Test methods stressing systems

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

Unfortunately, the basic physical mechanisms that control the attrition process are still poorly understood. As a consequence, particular test methods are used to evaluate the degradation tendency of the materials or to predict the rate of attrition for a given process. There are a lot of procedures using widely different devices and operations. Some of them observe the degradation of only one individual particle, whereas others treat a considerable amount of material. The particles are subjected to stress systems which range from well-defined ones like impact or compression, to those which are similar to the more or less randomized stresses occurring in natural processes. Section 4 attempts to summarize the huge variety of attrition tests in a systematic way. 

ISO 14236 2000 Plastics pipes and fittings - Mechanical-joint compression fittings for use with polyethylene pressure pipes in water supply systems ISO 14616 1997 Plastics - Heatshrinkable films of polyethylene, ethylene copolymers and their mixtures - Determination of shrinkage stress and contraction stress ISO 14632 1998 Extruded sheets of polyethylene (PE-HD) - Requirements and test methods... 

Corrosion—While corrosion is usually not a concern on hot surfaces, recognize that all systems have shut down periods, with the probability that moisture will find ingress and condense. Many insulalions arc alkaline and have little adverse effect on iron and copper, but aluminum is affected adversely. A major concern is stress-corrosion of stainless steel induced by even trace amounts of soluble chlorides un ASTM Test Method maybe used. 

Finally, it should be recognized that, when a stress is applied to a pressure-sensitive adhesive, it is either a tensile stress, a shear stress, or a combination of both. In the specific end use of a given pressure-sensitive adhesive system, a clear understanding should exist as to what type of stresses can be encountered, to ensure that the test methods applied bear a relationship to use. The various standard test methods can now be considered. 

One major cause of adhesive tape failure is the gradual disentanglement of the adhesive polymer system under slight but prolonged shear stress. While the standard shear stress test under static load (see Section II.B) is the accepted test method to evaluate this, the nature of the results, which could be in tape movement, time to fall, or no movement whatsoever, make it difficult to compare one adhesive with another. 

---