Uncured Matrix Research Articles

Effect of GO modification and curing on formation of ordered structures in epoxy composites

Modifications of GO by polymer chains may promote, in addition to exfoliation, also formation of ordered structures in epoxy. However, the contribution of self- assembly in the uncured matrix and reaction-induced phase separation to this process is not clear. SAXS study of analogous liquid and cured epoxy reveals that single grafted GO forms ordered structures only due to RIPS of grafted rubber. The marked self-assembly of bimodally grafted GO (BGO) before curing indicates that such modification changes its ordering performance substantially. Moreover, formation of ordered lamellar structures in liquid epoxy accompanied by easy migration of BGO may lead to formation of these arrays at the interface in carbon fibre composites. As a result, in-situ formation of effective nacre-like structures on the surface of CF, increasing delamination resistance, can be achieved.

Fabrication and properties of glass cloth reinforced multifunctional acrylic polymer substrate

Transparent glass cloth reinforced composite films were fabricated by ultraviolet (UV) light which induced chemical crosslinking of composite materials consisting of glass cloth and UV curable resin in film state. UV curable resin has been recognized to be the general trend of transparent glass cloth reinforced plastic (GCRP) resins because of its excellent heat resistance and chemical stability resulted from the dense network structure by UV curing of oligomers and monomers. But when GCRP is fabricated by UV curing of matrix resin, there exist three different refractive indices from cured resin, uncured resin, and glass cloth. To minimize uncured matrix resin and improve the transmittance of GCRP, the composite films were treated by heat after UV curing. As a result of heat treatment, optical properties of the composite films were enhanced and the excellent thermal and dimensional stability at the high temperature more than 300 °C were achieved.

Thermosetting hierarchical composites with high carbon nanotube loadings: En route to high performance

A wet powder impregnation route to manufacture carbon fibre reinforced thermoplastic composites was adapted to accommodate thermosetting matrices reinforced with high fractions (20 wt%/13.6 vol%) of multiwalled carbon nanotubes (CNTs). The produced carbon fibre prepregs were consolidated into laminates with fibre volume fractions of 50–58% and up to 6.1 vol% CNTs. Microscopic imaging confirmed successful consolidation at intermediate CNT loadings, but some voidage at the highest CNT loading due to the highly viscoelastic uncured matrix. Nonetheless, through-thickness electrical conductivity and Mode I interlaminar fracture toughness were enhanced by as much as 152% and 24% to unprecedented values of σ = 53 S m−1 and GIC = 840 J m−2, respectively. Fractographic characterisation indicated that crack deflection was the mechanism responsible for the improved fracture toughness. The material properties were shown to be strongly dependent on the microstructure of the matrix.

The effect of shear strength on the ballistic response of laminated composite plates

Abstract The ballistic performance of clamped circular carbon fibre reinforced polymer (CFRP) and Ultra High Molecular Weight Polyethylene (UHMWPE) fibre composite plates of equal areal mass and 0/90° lay-up were measured and compared with that of monolithic 304 stainless steel plates. The effect of matrix shear strength upon the dynamic response was explored by testing: (i) CFRP plates with both a cured and uncured matrix and (ii) UHMWPE laminates with identical fibres but with two matrices of different shear strength. The response of these plates when subjected to mid-span, normal impact by a steel ball was measured via a dynamic high speed shadow moire technique. Travelling hinges emanate from the impact location and travel towards the supports. The anisotropic nature of the composite plate results in the hinges travelling fastest along the fibre directions and this results in square-shaped moire fringes in the 0/90° plates. Projectile penetration of the UHMWPE and the uncured CFRP plates occurs in a progressive manner, such that the number of failed plies increases with increasing velocity. The cured CFRP plate, of high matrix shear strength, fails by cone-crack formation at low velocities, and at higher velocities by a combination of cone-crack formation and communition of plies beneath the projectile. On an equal areal mass basis, the low shear strength UHMWPE plate has the highest ballistic limit followed by the high matrix shear strength UHMWPE plate, the uncured CFRP, the steel plate and finally the cured CFRP plate. We demonstrate that the high shear strength UHMWPE plate exhibits Cunniff-type ballistic limit scaling. However, the observed Cunniff velocity is significantly lower than that estimated from the laminate properties. The data presented here reveals that the Cunniff velocity is limited in its ability to characterise the ballistic performance of fibre composite plates as this velocity is independent of the shear properties of the composites: the ballistic limit of fibre composite plates increases with decreasing matrix shear strength for both CFRP and UHMWPE plates.

The soft impact response of composite laminate beams

The quasi-static and dynamic responses of laminated beams of equal areal mass, made from monolithic CFRP and Ultra high molecular weight Polyethylene (UHMWPE), have been measured. The end-clamped beams were impacted at mid-span by metal foam projectiles to simulate localised blast loading. The effect of clamping geometry on the response was investigated by comparing the response of beams bolted into the supports with the response of beams whose ends were wrapped around the supports. The effect of laminate shear strength upon the static and dynamic responses was investigated by testing two grades of each of the CFRP and UHMWPE beams: (i) CFRP beams with a cured matrix and uncured matrix, and (ii) UHMWPE laminates with matrices of two different shear strengths. Quasi-static stretch-bend tests indicated that the load carrying capacity of the UHWMPE beams exceeds that of the CFRP beams, increases with diminishing shear strength of matrix, and increases when the ends are wrapped rather than through-bolted. The dynamic deformation mode of the beams is qualitatively different from that observed in the quasi-static stretch-bend tests. In the dynamic case, travelling hinges emanate from the impact location and propagate towards the supports; the beams finally fail by tensile fibre fracture at the supports. The UHMWPE beams outperform the CFRP beams in terms of a lower mid-span deflection for a given impulse, and a higher failure impulse. Also, the maximum attainable impulse increases with decreasing shear strength for both the UHMWPE and CFRP beams. The ranking of the beams for load carrying capacity in the quasi-static stretch-bend tests is identical to that for failure impulse in the impact tests. Thus, the static tests can be used to gauge the relative dynamic performances of the beams.

Effect of Curing and Functionalization on the Interface Thermal Conductance in Carbon Nanotube–Epoxy Composites

This study investigates the interface thermal conductance in a functionalized carbon nanotube (CNT)–epoxy composite system and how it is modified when the surrounding matrix is cured. We have used nonequilibrium molecular dynamics simulations to study the interface thermal conductance in both cured and uncured matrices, based on diglycidyl ether of bisphenol F (EPON-862) and diethylenetoluenediamine. The functionalization is modeled using a dynamic crosslinking algorithm and represents a realistic model of the matrix-filler interface. The thermal interface conductance increases linearly with the degree of functionalization up to the studied 2.5% due to stronger thermal coupling between functionalized CNT and the matrix. In addition, it was observed that curing of the matrix increases the interface conductance by 20% relative to the uncured matrix. This increase is attributed to an increase in thermal conductivity of cured epoxy resulting from relative enhancement in nonbonded interactions (originating from volume reduction) and structural rigidity during curing. Our results suggest that the interface conductance can be strongly influenced by the thermal properties of the bulk matrix as well as the interface chemistry of the additives such as CNTs.

Direct Curing of Polymer Construction Material in Simulated Earth's Moon Surface Environment

The Earth’s industrial exploitation of the moon requires a hermetically sealed structure large enough for all services: the life-support systems, energy-producing units, the storage of air andwater, a greenhouse, and so on. The best way to achieve this is a light inflatable structure, which is transported to the moon in a packed position. The construction material has to be soft at deployment and made rigid at exploitation. One way of making the deployed structure rigid is a chemical reaction that forms a hard frame for the construction.However, a previous project based on an external hermetically sealed pocket experienced problems as a result of high pressure due to evaporation of the low-molecular-weight mass fractions of the uncured matrix and the resultant uncontrolled deployment of the inflatable structure. A structure is proposed in which the frame wall is external to the wall of the structure, which would eliminate the problem of uncontrolled inflation but requires that the structure be cured in a free-space environment.

A Calorimetric Study of Phase Separation in Liquid Crystal/Matrix Systems: Determination of the Excess Specific Heat of Mixing

Abstract The effects of concentration and state of cure on mixing and phase separation of binary systems of a low molecular weight liquid crystal (LC) and an organic matrix have been determined for the first time. We found that, as temperature is increased, mixing in uncured LC/matrix systems is accompanied by a step-like decrease in specific heat at T mix, the mixing temperature. This decrease is due, for the most part, to the (negative) excess specific heat of mixing. ΔC mix. The excess enthalpy of mixing. ΔH mix, may also contribute to the thermal effect. A plot of ΔC mix versus LC concentration exhibits a minimum, as expected from theory. Such a plot for a mixture of a specific LC (E7) with uncured matrix (NOA65) allows us to estimate the solubility limit of E7 in the matrix-rich phase (∼15%) and of NOA65 in the LC-rich phase (∼5%). Uncured E7/NOA65 mixtures exhibit phase diagrams with an upper critical solution temperature (UCST) slightly above 300 K. To avoid undesired phase separation prior to fina...