Key Engineering Materials Vols. 334-335

Abstract: The macroscopic hyperelastic behavior of fiber reinforced polymer composites is studied using the micromechanical model and finite deformation theory. It is assumed that the fiber and matrix are hyperelastic media and undergoing finite deformation. The local fields of a representative volume element are calculated by the hyperelastic finite element method. Then an averaging procedure is used to find the homogenized stress and strain and the macroscopic curves of stress-strain are obtained. The several microstructural parametric effects on the macroscopic hyperelastic behavior are considered. The numerical examples show the hyperelastic behavior and deformation of the composites.

Abstract: Aeroelastic tailoring studies using effective computational method with genetic algorithm have been conducted to find an optimized lamination set which give minimum structural weight. The efficient and robust computational system for the flutter optimization has been developed using the coupled computational method based on the micro genetic algorithm. It is shown that the wing structural weight with both divergence and flutter constrains can be significantly reduced using composite materials with proper optimum lamination compared to the case of isotropic wing model.

Abstract: In this study, advanced computational analysis system for nonlinear static aeroelastic problems has been successfully developed by the composite structure (FEM)-fluid (CFD) combined method with internal iteration steps. Major focus of the present study is to investigate the static aeroelastic characteristics of laminated composite wings including the strong normal shock waves in the transonic and low-supersonic flow regions. The results importantly indicate that the effect of airfoil camber on the load distribution of laminated composite wing models can be nonlinear due to the variation of ply orientations.

Abstract: This paper presents a real microstructure model which has the same fiber volume fraction and tows’ spatial configuration with 3D rectangular composites to simulate the ballistic impact damage of the composites struck by steel projectile. The commercial available FEM code of Ls-Dyna was employed to calculate the interaction between the composite targets and steel projectile. From the comparison of residual velocities between simulation and experiment, it is proven the microstructure model can simulate the ballistic penetration with higher precision than the continuum model. The acceleration vs. time curve reveals the complicated interaction between composite and projectile in ballistic penetration. The prominent advantage of the microstructure model is that it can simulate the local damage mode of the composites at real microstructure level and obtain vivid simulating results.

Abstract: A new type of composite used biodegradable resins and natural fibers is now being developed and this new type of composites is designated as a green composite. This paper presents a fabrication method and mechanical properties of the green composite used Kenaf fibers as the reinforcement and PLA as the matrix. In order to obtain the higher tensile strength, various kind of surface treatments were executed on the Kenaf fiber and some parameters were changed during the process of fabrication. Then, these effects on the strength of green composite are also reported.

Abstract: The aim of the current work was to investigate using fungi to treat hemp fibre to create better bonding characteristics in natural fibre reinforced polypropylene composites. X-ray diffraction (XRD), lignin testing and scanning electron microscopy (SEM), were used to characterise the effect of treatment on hemp fibres. A combined alkali and fungal treated fibre composite produced the highest tensile strength of 48.3 MPa, an increase of 32% compared to composites with untreated fibre.

Abstract: This study investigates the effect of recycling/reprocessing on the physical and mechanical properties of composites based on radiata pine (Pinus Radiata) fibre and polypropylene (PP) with a maleated polypropylene (MAPP) coupling agent, produced using a twin-screw extruder, followed by injection moulding. Composites containing 40wt% fibre and 4wt% MAPP were assessed mechanically and thermally, as well as for moisture absorption after being recycled up to eight times. Both the tensile strength (TS) and Young’s modulus (YM) of composites were found to decrease linearly from 41 MPa and 4556 MPa respectively to 31 MPa and 3800 MPa for composites recycled eight times. However, the elongation at break was found to increase with increased recycling due to fibre damage that occurred during reprocessing and the associated reduction of average fibre length, found to decrease from 2.36mm to 0.37mm after recycling eight times. Thermal stability and moisture resistance of composites improved with recycling due to the improvement of interfacial bonding between fibre and matrix.

Abstract: An experimental testing program is being conducted to evaluate the effects of environmental exposure on the mechanical properties of glass/vinyl ester filament wound pipes. The effects of artificial exposure on the flexural and fracture properties are reported in this paper. Three point bending specimens were employed to characterize the flexural properties. Fracture resistance was assessed using pre-cracked notched ring specimens. Specimens were exposed for 300, 1000, and 3000 hours in the environment of interest before testing at room temperature. The exposure conditions presented in this paper include: dry heat at 40
C, dry heat at 70
C, 65% and 100% relative humidity at room temperature; and salt spray and seawater environments at room temperature. The results of this study indicate that the flexural strength and stiffness; and the fracture resistance of the tested GFRP composite do not show significant degradation due to prior exposure to the environments investigated for up to 3000 hours. The flexural ductility is shown to degrade after exposure in high humidity environment.

Abstract: Fracture toughness and the possibility of recycling for Carbon Fiber Reinforced Plastics (CFRP) under mode one and mode two loadings are examined. Epoxy matrix is modified by CNBR rubber particle which diameter is smaller than 100 nano meter. Three kinds of rubber content (5,10,15%) are used. Two types of test methods whose modes are different are conducted. After the specimen fracture, recycled specimens are made by adhesion. Fracture toughness is measured at the tests. Fracture surface is also observed by SEM. As a result, following conclusions are obtained. When the interlaminar fracture test using recycled CFRP specimen is conducted under Mode one loading, fracture toughness is improved using rubber modified matrix. For recycled CFRP specimen under mode two loading, fracture toughness of CFRP using unmodified epoxy is improved. In this case, fracture toughness for modified CFRP is improved but it is not as high as than CFRP with unmodified recycle CFRP. From SEM ovservation on fracture sufface under mode two loading, there is a difference on fracture surfaces. Specimen whose fracture toughness is high has a ductile properties.