• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.04a
• /
• pp.154-157
• /
• 2005

This paper aims to investigate the tow deformation pattern with respect to shear angle and mold property during draping of plain weave carbon/epoxy prepreg. Aluminum and PVC foams with different foam density are used for the draping hemisphere molds with 250 mm diameters. Microscopic observation reveals that tow parameters like crimp angle and Y-directional tow intervals are influenced by shear angle and mold density at the same time. The correlation between crimp angle and Y-directional tow interval is also found out.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.7 s.250
• /
• pp.849-856
• /
• 2006

In this paper, fabric composite draping on hemisphere moulds were studied to find out the deformation behaviour of micro-tow structures of fabrics during draping and thermoforming. Aluminium and PVC foams were used to fabricate the hemisphere moulds for draping tests. In order to observe the local tow deformation pattern during the draping several specimens for microscopic observation were sectioned from the draped hemisphere structures. The effect of forming condition and mould properties on tow deformation was investigated by the microscopic observation of the tow parameters such as crimp angle. Normalization scheme was performed to compare tow parameter variations with different forming conditions. Stress-strain .elations of two different PVC foams (HT70 and HT110) were tested to investigate the effect of foam property on the micro-tow deformation during forming.

• Composites Research
• /
• v.29 no.1
• /
• pp.33-39
• /
• 2016

In this study, geometric modeling and finite element analysis of 3-dimensional plain weave composite unit cell consisting of 3 interlaced fiber tows and resin pocket were performed to predict effective properties. First, tow properties were obtained from micro-mechanics finite element unit cell analysis, which were then used in the meso-mechanics analysis. The effective properties were obtained from a series of unit cell analyses simulating uniaxial tensile and shear tests. Analysis results were compared to the analysis and experimental results in the literature. Various crimp angles were considered and the effect on the effective properties was investigated. Initial failure strengths and failure sequence were also examined.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.11
• /
• pp.1757-1764
• /
• 1997

The geometric and elastic models based on the unit cell have been proposed to predict the geometric characteristics and the engineering constants of plain and satin woven composites. In the geometric model, length and inclined angle of the yarn crimp and the fiber volume fraction of woven composites have been predicted. In the elastic model, the coordinate transformation has been utilized to transform the elastic constants of the yarn crimp to those of woven composites, and the effective elastic constants have been determined from the volume averaging of the constituent materials. Good correlations between the model predictions and the experimental results of carbon/epoxy and glass/epoxy woven composites have been observed. Based on the model, the effect of various geometric parameters and materials on the three-dimensional elastic properties of woven composites can be identified.

• Composites Research
• /
• v.17 no.6
• /
• pp.28-36
• /
• 2004

Micro-tow deformation during forming of PVC foam-fabric composite sandwich structure is investigated to find out the correlation between forming condition and material deformation. The foams used in this research are PVC foams which have 4 different densities and the fabric composite is Carbon/epoxy prepreg which is plain weave (3k) as a skin material. Tow parameters such as crimp angle and tow amplitude are measured using microscope and a proper image tool and are compared with each other. In order to find out the effect of foam deformation during forming on tow deformation the compressive tests of foams are performed in three different environmental temperatures ($25^{\circ}C$, $80{\circ}C$, $125^{\circ}C$). The microscopic observation results show that the micro tow deformations are quite different from each other with respect to the foam density and forming pressure.

• Composites Research
• /
• v.31 no.5
• /
• pp.276-281
• /
• 2018

In this paper, elastic behavior of woven fabric composites with various fiber yarn structure were predicted through a theoretical calculation model. A representative volume elements (RVE) that can represent the mechanical properties of the woven composites were selected and crimp angle of the weave yarn was defined by several sinusoidal functions. The effective material properties of the woven composite such as young's modulus, shear modulus and poisson's ratio was predicted by classical laminate theory (CLT). The fiber volume fractions were calculated according to the shape and pattern (plain, twill weave) of the fiber yarn, and the elastic behavior of each woven composite was obtained through a theoretical calculation model. Also, to verify the theoretical predictions, woven composite specimens of plain and twill weave were fabricated by vacuum assisted resin transfer molding (VARTM) process and then mechanical test was conducted. As a results, a good correlation between theoretical and experimental results for the elastic behavior of woven composites could be achieved.

• Composites Research
• /
• v.17 no.1
• /
• pp.38-46
• /
• 2004

This paper aims to correlate the micro-mechanical behaviour of tow geometry with applied in-plane forces during deformation of dry woven carbon-fibre fabric. These in-plane forces lead to differences in tow reorganisation during deformation and so changes in the way in which 'lock-up' occurs. In this paper, deformation of micro-mechanical parameters such as tow interval, crimp angle, change in tow amplitude and wavelength are investigated. To observe the micro-deformation of the fabric structure, appropriate specimens from bias extension and biaxial tests are sectioned and observed under the microscope. It was found that different loading conditions cause geometric deferences in the tow architecture. The variation in deformed tow geometry with shear angle is fitted using a simple parametric model.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.194-197
• /
• 2004

In this paper, compressive characteristics of carbon fabric skin with polymeric foam core sandwich structure were investigated by FE analyses and compressive tests of polyurethane foam were also conducted with respect to temperature changes, which were determined by curing processes of epoxy or polyester resin to obtain mechanical behaviour of polyurethane foam. FE analyses indicated variation of parameters with respect to manufacturing pressure, which have comparatively massive effect upon mechanical properties of sandwich structures, i.e. wavelength as well as crimp angle of carbon fabric

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.198-201
• /
• 2004

This paper aims to investigate the micro-mechanical behaviour of tow geometry with forming pressures and densities of foams during the curing process of plain weave carbon fibre fabric prepregs onto polymer foams. In order to find out and compare deformation patterns between different forming conditions, tow parameters such as amplitude and crimp angle etc. are investigated. From the observation results, geometric difference in the tow architecture with respect to forming conditions and foam characteristics were found. To observe the micro-deformation of the fabric structure, appropriate specimens from carbon fibre-foam sandwich structures are sectioned and observed under the microscope.

• Composites Research
• /
• v.32 no.5
• /
• pp.206-210
• /
• 2019

As the use of composite materials of woven structure has expanded to various fields such as automobile and aviation industry, there has been a need for reliability problems and prediction of mechanical properties of woven composites. In this study, finite element analysis for predicting the mechanical properties of composite materials with different weaving structures was conducted to verify similarity with experimental static properties and an effective modeling method was developed. To reflect the characteristics of the weave structure, the meso-scale representative volume element (RVE) was used in modeling. Three-dimensional modeling was carried out by separating the yarn and the pure matrix. Hashin's failure criterion was used to determine whether the element was failed, and the simulation model used a progressive failure model which was suitable for the composite material. Finally, the accordance of the modeling and simulation technique was verified by successfully predicting the mechanical properties of the composite material according to the weave structure.