins are widely used in a variety of applications because of their high chemical and corrosion resistance and good mechanical properties. But few types of epoxy resins are brittle and possess low toughness which makes them unsuitable for several structural applications. In this work, carbon nanofibres have been dispersed uniformly into the epoxy resin at a very low concentration (0.07 vol. %). Improvement of 98% in Young modulus, 24% in breaking stress and 144% in work of rupture was achieved in the best sample. The emphasis is on achieving uniform dispersion of carbon nanofibers into epoxy resin using a combination of techniques such as ultrasonication, use of solvent and surfactants. The fracture surfaces of the specimens were studied under scanning electron microscope to see the fracture mechanism of nanocomposites under tensile load and correlate it to the enhancement in their properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synthesis and characterization of novel poly(arylene ether)s based on 9,10-bis-(4-fluoro-3-trifluoromethylphenyl) anthracene and 2,7-bis-(4-fluoro-3-trifluoromethylphenyl) fluoreneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Arun K. Salunke Abstract Two new bisfluoro monomers 9,10-bis-(4-fluoro-3-trifluoromethylphenyl) anthracene and 2,7-bis-(4-fluoro-3-trifluoromethylphenyl) fluorene have been synthesized by the cross-coupling reaction of 2-fluoro-3-trifluoromethyl phenyl boronic acid with 9,10-dibromo anthracene and 2,7-dibromo fluorine, respectively. These two bisfluoro compounds were used to prepare several poly(arylene ether)s by aromatic nucleophilic displacement of fluorine with various bisphenols; such as bisphenol-A, bisphenol-6F, bishydroxy biphenyl, and 9,9-bis-(4-hydroxyphenyl)-fluorene. The products obtained by displacement of the fluorine atoms exhibits weight-average molar masses up to 1.5 ×105 g mol,1 and number average molecular weight up to 6.8 × 104 g mol,1 in GPC. These poly(arylene ether)s show very high thermal stability even up to 490°C for 5% weight loss occurring at this temperature in TGA in synthetic air and showed glass transition temperature observed up to 310°C. All the polymers are soluble in a wide range of organic solvents, e.g., CHCl3, THF, NMP, and DMF. Films cast from DMF solution are brittle in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Structure modification of isotactic polypropylene through chemical crosslinking: Toughening mechanismJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007S. Bouhelal Abstract Reversibly crosslinked isotactic polypropylene (iPP) was prepared in the presence of dicumyl peroxide. The effects of the peroxide oxy-radicals in the melt were investigated in relation to the modification of the polymer. The dynamic rheology analysis of the crosslinking process was carried out by using a plastograph. The crosslinking reaction was evaluated by the Monsanto method. The resulting structure of the modified samples was studied by means of differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), microhardness, and mechanical properties. The degree of crystallinity of the modified iPP, derived from DSC and WAXS, remains almost unchanged, i.e., the crystalline structure is unaffected, though the lamellar thickness slightly decreases. The impact strength of the crosslinked iPP is greatly improved with reference to that of the unmodified material. A transition from brittle to ductile behavior appears in the modified iPP for all the crosslinking agents studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2968,2976, 2007 [source] Gamma irradiation alters fatigue-crack behavior and fracture toughness in 1900H and GUR 1050 UHMWPEJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2002Jantzen C. Cole Abstract Pitting and delamination remain causative factors of polyethylene failure in total knee replacement. Gamma irradiation induces cross linking in ultra-high-molecular-weight polyethylene, which has been shown to improve wear resistance. Irradiation may reduce fracture toughness and fatigue strength, however, and the effects of irradiation are dependent upon the resin, processing technique, and radiation dose. The effects of varying levels of gamma irradiation (0, 33, 66, and 100 kGy) on the fracture toughness and fatigue-crack resistance of UHMWPE, isostatically molded from 1900H and GUR 1050 resins, were examined. Paris law regressions were performed to quantify fatigue-crack propagation rates as functions of change in stress intensity, and J -integral methods were used to quantify the elastic,plastic fracture toughness. The results indicated that gamma irradiation reduced the resistance of both materials to fatigue-crack growth, and that the reductions were radiation dosage and resin dependent. Irradiation at any level was detrimental to the fracture toughness of the 1900H specimens. Irradiation at 33 kGy increased fracture toughness for the GUR 1050 specimens, and substantial reductions were observed only at the highest irradiation level. Scanning electron microscopy of the fracture surface revealed diamond-like fracture patterns of the nonirradiated specimens indicative of ductile, multilevel fracture. Pronounced striations were apparent on these fracture surfaces, oriented perpendicular to the direction of crack growth. The striations appeared as folds in surface layers of the GUR 1050 specimens. At the highest irradiation levels, the striations were nearly eliminated on the fracture surfaces of the 1900H specimens, and were markedly less severe for the GUR 1050. These results demonstrated that at higher irradiation levels the materials became more brittle in fatigue, with less ductile folding and tearing of the fracture surfaces. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 559,566, 2002 [source] Genetic Hypercalciuric Stone-Forming Rats Have a Primary Decrease in BMD and Strength,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2009Marc Grynpas Abstract Kidney stone patients often have a decrease in BMD. It is unclear if reduced BMD is caused by a primary disorder of bone or dietary factors. To study the independent effects of hypercalciuria on bone, we used genetic hypercalciuric stone-forming (GHS) rats. GHS and control (Ctl) rats were fed a low Ca (0.02% Ca, LCD) or a high Ca (1.2% Ca, HCD) diet for 6 wk in metabolic cages. All comparisons are to Ctl rats. Urine Ca was greater in the GHS rats on both diets. GHS fed HCD had reduced cortical (humerus) and trabecular (L1,L5 vertebrae) BMD, whereas GHS rats fed LCD had a reduction in BMD similar to Ctl. GHS rats fed HCD had a decrease in trabecular volume and thickness, whereas LCD led to a ,20-fold increase in both osteoid surface and volume. GHS rats fed HCD had no change in vertebral strength (failure stress), ductibility (failure strain), stiffness (modulus), or toughness, whereas in the humerus, there was reduced ductibility and toughness and an increase in modulus, indicating that the defect in mechanical properties is mainly manifested in cortical, rather than trabecular, bone. GHS rat cortical bone is more mineralized than trabecular bone and LCD led to a decrease in the mineralization profile. Thus, the GHS rats, fed an ample Ca diet, have reduced BMD with reduced trabecular volume, mineralized volume, and thickness, and their bones are more brittle and fracture prone, indicating that GHS rats have an intrinsic disorder of bone that is not secondary to diet. [source] How Well Are Bones Designed to Resist Fracture?,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2003John D Currey Abstract Because bone is obviously in some way adapted to the loads falling on it and because fracture is usually the failure of mechanical competence of main clinical importance, it is often thought that bones are adapted to resist fracture. In this perspective, I consider that this may not be the case. Bones may be designed to be very stiff, and therefore highly mineralized, and therefore brittle; they may be adapted to normal loads, but not to the characteristic loads occurring in falls, or may be very poorly designed to stop cracks traveling once they have started. Bones may also potentially fail in completely contrasting modes, and therefore their design has to be a compromise that does not resist either mode completely successfully. The greatly differing fracture incidences in different bones seen in pre-senile adults suggest that safety factors have been adapted, over evolutionary time, to produce the best compromise for a host of different design constraints. [source] RHEOLOGY AND TEXTURE OF COMMERCIAL QUESO FRESCO CHEESES MADE FROM RAW AND PASTEURIZED MILKJOURNAL OF FOOD QUALITY, Issue 2010MICHAEL H. TUNICK ABSTRACT Queso Frescos made in Mexico from raw milk (RM) were compared with cheeses made in Mexico and the U.S.A. from pasteurized milk (PM) to determine textural and rheological differences. RM cheese, considered the ideal Queso Fresco, contained more moisture than PM cheeses, displayed higher cohesiveness and shear strain and exhibited lower hardness and shear stress. The U.S.-made cheeses were harder and more brittle and crumbly than the Mexican cheeses. The shear stress decreased as fat content increased in all samples, and the shear strain decreased as the pH increased in the Mexican cheeses. An understanding of the differences between the RM and PM versions should allow cheese makers to adjust manufacturing procedures so that PM Queso Fresco cheeses will meet consumer expectations. PRACTICAL APPLICATIONS Hispanic cheeses such as Queso Fresco are gaining in popularity in the U.S.A. The milk for making Queso Fresco in the U.S.A. must be pasteurized, and the resulting cheese is perceived by some consumers to be inferior in flavor and texture to the traditional variety made from raw milk. Queso Fresco samples made in Mexico from both kinds of milk and made in the U.S.A. from pasteurized milk were analyzed to see if there were differences in texture, structure, and the ability to twist and break pieces of the cheese. The cheeses made in the U.S.A. contained less moisture and were too hard, crumbly, and brittle when compared to the raw milk cheeses. The differences observed should enable U.S. companies to make Queso Fresco with properties close to those of the raw milk variety. [source] Fluid evolution and thermal structure in the rapidly exhuming gneiss complex of Namche Barwa,Gyala Peri, eastern Himalayan syntaxisJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2005D. CRAW Abstract High-grade gneisses (amphibolite,granulite facies) of the Namche Barwa and Gyala Peri massifs, in the eastern Himalayan syntaxis, have been unroofed from metamorphic depths in the late Tertiary,Recent. Rapid exhumation (2,5 mm year,1) has resulted in a pronounced shallow conductive thermal anomaly beneath the massifs and the intervening Tsangpo gorge. The position of the 300 °C isotherm has been estimated from fluid inclusions using CO2,H2O immiscibility phase equilibria to be between 2.5 and 6.2 km depth below surface. Hence, the near-surface average thermal gradient exceeds 50 °C km,1 beneath valleys, although the thermal gradient is relatively lower beneath the high mountains. The original metamorphic fluid in the gneisses was >90% CO2. This fluid was displaced by incursion of brines from overlying marine sedimentary rocks that have since been largely removed by erosion. Brines can exceed 60 wt% dissolved salts, and include Ca, Na, K and Fe chlorides. These brines were remobilized during the earliest stages of uplift at >500 °C. During exhumation, incursion of abundant topography-driven surface waters resulted in widespread fracture-controlled hydrothermal activity and brine dilution down to the brittle,ductile transition. Boiling water was particularly common at shallow levels (<2.5 km) beneath the Yarlung Tsangpo valley, and numerous hot springs occur at the surface in this valley. Dry steam is not a major feature of the hydrothermal system in the eastern syntaxis (in contrast to the western syntaxis at Nanga Parbat), but some dry steam fluids may have developed locally. [source] Role of fluids in the metamorphism of the Alpine Fault Zone, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001J. K. Vry Abstract Models of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole-rock ,D values (,DWR = ,56 to ,30,, average = ,45,, n = 20), irrespective of rock type, degree of chloritization, location along the fault, or across-strike distance from the fault in the garnet zone. The green, chlorite-rich fault rocks, which probably formed from Australian Plate precursors, record nearly isothermal fluid/rock interaction with a schist-derived metamorphic fluid at high temperatures near 450,500°C (,D of water in equilibrium with the green fault rocks (,DH2O, green) ,,,18,; ,D of water in equilibrium with the greyschists and greyschist-derived mylonites (,DH2O, grey) , ,19, at 500°C; ,DH2O, green , ,17,; ,DH2O, grey , ,14, at 450°C). There is no indication of an influx of a meteoric or mantle-derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late-stage retrogression or veining, which might be attributed to down-temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the Alpine Fault up to the surface, owing to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle,ductile transition. Such fluids could mix with meteoric fluids to deposit quartz-rich, possibly gold-bearing veins in the region c. 5,10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) programme. [source] A general model for the intrusion and evolution of ,mantle' garnet peridotites in high-pressure and ultra-high-pressure metamorphic terranesJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2000Brueckner Garnet-bearing peridotite lenses are minor but significant components of most metamorphic terranes characterized by high-temperature eclogite facies assemblages. Most peridotite intrudes when slabs of continental crust are subducted deeply (60,120 km) into the mantle, usually by following oceanic lithosphere down an established subduction zone. Peridotite is transferred from the resulting mantle wedge into the crustal footwall through brittle and/or ductile mechanisms. These ,mantle' peridotites vary petrographically, chemically, isotopically, chronologically and thermobarometrically from orogen to orogen, within orogens and even within individual terranes. The variations reflect: (1) derivation from different mantle sources (oceanic or continental lithosphere, asthenosphere); (2) perturbations while the mantle wedges were above subducting oceanic lithosphere; and (3) changes within the host crustal slabs during intrusion, subduction and exhumation. Peridotite caught within mantle wedges above oceanic subduction zones will tend to recrystallize and be contaminated by fluids derived from the subducting oceanic crust. These ,subduction zone peridotites' intrude during the subsequent subduction of continental crust. Low-pressure protoliths introduced at shallow (serpentinite, plagioclase peridotite) and intermediate (spinel peridotite) mantle depths (20,50 km) may be carried to deeper levels within the host slab and undergo high-pressure metamorphism along with the enclosing rocks. If subducted deeply enough, the peridotites will develop garnet-bearing assemblages that are isofacial with, and give the same recrystallization ages as, the eclogite facies country rocks. Peridotites introduced at deeper levels (50,120 km) may already contain garnet when they intrude and will not necessarily be isofacial or isochronous with the enclosing crustal rocks. Some garnet peridotites recrystallize from spinel peridotite precursors at very high temperatures (c. 1200 °C) and may derive ultimately from the asthenosphere. Other peridotites are from old (>1 Ga), cold (c. 850 °C), subcontinental mantle (,relict peridotites') and seem to require the development of major intra-cratonic faults to effect their intrusion. [source] Super-silicic garnet microstructures from an orogenic garnet peridotite, evidence for an ultra-deep (>6 GPa) originJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2000Van Roermund We report the field, petrographic and mineral chemical characteristics of relict super-silicic (=majoritic) garnet microstructures from the Otrøy peridotites in the Western Gneiss Region, Norway. The evidence for the former existence of super-silicic garnet consists of two-pyroxene exsolution microstructures from garnet. Estimates of the initial composition of the super-silicic garnet imply pressures of 6,6.5 GPa, indicating that the Otrøy garnet peridotites were derived from depths >185 km. The garnet peridotites consist of inter-banded variable compositions with c. 50% garnet peridotite and 50% garnet-free peridotite. Two distinct garnet types were identified: (a) normal matrix garnet, grain-size ,4 mm, and (b) large isolated single garnet crystals and/or (polycrystalline) garnet nodules up to 10 cm in size. Large garnet nodules occur only within limited bands within the garnet peridotites. The relicts of super-silicic garnet were exclusively found in some (not all) of the larger garnet nodules. Petrographic observations revealed that the microstructure of nodular garnet consists of the following four characteristic elements. (1) Individual garnet nodules are polycrystalline, with grain sizes of 2,8 mm. Garnet grain boundaries are straight with well-defined triple junctions. (2) Some garnet triple junctions and garnet grain boundaries are decorated by interstitial orthopyroxene. (3) Cores of larger polycrystalline garnet contain two-pyroxene exsolution microstructures. (4) Precipitation-free rims (2 mm thick) surround garnet cores containing the exsolved pyroxene microstructure. Pyroxene exsolution from super-silicic garnet was subsequently followed by brittle,ductile deformation of garnet. Both exsolved pyroxene needles and laths become undulous or truncated by fractures. Simultaneous garnet plasticity is indicated by the occurrence of high densities of naturally decorated dislocations. Transmission electron microscopy observations indicate that decoration is due to Ti-oxide precipitation. Estimates of the P,T conditions for mineral chemical equilibration were obtained from geothermobarometry. The mineral compositions equilibrated at mantle conditions around 805±40 °C and 3.2±0.2 GPa. These P,T estimates correspond to cold continental lithosphere conditions at depths of around 105 km. From a combination of both depth estimates it can be concluded that the microstructural memory of the rock extends backwards to twice as great a depth range as obtained by thermobarometric methods. Available geochronological and geochemical data of Norwegian garnet peridotites suggest a multi-stage, multi-orogenic exhumation history. [source] Comparisons between a mixing ability test and masticatory performance tests using a brittle or an elastic test foodJOURNAL OF ORAL REHABILITATION, Issue 3 2009T. SUGIURA Summary, A variety of chewing tests and test items have been utilized to evaluate masticatory function. The purpose of this study was to compare a mixing ability test with masticatory performance tests using peanuts or gummy jelly as test foods. Thirty-two completely dentate subjects (Dentate group, mean age: 25·1 years) and 40 removable partial denture wearers (RPD group, mean age: 65·5 years) participated in this study. The subjects were asked to chew a two-coloured paraffin wax cube as a test item for 10 strokes. Mixing Ability Index (MAI) was determined from the colour mixture and shape of the chewed cube. Subjects were asked to chew 3 g portions of peanuts and a piece of gummy jelly for 20 strokes, respectively. Median particle size of chewed peanuts was determined using a multiple-sieving method. Concentration of dissolved glucose from the surface of the chewed gummy jelly was measured using a blood glucose meter. Pearson's correlation coefficient was used to test the relationships between the MAI, median particle size and the concentration of dissolved glucose. Mixing Ability Index was significantly related to median particle size (Dentate group: r = ,0·56, P < 0·001, RPD group: r = ,0·70, P < 0·001), but not significantly related to glucose concentration (Dentate group: r = 0·12, RPD group: r = 0·21, P > 0·05). It seems that ability of mixing the bolus is more strongly related to the ability of comminuting brittle food than elastic food. [source] Effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous boneJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2000O. Cornu Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness. [source] Synthesis and properties of methacrylate-based networked polymers having ionic liquid structuresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2010Kozo Matsumoto Abstract Methacrylate-based networked polymers having ionic liquid structures were prepared by radical copolymerization of methyl methacrylate (MMA) with multifunctional crosslinkers: ethyleneglycol dimethacrylate (EGDMA), trimethylolpropane trimethacrylate (TMPTMA), or triethyleneglycol dimethacrylate (TEGDMA), in the presence of 1-ethyl-3-methylethyl-1-imidazolium bis(trifluoromethane)sulfonyl imide (EMImTFSI). The fundamental physical properties of several film samples prepared by varying the monomer composition and ionic liquid content were investigated. The obtained materials became turbid with increasing crosslinker content and ionic liquid content. Their ionic conductivity increased with increasing ionic liquid content, while it was almost independent of the crosslinker content. EGDMA-derived materials and TMPTMA-derived materials showed higher ionic conductivity than TEGDMA-derived materials. TMPTMA-derived materials showed higher thermal stability than EGDMA or TEGDMA-derived materials. EGDMA and TMPTMA-derived materials were stiffer than the TEGDMA-derived materials. The elastic modulus of the film samples increased but the film became more brittle with the increase of crosslinker content. Scanning electron microscopy and atomic force microscopy observation revealed that phase separation of networked polymers and ionic liquid occurred in the highly crosslinked samples, and the phase separation structures became larger in scale with the increase of crosslinking density. This phase separation was considered to have a strong effect on the mechanical properties of the film samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source] Facile, one-pot synthesis of aromatic diamine-based phosphinated benzoxazines and their flame-retardant thermosetsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2010Ching Hsuan Lin Abstract Three aromatic diamine-based, phosphinated benzoxazines (7,9) were prepared from three typical aromatic diamines,4,4,-diamino diphenyl methane (1), 4,4,-diamino diphenyl sulfone (2), and 4,4,-diamino diphenyl ether (3) by a one-pot procedure. To clarify the reaction mechanism, a two-pot procedure was applied, in which the reaction intermediates (4,6) were isolated for characterization. The structures of intermediates and benzoxazines were confirmed by high resolution mass, IR, and 1D and 2D-NMR spectra. In addition to self-polymerization, (7,9) were copolymerized with cresol novolac epoxy (CNE). After curing, the homopolymers of P(7,9) are brittle while the copolymers of (7,9)/CNE are tough. Dynamic mechanical analysis shows the Tgs of (7,9)/CNE copolymers are 187, 190, and 171 °C, respectively. Thermal mechanical analysis shows the CTEs of (7,9)/CNE copolymers are 46, 38, and 46 ppm, respectively. All the (7,9)/CNE copolymers belong to an UL-94 V-0 grade, demonstrating good flame retardancy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source] Synthesis, properties, and sulfonation of novel dendritic multiblock copoly(ether-sulfone)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2008Sumiko Matsumura Abstract Multiblock copoly(ether-sulfone)s (PESs) bearing anchor units for the construction of dendritic blocks were synthesized by two-step reactions: (1) synthesis of PES block with both phenoxide end-groups; (2) chain extension and end-capping of the block by use of excess novel hexafunctional agent, hexakis(4-(4-fluorophenylsulfonyl)phenyl)benzene. The optimum average block length (n) and amount (x) of the hexafunctional agent used for the synthesis of high-molecular-weight PES without crosslinking were n = 26 and x = 2.6 equiv, respectively. The dendritic blocks in the PES were constructed by the aromatic nucleophilic substitution reaction of the activated aromatic fluoride groups on the anchor units using 4-tritylbenzenethiol. The clean substitution of the fluoride groups in the PES was confirmed by 1H NMR and 19F NMR. Three sulfonic acid groups were introduced on the pendant phenyl rings of the trityl groups in the PES by the reaction with chlorosulfonic acid. This is the first example of a dendritic PES bearing clusters of sulfonic acid groups only on the dendritic blocks. Cast films of presulfonated dendritic PES were strong and flexible, however, the membranes of sulfonated dendritic PES were brittle so that the conductivity measurements were not performed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6365,6375, 2008 [source] Synthesis and properties of novel polyimides derived from 2,2,,3,3,-benzophenonetetracarboxylic dianhydrideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2004Xing-Zhong Fang Abstract A new synthetic route to 2,2,,3,3,-BTDA (where BTDA is benzophenonetetracarboxylic dianhydride), an isomer of 2,3,,3,,4,-BTDA and 3,3,,4,4,-BTDA, is described. Single-crystal X-ray diffraction analysis of 2,2,,3,3,-BTDA has shown that this dianhydride has a bent and noncoplanar structure. The polymerizations of 2,2,,3,3,-BTDA with 4,4,-oxydianiline (ODA) and 4,4,-bis(4-aminophenoxy)benzene (TPEQ) have been investigated with a conventional two-step process. A trend of cyclic oligomers forming in the reaction of 2,2,,3,3,-BTDA and ODA has been found and characterized with IR, NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and elemental analyses. Films based on 2,2,,3,3,-BTDA/TPEQ can only be obtained from corresponding polyimide (PI) solutions prepared by chemical imidization because those from their polyamic acids by thermal imidization are brittle. PIs from 2,2,,3,3,-BTDA have lower inherent viscosities and worse thermal and mechanical properties than the corresponding 2,3,,3,,4,-BTDA- and 3,3,,4,4,-BTDA-based PIs. PIs from 2,2,,3,3,-BTDA and 2,3,,3,,4,-BTDA are amorphous, whereas those from 3,3,,4,4,-BTDA have some crystallinity, according to wide-angle X-ray diffraction. Furthermore, PIs from 2,2,,3,3,-BTDA have better solubility, higher glass-transition temperatures, and higher melt viscosity than those from 2,3,,3,,4,-BTDA and 3,3,,4,4,-BTDA. Model compounds have been prepared to explain the order of the glass-transition temperatures found in the isomeric PI series. The isomer effects on the PI properties are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2130,2144, 2004 [source] Effect of single-mineral filler and hybrid-mineral filler additives on the properties of polypropylene compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2009A.K. Nurdina The present study was carried out to determine the filler characteristics and to investigate the effects of three types of mineral fillers (CaCO3, silica, and mica) and filler loadings (10,40 wt%) on the properties of polypropylene (PP) composites. The characteristics of the particulate fillers, such as mean particle size, particle size distribution, aspect ratio, shape, and degree of crystallinity were identified. In terms of mechanical properties, for all of the filled PP composites, Young's modulus increased, whereas tensile strength and strain at break decreased as the filler loading increased. However, 10 wt% of mica in a PP composite showed a tensile strength comparable with that of unfilled PP. Greater tensile strength of mica/PP composites compared to that of the other composites was observed because of lower percentages of voids and a higher aspect ratio of the filler. Mica/PP also exhibited a lower coefficient of thermal expansion (CTE) compared to that of the other composites. This difference was due to a lower degree of crystallinity of the filler and the CTE value of the mica filler. Scanning electron microscopy was used to examine the structure of fracture surfaces, and there was a gradual change in tensile fracture behavior from ductile to brittle as the filler loading increased. The nucleating ability of the fillers was studied with differential scanning calorimetry, and a drop in crystallinity of the composites was observed with the addition of mineral filler. Studies on the hybridization effect of different (silica and mica) filler ratios on the properties of PP hybrid composites showed that the addition of mica to silica-PP composites enhanced their tensile strength and modulus. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers [source] Large-scale specimen testing on friction and wear of pure and internally lubricated cast polyamidesLUBRICATION SCIENCE, Issue 3 2006Pieter SamynArticle first published online: 4 JUL 200 Abstract Due to the casting process for nylons, their composition can easily be modified to cover a wide range of mechanical properties and applications, especially as large wear surfaces in, for example, crane guidances. Presently, selection tests for working conditions up to 40MPa are presented on pure Na-catalysed polyamides, oil-filled polyamides with homogeneous oil dispersions and holes in the surface containing oil lubricant and two types of thermoplastic solid-lubricated polyamides. Pure polyamides are, however, prone to high and unstable sliding at pressures as low as 10MPa with brittle fracture and lumpy transfer. Oil lubrication is not able to remove the sliding instabilities as oil supply to the sliding interface is controlled by migration effects that are restricted by deformation and thermal softening or melting of the polyamide matrix. Although friction and wear are lower and more stable for samples with oil supplied through lubricating holes, additional running-in phenomena are attributed to a relatively thick transfer film that is brittle and easily peels off. A continuous thick molten film or island-like deposition occurs on the polyamide surface. Solid lubricants are able to stabilize friction and lower wear down to the formation of a thin and coherent transfer film. However, increasing the amount of lubricants induces lower mechanical properties and higher deformation of the test samples. The differences in transfer behaviour are discussed with reference to optical microscopy and calculations of bulk and flash temperatures. Copyright © 2006 John Wiley & Sons, Ltd. [source] Phenolic Hydroxy Groups Incorporated for the Peroxidase-Catalyzed Gelation of a Carboxymethylcellulose Support: Cellular Adhesion and ProliferationMACROMOLECULAR BIOSCIENCE, Issue 3 2009Yuko Ogushi Abstract The effect of Ph-OH group content on gelation time, mechanical properties, hydrophobicity, and cellular adhesiveness of hydrogels produced from carboxymethylcellulose derivatives is investigated. A higher Ph-OH group content induces faster gelation and yields more brittle and hydrophobic gels. After 4 h of seeding, a larger number of L929 fibroblasts adhere to the hydrogel of the CMC-Ph that contains 15.4 Ph-OH groups per 100 repeat units of uronic acid (97% adhesion rate) than to the gel of CMC-Ph with only 8.4 Ph-OH groups (62% adhesion rate). The results demonstrate that controlling the Ph-OH group content is an effective and useful way to control cellular adhesion and proliferation on the hydrogels, as well as gelation time and mechanical properties of the gels. [source] Bio-Based Rubbers by Concurrent Cationic and Ring-Opening Metathesis Polymerization of a Modified Linseed OilMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2009Wonje Jeong Abstract Bio-based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl-modified linseed oil, DilulinÔ, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio-based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio-based rubbers have maximum decomposition temperatures of over 450,°C with their thermal stability decreasing with increasing loadings of NBDC. [source] Processing and Properties of Biobased Blends from Soy Meal and Natural RubberMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10-11 2007Qiangxian Wu Abstract Vulcanized blends from soy meal and natural rubber were successfully processed through semi-pilot scale extrusion, roll milling and compression-molding. Blends containing about 50 wt.-% of soy meal are elastic and water resistant, compared with the brittle and hydrophilic soy meal. The natural rubber component was well embedded into the soy meal matrix, indicating the existence of an interaction between them. The glass transition temperature of the rubber component in the blends increased due to the existence of this interaction. Calcium sulfate, as a compatibilizer, was a physical cross-linker to the proteins in the soy meal and in the rubber. The morphological analysis of the soy meal and natural rubber blend through scanning electron microscopy revealed a partial compatibility of the blend. The blends containing near 50 wt.-% of inexpensive soy meal have potential for various applications. [source] | ||||||||||||||||||||||||||||||||||