Fiber reinforced composites loading conditions

The evaluations of short fiber reinforced composites for fracture behavior includes studies with respect to material parameters such as the fiber content [42,103,120], fiber length and orientation [69,97,103,115], and fiber bundling [115.120] testing conditions such as the temperature [24,42,121,122] and the loading rate [121,123,124] and fractography [42,43,103,123], The influence of some of these parameters, e.g fiber content, rate of loading, and the test temperature on the fracture toughness of composites can be presented in the form of property maps [125,126],... 

Stress during service can be checked considering the fact that fiber-reinforced composite stresses, computed for the quasi-permanent loading condition, should satisfy the limitation Of <>//n , whereis the FRP characteristic strength at failure and n is the conversion factor whose values are those suggested in the related tables. Stresses in concrete and steel should be limited according to that described under the current regulation. 

Table I lists some properties of SMC and BMC. These are a function of resin composition, reinforcement, and molding conditions atid may be regarded as typical. This will serve as a frame of reference as to the property levels obtained with SMC and BMC. The differences which exist between SMC and BMC in tensile, flexural, and impact strengths are attributable to more than just the difference in glass loading. Fiber attrition arising from the compounding techniques for BMC as well as the shorter input fiber length account for the lower strengths.

Creep resistance is of primary concern in rotating components of a turbine engine. High creep rates can lead to both excessive deformation and uncontrolled stresses. Creep resistance of fiber-reinforced ceramic matrix composites depend on relative creep rates of, stress-relaxation in, and load transfer between constituents. The tensile creep behavior of SiC/RBSN composites containing 24 vol% SiC monofilaments was studied in nitrogen at 1300 C at stress levels ranging from 90 to 150 MPa. Under the creep stress conditions the steady state creep rate ranged from 1.2 x 10 to 5.1 x 10 At stress levels below... 

It is important to note that isostress and isostrain loading conditions represent theoretical limits for the design of a composite material reinforced by continuous fibers. In practice, most of the time, mechanical performances fall between these limits. On the other hand, in the isostrain loading situation, a lower volume fraction of fibers is required to obtain a similar stiffness of the composite. 

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