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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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The Interfacial Reactions and Reliability of SnAgCu Solder Joints under Thermal Shock Cycles (열충격 사이클에 따른 SnAgCu 솔더별 솔더 접합부의 신뢰성 및 계면반응)

  • Oh, Chulmin;Park, Nochang;Han, Changwoon;Bang, Mansoo;Hong, Wonsik
    • Korean Journal of Metals and Materials
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    • v.47 no.8
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    • pp.500-507
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    • 2009
  • Pb-free solder has recently been used in electronics in efforts to meet environmental regulations, and a number of Pb-free solder alloy choices beyond the near-eutectic SnAgCu solder are now available. With increased demand for thin and portable electronics, the high cost of alloys containing significant amounts of silver and their poor mechanical shock performance have spurred the development of low Ag SnAgCu solder, which provides improved mechanical performance at a reasonable cost. Although low Ag SnAgCu solder exhibits significantly higher fracture resistance under high-strain rates, little thermal fatigue data exist for this solder. Therefore, it is necessary to investigate thermal fatigue reliability of low Ag SnAgCu solder under variation of thermal stress in order to allow its implementation in electronic products with high reliability requirements. In this study, the reliability of Sn0.3Ag0.7Cu(SAC0307), a low Ag solder alloy, is discussed and compared with that of Sn3Ag0.5Cu(SAC305). Three sample types and six samples size are evaluated. Mechanical properties and microstructure of the solder joint are investigated under thermal shock cycles. It was observed that the mechanical strength of SAC0307 dropped slightly with thermal cycling relative to that of SAC305. This reveals that the failure mode of SAC0307 is different from that SAC305 under this critical condition.

A Study on the Mechanical Strength Change by Thermal Aging of 2.25Cr-1Mo Steel (발전설비용 2.25Cr-1Mo 강의 시효에 의한 기계적 강도 특성 변화에 대한 연구)

  • Yang, Hyeon-Tae;Kim, Sang-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.7 s.178
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    • pp.1771-1778
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    • 2000
  • The purpose of this study is to investigate the thermal embrittlement and the mechanical properties of 2.25Cr-1Mo steel aged at high temperature for the extended periods. Original, aged artificiall y and used material were tested to obtain the tensile strength, hardness and impact absorbed energy. Tensile strength, hardness and impact absorbed energy decreased with the increasing aging time. The carbide morphology with the thermal embrittlement was found to contribute to the mechanical property change by X-Ray diffraction method.

The Study of Fatigue Lifetime Evaluation on the Interconnect of semiconductor sensor according to the various materials (재료에 따른 반도체 센서 배선의 피로 수명 평가에 관한 연구)

  • Shim Jae-Joon;Ran Dong-seop;Ran Geun-Jo;Kim Tae-Hyung
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2005.10a
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    • pp.283-288
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    • 2005
  • Application of semiconductor sensors has widely spreaded into various industries because those have several merits like easy miniaturization and batch production comparison with previous mechanical sensors. But external conditions such as thermal and repetitive load have a bad effect on sensors's lifetime. Especially, this paper was focused on fatigue life of a interconnect made by various materials. Firstly we implemented the stress analysis for interconnect under thermal load and wording pressure. And the fatigue lifetime of each material was induced by Manson & Coffin Equation using the plastic stress-strain curve obtained by the plastic-elastic Finite Element Analysis.

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Fatigue Characteristics of Work roll of Roughing Stand in Hot Strip Mill (열연 조압연 Work Roll의 피로 특성)

  • 이원호;김상준;이영호;장준상;이준정;김종근
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.4
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    • pp.819-827
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    • 1992
  • Investigations of the fatigue damage of roughing mill roll and experimentally. By the computer simulation for analysing the stresses on the roll surface and experimental hot rolling, the following results were drawn : The crakcs observed on the roll surface were initiated thermally in the initial stage of the rolling and propagated by repeated thermal and bending stresses. The size of the roll surface cracks smaller than 4.87mm could avoid the occurrence of tiny scab, surface defect of hot steel strip. Since the size of surface cracks observed on the roughing mill roll was very small, the fatigue damage of roll surface was found not to be the major factor for the formation of the scab.

Thermal Fatigue Analysis of Wafer Level Embedded SiP by Changing Mold Compounds and Chip Sizes (몰드물성 종류 및 칩 크기 변화에 따른 웨이퍼 레벨 Sip에서의 열 피로 해석)

  • Jang, Chong Min;Kim, Seong Keol
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.22 no.3_1spc
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    • pp.504-508
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    • 2013
  • This paper describes in detail the life prediction models and simulations of thermal fatigue under different mold compounds and chip sizes for wafer-level embedded SiP. Three-dimensional finite element models are built to simulate the viscoplastic behaviors for various mold compounds and chip sizes. In particular, the bonding parts between a mold and silicon nitride (Si3N4) are carefully modeled, and the strain distributions are studied. Three different chip sizes are used, and the effects of the mold compounds are observed. Through the numerical studies, it is found that type-C, which has a relatively lower Young's modulus and higher CTE, has a better fatigue life than the other mold compounds. In addition, the 4×4 chip has a shorter life than the 6×6 and 8×8 chips.

Fatigue Life Evaluation on Compressive & Tensional Residual Stress Induced Materials and Residual Stress Measurement using Hole Drilling Method (HDM을 이용한 잔류응력측정과 압축·인장 잔류응력이 인가된 재료의 피로수명평가)

  • Baek, Seung Yeb
    • Journal of Welding and Joining
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    • v.31 no.2
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    • pp.43-48
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    • 2013
  • This paper Investigated the characteristics of residual stress in weld is composed of typical specimens, are investigated by using three dimensional thermal elasto-plastic FEM analysis. Numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. Using the stress amplitude (σa)R at the hot spot point of gas weld, the relations obtained as the fatigue test results for typical specimens having various dimensions and shapes were systematically rearranged to obtain the (σa)R-Nf relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using (σa)R.

Study of Thermal Stratification into Leaking Flow in the Nuclear Power Plant, Emergency Core Coolant System (원자로 비상 냉각재 누설에 의한 열성층의 비정상 특성에 관한 연구)

  • Han Seong-Min;Choi Yong-Don;Park Min-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.3
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    • pp.202-210
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    • 2006
  • In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can be occurred due to coolant leaking in the check valve. The thermal stratification produces excessive thormal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, when the turbulence penetration occurs in the branch pipe, the maximum temperature differences of fluid at the pipe cross-sections of the T-branch with thermal stratification are examine.

A review of fatigue failures in LWR plants in Japan

  • Kunihiro, Iida
    • Proceedings of the KWS Conference
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    • 1996.10a
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    • pp.19-34
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    • 1996
  • A review was made of fatigue failures of nuclear power plant components in Japan, which were experienced in service and during periodical inspection. No case has been recently reported of a service fatigue failure of a reactor pressure vessel itself, excluding nozzle corner cracks, that occurred many years ago. But, service fatigue failures have been occasionally experienced in piping systems, pumps, and valves, on which fatigue design seems to have been inadequately applied. The causes of fatigue failures can be divided into two categories: mechanical-vibration-induced fatigue and thermal-fluctuation-induced fatigue. Vibration-induced fatigue failure occurs more frequently than is generally thought. The lesson gleaned from the present survey is a recognition that a service fatigue failure may occur due to any one or a combination of the following factors: (1) lack of communication between designers and fabrication engineers, (2) lack of knowledge about a possibility of fatigue failure and poor consideration about the effects of residual stresses, (3) lack of consideration on possible vibration in the design and fabrication stages, and (4) lack of fusion or poor penetration in a welded joint.

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Effect of Metal Removal and Initial Residual Stress on Contact Fatigue Life (초기 잔류응력과 접촉표면 제거가 접촉피로수명에 미치는 영향)

  • Hur Hun-Mu;Goo Byeong-Choon;Choi Jae-Boong;Kim Young-Jin;Seo Jung-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.2 s.233
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    • pp.341-349
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    • 2005
  • Damage often occurs on the surface of railway wheel by 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 life by the metal removal of the contact surface were shown by many researchers, but it has not explained precisely why fatigue life increases or decreases. In this study, the effect of metal removal depth on the contact fatigue life for railway wheel has been evaluated by applying finite element analysis. It has been revealed that the residual stress and the plastic flow are the main factors determining the fatigue life. 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. It has been found that the initial residual stress determines the amount of metal removal depth. Also, the effects of the initial residual stress and metal removal on the contact fatigue lift has been estimated, and an equation is proposed to decide the optimal metal removal depth for maximizing the contact fatigue life.

Effects of Temperature and Stress Ratio on Low-Cycle Fatigue Crack Growth of G91 Steel (G91강 저주파 피로균열 성장에 미치는 온도와 응력비의 영향)

  • Kim, Jong Bum;Hwang, Soo-Kyung;Kim, Bum Joon;Lee, Jong Hoon;Park, Chang Gyu;Lee, Hyeong Yeon;Kim, Moon Ki;Lim, Byeong Soo
    • Korean Journal of Metals and Materials
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    • v.50 no.4
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    • pp.271-279
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    • 2012
  • 9-12% Cr steels have been used in thermal power plants which repeat start and stop operations. Major factors of fatigue life are temperature, frequency, stress ratio, holding time, microstructure, and environment. Normally, fatigue life decreases at high temperature, low frequency, high stress ratio, and long holding time conditions. A Mod.9Cr-1Mo steel, called G91, was developed at ORNL (Oak Ridge National Laboratory, USA) and was adopted as a high-temperature structural material in the ASME Code in 2004. However, its low-cycle fatigue and fatigue crack growth characteristics have been rarely studied. In this work, we have investigated the low-cycle fatigue crack growth behaviors of G91 steel under various test conditions in terms of temperature and stress ratio. As temperature and stress ratio increase, the crack growth rate becomes faster and striation distance also increases. On the other hand, the number of branch cracks decreases.