Deflection properties

Compression Force Deflection Test ASTM D 3574 - Test C. This test consists in measuring the force necessary to produce a 50% compression over the entire top area of a flexible foam specimen. The 

50% compression deflection value is reported in pascals. Prior to testing at the 50% value the specimen is preflexed twice to 75-80% of its original thickness, then allowed to rest for ten minutes. 

Engineering specifications for elastomers are usually defined in terms of their load-bearing properties and hard (i.e. greater than 75 IRHD) polyurethane elastomers are superior (i.e. show less deflection) to other elastomers of similar hardness in load-bearing properties. Below a hardness of 75 all elastomers have similar compression-deflection characteristics but only the polyurethanes retain their elastic characteristics at hardnesses of 

85 and above. Compression-deflection curves for a series of commercial elastomers are given in Figs 13.3 and 13.4, and the effect of shape factor on deflection is also demonstrated. Usually, solid polyurethanes of the same hardness have similar load-bearing characteristics. 

GLASS FIBRE REINFORCED POLYESTER AND EPOXIDE RESINS 

VULCANIZED FIBRE-RIGID PVC-ACRYLIC RESIN POLYCARBONATE-POLYAMIDE- 

POLYURETHANE ELASTOMER PROPERTIES COMPARED WITH THE PROPERTIES OF VULCANIZED RUBBER AND RUBBER-LIKE POLYMERS 

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Plasticizers and waxy additives can give good initial color and physical property results yet cause the finished product to have poor heat deflection properties that can lead to latent part warpage. Much of this delayed defect phenomenon is associated with crystalline or semicrystalline products that must recrystallize after melting in order to reach their full property potential. Waxes and plasticizers can hinder recrystallization, and the effects can be different in thick sections that cool slower than thin sections. 

Three experimental units each with different experimental focus were designed, fabricated and delivered to NASA Langley. The first unit contains four passive and four active films samples to be exposed to combined atomic oxygen and vacuum UV. The second unit contains 11 passive and four active samples to be exposed only to vacuum UV (see Fig. 2). The third unit has two passive samples with different thicknesses of protective aluminum layers to be exposed to atomic oxygen and vacuum UV. All passive samples will be characterized, both in terms of chemical and physical properties, after the mission and compared with pre-exposure characterization to determine the effects of the space environmental exposure. Thin foil-type thermocouples are attached and logged underneath the samples to measure actual temperatures experienced. By recording the temperature it will be possible to correlate the deflection properties with temperature conditions of the active samples. 

Indentation-Force Deflection (See also Compression/Deflection Properties)... 

For polar molecules with an electric dipole moment, Rabi spectrometers with electrostatic quadrupole deflection fields offer the possibility to detect rotationally inelastic collisions since the focusing and deflecting properties of the quadrupole field depend on the quantum state J, M) of a polar molecule. This technique is, however, restricted to molecules with a large electric dipole moment and to small values of the rotational quantum number J [1076]. 

On UV exposure, Triax CBE does not show any signs of discoloration whereas polyphenyleneether, PPE, and ABS are severely discolored, the blend shows better stabihty than UV stabilized ABS and polycarbonate. Triax CBE has almost identical heat deflection properties as ABS even though it contains PVC which vmder conditions of an experiment is completely deflected. 

Poisson s ratio is a required constant in engineering analysis for determining the stress and deflection properties of plastic, metal, and other structures such as beams, plates, shells, and rotating discs. Temperature, the magnitude of stresses and strains, and the... 

Flexural probes measure deflection properties in three-point bending, such as flexural strength and modulus of stiff materials and fiber-reinforced composites... 

Another approach for toughening UP and VE resins which has had success with epoxy resins is the use of liquid rubber (or elastomer) additives. The chief benefit of emplojdng liquid rubbers (LR) versus a flexibilized resin is that decreases in hardness, stiffness and heat-deflection properties can be minimized. During cure, the liquid rubber phase separates from the resin and is concentrated in a particulate phase. Very little of the rubber remains in solution with the cured resin so the resin s heat deflection temperature is for the most part unaffected. The toughness of the two-phase, or composite, material will be a function of the microstructure, which in turn will depend on processing and cure conditions. The subject of epoxy resin toughening is covered in separate articles in this book. 

This procedure may be used unless the rate-dependence, load history-dependence, or deformation-hardening characteristics of the isolation system necessitate explicit consideration of their nonlinear and/or velocity-dependent force-deflection properties. 

The load deflection characteristics of these types of component are often critical for their application. Natural rubber and the high cis-polyisoprenes have load/deflection properties which are not dissimilar, however, the uniformity of the synthetic polymer is always greater than for the natural product and reproducibility of properties is assured. Since engineering components such as railway locomotive suspension units are often complex and extremely expensive to produce, this uniformity of product ensures a lower incidence of rejection. 

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