The present paper presents an analysis of the thermal aging process of a polyamide 66 at two different temperatures: −6 °C and 60 °C, and throughout a time span of 9000 h. The paper proposes a unified expression to estimate the mechanical behavior of the polyamide in tensile tests at the different aging stages. The goal is to present an algebraic equation able to describe the stress-strain curves that would be obtained using the ASTM D638-14 standard for a wide range of aging times, without the actual necessity of performing all the tests. It is shown that with a minimum of three tests performed at different aging stages, it is possible to obtain a reasonable approximation of the stress-strain curve for this range of time.
Composite repair systems have been gaining each time more space in industry, especially when it comes to repairing through-wall defects in pipes. They are simpler to apply, have no costly downtime and provide lower risks to the environment when compared to metallic repairs. ASME PCC-2 and ISO 24817 standards are responsible for defining the parameters necessary to a successful repair, however neither of them addresses a very common practice in such repairs, which is the addition of a bonded metallic patch over the defect. Several companies are adepts of such practice and it has already been proven that is actually the metallic patch and not the composite sleeve itself that sustains most of the load applied on the repair, and for that reason it becomes necessary to conduct further studies regarding the behavior of the patch alone. One important issue is to understand why the strength of similar repairs due to operation errors with very similar amplitude of pressure transients seems to vary randomly, with unexplained early failures. The present paper is concerned with an experimental study about how pressure variations can generate cyclic inelastic strains in the pipe, which can weaken the adhesion between pipe and patch, leading the repair to fail prematurely.
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