• Title/Summary/Keyword: Crack Tip

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Fracture Analysis of Thick Plate for Partial Penetration Multi-pass Weldment Using J-integral (J-적분을 이용한 후판 부분용입 다층용접재의 파괴 해석)

  • Kim, Seok;Song, Jung-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.2
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    • pp.300-307
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    • 2002
  • Partial penetration welding joint is defined as groove welds welded from one side, without steel backing or groove welds welded from both sides but without back gouging. So it has an unwelded portion at the root of the weld. Study of partial penetration weldment fracture behavior includes residual stress analysis and fracture analysis. The J-integral loses its path independency in residual stress field. Therefore, it is necessary to introduce a new J-integral, J, which is defined including the effect of plastic deformation and thermal strain. In this study, theoretical formulation and program were developed for the evaluation of J-integral for the crack tip located in the weldment. Evaluations of fracture behavior were performed for partial penetration multi-pass weldment of 25.4mm thick plate by J-integral. From a point of fracture in partial penetration multi-pass welding, it seemed to be better to control root face smaller than 6.35mm.

Study on Filtering Method of Acoustic Emission and Characteristic of Signals for the Deformation Process of Steel (강재 변형과정에서 음향방출잡음제거와 신호특성에 관한 연구)

  • Na, E.G.;Oh, S.H.;Lee, S.K.
    • Journal of Power System Engineering
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    • v.13 no.4
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    • pp.43-48
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    • 2009
  • The purpose of this study is to show how to eliminate the noises and to obtain the data related with the relationship between AE signal characteristics and mechanical behaviors for the pressure vessel steel. Various kinds of noises are introduced into the AE data in the course of experiments. Accordingly, real AE data have to be obtained after tests. AE test was carried out under four point bending load. Among AE signals, counts and signal strength are used to find out the differences of AE characteristics between the basemetal and weldment. After tests, this paper shows the procedures of filtering the noises against basemetal of the pressure vessel steel to obtain the real data around crack tip. Relationships between plastic zone size and cumulative AE counts are shown also. AE signals were absent within an elastic region, regardless of the specimens. Most of AE signals are produced in the process of plastic deformation. The deformation and fracture modes of basemetal and weldment are quiet different.

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Failure Behaviors Depending on the Notch Location of the Impact Test Specimens on the HAZ (용접열영향부 충격시험편 노치 위치에 따른 파괴거동)

  • Jang, Yun-Chan;Hong, Jae-Keun;Park, Ji-Hong;Kim, Dong-Wook;Lee, Young-Seog
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.706-711
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    • 2007
  • Numerical studies were performed to examine the effects of notch location of impact specimens on the failure behavior of HAZ (heat affected zone) when Charpy V-notch impact test were made at a low temperature ($1^{\circ}C$). Carbon steel plate (SA-516 Gr. 70) with thickness of 25mm for pressure vessel was welded by SMAW (shielded metal-arc welding) and specimens were fabricated from the welded plate. Charpy tests were then performed with specimens having different notch positions of specimens varying from the fusion line through HAZ to base metal. A series of finite element analysis which simulates the Charpy test and crack propagation initiating at the tip of V-notch was carried out as well. The finite element analysis takes into account the irregular fusion line and non-homogenous material properties due to the notch location of the specimen in HAZ. Results reveals that the energies absorbed during impact test depend significantly on the notch location and direction of specimen. Finite element analysis also demonstrates that the notch location of specimens, to a great extent, influences the reliability and consistency of the test.

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Study on the Cold Formability of Drawn Non-heat Treated Steels (신선 가공된 열처리 생략강의 냉간 성형성에 대한 연구)

  • 박경수;박용규;이덕락;이종수
    • Transactions of Materials Processing
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    • v.12 no.4
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    • pp.364-369
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    • 2003
  • Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to study their mechanical properties and the cold formability. The cold formability of three steels was investigated by estimating the deformation resistance and the forming limit. The deformation resistance was estimated by calculating the deformation energy, and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strains of ultra low carbon bainitic steel and low-Si steel were higher than that of commercial SWRCH45F steel.

Analysis of Piezoelectric Ceramic Multi-layer Actuators Based on the Electro-mechanical Coupled Meshless Method (전기-기계 결합 하중을 받는 압전 세라믹 다층 작동기의 무요소 해석)

  • Kim, Hyun-Chul;Guo, Xianghua;Kim, Won-Seok;Fang, Daining;Lee, Jung-Ju
    • Transactions of the Korean Society of Automotive Engineers
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    • v.15 no.2
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    • pp.101-108
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    • 2007
  • This paper presents an efficient meshless method for analyzing cracked piezoelectric structures subjected to mechanical and electrical loading. The method employs an element free Galerkin (EFG) formulation and an enriched basic function as well as special shape functions that contain discontinuous derivatives. Based on the moving least squares (MLS) interpolation approach, The EFG method is one of the promising methods for dealing with problems involving progressive crack growth. Since the method is meshless and no element connectivity data are needed, the burdensome remeshing procedure required in the conventional finite element method (FEM) is avoided. The numerical results show that the proposed method yields an accurate near-tip stress field in an infinite piezoelectric plate containing an interior hole. Another example is to study a ceramic multilayer actuator. The proposed model was found to be accurate in the simulation of stress and electric field concentrations due to the abrupt end of an internal electrode.

Temperature Effect on Tensile Strength of Filled Natural Rubber Vulcanizates (가황 천연고무의 인장강도에 미치는 온도의 영향)

  • Ko, Young-Chon;Park, Byung-Ho
    • Elastomers and Composites
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    • v.36 no.4
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    • pp.255-261
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    • 2001
  • This study was related with the effect of elevated temperature on the tensile strength of edge-cut samples. There was a different tensile strength behavior of uncut samples and pre-cut samples under different test temperatures. Tensile strength of uncut sample decreases with increasing test temperature. When pro-cut size(C) is larger than critical cut size($C_{cr}$), tensile strength or pre-cut specimen at $80^{\circ}C$ is higher than that of pre-cut specimen at room temperature (RT). Test specimens under $80^{\circ}C$ condition exhibited more secondary cracks at the crack tip region compared to room temperature conditions. However, secondary cracks of pre-cut specimens are not clearly developed at $110^{\circ}C$. Differences in tensile strength induced by different test temperature seem to be responsible for the strain-induced crystallization and micro-cracking patterns.

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A study on the KLA behaviors in HAZ and the mechanical properties of austenitic stainless steel weld (스테인레스강용접 열영향부의 KLA거동 및 기계적 특성에 관한 연구)

  • 조종춘;김영석;김학민
    • Journal of Welding and Joining
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    • v.8 no.4
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    • pp.27-34
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    • 1990
  • Integranular corrosion behaviors of KAL (Knife Line Attack) and mechanical properties such as tensile and creep rupture were investigated for the tube material used for nearly 20 years under the condition of 463.deg. C and 28 $kg/cm^2$. Based and weld metal were austenitic stainless steel AISI 321 containing Ti, AISI 347 containing Nb, respectively. KLA is a kind of the intergranular corrosion which often occurs just near the HAZ (heat affected zone) of AISI 321 and AISI 347 stainless steel due to the grain boundary sensitization. In KLA zone, intergranular corrosion crack has propagated outwards from the inner surface and carbides of white and narrow band type assuming as (Cr, Fe) carbide were confirmed. All the delta-ferrite formed in the weld metal during weld solidification has been transformed into sigma-phase since delta-ferrte was exposed for 20 years at 463.deg. C. Elongation was very low at the range from room temperature to 600.deg. C and it was confirmed that creep-rupture properties were not consideralbly affected.

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The Effect of PWHT on Fracture Toughness in HAZ of Cr-Mo Steel (Cr-Mo鋼 熔接熱影響部 의 破壞靭性 에 미치는 熔接後 熱處理 의 影響)

  • 정세희;임재규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.2
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    • pp.97-103
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    • 1984
  • Post weld heat treatment(PWHT) of weldment of the low alloy steel is carried out to remove residual stress existing in weldment and to improve fracture toughness, but it is often observed that there occurs grain boundary failure and that fracture toughness decreases in weld heat affected zone(HAZ)because of PWHT. In this paper, the effect of heating rate and holding time of PWHT on fracture toughness were evaluated by crack opening displacement (CDD)test and micro-hardness test under the constant stress simulated residual stress in HAZ of Cr-Mo steel. The experimental results are as follow; (1)Transition temperature of weld HAZ after PWHT was dependent upon heating rate greater than holding time, and fracture toughness was decreased with an increase of the heating rate. (2)Softening ration of the notch tip was increased with holding time within one hour and saturated after one hour, but under applied stress it was increasing continuously. (3)The average hardness value in weld HAZ was increased with heating rate of PWHT.

Fracture Toughness Improvement of Graphite/Epoxy Composite by Intermittent Interlaminar Bonding (간헐적인 층간접착 을 이용한 Graphite/Epoxy 복합재료 의 파괴인성 개선)

  • 임승규;홍창선
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.5
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    • pp.425-434
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    • 1984
  • The concept of intermittent interlaminar bonding is investigated as a means of improving the fracture toughness of cross-ply Gr/Ep composites without significant loss of tensile strength and modulus. The concept of linear elastic fracture mechanics(LEFM)is used to study the effects of strong bonded area and bonding composites. The experimental results indicate that the fracture toughness and notch strength of intermittent interlaminar bonded composities are improved and the tensile strength only decreased by 3-8% in comparison to those of the fully bonded composites. Damage zones around the crack tip are detected by the modified X-Ray non-destructive testing technique and the fractography. The improvement of toughness is explained based on the damage zones. The mechanisms of damage zone are shown to be caused by subcrack along the fiber on the 0.deg. ply, matrix cracking along the fiber on the 90.deg. ply, interlaminar delamination, and ply pull-out of the 0.deg. ply.

Variation of the Fracture Resistance Curve with the Change of a Size in the CT Specimen (CT시험편의 크기 변화에 따른 파괴저항곡선의 변화)

  • Seok, Chang-Seong;Kim, Su-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.12
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    • pp.2963-2971
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    • 2000
  • In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.