Continuous Carbon Fiber Polymer-matrix Composites Research Articles

Effect of fiber lay-up configuration on the electromagnetic interference shielding effectiveness of continuous carbon fiber polymer-matrix composite

Continuous carbon fiber polymer-matrix multifunctional structural composites capable of electromagnetic interference (EMI) shielding are needed for electronics and radiation sources. The laminate's fiber lay-up configuration affects the shielding effectiveness, as shown in this work for unmodified conventional carbon fiber polymer-matrix composite laminates with high-strength PAN-based carbon fiber and a polyamide thermoplastic matrix. The radiation is normal-incidence unpolarized plane wave, as commonly used. The shielding is dominated by absorption rather than reflection – more so for crossply composites than unidirectional composites. Due to the electrical conductivity longitudinal-to-transverse ratio of 930 for a lamina, the absorption-loss/thickness longitudinal-to-transverse ratio is 30 at 1.0 GHz. This factor of 30 means that the contribution of the fibers transverse to the electric field to absorption is negligible compared to that of the fibers parallel to the electric field. The ratio of absorption-loss/thickness for the crossply composite to that for the unidirectional composite with the same number of laminae is ∼4, and the ratio of the reflection loss for the crossply composite to that for the unidirectional composite is ∼2. The values of these ratios are consistent with electromagnetic theory for unpolarized radiation. This work strengthens the science base for the design of continuous fiber composites for shielding.

Continuous carbon fiber polymer–matrix composites in unprecedented antiferroelectric coupling providing exceptionally high through-thickness electric permittivity

Continuous carbon fiber polymer–matrix composites in unprecedented antiferroelectric coupling, as enabled by stacking composites with positive value (up to 400) and negative value (down to −600) of the electric permittivity, provide exceptionally high through-thickness permittivity up to 78,000 (≤2.0 MHz), corresponding to a capacitance of 370 μF/m2. The high capacitance is consistent with the equation for negative and positive capacitors in series. The permittivity tailoring of the composites involves dielectric cellulosic tissue paper interlaminar interlayers. Negative permittivity (not previously reported for carbon fiber composites) requires the paper to be wet with tap water (resistivity 1.5 kΩ cm) during incorporation in the composite, though the water evaporates and leaves ions at very low concentrations during composite fabrication, and also requires optimum through-thickness resistivity (e.g., 1 kΩ cm, as given by paper thickness 35 μm); it is probably due to interactions between the functional groups on the carbon fiber surface and the residual ions (mainly chloride) left after tap water evaporation.

Carbon materials for structural self-sensing, electromagnetic shielding and thermal interfacing

This paper reviews carbon materials for significant emerging applications that relate to structural self-sensing (a structural material sensing its own condition), electromagnetic interference shielding (blocking radio wave) and thermal interfacing (improving thermal contacts by using thermal interface materials). These applications pertain to electronics, lighting (light emitting diodes), communication, security, aircraft, spacecraft and civil infrastructure. High-performance and cost-effective materials in various forms of carbon have been developed for these applications. The forms of carbon materials include carbon fiber, carbon nanofiber, exfoliated graphite, carbon black and composite materials. Short carbon fiber cement-matrix composites and continuous carbon fiber polymer-matrix composites are particularly effective for structural self-sensing, with the attributes sensed including strain, stress, damage and temperature. Flexible graphite as a monolithic material and nickel-coated carbon nanofiber as a filler are particularly effective for electromagnetic shielding. Carbon black paste, graphite nanoplatelet paste and flexible graphite (filled with carbon black paste) are particularly effective for thermal interfacing; carbon nanotube arrays are less effective than these pastes. The associated science pertains to the relationship among processing, structure and properties in relation to the abovementioned applications. The criteria behind the design of materials for these applications and the mechanisms of the associated phenomena are also addressed.

Increasing the through-thickness thermal conductivity of carbon fiber polymer–matrix composite by curing pressure increase and filler incorporation

The low through-thickness thermal conductivity limits heat dissipation from continuous carbon fiber polymer–matrix composites. This conductivity is increased by up to 60% by raising the curing pressure from 0.1 to 2.0 MPa and up to 33% by incorporation of a filler (⩽1.5 vol.%) at the interlaminar interface. The 7-μm-diameter 7-W/m K-thermal-conductivity continuous fiber volume fraction is increased by the curing pressure increase, but is essentially unaffected by filler incorporation. The thermal resistivity is dominated by the lamina resistivity (which is contributed substantially by the intralaminar fiber–fiber interfacial resistivity), with the interlaminar interface thermal resistivity being unexpectedly negligible. The lamina resistivity and intralaminar fiber–fiber interfacial resistivity are decreased by up to 56% by raising the curing pressure and up to 36% by filler incorporation. The curing pressure increase does not affect the effectiveness of 1-mm-long 10-μm-diameter 900–1000-W/m K-thermal-conductivity K-1100 carbon fiber or single-walled carbon nanotube (SWCNT) as fillers for enhancing the conductivity, but hinders the effectiveness of carbon black (CB, low-cost), which is less effective than K-1100 or SWCNT at the higher curing pressure, but is almost as effective as K-1100 and SWCNT at the lower curing pressure. The effectiveness for enhancing the flexural modulus/strength/ductility decreases in the order: SWCNT, CB, K-1100.

Piezoresistivity in unidirectional continuous carbon fiber polymer-matrix composites: single-lamina composite versus two-lamina composite

Piezoresistivity in unidirectional carbon fiber epoxy-matrix composites was studied by measurement of the electrical resistance of single-lamina and two-lamina composites in the longitudinal (fiber) direction during elastic tensile loading and unloading in the same direction. The piezoresistive effect was reversible. The resistivity increased slightly with longitudinal tensile strain for the single-lamina composite, but decreased with strain for the two-lamina composite. The gage factor was around +2 and -6 for single-lamina and two-lamina composites, respectively. The very weak piezoresistivity in the single-lamina composite was probably due to decrease in the extent of fiber-fiber contact upon tension. The relatively strong piezoresistivity in the two-lamina composite was probably due to increase in the degree of fiber alignment upon tension.

Thermoelectric property tailoring by composite engineering

The tailoring of the thermoelectric properties (the sign and magnitude of the absolute thermoelectric power) was achieved by composite engineering. The techniques involved the choice of the reinforcing fibers (continuous or short) in a structural composite and the choice of the particulate filler between the laminae in a continuous fiber composite. The tailoring resulted in thermoelectric structural composites, including continuous carbon fiber polymer-matrix composites and short fiber cement-matrix composites. In addition, it resulted in thermocouples in the form of structural composites. The choice of fibers impacted the thermoelectric behavior in the fiber direction of the composite. The choice of interlaminar filler impacted the thermoelectric behavior in the through-thickness direction.

Interlaminar damage in carbon fiber polymer-matrix composites, studied by electrical resistance measurement

Interlaminar thermal damage in continuous carbon fiber polymer-matrix composites was monitored in real time during thermal cycling by measurement of the contact electrical resistivity of the interlaminar interface. Damage was accompanied by an abrupt increase of the resistivity for a thermoset-matrix composite, and by an abrupt decrease of the resistivity for a thermoplastic-matrix composite. Both phenomena are due to the effect of matrix damage on the chance of fibers of one lamina touching those of an adjacent lamina. The damage involved matrix molecular movement in the thermoplastic case, but not in the thermoset case.

Thermoelectric structural composites and thermocouples using them

ABSTRACTThe tailoring of the sign and magnitude of the absolute thermoelectric power was achieved in structural composites by the choice of the reinforcing fibers and of the particulate filler between laminae. The resulting thermoelectric structural composites included continuous carbon fiber polymer-matrix composites and short fiber cement-matrix composites. In addition, it resulted in thermocouples in the form of structural composites. The fibers and interlaminar filler impacted the thermoelectric behavior in the longitudinal and through-thickness directions respectively.

Thermal Analysis by Electrical Resistivity Measurement

Thermal analysis in the form of electrical resistivity measurement is reviewed. It is useful for studying phase transitions and electrical conduction mechanisms. The resistivity can be the volume resistivity or the contact resistivity, as illustrated for the case of continuous carbon fiber polymer-matrix composites.