• Nuclear Engineering and Technology
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• 제47권1호
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• pp.115-125
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• 2015

Background: Residual stress always exists on any kind of welded area. This residual stress can cause the welded material to crack or fracture. For many years, the hole-drilling method has been widely used for measuring residual stress. However, this method is destructive. Nowadays, electronic speckle pattern interferometry (ESPI) can be used to measure residual stress with or without the hole-drilling method. ESPI is an optical nondestructive testing methods that use the speckle effect. Mechanical properties can be measured by calculation of the phase difference by the variation of temperature, pressure, or loading force. Methods: In this paper, the residual stress on the butt-welded area is measured by using ESPI with a suggested numerical calculation. Two types of specimens are prepared. Type I is made of pure base metal part and type II has a welded part at the center. These specimens are tensile tested with a material test system. At the same time, the ESPI system was applied to this test. Results: From the results of ESPI, the elastic modulus and the residual stress around the welded area can be calculated and estimated. Conclusion: With this result, it is confirmed that the residual stress on the welded area can be measured with high precision by ESPI.

• 화약ㆍ발파
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• 제21권2호
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• pp.1-13
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• 2003

여굴 또는 미굴은 터널발파 결과를 평가하는데 있어서 가장 중요한 지표중 하나이다. 폭약량과 종류, 암질상태, 천공상태에 따라 좌우되는 여굴은 터널시공의 경제성과 직결되므로 현장의 많은 발파기술자들은 이를 최소화하기 위한 노력을 끊임없이 시도하여 왔다. 일반적으로 천공은 여굴을 야기하는 가장 중요한 요소로 알려져 있다. 따라서 본 연구에서는 천공과 관련된 다양한 작업방법들이 여굴과 천공의 정확도에 미치는 영향을 분석하여 여굴을 저감하기 위한 실제 작업모델을 제시하고자 하였다. 이를 위해 1차적으로 굴착선공 적정 공간격, 점보드릴의 천공각 변화, 굴착선공 천공착점 위치, 굴착선공 표시 등 4개 항목 45회의 실험을 실시하였다. 여굴을 줄이기 위해서는 작업자 및 감독자들의 의지와 노력이 무엇보다도 중요하였고 천공방법 및 패턴을 일부 개선하므로써 천공으로 인한 여굴량을 적지 않게 줄일수 있다고 판단되었다.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.183-190
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• 2007

Injection molding is one of the most common operations in polymer processing. Good quality products are usually obtained and major post-processing treatment is not required. However, residual stresses which exist in plastic parts affect the final shape and mechanical properties after ejection. Residual stresses are caused by polymer melt flow, pressure distribution, non-uniform temperature field, and density distribution. Residual stresses are predicted in this study by numerical methods using commercially available softwares, $Hypermesh^{TM},\;Moldflow^{TM}\;and\;ABAQUS^{TM}$. Cavity filling, packing, and cooling stages are simulated to predict residual stress field right after ejection by assuming an isotropic elastic solid. Thermo-viscoelastic stress analysis is carried out to predict deformation and residual stress distribution after annealing of the part. Residual stresses are measured by the hole drilling method because the automotive part selected in this study has a complex shape. Residual stress distribution predicted by the thermal stress analysis is compared with the measurement results obtained by the hole drilling method. The molded specimen has residual stress distribution in tension, compression, and tension from the surface to the center of the part. Viscoelastic deformation of the part is predicted during annealing and the deformed geometry is compared with that measured by a three dimensional scanner. The viscoelastic stress analysis with a thermal cycle will enable us to predict long term behavior of the injection molded polymeric parts.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제28권3호
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• pp.213-221
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• 2006

Purpose This study was aimed to evaluate the effect of the location and angle of drilling on the changes of the distance between the two block specimens. Materials and methods In experimental group 1, the screw holes were prepared by drilling in the distal portion of compression part of the plate at $90^{\circ}$. In experimental group 2, the drilling was performed at an angle of $30^{\circ}$ proximal to the miniplate, and in experimental group 3, at $30^{\circ}$ distal respectively. In control group, the drilling was performed to the center of hole at $90^{\circ}$. The fixation screw length was 5 mm, 7 mm, and 9 mm in all groups. The results were as follows. Results 1. In control group, the mean changes between two specimens were 0.01 mm, 0.02 mm, and 0.00 mm in 5 mm, 7 mm, and 9 mm screws respectively. 2. In experimental group 1, the compression part was moved toward the retention part. The range of mean changes were from -0.39 mm to -0.43 mm. 3. In experimental group 2, the compression part was moved toward the retention part. The range of mean changes were from -0.51 mm to -0.56 mm. 4. In experimental group 3, the compression part was moved apart from the retention part and the range of mean changes were from 0.55 mm to 0.56 mm. 5. The changes were significantly different between all groups(p<0.01). Conclusion These results suggest that 0.4$\sim$0.5 mm of compressive effect can be achieved by drilling on the distal area of the screw hole at an angle of $90^{\circ}$ and by the proximal angulation to the miniplate, and the gap between specimens can be increased by distal angulation to the miniplate during drilling.

• 한국지구과학회지
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• 제25권4호
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• pp.270-276
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• 2004

지반의 횡파 속도 단면은 주로 다운흘 탄성파 탐사에 의존해 왔으나 최근에 MASW와 같은 표면파 탐사방법과 SCPT와 같은 탄성파 콘 관입시험법 등이 개발되어 사용되고 있다. 본 연구에서는 비고결 퇴적물에서 다운홀 탄성파 탐사, MASW, SCPT 등을 사용하여 횡파 속도 단면을 구하고 이들을 시추조사 결과와 비교하였다. 그 결과 퇴적물상의변화와 횡파 속도 변화는 밀접한 관계가 있음을 알 수 있었으며, 세 가지 횡파 속도 단면 중 SCPT가 퇴적물상의 변화에 가장 민감하게 반응하는 것을 알 수 있었다. SCPT 결과 퇴적층 내 약 8${\sim}$l2m 깊이에 주로 점토질 모래로 구성되어 있는 저속도 층이 있음을 알 수 있었다.

• 기술사
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• 제14권3호
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• pp.9-21
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• 1981

The rationalization for Tunnel Drifting is based on the high productivity which is achievable due to Continuous work with a Jumbo Drill, resulting in a much higher efficiency them the Conventional method of blasting, mucking and supporting services. Large projects of over 4,000m Tunnel Drifting are condidated to justify the use of a Jumbo Drill with a combination of superior explosives, machinery and techniques. During a Tunnel Drifting test, Gulita, Nabit and slurry made by Nitro Nobel were employed with following results. 1, Conditions: a. Granite Rock with Two free face b. Burden (W), 2m c. Diameter of hole, 42mm d. Depth of hole 3.5m e. Hole pitch 0.6m f. Charged Explosive per hole Gelatin Dynamite 4 pieces (112.5${\times}$4ea)+Guuita 5 pieces(110g${\times}$5ea) g. Simal-taneous Detonation h. After the blasting resultant rock size was Less 40% of the 0.3m Lumps. 2. Calculation results W=q/Wn=100cm‥‥‥Burden in simultaneous blasting 0.865kg(7.7ea)/hole ‥‥‥Amount of charge but hole pitch is 1.5W-2W The estimated cost of using a Jumbo Drill for the Construction of a 3,000,000 bbL sub-surface oil storage would be as follows: This calculation is based on the Jumbo Drill advancing 3.6m per blasting cycle. Unit cost/bbL Excavation $3.13 The attached sheet shows ideal Drilling pattern with Burn Cut & Smooth blasting method. In conclusion, it is my opinion that this method will assure safety and save cost and improve our technical know-how.

• 한국주조공학회지
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• 제40권1호
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• pp.1-6
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• 2020

Many studies involving a thermal stress analysis using computational methods have been conducted, though there have been relatively few experimental attempts to investigate thermal stress phenomena. Casting products undergo thermal stress variations during the casting process as the temperature drops from the melting temperature to room temperature, with gradient cooling also occurring from the surface to the core. It is difficult to examine thermal stress states continuously during the casting process. Therefore, only the final states of thermal stress and deformations can be detemined. In this study, specimens sensitive to thermal stress, were made by a casting process. After which the residual stress levels in the specimens were measured by a hole drilling method with Electron Speckle-Interferometry technique. Subsequently, we examined the thermal stresses in terms of deformation during the casting process by means of a numerical analysis. Finally, we compared the experimental and numerical analysis results. It was found that the numerical thermal stress analysis is an effective means of understanding the stress generation mechanism in casting products during the casting process.

• Steel and Composite Structures
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• 제28권6호
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• pp.759-766
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• 2018

Friction Stir Welding (FSW) is a solid-state process, where the objects are joined together without reaching their melting point. It has been shown that this method is a suitable way to join dissimilar aluminium alloys. The current article employed hole drilling technique to measure the residual stress distribution experimentally in different zones of dissimilar aluminium alloys AA6061-T6 and AA7075-T6 Butt welded using FSW. Results are compared with those of similar AA6061-T6 plates joined using a conventional fusion welding method called tungsten inert gas (TIG). Also, the evolution of the residual stresses in the thickness direction was investigated, and it was found that the maximum residual stresses are below the yield strength of the material in the shoulder region. It was also revealed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses. Meanwhile, Vickers micro hardness measurements were performed in the cross-section of the samples. The largest hardness values were observed in the stir zone (SZ) adjacent to the advancing side whereas low hardness values were measured at the HAZ of both alloys and the SZ adjacent to the retreating side.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.25-30
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• 2000

Residual stresses induced in U-bending and tube-to-tubesheet joining processes of PWR's steam generator row-1 tube were measured by X-ray method and Hole-Drilling Method(HDM). The stresses resulting from the Internal pressure and the temperature gradient in the steam generator were also estimated theoretically. In U-bent lesions, the residual stresses at extrados were induced with compressive stress(-), and its maximum value reached -319 MPa in axial direction at ${\psi}=0^{\circ}$ in position. Maximum tensile residual stress of 170MPa was found to be at the flank side at Position of${\psi}=90^{\circ}$, i.e., at apex region. In tube-to-tubesheet fouling methods, the residual stresses induced by the explosive joint method were found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the. transition region, and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction. Hoop stress due to an internal pressure between primary and secondary side was analyzed to be 76 MPa and thermal stress was 45 MPa.

• 한국지열·수열에너지학회논문집
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• 제17권1호
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• pp.14-22
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• 2021

Drilling equipment is an essential part used in various fields such as construction, mining, etc., and it has drawn increasing attention in recent years. The drilling method is generally divided into three types. There are a top hammer method that strikes on the ground, a DTH (Down-The-Hole) method that directly strikes a bit in an underground area, and a rotary method that drills by using rotational force. Among them, the DTH method is most commonly used because it enables efficient drilling compared to other drilling methods. In the conventional DTH hammer, the valve between the piston and the bit is opened and closed using a face to face method. In order to improve the power of the DTH hammer, a DTH hammer with foot valve which is capable of instantaneous opening and closing is used in the drilling field. In this study, we designed a lab-scale DTH hammer with the foot valve, and manufactured an evaluation device for the experiment of the DTH hammer. In addition, we analyzed the performance of the DTH hammer adopted with foot valve according to the pressure range of 3-10 bar. As a result, the internal pressure distribution in the DTH hammer was experimentally analyzed, and then, the movement of the piston according to the pressure was predicted. We believe that this study provides the useful results to explain the performance characteristics of the DTH hammer with the foot valve.