**3.1 Material and experimental procedure**

The compact tension specimens were manufactured from rectangular plates conforming to BS 7448-1: 1991 as shown in Fig. 21.

Fig. 21. Compact tension specimen

The fatigue tests were performed on a standard Mayes machine attached to a Pd system. The Pd system was switched on with the current circulating for 30 minutes before any readings were taken; the fatigue cycle was then begun. Data from the Pd system was exported into an excel spreadsheet and the number of cycles versus crack propagation was then plotted. From these results, values of stress intensity (ΔK) versus crack growth rate were then calculated. In order to calculate the stress intensity factor, a standard equation was used.

$$
\Delta K = \frac{\Delta PY}{B\sqrt{W}}\tag{14}
$$

Where*, Y =* geometry factor*, ∆P =* change in cyclic load (Pmax - Pmin)*, B =* sample thickness and *W =* sample width*.* Fatigue tests were conducted in fully tension - tension and at a constant frequency.
