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Both the fatigue limit and the fatigue life of a structural member are highly dependent upon its surface condition and on the microcrack growth rate. A model based on linear elastic fracture mechanics has been developed which involves both parameters and predicts with good accuracy the available experimental results. The factors that must be modified in order to improve the fatigue behaviour of cold drawn eutectoid steel wires are indicated. NOMENCLATURE a = crack depth c = surface half crack length a j c = aspect ratio N = number of cycles da/dN =crack depth growth rate dc/dN = surface crack growth rate D = wire diameter CT, = yield stress u; = failure stress C T~ = fatigue limit ACT = stress range AK = stress intensity factor range AKth = threshold stress intensity factor range R, = nominal stress ratio R = stress intensity factor ratio A , = surface residual stress A,,, = residual stress gradient rp = plastic zone size at crack tip

The effect of three different aging methods (immersion in hot water, freeze-thaw cycles and wet-dry cycles) on the mechanical properties of GRC were studied and compared.Test results showed that immersion in hot water may be an unreliable method for modified GRC formulations, with it being in probability a very harmful procedure.A new aging method, mixing freeze-thaw cycles and wet-dry cycles, seems to be the most accurate simulation of weather conditions that produce a noticeable change in GRC mechanical properties. Future work should be carried out to find a correlation between real weather and the proposed aging method.

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