English The film shows the formation and the propagation of fatigue cracks in defective spot welds of 2 mm sheets of AlCuMg2 pl. The crack propagation under dynamic load has been filmed by time-lapse photography. The specimens were illuminated by a stroboscope. The film demonstrates that fatigue cracks always start at the margin of the defective spotwelds without regard to the size and orientation of defects in the weld nugget. In two of the five defective weld nuggets being analyzed hot cracks did not propagate during the whole cyclic-load time. In the other defective spot weldings the hot cracks propagated after the fatigue cracks from the margin of the weld nugget had propagated over a distance greater than the single sheet-thickness. | 
