Load-deflection curve

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.)...

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. 

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. 

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 ... 

Experimental load deflection curves (Fig. 3.) illustrate the large difference in crack propagation observed in each case. A difference in stiffness between both bonded specimens is observed and results from either a difference in the bond line quality or from interfacial conditions. For both specimens, adherends were made from the same sample of wood. Both wood substrates contained no apparent defects and had the same longitudinal Young s modulus (14500 MPa). Both also had the same growth characteristics (oven dry specific density, annual growth rings), and as a consequence very close values of transverse and shear modulus adjacent to the bond line. Thus, any difference in stiffness is likely to be due to... 

Fig. 3 Adhesive cracked surfaces observed in shear and experimental load deflection curves (a) high roughness surface, (b) low roughness surface, (c) solid wood.

Both specimens whose cracked surfaces and experimental load deflection curves appear Fig. 3, show, in Fig. 4 different types of damage. 

Fig, 5. Load-deflection curve of a 3D glass-fiber specimen. 

Figure 15 illustrates the load-deflection curves that were obtained from the experimental data. The Heilman-Gulf epoxy and the f rf-butylstyrene monomers were an improvement over the MMA. When the t rf-butylstyrene was diluted with 50% methanol the wood-polymer composite contained half of the maximum polymer loading, and the load-deflection data were the same as the untreated basswood. To obtain the maximum improvement in physical properties the wood must be fully loaded with polymer. In another study... 

Figure 15. Load deflection curves for hasswood-polymer composites. Key H-G, Heilman-Gulf epoxy monomer TBS, tert-butylstyrene and MMA, methyl methacrylate. (Reproduced with permission from Ref. 32. Copyright 1969, Forest Products Research Society.)...

Absorbed energy was calculated from the area under the load-deflection curves. Flexural modulus of elasticity was calculated from the load-deflection relation between 0 and the maximum load. Average properties of all composites are shown in Table 6. 

Figure 5 represents the flexural load-deflection curves for artificial woods. In general, the maximum flexural load of the artificial woods tends to increase with an increase in carbon fiber content, and the deflection at the maximum flexural load increases with increasing shirasu balloon content and HPMC content. A drop in the post-maximum flexural load shows a more ductile behavior with raising HPMC content from 0.4 to 0.8wt%. From the above-mentioned results, the flexural deformation behavior of the artificial woods is markedly improved by using carbon fibers, HPMC and shirasu balloon. 

Fig. 5 Flexural load-deflection curves for artificial woods.

The load-deflection curves of sandwich plates are shown in Figs. 6 to 11. In case of Series A, B and C, a small plateau at about 20-25 kgf was observed and the behavior was scattered. On the other hand,... 

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