Carbon fiber reinforced composites, creep

Recent tests have revealed surprisingly good fatigue and creep resistance for carbon/carbon composites. Figure 29 presents some results of torsion and flexure tests in which the fatigue properties of carbon-fiber-reinforced carbon (CFRC) 3D composites are compared with those of carbon-fiber-reinforced polymer (CFRP) 3D composites (53). 

Katouzian M, Bruller OS, Horoschenkoff A, On the effect of temperature on the creep-behaviour of neat and carbon-fiber-reinforced PEEK and epoxy-resin, J Composite Mater, 29(3), 372 387, 1995. 

Creep tendency in glass and carbon fibers is very low, in aramid fibers it is higher. In combination with organic matrices or adhesives, their viscoelastic behavior determines creep tendency in the composite. In comparative relaxation tests up to 1000 h at approx. 50% short-term strength, carbon fiber reinforced plastics indicated virtually no creep, glass fiber reinforced plastics exhibited low creep (approximately twice as much as pre-tensioned steel, while aramid fiber reinforced plastics showed four to five times as much creep [1011]. 

The creep of a composite material will depend on the reinforcement and the matrix. Carbon fibers are not much affected by creep, although there will be some loss of strength... 

Polypropylene is a very versatile polymer. It has many properties that make it the polymer of choice for various applications (e.g., excellent chemical resistance, good mechanical properties and low cost). There are many ways in which the mechanical properties of polypropylene can be modified to suit a wide variety of end-use applications. Various fillers and reinforcements, such as glass fiber, mica, talc, and calcium carbonate, are typical ingredients that are added to polypropylene resin to attain cost-effective composite mechanical properties. Fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, creep resistance, and sometimes impact strength. Fillers, such as talc and calcium carbonate, are often used as extenders to produce a less-costly material. However, some improvement in stiffness and impact can be obtained with these materials. 

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