Abstract
AbstractDo crosslinks between the molecular chains of a glassy polymer impede the growth of fatigue cracks? Three polymers H, M, and L of equal chemical composition but differing in crosslinking densities were prepared by the polyaddition reaction of stoichiometric mixtures of 1,4‐butanediol diglycidyl ether, N,N'‐dimethylethylenediamine, and 1,4‐diaminobutane. The growth of the fatigue cracks under cyclic loading (2 Hz) was studied in the glassy polymers at ‐100°C and ‐60°C with the help of strain gauges bonded to the back side of the compact tension specimens. Crack growth rate da/dN ranged from a few nm to 10 μm depending on the stress intensity amplitude K̂1/2 at the crack tip. Log (da/dN) plotted against K̂1 revealed a linear relationship in accordance with the model calculation. The slopes, m, of the straight lines characterizing the fatigue crack growth were found to scale with M̄‐1/2 in the case of the studied polymers. (M̄c: average molar mass of chain segments between crosslinks). Glassy polymers with a low degree of crosslinking are less prone to fatigue crack growth than are the more tightly crosslinked polymers, as shown by the presented examples.
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