Papers by Author: Sung In Bae

Abstract: It is not easy to simulate realistic mechanical behaviors of elastically deformable objects with most existing mass-spring systems for their lack of simple and clear methods to determine spring constants considering material properties (e.g. Young's modulus, Poisson’s ratio). To overcome this obstacle, we suggest an alternative method to determine spring constants for mechanical simulation of deformable objects under compression. Using the expression derived from proposed method, it is possible to determine one and the same spring constant for a mass-spring model depending on Young's modulus, geometric dimensions and mesh resolutions of the 3-D model. Determination of one and the same spring constant for a mass-spring model in this way leads to simple implementation of the mass-spring system. To validate proposed methodology, static deformations (e.g. compressions and indentations) simulated with mass-spring models and FEM reference models are compared.

Abstract: The mechanical properties of bone have been found varying at different structural levels. The different mechanical properties might indicate some important information, such as the ultrastructure of various bone tissue. Descriptions of the structural features of bone are intensive in current studies. However, the mechanical properties of bone, in particular those at the micro-and nanostructural level (material level) remain poorly understood. To probe the mechanical properties at the microstuctural level, the nanoindentation technique is applied. Nanoindentation as a promising technique is widely used in the materials science community for probing the mechanical properties of thin films, small volumes, and small microstructural features. Nanoindentation has been shown to be an effective method to probe the mechanical properties of microstructures at the micron scale.

Abstract: The effect of axial loading resulting from torque on the fatigue life of bolts has been investigated. It was found that the fatigue limit of bolts increased by an amount proportional to the increase in torque. There was a linear relationship between torque and fatigue limit. Using the Shigley method, the prediction of fatigue limit from calculated stress concentration factors was also examined. A good correlation was found between the experimental and predicted fatigue limit. The Shigley method was appropriate for the prediction of fatigue life of bolts.

Abstract: In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

Abstract: Automobile pedal which is loaded by driver’s input is transmitting load to throttle cable, braking device and clutch device and controlling automobile. Measuring working condition and applying equivalent damage are needed for reliability of developing pedal. The measuring working condition is requiring more investigation with various respects because of widely ranged drivers, road condition and environmental condition. Additionally, when equivalent damage is applied, there are not suitable for test condition if equivalent damage is too high level to apply or unused region. In this study, load history is measured with 95percentile customer. Measured load history is converted to stress history about critical area of pedal by FEM. There are drawn up histogram of pedal cycles and load from stress history with rain flow cycle counting method, calculated relative damage of extended stress history with Palmgren-Miner rule. From the results, calculated total relative damage is applied to calculation method of test time and load. Calculation method for test condition is carried out with three methods which are enforcing with total stress by rain flow cycle counting, representative load and blocked load. Accelerated durability test condition of pedal using with relative damage and acceleration factors are proposed.

Abstract: In this study, the fatigue life evaluation of automatic transfer devices under stress concentrations due to the notch effect is performed. To investigate residual life of a notched component, load histories were obtained through strain measurement. A fatigue test was performed on a specimen imitating a real component and results were compared with each notch root radius of the concentration area. Three-dimensional finite element analysis was also performed to evaluate the local stress fields. Miner’s rule was used to predict the fatigue life calculation. As a result, the predicted life of a notched component was in good agreement with a real component and introduced a special method for measuring load using real machine components.

Abstract: A fatigue analysis program to calculate fatigue lives of mechanical components and structures from FE(Finite Element) results is developed. The useful characteristic of this program is operated under Web environment. So, any designer who design fatigue strength of components and structures can use without other program installation. For the assessment of multi-axial fatigue damage, signed equivalent stress method and critical plane approach have been employed. Each method is compared and the results of Signed von Mises stress method has similar to the results of Smith-Waston-Topper's parameter using critical plane approach. The results were compared with those from commercial program FE-Fatigue6.0 and it was observed that fatigue life and cumulative damage distribution calculated applying same fatigue resistance curve. The results of calculated fatigue life using Web based program agree well with those from FE-Fatigue6.0.

Abstract: The fatigue life of hexagon head and socket head bolts, attached to vehicle a wheel, is assessed and the estimation of the residual life of existing bolts in vehicle wheel is investigated. Fieldmeasured load histories were applied in this test. Tensile tests and fatigue tests were performed to evaluate the effect of tightening torque and to obtain the basic experimental data. Miner’s rule was used to predict the fatigue life of bolts. The results indicate the prediction of fatigue life of the bolts was in good agreement with the real life of vehicle wheel bolts in this test.

Abstract: Automatic belt tensioner for stabilization of Engine accessory belt system is made increase its life, decrease noise and vibration and increase its commercial value. Therefore, it is important finding test mode to assess life of automatic belt tensioner. However, measurement and analysis test result in practical test condition on real road needs requiring much test time and finance. In this study, there is analyzed and established test mode which is loaded measured equivalent damage in real working condition, compared test condition of pre-established test mode and FTP- 75 mode of fuel efficiency test and verified advantages and disadvantages of each mode. Because FTP-75 Mode is for measuring fuel efficiency related with engine, applying FTP-75 mode is estimated suitability for test of engine accessory. Comparison and assessment of damage is investigated structure and pulley part. Equivalent damage is calculated with Palmgren-Miner Rule and representative stress method, test condition of automatic belt tensioner is investigated. This investigation is regarded as being useful to life evaluation of both automatic belt tensioner and other engine accessory component.

Abstract: Impact behaviors of Aluminum Honeycombs Sandwich Panel (AHSP) by drop weight test were investigated in this study. Two types of specimens with l/2" and l/4" cell size were tested by two impactors with the weight of 5.25kgf and 11.9kgf respectively. Transient, contact and elastic-plastic analyses were performed by finite element method. Impact behavior of AHSP about impact sites appeared nearly the same in low impact energy, but it was different in high impact energy. Face was the strongest about impact and short-edge was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is corresponding to impact energy. After 3-point bending test, fracture modes of AHSP were analyzed with AE counts, lower face sheet was fractured in the long-edge direction first, and then separation between face sheet and core happened. In the short-edge direction after core wrinkled, lower face sheet was torn, impact behavior by FE analysis were increased localized damage in high velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity gave rise to localized damaged area.