This study investigates the effects of interface edge configuration on the stress distribution near the edge of a ceramics/metal joint system interface using numerical thermal elastoplastic analysis. Finite element bonded dissimilar models were employed, which consisted of an elastic material to represent the ceramics and an elastoplastic material in the case of the metal. In this finite element method (FEM) study, it was assumed that silicon nitride and nickel were bonded at high temperatures and cooled slowly. The thermal elastoplastic behavior on the free surface of the ceramic side near the edge of the interface was determined numerically. The dependence of thermal elastoplastic behavior on geometrical interfacial configuration was also clarified numerically using FEM models with various interface edge configurations. Results of the numerical analysis were compared with the dependence of practical tensile bonding strength on the interface edge angle of a silicon nitride/nickel joints system bonded at 780°C, with the same interface shape as that of the analytical model. The practical tensile bonding strength was improved by setting the optimum interface shape. The optimum interface shape was obtained by determining the effects of the interface wedge angle on practical tensile bonding strength. Results of thermal elastoplastic analysis for the FEM model and fracture patterns suggest that an appropriate interface shape can reduce thermal residual stress near the interface edges on the ceramic side.
Wear is the major mode of failure in machine components made out of polymer and its composites. The low thermal conductivity of the polymer causes heat accumulation near the contact surface and the resulting thermal softening accelerates the wear. In this research work, an attempt is made to enhance the thermal conductivity and wear resistance of the polymer composite using the network reinforcement. Two different composite specimens were prepared with an equal quantity of reinforcement with different geometric form - one with discrete particles and another with the interconnected network. The thermal conductivity and tribological properties of the composites were measured. In particle reinforced composite, the presence of low thermal conductive matrix between the discrete particles act as a barrier for heat conduction and does not enhance the thermal conductivity considerably. In the case of network reinforced composite, the three-dimensional continuity provides an effective heat transfer path and increases the thermal conductivity significantly. The reinforcement in the form of network reduces the wear significantly compared to discrete particle form. The struts in the network reinforcements enhance the strength and arrest the removal of material from the surface.
Digital Image Correlation (DIC) is a non-contact method to analyse the deformation of materials that can measure displacement or strain behaviour during tensile loading. In this study, DIC is used to measure the deformation of cross-ply carbon fibre reinforced plastics (CFRP) laminates and for the detection of damages in them. The objective of this study is to measure the deformation around the damages in cross-ply CFRP laminates by using the DIC system from both width and thickness directions. For this purpose, thick CFRP [04/9024]s and thinner [0/906]s laminates were tested. In cross-ply laminates, usually a straight transverse crack will initially occur in 90 degree ply followed by the following damages such as delamination, fiber fracture, and etc. To start, straight transverse cracks are induced in the laminates by using an artificial crack method. Then, X-ray radiography is used to detect the location of the straight cracks in order to be used for DIC observation to examine the strain distribution around the existed cracks. The DIC observation from the surface of the laminate around the cracks area clearly showed how strain is distributed from one crack to another adjacent crack. From the result, secondary mode damages of matrix cracking such as oblique and curved cracks can also be observed and are being discussed in this paper.
Research and development of SiC/SiC composite materials as structural members of aerospace engines is progressing. In order to manufacture SiC/SiC composites with excellent high-temperature characteristics, the SiC fibers which have high mechanical properties at high temperature are necessary; thus, further development of SiC fibers is considered a critical issue. In addition, the development of low-cost SiC fibers is necessary for the practical application of SiC/SiC composites. Here, the low-cost SiC fibers can be fabricated by dry spinning method. In the dry-spinning method, the raw material, Polycarbosilane (PCS) is dissolved in an organic solvent and the solution is spun at room temperature. As high-molecular-weight Polycarbosilane is prepared in advance, the infusible process conventionally required in the melt-spinning method is not required. In this study, to evaluate the differences among dry-spun SiC fibers fabricated under various conditions, monofilament tensile tests were conducted. Examination of the fracture surface and elemental analysis of arbitrary cross-sections were then performed to investigate the effects of the fabrication conditions. The tensile strength results indicated that defects were suppressed by excluding low-molecular-weight components and that heat treatment between 1300°C and 1500°C resulted in the maximum strength. Weibull analysis revealed that the dry-spun fibers exhibited lower tensile strength but smaller variation of fiber strength than that of the melt-spun fiber because the dry-spun fibers were more homogeneous. However, evaluation of the crystallinity indicated that the interference pattern derived from the crystal was unclear in the dry-spun fibers but clear in the melt-spun fiber. Therefore, it was suggested that the dry-spun fibers exhibited lower crystallinity than the melt-spun fiber. In addition, the dry-spun and melt-spun fibers exhibited similar C/Si ratios, whereas a large amount of oxygen was detected on the surface of the dry-spun fiber relative to that on the surface of the melt-spun fiber. Further improvement of the mechanical properties is expected upon increasing the molecular weight of the raw material and improving the microstructure.
The derailment coefficient, which is calculated based on the wheel-rail contact forces, indicates the running safety of a railway vehicle with respect to flange climb derailment. The value of the derailment coefficient changes constantly due to numerous factors associated with the vehicle and track conditions while the vehicle runs on a service line. Therefore, it is desirable to monitor the state of the wheel/rail contact in order to ensure the running safety. Recently, a new monitoring bogie, which can measure the derailment coefficient during commercial operations, has been developed and introduced into some service lines. Large-scale data have been collected by this monitoring bogie. In this paper, the temporal subtraction analysis is carried out for preparing appropriate plan for reducing the derailment coefficient based on these data. In the analysis, the vehicle running position is important for accurate calculation of the difference between two waveforms. However, the vehicle running position contains errors because of the accumulated error of integral calculation of the vehicle velocity. The present paper proposes a method which modifies the running position along track so that the two waveforms are well matched. The proposed method is based on DP matching, and the waveforms of the track irregularity of twist estimated by the monitoring bogie are used in the method. After DP matching, an example of temporal subtraction analysis of the derailment coefficient between two periods is performed. Finally, by using the long-term measurements acquired by the monitoring bogie, the monthly variation of the derailment coefficient for a certain spot on the track is shown as a practical example.
Carbon nitride has noteworthy properties including high hardness levels. If the c-C3N4 or β-C3N4 structure can be synthesized, then hardness levels higher than that of diamond can be obtained. It is important to clarify the effect of ion impact on the growth of crystalline carbon nitrides on the synthesis of super-hard carbon nitrides. The ion beam-assisted deposition (IBAD) technique provides independent control over parameters, such as ion energy, temperature, and arrival rate of the atomic species during deposition. In this study, we investigated the structure and composition of a carbon nitride film prepared using graphitic carbon nitride as the evaporation source for the IBAD. The graphitic carbon nitride was formed into a pellet by press molding. The film deposited without nitrogen ion beam was obtained by evaporation using the pellet molded at 200 °C and 300 °C as the evaporation source. An amorphous carbon nitride film was obtained by IBAD using g-C3N4 as the evaporation source. The main chemical bonding in the carbon nitride film changed from C-N=C to C-C by varying the acceleration voltage of the nitrogen ion beam. Accordingly, the hardness of the film was increased. The hardness of the film at an acceleration voltage of 500 V was 23 GPa. This is due to the breaking of the CN bond by the ion beam, depending on the acceleration voltage of the ion beam.
This paper describes the fabrication of a metal matrix piezoelectric composite using surface-oxidized nickel fiber as the internal electrode. Piezoelectric ceramics, which have excellent piezoelectric properties, are widely used as energy conversion materials. However, their application is limited by their brittleness. To solve this problem, a metal-core piezoelectric ceramic fiber/aluminum composite has been developed by using the interphase forming/bonding method. Here, a piezoelectric ceramic is reinforced by embedding it in an aluminum matrix, and this process causes the piezoelectric ceramic to have better mechanical properties than a bulk ceramic. However, this composite has some serious disadvantages considering that it cannot be designed to possess arbitrary piezoelectric properties because the metal-core piezoelectric fiber is formed by the extrusion method, so that the sectional shape cannot be arbitrarily changed. In this paper, a metal matrix piezoelectric composite using a surface-oxidized nickel fiber as the internal electrode is proposed. This composite provides design flexibility in that its piezoelectric property can be changed by varying the size and materials of the composite. The fabrication procedure of this composite consists of three steps: oxidation of the internal electrode, molding and sintering of the piezoelectric ceramic, and embedding of the piezoelectric ceramic into the metal matrix. The proposed composite is fabricated under optimized oxidizing and molding conditions. An impact test is performed on the fabricated composite, and the output voltage is measured. The test results indicate that the composite is capable of generating piezoelectricity. Overall, the study results substantiate the validity of the concept and fabricating method of the proposed composite.
Influence of stepwise ram motion, one of practical ram motion controls of servo press, on shape and dimensional accuracies of forged billet was investigated in cold cup forging process by the finite element analysis. In the process with stepwise ram motion, the billet inserted in the container was forged by the punch with upper ram of press, and the punch was operated with repetition of advance and pause modes. Following four stages were analyzed; (i) forging, (ii) removal of the punch from the forged billet, (iii) ejection of the forged billet from the container by the knockout punch and (iv) air cooling of the forged billet. In the analysis, the shape and dimensional changes of the inner wall of the billet during the four stages were investigated with several stepwise ram motions under the same forging duration. It is found that repetition of the punch advance with short stroke reduces heterogeneity of the temperature and stress distributions, so that the shape and dimensional accuracies of the inner wall of the forged billet were improved. The results of the finite element analysis were confirmed to be qualitatively agreed with the results of forging experiment on a link-type servo press.
The micro-pressure wave (MPW) phenomenon caused by a high-speed train entering a tunnel consists of three stages: generation of the tunnel compression wave upon train entry, propagation of the tunnel compression wave through the tunnel, and emission of the MPW outward. Model experiments using train launcher facilities (TLFs) are effective for analyzing MPWs. However, the use of those facilities to study the latter two stages, i.e., the compression wave propagation and MPW emission, is hindered by two problems: high costs required for facility operation and construction, and low data productivity. Compression wave generators can potentially provide reasonable experiments. In this study, a new, simple facility was developed for the simulation of tunnel compression waves. The proposed generator consists of small solenoid valves, a pressure chamber, compressor, power supply system, and tunnel model. The performance analyses indicate that the compression waves generated by the designed facility effectively simulate tunnel compression waves generated by train entry. The pressure rise and wavelength of the compression wave are controlled by adjusting the chamber pressure and the voltage applied to the valves. The generator is expected to provide sufficient data to develop measures against MPWs in the propagation and emission stages as it reduces the required time by over 60% compared to that required by TLFs for each generation of the compression waves.
This paper treats the Joule heat welding of thin Pt wires having various diameters. Joining of fine-scale materials, such as micro- or nanowires, has been essential to create advanced materials systems. Joule heat welding is one of the suitable way for this purpose. It has been reported that thin wires were welded together under the supply of constant direct current, and the welding condition was sensitive to the thermal boundary conditions around the wires under the current supply, which was affected by the heat transfer from the wire surface to the ambient and the heat conduction at the ends for the current supply. The diameters of thin Pt wires were 0.8-20 μm, and the current required to cut the wire by Joule heating was investigated. The temperature of the wire having the smaller diameter was easily increased by Joule heating, and this became remarkable with increasing the slenderness ratio, i.e., the ratio of the diameter to the length for current supply. An index related to the temperature of the wire under the current supply was introduced to describe the thermal boundary conditions around the wire. The behavior of the index against the diameter was approximated by the exponential functions, and the thermal boundary conditions around the wires having various diameters became predictable. Finally, the validity of the thermal boundary conditions determined and predicted in this study was verified by conducting the experiments to cut and weld the wires by Joule heating.
Multi-material structure is expected to be the main scheme to construct automobiles. Many methods have been studied to properly fix or bond dissimilar materials. The fixing by the bolts and nuts is one of the primary fixing methods, and has the advantage of easy assembly and disassembly. The interfacial stiffness of the bolted joints is lower than the stiffness of the base materials and varied by the clamping force of the bolts and nuts, because the micro asperities formed on the interfaces just contact each other. The contact analysis by using the surface profile of the interfaces in microscale is one of the accurate estimations. However, the estimation method of the interfacial stiffness in macroscale is also necessary for the in-situ evaluation. This study has developed an estimation method of the interfacial stiffness by the inverse analysis of the clamping force and the natural frequency of the structure. The inverse analysis algorithm introduces the mathematical model of the interfaces in which the contact of the surfaces is assumed to be the contact of the elastic asperities whose peak heights obey the Gaussian distribution. The hammering test was conducted by using the specimen which consisted of the steel plate and the aluminum alloy plate joined by the bolts and nuts. Moreover, as the contact analysis, the finite element method simulated the contact of the asperities formed on the interfaces by using the surface profile of the interfaces. The results showed that the proposed method could estimate the interfacial stiffness which reproduced the natural frequency of the specimen subjected to the clamping force of the bolts and nuts. The interfacial stiffness estimated by the proposed method was comparable to that calculated by the contact analysis.
Aligned MWCNT/epoxy composites made with the three types of the multi-walled carbon nanotubes (MWCNTs) with different thermal annealing temperature have been prepared, and the tensile tests and thermal expansion tests of the composites in the MWCNT alignment direction were conducted to evaluate the effects of crystallinity of MWCNTs on the mechanical and thermal expansion properties of aligned MWCNT reinforced epoxy composites. Additionally, the coefficients of thermal expansion (CTEs) of the MWCNTs in the axial direction were computed by using the Young's modulus of the MWCNTs and the CTE of the composites in Turner's model. The annealing temperatures of the MWCNTs were 2400°C and 2900°C. It was shown that the thermal annealing of MWCNTs was effective for improving the crystallinity of the MWCNTs, while it had no major effects on both tensile strength and Young's modulus of the composites. This is mainly because the thermally annealed MWCNTs themselves possessed almost comparable nominal tensile strength (~4-5 GPa) and Young's modulus (~200 GPa) compared with the as-grown MWCNTs. On the other hand, we demonstrated by thermal expansion testing that the thermal contraction of the composites in the nanotube alignment direction was observed by the addition of MWCNTs. All the MWCNTs possessed negative CTEs and the CTEs tend to become more negative with increasing annealing temperature. This is probably because of a decrease in the number of small defects (vacancies and Stone-Wales defects) and intershell cross-linking defects associated with sp3 carbons, and an increase in the sp2 carbons owing to the high-temperature thermal annealing.