Crack Paths 2012

R E S U L T S

Within this study the absolute overload ratio N, introduced in [6] as ratio between the

applied overload (OL) stress intensity factor and the critical stress intensity factor for

crack initiation, is used for the assessment of the overload effects.

N = K I (OL) / KIq

(5)

However, there are also other definitions of the overload ratio in the literature. But in

this study the absolute overload ratio N is preferred, since by using N there is a direct

relation in which region of the cyclic crack growth curve the experiment is performed.

Furthermore, using this overload ratio a correlation to an absolute crack initiation value

(KIq) is possible, what is relevant for the observed overload phenomena.

First we will focus on the crack extensions caused by the different overloads. The graph

presented in Fig. 4 shows the crack growth versus number of cycles for the SENB3

overload experiment. These results were obtained by crack length foils applied on the

back side of the specimen. One can obviously see the influence of the increasing

overload ratio Rol of the different overloads. The first noticeable crack extension takes

place, when the overload with Rol=1.5 is applied, and there are larger crack extensions

resp. crack growth accelerations for further increasing overload ratios Rol. Furthermore,

there are also little crack extensions for the overloads with Rol<1.5. For the overload

with Rol>2.4 static fracture is almost reached resulting in relatively large crack

extensions of about 0.1 m mand larger.

Figure 4. Crack length versus number of cycles for SENB3overload experiment.

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