Autoclave moulding

A process using a two-sided mold set that forms both surfaces of the panel. On the lower side is a rigid mold and on the upper side is a flexible membrane made from silicone or an extruded polymer film such as nylon. Reinforcement⁸ materials can be placed manually or robotically. They include continuous fiber forms fashioned into textile constructions. Most often, they are pre-impregnated with the resin in the form of prepreg fabrics or unidirectional tapes. In some instances, a resin film is placed upon the lower mold and dry reinforcement is placed above. The upper mold is installed and vacuum is applied to the mold cavity. The assembly is placed into an autoclave. This process is generally performed at both elevated pressure and elevated temperature. The use of elevated pressure facilitates a high fiber volume fraction and low void content for maximum structural efficiency.

Resin transfer moulding (rtm)

A process using a two-sided mold set that forms both surfaces of the panel. The lower side is a rigid mold. The upper side can be a rigid or flexible mold. Flexible molds can be made from composite materials, silicone or extruded polymer films such as nylon. The two sides fit together to produce a mold cavity. The distinguishing feature of resin transfer molding is that the reinforcement materials are placed into this cavity and the mold set is closed prior to the introduction of matrix material. Resin transfer molding includes numerous varieties which differ in the mechanics of how the resin is introduced to the reinforcement in the mold cavity. These variations include everything from vacuum infusion (for resin infusion see also Boat building) to vacuum assisted resin transfer moulding. This process can be performed at either ambient or elevated temperature.

Other

Other types of molding include press molding, transfer molding, winding, casting, centrifugal casting and continuous casting. There are also forming capabilities including CNC filament winding, vacuum infusion, wet lay-up, compression molding, and thermoplastic molding, to name a few. The use of curing ovens and paint booths is also needed for some projects.

Tooling9

Some types of tooling materials used in the manufacturing of composites structures include invar, steel, aluminum, reinforced silicone rubber, nickel, and carbon fiber. Selection of the tooling material is typically based on, but not limited to, the coefficient of thermal expansion expected number of cycles, end item tolerance, desired or required surface condition, method of cure, glass transition temperature of the material being molded, molding method, matrix, cost and a variety of other considerations.

II. Basic Types of Deformation

Deformation of structural and machine elements produced by external forces may be very complex. However, these complex deformations can always be represented as consisting of a small number of basic types of deformation.

The basic types of deformation of structural members which are studied in strength of materials are: tension,¹⁰ compression, shear, torsion and bending.

Examples of complex deformations are provided by combined tension and torsion or combined tension and bending.

The above types of deformation will be considered in detail and methods for determining strains and stresses will be given in the relevant chapters of the book. It should be noted that strength of materials deals with only simple-shaped bodies. These are rods, plates and thin-walled shells.

A rod¹¹ is a body whose length is considerably greater than the transverse dimensions¹² which are of the same order of magnitude. Rods with straight axes are called bars, beams, columns, depending on their purpose.

A plate and a thin-walled shell are bodies whose thickness is considerably smaller than the other two dimensions. For instance, boilers, tanks, various vessels are thin-walled shells, the flat bottom of a boiler is a plate. Strength of materials deals mainly with rods. In the sequel we shall consider rods with straight axes and almost invariably of uniform section.

In machine design elements of complex shape are sometimes encountered. Such elements cannot be handled by the methods of strength of materials. However, most machine parts can be treated approximately as rods using the methods of strength of materials. The results thus obtained may be refined by experiment.

At presents, wide use is made in practice of experimental methods of strain measurement which make it possible to determine sufficiently stresses in complex-shaped members which do not lend themselves to theoretical calculation. In the first place mention should be made of the application of wire resistance strain gauges which indicate stresses through the change of electrical resistance.

Problems involving¹³ the accurate determination of strains and stresses are dealt with in a science called the theory of elasticity. It uses rigorous mathematical methods. In practice, however, the design of machine and structural parts often does not require too much accuracy, it should be just sufficient but the methods of analysis should be simple and thus easy to apply. It is therefore customary in the design of machines and structures to use the methods of strength of materials which are considerably simper than those of the theory of elasticity and give sufficiently accurate results. There are, however, problems which are solvable only by the methods of the theory of elasticity, such as the determination of stresses in balls or rollers of bearings. A simplification of the methods of analysis in strength of materials is achieved by introducing some assumptions.

Both the theory of elasticity and strength of materials usually consider elastic deformations. In engineering practice, however, there are many cases where a material develops plastic deformations. Plastic defoliations are studied in a science called the theory of plasticity which has been extensively elaborated in the last few years.