Earticle

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.

The conventional medium and large caliber gun, in general, utilize the hydro-pneumatic recoil mechanism to control the firing impulse and to return to the battery position. However, this kind of mechanism may cause the problems like the leakages and the property changes in oil and gas due to the temperature variations between low and high temperatures. Accordingly, the friction spring mechanism has recently been researched as an alternative system. The friction spring mechanism consists of a set of closed inner and outer rings with the concentric tapered contact surfaces assembled in the columnar form, and can only be used under the compression load. When the spring column is axially loaded, the tapered surfaces become overlapped, causing the outer rings to expand while the inner rings are being contracted in diameter allowing an axial displacement. Because of friction between tapered contact surfaces, much higher spring stiffness is obtained on the stroke at the increase in load than the stroke at the decrease. In this paper, the dynamic equations regarding the friction spring system and the design approach have been investigated. It is also tried for a dynamic model representing the recoil motion and the friction spring forces. And the model has been proved from firing test using a gun system with friction springs. All the results show that the recoil mechanism using friction springs can substitute for the classic hydro-pneumatic recoil system.

강선설계문제는 실수형 설계변수인 형상변수와 정수형 설계변수인 강선의 개수로 이루어져 있다. 또한, 탄이 강선의 통과하는 거동을 표현하기 위하여 비선형 유한요소 해석을 사용하므로 많은 해석시간이 요구된다. 따라서, 본 연구에서는 실험계획법 기반의 효율적인 강선설계 방법을 제안한다. 첫 번째로, 3 개의 형상변수와 1 개의 정수형 변수를 포함하는 4 개의 설계변수에 대해서 보스의 직교배열표를 사용하여 25 개의 실험점을 생성한 후 각 실험점에 대해서 비선형 유한 요소 해석을 수행한다. 다음으로는 포열에서 탄이 탈출할 때의 탄의 속도와 각속도를 만족시키는 동시에 탄의 저항력을 최소화 하기 위해서 가상설계개념을 수행한다. 제안하는 가상설계개념은 설계 목적과 제약조건 그리고 효과분석을 포함하는 범함수로 생성된다. 마지막으로 가상설계개념으로부터 주어지는 새로운 설계는 초기 설계보다 나은 결과를 보여주고 있다.

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, Bose's 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.

간헐 회전식 약실 계가 화력 대 무장 공간의 비율 관점에서 볼 때 중구경 자동포에 크게 유익하다고 보고되었다. 그러나 약실계의 핵심 부품인 평행 인덱스가 인덱스 터릿에 설치되는 캠종동절의 상대적으로 낮은 횡 강성으로 인하여 비틀림 방향으로 유연해지는 경향이 있으며, 이는 결국 터릿과 약실 사이의 연결 축이 상당한 크기의 비틀림 잔류 진동에 노출되어 탄 장전과 발사 시에 심각한 비정렬 문제를 야기시킬 수 있다. 이러한 맥락에서 본 논문에서는 상기 진동을 억제하는 ER 유체 작동기와 그에 적합한 반능동 제어 알고리듬을 제안하게 되었으며, 전체 계의 수학적 모델링과 컴퓨터 시뮬레이션을 통하여 그 성능이 만족스러움을 입증하였다.

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.

마찰 스프링은 부하가 가해질 때와 가해지지 않을 때 서로 다른 특성을 가지고 있다. 마찰스프링의 이러한 특성으로 인해 충격 시스템에 주로 사용된다. 본 논문에서는 마찰 스프링을 포함한 발사장치의 주퇴복좌기 설계 연구가 수행되었다. 마찰 스프링의 강성을 결정하기 위해서는 충격량과 운동량 관계를 고려한 단순한 발사장치 모델의 운동방정식이 개발되었다. 발사장치의 동적 거동시뮬레이션 결과에 기초하여, 주퇴복좌 시스템의 마찰 스프링의 지름을 결정하였다.

Friction springs have different characteristics while loading and un-loading. Because of these characteristics, they are utilized in impact systems. In this paper, the design of a recoil system with friction springs for use in a machine gun system has been presented. In order to determine the stiffness of a friction spring, equations of motion for a simple gun model with a recoil system have been derived. The impulse balance scheme has been adopted. On the basis of simulation results, the diameter of the friction spring has been determined.

포신과 같은 충격하중을 받는 파이프 형태의 구조물 진동을 측정하기 위해 가속계가 널리 사용된다. 포약의 폭발로 인해 발생하는 응력파는 포신의 횡진동에 미미한 영향을 미치지만 매우 큰 가속도 성분을 가지고 있어 미세 진동의 계측을 어렵게 한다. 기계적 필터는 가속도계를 부착하는 기계적 구조물과 진동감쇠재료로 구성되어, 고주파의 응력파를 제거하고 횡진동에 관련된 가속도 성분만을 가속도계로 전달하는 역할을 한다. 진동감쇠재료는 비선형성이 강하여 수학적 모델링이나 수치적 해석에 어려움이 있다. 본 논문에서는 9 가지의 진동감쇠재료의 진동특성을 실험적으로 확인하여, 기계적 필터에 가장 적합한 재료를 선택하였다. 또한, 압착에 따른 진동특성의 변화를 통해, 기계적 필터의 설계 데이터를 얻을 수 있었다. 기계적 필터를 설계 제작하여, 필터의 성능을 확인하였다.

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.

This paper presents the modeling and validation of a pile-driver breech fatigue testing system model to replicate actual high pressure in a large caliber gun barrel. A hysteresis damping function was incorporated in the nonlinear impact force model. Test of real pile-driver breech fatigue testing system had been performed for model validation. Comparison of the experimental result and model simulation during impact were made. Numerical studies were performed to evaluate how the actual chamber pressure pattern in the live firing of gun barrel was affected by parameters' variation. Some of the parameters simulated included input velocity, damping coefficient and stiffness. As a result, a variety of actual chamber pressure pattern could be reproduced and controlled through current simulation model.

Rifling force has a torsion impulse effect on the gun tube and thus generates undesirable vibration of the gun tube about its bore axis, putting additional stress on the projectile. High rifling force at the muzzle of the gun tube may adversely influence the trajectory of the projectile. And, the service life of rifled gun barrels is known to depend on the rifling force. Rifling force along the path of the projectile in the longitudinal direction of the gun tube can be described with projectile mass, projectile velocity, gas pressure curve and rifling angle. Under the same conditions, the character of the rifling of the gun barrel decisively influences the rifling force curve. To reduce the above mentioned harmful effect, locally distinct maximum of rifling force has to be avoided and maximum rifling force needs to be minimized. The best way to minimize the maximum rifling force is to design a rifling angle function so that the rifling force curve has a near trapezoidal shape. In this paper a new approach to make the optimal rifling force curve is described. The rifling angle determining the rifling force is developed by combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems.

자주포 또는 원자로와 같은 두꺼운 실린더는 압력용기 내부에 유익한 잔류 압축응력을 유도하여 작용압력과 피로수명을 증가시키도록 자긴 가공되고 있다. 자긴가공도가 증가하면 구멍에서 압축잔류응력의 크기도 증가한다. 본연구의 목적은 ASME 코드에 의해 적용된 Kendall 모델을 이용하여 고강도 SCM440 강의 정확한 잔류응력을 예측하는 것이다. SCM440 후육실린더의 내부에 유압이 적용되고 30% 변형률까지 자긴 가공하였다. 자긴가공된 시편은 전해연마하고 X-ray 회절법을 이용하여 정확한 잔류응력을 산출하도록 하였다. 그리고 주사전자현미경을 이용하여 자긴가공에 의해 소성변형된 표면층을 분석하였다. 측정한 잔류응력과 계산된 결과를 비교하여 약간의 차이는 있으나 비교적 서로 잘 일치하고 있다.

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. The purpose of the present paper is to predict the accurate residual stress of SCM440 high strength steel using the Kendall model which was adopted by ASME Code. Hydraulic pressure process was applied in the inner part and thick-walled cylinders were autofrettaged up to 30% overstrain levels. Electro polishing on the surface of autofrettage specimen was performed to get more accurate residual stress. Residual stresses were measured by X-ray diffraction method. The autofrettage surface which was plastically deformed analyzed using a scanning electron microscope(SEM). Although there were some differences in measured residual stress and numerical results, it has a tendency to agree comparatively with each other.

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.

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. However, the Bauschinger effect reduces the compressive residual stresses as a result of prior tensile plastic strain, and decreases the beneficial autofrettage effect. The purpose of the present paper is to predict the accurate residual stress of SNCM8 high strength steel using the Kendall model which was adopted by ASME Code. The uniaxial Bauschinger effect test was performed to decide BEF, then this constant was used in calculation. There were some differences between theoretical solution and modified solution.

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.

항공기 제작 시 중요한 요소는 항공기 구조의 안전성과 경량화라 할 수 있다. 자긴가공 공정을 통하여 고압의 항공기 부품을 신뢰성 증대와 함께 재료의 경량화도 같이 얻을 수 있다. 이 방법은 주로 단일 실린더에 적용되었다. 그러나 바우싱거 효과에 의하여 자긴가공의 유용함이 줄어든다. 바우싱거 효과를 줄이기 위한 억지 끼워맞춤과 자긴가공을 이용한 복합실린더에 대한 관심이 증대하고 있다. 본 연구에서 동일한 치수를 가진 단일 및 복합실린더를 고려하였다. 복합실린더에서 억지 끼워맞춤에 의하여 경계면에서 낮은 압축 잔류응력이 유도되며, 내경에서 보다 낮은 소성 변형률이 유도된다. 이는 바우싱거 효과를 줄여, 내경에서 더욱 유용한 잔류응력을 얻을 수 있음을 의미한다.

In manufacturing aircraft, safety and lightness of structure are important factors. Utilizing autofrettage technique, these benefits can be obtained. This technique is most frequently applied to a single cylinder. However, the Bauschinger effect reduces the benefits of autofrettage process Therefore, there is increasing interest in the use of compound cylinder that combine shrink fit and autofrettage. In this paper, single and compound cylinders that has same geometry were considered. It was found that compound cylinder which was autofrettaged has lower tangential hoop stress and plastic strain than single cylinder at bore. This means a reduction in the impact of the Bauschinger effect after shrink-fitting which produces the beneficial bore hoop stress.

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. The purpose of the present paper is to predict the accurate residual stress of SCM440 high strength steel using the Kendall model which was adopted by ASME Code. Hydraulic pressure process was applied and thick-walled cylinders were autofrettaged up to 30% overstrain levels. Electro polishing was performed to get more accurate data. Residual stresses were measured by X-ray diffraction method. The autofrettaged surface which was plastically deformed analyzed using a scanning electron microscope(SEM). Although there were some differences in measured residual stress and numerical, there is a tendency to agree.

Autofrettage process is used for internal forming and sizing of cylinder designed to withstand high internal pressures. Once the tube is autofrettaged, it needs to be machined to its final dimensions both at the bore and its outer surface. This paper presents an analytical analysis and numerical analysis of machined compound cylinder using finite element code, ANSYS10.0. An analytical model for predicting the level of autofrettage following either inner, outer, or combined machining of the compound cylinder is developed for the autofrettage residual stress field is simulated by an autofrettaged pressure. The autofrettaged pressures are obtained by using trying-error method. As autofrettage percentage is 20 % and 40 %, the numerical results are found to be in almost agreement with the analytical ones. However, as autofrettage percentage is 60 %, the numerical results have a little difference with the analytical ones.

Autofrettage process is used for internal forming and sizing of cylinder designed to withstand high internal pressures. Once the tube is autofrettaged, it needs to be machined to its final dimensions both at the bore and its outer surface. This paper presents an analytical analysis and numerical analysis of machined compound cylinder using finite element code, ANSYS10.0. An analytical model for predicting the level of autofrettage following either inner, outer, or combined machining of the compound cylinder is developed for the autofrettage residual stress field is simulated by an autofrettaged pressure. The autofrettaged pressures are obtained by using trying-error method. As autofrettage percentage is 20 %, the numerical results are found to be in almost agreement with the analytical ones. However, as autofrettage percentage is 60 %, the numerical results have a little difference with the analytical ones.

Lately, there exist growing demands to increase the firepower of mid-calibre automatic guns despite spatial limitations of armament. In this context, ammunitions of simple cylindrical shape are considered so advantageous that associated automatic guns are under development incorporating an intermittently rotating chamber mechanism. In this paper, relevant subsystems for such guns are to be described, and a digital controller to automate the entire system as well. Via dynamic simulations it proves to function well being able to drive the chamber at any constant speed up to 200spm, which is merely limited by the recoil performance. It is remarkable that the system synchronization idea in use is applicable to any other multi-actuator systems that should operate on the basis of event rather than time.

Lately, there exist growing demands for the use of CTAs(Cased Telescoped Ammunitions) to increase the firepower of mid-calibre automatic guns despite spatial limitations of armament. In this paper, for automatic CTA guns a rotating chamber mechanism is designed based on parallel index concept. Via dynamic simulations it proves capable of smooth operation even at as high a firing rate as 200spm. Subsequently, motor controllers are synthesized to drive the chamber at any constant speed and also to control positions in the presence of large disturbances caused by the intermittently-rotating load. It is remarkable that we successfully adopted a disturbance observer to treat disturbances only with a moderate bandwidth of the closed-loop system.

The breech system can be considered as a pressure vessel with an internal plug under high explosive pressure. The system consists of a breech block(internal plug) whose front surface subjects to pressure, and a breech ring(pressure vessel). There is the geometric discontinuity around roots of connection parts and then stress concentration is introduced due to pressure, where contact effect may be ignored because contact plane between two equipments is parallel ideally, Generally high stress concentration phenomena shorten the life cycle of the mechanical system. It is well known that shock load is much more harmful on safety of the system than static load. In this present paper, several geometric design variables which may affect stress condition on the system are chosen and the parametric study on the design variables is carried using commercial FEM codes. Finally, the obtained results in the single lug breech system are applied to design the 3 lugs breech system. The 3 lugs breech system can reduce the maximum stress level.

Numerical solutions for two-dimensional, steady, free convection are presented for a cylinder filled with saturated porous media. An annulus is bounded by inner wall with constant heat flux and two adiabatic horizontal walls with outer wall isothermally cooled. Governing equations are numerically solved for the range of Aspect Ratio 1 to 20, Radius Ratio, 1 to 20, and Rayleigh number, 50 to $10^4$ by Finite Difference method utilizing upwind scheme. Results are presented in terms of stream lines and isotherms, temperature distributions and local Nusselt numbers at the heated wall. Average Nusselt numbers are also presented for the comparisons.