Eventos Anais de eventos
CONEM 2018
X Congresso Nacional de Engenharia Mecânica
A numerical study on fatigue life predictions based on nominal and local approaches
Submission Author:
Luiz Carlos de Andrade Ribeiro Junior , RJ , Brazil
Co-Authors:
Luiz Carlos de Andrade Ribeiro Junior, Jorge Alberto Rodriguez Duran
Presenter: Luiz Carlos de Andrade Ribeiro Junior
doi://10.26678/ABCM.CONEM2018.CON18-0461
Abstract
The aim of the present paper is to highlight the advantages of the local strain-based approach sN for fatigue assessment of notched components over the more traditional stress-based approach σN . A brief theoretical explanation is followed by a comparison between the predicted fatigue life for these two approaches for a group of 60 ductile structural steels under uni-axial constant stress amplitude. Hypothetical notched parts with different stress concentration factors SCFs in the range of 1.5 to 4.0 were used. The minimum to maximum load ratio R was kept constant and equal to 0.1. In order to focus the comparison on the local stress-strain analysis, the simulation was limited to the nominal elastic regime where both methods use the same fatigue strength curve. With this aim, the σan to σo ratio remained between 0.1 and 0.4. Also, the same function to account for the mean stress effects was incorporated in both approaches in such a way that fatigue strength curves for different mean loads were collapsed, for a given stress ratio (normally R = 1), towards the σan direction. The results are expressed in universal graphs with the σan/σo ratio in the abscissa and the Nf ratio in the ordinates. The Nf ratio is defined as the quotient between the Nf predictions according to the σN and sN approaches, considering the average values for the group of 60 structural steels in each load level. For low SCFs the Nf ratio has a trend to fall below the unity as the load level increases. This trend also remains for high SCFs until a σan/σo ratio around 0.3 but reverses for high load levels. Both scenarios result from the improved local stress-strain analysis performed under the strain-based approach and confirm its advantages for fatigue life assessment.
Keywords
fatigue strain-based approach, strain-life curves, elastic-plastic stress-strain analysis
