Kee Joo Kim

Fatigue Crack Growth of Glass Fiber Reinforced Aluminum Alloy Laminate (Al/GFRP) According to the Micro Hole Location

The diverse studies on Al/GFRP laminates with the circular holes, therefore, have been carried out recently. The recent studies just focused on the behavior of the fatigue crack propagation and the delamination when the shape and the size of the notches were changed. Therefore, this study evaluated the location effect of the defects in the vicinity of the circular notch of the high strength monolithic aluminum and Al/GFRP laminates on the initiation life (Ni) of the fatigue cracks, the relationship between the crack length (a) and the fatigue life (N). In addition, the fatigue crack behavior of Al/GFRP laminates was studied when the fatigue loading and the interlaminar delamination took place at the same time during crack propagation. In conclusions, (1) for the monolithic aluminum, 10% of the failure life at θ2=30° was more increased than that at θ3=60°. (2) The crack length and the fatigue life behavior of Al/GFRP laminates according to the location of the artificial defect were different from those of the monolithic aluminum. Namely, the fatigue life of θ1=0° and θ2=30° were remarkably shorter than those of θ3=60° and θ4=90°.

Simulation of Hydroformed High Strength Steel Chassis Parts

The environment and energy related problem has become one of the most important global issues in recent years. One of the most effective ways of improving the fuel efficiency of automobiles is the weight reduction. In order to obtain this goal the hydroforming technology is adapting for the high strength steel and its application is being widened. In present study, the whole process chain of chassis components (cross members) simulation and development by hydroforming technology to apply high strength steel having tensile strength of 440 MPa grade is covered. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Design) to confirm hydroformability in details. Overall possibility of hydroformable chassis parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydroforming. At the die design stage, all the components of prototyping tool are designed and interference with press is investigated from the point of geometry and thinning.

Evaluation of Fatigue Transverse Cracking Behavior by Cooperation of Sliding Core and Endplate in Artificial Intervertebral Disc

The research of the stress distributions and the structural deformation at the sliding core in artificial intervertebral disc under the dorsiflexion is becoming more significant. This research analyzes the finite element model of sliding core and evaluates the effect of radius of curvature and the friction coefficient at the sliding core on von-Mises stress and the contact pressure. New Models of the artificial intervertebral disc are suggested by the results of the sliding core is evaluated by the comparison of that of SB Charité III. Based on the above facts, the optimized radius of curvature of the sliding core is also suggested.

Development of High Technology for Improvement of Fatigue Strength in the Intervertebral Disc Herniation's Cervical Attachment System

The fixation of the vertebral column using transpedicular screws is a well-establish technique. Multi-axial pedicle screw designs allow deviation of the screw away from the perpendicular to the longitudinal rod, which facilitates application of a screw-rod system such as Cervical Attachment System (CAS) into the curved spine. This study was performed a static (compression bending and torsion) and dynamic (compression bending fatigue) empirical analysis of CAS component such as pedicle screw, rod and set screw based on the guideline of ASTM F136- 98 using Ultra-high Molecular Weight Polyethylene (UHMWPE) blocks as test vertebral bodies.

Modified Bernoulli-Euler laminate beam theory using total effective moment in LIPCA

The applicable bending moment equation of LIPCA is necessary even though the fiber layer ply orientation is changed. The aim of this research is to evaluate the relationship between the total effective moment (ME) and Bernoulli-Euler bending moment (M) when the ply orientations of unidirectional CFRP, which is one of the various laminate configurations in LIPCA, are changed. Since the related previous equation between the performance stroke range (h) and the radius of curvature (ρ) was just applicable to the CFRP ply orientation [0], it will be modified using these results. The related modified equation, which has nothing to do with the various CFRP ply orientation, is also suggested and compared with the previous equation.

Damage Characteristics of Cross Ply GFRP and Woven AFRP under Various Impact Velocities

Ankle Foot Orthosis (A.F.O) should endure the uncountable repeating impact and fatigue loadings due to the gait characteristics. This study investigated the impact deflection and relationship between the absorbed energy and the residual strength rate using the cross ply GFRP (glass/epoxy) and the woven AFRP (aramid/epoxy) for the leaf spring in A.F.O. In conclusion, the equation was suggested to evaluate the absorbed energy and the residual strength rate by the different impact velocities. When the cross ply GFRP and the woven AFRP was selected for the leaf spring in A.F.O, it was reasonable to use the cross ply GFRP for the parts subject to the large impact and the woven AFRP for the parts to require the high elastic energy such as the large deformation.

Modeling and Simulation of Driveline Test Bench for Automotive Chassis Component System

Vibration in a driveline is presented in this paper. In the experiment, the rear subframe and propeller shafts and axle were composed and mounted with rubber each other. For applying the vibration input instead of the torsional vibration effect of an engine, the shaker was taken. In particular, torsional vibration due to fluctuating forced vibration excitation across the joint between driveline and rear subframe was carefully examined. Accordingly, the joint response was checked from experiments and the FE-simulation using FRF (frequency response function) analysis was performed. All test results were signal processed and validated against numerical simulations. In present study, the new test bench for measuring the vibration signal and simulating the vehicle chassis system was proposed. The modal value and the mode shape of components were analyzed using the model to identify the important components affecting driveline noise and vibration. It could be reached that the simplified test bench could be well established and be used for design guide and development of the vehicle chassis components.

Texture Evolution of Rolled AA3003 Alloy Sheets after Annealing

To fabricate the aluminum alloys with good drawability, the textures evolution of the 3003 aluminum alloy sheets after rolling and subsequent annealing was studied. The measurement of the deformation textures was carried out for the sheets in which were cold rolled with high reduction ratio by using the symmetric roll. In addition, the change of the recrystallization texture was investigated after heat-treatments of the rolled sheets with various heat treatment conditions. Rolling without lubrication and subsequent annealing led to the formation of favorable rot-CND {001}<110> and γ-fiber ND//<111> textures in 3003 aluminum alloy sheets. From the results, the γ-fiber ND//<111> component well evolved during rolling at high reduction ratio (reduction over 90%, l/d parameter over 6.0). Among shear deformation textures, the γ-fiber ND//<111> was not rotated during recrystallization (350°C) in special condition.

Serration Phenomena of AA5182/Polypropylene/AA5182 Sandwich Sheets

It has been reported that the 5182 aluminum sheet shows Lüders band because of dissolved Mg atoms that cause fabrication process problem, especially surface roughness. The examination of serration phenomena has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum. All sandwich sheets and the 5182 aluminum skin showed serration phenomena on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of the polypropylene core. According to the results of the analysis of the surface roughness after tensile test, Lüders band depth of the sandwich sheet evidently showed lower than that of the 5182 aluminum skin. The strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching these skins to the polypropylene core, which has relatively large positive value of 0.050, m-value of the sandwich sheets changed to the positive value.

SERRATION BEHAVIOR OF AA5182/POLYPROPYLENE/AA5182 SANDWICH SHEETS

The examination of serration behavior has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum skins. All sandwich sheets and the 5182 aluminum skin showed serration behavior on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of the polypropylene core. According to the results of the analysis of the surface roughness following the tensile test, Luders band depth of the sandwich sheet evidently showed lower than that of the 5182 aluminum skin. The strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching these skins to the polypropylene core, which has relatively large positive value of 0.050, m-value of the sandwich sheets changed to a positive value. The serration reduction of the sandwich sheets was quantitatively investigated with respect to the effect on polypropylene thickness variation, that on the strain rate sensitivity and that on the localized stress state. It was found that the serration reduction degree from the experimental results of the sandwich sheet was higher than from the calculated values by the rule of mixture based on the volume fraction of the skins and the core.