Load deflection

Compressive Behavior. The most kiformative data ki characterising the compressive behavior of a flexible foam are derived from the entire load-deflection curve of 0—75% deflection and its return to 0% deflection at the speed experienced ki the anticipated appHcation. Various methods have been reported (3,161,169—172) for relating the properties of flexible foams to desked behavior ki comfort cushioning. Other methods to characterize package cushioning have been reported. The most important variables affecting compressive behavior are polymer composition, density, and cell stmcture and size. 

Fig. 3. Load—deflection curve for a SiC—C—SiC composite in four-point bending. Note the extreme change in behavior fora composite fabricated with a 0.17-p.m carbon layer between the SiC fiber and the SiC matrix as compared with a composite with no interfacial layer (28).

Figure 27.8. Typical load-deflection curves for (a) latex, (b) flexible PVC, (c) polyester polyurethane (curve C) and polyether polyurethane foams (curve D). Shell Chemical Co.)...

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

Figure 4-33 Load-Deflection Behavior of Metal Plates...

Figure 4-46 Spring Analogy for Laminate Load-Deflection Behavior...

The manner in which the laminate design is approached can be expressed in flow-chart form as in Figure 7-59. There, some initial laminate is arbitrarily selected to start the procedure. Then, the laminate load-deflection behavior is evaluated by use of the laminate strength analysis procedure described in Section 4.5. That evaluation is theoretical in nature. The next step is to evaluate the laminate fatigue life, and that evaluation can only be done experimentally, although progress is... 

Suppose we replace the 90° layers with a laminae in an attempt to increase the axial stiffness and to increase the first-ply failure load as in Figure 7-61. The load-deflection curve slope after first-ply failure also increases when a laminae replace the 90° layers. However, the energy absorption decreases with such a stacking sequence change. The associated fatigue lives are not known unless both laminates are made and subjected to fatigue loading. 

Table 3 Formulation of a O Type of Mount in a Load Deflection Operation...

A time dependent modulus is then calculated using the extreme fiber stress level for each of the materials at the initial stress value level using the loading-time curve developed. If the deflection at the desired life is excessive, the section is increased in size and the deflection recalculated. By iteration the second can be made such that the creep and load deflection is equal to the maximum allowed at the design life of the chair. This calculation can be programmed for a computer solution. 

Fig. 4-12(b) Typical load deflection that is characteristic of a marine structure. 

The flexural yield strength is determined from the calculated data of load-deflection curves that show a point where the load does not increase with an increase in deflection. 

The flexural modulus is the ratio, within the elastic limit, of stress to corresponding strain. It is calculated by drawing a tangent to the steepest initial straight-line portion of the load-deflection curve and using an appropriate formula. 

Worst case span is exterior, fixed-pinned boundary conditions. To add the effects of dead load to SDOF calculations, each pressure-time pair will be increased by the magnitude of the dead load and the initial displacement will be set equal to the dead load deflection. This will create a balanced condition at the start of the SDOF response calculation (refer to the pre-load discussion in Section 7.2.3). 

The heat deflection temperature (ASTM D-648) is determined by noting the temperature where a simple beam under a specific load deflects a specific amount (generally 0.01 in. 0.25 mm Figure 13.6) within an environment. As in other ASTM, the experimental conditions are specified including sample size. 

Flexural strengths tend to be higher than tensile strengths in SMC composites. Elexural load-deflection modulus values are nonlinear, which indicates the occurrence of microcracking even at low loading. In general, flexural properties follow the same trends as the tensile properties and are affected by fiber content, fiber lengths, type, and orientation. 

Aksel, C. and Riley, F.L., Young s modulus measurements of magnesia-spinel composites using load-deflection curves, sonic modulus, strain gauges and Rayleigh waves , J. Eur. Ceram. Soc., 2003 23(16) 3089-96. 

If the matrix can become more graphitic, as the above examples indicate, more shear planes become available hence more microcracking can occur, resulting in greater strain at lower stress levels. Thus the apparent or effective modulus of the 2D composite materials is reduced, and more energy is required to cause failure—an outcome indicated by the difference of area under the as-received and heat-treated load-deflection curves in Figures 7 and 9 ... 

Alternative to the constant load tensile test, a spring or proof ring is used in place of dead-weight and the load/deflection relationship for the particular geometry is... 

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