Glass fiber reinforced composites, creep

Silverman characterized flexural creep resistance at 120°C (33) and room temperature impact resistance (34) for test specimens from injection-molded composites of chopped fibers versus machined specimens from compression molded continuous long GFR polypropylene sheets. His concepts of glass fiber reinforcement in stampable composites tend to mirror many of the attributes related to megacoupling of short GFRP. 

Glass-fiber-reinforced amorphous TP composites generally have greater creep resistance than glass-fiber-reinforced crystalline TP composites containing the same amount of glass fiber. 

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]. 

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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