Structural loading

The many and varied developments treated in this chapter, which themselves only scratch the surface of their theme, bear witness to the central role of functional materials in modern MSE. There are those who regard structural (load-bearing)... 

Skins with bonded doublers have been used successfully on a large number of civil aircraft and are still used on new designs. The only widespread in-service problem with bonded doubler assemblies has been delamination caused by unstable surface preparation. Early fuselage skins with bonded doublers and inadequate surface preparation experienced severe delamination and subsequent corrosion. A majority of these delaminated doublers were the fail-safe tear straps (Fig. 27). Although the tear strap bond does not cany structural load, the bond... 

Stiffened panel designs. Stiffened panels are exterior fairing panels that are attached on three or four sides. They carry little to no structural loads they are designed primarily to take air loads. Early designs using simple riveted concepts were heavy and prone to rapid sonic fatigue. 

When subjected to a step function loading, solid samples respond in one of the characteristic response modes described in Chap. 2. Often it is desired to investigate materials response to structured loading or even to shear-pulse loading. Both of these loadings can be achieved with the use of an intervening disk of a solid material placed between the loading and the sample. 

Alternately (and showing the versatility of the impact technique), impac-tors can be designed to achieve structured loading. The pillow technique of Barker used a graded shock impedance to achieve a small amplitude shock followed by a slowly increasing pressure [88C04]. Materials synthesis studies... 

For describing structural loading functions needed for design analysis, the use of overdriven detonation data representing the net overpressure (run-up side less protected side overpressure) on the arrester element and supporting structure is preferable to data representing only the run-up side, side-on overpressure. However, the run-up side transient history of side-on overpressure for overdriven detonations should provide a conservative estimate for design purposes (see Chapter 6). 

The policy of Standard 4D, that the manufacturer specify the structure load capacity for various loading configurations, has been applied in detail in Standards 4E (superseded by Standard 4F) and 4F. Standard 4F calls for detailed capacity ratings that allow the user to look up the rating for a specific loading configuration. These required ratings are as follows. 

Once the primary considerations of size, height, conceptual layout, structural loads, servicing (mechanical, electrical, communications, public health, statutory services) requirements, access, material and personnel traffic, etc. have been addressed, a facility brief can be produced to allow collation of the basic project planning information ... 

Identity specific functions Dimensions, structural loads, govl/industry standards, service environments, etc. 

For those not familiar with this type information recognize that the viscoelastic behavior of plastics shows that their deformations are dependent on such factors as the time under load and temperature conditions. Therefore, when structural (load bearing) plastic products are to be designed, it must be remembered that the standard equations that have been historically available for designing steel springs, beams, plates, cylinders, etc. have all been derived under the assumptions that (1) the strains are small, (2) the modulus is constant, (3) the strains are independent of the loading rate or history and are immediately reversible, (4) the material is isotropic, and (5) the material behaves in the same way in tension and compression. 

An explosion results in several structural loading effects, which can produce destmctive consequences to buildings and equipment. These consequences range from minor damage to complete collapse, depending on the structure s ability to withstand the loading effects. Table 5.1 summarizes the structural loadings that result from various explosion effects. 

The ideal side-on parameters almost never represent the actual pressure loading applied to structures or targets following an explosion. So a number of other properties are defined to either more closely approximate real blast loads or to provide upper limits for such loads. (The processes of reflection and diffraction will be discussed later.) Properties of free-field blast waves other than side-on pressure which can be important in structural loading ares... 

A good applications-oriented measure of the use temperature for a ma-teral is the heat distortion or heat deflection test (HDT). The HDT is described by ASTM-D648 as the temperature at which a sample of defined dimensions (5 X Vi X Vs (or Va) in.) deflects under a flexural load of 66 or 264 psi placed at its center. In case of a largely amorphous polymer, the HDT temperature is typically slightly (10 to 20 °C) lower than the Tg as determined by DSC or DTA, whereas with more-crystalline polymers, it more closely correlates with the Tm. The HDT temperature is a useful indicator of the temperature limits for structural (load-supporting) applications. A loaded cantilever beam is used in another heat deflection test called the Martens method. 

For tests other than E-84, there have been some studies on the effects of fiber loading and fiber layup on composite flammability. This has primarily been work done by the U.S. Navy on the flammability of composites used in naval vessel flammability,19-20 or work by Kandola et al.10-21-22 on the effect of fiber type and content on polymer composites studied by cone calorimeter. More work is being conducted in studying the effects of fiber orientation and lay-up not on overall flammability performance, but flammability performance under structural load. This is the most important for aircraft, vehicles, and buildings where the composites are structural members. The concern here is... 

In volume limited applications, high density propellant combinations are favored and some appropriate trade-off between performance and density is established. In a truly volume limited system as shown in section IV. A. 1., the appropriate performance parameter is the product of the specific impulse and the propellant bulk density, a quantity usually labeled the density impulse. Conceivably, mixture ratio may be determined by yet other vehicle system considerations. If a new propellant combination is to be utilized in an existing vehicle, the optimum mixture ratio may be influenced by such considerations as existing pump flow rate capacities, tank volumes, and structure load carrying capacities. Even other system considerations, such as the desirability of operating at equal fuel and oxidizer volume flow rates to allow interchange of fuel and oxidizer flow hardware, may determine the propellant mixture ratio. 

Dendrimers Well-defined, nanosized, monodispersing macromolecules with hyperbranched structures Loading all kinds of active agents for good bioavailability, targeted delivery, and controlled release 23... 

In order to estimate the amount of settlement it is necessary to know the initial and final void ratios. If Figure 2.10 is representative, the soil is underconsolidated. We can take the initial void ratio as 0.85. The total load after consolidation will be the sum of the consolidated overburden plus the structural load. If we assume a unit weight of 100 pcf, the average pressure (at 33 feet) is 3300 psf. The structural load will add 3000 psf for a total of 6300 psf or 3.15 tsf. This corresponds to a final void ratio of 0.67. Then settlement is computed (see equation 2.8) ... 

Sand piles may also be created in cohesive soils, but do not density the formation as the piles are placed. Remolding can occur, which over a short period of time may increase the adhesion to the pile above the cohesion value. The sand piles will reduce the drainage paths for consolidation to take place. In a loaded soil mass, the resulting settlement may result in downdrag on the piles, decreasing their capacity to carry structural loads. 

Hollow tubes driven into cohesive soils are filled with loose, narrowly graded sand to make sand drains. If such tubes are filled with well graded compacted sand, sand piles result, capable of carrying structural loads. Compacted gravel and crushed stone may also be used for this purpose. 

As moisture barriers, slurry walls are most effective when the bottom of the wall is keyed into an impermeable stratum. When used to support structural loads, the bottom should be keyed into rock, or other suitable bearing material. Hanging walls (those not keyed into clay or rock) may be used to buttress the walls of shallow excavations, or for containing contaminents floating on the surface of the water table. 

Slurry walls and trenches have been in use for many decades to install barriers against groundwater flow into an excavation, and to provide support for soil masses and structural loads. A slurry, generally consisting of bentonite and water, is used to keep the walls of a trench from collapsing, until the desired material is placed in the trench. Slurry walls are most... 

Figure 3. Generalized design diagram used for structural ceramics showing minimum failure time os. applied structural load. Each curve represents a differed ratio of the proof test load to the service load.

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