Crack Paths 2012

Table 1. Mechanical properties of the 10HNAPsteel

Ultimate streMssP aσU

Elastic modGulPuas E Poriastison`νs Fatigue limit MσaPf a Numberof

YielMdσYPsStaress

cycles for σaf

N0

418

566

215

300

0.29

3.135·106

Histories of these moments are independent (separate drives and control systems) and

they are polyharmonic (pseudo-random). The histories are sums of four harmonic

components with different amplitudes, frequencies and phases. The stand enables

testing of the influence of cross-correlation between normal and shear stresses (also

phase shifts), their frequencies and amplitudes on the fatigue life of the material tested.

T H ET E S TR E S U L TASN DT H E I RA N A L Y S I S

The critical plane position for a given material depends on values of loadings, the

cross-correlation coefficient of stresses, and the ratio of maximumstresses. Using

mathematical relationships, while calculations we obtain one or more positions of the

critical plane. Moreover, material is never perfect and a damage can occur in the point

where its structure is heterogeneous. Fig. 3 shows definition of the critical plane

position. Fig. 3 shows howdetermined the angle ατ = αFP ± 45° (αFP – average angle of

fracture plane position).

Figure 3. Definition of the critical plane position and estimated shear fracture plane.

In the present paper, on base of earliest analysis experimental tests [6], the failure

criterion of maximumshear stress in the critical plane was assumed for fatigue life

calculation. According to this criterion, the equivalent stress σeq (t) takes the following

form

) 2 c o s ( ) t ( 2 ) 2 s i n ( ) t ( ) t ( xy x eq α ⋅ τ + α ⋅ σ , (1)

where: σx (t) - normal stress along the specimen axis,

τxy (t) - shear stress in the specimen cross section,

α - angle determining the critical plane position (Fig. 3).

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