Energy-absorbing foams

A comparative stndy is made of the properties of energy absorbing foams nsed in passenger protection in cars, with particular reference to dynamic impact and compression strength. Materials examined inclnde polyurethanes, PP, PS and polyphenylene oxide/PS. 7 refs. 

Due to the high energy-absorbing abilities of viscoelastic foams, the foams are sometimes called energy-absorbing foams or sound-damping foams. However, die sound-absorption and impact-absorption properties are somewhat different. Therefore, optimum formulations for making them are not exactly the same. 

An energy-absorbing foam has been used as a bumper core material for automobiles (195). Sound and vibration damping of viscoelastic MDI-based IPN foams was reported by klempner et al (50) and Gansen et al (194). 

Suprasec 1042 Suprasec 1249 Suprasec DND Suprasec DNR Hexacal F Hexacal SN Hexacal LN 2-7 Low viscosity polymeric MDI. Low density rigid foams. Semi-rigid foams. Isocyanurate foams. Particle binders. Insulating foams. Energy absorbing foams. Isocyanurate foam building panels. Mine-face consolidation. Chipboard and foundry sand binders. 

Static and dynamic property The uses of these foams or porous solids are used in a variety of applications such as energy absorbers in addition to buoyant products. Properties of these materials such as a compressive constitutive law or equation of state is needed in the calculation of the dynamic response of the material to suddenly applied loads. Static testing to provide such data is appealing because of its simplicity, however, the importance of rate effects cannot be determined by this one method alone. Therefore, additional but numerically limited elevated strain-rate tests must be run for this purpose. 

Interest in the use of syntactic foam as a shock attenuator led to studies of its static and dynamic mechanical properties. Particularly important is the influence of loading rate on stiffness and crushing strength, since oversensitivity of either of these parameters can complicate the prediction of the effectiveness of a foam system as an energy absorber. 

In other words the area under the stress/strain curve is a measure of the energy absorbing characteristics. The effect of APES additions on the stress/strain properties of an anhydride cured epoxide syntactic foam at a nominal density of... 

Figure 7 shows the family of curves for anhydride cured foams containing 5 wt% of various silanes and it can be seen that although every silane improved the energy absorbing efficiency to a marked extent, the APES foam was the most efficient, followed closely by MPS and AAMS. Figure 8 shows similar data for the polyamide cured epoxide foams, from which it can be seen that the MPS foam was the most efficient. In these foams the flat response only held up to 25-30% strain. 

In a brittle polymer, Gjc measures the energy absorbed in forming unit area of fracture surface. Voids reduce the effective area of the fracture surface, and the effective area model predicts that the fracture surface energy G/c(0) of a foam should be related to the vcdume fraction 0 of voids and the fracture surface energy < ic(0) of the matrix by the equation ... 

In foam injection-molded parts the anooth-skinned resilient foam produces a tough energy-absorbing structure that is being used as a wood substitute in athletic products such as lacrosse-stick heads and hockey-stick blades. Protective structures for helmets and automotive parts are under development. All are being produced in densities ranging for 0.35 to 0.7 g/cc (22 to 44 Ib/ft ). In those applications where added sti ess is desirable the use of glass or titanate fiber reinforcement with the foamed structure is very effective (6). 

The mounting bases are intended for use with electronic equipment to absorb shock and vibration energy. The foam must be in accordance with MlI F-81334. 

Energy-Absorbing Multicomponent Interpenetrating Polymer Network Elastomers and Foams... 

Three-component IPNs prepared from polyurethane, epoxy, and unsaturated polyester resin resulted in even broader tan 5 values when compared to two component (PU/E) IPN elastomers. Furthermore, the tan S values for the three component IPN systems were still high after the transitions were apparently complete, which is of enormous significance in sound energy absorption applications. IPN foams prepared by using PU/E (two-component) showed excellent energy absorbing abilities. This was reflected in rebound, hysteresis, and sound absorption studies. 

Foams made from the two-component IPNs showed a significant Increase in energy absorbing ability as compared to the 100% polyurethane foams. This is indicated by increased sound absorption. Increased hysteresis, and decreased rebound. 

Two procedures described in BS4443, Part 2, 1988 [48] are suitable in particular for latex, PVC, and polyurethane foams. One is faster to carry out and can be used as a quality control method (Procedure A). Procedure B can be used to determine the load to give indentations of 25, 40, and 65% deflections and hence the sag factor can be determined. In addition, by measuring the load for specified indentations of the foam on loading (as with Procedure B), followed by measuring the indentations on unloading, a measure of the foam hysteresis can be determined. Hysteresis is a measurement of the energy absorbed by a foam when subjected to a deformation. 

Arco Chemical s line of Arpro expanded PP and Arpak expanded PE bead resins are used for the interior components. Polyolefin foams provide a higher degree of chemical resistance, heat resistance, and cushioning as compared to foamed polystyrene. Potential applications include seat backs, head rests, and other critical energy-absorbing areas. 

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