• Title, Summary, Keyword: Fracture behaviour

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Behaviour and design of Grade 10.9 high-strength bolts under combined actions

  • Li, Dongxu;Uy, Brian;Wang, Jia;Song, Yuchen
    • Steel and Composite Structures
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    • v.35 no.3
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    • pp.327-341
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    • 2020
  • The use of high-strength steel and concrete in the construction industry has been gaining increasing attention over the past few decades. With it comes the need to utilise high-strength structural bolts to ensure the design load to be transferred safely through joint regions, where the space is limited due to the reduced structural dimensions. However, research on the behaviour of high-strength structural bolts under various loading combinations is still insufficient. Most of the current design specifications concerning high-strength structural bolts were established based on a very limited set of experimental results. Moreover, as experimental programs normally include limited design parameters for investigation, finite element analysis has become one of the effective methods to assist the understanding of the behaviour of structural components. An accurate and simple full-range stress-strain model for high-strength structural bolts under different loading combinations was therefore developed, where the effects of bolt fracture was included. The ultimate strength capacities of various structural bolts obtained from the present experimental program were compared with the existing design provisions. Furthermore, design recommendations concerning the pure shear and tension, as well as combined shear and tension resistance of Grade 10.9 high-strength structural bolts were provided.

A Study on the Cutting Characteristics in the Machining of SKD11 by Face Milling (난삭재인 SKD11의 정면밀링 가공시 절삭특성에 관한 연구)

  • 김형석;문상돈;김태영
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.73-78
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    • 1994
  • Wear and fracture mode of ceramic tool for hardened SKD11 steel was investigated by face milling in this study. The cutting force and Acoustic Emission(AE) signal were utilized to detect the wear and fracture of ceramic tool. The following conclusions were obtained : (1) The wear and fracture modes of ceramic tool are characterized by three types: \circled1wear which has normal wear and notch wear, \circled2 wear caused by scooping on the rake face, \circled3 large fracture caused by thermal crack in the rake face. (2) The wear behaviour of ceramic tool can be detected by the increase of mean cutting force and the variation of the AE RMS voltage. (3) The catastrophic fracture of ceramic tool can be detected by the cutting force(Fz-component). (4) As the hardness of work material increased, Acoustic Emission RMS value and mean cutting force(Fz) increased linearly, but the tool life decreased.

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A Study on the Fracture Characteristics of 7075 Aluminum Alloy (7075 Al 합금의 파괴특성에 관한 연구)

  • Joung, Tai-Seoung;Kang, In-Chan
    • Journal of Korea Foundry Society
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    • v.12 no.1
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    • pp.32-39
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    • 1992
  • In this study, electron microscopy, Fractography and $J_{IC}$ test have been used to investigate the fracture behaviour in the scope of aging temperature which 7075 Al-alloy can have high strength. Conclusions obtained on this study are as followed. 1) When the 7075 Al-alloy was aged for 24hrs at $120^{\circ}C$, it's mechanical properties was excellent but fracture toughness decrement resulted from intergranular fracture was emerged. 2) The state of aged for 24hrs at $100^{\circ}C$, had the highest fracture toughess. 3) We could infer that intergranular fracture occurred because preferrential precpitated precipitates in the grain boundary growed in the form of colinear along the grain boundary.

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Retrofitting of RC girders using pre-stressed CFRP sheets

  • Bansal, Prem Pal;Sharma, Raju;Mehta, Ankur
    • Steel and Composite Structures
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    • v.20 no.4
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    • pp.833-849
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    • 2016
  • Pre-stressing of existing structures using steel cables, FRP cables or FRP laminates has been successfully tried in the past. Retrofitting of beams using pre-stressed laminates does not utilize the full strength of the FRP due to de-bonding of the laminates before the fibre fracture. In the present study attempt has been made to overcome this problem by replacing the FRP laminates by the FRP sheets. In the present paper the effect of initial damage level and pre-stress level on strength, stiffness, cracking behaviour and failure mode of girders retrofitted using pre-stressed CFRP sheets has been studied. The results indicate that rehabilitation of initially damaged girders by bonding pre-stressed CFRP sheets improves the flexural behaviour of beams appreciably. However, it has been observed that with increase in pre-stressing force the load carrying capacity of the girders increases up to a particular level up to which the mode of failure is fibre fracture. Thereafter, the mode of failure shifts from fibre fracture to de-bonding and there is no appreciable increase in load carrying capacity with further increase in pre-stressing force.

Study on Fatigue Analysis of DCB Specimen Bonded (접착제로 접합된 DCB 시험편의 피로 해석에 관한 연구)

  • Choi, Hae-Kyu;Hong, Soon-Jik;Kim, Sei-Hwan;Cho, Jae-Ung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.7
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    • pp.2865-2871
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    • 2012
  • In this study, the fracture behaviour of DCB(double cantilever beam) specimen with aluminum foam composite materials is analyzed by simulation. By comparing the analysis results with two models of 25 mm and 40 mm, the model with thickness of 25 mm is weaker than 40 mm at fatigue life and damage. Two models are unfavorable at 'SAE Transmission' in case of nonuniform fatigue load and rainflow matrices are weakest at 'SAE Bracket history'. In damage matrices, the model with 25 mm of thickness is weaker than the model with 40 mm of thickness but the model with 40 mm of thickness relative damage possibility is higher than in case of 25 mm. As two models are safest at 'SAE Transmission', the relative damage becomes the lowest value from 1.1 to 1.8 %. The mechanical property can be investigated by applying these analyses results with the real composite structure bonded with adhesive and analyzing fracture behaviour.

Fatigue Fracture Behaviour of Hollow Section Joints

  • Lichun Bian;Lim, Jae-Kyoo
    • Proceedings of the KWS Conference
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    • pp.281-284
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    • 2001
  • Fatigue behaviour of eight different hollow section T-joints was investigated experimentally using scaled steel models. The joints had circular brace members and rectangular chords (CRHS). Hot spot stresses and the stress concentration factors (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The experimental SCF values for CRHS joints were found to be between those of circular-to-circular (CCHS) and rectangular-to-rectangular (RRHS) hollow section joints. The fatigue strength referred to experimental hot spot stress was in reasonably good agreement with current fatigue design codes for tubular joints.

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ACOUSTIC EMISSION ANALYSIS FOR FRACTURE CHARACTERISTICS OF DENTAL POSTERIOR COMPOSITES (구치부 수복용 복합레진의 파괴특성에 관한 Acoustic Emission 연구)

  • Park, Jin-Hoon;Kim, Kyo-Han
    • Restorative Dentistry and Endodontics
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    • v.17 no.1
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    • pp.153-165
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    • 1992
  • Dental composite resin is a kind of the particle - reinforced composite material, and is widely used in recent dental restoration of anterior and posterior tooth region. The purpose of this study was to investigate the fracture behaviour according to volume fractions and external findings of the filler particles for better interpretation of the fracture characteristics of posterior dental composite resins by analytic method of fracture mechanics. The plane strain fracture toughness($K_{IC}$) and Acoustic Emission were determined with three - point bending test using the single edge notch specimen according to the ASTM - E399, and its analyzed data was compared with filler volume fractions derived from the standard ashing test and scanning electron fractographs of each specimen including the unfilled experimental resin as a control. The results were that the value of fracture toughness of the composite resin material was in the range from 0.85 MPa$\sqrt{m}$ to 1.60 MPa$\sqrt{m}$ and was higher than the value of the unfilled experimental resin, and the fracture behaviours dervied from Acoustic Emission analysis show prominent differences according to the volume fraction and the size of filler particles used in each composite resin. The degree of resistance against crack propagation seems to be increase and the fractographs demonstrate the high degree of surface roughness and irregularity according with the increase of fracture toughness value.

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Low Cycle Fatigue Behaviour of AISI 304L Austenitic Stainless Steel Weldment (AISI 304L 오오스테나이트 스테인레스 강 용접부 의 Low Cycle Fatigue 거동에 관한 연구)

  • 김환태;황선효;남수우
    • Journal of Welding and Joining
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    • v.2 no.1
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    • pp.49-57
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    • 1984
  • The influence of weld defect, residual stress and microstructure on the Low Cycle Fatigue(L. C. F.) behaviour of AISI 304L austenitic stainless steel weldment has been studied. The specimens were welded by shielded metal are welding process, post weld heat treated(PWHT) at 900.deg.C for 1.5hrs, and tested under total strain controlled condition at room temperature. The results of the experiment showed that weld defect affected the L.C.F. behaviour of weldment deleteriously compared to the residual stress or microstructure, and it reduced the L.C.F. life about 70-80%. The PWHT exhibited beneficial effect on the L.C.F. behaviour and increased the L.C.F. life about 120%. This enhancement by PWHT was attributed to the removal of residual stress and recovery of weld metal ductility. The cyclic stress flow of as welded specimens showed intermediate cyclic softening, whereas those of heat treated specimens showed continuous cyclic hardening, and this difference was explained in terms of the residual stress removal and dislocation behaviour. Scanning electron microscopy studies of fatigue fracture surface showed that weld defects of large size and near weld surface were detrimental to the L.C.F. behaviour of weldment.

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Simulation of Plastic Collapsing Load and Deformation Behaviours(I) (소성 붕괴하중 및 변형거동 해석(1))

  • 김영석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2165-2172
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    • 1995
  • Optimization of mesh discretization has been proposed to improve the accuracy of limit analysis solution of collapse load by using the Rigid Body Spring Model(R. B. S. M) under the plane strain condition. Moreover, the fracture behaviour of materials was investigated by employing the fracture mechanism of a spring connecting the triangular rigid body element. It has been clarified that the collapse load and the geometry of slip boundary for optimized mesh discretization were close to those of the slip line solution. Further, the wedge-shaped fracture of a cylinder under a lateral load and the central fracture of a strip in the drawing process were well simulated.

A Comparative Study of Microstructure and Fracture Behavior in Reaction-Bonded Alumina (반응결합한 알루미나의 미구조와 파괴거동에 대한 비교 연구)

  • 이종호;장복기
    • Journal of the Korean Ceramic Society
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    • v.29 no.7
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    • pp.517-524
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    • 1992
  • For the present study two alumina bodies were prepared. The sinter-aid alumina body(SAA) was made by conventional sinter-process using sintering additives of TiO2 & MgO/CaO and the reaction-bonded alumina (RBA) made from Al-Al2O3 mixed powder. A comparison was made between those two bodies and this investigation seeks to evaluate their microstructure, physical properties and material's reliability as well as their fracture behaviour. In spite of its considerable microstructural densification accompanied by sintering shrinkage, SAA is largely inferior to RBA in fracture strength. However, SAA shows a somewhat higher m-value than RBA in respect to the material's reliability, the Weibull modulus(m). RBA, which has high fracture strength, shows much longer lifetime under static loading than SAA. Though, as with m of fracture strength, the reliability(mt) of lifetime prediction in RBA is less high than of SAA.

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