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Andreas Mortensen - One of the best experts on this subject based on the ideXlab platform.
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fracture of High Volume Fraction ceramic particle reinforced aluminium under multiaxial stress
Acta Materialia, 2010Co-Authors: Aude Hauert, A. Rossoll, Andreas MortensenAbstract:Circumferentially notched cylindrical bars of High Volume Fraction Al2O3 particle reinforced aluminium are tested in tension to probe the role of tensile stress triaxiality on damage and failure of such materials. The transverse strain is monitored with a specially designed video extensometer. A significant dependence of the peak average stress and failure strain on notch radius is observed. Finite-element simulations of the tests are conducted on the basis of a micromechanical model derived from earlier studies of damage and failure of these composites under uniaxial tensile deformation (Journal of the Mechanics and Physics of Solids 2009;57:1781). The simulations show that stress and strain distributions within the notched composite samples deviate significantly from predictions of Bridgman’s simplified analysis. Comparison with data shows that, whereas calculations capture satisfactorily the evolution of the average composite flow stress as a function of notch radius at small strains, the notched samples damage faster and fail at strains lower than predicted. Two phenomena may explain the discrepancy, namely (i) damage coalescence beyond a threshold level, and (ii) the incapacity of the matrix to sustain large hydrostatic stresses, which results from the presence of internal surfaces (cracked particles and possibly matrix voiding).
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Particle fracture in High-Volume-Fraction ceramic-reinforced metals: Governing parameters and implications for composite failure
Journal of the Mechanics and Physics of Solids, 2009Co-Authors: Aude Hauert, A. Rossoll, Andreas MortensenAbstract:Abstract Weibull parameters of angular alumina particles are determined from experimental tensile test data on High-ceramic-content metal matrix composites using a micromechanical model that accounts for internal damage in the form of particle cracking, the dominant damage mode in these composites. The Fraction of broken particles is assessed from the drop of Young's modulus and particle fracture is assumed to be stress controlled. Two extreme load-sharing modes, namely a purely local and a global load-sharing mode, are considered to account for the load redistribution due to particle fracture. Consistent powder strength parameters can be thus “back-calculated” for particles that are embedded in different Al–Cu matrices. On the other hand, this calculation fails for pure Al matrix composites, which exhibit a much larger strain to failure than Al–Cu matrix composites. It is shown that for Al matrix composites, the role of plastic (composite) strain on particle fracture constitutes a second parameter governing particle damage. This finding is rationalized by particle–particle interactions in these tightly packed ceramic particle-reinforced composites, and by the increase of matrix stress heterogeneity that is brought with increasing plastic strain. Failure of the alloyed matrix composites is well described by the (lower bound) local load-sharing micromechanical model, which predicts a catastrophic failure due to an avalanche of damage. The same model predicts failure of pure aluminium matrix composites to occur at the onset of tensile instability, also in agreement with experimental results once the role of plastic strain on damage accumulation is accounted for.
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investigation of crack tip plasticity in High Volume Fraction particulate metal matrix composites
Engineering Fracture Mechanics, 2004Co-Authors: Ali Miserez, A. Rossoll, Andreas MortensenAbstract:Crack-tip strain fields in High Volume Fraction ceramic particle reinforced metal matrix composites are assessed using photoelastic measurements. It is shown that the size of the significant crack-tip plastic zones that form in these materials depends on the type and diameter of the reinforcement and on the matrix material. This plastic zone size correlates well with the macroscopic toughness values assessed through J -integral testing. The composites are thus ‘‘metallic’’ in the sense that their toughness is mostly composed of plastic energy dissipation around the crack tip. Plastic deformation also induces marked constraint effects that influence the shape of the surface strain fields. It is shown that finite element analysis must be three-dimensional to describe these strain fields, as two-dimensional plane-stress analysis fails to reproduce the experimental data. � 2004 Elsevier Ltd. All rights reserved.
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quantification of microdamage phenomena during tensile straining of High Volume Fraction particle reinforced aluminium
Acta Materialia, 2001Co-Authors: M Kouzeli, L Weber, San C Marchi, Andreas MortensenAbstract:Particle reinforced composites are produced by infiltrating ceramic particle beds with 99.99% Al. Resulting materials feature a relatively High Volume Fraction (40-55 vol. pet) of homogeneously distributed reinforcement. The evolution of damage during tensile straining of these composites is monitored using two indirect methods; namely by tracking changes in density and in Young's modulus. Identification and quantification of the active damage mechanisms is conducted on polished sections of failed tensile specimens: particle fracture and void formation in the matrix are the predominant damage micromechanisms in these materials. The damage parameter derived from the change in density at a given strain is found to be one to two orders of magnitude smaller than the parameter based on changes in Young's modulus. A simple micromechanical analysis inspired by the observed damage micromechanisms is used to correlate the two indirect measurements of damage. The predictions of this analysis are in good agreement with experiment. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. AII rights reserved.
Wei Guo - One of the best experts on this subject based on the ideXlab platform.
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joining High Volume Fraction sic particle reinforced aluminum matrix composites sicp al by low melting point stannous oxide zinc oxide phosphorus pentoxide glass
Ceramics International, 2020Co-Authors: Wei Guo, Jing Hou, Tiesong LinAbstract:Abstract This study focused on joining High Volume Fraction SiC particles reinforced aluminum matrix composites (55 vol% SiCp/Al) with 50SnO–20ZnO–30P2O5 (SZP) glass directly in air. Prior to joining, various properties of the SZP glass and its wettability on the composites were investigated. The results showed that the coefficient of thermal expansion of the glass was 10.58 × 10-6/°C (20–369 °C), which closely match with 55 vol% SiCp/Al composites. The glass transition, crystallization, and softening temperature were identified to be 369, 397, and 486 °C, respectively. Subsequent wetting tests confirmed excellent wettability of the glass on the composites. The joint exhibited sound bonding that was free of defects when brazed at 550 °C for 10 min Zn2P2O7 was formed adjacent to the composites due to the crystallization of the glass. The mechanical properties of the joint were proven to be suitable, exhibiting an average shear strength of 55.3 MPa.
Hulya Cebeci - One of the best experts on this subject based on the ideXlab platform.
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understanding the polymer type and cnt orientation effect on the dynamic mechanical properties of High Volume Fraction cnt polymer nanocomposites
Composite Structures, 2016Co-Authors: Deniz Urk, Elif Demir, Osman Bulut, Dilek Cakiroglu, Fevzi Cakmak Cebeci, L Ovecoglu, Hulya CebeciAbstract:Dispersion and distribution of CNTs in polymers without applying any functionalization and using traditional processes such as mixing, sonication do not exhibit the full potential of CNTs due to agglomeration and limits the use of weight Fractions when bulk CNTs is considered. In this work, vertically aligned CNTs (VACNT) and randomly oriented CNTs (RCNT) are used to fabricate vertically aligned CNT polymer nanocomposites and randomly oriented polymer nanocomposites with an elastomer and epoxy as two distinctive polymer types. The comparison of alignment effect is investigated by using both vertically aligned and randomly oriented CNTs. These CNTs were also studied at different Volume Fractions (up to 10% Volume Fraction) with a mechanical densification process. Dynamic mechanical analysis of both vertically aligned and randomly oriented CNT polymer nanocomposites were performed with single cantilever clamp and the results showed that longitudinal storage modulus of High Volume Fraction vertically aligned CNT polymer nanocomposites is Higher than randomly oriented polymer nanocomposites due to the alignment effect of CNTs. However, the transverse direction mechanical properties showed an opposite affect that within High Volume Fractions of CNTs in vertically aligned CNT polymer nanocomposites. Also, due to the nature of elastomer, the reinforcing capability of CNTs showed a Higher enhancement on the modulus of PNCs compared to the thermoset resin.
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multifunctional properties of High Volume Fraction aligned carbon nanotube polymer composites with controlled morphology
Composites Science and Technology, 2009Co-Authors: Hulya Cebeci, Roberto Guzman De Villoria, John A Hart, Brian L WardleAbstract:Abstract Advanced composites, such as those used in aerospace applications, employ a High Volume Fraction of aligned stiff fibers embedded in High-performance polymers. Unlike advanced composites, polymer nanocomposites (PNCs) employ low Volume Fraction filler-like concepts with randomly-oriented and poorly controlled morphologies due to difficult issues such as dispersion and alignment of the nanostructures. Here, novel fabrication techniques yield controlled-morphology aligned carbon nanotube (CNT) composites with measured non-isotropic properties and trends consistent with standard composites theories. Modulus and electrical conductivity are maximal along the CNT axis, and are the Highest reported in the literature due to the continuous aligned-CNTs and use of an unmodified aerospace-grade structural epoxy. Rule-of-mixtures predictions are brought into agreement with the measured moduli when CNT waviness is incorporated. Waviness yields a large (∼10×) reduction in modulus, and therefore control of CNT collimation is seen as the primary limiting factor in CNT reinforcement of composites for stiffness. Anisotropic electron transport (conductivity and current-carrying capacity) follows expected trends, with enhanced conductivity and Joule heating observed at High current densities.
Shanju Zhang - One of the best experts on this subject based on the ideXlab platform.
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surface induced polymer crystallization in High Volume Fraction aligned carbon nanotube polymer composites
Macromolecular Chemistry and Physics, 2010Co-Authors: Shanju Zhang, Wei Lin, Chingping Wong, Stephen Z D Cheng, David G BucknallAbstract:Surface-induced crystallization of High-density polyethylene in vertically aligned multiwalled carbon nanotube arrays has been investigated by means of scanning electron microscopy (SEM), wide-angle X-ray difFraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).1-mm long nanotube arrays are infiltrated by polyethylene solutions and then the system is allowed to crystallize under controlled conditions. Periodic disk-shaped polyethylene single crystals grow perpendicularly to the aligned nanotubes but do not completely fill the intertube spacing, forming oriented 3D porous structures. This unique morphology leads to low density, High nanotube mass Fraction (up to 80 wt.-%) composites. Microstructure (WAXD) analysis shows that the nanotubes act as both orientation templates as well as nucleating agents for polyethylene crystallization creating orthorhombic and monoclinic forms, although the overall crystal structure is dominated by the orthorhombic form. Thermal analysis (DSC) shows that the nanocomposite exhibits multiple phase transitions during heating and cooling with a weak superheating and supercooling dependence on different scanning rates. Three phase structures have been identified and a possible model is proposed to explain the observed phenomenon.
Mingli Qin - One of the best experts on this subject based on the ideXlab platform.
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net shape forming and properties of High Volume Fraction sicp al composites
Journal of Alloys and Compounds, 2009Co-Authors: Shubin Ren, Mingli Qin, Jia Guo, Xiaoyu ShenAbstract:Abstract High performance SiCp/Al composites have been realized their net-shape forming by use of a novel process—ceramic injection molding (CIM) for the preparation of SiC preform and pressureless infiltration of aluminum alloys. The dimension precision of prepared SiCp/Al parts could reach about ±0.3%, and their properties could also better meet the requirement of electronic packaging on the materials. In this paper, the CIM process to fabricate SiC preform and the infiltration of SiC preform by Al alloys have been discussed in detail. Additionally, the properties of prepared SiCp/Al composites have also been given research and evaluation.
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dry sliding wear properties of High Volume Fraction sicp cu composites produced by pressureless infiltration
Wear, 2008Co-Authors: Laiqi Zhang, Bohua Duan, Mingli QinAbstract:Abstract The dry sliding wear behaviour of High Volume Fraction (61%) SiC p /Cu composite produced by pressureless infiltration was studied with a pin-on-disc system. The wear tests were carried out under an applied load from 50 N to 200 N and sliding speed of 1.3 m/s and 2.6 m/s. The results indicate that the Volume loss increases with applied load, sliding speed and sliding distance. The wear resistance of the composites containing larger reinforcement is Higher than those of the composites with smaller particles due to the enlargement of the mean free path between particles. The main wear mechanisms are abrasive wear and oxidative wear. The mechanically mixed layer (MML) controls greatly the wear rate and friction coefficient of the composites. The composites tested at High sliding speed exhibit High value of friction coefficient and intense fluctuation, which is associated with the intermittent formation and removal of the MML. High reinforcement content, small size ratio of abrasive size to reinforcement size and strong interfacial bond are all contribute to the excellent wear resistance of SiC p /Cu composites.
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thermo physical and mechanical properties of High Volume Fraction sicp cu composites prepared by pressureless infiltration
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Laiqi Zhang, Bohua Duan, Shubin Ren, Mingli QinAbstract:Abstract SiCp/Cu composites with High reinforcement content were fabricated by pressureless infiltration of copper alloy into porous SiC preform obtained by powder injection molding. The microstructure, thermo-physical and mechanical properties were investigated. The relative density of the SiCp/Cu composite reached 98.1%. The reinforcement Volume Fraction achieved 57–68% by using bimodal or trimodal particle distributions. The coefficients of thermal expansion in the range of 20–500 °C were found to be between 7.9 and 10.5 × 10−6 K−1. The CTEs agree well with estimated value based on Kerner's model. The composites exhibit negligible hysteresis loop and small residual plastic strain, implying that it has High thermal stability. The thermal conductivity was in the range of 125–153 Wm−1 K−1. The bending strength ranged from 176 to 259 MPa, depending on the particle size. The elastic modulus reached 250 GPa, which is close to the prediction by H–S model.