Determination of safety factors in composite structures
Andrzej Bełzowski Politechnika Wrocławska, Wydział Mechaniczny, Wydziałowy Zakład Wytrzymałości Materiałów, ul. Smoluchowskiego 25, 50-370 Wrocław
Annals 4 No. 12, 2004 pages 395-403
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abstract Discussed are various concepts of determining δ safety factors and working strains/stresses in structural components made of polymer composites. First, the classic deterministic approach is presented (Table 1) which recommends minimum values of δ with respect to the short-term strength. This approach is not favourable to optimising attempts in the design process and presumes a designer to possess a considerable experience in a particular area of composite design and application. High-pressure vessels were chosen to show this approach in action. The second concept involves working strains as determined with respect to the threshold microstructural damage (FPF). The concept is shown to be more rational than the first one, but outside the chemically-resistant equipment it can produce designs with excessive load capacity. The third approach involves working stresses as determined with respect to the long-term strength. The resulting designs are safe and reliable, but the required reference tests are costly and time-consuming (Figs. 1, 2). The fourth concept involves partial safety factors used earlier in the reliability theory. Some essential theory behind the concept is presented (formulas (3)-(7)) along with a particular implementation concerned with civil engineering structures (formula (8)). A few examples are presented of how the remaining life estimation may differ for a given design if various approaches are used. Key words: polymer-matrix composites, safety factor