• Title, Summary, Keyword: Fracture behaviour

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Ductile Fracture Behaviour under Mode I Loading Using Rousellier Ductile Damage Theory

  • Oh, Dong-Joon;Howard, I.C.;Yates, J.R.
    • Journal of Mechanical Science and Technology
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    • v.14 no.9
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    • pp.978-984
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    • 2000
  • The aim of this study is to investigate the ductile fracture behaviour under Mode I loading using SA533B pressure vessel steel. Experiments consist of the Round Notch Bar Test (RNB), Single Edge Crack Bending Test (SECB), and V-Notch Bar Test (VNB). Results from the RNB test were used to tune the damage modelling constant. The other tests were performed to acquire the J-resistance curves and to confirm the damage constants. Microstructural observation includes the measurement of crack profile to obtain the roughness parameter. Finally, simulation using Rousellier Ductile Damage Theory (RDDT) was carried out with 4-node quadrilateral element ($L_c=0.25\;mm$). For the crack advance, the failed element removal technique was adopted with a ${\beta}$ criterion. In conclusion, the predicted simulation using RDDT showed a good agreement with the experimental results. A trial using a roughness parameter was made for a new evaluation of J-resistance curve, which is more conservative than the conventional one.

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A Study on Deformation and Strength of High-Strength Polymer Composites Using Automobiles (자동차용 고강도 폴리머 복합재료의 변형과 강도에 관한 연구)

  • Im, Jae-Gyu;Sin, Jae-Hun;Park, Han-Ju;Shoji, T.;Takeda, H.
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.7
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    • pp.1082-1088
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    • 2001
  • Nowadays study on recycling disused plastics for automobiles was lively progressed. Rubber and talcum powder was added to retrieve degradation of physical properties caused by recycling disused polypropylene. The effect of the temperature, the fatigue load and the loading speed on DEN(double edged notch) specimen which was made by the pp-rubber composites during fracture was studied by. DEN specimen was made on PP-rubber composites through the injection molding. With increasing temperature the fracture strength was linearly decreased and the fracture energy was increased by $0^{\circ}C$ and after that decreased. In the same temperature the fracture strength during increasing the notch radius was hardly increased. The fracture behaviour at low and high loading speed was different entirely. At high loading speed plastic region was small and fracture behaviour was seen to brittle fracture tendency. With increasing fatigue load fracture energy was first rapidly decreased and subsequently steady when radius of notch tip was 2mm, but Maximum load during fracture scarcely varied. The deformation mechanism of polypropylene-rubber composites during fracture was studied by SEM fractography. A strong plastic deformation of the matrix ahead of the notch/crack occurred. The deformation seem to be enhanced by a thermal blunting of the notch/crack.

A Study on Behaviour of Tunnel Considering the Location of Groundwater Leaching and Fault Fracture Zone under Tunnel Construction (지하수 용출과 단층파쇄 위치에 따른 터널 거동 연구)

  • Son, Yongmin;Kim, Nagyoung;Min, Kyungjun
    • Journal of the Korean Geoenvironmental Society
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    • v.16 no.12
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    • pp.37-43
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    • 2015
  • Ground characteristics is important in tunnel structure utilizing the strength of underground. In the case of the fault fracture zone such as weak soil conditions exists in the tunnel section and groundwater leaching occurs at the same time, it happens to occur to excessive displacement or collapse of tunnel frequently. Fault fracture zone is an important factor that determines the direction of displacement and the collapse of the tunnel under construction. Behavior of fault fracture zone is determined depending on the size and orientation of the surface portion of the tunnel. If the groundwater occurs in the face of tunnel, groundwater causes displacement and collapse. And the collapse characteristics of tunnel is a major factor in determining that the time-dependent behavior. It is difficult to accurately predict groundwater leaching from the fault fracture zone in the numerical analysis method and analyze the interaction behavior of groundwater and fault fracture zone. Therefore numerical analysis method has limitations the analysis of ground water in the ground which the fault fracture zone and groundwater occurs at the same time. It is required to comprehensively predict the behavior of tunnel and case studies of tunnel construction. Thus, the location of fault fracture zone is an important factor that determines the direction of displacement and the collapse of the tunnel. In this study, behavior characteristics of the tunnel according to the location of the fault fracture was analyzed.

Influence of Notch Change on Corrosion Fatigue Fracture in F.E.M. Dual phase Steel of SS41 Steel (SS41강의 F.E.M.복합조직강에서 노치변화가 부식피로파괴에 미치는 영향)

  • 도영민;이규천
    • Journal of the Korean Society of Safety
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    • v.16 no.2
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    • pp.44-50
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    • 2001
  • The rotated bending fatigue test was conducted in air md in 3.5% NaCl salt solution to investigate the fatigue fracture behaviour of raw material and F.E.M dual phase steel made from raw material(SS41) by a suitable heat treatment. This study has compared the initial microcrack creation of material by tensile test with that by fatigue test. And the rotated bending test of cantilever type under the condition of 3.5% NaCl salt solution and air has investigated the corrosion fatigue fracture behaviour with the variation of stress concentration factor determined by each of notch shapes. The initial microcrack have been developed in fragile grainboundary with general corrosion occurring in raw material : in the pits built up by corrosion in F.E.M. dual phase steel because pits bring out stress concentration. It is small that the degree of decrease in corrosion fatigue life for F.E.M. dual phase steel compared with raw material because the notch sensitivity of F.E.M. dual phase steel is lower than raw material in reason of characteristics with two-phase construction.

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The Influence on the Corrosion Fatigue Crack Propagation in Changing of the Second Phase Hardness of Dual Phase Steel (複合組織鋼의 第2相 硬度變化가 腐蝕疲勞 크랙傳播에 미치는 影響)

  • 오세욱;김웅집
    • Journal of Welding and Joining
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    • v.11 no.2
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    • pp.42-52
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    • 1993
  • The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.

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The Influence of CNTs and Lamination Structure on the Intralaminar Fracture of CFRP/GFRP Composites (CFRP/GFRP 복합재료의 층내 파괴에 대한 CNT 및 적층구조의 영향)

  • Kim, Seong Hun;Yun, Yu Seong;Kang, Ji Woong;Kwon, Oh Heon
    • Journal of the Korean Society of Safety
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    • v.32 no.6
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    • pp.9-15
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    • 2017
  • Recently many researches were conducted on the interlaminar fracture that is a delamination between laminates by using ASTM standardized methods. However the experiment of the intralaminar a fracture is difficulty. In this study, four types of CFRP/GFRP composites with different layer structures were compared to evaluate an intralaminar fracture toughness under the mode I. Also the CNTs were added to the layer for the examination of the fracture toughness improvement. And the characteristics of the crack propagation behaviour was observed using a microscope. The obtained results can be useful for the evaluation of the intralaminar fracture toughness of the CNT reinforced CFRP/GFRP composites.

Fracture Behavior of $Al_2O_3$ Macro-composites with Layered and Fibrous Structure (층상 및 섬유상 $Al_2O_3$ 거시복합체의 파괴거동)

  • 신동우;윤대현;박삼식;김해두
    • Journal of the Korean Ceramic Society
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    • v.34 no.7
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    • pp.758-766
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    • 1997
  • Non-brittle fracture behaviour of the two composite structures made of two different brittle materials was investigated using 3-point bending test. First, the layered and fibrous macro-composites were fabricated using the material easily formed, yet showing a brittle fracture behaviour similar to ceramics. The layered and fibrous Al2O3 /Al2O3 composites with weak interface were also fabricated using plate of 2 mm thickness and rod of 3 mm diameter respectively. Comparison of the mechanical properties between these two structures was performed in the lights of flexural strength and work of fracture for the composites consisting of Al2O3 and simulated materials respectively. The strength ratio of layered structure to the monolith of same volume was 0.6 and the ratio of fibrous one was about 0.2 for the composites made of simulated brittle material. The ratio of the work of fracture of the fibrous to the layered was 0.47. For Al2O3/Al2O3 composites, the strength ratio of layered and fibrous structures to the monolith with same volume were about 0.6 and 0.2 respectively. The ratio of work of fracture of the fibrous to the layered was 0.6. These confirmed that the layered structure was superior to the fibrous one in terms of flexural strength and work of fracture.

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Effects of Material Characteristics on the Dynamic Response of the Reinforced Concrete Slabs (재료 특성이 철근 콘크리트 슬래브의 동적 거동에 미치는 영향)

  • Oh, Kyung-Yoon;Cho, Jin-Goo;Hong, Chong-Hyun
    • Journal of The Korean Society of Agricultural Engineers
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    • v.49 no.4
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    • pp.43-49
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    • 2007
  • The reinforced concrete slab is one of main structure members in the construction industry sector. However, most of researches regarding to RC slabs have been focused on two-dimensional Mindlin-type plate element on the basis of laminated plate theory since three-dimensional solid element has a lot of difficulties in finite element formulation and costs in CPU time. In reality, the RC slabs are subjected to dynamic loads like a heavy traffic vehicle load, and thus should insure the safety from the static load as well as dynamic load. Once we can estimate the dynamic behaviour of RC slabs exactly, it will be very helpful for design of it. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The applicability of the proposed finite element has been tested for dynamic behaviour of RC slabs with respect to characteristics of concrete materials in terms of cracking stress, crushing strain, fracture energy and Poisson's ratio. The effect on dynamic behaviour is dependent on not crushing strain but cracking stress, fracture energy and Poisson's ratio. In addition to this, it is shown the damping phenomenon of RC slabs has been identified from the numerical results by using Rayleigh damping.

Monitoring Failure Behaviour of Pultruded CFRP Composites by Electrical Resistance Measurement

  • Mao, Yaqin;Yu, Yunhua;Wu, Dezhen;Yang, Xiaoping
    • Carbon letters
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    • v.5 no.1
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    • pp.18-22
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    • 2004
  • The failure behaviours of unidirectional pultruded carbon fiber reinforced polymer (CFRP) composites were monitored by the electrical resistance measurement during tensile loading, three-point-bending, interlaminar shear loading. The tensile failure behaviour of carbon fiber tows was also investigated by the electrical resistance measurement. Infrared thermography non-destructive evaluation was performed in real time during tensile test of CFRP composites to validate the change of microdamage in the materials. Experiment results demonstrated that the CFRP composites and carbon fiber tows were damaged by different damage mechinsms during tensile loading, for the CFRP composites, mainly being in the forms of matrix damage and the debonding between matrix and fibers, while for the carbon fiber tows, mainly being in the forms of fiber fracture. The correlation between the infrared thermographs and the change in the electrical resistance could be regarded as an evidence of the damage mechanisms of the CFRP composites. During three-point-bending loading, the main damage forms were the simultaneity fracture of matrix and fibers firstly, then matrix cracking and the debonding between matrix and fiber were carried out. This results can be shown in Fig. 9(a) and (b). During interlaminar shear loading, the change in the electrical resistance was related to the damage degree of interlaminar structure. Electrical resistance measurement was more sensitive to the damage behaviour of the CFRP composites than the stress/time curve.

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