• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.60-63
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• 2002

Metal/intermetallic laminated composites have been manufactured by SHS reactions between Ni and Al elemental metal foils. Microstructure showed that the intermetallic volume fraction was 55%, 45%, 35% in the 1:1, 2:1, 4:1 thickness ratio(Ni:Al) specimen and the main phases of the intermetallic were transformed from $Ni_2Al_3$ to NiAl when the thickness ratio was increased. Tensile strength and elongation were increased when the volume fraction of Ni metallic phase was increased. Under assumptions of isostrain condition, the tensile strength of metal/intermetallic laminated composites didn't obey the ROM due to the thermal residual stress and this was confirmed by X-ray residual stress analysis. Fracture toughness results by the SENB test showed R-curves with upward curvature based on LSB condition. Bridging stress based on LSB condition was determined by the curve fitting analysis, In-situ observed microstructure during fracture test showed that the various bridging mechanism such as crack bridging, crack branching and ductile failure of metallic layer were occurred

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.99-103
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• 2005

It is generally accepted that fracture toughness of fiber-reinforced polymer composites is affected by strain rate in an atmospheric pressure condition. For a present study, the strain rate effect on the fracture toughness of fiber-reinforced laminated composites in the hydrostatic pressure condition was investigated. For this purpose, fracture tests have been conducted using graphite/epoxy laminated composites applying three steps of the strain rate at 270 MPa hydrostatic pressure condition. The strain rates applied were $0.05\%/sec,\;0.25\%/sec$, and $0.55\%/sec$. Fracture toughness was determined from the work factor approach as a function of applied strain rate. The result showed that fracture toughness decreased as the strain rate increased. Specifically, the fracture toughness decreased $12\%$ as the strain rate increased from $0.05\%/sec$ to $0.55\%/sec$.

• Steel and Composite Structures
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• v.42 no.5
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• pp.685-697
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• 2022

In this paper, a vibration-based method using the change ratios of modal data and the experience-based learning algorithm is presented for quantifying the position, size, and interface layer of delamination in laminated composites. Three types of objective functions are examined and compared, including the ones using frequency changes only, mode shape changes only, and their combination. A fine three-dimensional FE model with constraint equations is utilized to extract modal data. A series of numerical experiments is carried out on an eight-layer quasi-isotropic symmetric (0/-45/45/90)s composited beam for investigating the influence of the objective function, the number of modal data, the noise level, and the optimization algorithms. Numerical results confirm that the frequency-and-mode-shape-changes-based technique yields excellent results in all the three delamination variables of the composites and the addition of mode shape information greatly improves the accuracy of interface layer prediction. Moreover, the EBL outperforms the other three state-of-the-art optimization algorithms for vibration-based delamination detection of composites. A laboratory test on six CFRP beams validates the frequency-and-mode-shape-changes-based technique and confirms again its superiority for delamination detection of composites.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.89-92
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• 2002

Traditionally unidirectional laminated composite which are characterized by high specific stiffness and strength were used for structural application. But theses composites are highly susceptible to impact damage because of lower transverse tensile strength. The main failure modes of laminated composite are fiber breakage, matrix cracking and delamination for low velocity impact. The modified failure criterions are implemented to predict these failure modes with finite element analysis. Failure behavior of the woven fabric laminated composite which is used in forehead part of subway to lighten weigh has been studied. The new failure criterions are in good agreement with experimental results and can predict the failure behavior of the woven fabric composite plate subjected to low velocity impact more accurately.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.48-52
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• 1999

• Structural Engineering and Mechanics
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• v.22 no.6
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• pp.665-683
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• 2006

The strength behaviors of Fiber Reinforced Plastics (FRP) Composites can be greatly influenced by the properties of constitutive materials, the laminate structures, and load conditions etc, accompanied by many uncertainty factors. So the reliability study on FRP is an important subject of research. Many achievements have been made in reliability studies based on the probability theory, but little has been done on the roles played by fuzzy variables. In this paper, a fuzzy reliability model for FRP laminates is established first, in which the loads are considered as random variables and the strengths as fuzzy variables. Then a numerical model is developed to assess the fuzzy reliability. The Monte Carlo simulation method is utilized to compute the reliability of laminas under the maximum stress criterion. In the second part of this paper, a generalized fuzzy reliability model (GFRM) is proposed. By virtue of the fact that there may exist a series of states between the failure state and the function state, a fuzzy assumption for the structure state together with the probabilistic assumption for strength parameters is adopted to construct the GFRM of composite materials. By defining a generalized limit state function, the problem is converted to the conventional reliability formula that enables the first-order reliability method (FORM) applicable in calculating the reliability index. Several examples are worked out to show the validity of the models and the efficiency of the methods proposed in this paper. The parameter sensitivity analysis shows that some of the mean values of the strength parameters have great influence on the laminated composites' reliability. The differences resulting from the application of different failure criteria and different fuzzy assumptions are also discussed. It is concluded that the GFRM is feasible to use, and can provide an effective and synthetic method to evaluate the reliability of a system with different types of uncertainty factors.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.1
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• pp.46-53
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• 2010

A Compton X-ray backscatter technique has been developed to quantitatively assess impact damage in quasi-isotropic laminated composites made by a drop-weight tester. X-ray backscatter imaging system with a slit-type camera is constructed to obtain a cross-sectional profile of impact-damaged laminated composites from the electron-density variation of the cross section. A nonlinear scattering model based on Boltsman equation is introduced to compute Compton X-ray backscattering field for the defect assessment. An adaptive filter is also used to reduce noises from many sources including quantum noise and irregular distributions of fibers and matrix in composites. Delaminations masked or distorted by the first delamination are detected and characterized effectively by the Compton X-ray backscatter technique, both in width and location, by application of error minimization algorithm.

• Journal of the Korean Wood Science and Technology
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• v.40 no.2
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• pp.101-109
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• 2012

Wood composites are a hygroscopic material and have ability to exchange its moisture content with air. This study investigated the formaldehyde emission and moisture content change of four wood composites (particleboard (PB), medium density fiberboard (MDF), high density fiberboard (HDF), laminated HDF (L-HDF)) as a function of bake-out temperature and time. The composites were baked out for 1, 3, 5, 7, 10, 14, 21, and 28 days at temperatures of $20{\pm}2$, $35{\pm}2$, and $50{\pm}2^{\circ}C$ in a dry oven. The moisture content change was used to determine the emission bake-out of the composites. Best bake-out time results were obtained with after 7 days all composites. Formaldehyde emission values of composites decreased with decreasing moisture content for both temperatures. The formaldehyde emission results of bake-out temperature 35 and $50^{\circ}C$ showed a similar tendency.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.461-466
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• 2013

Advanced fiber-reinforced laminated composites are widely used in various fields of engineering to reduce weight. The material property of each ply is well known; specifically, it is known that ply is less reliable than metallic materials and very sensitive to the loading direction. Therefore, it is important to consider this uncertainty in the design of laminated composites. In this study, reliability analysis is conducted using COMSOL and MATLAB interactions for a laminated composite plate for the case in which the tip deflection is the design requirement and the material property is a random variable. Furthermore, the efficiency and accuracy of the approximation method is identified, and a probabilistic sensitivity analysis is conducted. As a result, we can prove the applicability of the advanced design method for the stabilizer of an underwater vehicle.

• Structural Engineering and Mechanics
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• v.50 no.2
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• pp.231-240
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• 2014

In the present research, fatigue behavior of chopped strand mat/epoxy composites has been studied with two different techniques. First, the normalized stiffness degradation approach as a well-known model for unidirectional and laminated composites was utilized to predict the fatigue behavior of chopped strand mat/epoxy composites. Then, the capability of the fatigue damage accumulation model for chopped strand mat/epoxy composites was investigated. A series of tests has been performed at different stress levels to evaluate both models with the obtained results. The results of evaluation indicate a better correlation of the normalized stiffness degradation technique with experimental results in comparison with the fatigue damage accumulation model.