• Title/Summary/Keyword: High fracture toughness

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Effect of Temperature on Interlaminar Fracture Toughness of Filament-Wound Carbon/Epoxy Composites (필라멘트 와인딩된 카본/에폭시 복합재의 층간파괴인성에 미치는 온도 영향)

  • Im, JaeMoon;Shin, KwangBok;Hwang, Taekyung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.5
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    • pp.491-497
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    • 2015
  • This paper reports an experimental study for evaluating the effect of temperature on the mode I, mode II and mixed-mode interlaminar fracture toughness of adhesive joints with a curved cross-section of filament-wound dome-separated composite pressure vessel. Mode I and mixed-mode interlaminar fracture toughness were evaluated using DCB specimens, while mode II interlaminar fracture toughness was determined using ENF specimens. $[{\pm}10^{\circ}]_6$, $[{\pm}27^{\circ}]_6$ and ($[{\pm}10^{\circ}]_3/FM73/[{\pm}27^{\circ}]_3$) winding specimens with the curved cross-section were considered. In-situ temperature environments were simulated with a range of $-30^{\circ}C-60^{\circ}C$ using an environmental chamber and furnace. Experimental results on the effect of temperature indicate that interlaminar fracture toughness tends to be high at low temperature and is degraded with increase in temperature. For specimen types, it was found that interlaminar fracture toughness of $[{\pm}10^{\circ}]_3/FM73/[{\pm}27^{\circ}]_3$ winding specimens considered as adhesive joints of dome and helical part was higher than other specimens.

R-Curve Behavior of Particulate Composites of ${Al_2}{O_3}$ Containing SiC and $ZrO_2$: I. Experiment (SiC와 $ZrO_2$를 함유하는 ${Al_2}{O_3}$ 입자복합체의 균열저항거동 : I. 실험)

  • 박관수;이승환;이재형
    • Journal of the Korean Ceramic Society
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    • v.37 no.4
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    • pp.359-367
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    • 2000
  • Particulate composites of Al2O3/SiC, Al2O3/ZrO2 and Al2O3/ZrO2/SiC have been fabricated to investigate their R-curve behaviors and toughening mechanisms. Al2O3 containing 30 vol% SiC particles of 3${\mu}{\textrm}{m}$ showed rising R-curve behavior owing to the strong crack bridging by SiC particles. The fracture toughness reached 9.1 MPa {{{{ SQRT {m} }} at the crack length of 1000${\mu}{\textrm}{m}$. On the other hand, ZrO2-toughened Al2O3 had a high flat R-curve since it rose steeply in the short crack region due to the well known transformation toughening. For Al2O3/ZrO2/SiC composites, the R-curve behavior was similar to that of Al2O3/SiC but with slightly higher toughness. The SiC particles in this composite decreased the amount of transformable tetragonal phase to reduce the effect of transformation toughening by 50%. It was also found that the fracture toughness of this composite with two different toughening mechanisms was markedly lower than that estimated by the simple addition of two contributions.

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A Study on Effect of PWHT in AH36-TMCP Steel (AH36-TMCP강의 용접후열처리 효과에 관한 연구)

  • 유효선;장원상;안병국;정세희
    • Journal of Welding and Joining
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    • v.16 no.6
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    • pp.44-51
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    • 1998
  • It is well known that the fine bainitic microstructure obtained by TMCP(thermo-mechanical control process) secures the high toughness of base metal. Besides, TMCP steel is very suitable for high heat input in welding as it has low carbon equivalent. In HAZ, however, the accelerated cooling effect imparted on the matrix by the weld thermal cycles is relieved and thus the weldment of TMCP steel has softening zone which shows low fracture toughness compared with base metal. Therefore, PHWT of weldment is carried out to improve the fracture toughness in weldment of TMCP steel which has softening zone. In this study, the effects of PWHT on the weldment of AH36-TMCP steel are investigated by the small punch (SP) test. From the several results such as SP energy and displacement at room temperature, the behavior of transition curves, the fracture strength at -196$^{\circ}C$, distribution of (DBTT)sp and (DBTT)sp, the PWHT condition of A.C. after 85$0^{\circ}C$-1 sec W.C. was suitable condition for recovering a softening zone of HAZ as welded.

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Development of Ceramic Roll Materials for Food Grinding Processing and Evaluation of Mechanical Behavior (식품분쇄용 세라믹 롤 재료 개발과 기계적 특성평가)

  • 강위수
    • Journal of Biosystems Engineering
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    • v.26 no.1
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    • pp.47-56
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    • 2001
  • In order to prevent the possibility of mixing of metal powder during food grinding processing with the metal roll mill this study was conducted to develope the materials of ceramics roll as a substitute of gray cast iron mill. Since the ceramics is brittle material and can be broken easily by a crack, it was needed to develope engineering ceramics roll materials with high elastic modulus and fracture toughness. Adding 0∼50 wt% Al$_2$O$_3$as densification additives to porcelain body material and forming the ceramics an different condition, mechanical properties were evaluated. The material structure’s densification process was analyzed by SEM and XRD. The evaluation of the mechanical properties of ceramics roll materials were compared and analyzed by non-destructive test using Young’s modulus and destructive test using 3-point bending strength and fracture toughness. The results showed several correlative results. Porcelain body material with 40 wt% Al$_2$O$_3$content heated at 1,200$\^{C}$ for 5h was high bulk density of 2.77, Young’s modulus of 118.4Gpa, 3-point bending strength of 137 MPa and fracture toughness of 2.88 MPa$.$m$\^$$\sfrac{1}{2}$/ . After analyzing the relationship between non-destructive test and destructive test, the coefficient of determination was more than 0.9. Therefore, the evaluation of non-destructive test by ultrasonic was turned out to be feasible in evaluating the mechanical properties of ceramics.

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Spark Plasma Sintering Behavior of Binderless WC Powders

  • Kim, Hwan-Tae;Park, Dong-Wook;Kim, Ji-Soon;Kwon, Young-Soon;Kwon, Hye-Suk;Baek, Eung-Ryul
    • Journal of Powder Materials
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    • v.10 no.3
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    • pp.176-180
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    • 2003
  • Pure WC powders which does not include a binder phase were consolidated by spark plasma sintering (SPS) process at 1600~185$0^{\circ}C$ for 0~30 min under 50 MPa. Microstructure alid mechanical properties of binderless WC prepared by SPS were investigated. With increasing sintering temperature, sintered density and Vickers hardness of binderless WC increased. The fracture toughness of binderless WC was 7~15 MPa $m^{1/2}$ depending on the sintered density and decreased with increasing the Vickers hardness. It is found that the binderless WC prepared by SPS at 175$0^{\circ}C$ for 10 min under 50 MPa showed nearly full densification with fine-grained structure and revealed excellent mechanical properties of high hardness (~HV 2400) and considerably high fracture toughness (~7 MPa $m^{1/2}$).

Simultaneous Synthesis and Densification of Wc-xvol.%Co Hard Materials by High-Frequency Induction Heated Combustion

  • Kim, H.C.;Oh, D.Y.;Jeong, J.W.;Shon, I.J.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2003.10a
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    • pp.41-42
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    • 2003
  • Using a developed high-frequency induction heated combustion method. the simultaneous synthesis and densification of WC-xvol.%Co($0{\leq}x{\leq}20$) hard materials was accomplished using elemental powders of W, C and Co. A complete synthesis and densification of the materials was achieved in one step within a duration of 1min. The final relative densities of the composite were over 98.5% for all cases, under the applied pressure of 60 MPa and the induced current. The hardness of the composites decreases and the fracture toughness increases with increasing cobalt content. As the carbon to tungsten ration increases, the hardness increase, but the fracture toughness decreases. The maximum values for the fracture toughness and hardness are 15.1 $MPa{\cdot}m^{1/2}$(at 20vol.%Co, W:C=1:1), and 1928 $kg/mm^{2}$(at 5vol.%Co, W:C=1:1.3), respectively. Therefore we concluded that the HFIHCS method. which can produce WC-xvol.%Co within 1 minute in one step is superior to conventional ones.

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Fabrication and High-temerature Mechanical Property of Liquid-Phase-Sintered SiC (액상소결 탄화규소 세라믹스의 제조 및 고온기계적 특성)

  • Lee, Moonhee;Kim, Sungwon;Lee, Jongho;Hwang, SeungKuk;Gwak, Jaehwan;Lee, Jinkyung;Lee, Sangpill
    • Journal of the Korean Society of Industry Convergence
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    • v.23 no.4_2
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    • pp.669-674
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    • 2020
  • Liquid-phase-sintered (LPS) SiC materials were briefly examined with their microstructure and mechanical property. Especially, effect of high-temperature exposure on the tendency of fracture toughness of LPS-SiC were introduced. The LPS-SiC was fabricated in hot-press by sintering powder mixture of sub-micron SiC and sintering additives of Al2O3-Y2O3. LPS-SiC represented dense morphology and SiC grain-growth with some amount of micro-pores and clustered additives as pore-filling. The strength of LPS-SiC might affected by distribution of micro-pores. LPS-SiC tended to decrease fracture toughness depending on increasing exposure temperature and time.

Characteristic and Measurement Technology of Inner Welding Residual Stresses in Thick Steel Structures (극후물재 용접부 내부잔류응력 측정기술 및 특성)

  • Park, Jeong-ung;An, Gyu-baek;Woo, Wanchuck
    • Journal of Welding and Joining
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    • v.34 no.2
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    • pp.16-21
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    • 2016
  • Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW), especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficient toughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thickness were compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the inside of the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.

Synthesis and Rapid Consolidation of W-1.5 ZrO2 Composite (W-1.5 ZrO2 복합재료 합성과 급속소결)

  • Kim, Seong-Eun;Shon, In-Jin
    • Korean Journal of Materials Research
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    • v.28 no.11
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    • pp.653-658
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    • 2018
  • $ZrO_2$ is a candidate material for hip and knee joint replacements because of its excellent combination of biocompatibility, corrosion resistance and low density. However, the drawback of pure $ZrO_2$ is a low fracture toughness at room temperature. One of the most obvious tactics to cope with this problem is to fabricate a nanostructured composite material. Nanomaterials can be produced with improved mechanical properties(hardness and fracture toughness). The high-frequency induction heated sintering method takes advantage of simultaneously applying induced current and mechanical pressure during sintering. As a result, nanostructured materials can be achieved within very short time. In this study, W and $ZrO_2$ nanopowders are mechanochemically synthesized from $WO_3$ and Zr powders according to the reaction($WO_3+3/2Zr{\rightarrow}W+3/2ZrO_2$). The milled powders are then sintered using high-frequency induction heating within two minutes under the uniaxial pressure of 80MPa. The average fracture toughness and hardness of the nanostructured W-3/2 $ZrO_2$ composite sintered at $1300^{\circ}C$ are $540kg/mm^2$ and $5MPa{\cdot}m^{1/2}$, respectively. The fracture toughness of the composite is higher than that of monolithic $ZrO_2$. The phase and microstructure of the composite is also investigated by XRD and FE-SEM.

An Evaluation of the Fracture Behavior for Flash Butt Welding zone by Acoustic Emission Method (AE방법에 의한 Flash Butt 용접부의 파괴거동 평가)

  • 김용수;이하성;강동명
    • Journal of the Korean Society of Safety
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    • v.9 no.1
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    • pp.9-18
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    • 1994
  • In this study, we conducted experimental tests to evaluate fracture behaviors of fresh-butt welded metal by Acoustic Emission technique. We selected similar welding and dissimilar welding process, the one welded for SM45C, SS41 and SUS304 of each material, the other for SM45C and SS41, SM45C and SUS304 and SS41 and SUS304. The fracturing processes of weld metal were estimatied through the fracture toughness test with compact tension specimens and fractography analysis. In ASTM test method E-399, type I curves for materials of this study were obtained by load-cod diagram of fracture toughness test. and 5% offset load( $P_{5}$) was estimated as the estimated crack initial load( $P_{Q}$), The estimated crack initial load( $P_{Q}$) of similar welding materials generally lower than base matal, and then SM45C appeared greatly in decreasing rate of PB, SS41 and SUS304 appeared in order. $P_{Q}$ of dissimilar welding materials were lower than the similar welding materials. $P_{Q}$ of welding of SM45C and SS41 appeared in small, SUS304 and SS41 appeared greatly in dissimilar welding materials. In fracture toughness test, AE counts increased before the inflection point of the slope, decreased after that. It was found that increasing of AE counts were due to the microcrack formation at the crack tip near the $P_{5}$ point through AE data. For welding materials in this study, both low and high AE amplitude appeared simulataneously. It was confirmed that the low AE amplotude was due to formation of micro void, micro crack or micro dimple, the high AE amplitude was caused by microvoid coalescence and quasi-cleavage fracture through analyses of fractograpy.apy.apy.apy.

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