Banca de QUALIFICAÇÃO: Natalia Gonçalves Torres

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : Natalia Gonçalves Torres
DATE: 17/07/2023
TIME: 09:30
LOCAL: Plataforma Microsoft Teams
TITLE:

INFLUENCE OF DEFECTS BY INDENTATION ON THE FATIGUE LIFE OF AL7075-T6511 ALUMINUM ALLOY

KEY WORDS:

fatigue life, small defects, indentation, 7075-T6511 aluminum alloy, mean stress.

PAGES: 67
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

This work investigates the fatigue life of aluminum alloy 7075-T6511 in the presence of small indentation defects. The defects measure 650 micrometers in diameter and 40 micrometers in depth and were produced with a Brinell hardness testing machine. Uniaxial – fully reversed, R = -1, and with load ratio R = 0.1 – and fully reversed torsional fatigue tests were conducted. The aluminum alloy presented significant life reductions in the presence of defects: when subjected to a stress amplitude of 240 MPa (less than half of the yield stress), for instance, the observed life of the indented specimen was 30 times smaller than the life of the smooth one, under a completely reversed loading program. When the specimens were subjected to mean stresses, the same pattern of life reduction was observed in the presence of indentation defects. In the case of torsional tests, the presence of indentation caused a reduction in fatigue life of up to 55 times, when compared with the results obtained for smooth specimens. In order to understand the stress distribution around the indentation defect, an elastoplastic finite element analysis was performed, in which indentation and loading cycles were simulated. In the simulation, the indentation process generated tensile residual stresses with magnitudes up to 300 MPa and compressive stresses of up to 545 MPa at the edge and at the region under the indentation defect, respectively. After the first loading cycle, the numerical simulation exhibited a significant reduction of the residual stresses, leading to elastic cycles along the subsequent loading cycles. The remaining tensile residual stresses, together with the stress concentration due to the geometry of the indentation defect, can be correlated with the significant reduction in the fatigue life. The SWT parameter was preliminarily used to estimate the fatigue life of the material from the numerically simulated local stress field around the defect, producing a very satisfactory life estimate from a stress-life curve obtained with smooth specimens under completely reversed axial loading programs. On the other hand, this fatigue parameter did not perform well to estimate fatigue lives under torsional loading programs, and hence other fatigue parameters should be investigated.

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