Carbon Fiber Polymer Matrix Composites Research Articles

Early Fatigue Damage In Carbon Fiber Composites Observed By Electrical Resistance Measurement

ABSTRACTEarly fatigue damage during the first tenth (or less) of the fatigue life was observed in carbon fiber composites by DC electrical resistance measurement. The damage was most severe in the first loading cycle and the incremental damage in each subsequent cycle diminished cycle by cycle. For the continuous carbon fiber carbon-matrix composite, the resistance increased irreversibly during early fatigue due to matrix damage and possibly fiber fracture as well. For the short carbon fiber polymer-matrix and cement-matrix composites, the resistance decreased irreversibly during early fatigue due to matrix damage near the junction of adjacent fibers and the resulting increase in the chance that adjacent fibers touched one another.

An electromechanical study of the transverse behavior of carbon fiber polymer-matrix composite

The transverse behavior of continuous carbon fiber epoxy-matrix composite was studied by measuring the 0° electrical resistance of a [90]32 composite during 0° tension and compression. The number of fiber-fiber contacts was found to decrease by 0.7% upon tension to 0.5% strain (resistance increasing) and increase by 1.1% upon compression to -0.5% strain (resistance decreasing), such that this number decreased with increasing strain and the resistance varied linearly with strain (fractional resistance change per unit strain = 2), until damage (probably matrix cracking) occurred and caused the resistance to increase with compressive strain beyond 1% (84 MPa stress) and increase abruptly with tensile strain beyond 0.5% (43 MPa stress). Prior to damage, the resistance varied with strain reversibly; slight reversibility was due to plastic deformation of the matrix.

Semi-solid slurry process for making short carbon fibre dispersed aluminium alloy matrix composites

Carbon fibre is one of the most important reinforcing materials in polymer, metal, carbon and ceramic matrices because of its high specific strength and high specific modulus. Carbon fibre polymer matrix composites are now extensively used in critical areas of application. However, carbonmetal matrix composites have not reached that stage. The possibilities of making carbon-fibre reinforced A1 alloy matrix composites by diffusion bonding [1], powder metallurgy technique [2], infiltration [3], stir casting [4], etc., have been reported in the literature. However, in most cases, the reaction between the fibre and the matrix seems to deteriorate the interface, thereby lowering the mechanical properties. Presently a semi-solid slurry casting/rheocasting/compocasting technique [5, 6] has been used for synthesizing the composite. The specific advantage of this process being [7] that it is carried out at a temperature within the freezing range (between the liquidus and solidus) of the alloy. This totally eliminates the superheat, as well as lowering the temperature of operation which reduces the temperature-aided chemical reactions at the fibre-matrix interface. The higher viscosity of the matrix alloy slurry eliminates the gravity aided segregation of reinforcement during mixing, as well as during solidification of the castings. The thixotropic nature of the slurry makes it amenable for smooth die filling without turbulence during pressure diecasting [8]. However, during gravity diecasting the fluidity of this slurry is very poor. This paper gives an account of processing and evaluation of a short carbon fibre dispersed aluminium alloy matrix composite prepared by the rheocasting route. The matrix alloy A1-6.2-Zn-2.45-Mg-l.7-Cu0.15-Zr-0.12-Fe-0.1-Si was stirred while-it was held within its freezing range (870-920 K): PANbased carbon fibres T-300 grade (Courtaulds, Grafil) of two different lengths, 1 and 3 mm, were introduced into the non-dendritic slurry after surface treatment [9], which was kept isothermally with about 25-30 wt % primary solid content. With the introduction of the fibres the composite slurry temperature was raised to keep more or less the same solid content. About 8 wt % of the fibres were added. After the additions the slurry was further stirred for ca. 10-20 min to achieve uniform disper-