Flexural stiffness

Use pipe with a minimum wall thickness of 13 mm to increase flexural stiffness. 

The flexural stiffness of the beam will be proportional to El. So converting the section to an equivalent I beam as in the previous example... 

In any particular material, the flexural stiffness will be defined by the second moment of area, /, for the cross-section. As with a property such as area, the second moment of area is independent of the material - it is purely a function of geometry. If we consider a variety of cross-sections as follows, we can easily see the benefits of choosing carefully the cross-sectional geometry of a moulded plastic component. 

Fig. 2.25 illustrates the various cross-sections and Fig. 2.26 compares their flexural stiffnesses. An important conclusion from this is that T sections (or... 

Compare the flexural stiffness to weight ratios for the following three plastic beams, (a) a solid beam of depth 12 nun, (b) a beam of foamed material 12 mm thick and (c) a composite beam consisting of an 8 mm thick foamed core sandwiched between two solid skin layers 2 mm thick. The ratio of densities of the solid and foamed material is 1.5. (hint consider unit width and unit length of beam). 

A sheet of chopped strand mat-reinforced polyester is 5 mm thick and 10 mm wide. If its modulus is 8 GN/m calculate its flexural stiffness when subjected to a point load of 200 N midway along a simply supported span of 300 mm. Compare this with the stiffness of a composite beam made up of two 2.5 mm thick layers of this reinforced material separated by a 10 mm thick core of foamed plastic with a modulus of 40 MN/m. ... 

This is an injection moulding method which permits material costs to be reduced in large mouldings. In most mouldings it is the outer surface of an article which is important in terms of performance in service. If an article has to be thick in order that it will have adequate flexural stiffness then the material within the core of the article is wasted because its only function is to keep the outer surfaces apart. The philosophy of sandwich moulding is that two different materials (or two forms of the same material) should be used for the core and skin. That is, an expensive high performance material is used for the skin and a low-cost commodity or recycled plastic is used for the core. The way that this can be achieved is illustrated in Fig. 4.44. 

To illustrate the correct approach, consider applications in which a material is used in sheet form, as in automotive body panels, and suppose that the service requirements are for stiffness and strength in flexure. First imagine four panels with identical dimensions that were manufactured from the four materials given in Table 3-1. Their flexural stiffnesses and strengths depend directly on the respective material s modulus and strength. All the other factors are shared in common with the other materials, there being no significantly different Poisson ratios. Thus, the relative panel properties are identical with the relative material properties illustrated in Fig. 3-3. Obviously, the metal panels will be stiffer and... 

For the materials data given in Table 3-1 a GRP panel having 2.4 times the thickness of a steel panel has the same flexural stiffness but 3.6 times its flexural strength and only half its weight. The tensile strength of the GRP panel would be 50% greater than that of the steel panel, but its tensile stiffness is only 17% that of the steel panel. The designer s interest in this GRP panel would then depend in this context on whether tensile stiffness was what was required. 

There are different techniques that have been used for over a century to increase the modulus of elasticity of plastics. Orientation or the use of fillers and/or reinforcements such as RPs can modify the plastic. There is also the popular and extensively used approach of using geometrical design shapes that makes the best use of materials to improve stiffness even though it has a low modulus. Structural shapes that are applicable to all materials include shells, sandwich structures, and folded plate structures (Fig. 3-8). These widely used shapes employed include other shapes such as dimple sheet surfaces. They improve the flexural stiffness in one or more directions. 

El theory In each case displacing material from the neutral plane makes the improvement in flexural stiffness. This increases the El product that is the geometry material index that determines resistance to flexure. The El theory applies to all materials (plastics, metals, wood, etc.). It is the elementary mechanical engineering theory that demonstrates some shapes resist deformation from external loads. 

ISO 3616 2001 Textile glass - Chopped-strand and continuous-filament mats -Determination of average thickness, thickness under load and recovery after compression ISO 4603 1993 Textile glass - Woven fabrics - Determination of thickness ISO 4604 1978 Textile glass - Woven fabrics - Determination of conventional flexural stiffness - Fixed angle flexometer method... 

Generally, the sandwich composites combine light weight, good flexural stiffness and good stress distribution without weak points. Tensile and compression properties, particularly punching, can be weak. 

Fig. 27. Relationship between 10 sec flexural stiffness and deformation ratio (R, for different polymer grades. O 006, H120, A H020, 002 co-polymer...

Global buckling. Can occur in the absence of delamination just due to the local reduction in flexural stiffness. 

Examples of performance in TP matrix with carbon or graphite fibers include the use of epoxy and nylon (PA). Nylon 6 (DuPont) with a 30 wt% fiber content will increase flexural strength by about three times, and flexural stiffness may be raised by a factor of seven. Electrical properties, fiiction behavior and wear resistance may also be improved. The electrical applications largely fall into two categories to impart conductivity and prevent build-up of electrostatic discharge (which may... 

The panels are reported to have approximately 50% better flexural stiffness as a feature of their sandwich construction, while retaining the tensile properties of previous SRIM panels with similar reinforcement. They utilize approximately 30% recycled material. The new composite could be used for a broad range of automotive applications, such as interior trim panels, dashboard support systems, load floors, and other lightweight semi-structural parts. 

Flexural stiffness (El) (where E = Modulus of elasticity and / = Moment of inertia),... 

The flexural creep stiffness of bituminous binders in the range of 30 MPa to 1 GPa is determined by the bending beam rheometer test. Apart from the flexural stiffness, the w-value and the flexural creep compliance are also determined. The flexural creep stiffness test is performed on unaged or aged bituminous binders and at low to very low temperatures, ranging from 0°C to -36°C. 

According to EN 1992-2 2005. Eurocode 2, the flexural stiffness of pier shafts with constant cross-sections may he represented as follows ... 

In another study, three types of composite materials were obtained from (i) blends of soybean oil-based epoxy with commercial petroleum-based epoxy resin and E-glass fibre, (ii) blends of epoxidised methyl ester derived from canola oil with petroleum-based epoxy resin and E-glass fibre, and (iii) 100% petroleum-based epoxy resin and E-glass fibre. Panels made as in (i) exhibited comparable dynamic stiffness, flexural modulus and flexural stiffness properties to those derived from composite system (iii) However, bio-based samples from process (ii) were less promising. 

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