In this study, theoretical analyses are performed to investigate the characteristics of the static and dynamic stiffness of a nonlinear vibration isolator system. The vibration isolator system is modeled as an equivalent nonlinear oscillator. Based on the model, the static equilibrium and frequency response solutions are obtained with the variations of external static load and/or system parameters. It is shown that the static stiffness of the nonlinear vibration isolator tends to be hardened with the increase of external static load, which prevents the occurrence of excessively large deflection. This static stiffness-hardening effect is more remarkable with a larger spring constant ratio. The dynamic stiffness is also strengthened when the spring constant ratio increases, which enlarges the force transmissibility and reduces the isolation frequency bandwidth. Thus, the static stiffness- hardening improves the robustness of the nonlinear vibration isolator, whereas the dynamic stiffness-hardening rather degrades its performance. Thus, the opposite tendency of the static and dynamic stiffness-hardening effects should be considered in the design process of the nonlinear vibration isolator.

This paper presents the kinematic analysis and design of a three-point hitch mechanism used in agriculture tractors. Connecting the agricultural implement to the tractors allows for various motions of the agricultural implements by the force from the tractor. First, a three-point hitch mechanism is modeled as multiloop planar rigid body guidance mechanisms for two major motions: the lift and the pitch motions of the agricultural implement. The displacement matrix and the design equations for Upper and Lower links are applied to determine the hitch points using a numerical method. Then, the resulting implement movements are determined in terms of the lifting parameters for the two major motions of the vertical and pitching displacement. Finally, the design process is provided to determine the dimensions of the mechanism. This should satisfy the requirements of the ISO Standards for Agricultural wheeled tractors: rear-mounted three-point linkage: Categories 1N, 1, 2, 3N, 3, 4N and 4[1].

This study developed a flame-retardant fiber-reinforced composite material that satisfies the required regulations of railway vehicle interior parts for the purpose of reducing weight and simplifying the production process using SMC(sheet molding compounds) composite materials. It is essential to secure flame-retardant performance that minimizes flames and smoke for the safe evacuation of passengers in case of fire for interior parts of railway vehicles. In this study, the resin for SMC was developed by adding various flame retardant materials such as vinyl ester (halogen-based and phosphorus-based) and antimony trioxide, and chopped glass fibers were used as the reinforcing material. As a result of preparing specimens for phosphorus-based and halogen-based SMC materials, and comparing the flame retardant performance, the phosphorus-based SMC material had an oxygen index of 36.1, smoke density (1minute 30 seconds, 4minutes, 10minutes) of 1.7, 51.5, 195.1. It was measured with a toxicity index of 0.05 R and average heat for sustained burning of 4.5MJ/m, which satisfies all the flame retardant standards required for interior parts of railway vehicles, and it was found that most of the performance was better than that of halogen-based SMC.

In this study, Equivalent fracture strain and Fracture energy were evaluated with the small punch test(SP test) for friction stir welded(FSW) Al6061-T6 sheets. With the three rotation speeds and the three feeding rate, The nine different conditions of FSW were prepared for the SP test. The SP test specimens were manufactured and tested on the advancing side, center, and retreating side to the tool rotation direction. From the SP test data, the equivalent fracture strain and the fracture energy were analyzed. The high value of equivalent fracture strain was attained form tool rotational speed 900RPM and feeding rate 330mm/min. It is found that its characteristic is about 14% higher than the value of condition 1100RPM-330mm/min that have the lowest value. The high value of fracture energy was obtained from the tool rotation speed 900RPM and feeding rate 330mm/min. The lowest fracture energy, which from 1000RPM-300mm/min, was approximately 16% difference to the highest value.