Kwang Seop Jeong

Composite side-door impact beams for passenger cars

Abstract The fuel efficiency and emission gas regulation of passenger cars are two important issues nowadays. The best way to increase fuel efficiency without sacrificing safety is to employ fibre-reinforced composite materials in the body of cars because fibre-reinforced composite materials have higher specific strengths than those of steel. In this study, the side-door impact beam for passenger cars was developed using glass-fibre-reinforced composite materials as metals usually have a lower capacity of impact absorption energy at low temperature compared with that of glass-fibre-reinforced composite materials. Static tests were carried out to determine the optimum fibre stacking sequences and cross-sectional thickness for the composite impact beams taking consideration of the weight saving ratio compared to the high strength steel. Dynamic tests were carried out at several different temperatures using the pneumatic impact tester, which was developed to investigate the dynamic characteristics of impact beams at a speed of 30 mph. Also, finite-element analyses were performed using ABAQUS, a commercial software to compare the simulated characteristics of the impact beams with the experimental results. From the comparison, it was found that the results from the finite-element analyses showed good agreement with the experimental results, although several assumptions were made in the finite-element analyses.

Development of the anthropomorphic robot with carbon fiber epoxy composite materials

Abstract The material for the robot structure should have high specific stiffness (stiffness/density) to give positional accuracy and fast maneuverability to the robot. Also, the high material damping is beneficial because it can dissipate the structural vibration induced in the robot structure. This cannot be achieved through conventional materials such as steel and aluminum because these two materials have almost the same specific stiffnesses which are not high enough for the robot structure. Moreover, steel and aluminum have low material dampings. Composites which usually consist of very high specific modulus fibers and high damping matrices have both high specific stiffnesses and high material dampings. Therefore, in this work, the forearm of an anthropomorphic robot which has 6 degrees of freedom, 70 N payload and 0·1 mm positional accuracy of the end effector was designed and manufactured with high modulus carbon fiber epoxy composite because the magnitudes of the mass and moment of inertia of the forearm of an anthropomorphic robot are most important due to its farthest position from the robot base. Two power transmission shafts which deliver the power of the motors positioned at the rear of the robot forearm to the wrist and the end effector were also designed and manufactured with high modulus carbon fiber epoxy composite to reduce weight and rotational inertia. The mass reduction of the manufactured composite forearm was 15·9 kg less than the steel forearm. The natural frequencies and damping capacity of the manufactured composite arm were measured by the fast Fourier transform method and compared to those for the steel arm. From the test, it was found that both the fundamental natural frequency and damping ratio of the composite arm of the robot were much higher than those of the steel arm.

Design and manufacture of a three-axis ultra-precision CNC grinding machine

Abstract A three-axis CNC grinding machine tool for the ultra-precision mirror surface grinding of advanced materials such as ceramics and other hard and brittle materials has been designed. The grinding machine is composed of the air spindle, a high-damping resin concrete bed, and a three-axis CNC controller with high resolution AC servo motors. For the stiffness calculations of the grinding machine, a new modeling method for linear motion guides and ball screws using the three dimensional finite-element method was introduced. From comparison of the calculated results with the experimental results, it was found that the modeling method gives accurate results in the prediction of the stiffness of machine tools. Based on the results, a prototype three-axis CNC grinding machine was designed and manufactured. To investigate the dynamic properties of the grinding machine, the natural frequencies and damping of the spindle and the headstock were measured experimentally. Also, the mode shape of the machine tool x-table at the first natural frequency was obtained experimentally. From the grinding operation of ceramic materials, it was found that the prototype grinding machine tool produced mirror surfaces on aluminum oxide and titanium carbide, with arithmetic surface roughnesses of less than 50 nm.

Static and Dynamic Torque Characteristics of Composite Cocured Single Lap Joint

In this paper, the static and dynamic torque capacities of the cocured joints were observed with respect to several bonding parameters such as surface roughness, bonding length and stacking angle and compared with those of conventional adhesively bonded joints. In order to analyze the stresses of the cocured joint, finite element analysis was performed incorporating the nonlinear shear behavior of epoxy resin. The dependence of the static torque capacities on the bonding parameters was investigated numerically.

Strength analysis of adhesively-bonded tubular single lap steel-steel joints under axial loads considering residual thermal stresses

Abstract The static tensile load bearing capability of adhesively-bonded tubular single lap joints calculated using linear mechanical adhesive properties is usually far less than the experimentally-determined one because the majority of the load transfer of adhesively-bonded joints is accomplished by the nonlinear behavior of the rubber-toughened epoxy adhesive In this paper, both the nonlinear mechanical properties and the residual thermal stresses in the adhesive resulting from joint fabrication were included in the stress calculation of adhesively-bonded joints. The nonlinear tensile properties of the adhesive were approximated by an exponential equation which was represented by the initial tensile modulus and ultimate tensile strength of the adhesive. From the tensile tests and the stress analyses of adhesively-bonded joints, a failure model for adhesively-bonded tubular single lap joints under axial loads was proposed.

Interlaminar shear behavior of thick carbon/epoxy composite materials

The interlaminar shear behavior of thick carbon/epoxy composite laminates was investigated using the Iosipescu shear test. In order to manufacture thick test specimens, both the conventional autoclave cure cycle recommended by prepreg manufacturer and the modified autoclave cure cycle incorporating cooling and reheating steps were used. A 3-dimensional linear finite element analysis was performed to assess the uniformity of the shear stress field in the test section as well as to predict the failure mode of the specimen. For more accurate analysis of the stress field, contact elements were used between the specimen and the fixture, and the shear stress field in the thickness direction was taken into account. From the analysis, the failure region in the specimen was predicted and the correction factor was calculated to compensate for the non-uniformity of the shear stress field in the gage section. From the shear test, the interlaminar shear strength and shear modulus were obtained, and the interlaminar properties of the specimens manufactured by the conventional autoclave cure cycle were compared with those of the specimens manufactured by the modified autoclave cure cycle.

Development of the composite flexspline for a cycloid-type harmonic drive using net shape manufacturing method

Abstract The flexspline for a harmonic drive must be flexible in the radial direction for the elastic deformation, but must be stiff in the torsional direction for accurate transmission of rotational motion. Since these requirements cannot be satisfied simultaneously with conventional metals such as steel or aluminium, in this work the carbon fiber epoxy composite material was employed for the flexspline material in order to increase the torsional stiffness by tailoring the stacking sequence and to improve the manufacturing productivity by moulding rather than machining. The toothed composite flexspline was manufactured with the elastomeric cascade tooling that is composed of the steel tooth die, the silicon rubber mandrel and the cone-shaped steel core. Also, the steel flexspline with the same dimensions of the composite flexspline was manufactured by CNC wire cutting method. The static and dynamic performances of the composite flexspline and the steel flexspline were experimentally tested. From the test results, it was found that the developed composite flexspline had better flexibility in the radial direction and high damping capacity at the fundamental natural frequency.

Design and manufacture of the composite flexspline of a harmonic drive with adhesive joining

Abstract The harmonic drive, which is composed of a circular spline, a wave generator and a flexspline, is a compact, light-weight, and precise torque transmission mechanism with little backlash. From these components, the flexspline is the key element for motion transmission. It must be flexible in the radial direction but stiff in the tangential direction to accurately transmit rotational motion. In order to satisfy this dual role, the conventional steel flexspline is usually manufactured as a thin cup shape which requires a large amount of machining using special jigs. Because of the thin cup shape, the steel flexspline produces noise and vibration when operated at high speed. Since the dual role cannot be satisfied effectively with conventional isotropic materials, anisotropic composite materials have been considered. In this paper the cup section of the flexspline was manufactured with carbon-fiber epoxy composite material and the tooth section using steel. Then the two components were joined by adhesive bonding. Also, in order to make the manufacture of the steel flexspline easy and reduce the noise and vibration of the harmonic drive, the cup and tooth sections were manufactured separately and adhesively bonded. The static torque transmission capabilities and the vibration characteristics of the composite flexspline with adhesively bonded steel teeth and the steel flexspline with adhesively bonded steel teeth were experimentally tested. From these tests it was found that the flexspline manufactured with adhesive bonding had sufficient torque transmission capabilities and both the composite flexspline and the bonded steel flexspline had better dynamic characteristics than the conventional one-piece steel flexspline.

Experimental investigation of the dynamic characteristics of carbon fiber epoxy composite thin beams

Abstract The dynamic characteristics of high strength symmetrically laminated carbon fiber epoxy composite thin beams were experimentally investigated in a vacuum chamber equipped with a fiber optic vibrometer and the electromagnetic hammer. The measured dynamic characteristics were compared to those calculated by the macromechanical theory based on the anisotropic plate theory and the Bernoulli-Euler beam theory. From the comparison, it was found that the macromechanical theory could accurately predict the dynamic characteristics of the carbon fiber epoxy composite thin beams when the undirectional properties of the composite material were known.

Application of Adhesive Joining Technology for Manufacturing of the Composite Flexspline for a Harmonic Drive

Abstract A new manufacturing method for the cup-type composite flexspline for a harmonic drive was developed using adhesive joining technology to obviate the manufacturing difficulty of the conventional one-piece cup-type steel flexspline and to improve the dynamic characteristics of the flexspline. In this method, the boss, tube and tooth sections of the flexspline were designed and manufactured separately, and adhesively bonded. The tube section was manufactured with high strength carbon fiber epoxy composite material and its dynamic properties were compared with those of the conventional steel flexspline. The torque transmission capability of the adhesively-bonded joint was numerically calculated using the nonlinear shear stress-strain relationship which was represented by an exponential form. From the test results of the manufactured composite flexspline and the conventional steel flexspline, it was found that the manufactured composite flexspline had better torque transmission characteristics. Also, ...