PSI - Issue 13

Rodrygo Figueiredo Moço et al. / Procedia Structural Integrity 13 (2018) 1915–1923 1917 Rodrygo F. Moço, Fábio G. Cavalcante and Gustavo H. B. Donato / Structural Integrity Procedia 00 (2018) 000–000 3

ASTM A36 steel. Such material was prestrained before specimens were machined to try to minimize residual stress effects and closely reproduce real conditions of uniformly strained regions – after that, C(T) specimens were machined and Fatigue Crack Growth (FCG) testing could be conducted according to ASTM E647 (2011); all details regarding FCG description using Paris Law, the experimental procedures, microstructures and mechanical properties of the studied ASTMA36 steel (2008) can be found in Donato and Cavalcante (2015). Table 1 presents selected mechanical properties, while Fig. 1 presents the da/dN- Δ K evolutions for plastic prestrains of 4.3%, 8.3% and 14.7%. Considering Paris Law (Eq. 1) for the description of the stage II FCG, C and m values can be observed in Fig. 2 and in Eqs. (2-3) as a function of the imposed plastic prestrain (PS): � � � � � ����� � (1) ��������� � ���� ��� � � ���� ��� � � ���� ��� � ���� �� (2) ��������� � ������ �� � � ������� ��� � ������ (3) Table 1 – Mechanical properties obtained from tensile tests of ASTMA36 steel.

1 [MPa]

2 [MPa]

S YS Offset

S YS Autographic

S

UTS [MPa]

E [GPa]

Elongation [%]

AVERAGEVALUES

213.1

292.9

289.3

438.6

9.61

STANDARD DEVIATION 0.31 ASTM E8/E8M [15] yield st rength evaluat ion method: (1) for materials exhibit ing no discont inuous yielding. (2) for materials exhibit ing discont inuous yielding. 5.8 5.1 5.7 2.3

1.E-2

2.E-3

0%PS - Sample 01 0%PS - Sample 05 0%PS - Sample 03 4.3%PS - CP 03 2A 4.3%PS - CP 06 2A 4.3%PS - CP 03 2B 4.3%PS - CP 04 2B 8.3%PS - CP 04 3A 8.3%PS - CP 05 3A 8.3%PS - CP 05 3B 8.3%PS - CP 06 3B 14.7%PS - CP 02 1A 14.7%PS - CP 05 1A

1.E-3

0%PS - Sample 01 0%PS - Sample 05 0%PS - Sample 03 4.3%PS - CP 03 2A 4.3%PS - CP 06 2A 4.3%PS - CP 03 2B 4.3%PS - CP 04 2B 8.3%PS - CP 04 3A 8.3%PS - CP 05 3A 8.3%PS - CP 05 3B 8.3%PS - CP 06 3B 14.7%PS - CP 02 1A 14.7%PS - CP 05 1A

1.E-4

Crack Growth Ra te - da /dN[mm/cycle] log

(a)

Crack Growth Ra te - da /dN[mm/cycle] log

(b)

1.E-5

2.E-4

45

65

15

35

Stress Intensity Factor Range - ΔK [MPa√m] log

StressIntensity Factor Range - ΔK [MPa√m] log

(a) (b) Fig. 1. da/dN vs. ΔK curves. (a) Region II. (b) Region II with magnification between Δ K = 35 and 45 MPa √ m.

Based on such mechanical properties and effects of plastic prestrain on FCG response of ASTM A36 steel, practical effects in the structural integrity of manufactured components (such as calendered pressure vessels and UOE pipes) could be assessed based on refined dynamic explicit nonlinear FE models; they were developed to simulate manufacturing processes and to obtain the plastic prestrain fields in the aforementioned kinds of structures - as expected both fields prove to be nonuniform. Finally, considering an idealized cyclic internal pressure loading, a MatLab dedicated algorithm was implemented to post process the plastic prestrain fields and the nonlinear model to predict fatigue crack growth rates until LBB condition takes place.