Masayoshi Abo

Titanium tends to seizure with other metals, so titanium unfits thread rolling for dental implant with φ3mm diameter or less. Therefore we lubricate the contact point and prevent the seizure by applying a textured surface on the die. We were examined for the textured surface for reducing the shear stress by plastically deformed analysis between titanium material and die, and fluid analysis of the oil around the textured surface. From this analysis, texture provides an effective of low-friction, and a dimple type texture reduces shear stress by 28%.

A new type of solid particle impact test, which is called Micro-Slurry-jet Erosion (MSE) test, is proposed recently. MSE test can evaluate the wear properties of thin, single layered or multilayered physical vapor deposited (PVD) coatings. In the MSE test, a slurry containing 1.2m alumina particles was impacted at high velocity about 100m/s perpendicular to thin PVD coatings. But MSE test needs to choose both of the impact velocity and the impact angle from the information about the grain size of alumina particle, or thickness and mechanical properties of hard coating , to obtain the optimum wear rate. The Discrete Element Method (DEM) is a numerical method used to compute the movements of particle in the slurry jet or fracture of brittle specimen consisted of a large number of particles such as grain architecture in the hard coating. This paper explores for the impactive fracture simulation, i.e. the crack initiation and propagation in thin hard coating, caused by the attack of slurry jet using the DEM model. A mathematical model taking into account adhesion, abrasion and impact wear which occur between the alumina particle in slurry and the thin hard coating is derived in order to predict the loss of material on coating. Our DEM simulated predictions are compared to published experimental data.

On a pin-on-disk tribosystem with a silicon nitride ball-ended pin and flat disk pair, ball motion during sliding was examined experimentally. A dynamic vibration model for the tribosystem was investigated by a computer simulation. In the experimental setup, small angular misalignment has existed between rotating disk and pin axes, without sinusoidal deflection of disk face in the direction of pin axis, that is loading direction, then the pin could not contact with the disk surface at exact right angle. The simulation showed that small angle deviation of only 0.1degrees from 90degrees induced inevitably some bouncing vibration. This occurred at specific rotational speeds of the disk, where the ball has repeated a jump and subsequent collision with the disk surface. The highest wear was recognized under the strongest bouncing vibration. The wear behavior suggested that wear rate of silicon nitride depends on numbers of collision and impact load thereby. The dynamic motion of the ball and related wear rate was well explained by the computer simulation.

In a pin-on-disk tribosystem with a silicon nitride ball-ended pin and flat disk pair, when the pin can not contact with the disk surface at exact right angle, caused by a misalignment between rotating disk axis and pin axis, some bouncing vibration of the ball often takes place during sliding, as shown in the previous paper. Occurrence of bouncing vibration was computer-simulated with the range of pin-disk contact angle between 90degrees+/-1degrees. The ball motion in the simulation model for the tribosystem is defined to be one-degree-of-freedom per independent mode of motion in the normal and tangential directions. To prevent possibly bouncing vibration, the following means are effective: decreasing misalignment between the axes and moment of inertia and stiffness of pin support system and increasing damping coefficient of pin support system and decreasing coefficient of restitution of the ball against the disk. The bouncing vibration behavior also depended on the kinetic friction variation with siding velocity.

Adhesive wear under vibratory load was investigated using a pin-on-disk apparatus. Wear tests were conducted with brass and aluminum pins sliding against a stainless steel disk without lubricant. Vibratory load with frequency ranging from 10 to 100Hz was applied to the contact point together with static load. On brass, specific wear amount did not change by vibration, and on aluminum, the vibration provided wear reduction of about 5%. Such a change in wear amount was found to be determined from dependence of wear rate on static applied load.

Various implants are employed to recover the function of the femur by providing mechanical fixation. However, these implants can have a very limited life and require replacement. In order to optimize implant life, it is necessary to improve the design of components and implantation techniques, which is clearly also beneficial to both patients and hospitals. The determination of the real displacement patterns across implanted bone is important in developing alternative and improved implants. Holographic interferometry, a displacement analysis technique permitting whole-field inspection of deformation patterns, was used as the experimental method. In this study, a one-shot holographic interferometry is developed for simultaneous measurements of three aspects of femur. The optical system consists of two sets of plane mirror each arranged to face the postcrior and antcrior of fcmur. Three objective images reconstructed from holograms are constructed in the CAD system and analyzed. By the proposed method, experiments become easy and the reliability of the data is improved. The feasibility of proposed method is shown by measuring displacement of the intact model bone.

In this study, stress condition of the femur with fixation using the Gamma nail, which is widely used as the intramedullary nail device of trochanteric fracture, is investigated by three-dimensional finite element method. Imitation bone model, which has mechanical properties as same as the human bone, is used to analyze. The stress analysis of the femur before and after the implantation of the nail is carried out in detail. As the results, the stress considerably decreases at the proximal part by the nail insertion, but the stress concentration appears around the nail tip. The stress rapidly increases, when the gap between nail and cancellous bone becomes small. The existence of the locking screw does not affect the stress distribution of the circumference. In the meantime, the stress distribution is considerably similar to the intact bone, when the nail is made of titanium alloy, which has material properties closer to the cortical bone in comparison with stainless steel. © 2003, The Japan Society of Mechanical Engineers. All rights reserved.

Various implants are employed to recover the function of the femur by providing mechanical fixation. However, these implants can have a very limited life and require replacement. In order to optimize implant life, it is necessary to improve the design of components and implantation techniques, which is clearly also beneficial to both patients and hospitals. The determination of the real displacement patterns across implanted bone is important in developing alternative and improved implants. Holographic interferometry, a displacement analysis technique permitting whole-field inspection of deformation patterns, was used as the experimental method. In this study, a one-shot holographic interferometry is developed for simultaneous measurements of three aspects of femur. The optical system consists of two sets of plane mirror each arranged to face the postcrior and antcrior of fcmur. Three objective images reconstructed from holograms are constructed in the CAD system and analyzed. By the proposed method, experiments become easy and the reliability of the data is improved. The feasibility of proposed method is shown by measuring displacement of the intact model bone.

In this study, stress condition of the femur with fixation using the Gamma nail, which is widely used as the intramedullary nail device of trochanteric fracture, is investigated by three-dimensional finite element method. Imitation bone model, which has mechanical properties as same as the human bone, is used to analyze. The stress analysis of the femur before and after the implantation of the nail is carried out in detail. As the results, the stress considerably decreases at the proximal part by the nail insertion, but the stress concentration appears around the nail tip. The stress rapidly increases, when the gap between nail and cancellous bone becomes small. The existence of the locking screw does not affect the stress distribution of the circumference. In the meantime, the stress distribution is considerably similar to the intact bone, when the nail is made of titanium alloy, which has material properties closer to the cortical bone in comparison with stainless steel. © 2003, The Japan Society of Mechanical Engineers. All rights reserved.

In the previous paper, frictional vibration with jumping induced on a silicon nitride pin-on-disk tribosystem was investigated by a computer simulation, showing good agreement with the experimental results. This paper discusses the wear rate of pin (ball) and disk under the frictional vibration with jumping. With the increase of sliding velocity, the contact condition between ball and disk changes from stable contact to unstable one with jumping of the ball. So the real contact time drops below 1/100 of total sliding time, and then wear rate decreases less than 1/10 of wear rate without jumping. Wear rate estimation was possible under the consideration on application of Hertzian theory to repeated impact stress during intermittent contact.

On a pin-on-disk test configuration, some bouncing vibration of the pin specimen takes place especially under higher sliding velocity. In the present study, jumping motion of a silicon nitride ball sliding against a silicon nitride flat disk was examined experimentally and by a computer simulation. As the source of jumping motion, a sinusoidal deflection of the disk surface developed by disk rotation was transmitted to the ball that is an element of vibration body in a single-degree-of-freedom linear system. During sliding With jumping, the ball repeats in general a jump and subsequent collision against the disk surface. The ball rebound motion at each collision was assumed to be determined from the coefficient of restitution. Actually measured coefficient of restitution was found to be about 0.8, irrespective of contact conditions, such as sliding velocity, sliding distance that relates to wear and geometry of real contact, etc. The present computer simulation could provide the actual dynamic behavior of the sliding body and the following result was obtained: Jumping can be suppressed by decreasing sliding velocity, mass of sliding body and coefficient of restitution between sliding pair and increasing system stiffness and applied load to the contact.

It is important to investigate the influence of microstructure on the behavior of welded joint for the design and life assessment of the welding structure. Tbis paper shows the possibility of applying holographic interferometry to the analysis of displacement behavior of welded joints. The specimens were prepared from the joints of pressure vessel made by multilayer welding. The' deformation of the cylindrical surface with base metal, heat affected zone (HAZ) and weld metal structure under the axial load are measured continuously by real-time holographic interferometry and the effect of microstructure is discussed The experimental results indicate that the location of HAZ for loading direction has predominant effects on the deformation of weldad joints.

It is important to investigate the influence of microstructure on the behavior of welded joint for the design and life assessment of the welding structure. Tbis paper shows the possibility of applying holographic interferometry to the analysis of displacement behavior of welded joints. The specimens were prepared from the joints of pressure vessel made by multilayer welding. The' deformation of the cylindrical surface with base metal, heat affected zone (HAZ) and weld metal structure under the axial load are measured continuously by real-time holographic interferometry and the effect of microstructure is discussed The experimental results indicate that the location of HAZ for loading direction has predominant effects on the deformation of weldad joints.