PSI - Issue 5

D. Rozumek et al. / Procedia Structural Integrity 5 (2017) 896–903 D. Rozumek et al. / Structural Integrity Procedia 00 (2017) 000 – 000

901

6

, 1 0.55( a / W a ) 0.08( a / W a ) 0.26 2.65( a / W a ) 2      





K F a cos 

(3)

I

Wt( 1 a / W ) 

. 1 0.67( a / W a ) 2.08( a / W a ) 0.23 1.4( a / W a ) 2       





K F a sin 

(4)

II

Wt( 1 a / W ) 

For mixed mode I+III specimen the ranges of stress intensity factors  K I for mode I and  K III for mode III are the following   a a , cos K Y I       0 2 1 (5)   a a , cos K Y sin III        0 3 (6) where  is the stress range, a 0 - notch length. For modes I and III, according to Refs. Harris (1967) and Chell and Girvan (1978), the correction coefficients take the forms         a a / w a a / w , / Y 2 0 0 1 7 5 20 13      (7)           Y w / a a tan a a / w . 2 2 0 0 3     (8) Figs. 6, 7 and 8 for load ratio R = 0.1 (mixed mode I+II), R = 0 (mixed mode I+III) show fatigue crack growth rates da/dN versus  K parameter for two angles. The test results of mixed modes I+II and I+III loading have been divided into pure mode I, mode II and mode III. For constant cracking growth rate, different values of  K were obtained for mixed mode I+II, mixed mode I+III and pure modes I and III. It was found that for  = 30  the crack growth rate was higher for mode III than for mode I in the case of the same value of  K (Fig. 6b). For  = 45  , a higher crack growth rate was found for mode I to da/dN = 9.5  10 -8 m/cycle (Fig. 7b) above that value mode III was dominating together with increase of the material plasticity. a) b)

Fig. 6. Comparison of the experimental results for  =  = 30  and mode: a) I and II, b) I and III.