• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.4
• /
• pp.171-178
• /
• 1996

DCB(pure mode I) and CLS(mixed mode) tests were performed to investigate the effect of fracture mode on the interlaminar fracture of composite laminate. Mode I critical strain energy release rate was found to be $133J/m^2$ from the DCB test and total strain energy release rate decreased from $1, 270J/m^2$ as thickness ratio(tl/t) varied from 0.333 to 0.667 from the crease from the CLS test. Crack length had no effect on the total strain energy release rate and load was almost constant during the crack growth of the specimen which had the specific thickness ratio. Crack initiated when the stress of the strap ply reached constant stress $42kgf/mm^2$ which was found to be independent of the thickness ratio.

• Transactions of Materials Processing
• /
• v.31 no.1
• /
• pp.29-38
• /
• 2022

Recently, the composite material market is gradually growing. Various composite forming processes have been developed in order to reduce the production cost of the composite material. Unlike the conventional forming process, the microwave composite forming process has the advantage of reducing the processing time because the composite material is heated directly or indirectly at the same time. Due to this advantage, in this study, a double cantilever beam test was conducted with specimens manufactured by the microwave composite forming process. The purpose of this study was to compare mode-I energy release rate for specimens manufactured by prepreg compression forming and microwave composite forming processes. First, a microwave oven was proposed to conduct the microwave composite forming process. Double cantilever beam specimens were manufactured. After that, the double cantilever beam test was conducted to obtain the mode-I energy release rate. Mode-I energy release rates of specimens manufactured by the microwave composite forming and prepreg compression forming processes were then compared. As a result, mode-I energy release rates of specimens fabricated by the microwave composite forming process were similar to those fabricated with the prepreg compression forming process with a relatively reduced process time.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.9
• /
• pp.81-86
• /
• 2000

This paper was carried out to investigate the characteristics of interlaminar fracture toughness of foam core sandwich structures under opening loading mode by using the double cantilever beam (DCB) specimens in Carbon/Epoxy and foam core composites. instead of using symmetric geometry of DCB specimen non-symmetric DCB specimen was used to calculate the interlaminar fracture toughness. Three approaches for calculating the energy release rate({{{{ {G }_{IC } }}}}) were compared. Fracture toughness of foam core sandwich structures by autoclave vacuum bagging and hotpress were compared and analyzed. Experiment nonlinear beam bending FEM method were performed. Suggested bonding surface compensation and equivalent area inertia moment was used to calculate the energy release rate in nonlinear analytical results. The conclusions among experimental nonlinear analytical and FEM results was observed. The vacuum bagging method was shown to be able to substitute method in stead of autoclave without serious loss of Mode I energy release rate({{{{ {G }_{IC }}}}}) to be able to substitute method in stead of autoclave without serious loss of Mode I energy release rate({{{{ {G }_{IC }}}}}).

• Composites Research
• /
• v.31 no.5
• /
• pp.177-185
• /
• 2018

Fiber metal laminate (FML) is a type of hybrid composites which consist of metallic and fiber-reinforced plastic sheets. As the FML has a drawback of the delamination that is a failure of the interfacial adhesive layer, the nominal stresses and the energy release rates should be determined to identify the delamination behavior. However, it is difficult to derive the nominal stresses and the energy release rates since the operating temperature of the equipment is restricted. For this reason, the objective of this paper is to predict the mode-I nominal stress and the mode-I energy release rate of the adhesive layer using the inverse analysis based on the Levenberg-Marquardt method. First, the mode-I nominal stress was assumed as the tensile strength of the adhesive layer, and the mode-I energy release rate was obtained from the double cantilever beam test. Next, the finite element method was applied to predict the mode-I delamination behavior. Finally, the mode-I nominal stress and the mode-I energy release rate were predicted by the inverse analysis. In addition, the convergence of the parameters was validated by trying to input two cases of the initial parameters. Consequently, it is noted that the inverse analysis can predict the mode-I delamination behavior, and the two input parameters were converged to similar values.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.03a
• /
• pp.220-226
• /
• 1998

In this pater, a method of strength evaluation applying fracture mechanics in adhesively bonded joints of A1/A1 materials was investigated. Various adhesively bonded joints of double-cantilever beam with a interfacial crack in its adhesive layer were prepared for the fracture toughness test of comprehensive mixed mode conditions from nearly pure mode I to mode II. The experiment of fracture toughness was carried out under various mixed mode conditions with an interfacial crack and critical energy release rate, Gc by the experimental measurements of compliances was determined. From the results, fracture toughness on mixed mode with an interfacial crack is well characterized by strain energy release rate and a method of strength evaluation by the fracture toughness in adhesively bonded joints of A1/A1 materials was discussed.

• Composites Research
• /
• v.32 no.1
• /
• pp.6-12
• /
• 2019

This paper describes the characteristics for mode I interlaminar and intralaminar fractures of cross-ply carbon/epoxy composite laminates. We obtained mode I interlaminar fracture toughness and mode I intralaminar fracture toughness based on energy release rate and Finite Element Analysis (FEA). For this purpose, the Double-Cantilever Beam (DCB) test and FEA were performed for cross-ply DCB specimens. Also, the behavior of load-displacement curve at the interlaminar and intralaminar crack was analyzed. The results show that mode I intralaminar fracture toughness was lower than mode I interlaminar fracture toughness in the cross-ply DCB specimen.

• Journal of the Korean Society of Safety
• /
• v.34 no.3
• /
• pp.1-7
• /
• 2019

A variety of composite materials are applied to industries for the realization of light weight and high strength. Fiber-reinforced composites have different strength and range of application depending on the weaving method. The mechanical performance of CFRP(Carbon Fiber Reinforced Plastic) in many areas has already been demonstrated. Recently, the application of hybridization has been increasing in order to give a compensation for brittleness of CFRP. Target materials are UHMWPE (Ultra High Molecular Weight Polyethylene), which has excellent cutting and chemical resistance, so it is applied not only to industrial safety products but also to places that lining performance is expected for household appliances. In this study, the CFRP and UHMWPE of plain weave, which are highly applicable to curved products, were molded into laminated hybrid composite materials by autoclave method. The mechanical properties and the mode I failure behavior between the layers were evaluated. The energy release rate G has decreased as the initial crack length ratio increased.

• 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.

• Journal of the Korean Society of Safety
• /
• v.35 no.5
• /
• pp.9-14
• /
• 2020

In order to realize high strength and light weight for various industrial facilities and structural materials, various new materials are applied to product design. Among them, CFRP has excellent specific strength and non-rigidity, and the scope of use is expanding throughout the industry, such as mobility products and building materials. GFRP is cheaper than CFRP, and has excellent specific strength and non-rigidity, and has excellent heat resistance and sound insulation, so it has been adopted as a core material for flooring and interior flooring. CFRP of twill weave structure has better resistance to deformation of fiber than plain weave structure, so the outermost layer is applied as twill weave structure in product design. After fabrication with DCB specimens, Mode I fracture toughness was evaluated according to the crack length. As the crack length increases, the energy release rate and stress intensity factor values tended to decrease overall.

• International Journal of Precision Engineering and Manufacturing
• /
• v.2 no.3
• /
• pp.47-53
• /
• 2001

This paper investigates the characteristics of interlaminar fracture toughness of foam core sandwich structures under opening mode by using the double cantilever beam (DCB) specimens which are Carbon/Epoxy and foam core composites. Instead of using a DCB specimen of symmetric geometry, a non-symmetric DCB specimen was used to calculate the interlaminar fracture toughness. Three approaches for calculating the energy release rate(G$\sub$IC/) were used and fracture toughness of foam core sandwich structures made by autoclave, vacuum bagging and hotpress were compared. Experiment, analysis using nonlinear beam bending theory, and numerical work by FEM methods were performed. Bonding surface compensation and equivalent moment of inertia were used to calculate the energy release rate in nonlinear analytical work. Conclusions of experimental, nonlinear analytical and FEM methods were compared. It is, also, shown that the vacuum bagging forming can substitute the method of autoclave without serious loss of Mode I energy release rate(G$\sub$I/).