Polymeric material flexural properties

ISO 844 2001 Rigid cellular plastics - Determination of compression properties ISO 3386-1 1986 Polymeric materials, cellular flexible - Determination of stress-strain characteristics in compression - Part 1 Low-density materials ISO 3386-2 1997 Flexible cellular polymeric materials - Determination of stress-strain characteristics in compression - Part 2 High-density materials ISO 5893 2002 Rubber and plastics test equipment - Tensile, flexural and compression types (constant rate of traverse) - Specification ISO 7743 2004 Rubber, vulcanized or thermoplastic - Determination of compression stress-strain properties... 

Stress-strain curves developed during tensile, flexural and compression tests may be quite different from each other. The moduli determined in compression are generally higher than those determined in tension. Flaws and sub-microscopic cracks significantly influence the tensile properties of brittle polymeric materials. However, they do not play such an important role in compression tests as the stresses tend to close the cracks rather than open them. Thus, while tension tests are more characteristic of the defects in the material, compression tests are characteristic of the polymeric material as it is. The ratio of compressive strength to tensile strength in the case of polymers is in the range 1.5 to 4.0 [Dukes, 1966]. 

For a very large proportion of polymeric materials in commercial use, mechanical properties are of paramount importance, because they are used as structural materials, fibers, or coatings and these properties determine their usefulness. Properties that also determine their utilization are compressive, tensile, and flexural strength, and impact resistance. Hardness, tear, and abrasion resistance are also of concern. In addition, polymers may be shaped by extrusion in molten state into molds or by deposition from solutions on various surfaces. This makes the flow behaviors in the molten state or in solution, the melting temperatures, the amount of crystallization, as well as solubility parameters important. 

Stress-strain curves developed during tensile, flexural, and compression tests may be quite different from each other. The moduli determined in compression are generally higher than those determined in tension. Haws and submicroscopic cracks significantly influence the tensile properties of brittle polymeric materials. 

Flexibility is an important end-use property for elastomers. The Tg, which is the point at which an elastomer (on cooling) goes from a flexible more rubber-like form to a more rigid inflexible form, is a critical parameter in determining the elastomer s suitability for specific applications. Plots of flexural storage modulus G (Pa) versus specimen temperature are very useful in evaluating the stiffness and flexibility of polymeric materials. 

Suppression of flexural vibrations in metal plates and bars by application of a thin layer of polymeric material, either spread directly or applied in the form of a tape, has become of great importance both for elimination of noise (especially in vehicles and airplanes) and for improving fatigue characteristics. It was mentioned in Chapter 7 that measurements of resonance frequencies and damping in such compound layered systems can be used for obtaining the viscoelastic properties of the polymeric stratum. Conversely, knowledge of the viscoelastic properties and their dependence on frequency and temperature (and plasticization, incorporation of fillers, etc.) aids in the selection of antidamping materials for specific applications. ... 

The mechanical properties of polymeric materials including blends are reported in detail in commercial product literature and provide a basis of comparison of the engineering properties of materials for various end-use applications. The specific mechanical properties of interest include the modulus (tensile, flexural or bulk), strength (tensile, flexural or compressive), impact strength, ductility, creep resistance as well as the thermomechanical properties (e.g., heat distortion temperature). The mechanical property profile can be employed to determine the compatibility of the blend by comparison with the unblended constituents. Compatibi-lization methods can be evaluated easily by comparison of the mechanical property profile with and without compatibihzation. 

The most common mechanical properties include tensile strength, flexural strength, and Izod impact strength. The electrical properties of concern are dielectric strength, surface or volume resistivity, arc resistance, and arc tracking. The test specimens are standard ASTM test bars, depending upon the type of test. The UL publication Polymeric Materials—Short-Term Property Evaluations, UL 746A, describes the specimen and test procedures to determine mechanical and electrical properties. 

Polymeric foams have a closed-shell structure approximately 10 pm in diameter, with a cell density between 10 and 10 cells cm. These foamed materials have superior properties to their unfoamed counterparts in terms of enhanced ratio of flexural modulus to density and impact strength [58]. High-pressure CO2 offers a particularly attractive alternative to traditional blowing agents because of its environmentally benign nature and relatively low cost The phasing out of ozone-depleting substances associated with the Montreal Protocol acts as... 

The properties of PLA depend on the stereoisomers used for their preparation. PLLA and PDLA are semicrystalline hard materials with modulus of 2.7 GPa, tensile strength of 50-70 MPa, elongation at break of 4%, flexural modulus of 5 GPa, and flexural strength of 100MPa [116-119]. The melting point is around 180°C and Tg is 60-65°C. The molar mass of the polymer as well as degree of crystallinity have a significant influence on the mechanical properties [120-124]. Polymerization of a racemic mixture of 1 1 d,d-LA... 

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