Reinforced Plastic

More extensively used are the conventional engineering plastics that are not reinforced to maximize mechanical performances of plastics. However there are reinforced plastics (RPs), as reviewed throughout this handbook, that offer certain important structural and other performance requirements. These requirements provides the designer great flexibility and provides freedom pracdcally not possible with most other materials. However, it requires a greater understanding of the interreladons to take full advantage of RPs. It is important to understand that RPs has an extremely wide range of properties, structural responses, product performance characteristics, product shapes, manufacturing processes, and influence on product performances.

The usual approach is that the designer is involved in "making the material." RP designed products have often performed better than expected, despite the use of less sophisticated fabricadng tools in their design. Depending on construction and orientadon of stress relative to reinforcement, it may not be necessary to provide extensive data on time-dependent stiffness properties since their effects may be small and can frequently be considered by rule of thumb using established practical design approaches. When time dependent strength properties are required, creep, fatigue, and other data are used most effectively. These type data are available.

The arrangement and the interaction of the usual stiff, strong fibers dominate the behavior of RPs with the less stiff, weaker plastic matrix [thermoset (TS) or thermoplastic (TP)]. A major advantage is that directional properties can be maximized in products by locating fibers that maximize mechanical performances in different directions.

When compared to unreinforced plastics, the analysis and design of RPs is simpler in some respects and more complicated in others. Simplifications are possible since the stress-strain behavior of RPs is frequently fairly linear to failure and they are less time-dependent. For high performance applications, they have their first damage occurring at stresses just below their high ultimate strength properties. They are also much less temperature-dependent, particularly RTSs (reinforced TSs).

When constructed from any number and arrangement of RP plies, the stiffness and strength property variations may become much more complex for the novice. Like other materials, there are similarities in that the first damage that occurs at stresses just below ultimate strength. Any review that these types of complications cause unsolvable problems is incorrect. Reason being that an RP can be properly designed, fabricated and evaluated to take into account any possible variations; just as with other materials. The variations may be insignificant or significant. In either case, the designer will use the required values and apply them to an appropriate safety factor; similar approach is used with other materials. The designer has a variety of alternatives to choose from regarding the kind, form, amount of reinforcement to use, and the process versus requirements.

With the many different fiber types and forms available, practically any performance requirement can be met and molded into any shape. However they have to be understood regarding their advantages and limitations. As an example there are fiber bundles in lower cost woven rovings that are convoluted or kinked as the bulky rovings conform to the square weave pattern. Kinks produce repetitive variations in the direction of reinforcement with some sacrifice in properties. Kinks can also induce high local stresses and early failure as the fibers try to straighten within the matrix under a tensile load. Kinks also encourage local buckling of fiber bundles in compression and reduce compressive strength. These effects are particularly noticeable in tests with woven roving in which the weave results in large-scale reinforcement.

Fiber content can be measured in percent by weight of the fiber portion (wt%). However, it is also reported in percent by volume (vol%) to reflect better the structural role of the fiber that is related to volume (or area) rather than to weight. When content is only in percent, it usually refers to wt%.

Basic behaviors of combining actions of plastics and reinforcements have been developed and used successfully. As an example, conventional plain woven fabrics that are generally directional in the 0° and 90° angles contribute to the highest mechanical strength at those angles. The rotation of alternate layers of fabric to a layup of 0°, +45°, 90°, and -45° alignment reduces maximum properties in the primary directions, but increases in the +45° and -45° directions. Different fabric and/or individual fiber patterns are used to develop different property performances in the plain of the molded RPs. These woven fabric patterns CAN include basket, bias, cowoven, crowfoot, knitted, leno, satin (four-harness satin, eight-harness satin, etc.), and twill.

For almost a century many different RP products have been designed, fabricated, and successfully operated in service worldwide. They range from small to large products such as small insulators for high voltage cable lines to large 250 ft diameter deep antenna parabolic reflectors. RPs have been used in all types of transportation vehicles, different designed bridges, road surfacing such as aircraft landing strips and roads, mining equipment, water purification and other very corrosive environmental equipment, all types of electrical/electronic devices, etc.

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