Filamentary Composites Research Articles

Reliability Prediction of Composite Tubular Structure Under Mechanical Loading by Finite Element Method

The diversified use of filamentary composites in harsh marine environments, recorded in recent years, has prompted researchers to focus their work on the reliability prediction. Through failure criteria, Tsai–Wu and the maximum stress, the reliability of multilayer tubular structures under mechanical loading is the subject of this paper, where Monte Carlo method estimated the failure probability. A sensitivity analysis was performed in order to identify the influence of the different parameters, such as materials’ properties, geometry, manufacturing and loading, on the reliability of the composite cylindrical structure studied. To achieve a high accuracy of the results, we have carried out 105 simulations. The results showed great influence on pressure loading, ply thickness and finally winding angle of filament composite.

Design of multi materials combining crystalline and amorphous metallic alloys

Multi materials, associating zirconium based bulk metallic glasses and crystalline metallic alloys like magnesium alloys or copper are elaborated by co-deformation processing performed in the supercooled liquid regions (SLR) of the bulk metallic glasses. Two processes are investigated: co-extrusion and co-pressing. In the first case, filamentary composites with various designs can be produced whereas in the second case sandwich structures are obtained. The experimental window (temperature, time) in which processing can be carried out is directly related to the crystallisation resistance of the glass which requires getting information about the crystallisation conditions in the selected metallic glasses. Thermoforming windows are identified for the studied BMGs by thermal analysis and compression tests in their SLR. The mechanical properties of the produced multi materials are investigated thanks to specifically developed mechanical devices and the interfaces between the amorphous and the crystalline alloys are characterised.

Effect of homogenization treatment on microstructure and properties for Cu–Fe–Ag in situ composites

Abstract The effects of homogenization treatment on the microstructure and properties of Cu–8Fe–0.1Ag and Cu–8Fe–0.5Ag (wt.%, similarly hereinafter) in situ composites were investigated. The composites were prepared by inductive melting, casting, homogenization treatment and subsequent cold work. Microstructures of the composites were observed and the tensile strength plus electrical conductivity was measured respectively. The results show that the prior homogenization treatment results in refinement of the primary Fe dendrites in Cu matrix and promotes the precipitation of the secondary Fe particles from the Cu matrix, which leads to increase in the strength and conductivity of the composites. During the following cold deformation, the homogenized alloys are readily elongated into fine and continuous filamentary composites compared with the as-cast, leading to high strength due to the increased interface density.

Influences of different prior heat treatments on the microstructural and mechanical properties of Cu–Fe filamentary composites

Cu–6 wt.% Fe and Cu–12 wt.% Fe filamentary composites were prepared by casting and cold drawing. And a different heat treatment of quenching and aging or homogenizing was introduced before cold drawing process, respectively. The microstructure was observed and the tensile strength measured for the composites at different drawing strains. The quenching and aging or homogenizing prior to drawing deformation refine the as-cast microstructure and result in the increase in interface density in the drawn microstructure. The drawn alloys with the homogenizing treatment show smaller filament spacing than those with the quenching and aging treatment because homogenizing results in smaller and more dispersive primary Fe dendrites before drawing deformation. The heat treatments can improve the strength of the composites by increasing precipitation strengthening and interface strengthening levels. With the reduction in filament spacing during drawing deformation, the strength of the alloys with smaller initial size of Fe dendrites increases more obviously.

Strain Strengthening of Ag-10Cu in situ Filamentary Composite Prepared by Heavy Deformation

Abstract Ag-10Cu in situ filamentary composite was prepared by hot extrusion and cold wire drawing. The as-cast and as-extruded Ag-10Cu alloys consist of Ag matrix, (Ag+Cu) eutectic and Cu precipitates which will become a structure of Ag matrix and Cu filaments after heavy deformation. The size of Cu filaments, transformed from coarse Cu precipitates, changes with drawing strain, and their relationship can be expressed as d = d o exp(−0.144 η ). Two-stage strengthening characteristics were obtained and the strengthening mechanism of this composite was discussed. A combination of ultimate tensile strength approaching 1 GPa and electrical conductivity exceeding 60% IACS can be achieved for this composite. The effect of intermediate heat treatment was also discussed.

Heat and Mass Transfer Modeling and Simulation during Liquid Route Processing of SiC/Ti Filamentary Composites

To process SiC/Ti filamentary composites using a liquid route method, it is first necessary to overcome various major difficulties such as, high speed filament/matrix coupling, liquid titanium wetting of filament surfaces, and reduction of filament/matrix interaction. All of these requirements depend mainly on the heat and mass transfer, which occurs as the filament runs through a liquid titanium bath. Consequently, these transfers were modeled and simulated numerically during the different processing steps, particularly the cooling step. The results describe the physical phenomena which occur during the process: the carbon transfer from the carbon coated SiC filament to the liquid titanium, heat exchanges, formation of the TiC interphase at the filament surface, and, finally, the solidification of the titanium coating. Numerical simulation has shown the strong influence of running speed which governs the wettability of the filament by the liquid metal. Furthermore, the effects of an additional specific cooling device have been highlighted.

Effects of rare earth elements on annealing characteristics of Cu–6 wt.% Fe composites

The filamentary composites of Cu–6 wt.% Fe, Cu–6 wt.% Fe–0.05 wt.% RE and Cu–6 wt.% Fe–0.3 wt.% RE were prepared by casting, cold drawing and intermediate heat treatments. The microstructure was observed and the ultimate tensile strength, vickers hardness and electrical conductivity were determined for the composites annealed at different temperatures. The results show that (0.05–0.30) wt.% rare earth elements in Cu–6 wt.% Fe can refine the as-cast microstructure and facilitate the precipitation of secondary Fe particles in the Cu matrix. The filamentary structure of Cu–6 wt.% Fe–0.30 wt.% RE seems to have a higher recrystallized resistance than that of Cu–6 wt.% Fe. With the increase in annealing temperature, the strength and hardness of the composites decrease but the conductivity increases. In particular, there appears a remarkable change of the strength, hardness and conductivity with the annealing temperature over 400 °C. The rare earth elements increase the conductivity of the Cu–6 wt.% Fe composites annealed at different temperatures. The improvement in conductivity from the rare earth elements is more significant for the composites annealed at higher than 400 °C.

Effects of rare-earth additions on the microstructure and strength of Cu–Ag composites

The filamentary composites of Cu–6 wt.% Ag and Cu–12 wt.% Ag containing rare-earth elements with different contents were prepared by casting and cold drawing. The microstructure was observed and the tensile strength determined for the composites at different draw ratios. The rare-earth elements of 0.05–0.15 wt.% in Cu–6 wt.% Ag and 0.1–0.3 wt.% in Cu–12 wt.% Ag result in large spacing or low density of the filamentary interface in the composites. Some hard compound particles exist in the composites containing rare-earth elements and result in high stress concentration. The rare-earth additions in the composites can improve the strength at low drawing degrees but reduce the strength at high drawing degrees.

Effects of solute, temperature and strain on the electrical resistivity of Cu–Ag filamentary composites

The filamentary composites of Cu–6 wt%Ag, Cu–6 wt%Ag–0.2 wt%Zr and Cu–24 wt%Ag were prepared by heavy drawing. The electrical resistivity at various temperatures and draw ratios was determined in order to investigate the effects of the solute concentration, measured temperature and strain level on the electrical conductivity. The conductivity of all tested composites, especially for Cu–6 wt%Ag, decreases with the temperature increasing from 77 to 293 K. Minor constituent Zr or high Ag content in the filamentary composites significantly impairs the conductivity at temperatures lower than 293 K. The resistivity at 77–293 K slightly increases but at 373–573 K slightly decreases with the draw ratio increasing from 6.1 to 9.4 for Cu–6 wt%Ag. Additional solute atoms, large interfacial area and high dislocation density in Cu–6 wt% Ag–0.2 wt%Zr and Cu–24 wt%Ag are mainly responsible for the conductivity reduction. Dislocation scattering and interface scattering mainly affect the resistivity at low temperatures. Phonon scattering mainly affects the resistivity at high temperatures.

Analytical electromagnetic calculations for practical superconductors

The current distributions of twisted long filamentary composites are studied during the current sweep and under the transverse and longitudinal external field, using the inductance matrix among superconducting helical filaments and the inductive voltage between filaments and the external coil in the circuit equation. The self- and mutual inductances of helical conductors with a uniform helical current density are approximately calculated from the analytical expressions of long helical thin conductors. In addition, the magnetic field and the vector potential distributions of a twisted superconducting composite are also obtained by the numerical integral calculation over the cross section of the analytical expressions for the magnetic field and vector potential due to an infinitely long helical conductor.

Effect of Annealing on the Microstructure Change and Strength of Irradiated Quasi-Nano-Filamentary Copper-Silver Composites

Copper-silver quasi-nano filamentary composites prepared by hot isostatic pressing followed by heavy drawing were irradiated in CT hole of a domestic experimental nuclear reactor, HANARO to study the morphological change of the poly-crystalline nano-filaments with irradiation and annealing conditions. The irradiation was carried out for 36 days at 320 o C with the maximum neutron flux of 4.8x10 20 n/cm 2 (E>1.0 MeV). The gamma heating rate was in the range of 2.0-6.45 W/gm. Polycrystalline silver nano-filaments of the composites were equilibrium shape like the faceted sphere shape. Annealing results in the increase of the faceting rate of the irradiated specimen. Nano-indentation results supported that the morphology change of nano-filaments by annealing in this study is more effective on strength change of the irradiated nano-filamentary composites than irradiated hardening.

Irradiation Effect on Mechanical Properties and Oxidation Behavior of Nano-Filamentary Copper-Silver Composites

Quasi-nano filamentary copper-silver composites were irradiated and annealed to study irradiation degradation behavior. The specimen was irradiated in CT hole of HANARO of KAERI for 36 days at 320°C with the maximum neutron flux of 4.8x1020 n/cm2 (E>1.0 MeV). The gamma heating rate was in the range of 2.0-6.45 W/gm. Irradiation embrittlement was observed. Hardness determined by nano-indentation technique were 32.3 GPA for as-received condition, however, it decreased 24.6 GPa due to gamma heating, which was above the value of the specimen with same annealing effect without irradiation. Weight change of specimen with oxidation increased with annealing time, temperature and amount of dose 0.21-0.27 mR/h. Hardness change of the irradiated specimen followed by annealing was significantly dependent upon amount of dose of the specimen.

Effects of strain and annealing on the intensity and distribution of crystal texture in Cu–12 wt.% Ag

Cu–12 wt.% Ag filamentary composite was prepared by drawing and annealing. The intensity and distribution of crystal texture were determined. The preferred crystal orientation in Ag phase forms more rapidly during drawing strain than in Cu phase. Drawing deformation produces three texture components 〈1 0 0〉, 〈1 1 1〉 and 〈2 1 1〉 in Cu phase and single texture component 〈1 1 1〉 in Ag phase. In a certain strain range, the intensities of all texture components increase with drawing deformation. The 〈1 0 0〉 intensity in Cu phase keeps basically constant and the 〈1 1 1〉 intensity in Cu and Ag phases decreases as the strain exceeds a certain level. Annealing treatment modifies the intensities of deformation texture due to interface migrating, fiber breaking, grain propagating and structure spheroidizing. Annealing at lower temperatures enhances the 〈1 0 0〉 intensity and reduces the 〈1 1 1〉 intensity in Cu phase. Annealing at higher temperatures enhances the 〈1 1 1〉 intensity in Cu and Ag phases.

Electrical conductivity of Cu-Ag in situ filamentary composites

The electrical conductivity of Cu-10Ag in situ filamentary composite was studied during the deformation and annealing processes. The dependence of electrical resistivity of the deformed composites on the true strain presents a two-stage change with increase of the true strain. The intermediate heat treatment and the stabilized annealing treatment to the deformed composite promote the separation of Ag precipitate, and increase the electrical conductivity. The maximum conductivity of the composite experienced the stabilizing heat treatment can reach about 97% IACS with σ b ≥ 400 MPa at 550 °C annealing, and reach about 70% IACS with σ b ≥ 250 MPa at 300 °C annealing. The corresponded strength of the composite was reported. The microstructure reason for the changes of the conductivity was discussed.

Computational study of crack growth in SiC/Al composites

An elastic-plastic finite-element analysis has been carried out to study the fracture behaviour of a SiC/6061-Al filamentary composite. The composite was modelled as a two-material cylinder subjected to uniform displacement and consisting of an inner cylinder simulating the fibre and a surrounding shell simulating the matrix. Using the strain energy density criterion, the critical applied displacements for crack initiation and stable crack growth were determined for three studied cases: an intact fibre, a cracked fibre, and a fully broken fibre. The numerical results were compared, where possible, to experimentally obtained ones. Finally, results concerning the variation of strain energy density versus distance from the crack tip, for the determination of the critical value of applied displacement at crack initiation, are presented and discussed.

High-Field Performance and Structure of<tex>$(rm Nb,rm Ta)_3rm Sn$</tex>Wires Prepared from Sn-Ta Matrix

Sn-Ta-Cu buttons with enough ductility to be fabricated into thin sheets were synthesized by melting a mixture of Sn+Ta+(Cu) powder. (Nb,Ta)/sub 3/Sn wires have been prepared by a Jelly Roll (JR) process and a filamentary process. In the JR process a Sn-Ta(-Cu) sheet was laminated with a Nb sheet forming a JR composite. In the filamentary process a Sn-Ta(-Cu) sheet was wrapped around thirteen Nb-1.0 at%Ta rods forming a filamentary composite. Both composites were fabricated into wires without intermediate annealing, and then heat treated. The effect of Ge and Ti addition to the Sn-Ta-Cu sheet has been studied in the JR wires. A small amount of Ge addition improves the workability of the sheet, while that of Ti addition enhances appreciably the J/sub c/ of the JR wires. Meanwhile, the 13-core filamentary wires exhibit equivalent high-field performance as that of the JR wires. Present new (Nb,Ta)/sub 3/Sn wires can be fabricated through a relatively easy process, and show attractive J/sub c/ in the field range of 22-23 T at 4.2 K and that of 24-25 T at 2.1 K.

Interfacial structure of nanostructured Cu–Nb filamentary composite fabricated by the bundling and drawing process

A high-resolution electron microscope (HREM) has been used to study the interfacial structure of Cu–Nb filamentary composites fabricated by the bundling and drawing process. At the matrix/filament interface, misfit interface dislocations were introduced periodically to relieve the misfit strain. The spacing between interfacial misfit dislocations for the interface between (1 1)Cu and (10 )Nb planes was observed to vary with the local tilt angle of the interface. The moiré fringes appeared in association with interfacial dislocations and the spacing between moiré fringes was found to be quite close to that between interfacial dislocations.

High strain rate superplasticity of deformation processed Cu–Ag filamentary composites

High strain rate superplasticity was observed in deformation processed Cu–Ag composites. The elongation was 1160% at the strain rate of 1 × 10 −1/s at 650 °C. The filamentary nanostructure in the as-drawn Cu–Ag nanocomposite was replaced by ultra-fine grained two-phase structure after superplastic deformation.

Ｓｎ‐Ｔａシートを用いて作製した（Ｎｂ，Ｔａ）３Ｓｎ超伝導線材の組織と特性

Sn-Ta (-Cu) alloys with enough ductility to be fabricated into a thin sheet were synthesized by melting a mixture of Sn+Ta (+Cu) powder. The (Nb, Ta)3Sn wires were prepared by Jelly Roll (JR) process and filamentary process. In the JR process a Sn-Ta (-Cu) sheet was laminated with a Nb sheet and wound into a JR composite. In the filamentary process a Sn-Ta (-Cu) sheet was wrapped around Nb-1 at%Ta rods and bundled into a filamentary composite. Both composites were fabricated into wires without intermediate annealing and then heat treated. The composition and micro-structure of (Nb, Ta)3Sn layers formed in the wires were studied. Ta in the sheet improves the high-field performance, while Cu addition to the sheet decreases the reaction temperature of the wire. The non-Cu Jc of the JR wire without Cu addition to the sheet and reacted at 900°C is about 1.0×108 A/m2 at 23 T and 4.2 K. A nearly the same non-Cu Jc of the wire is obtained at 25 T and 2.1 K, the upper critical field of the wire being about 28.5 T. The JR wire and 13-core filamentary wire with a few mass% Cu addition to the sheet and reacted at 800°C show a non-Cu Jc of about 1.0×108 A/m2 at 22 T and 4.2 K. Both wires exhibit a n value of about 30 at 22-23 T and 4.2 K, which represents a potentiality of the wires for high magnetic field use.

Interfacial and twin boundary structures of nanostructured Cu–Ag filamentary composites

A high-resolution transmission electron microscope was used to study the interfacial and twin boundary structure of nanostructured Cu–Ag filamentary composites. Copper matrix and silver filaments have the orientation relationship {111}Cu∥{111}Agand 〈111〉Cu∥〈111〉Ag. In some regions, twin bands propagated through the silver filaments with some boundary steps at the matrix/filament interface, and the silver filament appeared to be kinked in the twin band in the same direction as the twinning shear. This suggests that twins propagated after the formation of silver filament, and twin bands were deformation twins. At the matrix/filament interface, misfit interface dislocations were introduced periodically to relieve the misfit strain. The distance between interfacial misfit dislocations along the matrix/filament interface in the longitudinal section was measured to be 1.88 nm, which is in good agreement with that (1.81 nm) calculated based on lattice misfit. In Cu–Ag nanocomposites, the spacing between Moire fringes was found to be quite close to that between interfacial misfit dislocations.