Dynamic stress intensity factor

Fig. 9 Dynamic stress intensity factor calculated from a finite element model (o) plotted as a function of crack velocity and compared to experimental data ( ) obtained for PMMA (after [34,35])...

Available theoretical solutions in dynamic fracture are few, and limited to finite or semi-infinite cracks in an infinite solid for Mode I, self-similar crack extension. Despite the above limitations, short of conducting detailed numerical analysis of the crack tip state of stress, these solutions must be used to deduce the characteristics of the crack tip state of stress, as well as to extract the dynamic stress intensity factor for elastodynamic fracture mechanics. In the following sections, a brief description of available theoretical solutions is presented. 

The dynamic stress intensity factor, KId, of a stationary semi-infinite crack, which is impacted by a square plane tension wave, or0, of duration t, in... 

Fig. 3.19 Percentage area of transgranular fracture versus dynamic stress intensity factor for alumina.

Table 3.4 Fracture surface features correlated with dynamic stress intensity factor...

The crack opening can be determined (p = 1), if the fringe order n is known. This method has been used in investigations of stationary cracks to determine static and dynamic stress intensity factors, the latter being induced by a shock wave. 

Zehnder, A.T. and Rosakis, A.J. (1990). Dynamic Fracture Initiation and Propagation in 4340 Steel under Impact Loading, International Journal of Fracture, 43, pp. 271-285. Kalthoff, J.F., Beinert, J. and Winkler, S. (1977). Measurements of Dynamic Stress Intensity Factors for Fast Running and Arresting Cracks in Double-Cantilever-Beam Specimens. n Fast Fracture and Crack Arrest, ASTMSTP 627, pp. 161-176, Hahn, G.T. and Kanninen, M.F. (Eds.). American Society for Testing and Materials. 

The minimum fracture toughness of the material at the normal operating temperature of the flywheel will be equivalent to a dynamic stress Intensity factor dynamic) of at least 100 ksi/Tn. Compliance will De demonstrated by either of the following ... 

Dally, J.W. and Sanford, R.J. (1987). Strain-Gage Methods for Measuring the Opening-Mode Stress-Intensity Factor, Kj. Experimental Mechanics 27 4, pp. 381-388. Takahashi, K. and Arakawa, K. A parameter influential in dynamic fracture. 

In this paper we have calculated the three dimensional stress fields at the tip of the crack associated with the standing waves across the plate, assuming the waves modulate the stress intensity factor of the crack. Thus the present analysis takes account of these important experimental observations for the microcrack branching instability described above. We are unable, however, to clarify the direct cause of this instability but we have pointed out that the transient interference pattern of the standing waves could enhance the stress fields at the tip of the crack, as shown in Fig. 5, and possibly change the dynamics of the propagating crack. 

Fracture toughness, expressed in term of the critical stress intensity factor Kc, was determined at fracture initiation and that point was identified from the load diagram. Although linearity requirements as set out in the protocol were generally satisfied, the identification of the point of fracture initiation from the load diagram was often uncertain because of the difficulty to distinguish small, residual fluctuations in the load signal due to dynamic effects from a pop-in effect. When in doubt about that the test was discarded. 

---