Crack Paths 2012

thicknes increased considerably from the smallest net cross-section towards the

clamping region due to shouldering. This mild notch effect enforced the fatigue crack to

search its path in the region of small cross section, thus increasing the mode II

contribution by torsion compared to a tube specimen with constant wall thickness. A

seventh influence parameter – the component’s geometry in general – has therefore

been identified of affecting the non-proportional (and the proportional) mixed-mode

fatigue crack growth.

Table 1. Comparison of fatigue lives under porportional and non-proportional loading

(mainly after [46])

Material

N90°/N0°

N90°/N0°,

control

Reference

for

condition in

for

Va = const.

Ha = const.

test

Steel

0.1

-

Va

Tipton [47]

S460N

10 ... 20

0.21 ... 0.28

Ha

Hoffmeyer [48]

Va, Ha

S460N

2 ... 3

0.3

Sonsino [49]

Va, Ha

CK45

0.4

-

Sonsino [50]

Va, Ha

S A E1045

0.6

5

Pan [51]

25 CrMo4

0.6

-

Va

Grün [52]

Va, Ha

30 CrNiMo8 1.1

0.4

Sonsino [49]

0.54 ... 1.4 (LCF) Ha

X6CrNiNb18-10 .

Hoffmeyer [48]

Hug[53]

Va, Ha

X6CrNiTi18-10 3.8

0.5

Va, Ha

X10CrNiTi18-9 1.1

0.5

Sonsino [49]

0.77 ... 0.9

AlMg4.5Mn 1

Ha

Hoffmeyer [48]

6061 Al T6

-

0.2

Ha

Xia [54]

AlMgSi1

-

0.5

Ha

Ahmadi [55]

AZ91

Renner [56]

-

3 ... 4

Ha

0.1

Ti-6Al-4V

-

Ha

Nakamura [57]

1045

-

0.17 ... 2.81

Ha

Fatemi [58]

C O N C L U S I O N

A lack of tailored, validated and accepted mixed-mode hypotheses for application

with especially non-proportional crack tip conditions must be stated. Specifying simply

the sum of crack growth rated from each modecontribution as suggested by Doquet and

Pommier [37] as well as Döring [46] is certainly not the final end of the development. A

way out of purely empirical descriptions of experimental finding for special loading

situations might be pointed by a rather unknown suggestion published by Hertel et al.

[62]. The 'J-integral at a crack tip under non-proportional mixed mode loading remains

– despite sound expectations – a fairly path independent quantity. The path

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