• Structural Engineering and Mechanics
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• 제65권6호
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• pp.699-706
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• 2018

In the present contribution, fracture resistance of U-notched GPPS members under mixed mode I/III loading conditions is assessed by using the Averaged Strain Energy Density (ASED) criterion. This criterion has been founded based on the ASED parameter averaged over a well-defined control volume embracing the notch edge. The validation of the theoretical criterion predictions is evaluated through comparing with the results of a series of mixed mode I/III fracture tests conducted on rectangular-shaped GPPS specimens weakened by a single edge U-notch. A recently developed apparatus for mixed mode I/III fracture experiments is employed for measuring the fracture loads of the specimens. The test samples are fabricated with different notch tip radii with the aim of evaluating the influence of this major feature of the U-notched components on the mixed mode I/III fracture behavior. It is shown that the onset of brittle fracture in U-notched GPPS specimens under various combinations of tension and out-of-plane shear can well be predicted by means of the ASED criterion.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1263-1274
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• 1996

In this paper, as elastic-plastic fracture toughness test under mixed mode loading was proposed using a single edge-cracked specimen subjected to bending moment(M), shearing force(F), and twisting moment(T). The J-integral of a crack in the specimen is expressed in the form J=$J_I$+ $J_II$$J_III$, where $J_I$, $J_II$ and $J_III$ are the components of mode I, mode II and mode III deformation, respectively. $J_I$, $J_II$ and $J_III$ can be estimated from M-$\theta$ ($\theta$;crack opening angle), F-U(U; crack shear displacement) and T-$\alpha$ ($\alpha$;crack twisting angle). In order to obtain the the M<-TEX>$\theta$, F-U and T-$\alpha$ diagram inreal time, a new deformaiton gage for mixed mode loading was proposed using the optical position sensing device(PSD). The elastic-plastic fracture toughness test was carried out with an aluminum alloy. The loading apparatus was designed and manufactured for this experiment. For the loading condition of the crack initatio in the mixed mode, the MMT -3(mode I+ mode II+ mode III) has the lowest values out of the all specimens. This implies that MMT-3 is possible of the crackinitation at lower load, if the specimen acts on together with the torque under the same loading condition. An elastic-plastic fracture toughness test using the PSD brings a successful experimentation in measuring the crack deformation(mode I+ mode II+ mode III).

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.725-736
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• 2020

In this work the mixed mode I/III fracture of sandstone has been studied experimentally and numerically. The experimental work used three-point bending specimens containing pre-existing cracks, machined at various inclination angles so as to achieve varying proportions of mode I to mode III loading. Dimensionless stress intensity factors were calculated using the extended finite element method (XFEM) for and compared with existing results from literature calculated using conventional finite element method. A total of 28 samples were used to conduct the fracture test with 4 specimens for each of 7 different inclination angles. The fracture load and the geometry of the fracture surface were obtained for different mode mixities. Prediction of the fracture loads and the geometry of the fracture surface were made using XFEM coupled with a cohesive zone model (CZM) and showed a good comparison with the experimental results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.725-728
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• 2004

In this study, the effect of mode II by variation of multilevel loading direction was experimentally investigated in the fatigue crack propagation behavior. To generate mixed-mode I+II loading state, the compact tension shear(CTS) specimen and loading device were used in this tests. The experimental method divided into three steps and three cases that were step I(0$^{\circ}$), step II(30$^{\circ}$, 60$^{\circ}$, 90$^{\circ}$),step III(0$^{\circ}$) and case I(0$^{\circ}$ ⇒ 30$^{\circ}$ ⇒ 0$^{\circ}$), case II(0$^{\circ}$ ⇒ 60$^{\circ}$ ⇒ 0$^{\circ}$), case III(0$^{\circ}$ ⇒ 90$^{\circ}$ ⇒ 0$^{\circ}$). The result of test, the step II affected to the step III in the all case. Specially, The fatigue crack propagation rate was faster and the fatigue life was smaller than of mixed mode I+II(30$^{\circ}$,60$^{\circ}$) due to the effect of mode II in the step III of the case III

• Structural Engineering and Mechanics
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• 제75권5호
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Journal of Advanced Marine Engineering and Technology
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• 제30권4호
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• pp.474-482
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• 2006

Generally almost all fatigue crack growth is affected by mode I. For this reason a study on mode I has concentrated in the field of fracture mechanics. However the fatigue crack initiation and growth in machines and structures usually occur in mixed mode loading. If there is any relationship between the cause of fracture in mixed mode loading and fracture surface, fracture surface pattern will be the main mean explaining reasons of fatigue fracture and obtaining further information about fracture process. In this paper low point shear-fatigue test with Aluminum alloy hi 5083-O is carried out from this prospect and then the mixed mode distribution of fracture surface is examined from the result after identifying the generation of fatigue crack surface pattern. It was found from the experimental results that the fatigue crack surface pattern and the fatigue crack shear direction are remarkably consistent. Furthermore It is possible that the analysis of distribution of mixed mode through the fatigue crack surface pattern.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2292-2306
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• 2024

This study addresses cracks and fracture problems in engineering structures that may cause significant challenges and safety concerns, with a focus on pressure vessels in nuclear power plants. Comprehensive parametric three-dimensional mixed mode fracture analyses for inclined and deflected nozzle corner cracks with various crack shape aspect ratios and depth ratios in nuclear reactor pressure vessels are carried out. Stress intensity factor (SIF) solutions are obtained using FRAC3D, which is part of Fracture and Crack Propagation Analysis System (FCPAS), employing enriched finite elements along the crack front. Also, improved empirical equations are developed to allow the determination of mixed mode SIFs, K_I, K_II, and K_III, for any values of the parameters considered in the study. This study provides practical solutions to assess the remaining life and fail-safe conditions of nuclear reactors by providing accurate SIF determination.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.304-310
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• 2001

Cracks at mechanical fastener holes usually nucleate as elliptical comer cracks at the faying surface of the mechanical joints and grow as elliptical arc through cracks after penetrating the opposite surface. In this study mode I, II and III stress intensity factors at two surface points of elliptical arc through cracks at mechanical fastener holes are analyzed by applying weight function method. The weight function method for two dimensional mixed-mode problem is extended to three dimensional one and it is verified.

• 대한기계학회논문집A
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• 제24권3호
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• pp.567-580
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• 2000

This paper proposes an integrated approach, which is independent of specimen geometry and loading type, for predicting the fatigue life of spot welded specimens. We first establish finite element models reflecting the actual specimen behaviors observed on the experimental load-deflection curves of 4 types of single spot welded specimens. Using finite element models elaborately established, we then evaluate fracture parameter J-integral to describe the effects of specimen geometry and loading type on the fatigue life in a comprehensive manner. It is confirmed, however, that J-integral concept alone is insufficient to clearly explain the generalized relationship between load and fatigue life of spot welded specimens. On this ground, we introduce another effective parameter $J_e$ composed of $J_I$, $J_{II}$, $J_{III}$, which has been demonstrated here to more sharply define the relationship between load and fatigue life of 4 types of spot welded specimens. The crack surface displacement method is adopted for decomposition of J, and the mechanism of the mixed mode fracture is also discussed in detail as a motivation of using $J_e$.

• Structural Engineering and Mechanics
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• 제89권5호
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• pp.539-547
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• 2024

This study examines crack behavior within orthopedic cement utilized in total hip replacements through the finite element method. Its main goal is to compute stress intensity factors (SIF) near the crack tip. The analysis encompasses two load types, static and dynamic, applied to a crack starting from the interface between the cement and bone. Specifically, it investigates SIFs under mixed mode conditions during three activities: normal walking, climbing upstairs, and downstairs. The results highlight that a crack originating from a micro-interface under substantial loading can cause cement damage, leading to prosthetic loosening. Stress intensity factors in modes I, II, and III are influenced by the crack tip's orientation and location in the bone cement, with a 90° orientation yielding notably higher values across all three modes.