Crack growth behaviour is represented by the crack growth curve. The crack growth curve depicts the crack growth rate as a function of stress intensity factor. According to literature, crack growth curves of short cracks differ considerably from those of long cracks. Short cracks grow beneath the threshold of stress intensity for long cracks and exhibit considerably higher crack growth rates at equivalent stress intensity factors compared to long cracks. To analyse the influence of short cracks on the life time of a component crack growth curves for long and short cracks of two light metals, namely AlSi9Cu3 and Ti-6Al-4V were recorded. Long crack growth curves were recorded under single edge bending loading, thereby crack length was measured by the potential drop method. For recording crack growth curves of short cracks flat tension compression specimen with initial crack lengths of 0.2 and 0.4 mm were loaded under uniform tension/compression. Crack length measurement was performed by a purpose designed camera system. Abnormal crack growth behaviour of short cracks could only be observed for AlSi9Cu3. For Ti-6Al-4V short crack growth curves coincided with those of long cracks. It was discovered that crack lengths of 0.2 and 0.4 mm cannot be considered short for Ti-6Al-4V. The recorded crack growth curves were then used for lifetime estimation of flawed components and the results were compared with existing test results. For AlSi9Cu3 a clear reduction of the estimated lifetime of components with initial short cracks could be observed. The reduction in lifetime of components with short cracks was confirmed by test results. Thereby lifetime was estimated from crack growth curves of long and short cracks according to initial crack lengths. Because of best agreement with test results short crack growth curves were used for estimation through a crack length of 1 and 2 mm respectively depending on stress rate. Finally the present work deals with the estimation of SN-curves from crack growth curves without integration. Thereby the decline of low and high cycle fatigue lines of the SN-curve is equivalent to the incline of the Paris-line and the line in the near threshold regime respectively. Additionally the fatigue limit can be calculated from the well known El Haddad equation, which describes the fatigue limit as a function of threshold stress intensity factor and initial crack length.
|Translated title of the contribution||Short crack growth in AlSi9Cu3 and Ti-6Al-4V: Influence of short cracks on lifetime|
|Award date||18 Dec 2009|
|Publication status||Published - 2009|
Bibliographical noteembargoed until null
- short crack growth short cracks AlSi9Cu3 Ti-6Al-4V Lifetime estimation