The instron depicted above is an instrument which is used to look at tensile properties of composites. The ASTM for a coating's tensile analysis is similar to the procedure used in the tensile testing of many types of materials. The method covers the determination of the elongation, tensile strength, and stiffness (modulus and elasticity) of organic coatings when tested as free films (no panel). Tensile properties determined by this method are of value in studying the behavior of coatings subjected to environmental stresses, such as those produced by aging and weathering. Tensile properties can change with specimen thickness, method of preparation, gage length, rate of load application, tensile tester response, and type of grips used. Consequently, when precise comparative results are desired, these factors must be carefully controlled.
Terms used in mechanical testing:
1. Tensile strenth-The load
per original unit area at which a specimen fails or yields in a tension
(pull) test.
2. Elongation-The increase
in specimen length from the point of initial load application to the point
of film rupture under
tension.
3. Stress/strain curve-The
curve generated from a plot of tensile load against the distance of jaw
separation (elongation of
specimen).
4. Stiffness(modulus of elasticity)-The
load per unit area required to elongate the film 1% from the first point
in the
stress-strain curve where the slope becomes constant.
5. Gage length-The initial
length of the test specimen between the jaws of the tensile tester.
These particular mechanical properties are very pertinent to the application of composites including coatings. Solvent resistance, gloss, and film hardness are all important to the characterization of coatings but mechanical properties are the most significant in terms of a products range of potential uses in the environment. Below is a depiction of a stress versus strain curve for proprietary polymeric system. For a complete analysis of mechanical properties and the curves that relate them, please read the following site in grave detail: Macrogalleria mechanical properties section.
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