The densities range from 1260 to 1820 kg/in3 for composites to 2800 kg/in3 for aluminium.2 2. The specific tensile strength of unidirectional fiber composites is almost 4 to 6 time higher than steel and aluminium. Also, they have high specific -modulus (ratio of the material stiffness to density) about which is 3 to 5 times greater than that of steel and aluminium.
3 3. The value of fatigue endurance limit of composites can be 60% of their ultimate tensile strength which is very less for steel and aluminium.
4 4. Excellent damping features of fiber reinforced composites make them to possess less noise and lower vibration transmission than metals.
5 5. Due to excellent high corrosion resistance, composite’s life cycle is more than metals.
6 6. As compared to metals, the fiber composites are more adaptable to meet performance needs and complex design requirements of aircraft.
7 7. The costs of composites manufacturing is lower because of parts simplification and integrated design.
8 8. As compared to metals, the composites possess long term durability.
2.12 Advantages of Composites
1 1. Fiber to fiber redundant load path.
2 2. Improved friction and wear properties.
3 3. High ‘strength or stiffness to weight’ ratio.
4 4. Due to greater reliability, there are fewer inspections and structural repairs.
5 5. Close tolerances can be achieved without machining.
6 6. High resistance to fatigue and corrosion degradation.
7 7. High resistance to impact damage.
8 8. Resistant to dent.
9 9. High torsional stiffness resulting in high whirling speeds, reduced number of intermediate bearings and supporting structural elements.
10 10. Composites are dimensionally stable due to low coefficient of thermal expansion and low thermal conductivity.
11 11. Due to their excellent heat sink and lightweight properties, Carbon-Carbon composites are utilized for aircraft brakes.
12 12. Thermoplastics can be easily reformed and so are highly attractive for high volume commercial applications.
13 13. Manufacturing and assembly of part integration in composites simple as there are no joints or fasteners which also reduce overall cost.
14 14. The composites are corrosion resistant and more durable and so excessively utilized in a marine environment.
2.13 Disadvantage of Composites
1 1. Low toughness owing to the weak matrix.
2 2. Analysis is difficult.
3 3. Difficult to reuse and dispose.
4 4. Transverse properties may be weak.
5 5. High cost of raw materials and manufacturing process.
6 6. Difficult to attach.
7 7. More brittle than wrought metals and so get damaged easily.
8 8. Matrix is subject to environmental degradation.
2.14 Conclusion
Despite the several disadvantages, the material selection and its design can evade most of the failings. New research and the improvement in the technologies have resulted in the development of new matrices and reinforcing fibers which have produced new composites having exceptional properties. The newly developed composites are lighter in weight and more efficient then their metallic counterparts, and so have emerged as the key materials for futuristic use. For example, in aviation industry, the fiber reinforced composites are used in the structural applications, while they are also used in the processing of civil infrastructures, including power long span bridges, generating wind mills, earthquake proof highway supports, etc. However, their higher initial cost is the key barrier for wide utilization. The utility of a material over its life cycle in commercial industry is mainly decided by its overall cost and is also the main reason for inhibiting the research of new materials. The recycling of the composite materials is also a growing concern in industry which produces millions of parts per year, such as automotive industry. Also, with the new government policies into practice and rising environmental problems, the utilization of composite is concerning for its problematic recycling.
Acknowledgments
NJ wants to acknowledge the Brazilian funding agencies: Sao Paulo Research Foundation-FAPESP (2014/23546-1, 2016/23474-6).
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