Ki-Up Cha

Study on Designing Recoil System with Friction Springs

기존에 사용되고 있는 발사장치에는 탄의 발사 에 의해 발사장치에 가해지는 충격을 완화시켜주 는 장치인 주퇴복좌 시스템이 장착되어 있다. 일반적으로 주퇴복좌 시스템은 주로 유기압 시 스템으로 구성되어 있다. 유기압 시스템은 진동 이 적으며, 제어가 단순하고 반응속도가 빠르다는 장점을 지니고 있지만, 주요 부품의 가격이 비싸 고, 에너지 손실이 크며 설치 공간을 많이 차지한 다는 단점을 가지고 있다. 새로운 발사장치 시스템에서는 유기압식 주퇴복 좌 시스템 대신 댐핑 효과를 가지고 있는 마찰 스 프링을 주퇴복좌 시스템에 적용하여 발사장치의 크기와 무게, 비용을 효율적으로 감소시키는 방안 에 대해서 연구가 진행되고 있다. 본 논문에서는 발사장치 시스템 주퇴복좌 운동 요구도에 따른 적합한 마찰 스프링의 설계 변수를 구하는 것이 최종 목표로서, 이를 달성하기 위하 여 마찰 스프링을 이용한 주퇴복좌을 포함하는 발 사장치 시스템의 수학적 모델을 제시하였다. 수학 적 모델에는 마찰 스프링, 제퇴기 효율, 발사장치 에서 발생하는 마찰력, 주퇴 고각, 제퇴 압력 등의 효과를 고려하였다. 제안된 주퇴복좌 시스템에서 사용될 마찰 스프 링의 설계 변수를 결정하기 위해, 주퇴복좌 시스 템의 주퇴장, 주퇴 시간, 제퇴기 효율 등을 변화시 켜가며 시뮬레이션을 수행하였다.

Barrel Rifling Shape Optimization by Using Design of Experiment Approach

The rifling design problem has continuous-type shape variables and an integral number of riflings. In addition, it requires considerable time for analysis because its behavior should be described by a nonlinear finite element model (FEM). Therefore, this study presents an efficient design process for rifling based on a design of experiment (DOE) approach. First, Boses orthogonal array is used to represent 25 runs for four design variables including three shape variables and one integer variable. Then, nonlinear FE analyses are performed. Next, to minimize the bullet resistance without affecting the bullet velocity and bullet rotational angle immediately before a bullet leaves the gun barrel, a what-if design is performed. In the proposed what-if design, a functional including the design objective and constraints is constructed and effect analysis is performed by using the functional. It is found that the new design obtained from the what-if design shows better results than the current one.

Torsional Vibration Control of a Rotating Chamber Shaft System Using Electrorheological Fluid

It is reported that an intermittently rotating chamber system will improve the ratio of firepower to armament space in the case of mid-calibre automatic guns. However, the parallel index, which is a main component of the system, tends to be torsionally flexible due to the low lateral stiffness of cam followers on the index turret. This may cause the shaft system connecting the turret with the chamber prone to considerable residual torsional vibration so that serious misalignment problems occur during ammunition loading and firing processes. Herein, an electrorhelogical (ER) fluid actuator that can suppress such vibrations and the associated semiactive control algorithm are proposed. By mathematical modeling and computer simulations, the performance of the entire system is proved satisfactory.

An Experimental Study on the Material Characteristics of Mechanical Filters for Eliminating High-Frequency Noise in Accelerometer Measurements

Accelerometers are widely used to measure the lateral vibrations of pipe-like structures such as a gun tube under impulse loads. Stress waves that precede the lateral vibrations due to the explosion within a gun contribute little to the vibrations, but saturate the accelerometer input. A mechanical filter eliminates this high-frequency stress wave and only transmits the signal corresponding to the lateral vibrations. The mechanical filter consists of a mechanical structure for mounting the accelerometers and a damping material. The low-pass filter characteristics are determined from the equivalent damping and stiffness property of this damping material. In this paper, we tested nine commercially available damping materials for their vibration characteristics by using a test rig. We also observed the change in the vibration characteristics while compressing the material. We designed and manufactured a mechanical filter and verified its filtering performance.

A Study on the Fatigue Life of Autofrettaged Compound Cylinder

Abstract Thick-walled cylinder with high pressure have had wide application in the armament industry. In the thick-walled cylinder, fatigue crack is generated at inner radius and developed toward the outer radius. To prevent generation of fatigue crack, the autofrettage process had been used. The compressive residual stress induced by the autofrettage process extends loading pressure and fatigue life of the thick-walled cylinder. In this study, the residual stress of single and compound cylinder by the autofrettage process was evaluated. The analytical compressive residual stress of single cylinder was good agreement with experimental result at inner radius. The analysis on the residual stress of compound cylinder was conducted. The compressive residual stress at inner radius was increased with the overstrain level. And fatigue life of the compound cylinder with initial crack was evaluated. The considered initial crack shape was straight and semi-elliptical. The fatigue life was extended with the overstrain level. The fatigue life of the compound cylinder with semi-elliptical crack was longer than straight crack. The suitable way to extend fatigue life of the compound cylinder was proposed.

Autofrettage Analysis of Compound Cylinder with Power Function Strain Hardening Model

In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

A Study on the Design of Rifling Angle by Setting up an Idealized Rifling Force Curve

Rifling Force can be described with projectile velocity, gas pressure and rifling angle, etc. Under the same conditions, the character of the rifling angle decisively influences the rifling force. To reduce the harmful effect, locally distinct maximum of rifling force has to be avoided. The optimal design methodology of rifling angle curve had been developed by combined Fourier series and polynomial function. When it was tried newly to design the rifling angle curve, this design trial caused not to produce the lower rifling force than the existing design. Normally, the curve of the rifling angle is designed first, then the rifling force is set according to the rifling angle curve. However during the cause analysis, new design methodology was established to design the ideal rifling force curve before the rifling angle design. With this new methodology, the above optimal design method was analyzed and its limitation was confirmed.