PSI - Issue 24

Filippo Cianetti et al. / Procedia Structural Integrity 24 (2019) 526–540

529

4

Author name / Structural Integrity Procedia 00 (2019) 000–000 Table 1: Mechanical Properies of used Material

Material

Yeld S y [MPa]

Ultimate S ut [MPa]

Young E [GPa]

density ρ [kg / m3]

2.7 · 10 3 2.7 · 10 3

Aluminium Alloy 7075 T6 Aluminium Alloy 6061 T6

505 280

570 310

71 68

Wohler Curve (bending)

400 500 600

HCF 6061 T6 LCF 6061 T6 HCF 7075 T6 LCF 7075 T6

300

200

100

Stress amplitude log(MPa)

10 0

10 2

10 4

10 6

10 8

Cycles log(N)

(a)

Fig. 3: Wohler Curves Calculated

Table 2: Wohler Curves values of used Material

Material

S ut [MPa]

S 10 3 [MPa]

S e [MPa]

Aluminium Alloy 7075 T6 Aluminium Alloy 6061 T6

570 310

399 217

171

93

where

S 2

10 3

a =

(4)

S e

S 10 3 S e

1 3

log 10

(5)

b = −

obtained for a 50% reliability from the values of Tab. 2.

2.2. Modeling: from Physical Space to Modal Reduction

The frame has been modeled with finite elements (FEM) in the ANSYS APDL environment, the most complex geometric features have undergone a simplification process (Fig. 4 (b)), to reduce the computational cost, therefore the analysis times, ensuring consistency of the solution. For that purpose, a mesh dimension study of the sensitivity was carried out, based on the stabilization of natural frequencies. The result, a balanced compromise between the maximum size of the elements and the congruence of solution, was the interval between 2 and 4 mm. Then the skin elements technique was adopted, Bathe (2014) obtaining a perfectly plane stress state on the component surface, in accordance with theory. The frame, consisting of two parts (Fig. 4 (a)) connected with a suitable bolted connection,