Seung-Hwan Chang

Steel-composite hybrid headstock for high-precision grinding machines

During a typical machining operation in excess of 50% of the compliance (deflection) of the cutting tool comes from the headstock, with the remainder attributable to the bed, slides and structural joints. Therefore, a high dynamic stiffness for the headstocks of machine tool structures is essential to improve their performance. Since the dynamic stiffness is proportional to the static stiffness and damping, a high degree of damping is indispensable for precision grinding machines, especially when machining hard and brittle materials such as glasses and ceramics, i.e. small vibrations may affect the machined surface quality. Since fiber-reinforced composite materials have a high specific modulus, high damping and low thermal expansion it is predicted that the headstock dynamic and thermal characteristics will be improved when such materials are utilized in their manufacture. In this paper the headstock of a precision grinding machine was reinforced using glass fiber epoxy composite material. The static and dynamic characteristics were investigated analytically and experimentally in order to improve the grinding machine performance.

Microscopic investigation of tow geometry of a dry satin weave fabric during deformation

Abstract In this paper the changes in tow geometry during deformation of dry woven carbon-fibre satin-weave fabric are measured and correlated with the in-plane forces applied. The evolution of geometric tow parameters such as tow spacing, crimp angle, tow amplitude and wavelength is investigated. To observe the change in the fabric architecture, specimens from bias extension, biaxial and picture frame tests are sectioned and observed under the microscope. It is found that the different loading conditions cause differences in the evolution of tow architecture during deformation, in particular affecting the onset of ‘lock-up’. (At lock-up interactions between tows prevent further significant shear deformation.) In one picture frame test the fabric is deliberately misaligned with respect to the sides of the frame so that, during subsequent deformation, one set of tows is under tension, while the other is compressed. There is a significant difference in behaviour between the two sets of tows. The variation in deformed tow geometry with shear angle is fitted using a simple parametric model.

Damping improvement of machine tool columns with polymer matrix fiber composite material

In order to improve the damping capacity of the column of a percision mirror surface grinding machine tool, a hybrid column was manufactured by adhesively bonding glass fiber reinforced epoxy composite plates to a cast iron column. To optimize the damping capacity of the hybrid column, the damping capacity of the hybrid column was calculated with respect to the fiber orientation and thickness of the composite laminate plate and compared to the measured damping capacity. From experiments, it was found that the damping capacity of the hybrid column was 35% higher than that of the cast iron column.

Improvement of the dynamic properties of a steel-composite hybrid flexspline of a harmonic drive

Abstract The harmonic drive is a special gear-drive speed reduction system whose operation principle is based on elastic deformation rather than rigid-body motion of the general gearing system. From the components of the harmonic drive, the flexspline is the key element for the transmission of motion. It must be flexible in the radial direction, but must be stiff in the torsional direction to accurately transmit rotational motion. Because the contradictory dual role of the flexspline cannot be satisfied effectively with conventional isotropic materials, but can be achieved with anisotropic composite materials, in this paper the cup section of the flexspline was hybridly manufactured by laying-up composite material on the inside surface of the steel cup section. The static and dynamic characteristics of the hybrid flexspline were investigated with respect to the fibre volume fraction, stacking sequence and the mass ratio of the composite to steel.

How Isometric Are the Anatomic Femoral Tunnel and the Anterior Tibial Tunnel for Anterior Cruciate Ligament Reconstruction

PURPOSE The purpose of this study was to evaluate the isometry of an anatomic femoral tunnel and anterior tibial tunnel positions. METHODS Tibial tunnels were made at 2 different locations in 10 cadaveric knees: the conventional tunnel and a more anterior position. Three-dimensional computed tomography (CT) scanning was then performed at 0°, 30°, 60°, 90°, and 120°. After removal of the anterior cruciate ligament from its femoral attachment, the 2 different femoral tunnels were marked at (1) the vertical femoral tunnel point and (2) the anatomic femoral tunnel point. After scans were repeated for coordinate transformation, the change in length between the tunnels was calculated with imaging software (OsiriX, version 3.2; Apple, Cupertino, CA) and the center of rotation for the femoral tunnels was calculated with a least squares fitting algorithm. RESULTS The conventional tibial tunnel-vertical femoral tunnel combination showed the least excursion as knee flexion angle changed. The vertical femoral tunnel combination groups showed a trend toward increasing length as the knee flexion angle increased. In contrast, the anatomic femoral tunnel combination groups displayed a trend toward decreased length with increasing knee flexion. At less than 30° of flexion, the tibial anterior-anatomic femoral tunnel showed the least excursion. CONCLUSIONS The anatomic femoral tunnel was nonisometric, and the differences in isometry for each tunnel type were explained primarily by differences in relations between the centers of rotation of tunnels and tunnel position. When a femoral anatomic tunnel is chosen for anterior cruciate ligament reconstruction, the anterior tibial tunnel offers greater isometric benefits than the conventional tibial tunnel, especially in near full extension. CLINICAL RELEVANCE The distance between anatomic femoral and tibial tunnels is greatest in full extension and decreases with flexion. This would result in graft laxity. The surgeon should give consideration to a more anterior tibial tunnel position, which shows less excursion in early flexion.

Estimation of the movement of the inter-fragmentary gap of a fractured human femur in the presence of a composite bone plate

Composite bone plates made of carbon/epoxy prepregs were investigated for obtaining a more uniform strain distribution at the fracture site of human bones through finite element (FE) analysis. The fracture site was modeled by a multilayered structure. One conventional stainless steel bone plate and several composite bone plates were considered for calculating the strain distributions at the fracture site. The average stresses of bones and bone plates were also calculated for the evaluation of the stress-shielding effect. From the results of FE analysis, it was found that the composite bone plate caused an affirmative strain distribution at the fracture site, which stimulated callus generation.

Composite rotor for high-speed induction motors

Abstract In order to improve the dynamic characteristics of 3-phase AC induction motors, the squirrel cage rotor for a high speed built-in type motor spindle system was designed and manufactured with powder containing epoxy composite material and an aluminum squirrel cage. The Young’s modulus, coefficient of thermal expansion (CTE), resistivity and magnetic permeability of the epoxy containing ferrite powder and iron powder were measured with respect to powder volume fraction to determine the optimum powder volume fraction. Then the epoxy powder composite rotor was manufactured by embedding the aluminum squirrel cage into the composite. Finally, the dynamic and electrical performances of the AC induction motor equipped with the developed composite rotor were measured and compared with those of a conventional AC induction motor.

Anisometric nanocomposite hydrogels with temperature responsive compartments

Recently, anisometric structures, which are popular in nature but uncommon in artificial materials, have been actively investigated for the development of novel materials designed for sensors, optical systems, scaffolds, etc. In this study we investigated the hypothesis that the symmetry of two-compartment hydrogels influences their temperature responsive behavior and drug diffusivity. Composite hydrogels with isometric and anisometric compartments were prepared using poly(N-isopropylacrylamide), poly(acrylamide), and nanoclay. The anisometric hydrogel showed a markedly smaller volume transition and equilibrium swelling ratio than its isometric counterpart, possibly because of more restriction from the two-compartment structure. Furthermore, water retention and the release of cilostazol were significantly sustained in the case of the anisometric hydrogel. By incorporating Ag nanoparticles into one compartment, an IR responsive transition was achieved, which showed the consistent effect of the anisometric structure. Finite element analysis further confirmed the difference found in the experimental results by presenting a prevailing von Mises stress in the anisometric case. This study provides a novel engineering strategy for hydrogel properties and a fundamental understanding valuable for designing anisometric hydrogel materials.

Comparison of Flexor Tendon Suture Techniques Including 1 Using 10 Strands

PURPOSE To compare mechanical properties of a multistrand suture technique for flexor tendon repair with those of conventional suture methods through biomechanical and clinical studies. METHODS We describe a multistrand suture technique that is readily expandable from 6 to 10 strands of core suture. For biomechanical evaluation, 60 porcine flexor tendons were repaired using 1 of the following 6 suture techniques: Kessler (2-strand), locking cruciate (4-strand), Lim/Tsais 6-strand, and our modified techniques (6-, 8-, or 10-strand). Structural properties of each tenorrhaphy were determined through tensile testing (ultimate failure load and force at 2-mm gap formation). Clinically we repaired 25 flexor tendons using the described 10-strand technique in zones I and II. Final follow-up results were evaluated according to the criteria of Strickland and Glogovac. RESULTS In the biomechanical study, tensile properties were strongly affected by repair technique; tendons in the 10-strand group had approximately 106%, 66%, and 39% increased ultimate load to failure (average, 87 N) compared with those in the 4-, 6-, and 8-strand groups, respectively. Tendons in the 10-strand group withstood higher 2-mm gap formation forces (average, 41 N) than those with other suture methods (4-strand, 26 N; 6-strand, 27 N; and 8-strand, 33 N). Clinically, we obtained 21 excellent, 2 good, and 2 fair outcomes after a mean of 16 months (range, 6-53 mo) of follow-up. No patients experienced poor results or rupture. CONCLUSIONS The 10-strand suture repair technique not only increased ultimate strength and force at the 2-mm gap formation compared with conventional suture methods, it also showed good clinical outcomes. This multistrand suture technique can greatly increase the gap resistance of surgical repair, facilitating early mobilization of the affected digit. TYPE OF STUDY/LEVEL OF EVIDENCE Therapeutic IV.

A study on the bonding strength of co-cured T800/epoxy composite–aluminum single-lap joint under out-of-plane compressive pressure condition

In this paper, the bonding strengths of co-cured T800 carbon/epoxy composite–aluminum single-lap joints with and without additional pressures in the out-of-plane direction were investigated to simulate the stress condition at the interface between the composite layers and the aluminum liner of a Type III pressure vessel made by the filament winding process. All test specimens were fabricated by autoclave vacuum bag de-gassing molding under controlled forming pressures (absolute pressures of 0.1, 0.3, and 0.7 MPa including vacuum). A special device which can impose uniform additional pressures on the bonding part of the single-lap joint specimen was designed. Additional pressures were applied and, subsequently, the bonding strengths of the composite–aluminum single-lap joint specimen were estimated. After the three different additional pressures (absolute pressures of 0.1, 0.3, and 0.7 MPa) were applied to each of the specimens, the effects of the additional pressures on the bonding strengths of the co-cured single-lap joints were evaluated.