• Title/Summary/Keyword: Fracture toughness

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Systematic Study of Paper Breaks in Papermaking Process Using Fracture Mechanics - (1) Evaluation of fracture Toughness in Wet State

  • Seo, Yung-B;Roh, You-Sun
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.33 no.5
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    • pp.37-44
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    • 2001
  • Fracture toughness was considered as one of the good estimates of the paper break tendency of paper web in the press room. Paper break on the paper machine is caused by many factors such as paper machine irregular vibrations, impurities in the fiber furnish, shives, and so on. On the paper machine, the solid content of paper web is changing very rapidly from less than 1% to over 95%. We tried to measure the fracture toughness of paper web at different solid contents for providing the fundamental knowledge of paper break. Stretches of wet web were also measured and compared to the fracture toughness changes. Four different fiber furnishes (SwBKP, HwBKP, ONP, and OCC) were refined to different degrees, and at different solid contents (40%, 60%, 80% and 95%), their fracture toughnesses were measured. Two fracture toughness measurement methods (essential work of fracture and Tryding's load-widening method) were used, and we found they gave identical results. The stretch curves of the wet webs against the axis of solid contents were very similar to the fracture toughness curves of those.

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Study on Fracture Toughness and Heat Input in Weld HAZ of Cr-Mo Steel (I) (welding structure) (Cr-Mo강 용접열영향부의 파괴인성과 용접입열량에 관한 연구(I) (HAZ 고유조직을 중심으로))

  • 임재규;정세희
    • Journal of Welding and Joining
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    • v.2 no.2
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    • pp.54-61
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    • 1984
  • Construction of welding structure is greatly dependent upon welding heat cycle. Fracture toughness is decreased remarkablely due to coarse grained HAZ and inequal residual stress of three dimensions to originate in welding. Post weld heat treatment(PWHT) is carried out to increase the fracture toughness of HAZ and to remove the residual stress. There occur some problem such as toughness decrement and stress relief cracking(SRC) in the coarse grained HAZ subject to the effect of tempering treatment. Therefore, in this paper, the effect of heat inputs affecting cooling rate and PWHT under the no stress on fracture toughness were evaluated by crack opening displacement (COD), SEM and micro-hardness test. Experimental results are as follows; 1. Fracture toughness of weld HAZ is dependent upon weld heat cycle and it is decreased with increment of heat input, but the degree of improvement of fracture toughness after PWHT was linearly increased with heat input. 2. Hardness of the parent metal is not changed, but the softening of coarse grained HAZ is remarkable due to PWHT. 3. Fracture surface of as-weld show the perfect brittle fracture with the cleavage fracture, but after PWHT they appear the ductile fracture surface with dimple.

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A Study on the Impact Fracture Toughness of Epoxy Matrix Composites (에폭시기지 복합재료의 충격파괴인성에 관한 연구)

  • Kim, Jae-Dong;Jeon, Jin-Tak;Koh, Sung-Wi
    • Journal of Fisheries and Marine Sciences Education
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    • v.9 no.2
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    • pp.188-197
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    • 1997
  • The fracture toughness of three different kinds of epoxy-matrix composites containing the same volume fraction of reinforcement and the variation of fracture toughness of glass-carbon fiber/epoxy hybrid composites due to the change of test temperature and different glass fiber content were investigated in this study. Glass fiber/epoxy composite provided much higher fracture toughness than that of other composites because of the high strain at failure of glass fiber. Particularly the carbon fiber/epoxy composite exhibited the low fracture toughness caused by the low strain energy absorbing capacity of carbon fiber. And it was found that the strain at failure of reinforcement and interfacial delamination absorbing a significant amount of impact energy played an important role to increase fracture toughness of composites. The fracture toughness of the glass-carbon fiber hybrid composites increased with increasing the glass fiber content and decreased with raising the test temperature. The residual stress arising from the different thermal expansion between the matrix and reinforcement influenced the fracture toughness of composites.

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Dynamic Fracture Toughness of Chevron-notch Ceramic Specimens measured in Split Hopkinson Pressure Bar

  • Lee, Yeon-Soo;Yoon, Young-Ki;Yoon, Hi-Seak
    • International Journal of Precision Engineering and Manufacturing
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    • v.3 no.3
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    • pp.69-75
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    • 2002
  • Measuring dynamic fracture toughness of brittle and small ceramic specimen is very difficult in a SHPB (Split Hopkinson Pressure Bar). As a countermeasure to this difficulty, a dynamic fracture toughness measuring method by the Chevron-notch ceramic specimen was proposed. Tested chevron specimens were of Chevron notch angles of 90$^{\circ}$, 100$^{\circ}$ and 110$^{\circ}$. Through finite element analysis, shape parameters of the Chevron-notch specimens according to notch angles were calculated. And the static fracture tough1ess of the Chevron-notch alumina specimen was measured as 3.8MPa√m similar to that of CT specimen with a precrack. Dynamic fracture toughness was 4.5MPa√m slightly higher than the static one. It was shown in this study that the proposed Chevron-notch specimens are valid to measure dynamic fracture toughness of extremely brittle materials such as ceramic.

Evaluation of Fracture Toughness on Interface Cracks in Bonded Components of Dissimilar Materials (이종 접합부재의 계면균열 파괴인성의 평가)

  • Chung, Nam-Yong;Lee, Myung-Dae;Park, Chul-Hee
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.346-351
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    • 2003
  • In this paper, an evaluation method of fracture toughness on interface cracks has been investigated under various mixed-mode conditions of the bonded scarf joints. Two types of the bonded scarf joints with an interface crack were prepared to analyze the stress intensity factors using boundary element method(BEM) and to perform the fracture toughness test. From the results of fracture toughness experiments and BEM analysis, an evaluation method of fracture toughness on interface cracks in the bonded components of dissimilar materials has been proposed and discussed.

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Mehods of Fracture Toughness and Evaluation for Interface Crack in Adhesively Bonded Joints (접착이음의 계면균열에 대한 파괴인성 및 평가방법)

  • 정남용
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1998.03a
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    • pp.220-226
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    • 1998
  • In this pater, a method of strength evaluation applying fracture mechanics in adhesively bonded joints of A1/A1 materials was investigated. Various adhesively bonded joints of double-cantilever beam with a interfacial crack in its adhesive layer were prepared for the fracture toughness test of comprehensive mixed mode conditions from nearly pure mode I to mode II. The experiment of fracture toughness was carried out under various mixed mode conditions with an interfacial crack and critical energy release rate, Gc by the experimental measurements of compliances was determined. From the results, fracture toughness on mixed mode with an interfacial crack is well characterized by strain energy release rate and a method of strength evaluation by the fracture toughness in adhesively bonded joints of A1/A1 materials was discussed.

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Analysis of Economical Validity for Implementation of Telematics in Construction Fields (Telematics 기술의 건설현장 적용을 위한 경제적 타당성 분석)

  • Lee Sung Hyun;Lee Dong Wook;Koo Ja Kyung;Lee Tai Sik
    • Journal of the Korean Society for Railway
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    • v.8 no.5
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    • pp.444-453
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    • 2005
  • The safety evaluations of railway wheelsets make use of the static fracture toughness obtained in ingot materials. The static fracture toughness of wheelset materials has been extensively studied by experiments, but the dynamic fracture toughness with respect to wheelset materials has not been studied enough yet. It is necessary to evaluate the characteristics of the fracture mechanics depending on each location for a full-scale wheelset for high-speed trains, because the load state for each location of the wheelset while running is different the contact load between the wheel and rail, cyclic stress in the wheel plate, etc. This paper deals with the fracture toughness depend on load rates. The fracture toughness depending on load rate data shows that once the downward curve from quasi-static values was reached, subsequent values showed a slow increase with respect to the impact velocity. This means that dynamic fracture toughness should be considered in the design code of the wheelset material.

An Evaluation Method of fracture Toughness on Interface Cracks in Bonded Dissimilar Materials (이종 접합체의 계면균열에 대한 파괴인성의 평가방법)

  • 정남용
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.4
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    • pp.110-116
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    • 2003
  • In this paper, an evaluation method of fracture toughness on interface cracks has been investigated under various mixed-mode conditions of the bonded scarf joints. Two types of the bonded scarf joints with an interface crack were prepared to analyze the stress intensity factors using boundary element method(BEM) and to perform the fracture toughness test. From the results of fracture toughness experiments and BEM analysis, an evaluation method of fracture toughness on interface cracks in the bonded dissimilar materials has been proposed and discussed.

Relationship Between Refining, Wet Pressing and Fracture Toughness, Fracture Elongation -Fibers activation and fines activation- (고해와 압착에 의한 파괴 인성과 파괴 신장률의 변화 -섬유 활성화와 미세분 활성화-)

  • Lee, Jin Ho;Park, Jong-Moon
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.36 no.4 s.107
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    • pp.9-15
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    • 2004
  • To increase paper strength, refining and wet pressing are performed. Many researches were carried out to identify the origin of paper strength. Since fracture toughness was governed by stress concentration, fracture toughness reflects microscopic paper strength. The aim of this paper is to analyze how paper strength was affected by changes of refining and wet-pressing. Fiber properties and structural, tensile and fracture properties of hand­sheets were evaluated. Especially, fracture toughness was evaluated by J-integral. As the refining proceeds, stock properties maybe divided into two stages such as fibers activation and fines activation according to freeness. In fibers activation stages, about 750-450 mL CSF, the fracture toughness increased with refining and wet pressing but in fines activation stages, about 450-250 mL CSF, the fracture toughness increased only with wet pressing. It is clear that fracture toughness was affected not only by fibers properties but also by fines properties in fines activation stages.

Measurement of Fracture Toughness of WC-Co Composites by Micro-Vickers Indentation Cracks (미소 비커스 압입균열에 의한 초경합금의 파괴 인성치 측정)

  • Lee, O.S.;Son, I.S.;Park, W.K.;Hwang, S.K.
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.2
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    • pp.5-13
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    • 1995
  • Various techniques to measure fracture toughness which is an important parameter to predict fracture behavious of structural materials have been reported. Among these mathods, this paper describes the micro-Vickers indentation crack method to estimate the fracture toughness of some WC-Co composites. Two indentation crack patterns (such as radial-median cracks (orhalf-penny cracks) and Palmqvist cracks generated during indentation) are referred precisely. The fracture toughness of WC-4.7wt%Co, WC-6wr%Co and WE-9wr%Co composites were estimated by using some equations given by Shetty et al., Nihara et al. in this study. We show the reliability of indentation method by comparing the results with those from literatures. The appropriate equation to estimate the fracture toughness in the case of WC-Co composite is given. In addition, some technical informations in terms of the crack length by indentation in estimating the existence of the surface residual stress that prevents to obtain an accurate fracture toughness are presented.

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