Reinforcement
Steel materials in composites play an important role in reinforcing the strength and stiffness of the material. In general, the selection criteria for steel materials are based on specific gravity, tensile strength, tensile stiffness, compressive strength and compressive stiffness, fatigue strength and fatigue failure mechanism, electrical and thermal conductivity, and price. Here, specific gravity is a variable that reduces the weight of the material, and mechanical properties such as tensile strength (stiffness), compressive strength (stiffness), and fatigue strength (fracture) are important factors in the design of composite properties. Electrical and thermal conductivity are design factors that should be considered when designing functional composites. Price is a factor in determining the feasibility of mass production.
In order to achieve the desired properties, the stiffener has an interrelationship with the base material and must be selected according to the characteristics of each other, and the selection of the material may vary depending on the type, amount, and stacking angle of the stiffener. The types of stiffener materials can be classified according to their shape, which can be divided into fiber, spherical particles, and flat particles. Fibers are long cylindrical shapes and can be used to produce strongly brittle bases and composites, which inhibit the development of cracks. Spherical particles have an almost spherical shape with no elongated parts, are relatively easy to crack, and have a small tensile strength under load, which inhibits the plastic deformation of the base material. In addition, when strong particles are reinforced, they are subjected to concentrated stress and show weak strength characteristics. Plate particles have a flatter shape than spherical particles and have similar mechanical properties to spherical particles.
The classification of fibers by type is as follows: whiskers, short fibers, long fibers, strands, and chopped strands. and chopped strands. Whiskers are short fibers that grow in crystals, while short fibers are short fibers obtained by cutting long island Short fibers are short fibers obtained by cutting long islands of oil. A strand is a bundle of long fibers.
Furthermore, the classification according to the form of the fiber by secondary processing is divided into roving, woven roving, chopped strand mat, filament mat, yarn, and fabric. Roving is a combination of strands. Woven roving is a type of fabric made of roving, filament mat is a mat made of long strands stiffened in one direction, and yarn is a type of fabric made of warp yarn, Fabric is a thin and wide fabric made of roving, mainly used for additive molding.
| type | Tensile Strength (㎫) | Stiffness (㎬) | Specific Gravity | Specific Strength (x 106) | |
| Fiber for Reinforcement | Glass fiber | 3450~4300 | 73~87 | 2.5 | 1.4~1.8 |
| Carbon fiber | 1900~5600 | 230~760 | 1.8~2.1 | 1.1~1.3 | |
| Kevlar fiber | 3450~3620 | 130~180 | 1.46 | 2.3 | |
| Boron fiber | 3450 | 400 | 2.5 | 1.4 | |
| SiC Fiber | 3440 | 400 | 3.3 | 1.1 | |
| Al203 Fiber | 1400 | 380 | 3.95 | 0.4 |