Particulate-filled Polymer Composites Research Articles

Simulation of the Time-Dependent Wear and Surface Accumulation Behavior of Particle-Filled Polymer Composites

A simulation has been developed to model the transient wear of particle-filled polymer composites as a function of sliding distance. All inputs are parameters of physical significance, including filler bulk volume fraction, specific wear rate (relative to that of the matrix), and contact pressure. Run-in wear behavior is simulated by consideration of the accumulation of wear-resistant filler particles and the formation of a volume fraction profile near the composite sliding surface, facilitated by matrix cold flow. Simulation outputs include time-dependent volume fraction profile, and composite wear rate and wear volume. The simulation may be used for evaluation of candidate materials for applications in which nonsteady-state run-in wear effects are important, as well as a guide for the engineering of composite surfaces with graded volume fraction profiles that may provide resistance to initial transient wear contributions.

Fast current limitation by conducting polymer composites

The transition of materials from low resistivity to comparatively high resistivity can be utilized for current limitation, enabling permanent fuses that do not have to be replaced after an overload or short-circuit operation. An interesting class of materials for this purpose are particulate filled polymer composites with a strong positive temperature coefficient (PTC) of resistivity. If an applied current becomes too high, the PTC element is heated to its critical temperature and trips from the conducting into the insulating state. The dynamic heating of the composite upon current flow is described by a one-dimensional model. It is predicted that the heating of a composite depends on the size of the filler particles. Smaller filler particles should allow a faster heating and, hence, a better limitation of the current. Experimental verification is performed using composite of TiB2 particles in a polyethylene matrix. Commercial TiB2 powders with different particle-size distributions between 1 and 200 μm were used. The specific resistivity of the composites is small, in the range of 0.01–0.02 Ω cm. Around the melting temperature of the polymer, the resistivity increases within only 20 °C by seven orders of magnitude. In order to verify the expected dependence of the switching dynamic on the filler particle size, the tested elements had comparable electrical characteristics. Samples were prepared having, to a certain degree, the same specific resistivity, cross section, and total resistance. Free parameters were the length, and for some samples, the filler content. Short-circuit experiments show that for decreasing particle size the time until the material trips into the high-resistive state becomes shorter. The best current limitation occurs for composites containing particles in the range of 1–45 μm. Current limitation starts already after 150 μs, and a current density of up to 10 kA/cm2 can be switched off within a further 200 μs. The experiments are in excellent agreement with the predictions from theory. Due to the low resistance in the cold state and the very fast limitation of electrical currents, PTC elements based on conducting polymers can be highly attractive for power applications.

5470648 Composite fabrics of nonwoven nylon layers and fiberglass scrim

This article investigates the fabrication of functionally graded materials (FGMs) by selective laser sintering (SLS) of Nylon-11 composites filled with different volume fractions of glass beads (0–30%). The investigation involved a combination of experimental studies, theoretical modeling and numerical analysis. Optimal processing parameters for each composition were developed by design of experiments (DOE). These parameters were then compared with parameters predicted by numerical modeling. Specimens for tensile and compressive testing for each composition and for a 1D FGM composition were fabricated and tested. The experimentally measured tensile and compressive moduli were compared with moduli predicted by Halpin's theoretical model and were found to be in excellent agreement. The results showed that the tensile and compressive modulus increases while strain at break and strain at yield decreases as a function of glass bead volume fraction. A finite element model for the compressive properties of the 1D FGM specimen showed good agreement with experimentally measured values. Finally, to demonstrate the SLS-based FGM approach, two components exhibiting a one-dimensional functional gradient of particulate-filled polymer composites were fabricated.

State of Dispersion – Mechanical Properties Correlation in Small Particle Filled Polymer Composites

Abstract Correlation between state of dispersion and mechanical properties is obtained and failure mechanisms from falling weight impact tests are discussed. The state of dispersion is characterized for calcium carbonate filled polypropylene model composites by using a scanning electron microscope. A dispersion index is defined in terms of the fraction of agglomerates of the filler remained in the composites. Improvement of dispersion uplifts tensile strength and more prominently falling weight impact strength. It is pointed out that an initial failure in the falling weight impact test rises at the agglomerate existing near the loading point. Falling weight impact strength is found to be dependent upon the distance from loading point to failure initiation point where the agglomerate exists. This explains the dependency of impact strength on the state of dispersion and a large sample deviation often observed in the falling weight impact test.