Crack propagation stages

The second part of the investigation was directed toward the understanding of the crack propagation stages. Two questions were especially addressed (i) the determination of the transition from fatigue to brittle fracture (ii) the determination of the crack arrest conditions. Within the frame of linear elastic fracture mechanics, such an analysis requires the... 

Figure 15.11 Crack propagation stage in a PLC material subjected to a tensile force.

Stable crack propagation and unstable crack propagation stage... 

Intermediate temperature. The rubber is able to relax during the relatively slow build-up of stress at the base of the notch, but not during the fast crack propagation stage. Stress... 

Relatively large molecules are transformed by chain reactions, in which product distribution is defined by the limiting chain propagation stages. For example, Benson [12] presents the following version of -butane cracking ... 

Stage two crack propagation of well-defined cracks on the planes of high tensile stress in the direction normal to the maximum tensile stress. 

At intermediate stress intensity levels (stage 2) the crack propagation rate shows a plateau velocity Vpiateau that is virtually independent of the mechanical stress, but depends on the alloy/environment interface and the the rate-limiting environmental processes such as mass transport of the aggressive species to the crack tip. The plateau in a quenched and tempered low-alloy steel of 1700 MPa yield strength in deaerated water at 100°C... 

When some critical crack length (between 200 pm and 400 pm, i.e. about 15% of the contact diameter) is reached, a brittle propagation stage is observed which is associated with a sudden and drastic drop in the lateral stiffness, K. The measured crack width in the plane of the contact is then of the order of magnitude of the contact diameter. Post-mortem microscope observation of specimen cross sections in the contact zone (Fig. 8) indicates that the depth of the cracks is of the order of magnitude of the contact radius (i.e. about 900 pm). The two deep cracks induced at the edge of the contact may thus be viewed as some kind of half-penny cracks whose radii are approximately equal to the radius of the contact. In the subsequent part of this paper, the two deep cracks will be referred to as primary cracks . 

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