• Journal of Welding and Joining
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• 제21권6호
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• pp.55-63
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• 2003

Welded joint generally has heterogeneity of strength, material, and fracture toughness and it is important to understand the characteristics of material strength and fracture of welded joint considering heterogeneous effect. Characteristics of strength and fracture of an undermatched joint under dynamic loading was studied by round-bar tension tests and thermal elastic-plastic analyses in this paper. The strength and fracture of the undermatched joints should be evaluated based on the effects of the strain rate and the temperature including temperature rise during the dynamic loading. The differences of fracture characteristics like such as ductile-to-brittle transition behavior are well precisely explained from the stress-strain distribution obtained by numerical analysis.

• 한국지반공학회논문집
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• 제36권3호
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• pp.25-36
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• 2020

동토의 세립분 함유량에 따른 파괴특성을 파악하기 위해 -10℃의 온도에서 다양한 세립분 함유량과 초기 노치(notch)의 위치를 조정한 직사각형 공시체를 제작하여 Three-point bending 시험을 수행하였다. 시험결과를 바탕으로 동토의 mode I 파괴인성(fracture toughness)을 산정하였으며, 하중-변형 곡선의 최대점까지의 fracture energy를 산정하여 동토의 mixed-mode(mode I + II) 파괴특성을 파악하였다. 시험결과, 최대하중 및 mode I 파괴인성은 세립분 함유량 10%까지 증가하다가 15%에서 다시 감소하는 경향을 나타내었다. 또한, 노치의 위치가 공시체 중심에서 멀어질수록 mode II 하중의 증가로 인해 균열이 진행하는데 필요한 fracture enenrgy가 증가하는 것으로 나타났으며, 세립분 함유량이 증가할수록 mode II 하중의 증가비율 또한 증가하는 것으로 나타났다.

• 대한기계학회논문집
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• 제19권3호
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• pp.631-638
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• 1995

In this study, mechanical characteristics test of Functionally Gradient Materia (FGM) was performed by means of Modified Small Punch (MSP) Test with FGM; NiCrAlY-8YSZ and PSZ-Ni. To determine fracture mechanic factor, it was carried out MSP test that has possibility with small specimen (10*10*0.5 mm$^{t}$ ) and AE test to analyze micro fracture mechanism. As a result, fracture behavior became varied from brittle fracture to ductile as the content of Ni(or NiCrAlY) composition was increased and fracture energy was increased too. AE characteristics demonstrated that AE technique can detect the onset of fracture processes and AE energy was suddenly increased in the vicinity of maximum load. Since Young's modulus, fracture stress and fracture toughness was determined by MSP test, it can be known that the composition of NiCrAly 75%/8YSZ25% has the best mechanical property and furthermore this result is supported with fracture surface observation.

• Tribology and Lubricants
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• 제15권2호
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• pp.141-149
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• 1999

Fracture, fatigue and wear characteristics of Al-Si alloy used for compressor are experimentally studied. Plane strain fracture toughness test is carried out using three point bending specimen. Fatigue test is performed under constant loading condition and wear test is carried out as a function of sliding velocity and applied load. To obtain the crack propagation characteristics and wear mechanism of Al-Si alloy, fracture and worn surfaces are investigated using SEM. It is verified that fracture and fatigue strength of Al-Si alloy are improved by the fine microstructure of alloy. The wear behavior and specific wear amount of Al-Si alloy are not dependent on the microstructure but on a function of the silicon content. Anodizing on the surface of Al-Si alloy, surface hardness and wear characteristics are improved.

• Restorative Dentistry and Endodontics
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• 제17권1호
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• pp.153-165
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• 1992

Dental composite resin is a kind of the particle - reinforced composite material, and is widely used in recent dental restoration of anterior and posterior tooth region. The purpose of this study was to investigate the fracture behaviour according to volume fractions and external findings of the filler particles for better interpretation of the fracture characteristics of posterior dental composite resins by analytic method of fracture mechanics. The plane strain fracture toughness($K_{IC}$) and Acoustic Emission were determined with three - point bending test using the single edge notch specimen according to the ASTM - E399, and its analyzed data was compared with filler volume fractions derived from the standard ashing test and scanning electron fractographs of each specimen including the unfilled experimental resin as a control. The results were that the value of fracture toughness of the composite resin material was in the range from 0.85 MPa$\sqrt{m}$ to 1.60 MPa$\sqrt{m}$ and was higher than the value of the unfilled experimental resin, and the fracture behaviours dervied from Acoustic Emission analysis show prominent differences according to the volume fraction and the size of filler particles used in each composite resin. The degree of resistance against crack propagation seems to be increase and the fractographs demonstrate the high degree of surface roughness and irregularity according with the increase of fracture toughness value.

• 한국안전학회지
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• 제13권4호
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• pp.71-78
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• 1998

Real crack and fracture surfaces have irregularities producing zigzag contours. These irregularities are analysed by a fractal geometry which has been by a Mandelbrot. We obtained a fractal dimension which is one of the fractal characteristics. It is also estimated by an vertical section method that fractal characteristics in the fractured surfaces can be obtained as the crack grows. Moreover fractal fracture energy that corresponds to an energy release rate is shown to find relationships between fractal dimensions and crack behaviors. From these results, we concluded that a fractal characteristics analysis for a crack can be applied to a fracture mechanics.

• 대한물리치료과학회지
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• 제8권1호
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• pp.841-850
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• 2001

This study was conducted to find out current status and characteristics, so that the result could provide basic data to establish prevention programs for hip fracture among the elderly. The data were coolected from 199 cases hospitalized in 4 university hospitals in Pusan during three years period from January, 1966 to December, 1998. The data were obtained from medical records and by using questionnaires through telephone contact or direct personal interview with the subjects or their family, and were analyzed with x2-test. The results were as follow: The mean age of elderly hip fractured cases was 75.7 years, and 61.8% were female. The average hospital stay of the cases was 30.8 days, and 73.9% survived. Femur neck fracture cases comprised 51.7% of the toral cases, while trochanteric fracture cases comprised 48.3%. The hip fracture occurred more frequently during the day, shown as 66.9%, and the most frequently due to trips(44.2%), followed by slips(322%), c1ash(14.6%), dizziness(7.5%), and 00 on. Femur neck fracture, however, occurred the most frequently due to trips(51.5%) and, on the other hand, trochanteric fracture due to slips(40.6%) and trips(36.5%). About two third of hip fracture(67.8%) occurred inside of the building. The most frequently mentioned location for hip fractures was rooms or floors(32.1%), followed by streets(24.1%), bathrooms(17.6%), stairways(13.1%), and so on. Trochanteric fracture, especially, more frequently occurred inside of the building(71.9%) as compared to femur neck fracture(64.1 %). The rate of independent indoor walking in femur neck fractured cases reduced from 88.3% to 74.8% after fracture incidences, while the rate reduced from 86.0% to 45.8% in trochanteric fracture cases. It indicated that trochanteric fractures affected the walking ability of the elderly more severely that femur neck fractures. In conclusion, hip fracture occurs as a combined result of aging characteristics, environmental factors, and health related characteristics. Future studies that investigaterisk factors of hip fracture in elderly are recommended.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2000년도 추계학술대회
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• pp.69-73
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• 2000

We systematically analyze the influence of fracture junction, solute transfer characteristics on transport patterns in discrete, two-dimensional fracture network models. Regular lattices and random fracture networks with power-law length distributions are considered in conjunction with particle tracking methods. Solute transfer probabilities at fracture junctions are determined from analytical considerations and from simple complete mixing and streamline routing models. For regular fracture networks, mixing conditions at fracture junctions are always dominated by either complete mixing or streamline routing end member cases. Moreover bulk transport properties such as the spreading and the dilution of solute are highly sensitive to the mixing rule. However in power-law length networks there is no significant difference in bulk transport properties, as calculated by assuming either of the two extreme mixing rules. This apparent discrepancy between the effects of mixing properties at fracture junctions in regular and random fracture networks is explained by the statistics of the coordination number and of the flow conditions at fracture intersections. We suggest that the influence of mixing rules on bulk solute transport could be important in systematic orthogonal fracture networks but insignificant in random networks.

• 한국해양공학회지
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• 제16권2호
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• pp.67-71
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• 2002

Damage process of CFRP laminates was characterized by Acoustic Emission (AE). The main objective of this study is to determine if the sources of AE in CERP laminates could be identified from the characteristics of the waveform signals recorded during monotonic tensile test. The time history and power spectrum of each individual wave signal recorded during test were examined and classified according to their special characteristics. The wave from and frequency of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pull-out and fiber fracture as load is increased. Four distinct types of signals were observed regardless of specimen condition. The result showed that the AE method could be effectively used for analysis of fracture mechanism in CFRP laminates.

• 한국안전학회지
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• 제11권3호
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• pp.59-65
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• 1996

This study is to evaluate dynamic fracture characteristics of alloy tool steel, STD-11, according to various tempering conditions (heat treatment). The dynamic fracture initiation toughness and some of the dynamic fracturing characteristics were evaluated by using the instrumented Charpy impact testing procedures. The distributions of Victors hardness and dynamic fracture initiation toughness with respect to varying tempering temperatures are found to be symmetric type with the help of experimental results for the STD-11. It is also found that the dynamic fracture initiation toughness is a inverse proportion to Vickers hardness. In this experimental study, it is found that the best heat treatment condition is 55$0^{\circ}C$ tempering in alloy tool steel, STD-11, because the results show high values of Vickers hardness and dynamic fracture initiation toughness.