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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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Thermal aging of Gr. 91 steel in supercritical thermal plant and its effect on structural integrity at elevated temperature

  • Min-Gu Won;Si-Hwa Jeong;Nam-Su Huh;Woo-Gon Kim;Hyeong-Yeon Lee
    • Nuclear Engineering and Technology
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    • v.56 no.1
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    • pp.1-8
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    • 2024
  • In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 ℃ for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and service-exposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

A Comparative Study of the Fatigue Behavior of SnAgCu and SnPb Solder Joints (무연솔더(SnAgCu)와 유연솔더(SnPb)의 피로 수명 비교 연구)

  • Kim, Il-Ho;Park, Tae-Sang;Lee, Soon-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.12
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    • pp.1856-1863
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    • 2004
  • In the last 50 years, lead-contained solder materials have been the most popular interconnect materials used in the electronics industry. Recently, lead-free solders are about to replace lead-contained solders for preventing environmental pollutions. However, the reliability of lead-free solders is not yet satisfactory. Several researchers reported that lead-contained solders have a good fatigue property. The others published that the lead-free solders have a longer thermal fatigue life. In this paper, the reason for the contradictory results published on the estimation of fatigue life of lead-free solder is investigated. In the present study, fatigue behavior of 63Sn37Pb, and two types of lead-free solder joints were compared using pseudo-power cycling testing method, which provides more realistic load cycling than chamber cycling method does. Pseudo-power cycling test was performed in various temperature ranges to evaluating the shear strain effect. A nonlinear finite element model was used to simulate the thermally induced visco-plastic deformation of solder ball joint in BGA packages. It was found that lead-free solder joints have a good fatigue property in the small temperature range condition. That condition induce small strain amplitude. However in the large temperature range condition, lead-contained solder joints have a longer fatigue life.

Analysis of the Rolling Contact Fatigue for Work Roll in Finishing Mill of Hot Strip Rolling (열간 연속판재 압연기의 작업롤 전동피로해석)

  • 배원병;박해두;송길호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.1
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    • pp.292-300
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    • 1995
  • According to the number of cold-rolled coils, the amount of roll wear and thermal expansion, and roll gap profile were calculated, by using the actual data from the finishing mill. Also, based on those data, the calculations of the deflection, the flattening, and the contact pressure of vwork rolls and backup rolls were made respectively. Specially, in the calculation of contact pressure, the numerical results were obtained not only during the normal rolling, but also during the abnormal rolling, by modeling mathematically the dynamic impact force which occurs when the head section of the strip is threading through rolls. With those results the growth of the fatigue region and the fatigue damage of rolls were predicted. Also the optimum roll-grinding depth was determined to maximize the roll life.

Surface Densification Coupled with Higher Density Processes Targeting High-performance Gearing

  • Hanejko, Francis;Rawlings, Arthur;King, Patrick;Poszmik, George
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.738-739
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    • 2006
  • This paper will describe a powder and processing method that facilitates single press-single sintered densities approaching 7.5g/cm3. At this sintered density, mechanical properties of the powder metal (P/M) component are significantly improved over current P/M technologies and begin to approach the performance of wrought steels. High performance gears have the added requirement of rolling contact fatigue durability that is dependent upon localized density and thermal processing. Combining high density processing of engineered P/M materials with selective surface densification enables powder metal components to achieve rolling contact fatigue durability and mechanical property performance that satisfy the performance requirements of many high strength automotive transmission gears. Data will be presented that document P/M part performance in comparison to conventional wrought steel grades.

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Service Life Analysis of Control Valve for Automatic Turbine Startup of Thermal Power Plant (화력 발전소 증기 터빈의 자동기동을 위한 주증기 제어 밸브 수명해석)

  • Kim, Hyo-Jin;Kang, Yong-Ho;Shin, Cheul-Gyu;Park, Hee-Sung;Yu, Bong-Ho
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.7-12
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    • 2000
  • The automatic turbine startup system provides turbine control based on thermal stress. During the startup, control system monitors and evaluates main components of turbine using damage mechanism and life assessment. In case of valve chest, the temperature of inner/outer wall is measured by thermo-couples and the safety of these values are evaluated by using allowable ΔT limit curve during the startup. Because allowable ΔT limit curve includes life assessment, it is possible to apply this curve to turbine control system. In this paper, low cycle fatigue damage and combined rupture and low cycle fatigue damage criterion proposed for yielding the allowable ΔT limit curve of CV(control valve) chest. To calculate low cycle fatigue damage, the stress analysis of valve chest has peformed using FEM. Automatic turbine startup to assure service life of CV was achieved using allowable ΔT limit curve.

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A Study on the Creep Characteristics of Solder of 63 Sn-37Pb (63Sn-37Pb 땜납의 크리프 특성에 관한 연구)

  • 이억섭;김의상
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.2
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    • pp.138-144
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    • 2004
  • The initiation and the propagation of solder joint crack depend on its environmental conditions, such as high temperature creep and thermal fatigue. Creep is known to be the most important factor for the mechanical failure of solder joints in micro-electronic components and micro-systems. This is mainly caused by the different thermal expansion coefficients of the materials used in the micro-electronic packages. To determine the reliability of solder joints and consequently the electronic components, the characterization of the creep behavior of this group of materials is crucial. This paper is to apply the theory of creep into solder joints and to provide related technical information needed for evaluation of reliability of solder joint to failure. 63Sn-37Pb solder was used in this study. This paper experimentally shows a way to enhance the reliability of solder joints.

A Forging Analysis and Mechanical Properties Evaluation of Superalloy Exhaust Valve Spindle (초내열 합금 배기 밸브 스핀들 단조 해석 및 기계적 특성 평가)

  • Choi, S.G.;Oh, J.S.;Jeong, H.S.;Cho, J.R.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.84-88
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    • 2009
  • The nickel-based alloy Nimonic 80A possesses strength, and corrosion, creep and oxidation resistance at high temperature. The exhaust valves of low speed diesel engines are usually operated at temperature levels of 400-600C and high pressure to enhance thermal efficiency and exposed to the corrosion atmosphere by the exhaust gas. Also, the exhaust valve is subjected to repeated thermal and mechanical loads. So, the nickel-based alloy Nimonic 80A was used for the large exhaust valve spindle. It is composed a 540mm diameter head and a 125mm diameter stem. It is developed large products by hot closed-die forging. Manufacturing process analysis of the large exhaust valve spindle was simulated by closed die forging with hydraulic press and cooled in air after forging. The preform was heated to 1080C Numerical calculation was performed by DEFORM-2D, a commercial finite element code. Heat transfer can be coupled with the deformation analysis in a non-isothermal deformation analysis. Mechanical properties of the large exhaust valve spindle were evaluated by the variety of tests, including microstructure observation, tensile, as well as hardness and fatigue tests, were conducted to evaluate the mechanical properties for head part of exhaust valve spindle.

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Effect of Metal Removal and Traction Force on Contact Fatigue Life (견인력과 접촉표면 제거가 접촉피로수명에 미치는 영향)

  • Seo Jung-Won;Hur Hun-Mu;Choi Jae-Boong;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.10 s.241
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    • pp.1384-1391
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    • 2005
  • Damage often occurs on the surface of railway wheels due to wheel-rail contact fatigue. It should be removed before reaching wheel failure, because wheel failure can cause derailment with loss of life and property. The increase or decrease of the contact fatigue lift by the metal removal of the contact surface were investigated by many researchers, but they have not considered initial residual stress and traction force. The railway wheel has the initial residual stress formed during the manufacturing process, and the residual stress is changed by thermal stress induced by braking. The traction force and residual stress are operated on wheels of locomotive and electric motor vehicle. In this study, the effect of metal removal depth on the contact fatigue life for a railway wheel has been evaluated by applying lolling contact fatigue test. The effect of the traction force and metal removal on the contact fatigue life has been estimated by finite element analysis. It has been found that the initial residual stress determines the amount of metal removal depth if the traction coefficient is less than 0.15. If the traction coefficient is greater than 0.2, however, the amount of metal removal depth is independent on the intial residual stress.

Low Cycle Fatigue Behavior of 429EM Stainless Steel at Elevated Temperature (429EM 스테인리스강의 고온 저주기 피로 거동)

  • Lee, Keum-Oh;Yoon, Sam-Son;Hong, Seong-Gu;Kim, Bong-Soo;Lee, Soon-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.4
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    • pp.427-434
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    • 2004
  • Ferritic stainless steel is recently used in high temperature structures because of its good properties of thermal fatigue resistance, corrosion resistance, and low price. Tensile and low-cycle fatigue (LCF) tests on 429EM stainless steel used in exhaust manifold were performed at several temperatures from room temperature to 800C. Elastic Modulus, yield strength, and ultimate tensile strength monotonically decreased when temperature increased. Cyclic hardening occurred considerably during the most part of the fatigue life. Dynamic strain aging was observed in 200~500C, which affects the cyclic hardening behavior. Among the fatigue parameters such as plastic strain amplitude, stress amplitude, and plastic strain energy density (PSED), PSED was a proper fatigue parameter since it maintained at a constant value during LCF deformation even though cyclic hardening occurs considerably. A phenomenological life prediction model using PSED was proposed considering the influence of temperature on fatigue life.

Thermal Structural Analysis of the Engine Turbocharger under the Transient Temperature History Corresponding to the Motoring Fatigue Test (모터링 내구시험을 상사한 비정상 온도이력을 받고 있는 엔진 터보차져의 열적 거동해석)

  • Choi, Bok-Lok;Bang, In-Wan;Chang, Hoon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.6
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    • pp.126-132
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    • 2011
  • Fatigue cracks of the turbocharger are often observed for high performance engines under thermal shock tests. Maximum exhaust gas temperature of recently developed gasoline engines could reach approximately 950C. It's very important to estimate transient temperature histories during thermal shock cycles to predict the stress and the fatigue life of the turbocharger. With these temperature profiles, temperature-dependent material properties and boundary conditions, we could identify critical locations by the application of finite element simulation technologies. In this paper, we applied the reliable analysis approach to the actual turbocharger to predict the weak locations due to the repetitions of plastic strains and compared the results with the crack locations under physical engine test.