An improved methodology to quantitatively assess fatigue lives of automotive structures and to identify critical and non-damaging areas for design enhancement and weight reduction is presented. The methodology of automated fatigue assessment, called CAE-FATIGUE (Computer Aided Engineering in Fatigue), combines a load-time history file with the result file from an elastic finite element analysis to estimate fatigue lives (damage contours). The CAE-FATIGUE methodology is of particular value when it is used as a proactive tool in the early design stage to reduce design iterations and prototype costs.
CAE-FATIGUE is applicable to elastic finite element analysis results because the Glinka energy density method (plasticity correction approach) is used to approximate true stresses and strains from the elastic stresses. CAE-FATIGUE cannot be applied to cases where loading frequency is of importance, since the elastic stress components from all loading channels are superimposed to the resultant stresses at the same specific time. CAE-FATIGUE calculates fatigue lives based on the maximum normal stress and strain range on a critical plane on which maximum principal stresses for the entire loading history are maximized. Also, CAE-FATIGUE can generate life/damage contour plots to identify critical and nondamaging areas for design enforcement and weight reduction.
This report focuses on practical aspects of designing automotive suspension components to avoid fatigue failure. The design process for a proposed front suspension knuckle is presented for illustration purposes. Critical planes highlighted with damage contours can also be used to develop “smart” and efficient prototype tests. Emphasis is placed on how to optimize the component to meet the durability criteria through mechanical life test procedure and test field endurance schedules.
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