Papers by Author: Meng Hou

Abstract: Technique of including an amorphous thermoplastic film as the outermost layer of thermoset composites have been developed to join the thermoset composites using fusion bonding methods. Based on a WLF temperature dependence and a time dependence of t^1/4, isothermal and non-isothermal models were developed to relate the recovery of bonding strength to welding temperature and time. The isothermal model failed to take into account the time taken for the bonding interface to reach the glass transition temperature and final desired bonding temperature and lacked predictive power for experiments with short bonding times and low shear strength recovery. The non-isothermal model provided an excellent fit to the experimental date, showing a significant improvement over the isothermal model.

Abstract: Technique of including a thermoplastic film as the outermost layer of thermoset composites have been developed as an attempt to join the thermoset composites using fusion bonding methods. Special thermoplastic in the form of film was incorporated onto the surface of thermoset composites during co-curing process. Semi-Interpenetration Polymer Network [s-IPN] was formed between thermoplastic and thermoset polymers. The thermoset composites can be fusion bonded using co-consolidation and localized heating through their incorporated thermoplastic surfaces. The mechanical properties of thermoset composites bonded with thermoplastic adhesive were equivalent or superior to the benchmark composites bonded with Cytec FM300K adhesive in terms of lap shear strength, high temperature, low temperature and anti-chemical resistance.

Abstract: The effects of different processing conditions (pressure, holding time and temperature) on the impregnation/consolidation quality of CF/PEKK composite were investigated using compression molding process. Microscopic investigation of cross-sections, density measurements and flexural mechanical properties were used to examine the quality of impregnation and consolidation. A qualitative model to describe the impregnation and consolidation process of this material was developed. The model predicts the variations of void content during consolidation as well as the holding time, moulding temperature and pressure required to reach full consolidation. Good agreement between theoretical predictions and experimental data was achieved. Optimum processing conditions can be determined based on selected void content.

Abstract: The morphology of the interface between a commercial epoxy prepreg resin (HexPly M18/1) and Polyetherimide (PEI) is studied. Different cure cycles prescribed by the supplier were investigated to determine the influence of temperature and pressure on interface formation. Atomic Force Microscopy (AFM) was used as the main means of investigation. A phase-separated interphase spanning 9-10μm was observed for the PEI/epoxy prepreg interface. It was found that the temperature profile of the cure cycle strongly influences the formation of this interphase. Rapid formation of these relatively large interphase areas suggests that mechanisms other than diffusion are responsible for this phenomenon.

Abstract: Polyvinylidene fluoride (PVDF)/Carbon nanotubes (CNTs) and PVDF/Organo-modified layered silicates (OMLSs) nano-composites were prepared by phase inversion technique. Maleic anhydride grafted PVDF (PVDF-MAH), were used to fine tune the interface. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to characterize the nanocomposites. Elastic modulus and creep resistance of the PVDF nanocomposites were evaluated according to ASTM D-638. The results showed that both CNTs and OMLSs were good candidates to reinforce the PVDF and the addition of PVDF-MAH enhanced the interface between nanoparticles and PVDF, leading to further increase of mechanical property.

Abstract: A nano-filler network constructed by layered silicates and multi-wall carbon nanotubes (MWCNTs) has been prepared. The structure of the network was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and dynamic rheological test. The results showed that a plateau in the storage modulus at low frequency occurred, which indicated the pseudo solid-like behaviour for the sample with nano-filler network, and the jamming effect due to the nano-filler network dominated the viscoelatic behaviour at low frequency. This effect was sensitive to the frequency and decreased quickly with the increase of frequency. At the same time, the introduction of nanofillers and the presence of nano-filler network affected the complex viscosity and shear thinning too, especially at low frequency.

Abstract: Poly(vinylidene fluoride)/Microcrystalline cellulose (MCC) nanocomposites were prepared by ultrasonic treatment and magnetic stir. Poly(vinylidene fluoride)-graft-maleic anhydride (PVDF-g-MAH) was added to promote matrix–filler compatibility. Transmission electron microscopy (TEM) results showed that the diameter of the MCC was decreased to several tens nanometers by the treatment of ultrasonic and magnetic stir. The results of differential scanning calorimetry (DSC) showed that the peak crystallisation temperatures (Tc) and the crystallisation enthalpy ΔHc increased with the addition of MCC, and the melting enthalpy ΔHm increased. With the addition of the compatibilizer (PVDF-g-MAH), peak crystallisation temperatures increased further, while without further increase of the ΔHc. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) showed that the addition of MCC induced β-phase PVDF, and the addition of PVDF-g-MAH can induce more β-phase PVDF. Mechanical properties of the nanocomposites were evaluated and the results showed that the addition of MCC did not increase the Young’s modulus, while the tensile strength and elongation at break decreased.

Abstract: The blister test is a promising test method to determine the interface fracture toughness of thin films adhering to rigid fibre reinforced plastics. In this paper nonlinear finite element analysis is used to determine a suitable layout for both the shaft loaded and the pressurised blister test. On the example of a PET film adhering to a quasi-isotropic fibre reinforced plastic, it is shown that energy release rates in a range of 0-1500N/m can be obtained for a 0.5mm thick film if test parameters are carefully selected. The two main causes for deviations of the analytic solution from the FEA results is attributed to infringement of the membrane limit condition and plastic deformation in the film.

Abstract: Prepreg resin systems are typically of complex composition and require very specific manufacturing conditions. These characteristics restrict the use of some commonly used micro analysis techniques. This paper investigates the use of low acceleration voltage scanning electron microscopy and energy dispersive x-ray analysis for the characterization of diffused polymer interfaces. It is shown that, by operating at the dynamic charge balance, high resolution secondary electron images of polymer interfaces can be obtained and that conductive coating is not required. In addition, the effect of acceleration voltage on the interaction volume in EDX analysis is discussed using Monte Carlo simulation. X-ray intensity measurements in combination with afore mentioned Monte Carlo simulation is used to define practically obtainable spatial resolution limits. It is shown that by reducing the acceleration voltage below 5kV spatial resolution higher the 500nm can be obtained.

Abstract: The paper describes the manufacture of thin composite panels using high performance sheet moulding compound (SMC). Topics discussed within the paper include characterisation of curing and flow behaviour of SMC material, tooling design concept and determination of suitable processing conditions for compression moulding. A Full scale “Burst test” was carried out to evaluate the mechanical performance of SMC panels. The overall performance of the SMC panels was satisfactory with all panels failed beyond the specification value. The main failure mode was a through-thickness cracking. In addition, a geometrical non-linear numerical analysis was also carried out to investigate the stress distribution and deflection behaviour of SMC panel during “Burst testing”.