Composite pultrusions

Like other FRP composites, pultrusion products exhibit a high strength-to-weight ratio, excellent corrosion resistance, good electrical insulation and better dimensional stability. In addition, pultrusion offers additional advantages over other composite manufacturing processes (Sumerak and Martin, 1987) ... 

Ahmed, R, Joshi, S. C. and Lam, Y. C. (2004), Three-dimensional FE/NCV modelling of thermoplastic composites pultrusion . Journal ofThermoplastic Composite Materials, 17, 447-462. 

Tat, T. L. K. (2006), Optimization of thermoset composites pultrusion with feedback sensors , M.Sc. Dissertation, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore. 

Pultrusion is mainly used to process glass-, aramide-, carbon fiber rovings with a wide variety of thermoset matrices such as polyester-, vinylester- and epoxy-resins [10]. The processing speed can be up to 5 m/min. In addition, thermoplastic matrix based composite pultrusion has been developed over the last 20 years. Due to the higher viscosity of thermoplastics in compaxison to thermosets, the processing speed is about ten times slower in terms of thermoplastic pultrusion [11]. 

Pultrusion is also used to make structural shapes from composite materials. The incoming material is generally unidirectional and must be pulled through the pultrusion die because the uncured composite material is entirely too flexible to push (as in extrusion processes). The incoming material can be preshaped by various guides and rollers as in Figure 1-18. 

For composite stiffeners, all shapes are builtup from individual layers of material. Of course, some stiffener shapes can be produced by roll forming or pultrusion, for example, and then fastened to panels. Or, the stiffened panel could be made in a single operation involving the placement, usually by hand, of individual laminae of various dimensions in positions such that a builtup structure results. Stiffeners can be fastened to panels by bonding, stitching, or mechanical fastening. 

Composite processing uses specialized methods. For thermoplastics, glass mat thermoplastic (GMT) is the main method but prepreg, lay-up, tape winding, pultrusion are also used to produce composites. SMC/BMC are the main processes for thermosets but lay-up is currently used for large parts and prepregs are used for high-tech parts. 

Lam P.K. and Piggott M.R. (1989b). The durability of controlled matrix shrinkage composites Part 2, Properties of carbon fiber-epoxy copolymer pultrusion, J. Mater. Sci. 24, 4427-4431,... 

Differentiate between pultrusion, resin transfer molding, and filament winding methods for fiber-reinforced composite production. 

Figure 7.87 Schematic diagram of a typical pultrusion process. Reprinted, by permission, from M. Schwartz, Composite Materials Handbook, 2nd ed., p. 4.46. Copyright 1992 McGraw-Hill.

Figure 7.88 Viscosity change of a thermosetting resin in a pultrusion die. Reprinted, by permission, from P. K. Malhck, Fiber-Reinforced Composites, p. 349. Copyright 1988 by Marcel-Dekker, Inc.

Many different thermosetting polymers are used in pultrusion, eg, polyester, vinyl ester, epoxy, and urethane. Reinforcements must be in a continuous form such as rovings, tows, mats, fabrics, and tapes. Glass fibers are the low cost, dominant composition, but a ram id and carbon fibers are also used. 

The ring opening polymerization of cyclic monomers that yield thermoplastic polymers of interest in composite processing is reviewed. In addition, the chemistry, kinetics, and rheology of the ring opening polymerization of caprolactam to nylon 6 are presented. Finally, the rheo-kinetics modelsfor polycaprolactam are applied to the composite process of reaction injection pultrusion. 

Among the more common thermoplastics from ring opening polymerization of interest in composite processing are polylactams, polyethers, polyacetals, and polycycloolefins. It has also been shown that polycarbonates can be produced from cyclic carbonates [22], Anionic ring opening polymerization of caprolactam to nylon 6 is uniquely suited to form a thermoplastic matrix for fiber-reinforced composites, specifically by the reaction injection pultrusion process [23-25]. The fast reaction kinetics with no by-products and the crystalline... 

Pultrusion is a steady-state process in which the fiber-resin mass changes its properties as it moves from the entrance to the exit of the die. In order to track the temperature, polymer conversion, and other properties of the fiber-resin mass as it moves along the die, it is useful to define a representative volume element (RVE) that rides along the fiber at the line speed of the pultrusion process. An RVE is defined such that it will contain both the solid phase (i.e., fibers and resin), irrespective of its location in the composite. In real-life pultrusion, a thermocouple wire that passes through the pultrusion die tracks the temperature of an RVE in the composite. 

Figure 1.20 Conversion in an RVE during adiabatic (top line) and isothermal (bottom line) pultrusion of glass fiber nylon 6 composite when the initial temperature for adiabatic pultrusion and the isothermal pultrusion temperature were 136°C...

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