• Title, Summary, Keyword: porosities

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Fatigue Strength Estimation of the Fillet Weldments with Different Beveling Angle and Porosity (베벨각도와 미세기공에 따른 필렛 용접부의 피로강도평가에 관한 연구)

  • Hong, Chun-Hyi;Oh, Se-Jong;Lee, Won-Seok;Lee, Hyun-Woo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.11
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    • pp.1439-1446
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    • 2006
  • The fatigue test of the fillet weldments was executed with different beveling angles and porosities. The beveling angles of $0^{\circ}$, $45^{\circ}$ and $55^{\circ}$ were compared with fatigue lives. After the fillet weldment failure, the porosities which found at the fractured surface were observed to account the effect on fatigue life. Finite element analysis was performed to correlate the fatigue strength and the sizes and the locations of porosities. The stress-strain field was severely affected by the length of notch and the sizes and locations of porosities. Based on the quantitative analysis of porosity effect, the total volume of porosities was a key factor for fatigue strength of the fillet weldment.

A new suggestion for determining 2D porosities in DEM studies

  • Wang, Zhijie;Ruiken, Axel;Jacobs, Felix;Ziegler, Martin
    • Geomechanics and Engineering
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    • v.7 no.6
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    • pp.665-678
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    • 2014
  • In discrete element modeling, 2D software has been widely used in order to gain further insights into the fundamental mechanisms with less computational time. The porosities used in 2D DEM studies should be determined with appropriate approaches based on 3D laboratory porosities. This paper summarizes the main approaches for converting porosities from 3D to 2D for DEM studies and theoretical evaluations show that none of the current approaches can be widely used in dealing with soil mechanical problems. Therefore, a parabolic equation and a criterion have been suggested for the determination of 2D porosities in this paper. Moreover, a case study has been used to validate that the 2D porosity obtained from the above suggestion to be rational with both the realistic contact force distribution in the specimen and the good agreement of the DEM simulation results of direct shear tests with the corresponding experimental data. Therefore, the parabolic equation and the criterion are suggested for the determination of 2D porosities in a wide range of polydisperse particle systems, especially in dealing with soil mechanical problems.

COMPARISON OF STONE SURFACE POROSITIES CAUSED BY HYDROGEN GAS FROM ADDITION SILICONE IMPRESSION MATERIALS (부가 중합형 실리콘 인상재에서 발생하는 수고 기체가 경석고 표면에 미치는 영향)

  • Yoo, So-Jeong;Lee, Keun-Woo;Kim, Kyeung-Nam
    • The Journal of Korean Academy of Prosthodontics
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    • v.34 no.2
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    • pp.349-362
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    • 1996
  • To determine the factors to affect on stone surface porosities produced from hydrogen gas of additional silicone, both putty and syringe type of 7 commercially different additional silicone impression materials(Blend-A-Scon, Correct VPS, Exaflex, Express, Extrude, Provil, Reprosil) were chosen and NewFujirock(GC) was poured into the impressions of detail-reproducing test block at 1, 15, 30, 45, 60 minutes after the impression materials had set and 4 specimens were made for each pouring time, each type of impression material, and each consisency and So, 280 specimens were made in total. The number of surface porosities of same area($2826 mm^2$) which were typically caused by hydrogen gas using the stereoscope(X 7.5) by two observers. Comparison of putty-syringe type and among the impression materials are tested by Kruscal-Wallis method and Mann-Whitney method(p<0.05). The results are as follows. 1. The number of porosities decreased as the pouring time of stone was delayed on both putty and syringe type of additional silicone materials. 2. The putty type significantly produced more porosities than syringe type except for the group of Reprosil.(p<0.05). 3. In case of putty type, the number of porosities increased as following order. Reprosil / Blend-A-Scon and Provil / Correct VPS and Extrude / Express and Exaflex. 4. In case of syringe type, Blend-A-Scon and Extrude produced no porosity and Exaflex and Provil at 30 minites, but Express produced porosities even at 60 minutes and the most. Additional silicone impression material releases hydrogen gas, and that fact can make the resulting die stone model useless. So, to minimize these adverse effects, it is desirable not to expose putty type of additional silicone on critical impression surface because putty type has a tendency to produce more porosities than syringe type. And it is important to have sufficient time before pouring the stone on impression because porosities produce less as time passes after setting of impression material. Also, there are differences among 7 additional silicone impression materials, so it is desirable to choose adequate brand of additional silicone for good laboratory work.

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Effect of Process Parameters of P/M and Induction Heating on the Cell Morphology and Mechanical Properties of 6061 Aluminum Alloy (P/M법과 유도가열 공정변수가 6061 알루미늄 합금의 미세기공과 기계적 성질에 미치는 영향)

  • 강충길;윤성원
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.6
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    • pp.222-229
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    • 2003
  • The purpose of this study is to evaluate the mechanical properties of 6061 Al foams, which were fabricated by P/M and multi-step induction heating method, and to build the database, which is needed for computer aided modeling or foam components design. Aluminium foams, consisting of solid aluminium and large quantities of porosities, is widely used in automotive, aerospace, naval as well as functional applications because of its high stiffness at very low density, high impact energy absorption, heat and fire resistance, and greater thermal stability than any organic material. In this study, 6061 Al foams were fabricated for variation of fraction of porosities (%) according to porosities (%)-final heating temperature ( $T_{a3}$) curves. Mechanical properties such as compressive strength, energy absorption capacity, and efficiency were investigated to evaluate the feasibility of foams as crash energy absorbing components. Moreover, effect of the surface skin thickness on plateau stress and strain sensitivity of the 6061 Al foams with low porosities (%) were studied.d.

Critical buckling of functionally graded nanoscale beam with porosities using nonlocal higher-order shear deformation

  • Benahmed, Abdelillah;Fahsi, Bouazza;Benzair, Abdelnour;Zidour, Mohamed;Bourada, Fouad;Tounsi, Abdelouahed
    • Structural Engineering and Mechanics
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    • v.69 no.4
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    • pp.457-466
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    • 2019
  • This paper presents an efficient higher-order nonlocal beam theory for the Critical buckling, of functionally graded (FG) nanobeams with porosities that may possibly occur inside the functionally graded materials (FG) during their fabrication, the nonlocal elastic behavior is described by the differential constitutive model of Eringen. The material properties of (FG) nanobeams with porosities are assumed to vary through the thickness according to a power law. The governing equations of the functionally graded nanobeams with porosities are derived by employing Hamilton's principle. Analytical solutions are presented for a simply supported FG nanobeam with porosities. The validity of this theory is studied by comparing some of the present results with other higher-order theories reported in the literature, Illustrative examples are given also to show the effects of porosity volume fraction, and thickness to length ratios on the critical buckling of the FG beams.

Study for groove angle of Al 5083 in Butt Welding (Al 5083 Butt 용접시 개선각에 관한연구)

  • 이해우;김세환
    • Proceedings of the KWS Conference
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    • pp.222-225
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    • 1994
  • The weldability of aluminum is excel lent but weld metal is subject to include weld defects such as porosities, crack, incomplete penetration and incomplete fusion because of improper welding parameters. Especially, the porosities are main weld defects because the difference of hydrogen solubility change in melt ins and solidification state with temperature changing. Deformation of aluminum is larger than mi Id steel due to higher thermal conductivity. It is reported that porosities in deposited metal affect tensile strength and elongation. Therefore, the effect of groove angle on porosities and mechanical properties of weld metal were researched in this report where Al-5083 plate was used with 5356 filler metal that are excellent anti corrosion and strength.

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Mechanical Properties of $Al_2O_3-SiC$ Whisher Composite Materials ($Al_2O_3-SiC$ 위스커 복합재료의 기계적 특성)

  • ;;Weisskopf
    • Journal of the Korean Ceramic Society
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    • v.23 no.3
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    • pp.62-66
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    • 1986
  • Mechanical properties of $Al_2O_3$ based composite ceramics reinforced by SiC whiskers up to 40% by volume we-re investigated. Specimens were hot pressed at $1, 500^{\circ}C$ under 28.5MPa for 30min in Ar atmosphere. Porosities room temperaturefracture toughnesses and flexural strengths up $1, 000^{\circ}C$ were measured. Porosities were increa-sed as the SiC whisker cortent increased. After compensating the effect of porosities that means extrapolated in zero porosities the reinforced composites exhibited increases in flexural strength and fracture toughness as the whi-sker content increased, .

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Mechanical Properties of Aluminium Alloy with Cellular Structure. (미세기공 알루미늄 소재의 기계적 성질)

  • 윤성원;이승후;강충길
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.695-698
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    • 2002
  • Induction heating process is one of the most efficient heating process in terms of temperature control accuracy and heating time saving. In the past study, fabrication process of cellular 6061 alloys by powder metallurgical route and induction heating process was studied. To supplement the framing conditions that studied in past study, effect of induction heating capacity and holding time at foaming temperature were investigated. Under the achieved framing conditions, teamed 6061 alloys were fabricated for variation of foaming temperature, and porosities(%)-foaming temperature curves were obtained by try-error experimental method. Uniaxial compression tests were performed to investigate the relationship between porosities(%) and stress-strain curves of framed 6061 alloy. Also, energy absorption capacity and efficiency were calculated from stress-strain curves to investigated. Moreover, dependence of plateau stress on strain rate was investigated in case of cellular 6061 alloy with low porosities(%)

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A Feasibility Study on the Use of Autogeneous GTAW for Correction of Distortions in Welded Aluminum Alloy Structures (알루미늄 熔接構造物의 變形橋正을 위한 Autogeneous GTAW의 適用 可能性 硏究)

  • 하용훈;강춘식;유순영
    • Journal of Welding and Joining
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    • v.10 no.1
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    • pp.20-34
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    • 1992
  • Characteristics of two correcting methods, a new Autogeneous GTAW heating (TIG) method and the conventional GMAW bead-on plate welding(MIG) method, for distorted aluminum fabrication structures were studied. As a result of microscopic study of Autogeneous GTAW heating and GMAW bead-on plate welding areas, porosities in weld metal and surface cracks in local heating zone were found. Through the mechanical tests, it was verified that porosities decrease tensile strength and surface of distortion, angular displacement and transeverse shrinkage were measures and compared. In order to investigate changes of material properties in heating area and cause of defects such thermal stresses were calculated by ADINA. Through the computations of transient thermal stresses and microscopic observation of fracture surface, thermal stress was found to be the cause of crack during Autogeneous GTAW heating.

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The Effect of Water Contents on the Properties of Ceilulose Fiber Spun from the Solutions of Ceilulosel 4-Methylmorpholine N-oxide/Water (4-Metylmorpholine N-oxide/물 용액의 물 함량이 방사된 셀롤로오스 섬유의 물성에 미치는 영향)

  • 천석원;조성무;이화섭;김종득
    • Textile Science and Engineering
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    • v.29 no.6
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    • pp.44-52
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    • 1992
  • The effects of water contents in the cellulose solutions and coagulants were investigated on the properties of the cellulose fibers. For the spinning, cellulose was dissolved in the 4-methylmorpholine N-oxide(MMNO)/water systems. The solutions of 6 wt% cellulose with MMNO/water solvents, containing of 9.9 to 17.8 wt % water, were extruded and coagulated at water/MMNO solutions. The fibers from the solution with the less amounts of water showed the less void porosities and the improved mechanical property. The cellulose solution, however, dissolved with 9.9 wt% water at the elevated temperature of 110˚C, resulted in the degradation of cellulose. Therefore, the solution with 13.8 wt % water was chosen to avoid the degration. The cellulose solution was spun into coagulants containing the various contents of water and MMNO. The porosities of the fibers were measured to be 0.1 to 2.5. As the MMNO concentrations in coagulants increased, the apparent void porosities significantly decreased, but the structure of fibers was shown to be homogeneous under SEM. The fiber spun at pure water coagulant has the dosely packed filaments with large macropore, while the fiber from coagulants containing MMNO showed the homogeneous distributions of relatively small sizes of voids. At a fixed draw ratio, the most homogenous structure and improved mechanical properties of cellulose fibers were obtained in the coagulants of 10-20 wt% MMNO.

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