• Title, Summary, Keyword: hardening

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Characteristics of Surface Transformation Hardening for Rod-shaped Carbon Steels by Diode Laser (다이오드 레이저를 이용한 탄소강 환봉의 표면변태 경화특성)

  • Kim, Jong-Do;Kang, Woon-Ju;Lee, Su-Jin;Yoon, Hee-Jong;Lee, Jae-Hoon
    • Journal of Korean Society of Laser Processing
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    • v.11 no.4
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    • pp.7-12
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    • 2008
  • Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

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Laser surface hardening characterization of SM45C (SM45C의 레이저 표면경화특성)

  • Shin Ho-Jun;Yoo Young-Tae;Ahn Dong-Gyu;Im Kiegon
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • pp.246-251
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    • 2005
  • Laser surface hardening is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching to occur and the formation of martensitic structure. In this investigation, the microstructure features occurring in Nd:YAG laser hardening SM45C steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimism of the processing parameters for maximum hardened depth of SM45C steel specimens of 3mm thickness by using CW Nd:YAG laser. Travel speed was varied from 0.6m/min to 1.0m/min. The maximum hardness and case depth fo SM45C steel are 780Hv and 0.4mm by laser hardening.

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Surface Transformation Hardening for Rod-shaped Carbon Steels by High Power Diode Laser (고출력 다이오드 레이저(HPDL)를 이용한 탄소강 환봉의 표면변태경화)

  • Kim, Jong-Do;Kil, Byung-Lea;Kang, Woon-Ju
    • Journal of the Korean Society of Marine Engineering
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    • v.31 no.8
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    • pp.961-969
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    • 2007
  • The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

Study on Characteristics of Laser Surface Transformation Hardening for Rod-shaped Carbon Steel (I) - Characteristics of Surface Transformation Hardening by Laser Heat Source with Gaussian Intensify distribution - (탄소강 환봉의 레이저 표면변태경화 특성에 관한 연구 (I) - 가우시안 파워밀도 분포의 레이저 열원을 이용한 표면변태경화 특성 -)

  • Kim, Jong-Do;Kang, Woon-Ju
    • Journal of Welding and Joining
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    • v.25 no.3
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    • pp.78-84
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    • 2007
  • Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

Phase Transformation and Work-hardening Behavior of Ti-based Bulk Metallic Glass Composite

  • Hong, Sung Hwan;Kim, Jeong Tae;Park, Hae Jin;Kim, Young Seok;Park, Jin Man;Suh, Jin Yoo;Na, Young Sang;Lim, Ka Ram;Kim, Ki Buem
    • Applied Microscopy
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    • v.45 no.2
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    • pp.37-43
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    • 2015
  • In present work, work-hardening behavior of TiCu-based bulk metallic glass composite with B2 particles has been studied by systemic structural and mechanical investigations. After yield, pronounced work-hardening of the alloy was clearly exhibited, which was mainly related to the martensitic transformation as well as the deformation twinning in B2 particles during deformation. At the early plastic deformation stage (work-hardening stage), the stress-induced martensitic transformation from B2 phase to B19' phase and deformation-induced twinning of B19' phase was preferentially occurred in the around interface areas between B2 phase and amorphous matrix by stress concentration. The higher hardness value was observed in vicinity of interface within the B2 particles which are probably connected with martensitic transformation and deformation twinning. This reveals that the work-hardening phenomenon of this bulk metallic glass composite is a result of the hardening of B2 particles embedded in amorphous matrix.

Using Genetic Algorithm for Optimal Security Hardening in Risk Flow Attack Graph

  • Dai, Fangfang;Zheng, Kangfeng;Wu, Bin;Luo, Shoushan
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.9 no.5
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    • pp.1920-1937
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    • 2015
  • Network environment has been under constant threat from both malicious attackers and inherent vulnerabilities of network infrastructure. Existence of such threats calls for exhaustive vulnerability analyzing to guarantee a secure system. However, due to the diversity of security hazards, analysts have to select from massive alternative hardening strategies, which is laborious and time-consuming. In this paper, we develop an approach to seek for possible hardening strategies and prioritize them to help security analysts to handle the optimal ones. In particular, we apply a Risk Flow Attack Graph (RFAG) to represent network situation and attack scenarios, and analyze them to measure network risk. We also employ a multi-objective genetic algorithm to infer the priority of hardening strategies automatically. Finally, we present some numerical results to show the performance of prioritizing strategies by network risk and hardening cost and illustrate the application of optimal hardening strategy set in typical cases. Our novel approach provides a promising new direction for network and vulnerability analysis to take proper precautions to reduce network risk.

Softening and hardening tuned mass dampers

  • Khalili, Mohammad Khalil;Badamchi, Karim
    • Earthquakes and Structures
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    • v.14 no.5
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    • pp.459-465
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    • 2018
  • Reducing response of buildings during earthquakes by mass dampers, has been examined in many articles and books. Nowadays, many researchers are trying to realistically examine this type of dampers by new methods of performance. In this paper, for the better study of tuned mass damper (TMD), two schematic models are presented for a passive TMD with softening stiffness (softening TMD) and a passive TMD with hardening stiffness (hardening TMD). Then by modeling and analysis of the damper on a single degree of freedom (SDOF) structure and an 11-story steel building, the dampers performance was evaluated. State space was used for damper and structure modeling and to solve nonlinear equations, the Newton-Raphson method was used. The results show that when the structure is subjected to the Chi-Chi earthquake, response of the sixth floor in the system without TMD reduces 54.0% in comparison to the structure with softening TMD. This percentage of reduction for hardening TMD is 55.0%. Also for the Tabas earthquake, reduction in the RMS acceleration of the sixth floor in the system with hardening TMD is 96.2% more than the structure without TMD. This percentage of reduction for hardening TMD is 96.3%.

Effects of strain hardening of steel reinforcement on flexural strength and ductility of concrete beams

  • Ho, J.C.M.;Au, F.T.K.;Kwan, A.K.H.
    • Structural Engineering and Mechanics
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    • v.19 no.2
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    • pp.185-198
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    • 2005
  • In the design of reinforced concrete beams, it is a standard practice to use the yield stress of the steel reinforcement for the evaluation of the flexural strength. However, because of strain hardening, the tensile strength of the steel reinforcement is often substantially higher than the yield stress. Thus, it is a common belief that the actual flexural strength should be higher than the theoretical flexural strength evaluated with strain hardening ignored. The possible increase in flexural strength due to strain hardening is a two-edge sword. In some cases, it may be treated as strength reserve contributing to extra safety. In other cases, it could lead to greater shear demand causing brittle shear failure of the beam or unexpected greater capacity of the beam causing violation of the strong column-weak beam design philosophy. Strain hardening may also have certain effect on the flexural ductility. In this paper, the effects of strain hardening on the post-peak flexural behaviour, particularly the flexural strength and ductility, of reinforced normal- and high-strength concrete beams are studied. The results reveal that the effects of strain hardening could be quite significant when the tension steel ratio is relatively small.

Properties of Strength of Ultrarapid-Hardening Polymer-Modified Mortar (초속경 폴리머 시멘트 모르타르의 강도특성)

  • Lee, Youn-Su;Joo, Myung-Ki;Yeon, Kyu-Seok
    • Proceedings of the Korean Society of Agricultural Engineers Conference
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    • pp.115-118
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    • 2001
  • The effects of polymer-cement ratio and shrinkage-reducing agent content on the strength properties of ultrarapid-hardening polymer-modified mortars using redispersible polymer powder are examined. As a result, the flexural and tensile strengths of the ultrarapid-hardening polymer-modified mortars using redispersible polymer powder tend to increase with increasing polymer-cement ratio, and tend to decrease with increasing shrinkage-reducing agent content. However, the compressive strength of the ultrarapid-hardening polymer-modified mortars using redispersible polymer powder decrease with increasing polymer-cement ratio and shrinkage-reducing agent content.

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Zona Hardening of Mouse Oocytes Undergone Meiotic Resumption In Vivo (체내에서 성숙이 재개된 생쥐난자의 투명대 경화)

  • Kim, Ji-Soo;Kim, Hae-Kwon;Park, Jong-Min;Lee, Seung-Jae;Lee, Joon-Young;Kim, Moon-Kyoo
    • Clinical and Experimental Reproductive Medicine
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    • v.24 no.1
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    • pp.1-11
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    • 1997
  • It is well known that the zona pellucidae of mouse oocytes become "hardened" when they are allowed to mature in vitro in the absence of serum components. To see if oocytes already undergone meiotic resumption in vivo exhibit similar zona hardening, hardening of ZP of cumulus-enclosed oocytes(CEOs) was examined after culture in vitro since their release from follicles various hours after hCG injection. When CEOs matured in vivo for 3h or longer were subjected to culture in vitro for 14h with BSA alone, zona hardening was significantly reduced compared to those cultured in vitro from the begining of maturation. However, when CEOs matured in vivo for 5h were freed from cumulus cells and then cultured in vitro with BSA alone, little reduction of zona hardening was observed. Preincubation of CEOs for 5h with fetuin, one of the well known inhibitor of in vitro zone hardening, did not prevent zona hardening during its subsequent culture of CEOs for 14h without fetuin. However, when CEOs precultured with both fetuin and PMSG for 5h and then further cultured with BSA alone for 14h, zona hardening was dramatically reduced. Under these conditions, the expansion of cumulus cell was observed. In addition, CEOs cultured with both BSA and dbcAMP to prevent their meiotic resumption showed a significant increase of zona hardening. Whether the observed zona hardening was correlated with the conversion of ZP2 to $ZP2_{f}$ was examined. Zona pellucida, isolated from CEOs matured for 5h in vivo and then further cultured with BSA alone was subjected to SDS-PAGE. Most of ZP2 molecules from these CEOs did not undergo conversion from ZP2 to $ZP2_{f}$. From these results, it is concluded that CEOs undergone meiotic resumption in vivo do not exhibit zona hardening when they were subsequently cultured in vitro without serum components. It appears that cumulus cells play an important role in this phenomenon.

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