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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.
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.
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.
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.
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.
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.
Lee Yeon-Soo,Yoon Young-Ki,Jeong Bo-Young,Yoon Hi-Seak The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.3
In this study, we investigate the feasibility of in-situ crack propagation by using a double cleavage drilled compression (DCDC) specimen showing a slow crack velocity down to 0.03 mm/s under 0.01 mm/s of displacement control. Finite element analysis predicted that the DCDC specimens would show at least 4.3 fold delayed crack initiation time than conventional tensile fracture specimens under a constant loading speed. Using DCDC specimens, we were able to observe the in-situ crack propagation process in a particle reinforced transparent polymer composite. Our results confirmed that the DCDC specimen would be a good candidate for the in-situ observation of the behavior of particle reinforced composites with slow crack velocity, such as the self-healing process of micro-particle reinforced composites.