• Title/Summary/Keyword: Fracture roughness

검색결과 189건 처리시간 0.027초

조대결정 비자성강의 피로균열진전특성 (Fatigue Crack Growth Behavior of Non-Magnetic Steel with Large Grain Size)

  • 남정학;최성대;이종형;정선환
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2001년도 춘계학술대회 논문집
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    • pp.807-810
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    • 2001
  • Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Crystal grain size of the material is about 1000$\mu\textrm{m}$. For this material, the fatigue crack growth mechanism of high manganese steel was clarified from results such as observation of crack growth path and fracture surface. $\Delta$$K_{th}$ is about 8MPa$\surd$m which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low $\Delta$K regsion. The reason of this behavior is crack closure due to fracture surface roughness.

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다구찌 방법을 이용한 다발압출 금형설계에 관한 연구 (A Study on the Die Set Design for Multi-Hole Extrusion Process Using Taguchi Method)

  • 조성진;이재원
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2000년도 추계학술대회 논문집
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    • pp.322-325
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    • 2000
  • In the previous report1), the grinding characteristics of quartz were investigated. In this paper, the grinding mechanisms of brittle materials including ceramics and quartz are modeled and a new parameter SDR(Surface roughness Direction Ratio) is proposed to characterize the grinding mechanisms of such materials. A set of experiments were performed to verify the effectiveness of the suggested parameter. The experimental results indicate that the plastic deformation is the dominant material removal mode at the grinding conditions which show the higher value of SDR. In the case of quartz, the material was removed by brittle fracture in a lower value of SDR and by plastic deformation in a higher value of it. SDR is not affected by wheel mesh size when brittle fracture occured. But in the plastic deformation case, SDR value increases with wheel mesh size.

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Reliability Improvement of Titania Ceramics with Surface Flaw Through High Voltage Screening

  • Tanaka, Tomohiro;Kishimoto, Akira
    • The Korean Journal of Ceramics
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    • 제5권4호
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    • pp.386-389
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    • 1999
  • Effect of high voltage screening was examined on mechanical strength of titania ceramics with two different surface roughness. Roughly finished sample showed degraded mechanical strength meaning that the introduced flaw played the role of starting point of mechanical fracture. On such sample, electrically weak parts were eliminated by applying a screening field. Mechanical strength measurement on survived parts revealed that after screening the Weibull plots bended to become a convex curve while plots at high strength region were almost the same. This result means that relatively low mechanical strength parts were eliminated by the electrical method. As a result the Weibull modulus calculated from all the data increased, demonstrating the effect of high voltage screening on titania ceramics containing fracture controlling surface flaws. Roles of the surface flaw such as a common weak spot for both failures are disscussed in relation to the electric field concentration similar to that of mechanical stress.

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초경팁 부착형 둥근톱의 절단 특성에 미치는 기판 재질의 영향 (Effect of the Mechanical Properties of Disk Material on the Cut-off Characteristics of Tungsten Carbide Tipped Circular Saw)

  • 이재우
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2001년도 춘계학술대회 논문집
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    • pp.883-886
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    • 2001
  • The mechanical properties such as the Young's modulus, damping ratio, vibration mode and hardness of the disk materials heat-treated under various conditions are measured, and the relations between there properties and the cutting characteristics such as early tip fracture are examined. The results obtained from this study are as follows. The circular saw with the V-Cr added disk has higher young's modulus and damping ratio than the saw with STC5 disk, preventing the early fracture of tungsten carbide due to the above properties. The circular saw with the disk which is subjected to the heat treatment at the quenching temperature of $830^{\circ}C$ and at the temperature of $550^{\circ}C$ have the best tool life and surface roughness.

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알루미나 연삭표면 특성에 관한 연구 (A Study on the Surface Characteristics n the Alumina Grinding)

  • 하상백
    • 한국공작기계학회:학술대회논문집
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    • 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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    • pp.519-524
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    • 1999
  • To manufacture alumina products, sintering and grinding process are needed. In Al2O3 grinding, macro/micro surface fracture and cracks are easily occurred on the ground surface because of its high brittleness. In view point of fatigue fracture, surface profile produced by grinding is considered as notches. Therefore, it was reasonable that magnitudes and shapes of surface profiles effects on fatigue strength and life. Particularly, surface finish of Al2O3 which have high hardness and brittleness have an effect on fatigue strength. In this paper, some experiments are carried out to examine influence of grinding conditions to magnitude and shape of surface profile as well as the relationships of Ra, Rmax, Rmax/Ra, and Ku. Through the experimental results, It is found that Ra and Rmax was affected by grinding conditions, but Rmax/Ra and Ku was not. There are linear relations between Ra and Rmax, and between Rmax/Ra and Ku.

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CBN 볼 엔드밀의 절삭 및 마모특성에 관한 연구 (A Study on the Cutting Pertormance and Wear Characteristics of CBN Ball End-Mill)

  • 이기우
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1996년도 춘계학술대회 논문집
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    • pp.107-113
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    • 1996
  • This paper presents the experimental results on the cutting performance and wear characteristics of CBN ball end-mill. The influence of cutting fluids and rake angles on the tool performance is reported. It i found that the neat cutting oil is beneficial to obtain good surface roughness and 30 .deg. of rake angle gives the minimum tool wear. The microscopic investigations reveal that the coated carbide endmills wear by fracture whereas the CBN endimills wear by attritious mode.

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와이어 컷 방전가공에서 방전가공횟수가 파인 블랭킹 금형과 제품에 미치는 영향 (An Effect of Number of Passes in Wire-Cut Electric Discharge Machining on Fine Blanking Dies and Products)

  • 유헌일;김세환;최계광
    • 소성∙가공
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    • 제6권3호
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    • pp.192-202
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    • 1997
  • This study presents an effect of number of passes in wire-cut electric discharge machining on fine blanking dies and products. Three part fine blanking dies were produced by the difference of numbers of passes discharge machining. Brake pad was produced, through the die produced like that, the objective of this study is the improvement in surface roughness of die block and punch, life extension of die block, the decrease of second fracture dimensions, the rise of productive.

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Effect of Joint Reformation on Adhesive Strength of 6061 Aluminum Alloy to Polycarbonate Lap Structures

  • D. W. Seo;Kim, H. J.;J. K. Lim
    • International Journal of Korean Welding Society
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    • 제4권1호
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    • pp.53-60
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    • 2004
  • Adhesive-bonded joints are widely used in the industry. Recently, applications of adhesive bonding joints have been increased extensively in automobile and aircraft industry. The strength of adhesive joints is influenced by the surface roughness, adhesive shape, stress distribution, and etc. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, as the fundamental research of adhesive bonding joints, the effects of adhesive shape and loading speed on bonding strength properties and durability of aluminum to polycarbonate single-lap joints were studied. To evaluate the effect of adhesive shape, several modified shapes were used, and loading speeds were varied from 0.05 to 5mm/min. As a result, the load distribution showed a brittle fracture tendency. The trigonal edged single lap and bevelled lap joints showed the higher strength than the plain single lap, trigonal single lap, joggle lap and double lap joints in same adhesive area. The fractures of trigonal single lap and trigonal edged single lap joints that had the higher strength level were shown as the mixture type of the cohesive and interfacial-failure, mostly joggle lap joints that had the lower strength level were shown as the adhesive-failure.

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가공조건에 따른 강판의 구멍확장성 평가 (Evaluation of Role Flangeability of Steel Sheet with respect to the Role Processing Condition)

  • 이종섭;고윤기;허훈;김홍기;박성호
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2006년도 춘계학술대회 논문집
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    • pp.359-362
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    • 2006
  • In this paper, hole expanding tests are carried out in order to identify the effect of the hole process condition on the hole expanding ratio. Specimens with two different hole conditions are prepared: one is produced with punching process; and the other is reamed after punching to get smoother hole surface. The experimental results show that the facture mechanism and the hole expanding ratio are quite different with respect to the hole condition. The hole expanding ratio of a punched specimen is much smaller than that of a reamed one due to the difference of surface roughness and internal defects. For the thorough investigation of those effects, tensile tests of a specimen with a hole are performed. The fracture strain is obtained with different hole conditions and a finite element analysis of the hole flanging process carried out. The experimental results are confirmed and reevaluated by finite element analysis of the hole flanging process with ductile fracture criterion proposed.

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조대조직을 갖는 비자성강의 피로균열진전거동 (A Behavior of Fatigue Crack Growth of Nonmagnetic Steel with Large Grain Size)

  • 이종형;최성대;정선환;권현규;양성현
    • 한국기계가공학회지
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    • 제3권4호
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    • pp.88-94
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    • 2004
  • High manganese steel was maintained stability of Non-Magnetics performance. Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese steel. The fatigue crack growth mechanism of the high manganese steel was clarified from results such as observation of crack growth path and fracture surface. The result of getting this study was shown as following: 1) Remarkably ${\Delta}Kth$ of the high manganese steel is big with about 3 times of the general steel product. 2) In the low ${\Delta}K$ value region, da/dN is dependent on Kmax, and in the high ${\Delta}K$ value region, it is dependent on ${\Delta}Keff$. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. 3) It seems to ease the stress concentration of crack tip crack growth behavior in the ${\Delta}Kth$ vicinity by the generation of the secondary crack.

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