Environmental stress cracking accelerated tests

Because many polymers are resistant to attack by corrosives, tests for chemical resistance of polymers are particularly important. ASTM-D-543-67 (1977) measures weight and dimensional changes of test samples immersed for 7 days in many different test solutions. These tests may be coupled with tensile tests. Other ASTM tests include those under accelerated service conditions [ASTM-D756-76 (1971)], water absorption [ASTM-D570-63 (1972)], and environmental stress cracking of ethylene plastics [(ASTM-D1693-70)]. 

Stress rupture tests on test pieces are very important under conditions where, in addition to the stress, the atmosphere is chosen to accelerate failure. The best known t> pe of test is a test of the so-called environmental. stress cracking of plastics, where the aggressis e atmosphere is a chemical that causes cracking when the material is in a strained state. These tests are usually considered as a form of chemical resistance test and are cosered in Chapter 14. Ozone cracking of rubber, also an environmental resi.stance test, is another example. 

The notable exception is the exposure of rubber, including relex ant foams and coated fabrics, to ozone. Many rubbers are susceptable to cracking when exposed in the strained condition to ozone in very small quantities—this is in fact a case of environmental stress cracking discussed above for plastics. Ozone levels in the atmosphere arc generalK no more than the odd part per hundred million, but this is quite sufficient to cause severe damage. Accelerated tests are usually carried out in special ozone cabinets at levels between 25 and 200 parts per hundred million, and the procedures are described in Chapter 15. 

D1693, environmental stress cracking G23 (formerly E42), accelerated weathering Pipe tests (Commercial Standard CS 255-63)... 

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

Static fatigue is the slow growth of a crack under ambient stress and environmental conditions. The static fatigue failure in oxide materials can be accelerated by moisture or hydrogen, which weaken the chemical bonds at the crack tip. This moisture can be supplied by breathing on the films to condense moisture. This moisture condensation method is an easy way to quickly determine if the residual film stresses are high or the adhesion is poor, and the nature (compressive or tensile stress) of the stresses in a film. This moisture condensation is the basis of the bad breath adhesion test (Sec. 12.5.2). 

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