• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.911-920
• /
• 1989

It this study, beam-type bend specimen is used to evaluate the interlaminar fracture toughness of laminated composite under mixed-mode deformations. The specimen is loaded under three-point bending and hence produced mixed-mode deformations in the vicinity of the crack tip according to the variation of the thickness ratio on delamination plane. Total energy release rate is obtained by elementary beam theory considering the effect of shear deformation. The partitioning of total value into mode-I and mode-II components is also performed. The mixed-mode interlaminar fracture toughness is evaluated by experiments on specimens with several thickness ratios of delamination plane. As the part of delamination plane is thicker, the effect of shear deformation on total energy release rate is increased. Beam-type bend specimen men may be applied to obtain informations on the mixed-mode interlaminar fracture behavior of laminated composites.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.2
• /
• pp.105-113
• /
• 2014

The mode II fracture behavior of a single-layer graphene sheet (SLGS) containing a center crack was characterized with the results of an atomistic simulation and an analytical model. The fracture of zigzag graphene models was analyzed with molecular dynamics and the mode II fracture toughness was found to be $2.04MPa{\sqrt{m}}$. The in-plane shear fracture of a cellular material was analyzed theoretically for deriving the $K_{IIc}$ of SLGS, and FEM results were obtained. Mixed-mode fracture of SLGS was studied for various mode I and mode II ratios. The mixed-mode fracture criterion was determined, and the obtained fracture envelope was in good agreement with that of another study.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.3
• /
• pp.185-196
• /
• 2006

Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.

• Journal of the Korean Society for Railway
• /
• v.12 no.5
• /
• pp.719-724
• /
• 2009

In this study, DCB(double cantilever beam) specimens of woven fabric carbon/epoxy and glass/epoxy were manufactured and mode I fracture toughness of specimen was measured according to ASTM 5528-01. And FE analysis was conducted in the same condition and evaluated the behavior of delamination analytically. Mode I fracture toughness measured by test was $845.7\;J/m^2$ in the case carbon/epoxy and that of glass/epoxy was $1,042\;J/m^2$. FE analysis was conducted using cohesive elements for adhesive layer and applied measured fracture toughness. To verify the result of analysis, the reaction force measured at the end of specimen and that calculated by Timoshenko beam theory were compared. The numerical results show good agreements with the measured one.

• Journal of the Korean Society of Safety
• /
• v.32 no.6
• /
• pp.9-15
• /
• 2017

Recently many researches were conducted on the interlaminar fracture that is a delamination between laminates by using ASTM standardized methods. However the experiment of the intralaminar a fracture is difficulty. In this study, four types of CFRP/GFRP composites with different layer structures were compared to evaluate an intralaminar fracture toughness under the mode I. Also the CNTs were added to the layer for the examination of the fracture toughness improvement. And the characteristics of the crack propagation behaviour was observed using a microscope. The obtained results can be useful for the evaluation of the intralaminar fracture toughness of the CNT reinforced CFRP/GFRP composites.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.11
• /
• pp.2771-2776
• /
• 2000

In this work, the effect of surface treatment of prepreg on the mode I fracture behavior was studied. Unidirectional (0-deg) double cantilever beam (DCB) specimens were used for fracture tests. Two groups of DCB specimens were made: the first group was made of prepregs surface-treated by Ar(sup)+ ion beam under oxygen environment and the second group was made of regular prepregs. For both groups, fracture resistance curve (R-curve) was determined and compared to each other, Results showed that resistance behavior of the first group is better than that of the second group. That is, mode I fracture toughness, G(sub)Ic of the first group is 24% larger than that of the second group. SEM examination shows that the improvement of G(sub)Ic is due to the increase of interfacial strength between plies.

• Journal of the Korean Wood Science and Technology
• /
• v.17 no.4
• /
• pp.70-76
• /
• 1989

The fracture toughness of two species, Pinus rigida MILL and Pinus koraiensis S. et Z. grown in Korea, was investigated by means of single edge notch beam specimen for the six principal systems of crack propagation in wood. The values of the fracture toughness for the LR and the LT systems ($K_{IC}$LR and $K_{IC}$LT) were found to be similar to each other and about 8 times greater than those for the other systems ($K_{IC}$RL, $K_{IC}$TL and $K_{IC}$TR) in both species. The results indicate that the characteristics of fracture toughness in three principal directions of wood (L, R, T direction) are quite different from those of bending strength for the responsible direction. To predict $K_{IC}$ value based on the variation of specific gravity, the experimental values of $K_{IC}$LT and $K_{IC}$TL were compared to the predicted values by published relationship between $K_{IC}$ and specific gravity. However, there were 10 to 25% differences between the former and the latter.

• Proceedings of the KSR Conference
• /
• 2009.05a
• /
• pp.239-246
• /
• 2009

The Mode I interlaminar fracture toughness of woven fabric carbon/epoxy and glass/epoxy composites for a train carbody was measured and FEM analysis was conducted. The woven fabric epoxy composite manufactured by hand lay-up, has high stiffness and strength, good resistance for impact, fatigue, corrosion and in-plane failure. The DCB(Double Cantilever Beam) specimen made of woven fabric epoxy composite had the size of 180mm $\times$ 25mm $\times$ 5mm and the insert of 65mm. The Mode I interlaminar toughness of specimen was measured according to ASTM 5528-01. The crack propagation behavior of the DCB specimen was simulated using FEA with cohesive elements that model the adhesive layer between woven fabric plies.

• Journal of the Korean Society of Safety
• /
• v.28 no.4
• /
• pp.14-18
• /
• 2013

Blades of horizontal axis are nowadays made of composite materials. Generally, composite materials satisfy design provides lower weight and good stiffness, while laminate composites have often damages as like the delamination and cracks at the interface of laminates. The box spar and tail parts of a blade are composed of the CFRP/GFRP hybrid laminate composites. However, delamination and the interfacial crack often occur in the interface of CFRP/GFRP hybrid laminate composites under the mixed mode fracture condition, especially mode I and mode II. Therefore, there is a need for the evaluation of the mixed mode fracture behavior during the delamination of CFRP/GFRP hybrid laminates. This study shows the experimental results for the delamination fracture toughness in CFRP/GFRP hybrid laminate composites. Fracture toughness experiments and estimation are performed by using DMMB(Dissimilar mixed mode bending) specimen. The materials used in the test are a commercial woven type CFRP(Carbon fiber reinforced plastic) prepreg(CF3327) and UD type GFRP(Glass fiber reinforced plastic) prepreg(HD224A). A CFRP/GFRP hybrid laminate composite is composed by the 10 plies CFRP and GFRP prepreg for DMMB. A thickness of CFRP and GFRP layer is 2.5mm and 3.0mm, respectively. Also the fulcrum location which is a loading parameter is changed from 80 to 100mm on the specimen of length 120mm because it defines the ratio of mode I to mode II. In this study, the effects of the fulcrum location are evaluated in the viewpoint of energy release rate in mode I and mode II contribution. The results show that the delamination crack initiates at higher displacement and lower load according to the increase of the fulcrum location ratio. And the variation of the energy release rate for mode I and II contributions for the mode mixity are shown.

• Structural Engineering and Mechanics
• /
• v.75 no.5
• /
• pp.559-569
• /
• 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.