Bending stiffness factor

Stiffness For an isotropic material with a modulus of elasticity E, the bending stiffness factor (El) of a rectangular beam b wide and h deep stiffness is ... 

In a rectangular structural sandwich of the same dimensions as above whose facings and core have moduli of elasticity Eyand respectively, and a core thickness C, the bending stiffness factor El is... 

Further contrast between metal and composite stiffeners is revealed when we examine the objectives and characteristics of stiffener design. For a metal stiffener of uniform or even nonuniform thickness, we attempt to maximize the moment of inertia of the stiffener in order to maximize the bending stiffness of the stiffener. Those two factors are proportional to one another when we realize that the bending stiffness of metal stiffeners about the middle surface of the plate or shell to which they are attached is... 

In contrast, because of the spatially variable (inhomogeneous) nature of material in a composite stiffener, the bending stiffness cannot be separated into a material factor times a geometric term as in Equation (7.6). Instead, the composite stiffener bending stiffness is... 

Under transverse loading, bending moment deflection is proportional to the load and the cube of the span and inversely proportional to the stiffness factor, El. Shear deflection is proportional to the load and span and inversely proportional to shear stiffness factor N, whose value for symmetrical sandwiches is ... 

Another aspect to be considered is the difficulty in producing curved structures with the same fibre content as flat laboratory panels. This effect is shown in Figure 16, at the comer the laminate thickness is larger than at the flat section and fibre content is rather lower. This will affect the bending stiffness of the arm and the predicted failure load. This figure also shows the fillet, which is critical to initiation in the specimens without implanted defects. It is well known that fillets can significantly alter the load path in lap shear joints and increase the failure loads (see [1] and Figure 3 for example). If a fracture mechanics approach is to be applied this effect must be considered. Some recent studies on stress intensity factors for such cases may allow this to be addressed [22]. 

Other factors the same. The moment of inertia depends on the cross-sectional area of the fiber. Of course, the greater the cross-sectional area, the greater the moment of inertia and, hence, the greater the stiffness. Therefore, the flexural rigidity varies directly with the denier of the fiber. The flexural rigidity or bending stiffness for cellulose acetate fibers as a fimction of denier is shown in Table 11.9 [35]. 

These results can be compared to the same set of results obtained from the study on beam specimens (SLCOl and SLC02) in Section 8.2, which were subjected to four-point bending during 60 and 120 min fire exposure from the underside, see Table 8.6. In the former study, six-cell specimens were used in contrast to the four-cell specimens used here. The bending stiffnesses obtained from Section 8.2 were therefore corrected by a factor of 4/6 in order to make them comparable. At the end of fire exposure, the bending stiffness of the still-hot specimens (SLCOl/02) dropped to 46% and 43% of the initial value, which almost matched the values obtained for the column specimens. The post-fire stiffnesses (64% and 60%), however, were slightly lower than those of the column specimens (76% and 70%). 

The theory further explains that the total bending stiffness E/ef of the bipartite beam is the sum of the bending stiffnesses of the two component members and the Steiner component corrected with the y-factor. The calculations lead to the following result ... 

In addition to the above general criteria, the mechanical properties of implants also play an important role in determining their success. Four major properties of interest are strength, bending stiffness or, conversely, flexibility, abrasion resistance and durability or long-term mechanical patency. These are now examined along with the factors that can be used to optimize them. 

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