• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.198-207
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• 1986

This study investigates interlaminar fracture characteristics of Graphite/Epoxy composite (HFG Graphite/Epoxy) under mode I (opening mode), mode II (sliding mode) and mixed mode loading conditions. The effects on interlaminar fracture toughness due to different fiber orientations on the crack surface are also investigated. The antisymmetric test fixture proposed by M. Arcan is used for this test. Both critical stress intensity foctors and critical energy release rates were determined and several mixed mode fracture criteria were compared to the experimental data. Also fracture surfaces were investigaed to obtain informations on the fracture behaviors of Graphite/Epoxy composite by means of a scanning electron microscope(SEM).

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.4
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.432-440
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• 2007

In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

• Structural Engineering and Mechanics
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• v.50 no.6
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• pp.723-740
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• 2014

A fracture criterion based on the strain energy density (SED) over a control volume, which embraces the notch edge, is employed in the present paper to assess the fracture loads of some U-notched Brazilian disk (UNBD) specimens. The specimens are made of commercial graphite and have been tested under pure mode I, pure mode II and mixed mode I/II loading. The results show that the SED criterion allows to successfully assess the fracture loads of graphite specimens for different notch tip radii and various mode mixity conditions with discrepancies that fall inside the scatter band of ${\pm}20%$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.129-137
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• 2002

In this study, mixed-mode fracture behavior is simulated effectively through the numerical method using the axial defomation link elements which can predict the behavior of quasi-brittle material. The behavior of quasi-brittle material is modeled numerically using the exponential tension softening constitutive equation and verified by comparing with the result of published experimental result. In order to verify the mixed-mode fracture behavior through the developed numerical method, analysis of mode I is formulated and the result is compared with those of FEM first, and then mixed-mode analysis is analyzed and compared with existing theories and experimental data. Also the characteristics of fracture behavior is examined through the analysis of crack generation with respect to various mode mixity.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.475-486
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• 2015

Mode II fracture toughness ($K_{IIc}$) of fiber reinforced concrete (FRC) has been widely investigated under various patterns of test specimen geometries. Most of these studies were focused on single type fiber reinforced concrete. There is a lack in such studies for hybrid fiber reinforced concrete. In the current study, an experimental investigation of evaluating mode II fracture toughness ($K_{IIc}$) of hybrid fiber embedded in high strength concrete matrix has been reported. Three different types of fibers; namely steel (S), glass (G), and polypropylene (PP) fibers were mixed together in four hybridization patterns (S/G), (S/PP), (G/PP), (S/G/PP) with constant cumulative volume fraction ($V_f$) of 1.5 %. The concrete matrix properties were kept the same for all hybrid FRC patterns. In an attempt to estimate a fairly accepted value of fracture toughness $K_{IIc}$, four testing geometries and loading types are employed in this investigation. Three different ratios of notch depth to specimen width (a/w) 0.3, 0.4, and 0.5 were implemented in this study. Mode II fracture toughness of concrete $K_{IIc}$ was found to decrease with the increment of a/w ratio for all concretes and test geometries. Mode II fracture toughness $K_{IIc}$ was sensitive to the hybridization patterns of fiber. The (S/PP) hybridization pattern showed higher values than all other patterns, while the (S/G/PP) showed insignificant enhancement on mode II fracture toughness ($K_{IIc}$). The four point shear test set up reflected the lowest values of mode II fracture toughness $K_{IIc}$ of concrete. The non damage defect concept proved that, double edge notch prism test setup is the most reliable test to measure pure mode II of concrete.

• Journal of the Korean Wood Science and Technology
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• v.21 no.2
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• pp.15-22
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• 1993

This study was carried out to investigate the fracture criterion of glulam. The mixed mode fracture of glulam was investigated by means of single edge notched specimens with various crack inclination in the longitudinal-radial plane. While fracture of wood is not completely understood, the study on linear-elastic fracture mechanics is a rational and valuable tool for studying the strength behavior of glulam. The results are summarized as follows : 1. Glue line has no effect on fracture strength. 2. There is a definite interaction between fracture toughness $K_I$ and $K_{II}$ during the mixed mode fracture of glulam. Several criterions for mixed mode failure were compared. The criterion was expressed in the following form: $(\frac{K_I}{K_{IC}})^2+(\frac{K_{II}}{K_{IIC}})^2=1$ 3. As crack inclination increases, $K_{IC}$ value and $K_{IIC}$ value decreases. The equations relating crack angle to $K_{IC}$ and $K_{IIC}$, respectively, were obtained as follows; $K_{IC}$ = -77.42${\gamma}$+153.72 ($R^2$ = 0.78) $K_{IIC}$ = -9.17${\gamma}$+34.90 ($R^2$ = 0.48)

• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.63-69
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• 2000

This study investigates a new method of using a concrete disk to calculate stress intensity factor (SIF) for mixed mode cases. The results indicate that the disk method is more accurate than three point bending test (TPB) in obtaining correct SIF values for mixed mode fracture propagation. Stress intensity factors $K_{I}$ and $K_{II}$ are calculated using a center notched disk subjected to splitting load. The notch angle is calculated by finite element (FEM). Fracture toughness $K_\textsc{k}$ of the concrete is obtained from the load intensities at the initiation of crack propagation. According to the finite element analysis(FEA) and disk test, the results show that mode I and mixed mode cracks propagate toward the directions of crack face and loading point, respectively. The results from FEA with maximum stress theory compare well with the experimental date. Unlike TPB method where an accurate fracture toughness value is difficult to obtain due to the irregular shape of load deflection curve and delayed final crack propagation (following slow stable cracking). fracture toughness value is easily measured in the disk test from the crack initial load. Therefore, it is safe to conclude that disk method is more advantageous than TPB method in analyzing combined mode fracture problems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.8
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• pp.1322-1331
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• 1997

A method of strength evaluation applying fracture mechanics in the adhesively bonded joints of Al/Steel dissimilar materials was investigated in this paper. Various shapes of adhesively bonded Al/Steel scarf joints focussing on fracture criterion of mixed mode crack were prepared for the static tests. Also, stress intensity factors of the interface cracks in adhesively bonded joints of Al/Steel dissimilar materials were analyzed with 2-dimensional elastic program of boundary element method(BEM), and the experiment of fracture toughness were carried out under various mixed mode conditions. From the results, the fracture criterion and method of strength evaluation by the fracture toughness in adhesively bonded joints of Al/Steel dissimilar materials were proposed.

• Journal of the Korean Society for Railway
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• v.8 no.2
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• pp.195-201
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• 2005

Mode II interlaminar fracture behaviors of carbon fabric/epoxy composites, which are applicable to tilting train carbodies, was investigated by the ENF (End notched flexure) test. The specimens were made of CF3327 plain woven fabric with epoxy and a starter delamination at one end was made by inserting Teflon film with the thickness of 12.5$mu$m or 25.0$mu$m. The equation for mode II interlaminar fracture toughness was suggested based on the effective crack length from the compliance of load-displacement curve. Mode II interlaminar fracture toughness was evaluated for several types of the specimens. Also crack propagating behaviors and fracture surfaces were examined through an optical travelling scope and a scanning electron microscope.