Fatigue Behavior of Cracked Al 6061-T6 Alloy Structures Repaired with Composite Patch

Yoon, Young-Ki,Park, Jong-Joon,Kim, Guk-Gi,Yoon, Hi-Seak Korean Society for Precision Engineering 2001 International Journal of Precision Engineering and Vol.2 No.3

Due to the development of high-strength fibers and adhesives, it is now possible to repair cracked metallic plates by bonding reinforced patches to the plate over the crack. In this study, pre-cracked aluminum 6061-T6 alloy plates repaired with bonded carbon/epoxy composite patch are applied to investigate the effect of various patch shapes on the tensile strength and the fatigue behavior of the structure. A non-patch-boned cased and 2 type-50$\times$50, 40$\times$20 mm-composite patch-bonded cases were tested to obtain fracture loads and fatigue crack growth rate. The results showed that the patch-bonded repair improves the static strength by 17% and the fatigue life by 200% compared to non-repaired case. It means that patch-boned repair is more effective in the fatigue life. It was also revealed that the patching method along crack growth direction is more efficient in cost and weight reduction. By observing the fractography, patch-bonded repair specimens demonstrated zigzag fracture patterns compared with the non-patched specimens, which shows a typical ductile fracture.

홉킨슨 압력봉법을 이용한 Fe-6.5wt.%Si 합금의 고변형률속도 거동

Yoon, Young-Ki,Yoon, Hi-Seak,Umakoshi, Yukichi,Yasuda, Hiroyuki Y. 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.7

Many researches have published numerous papers about the high-strain-rate obtained from Split Hopkinson Pressure Bar(SHPB) tests. And 6.5wt%Si steel is widely known as an excellent magnetic material because its magnetostriction is nearly zero. Single crystals are prepared by the Floating Zone(FZ) method, which melts the alloy by the use of a high temperature electron beam in a pure argon gas condition. In this paper, the fracture behavior of the poly crystals and single crystals (DO$_3$phase) of Fe-6.5wt%Si alloy by SHPB test is observed. The comparison of high-strain-rate results with static results was done. Obtained main results are as follows: (1) Fe-6.5wt%Si alloy has higher strength at high-strain-rate tensile. SHPB results of polycrystal are twice as high as static results. (2) From the fractography, the cleavage steps are remarkably reduced in the SHPB test compared with the static test.

A Study of the Mechanical Properties of Patch-Bonded and Riveted Repairs on Cracked Al 6061-T6 alloy Structures

Yoon, Young-Ki,Kim, Guk-Gi,Yoon, Hi-Seak Korean Society for Precision Engineering 2000 International Journal of the Korean Society of Pre Vol.1 No.2

A comparison of Riveted and bonded repairs, bearing and net tension failures, and Al 6061-T6 plates is presented. The results are then compared with previous papers about bonded repairs on different patch materials and shapes. Aluminum alloys, including Al 6061-T6, have a face-centered-cubic crystal structure. Under normal circumstances, these types of crystal structures do not exhibit cleavage fractures even at very low temperatures. In aluminum-base structures, the cracked plate structures are frequently repaired using mechanical fasteners-either rivets of bolts- even though patch-bonding techniques are applied to repair and reinforce the structure. Static test results indicate that the riveted repairs are affected by the position of the rivers. When using the same size of patch, the bonded repair technique is stronger; the rate of elongation is also increased. Form FEM analysis, it is revealed the origin of patch debonding in patch-bonded structures is the edge of the patch along to the tensile strength.

Fatigue Behavior of Cracked Al 6061- T6 Alloy Structures Repaired with Composite Patch

Young-Ki Yoon,Jong-Joon Park,Guk-Gi Kim,Hi-Seak Yoon 한국정밀공학회 2001 International Journal of Precision Engineering and Vol.2 No.3

A Study of the Mechanical Properties of Patch-Bonded and Riveted Repairs on Cracked AI 6061-T6 alloy Structures

Young-Ki Yoon,Guk-Gi Kim,Hi-Seak Yoon 한국정밀공학회 2000 International Journal of Precision Engineering and Vol.1 No.2

DESIGN OPTIMIZATION OF A REAR INDEPENDENT SUSPENSION FOR THE KOREAN LIGHT TACTICAL VEHICLE

Kwonhee Suh,Hi Seak Yoon 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.2

Steering and suspension handle the direction of a vehicle according to the driver's intentions and control the disturbance from the road surface while supporting the vehicle body. The static and dynamic characteristics of two systems are critical factors for the ride comfort and the directional stability. In the layout stage, the hard points of steering and suspension systems are determined. In the next design stage, the detailed design of the system, including gearboxes, springs, shock absorbers, and control links, is carried out. While the optimal hard points of a suspension are determined at the precedent design, interference with other peripheral components should be carefully examined in the detailed design process. In the case of the design point change should be made to avoid the interference, subsequent position and shape changes of the link mechanism are required. Therefore, there is a need to examine the optimization of suspension compliance characteristics with chassis design changes and the durability performance of the modified design. This study proposes an integrated analysis method for the design optimization and the durability evaluation of such optimized design specifications of the rear independent suspension for a military vehicle.

LIFTING CAPABILITY AND STRESS ANALYSES OF THE CRANE SYSTEM FOR A LARGE-SIZED TACTICAL WRECKER

Kwonhee Suh,Hi Seak Yoon 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.5

A large-sized tactical wrecker is a special-purpose vehicle that lifts and tows tactical vehicles and heavy loads. It consists of a crane, a post structure, outriggers and a suitable chassis truck, and during its initial design, the structural safety and tipping stability should be preemptively examined in terms of the layout of these components. This paper proposes computer-aided engineering (CAE) methods to evaluate the maximum lifting capacity of the wrecker and the structural safety of its crane during the initial design. The analytical model for the large-sized wrecker is constructed with 236 degrees of freedom by combining the crane system developed using the ADAMS macros with the dynamic model of large chassis truck with an axle suspension. The design parameters for the wrecker model that influence the tipping stability are selected, and then the maximum lifting loads with the corresponding changes are calculated. This parametric study shows that the characteristics of the boom and the layout of the outriggers greatly affect the maximum lifting capacity. Finite element (FE) analyses of the 1st stage boom and the 3rd stage boom show the stresses under the maximum overturning moment condition are within the allowable strength.

Dynamic Fracture Toughness of Chevron-notch Ceramic Specimens measured in Split Hopkinson Pressure Bar

Lee, Yeon-Soo,Yoon, Young-Ki,Yoon, Hi-Seak Korean Society for Precision Engineering 2002 International Journal of the Korean Society of Pre Vol.3 No.3

Measuring dynamic fracture toughness of brittle and small ceramic specimen is very difficult in a SHPB (Split Hopkinson Pressure Bar). As a countermeasure to this difficulty, a dynamic fracture toughness measuring method by the Chevron-notch ceramic specimen was proposed. Tested chevron specimens were of Chevron notch angles of 90$^{\circ}$, 100$^{\circ}$ and 110$^{\circ}$. Through finite element analysis, shape parameters of the Chevron-notch specimens according to notch angles were calculated. And the static fracture tough1ess of the Chevron-notch alumina specimen was measured as 3.8MPa√m similar to that of CT specimen with a precrack. Dynamic fracture toughness was 4.5MPa√m slightly higher than the static one. It was shown in this study that the proposed Chevron-notch specimens are valid to measure dynamic fracture toughness of extremely brittle materials such as ceramic.

Analytical method to develop airlift equipment for Korean light tactical vehicle

Kwonhee Suh,Bugeun Song,Hi Seak Yoon 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3

The Korean light tactical vehicle (KLTV) is developed to meet the demands for a new military vehicle that fulfills certain conditions, such as multi-purpose, high mobility and survivability. Double-wishbone independent suspension is developed to improve the ride and handling performance and maximize the off-road driving performance of the new tactical vehicle. In particular, the KLTV is equipped with front and rear lifting provisions that support the vehicle safely during airlift operations. In this paper, a comprehensive analytical method to evaluate the structural safety of these components is presented. First, a vehicle dynamic model of the KLTV and a test rig for airlift simulation are developed using MSC.ADAMS/Car. Second, a finite element model of airlift kits, which are newly installed in the KLTV, is constructed. Third, stress analyses on vertical load conditions, MIL-STD-209K, and helicopter flight speeds are performed using ABAQUS. Finally, a dummy apparatus test and an actual vehicle test are conducted to verify the suitability of the airlift equipment for the KLTV. The computational method presented herein will provide useful information on the structural safety of airlift equipment during the early stages of a military-vehicle-designing process.

광 점퍼코드 ( OJC ) 보호용 미소 직경 복합재료 스프링 개발

윤영기(Young Ki Yoon),박성도(Seong Do Park),이연수(Yeon Soo Lee),윤희석(Hi Seak Yoon),이우일(Woo Il Lee) 한국복합재료학회 2002 Composites research Vol.15 No.4

미세 직경을 갖는 복합재료 나선형 스프링 (CS)가 광점퍼코드(OJC)를 보강하기위한 매체로써 개발되었다. 이 스프링의 외경은 약 2 ∼ 3㎜로써 광점퍼코드에 갑작스런 측면 하중으로부터 광섬유의 손실을 막기위해 삽입 보강할 수 있도록 제작되었다. 섬유 형태 (Y-type)와 밴드형태 (B-type)의 복합재료 스프링이 제작되어 그 효과를 비교하였다. 측면 하중에 대한 기계적 특성은 동일 직경의 금속 스프링 및 일반 광점퍼코드의 물성치와 비교하여 제시하였다. 실험 결과로부터 복합재료 스프링이 보강된 광점퍼코드의 경우 굽힘에 대한 높은 저항력을 지니고 있음에 따라 광섬유의 내부손상에 의한 광 손실의 감소률이 낮음을 알 수 있었다. 얻어진 주요 결과들은: ⑴ Y-type의 CS의 경우 B-type과 비교하여 높은 측압 저항력을 지님을 알 수 있었다. ⑵ 일반 OJC와 비교하여 CS-OJC의 경우 광 손실이 현격히 낮음을 알 수 있었다. ⑶ 일반 스프링의 측압 하중시의 응력 분포 형태를 제시하였으며, 실험으로부터 얻어진 결과로부터 복합재료 스프링이 보강된 광점퍼 코드의 경우 매우 높은 구조적 안정성을 보임을 알 수 있었다. Small diameter composite helical springs (CS) are developed using a hot plated mold for reinforcement of common optical fiber jumper cord (OJC). The outer diameters of the springs are about 2 ∼3㎜. These springs are inserted into the OJC to protect the damage of an optical fiber from the sudden lateral load. T재 types of CS, Yarn type (Y-Type) and Band type (B-type), are manufactured to compare the effectiveness for the damage protection. The experimental works were conducted to check the effect of the CS covered around OJC on the mechanical and optical properties. Experimental observations show a considerable effect on the flexural resistance, hence slowing down the deterioration of the optical power by the internal damage of the fiber. Obtained main results are as follows: ⑴ Y-type CS has better protection abilities to lateral loading than B-types. ⑵ Compared with bare OJC, CS-OJC has less power loss under the loading. ⑶ OJC covered with the composite coil spring has a possibility for a practical usage with full fruits.