• 대한기계학회논문집A
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• 제29권1호
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• pp.107-114
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• 2005

In order to analyze the elastic-plastic fracture behavior of a structure, the fracture resistance curve of the material should be known first. The standard CT specimen was used to obtain the fracture resistance curves of a piping system. However, it is known that the fracture resistance curve by the standard CT specimen is very conservative to evaluate the integrity of a structure. Also the fracture resistance curve is effected by the specimen geometry and the dimensions because of the constraint effect. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen and to provide an additional safety margin. For these, the fracture tests using a real pipe specimen and the standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. Also finite element analyses were performed with a CT specimen and a pipe in order to prove the additional safety margin. From the result of tests and analyses of the pipe and the standard CT specimen, it was observed that the fracture analysis with the standard CT specimen is conservative and the additional safety margin was proved.

• 한국세라믹학회지
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• 제34권10호
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• pp.1053-1059
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• 1997

The dynamic fatigue behavior of alumina ceramics was observed at room temperature using four point bending system. The dynamic fatigue fracture strength and the dynamic fatigue lifetime were observed as a function of crosshead speed and the notch length. The notched specimen showed the smaller deviation in dynamic fatigue fracture strength than the unnotched specimen. The crack growth exponent n and the material constant A of the notched specimen could be represented as functions of the notch length. Fracture strength of the specimen calculated from the notch length, when the notch length was regarded as the crack size, was in good agreement with the measured 4 point bending strength. Fracture surface of the specimen showed the different fracture modes according to the crosshead speed. The four point flexural strength, fracture toughness, Young's modulus and Weibull modulus of the alumina were measured as 360 MPa, 3.91 MPa.m1/2, 159GPa, 17.64, respectively.

• 한국자동차공학회논문집
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• 제13권5호
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• pp.171-180
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• 2005

Bending performances of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been evaluated using experimental tests combined with theoretical and finite element analyses. A finite element simulation for the three-point bending test was performed. Basic properties of aluminum materials used for initial input data of the finite element simulation were obtained from the true stress-true strain curves of specimens which had been extracted from the Al tube beams. True stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing, and true strains were obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Six kinds of aluminum tube beam specimens adhered by aluminum plates were employed fur the bending test. The bending deformation behaviors up to the maximum load described by the numerical simulation were in good agreement with experimental ones. After passing the maximum load, reinforcing plate was debonded from the aluminum tube beam. An aluminum tube beam strengthened by aluminum plate on the upper web showed an excellent bending capability.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.55-60
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• 2001

The automobile is made up of thousands of parts. Some parts are formed by pressing and combined by spot welding. To find weldability conditions of spot welding, clearance between two welding plates was made and after spot welding, weldability is evaluated by means of tensile shear load, nugget size and shape. Specimen used in this study was a steel plate of 1.2mm thickness and electrode was Cu-Cr alloy of 6mm diameter. When spot welding started, the clearance of two specimens was changed 0mm, 3mm and 5mm and distance from vise to measure influence of bending moment 25mm, 45mm, 65mm step by step. The fractured surface of specimen after this test was observed by Optical Microscope to measure microstructure and nugget shape. When clearance of two specimen was 3mm and 5mm, strength and nugget size was decreased and nugget shape was not clear. The much bending moment and crosshead speed are the much tensile shear load is.

• 한국주조공학회지
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• 제34권2호
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• pp.60-66
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• 2014

A Zr-based amorphous alloy specimen was produced by vacuum die casting process. The salt spray test was carried out using the specimens in the as-cast, $Al_2O_3$ and $ZrO_2$ particle blasted state. Using these specimens, the SEM-EDX and XRD analyses, DSC measurement and bending strength test were conducted. After the salt spray test, the specimens were not experienced phase change and thermal characteristics of the alloys were remained unchanged. In the as-cast specimen, corrosion products were not observed. However, in the $Al_2O_3$ particle blasted specimen, pitting corrosion occurred and the detected corrosion products were $ZrCl_2$ and $NaZrO_3$. Due to the salt spray test, bending strength of the $Al_2O_3$ blasted specimens showed about 100 MPa lower strength than the other specimens. The bending fracture surface was vein pattern which was shown typically in the amorphous alloys.

• 한국해양공학회지
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• 제12권3호통권29호
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• pp.49-59
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• 1998

The damage mechanism of $Cr_2O_3$ plasma coated soda-lime glass and uncoated glass by steel ball particle impact was analyzed in this study. And the shape variation of the cracks was investigated by stereo-microscope according to the impact velocity and steel ball diameter. In order to improve the damage reduction effect by $Cr_2O_3$ coating layer, crack size was measured and surface erosion state was observed for both of two kinds of specimen after impact experiment. And the results were compared with each other. The 4-point bending test was performed according to ASTM D790 testing method to evaluate the effect of coating layer for bending strength variation. As a result, it was found that the crack size of $Cr_2O_3$ coated specimen was smaller than that of uncoated one, because of the impact absorption by interior pores in the coating layer and the load dispersion by the structural characteristic of the coating layer. For the specimens subjected to the steel ball impact, the bending strength of coated specimen was higher than that of uncoated specimen.

• 대한기계학회논문집A
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• 제30권3호
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• pp.269-278
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• 2006

This paper proposes slip line fields for bending of unequally notched specimens in plane strain that have a sharp crack in one side and a sharp V-notch in the other side. Depending on the back angle, two slip line fields are proposed, from which the limit moment and crack tip stress fields are obtained as a function of the back angle. Excellent agreement between slip line field solutions with those from detailed finite element limit analysis based on non-hardening plasticity provides confidence in the proposed slip line fields. One interesting point is that, for the unequally notched specimen, the difference between the crack tip triaxial stress for tension and that for bending increases significantly with increasing the back angle. This suggests that such a specimen could be potentially useful to investigate the crack tip constraint effect on fracture toughness of materials. In this respect, the possibility of designing a new toughness testing specimen with varying crack tip constraint is discussed.

• 한국분말재료학회지
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• 제11권5호
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• pp.412-420
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• 2004

The purpose of the present study is to determine an optimum composition using cheaper powders keeping with high performance of hard rock cutting diamond saw blade. With 50Fe-20(Cu . Sn)-30Co specimen, a part of Co was replaced by Ni(5%, 10%, and 15%, respectively). These specimens were hot pressed and sintered for predetermined time at various temperature. Sintering is performed by two different methods of temperature controlled method and specimen dimension controlled method. In order to determine the property of the sintered diamond saw blade, 3 point bending tester, X-ray diffractometer, and SEM were used. As the Co in the bond alloy was replaced by Ni, the hardness of the specimen increased. Thus the 50Fe-20(CuㆍSn)-15Co-15Ni specimen showed the maximum hardness of 104(HRB). The results of 3 point bending test showed that flexure strength decreased along with increase in Ni content. This is attributed to the formation of intermetallic compound(Ni$_{x}$Sn) determined by X-ray diffraction. The fracture surface after 3 point bending test showed that diamond was fractured in the specimen containing 0%, 5%, and 10%Ni, and the fracture occurred at the interface between diamond and matrix in the specimen containing 15%Ni. The cutting ability test showed that the abrasive property was not changed in the specimen containing 0%, 5%, and 10%Ni. The optimum composition determined in this study is 50Fe-20(CuㆍSn)-20Co-10Ni.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.75-76
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• 2008

In this study, texture development and bending characteristics of strong {0002} textured were observed. AZ31 Mg alloy sheets were prepared along the angle of 0 and 12.5 degrees to the lolling direction or {0002} texture. Prepared samples with different angles to the rolling direction were rolled at room temperature condition and after subsequent heat treatment to investigate texture with x-ray diffractometer, respectively The specimen having along the angles of 0 degree to rolling direction shows the highest load and 12.5 degrees specimen shows the highest displacement among any other specimens in bending test.

• Journal of Advanced Marine Engineering and Technology
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• 제30권4호
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• pp.494-504
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• 2006

It is well known that the two-parameter $J-A_2$ solution can well characterize the crack-tip fields and quantify the crack-tip constraint for different flawed geometries in variety of loading conditions. However, this solution fails to do so for bending dominated specimens or geometries at large deformation because of the influence of significant global bending stress on the crack-tip field. To solve this issue, a modified $J-A_2$ solution is developed in this paper by introducing an additional term to address the global bending influence. Using the $J_2$ flow theory of plasticity and within the small-strain framework detailed finite element analyses are carried out for the single edge notched bend (SENB) specimen with a deep crack in A533B steel at different deformation levels ranging from small-scale Yielding to large-scale Yielding conditions. The numerical results of the crack-tip stress field are then compared with those determined from the $J-A_2$ solution and from the modified $J-A_2$ solution at the same level of applied loading Results indicate that the modified $J-A_2$ solution largely improves the $J-A_2$ solution, and match very well with the numerical results in the region of interest at all deformation levels. Therefore, the proposed solution can effectively describe the crack-tip field and the constraint for bending dominated specimens or geometries.