In order to study the subsurface crack initiation and propagation mechanism of high strength steel under a very high cycle fatigue regime, computational simulation with fracture surface topographic analysis (FRASTA) was carried out for subsurface fatigue crack initiated specimens of high speed tool steel (JIS SKH51) obtained from the rotating bending fatigue test in air. A remarkable area formed around the nonmetallic inclusion inside the fish-eye region on the fracture surface, which is a feature on the fracture surface in super long fatigue. This so-called GBF (granular-bright-facet) was observed in detail by a scanning probe microscope and a three-dimensional SEM. The GBF area, in which a rich carbide distribution was detected by EPMA, revealed a very rough and granular morphology in comparison with the area inside the fish-eye. It was clearly simulated by FRASTA that multiple microcracks were initiated and dispersed by the decohesion of a spherical carbide from the matrix around a nonmetallic inclusion, and converged into the GBF area during the fatigue process. After the formation of the GBF area, interior cracks grew radially and a fish-eye pattern formed on the fracture surface.
Microfracture process of 3mol% yttria stabilized zirconia (3Y-TZP) for artificial joints was evaluated using the acoustic emission technique. In order to investigate the effects of environment and strain rate on the microfracture process, four point bending tests were carried out in air and physiological saline (P.S.) at various loading rates. From the results of AE behavior, rapid AE increasing point was observed before the final unstable fracture. It was suggested from the previous work that the AE increasing point corresponds to the maincrack formation. The critical stress for maincrack formation, σC, was determined from the bending stress at the AE increasing point. The critical stress as well as bending strength, σB, decreased in physiological saline. In particular, the decrease in critical stress was remarkable. It was then understood that stress corrosion cracking (SCC) by water in physiological saline affected maincrack formation rather than the final fracture. Consequently, it was suggested that the evaluation of σC is essential for the reliability assessment of bioceramics.
The size effect of the diameter has been assessed for the tensile strength of Tyranno ZMI fiber. Uniform diameter section in sample fibers has been selected as tensile test sample. The single fibers of measured diameters have been tensile tested to provide two groups of data, i.e., “small diameter” group and “large diameter” group. The parameters of single-modal Weibull model showed inconsistency on the two groups, thus the Weibull parameters have shown the dependence on the sample diameter. Scanning electron microscope (SEM) analyses had revealed characteristic fracture patterns of “extremely weak” samples only in “large diameter” group. The key information for improving the reliability was then discussed through coupling the Weibull scaling and the fracture surface analyses. The potential in the strength improvement has been assessed for an imaginary fiber, which does not contain the sources of the characteristic fracture patterns.
Metal-fiber-preform-reinforced aluminum alloy composites were prepared by the infiltration of molten metal using a low-pressure casting process. The infiltration behavior of the filling pattern and the velocity profile obtained for alloys fabricated by the low-pressure casting process was investigated. A thermocouple was inserted into the preform to observe the infiltration behavior. The infiltrations at pressure acceleration times of 1sec, 2sec and 5sec under a constant pressure of 0.4MPa were respectively complete in 0.4sec, 0.8sec and 1.2sec. Under these conditions, molten aluminum alloy successfully infiltrated on FeCrSi metal fiber preform by the low-pressure casting process. The porosity of composites was observed to determine their reliability. An automobile piston was developed with an FeCrSi-reinforced aluminum alloy that has 0% porosity using the optimal applied pressure and pressure acceleration times.
Thermal residual stress (TRS) created in metal matrix composite influences the mechanical properties of composites. In this paper, we present the TRS-modulated tensile properties of continuous SiC fiber reinforced titanium (SiC/Ti) composite. The magnitude and distribution of TRS inside SiC/Ti were evaluated by using a simple 1-D beam model considering fiber-matrix structure and then a full 3-D FEM model. The bending of the SiC/Ti specimen resulting from the asymmetrical fiber placements was used as a measure to verify the pertinence of the mechanical models. A 3-D FEM simulation accounting all TRS information gives a good prediction of the composite’s tensile properties.
This paper describes development of high performance CFRP/metal active laminates mainly by investigating the kind and thickness of the metal. Various types of the laminates were made by hot-pressing of an aluminum, aluminum alloys, a stainless steel and a titanium for the metal layer as a high CTE material, a unidirectional CFRP prepreg as a low CTE/electric resistance heating material, a unidirectional KFRP prepreg as a low CTE/insulating material. The aluminum and its alloy type laminates have almost the same and the highest room temperature curvatures and they linearly change with increasing temperature up to their fabrication temperature. The curvature of the stainless steel type jumps from one to another around its fabrication temperature, whereas the titanium type causes a double curvature and its change becomes complicated. The output force of the stainless steel type attains the highest of the three under the same thickness. The aluminum type successfully increased its output force by increasing its thickness and using its alloys. The electric resistance of the CFRP layer can be used to monitor the temperature, that is, the curvature of the active laminate because the curvature is a function of temperature.
By folding a thin flat sheet with periodically set slits or punched out portions into the third dimension, ultra-lightweight strong and functional core models are newly devised. The basic idea of this modeling arises from the application of origami technique to engineering. Based on the space filling models, fundamental flat cores and skew type sponge cores have been newly developed. By applying these models, such modified core models as curved cores and 3D honeycomb core are newly devised.
Anti-symmetrical laminate composites exhibit a coupling effect between tensile stress and twisting deformation, and are very attractive as blade materials for aircraft engines. Blades made of anti-symmetrical laminate composites can automatically adjust their stagger angle to a better aerodynamic configuration with changing rotational speed. Thus, the aerodynamic efficiency and stability of aircraft engines can be greatly improved. In this study, the coupled deformation properties of anti-symmetrical laminate composites were evaluated with tensile tests. Two kinds of specimens fabricated from carbon/epoxy laminate composites with different anti-symmetrical stacking sequences were tested. On the basis of the tensile-test results, the anti-symmetrical laminate composites were then used as blade materials. The coupled deformation of the test blades at high rotational speed was evaluated by spin tests and FEM analyses. It was demonstrated that test blades twisted about 4° at 10000rpm.
Since the ceramic has excellent qualities in light weight, abrasion resistance and heat resistance etc, compared with the metal, it has been actively examined in order to apply for the structures such as gas turbine and turbo charger etc, which require high strength and heat resistance. But it is not desirable to be used for the structural material since the ceramic is fragile, so the join with the metal with abundant toughnees has been studied. However, during the cooling process, the joint residual stress develops on the ceramic/metal joint by the difference in thermal expansion coefficient between two materials and it affects the bending strength significantly. Also, in order to use the joint material as the structural material, the study about the fatigue of thermal cycle of actual use statement is necessary. Therefore, to ensure security and improvement of the bending strength of joint material, the state of residual stress distribution to the high temperature-thermal cycle, and studied the effects of thermal cycle and state of residual stress distribution on the strength of joint material as well.
A prototype of autonomous mobile robot with two vision sensors for automatic welding of steel plates was constructed. The robot can move straight, steer and turn around the robot center by controlling the driving speed of the two wheels respectively. At the tip of the movable arm, two CCD cameras are fixed. A local camera observes the welding line near the welding torch and another wide camera observes relatively wide area in front of the welding part. The robot controls the traveling speed in accordance with the shape of the welding line. In the case of straight welding line, the speed of the robot is accelerated and the welding efficiency is improved. However, if the robot finds a corner of welding line, the speed is decelerated in order to realize the precise seam tracking and stable welding. Therefore, the robot can realize precise and high speed seam-tracking by controlling the travel speed. The effectiveness of the control system is confirmed by welding experiments.
Characteristics of hydrogen permeation in the stainless steel 304 modified by either facing, ion sputtering, carbon coating or annealing were investigated in order to establish the safe hydrogen-energy-infrastructure using welding. A stationary hydrogen flux from the stainless steel surface was measured by using a system with an orifice. The pressure difference of the specimen was able to maintain constant by controlling the gas flow rate from the orifice in low pressure vessel. The hydrogen permeability was low in two cases of a thin stainless steel with fine facing and that annealed at 1370K for 2 hours. In these cases, the specimens’ surfaces were considered to play hydrogen trap role and to prevent from pairing hydrogen atoms. On the other hand, high hydrogen permeability was obtained in the case of Argon plasma cleaning a low-pressure-vessel side surface. These results suggest that oxide film on the specimens’ surface prevent hydrogen desorption.
For production of complex hollow 6xxx series aluminium extrusions, porthole dies are the predominant tooling set up. In porthole dies, the billet is divided into multiple metal streams, which are rejoined in the weld chamber to form ‘longitudinal weld seams’. Fundamental understanding of the solid state bonding process, as well as the ability to detect a well bonded (or a defective) weld seam are important for the production of high quality structural hollow extrusions. A study is being conducted to investigate the solid state bonding and weld seam formation processes during extrusion. The method chosen was to use a thermo-mechanical simulator (Gleeble 3500), thereby having the ability to vary process parameters such as strain, strain rate and temperature. The alloy investigated was primary and remelt AA6082. It was determined that the key parameter for bonding is surface stretching (creation of new surface at the interface) and bonding time.
The LIGA (Lithografie, Galvanoformung, Abformung [German: lithography, electroplating, and molding]) process is one of the promising techniques for fabrication of microstructures having high aspect ratios. Microstructures as high as a few hundred µm or more are widely used for various devices, such as micro-actuators, micro-mechanisms, and micro-sensors. The key to reducing the microstructure fabrication cost of the LIGA process is by using micro replication technology. Hot embossing is attracting the attention of engineers as one such technology for economically mass-fabricating microstructures on thin plastic sheets. This technology is especially effective for precisely replicating micro patterns on relatively large sheets. This paper describes the results of research the authors recently carried out to find the optimal conditions for hot embossing in the atmosphere and in a vacuum. For a series of experiments, we prepared two types of Ni molds each containing an area of 33 × 33mm2 distributed with hole or column patterns 60µm in diameter and 1.0 in aspect ratio. The LIGA process using synchrotron radiation fabricated these patterns. From the experiments, we could determine the optimal conditions for replicating these patterns on PMMA sheets in a normal-atmosphere and vacuum environments.
We developed a method for fabricating a three-dimensional spiral micro-inductor with high inductance using the LIGA process. The spiral inductor created had a diameter of 0.5mm, and a length of 1mm. The width of the spiral line was 10µm, the pitch was 20µm, and the number of turns was 15. It was made of plated copper. The master was a brass round bar coated with PMMA resist. Deep X-ray lithography was employed to fabricate a master for a metallic mold at the NewSUBARU synchrotron radiation facility, University of Hyogo. The inductor core was made of resin by injection molding. It has a spiral micro flute on the surface. We chose the worm injection molding technique in order to avoid the parting line across the spiral line. The worm injection molding was the method─for demolding the work such as that used in loosening a screw.
We have developed a microprobe that achieves low contact resistance under low contact force only for gold pads. However, in the case of Al pads, an oxide layer formed on the aluminum pad surface obstructs stable contacting, so higher contact force with a strong probe is required. The present study attempts to enhance the strength of the probe material by improving its mechanical properties. It is said that grain downsizing, functionally alloying, or impurity addition can increase material strength. Our study has adopted impurity addition to the electroforming bath because the process can be controlled. Thus, high-strength electroformed Ni has successfully been obtained. Improved Ni has a high Vickers hardness of Hv600 compared with Hv450 for conventional nickel, and a high Young’s modulus of E=200GPa compared with E=150GPa for conventional nickel.
Al2O3-TiC powders were produced from microwave and conventional-combustion synthesized mixtures of TiO2, C and Al. Different types of precursors such as rutile and anatase TiO2, as well as carbon black, graphite and activated carbon powders were used. The different types of precursors and heating methods affected the combustion behavior. Combustion using microwaves could be achieved in less than 3 min, which was 10 times faster than conventional combustion. The composition of rutile-carbon black-aluminum gave the shortest ignition time using microwave energy, whereas the mixture containing activated carbon ignited fastest using conventional heating. Nevertheless, in both cases samples with anatase required longer time to ignite and thus gave higher combustion temperatures than ones with rutile. An incomplete combustion product observed when activated carbon was the carbon source. The synthesized powder was fragmented and angular in shape with the largest agglomerate size limited to smaller than 25 microns.
The composite material was fabricated using alumina sludge, industry waste, and aluminum powder by spark plasma sintering (SPS). Sludge of industry waste was treated to change the α alumina crystal structure at temperature 1573K for 2 hours. The bending strength of the composite materials was investigated by changing the volume fraction of sludge 0-6% and forming conditions. As a result, it was found that the sludge content mainly affected on the bending strength. The bending strength showed the highest value at 2% sludge content. From the observation of crack propagation using optical microscope, it became clear that the sludge existed as agglomerated powder in the composite material, and this sludge prevented the crack to propagate.
The microstructure and mechanical properties of purity aluminum refined with salt containing Ti and B elements have been studied in detail with Optical Microscope and MTS (Mechanical Testing and Simulation). The salt containing weight ratio of 22.2Ti : 1B has the most refining effect on the purity aluminum with the finest structure and the best mechanical properties, meanwhile it also possesses the advantages of short reacting time (within 5 minutes) and long fading time (more than 20 hours). The refining effect of the salt increases with the content of Ti and B in the melting and the refining mechanism is mainly contributed to the heterogeneous nuclei of more fine TiAl3 particles dispersed in the melting, which come from the reaction between the salt and aluminum. Purity B contained salt has little or no directly refining effect, However, B contained salt has indirect refining effect on the purity aluminum when it is added simultaneously with Ti contained salt, this may be due to that the dispersive and fine boride (TiB2) could be taken as the heterogeneous nuclei for TiAl3 particle, and then prevents the coarsening of the TiAl3 particle.
The purpose of the present study is to elucidate the “ideal strength” of the Ni and Ni3Al single crystals, the main compositions of Ni-based superalloy, from the viewpoint of the lattice stability. The unit lattices of Ni and Ni3Al, fcc and L12 ordered alloy, are subjected to the  uniaxial tension/compression and hydrostatic tension/compression by using the Vienna Ab-initio Simulation Package (VASP) with the generalized gradient approximation (GGA) and ultrasoft pseudopotential. The elastic stiffness matrix is numerically evaluated at each point in the applied deformation pass, then the lattice stability is discussed based on the positiveness of the matrix. Both Ni and Ni3Al reach the Born’s stability criteria against the bifurcation to the anisotropic Poisson’s contraction in the  uniaxial tension, while they do the spinodal criteria against the structural transformation in the  uniaxial compression and hydrostatic tension. The hydrostatic compression increases the stability and shows no limit, however, it is also suggested that the spinodal instability appears when the ideal isotropy was broken. The “ideal strength” is evaluated with these stability limits and indicated as “yield curve” on the normal strain-lateral strain or normal stress-lateral stress planes.
Higher order Mode-I elastodynamic stress and displacement fields at the tip of a crack are calculated by the perturbation method up to the 1-st order. The present method of derivation utilizes a certain condition at the crack tip and resolves the difficulty encountered otherwise. Including the 1-st order stress field we find that the well known hoop stress maximum at high crack velocity, which is considered to determine the direction of the branching, disappears when the crack is accelerated.
The in-plane problem relating to the elastodynamic response of edge crack in an infinitely long elastic strip is analyzed. Fourier transform is used to reduce the mixed boundary value problem to Fredholm integral equation of second kind which was solved numerically to calculate the stress intensity factor at the tip of the crack. Stress intensity factor for various geometry parameters and frequency has been plotted to show the effect of strip width on stress intensity factor. Also normal stress at distant points from the crack has been evaluated numerically and plotted for various parameters.
Scratch tests and pin-on-disk wear tests were performed to clarify the cracking and delaminating behavior of CrN coatings. The CrN films were coated onto an aluminum alloy substrate, JIS A2024, by an arc ion plating method. Eight types of single-layered coating and multilayered coatings were prepared by changing the bias voltage during the deposition. LCI and LCII values were not improved by increasing the number of layers. The critical loads of the single-layered coatings decreased with increasing the bias voltage. It appears that, for the multilayered coatings, the combination of bias voltages influenced the critical loads. The critical loads strongly depended on dynamic hardness and Young’s modulus. In particular, the critical loads of the multilayered coatings were influenced by the properties of the intermediate and bottom layers as well as the surface roughness, hardness and Young’s modulus of the top layer. The large film delamination for single-layered coatings deposited using a high bias voltage occurred during pin-on-disk wear tests even though the critical loads of the single-layered coatings were higher than those of the multilayered coatings. If the brittle top layer could be broken and delaminated by the sliding contact, the ductile bottom layer coated under a bias voltage of 0V could endure the complete delamination of film.
The study on the bending of an elliptical plate clamped rigidly against deflection and restrained elastically against rotation along its periphery, subjected to the uniform lateral load and in-plane force simultaneously, is performed by introducing the elliptical coordinates. The analytical solution satisfying perfectly the differential equation of deflection and the boundary conditions is exactly derived in the form of Mathieu function series. The expressions for the bending moments are also derived rigorously. The deflection and bending moments obtained here coincide with those for a simply supported elliptical plate and the perfectly clamped elliptical plate when the rotational spring stiffness is zero and infinity, respectively. A limiting case of a circular plate is discussed in detail. The effects of the in-plane force and the rotational spring stiffness on the deflection and the bending moments are calculated numerically and are presented in tables and figures.
This paper addresses a viscoplastic constitutive model that allows a consistent way of modeling positive and negative rate sensitivities of flow stress, which is associated with dynamic strain aging occurring in a certain regime of loading rates and temperatures. Based on the concept of continuum mechanics, a phenomenological constitutive model includes the use of a yield surface within the framework of unified viscoplastic constitutive equations. An extension of modeling capability to negative rate sensitivity of flow stress is accomplished through a rate-dependent format of nonlinear kinematic hardening rule that causes the back stress to be rate-dependent. The negative rate sensitivity of the back stress enable to predict the influence of prior strain rate on relaxation behavior, which means that the relaxed stress of the fastest prior strain rate has the smallest magnitude at the end of relaxation period.
In cementless total hip replacement, initial stability of the femoral component is important in the long term fixation of the femoral stem. Initial stability is closely related to the relative displacement between the prosthesis and the cancellous bone of the proximal femur. After implantation of the prosthesis, the surrounding bone is partially shielded from load carrying and starts to resorb. Stress shielding causes the loss of the proximal bone. The stress distribution of femur must be assessed to predict stress shielding. The initial stability and the stress shielding were investigated for two loading conditions approximating a single leg stance and stair climbing. Two types of stems involving a distal filling and a distal short stem were studied by the finite element method to investigate the biomechanical distal filling effects. The distal short stem produced less stress shielding at the proximal bone than the distal filling stem, while both types of stems seemed to satisfy the initial stability requirement.