• 한국기계가공학회지
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• 제20권1호
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• pp.95-102
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• 2021

Analysis of the fracture surface is one of the most important methods for determining the cause of equipment structural failure. Whether structural failure is caused by impact or fatigue is necessary information in industrial fields. For ferrous and non-ferrous metal materials, two fracture phenomena are generated on the fracture surface: ductile and brittle fractures. In this study, machine learning predicts whether the fracture is based on ductile or brittle when structurural failure is caused by impact. The K-means algorithm calculates this ratio by clustering the brittle and ductile fracture data from a photograph of the impact fracture surface, unlike the existing method, which calculates the fracture surface ratio by comparison with the grid type or the reference fracture surface shape.

• 소성∙가공
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• 제5권1호
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• pp.72-80
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• 1996

During the shape rolling process the influence of reduction ration and taper of shape roller on deformation and limit of ductile fracture such as free surface cracks developing in the workpiece has been studied. The deformation behaviours were analyzed by the 3-dimensional elasto-pastic finite element method and the conditions of ductile fracture were determined from 3-dimensional elasto-plastic finite element method and modified Cockrogt-Latham criterion. The deformed geometry and prediction of ductile fracture by 3-dimensional elasto-plastic finite element method are compared with experimental results The calcuated results are in good agreements with experimental data. The analysis used in the study was found to be effective in predicting the shape rolling process.

• 대한치과기공학회지
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• 제36권4호
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• pp.231-237
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• 2014

Purpose: This study was performed fracture strength test by conducted change of abutment and coping shape for suggesting monolithic all ceramic crown which has thin thickness and superior strength of the occlusal surface. Methods: The specimens on the four kinds abutment was made according to thickness of occlusal surface and angle of axis surface. And All ceramic coping specimens of 6 different kinds was made by the CAD/CAM Method. Compression strength test using the UTM and the verification of compression-stress situation using the 3D finite element method were conducted under optimum conditions. Results: 516C specimen was showed the strongest compression-fracture strength, followed by 516FR, 516F45, specimens. Did not show significant differences between 516FR and 516F45. 516C of the universal testing machine the specimen's surface that are within the vertical load is small, finite element method of a uniformly distributed load, so the value received suggests otherwise. Conclusion: In conclusion, abutments of monolithic ziconia ceramic when having a same thickness of the occlusal, as the angle of occlusal edge is small, the stress is well dispersed and it can endure well in the fracture.

• Steel and Composite Structures
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• 제3권4호
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• pp.231-242
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• 2003

This paper deals with the formulation and development of fracture criteria for high-strength structural members containing surface damage in the form of notches (i.e., blunt defects). The important role of the yield strength of the material and its strain hardening capacity (evaluated by means of the constitutive law or stress-strain curve) is analysed in depth by considering the fracture performance of notched samples taken from high-strength steels with different levels of cold drawing (the most heavily drawn steel being commercial prestressing steel used in prestressed concrete). The final aim of the paper is to establish fracture-based design criteria for structural members made of steels with distinct yield strength and containing very different kinds of notch-shape surface damage.

• Design & Manufacturing
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• 제15권1호
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• pp.41-47
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• 2021

The Fine Blanking process is an effective precision shearing process that can obtain a smooth cutting surface and high product precision through a single blanking process. It is widely used in various manufacturing fields. However, shearing through this fine blanking process is only intended to minimize burrs, die rolls and fracture surfaces and does not completely remove them. Therefore, it is necessary to study the minimization of burrs, die rolls and fracture surfaces in the fine blanking process. In this study, a study was conducted on the relationship between the fracture surface and process conditions that occurred during product production using the fine blanking process. For this purpose, the shape of the V-ring indenter, the distance to the punch, and the pressure force, clearance, shear rate, and physical properties of the material were selected as process and design variables, and the relationship with the fracture surface according to each process and design condition was tested. It was analyzed through the Experimental Design Method.

• Nuclear Engineering and Technology
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• 제42권6호
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• pp.680-689
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• 2010

The crack-tip stress fields and fracture mechanics assessment parameters for a surface crack, such as the elastic stress intensity factor or the elastic-plastic J-integral, can be affected significantly by the adjacent cracks. Such a crack interaction effect due to multiple cracks can alter the fracture mechanics assessment parameters significantly. There are many factors to be considered, for instance the relative distance between adjacent cracks, the crack shape, and the loading condition, to quantify the crack interaction effect on the fracture mechanics assessment parameters. Thus, the current assessment codes on crack interaction effects (crack combination rules), including ASME Sec. XI, BS7910, British Energy R6 and API 579-1/ASME FFS-1, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates crack interaction effects by evaluating the elastic stress intensity factor and the elastic-plastic J-integral of adjacent in-plane surface cracks in a plate through detailed 3-dimensional elastic and elastic-plastic finite element analyses. The effects on the fracture mechanics assessment parameters of the geometric parameters, the relative distance between two cracks, and the crack shape are investigated systematically. As for the loading condition, an axial tension is considered. Based on the finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks are discussed. The present results can be used to develop more concrete guidance on crack interaction effects for crack shape characterization to evaluate the integrity of defective components.

• 한국주조공학회지
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• 제9권1호
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• pp.58-66
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• 1989

The effect of heat treating temperature and ${\alpha}$ phase In the ${\beta}$ phase matrix were investigated for ${\beta}-CuZnAl$ shape memory alloys by tension test, fatigue test, and shape memory effect test. After heat treatment at $677^{\circ}C$, $750^{\circ}C$, $800^{\circ}C$ and $850^{\circ}C$ for 10 min. respectively, static fracture stress(${\sigma}_f$), fatigue fracture stress(${\tau}_{max}$) at $10^6$ cycle, and elongation(${\epsilon}_f$) was $24.2kg/mm^2$, $17.21kg/mm^2$ and 11.8%, respectively. As heat treating temperature decreased, fracture surfaces of the specimens were changed from the intergranular to the transgranular fracture mode. Especially, the a phase precipitated in the ${\beta}$ phase matrix had an effect on crack propagation and the fracture surface was characterized by dimple-like pattern when crack propagated in transgranular cracking mode. Precipitation of the ${\alpha}$ phase in the ${\beta}$ phase matrix lowered the transformation temperature by $10^{\circ}C$, and about 2.5 vol.% ${\alpha}$ phase did not affect the shape memory effect examined by the bending test.

• 한국산업융합학회 논문집
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• 제24권4_2호
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• pp.435-441
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• 2021

This research was performed to study the effect of the Ni + Mo addition on the fatigue properties in 12Cr steel. After heat treatment of 12Cr steel and 12Cr-Ni-Mo steel, tensile tests, impact tests, hardness tests, and rotary bending fatigue tests were performed, respectively. The fatigue fracture surface was observed and analyzed using SEM and EDS. The fatigue limit of 12Cr steel was 554 MPa, which was 49 MPa higher than 505 MPa of 12Cr-Ni-Mo steel. Striations, which are the shape of the typical fatigue fracture surface, were observed at the fracture surface near the starting point of fatigue fracture in the 12Cr steel and 12Cr-Ni-Mo steel. However, unlike the case of 12Cr steel, 12Cr-Ni-Mo steel also had a mixed fracture surface with the fatigue and the ductile fracture surface. When brittle non-metallic inclusions exist near the starting point of fatigue failure, the crack propagation was further promoted and the fatigue life was drastically reduced.

• 대한치과기공학회지
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• 제41권4호
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• pp.279-285
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• 2019

Purpose: The dental CAD / CAM system has been popular with the development of the digital dental industry. Zirconia is a typical material in dental CAD / CAM systems. Zirconia crowns are classified into single layer and double layer. This study is about the double layer crown of zirconia. The surface roughness, bond strength and fracture patterns of the zirconia surface were observed. Methods: Zirconia blocks were cut using a low speed cutter. Sintered to form a plate shape (6mm × 6mm × 3mm). The prepared specimens were surface treated in four ways. Surface roughness and bond strength were measured. And the fracture pattern was observed. Results: Result of surface treatment of zirconia. The surface roughness test results were as ET 2.87 ㎛, ST 2.67 ㎛, LT 2.44 ㎛, AT 2.41 ㎛, CN 2.08 ㎛ order. Bond Strength results were as LT 25.09 MPa, AT 23.27 MPa, ST 21.27 MPa, ET 21.09 MPa, CN 16.12 MPa order. Fracture patterns showed cohesive failure of 25-50% of the bond area. Conclusion: Surface roughness, bond strength and fracture pattern of the zirconia surface were observed. Etching the surface treatment of zirconia materials has been shown to affect the surface roughness. Zirconia special binder treatment has been shown to affect the bond strength improvement.

• 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.