Structural validation of a pneumatic brake actuator using method for fatigue life calculation

In the field of structural integrity the accuracy of engineering judgment is bounded by the way the loadings are evaluated, the mathematical models are built and the material responses are idealized. In random vibration the loads are best described in terms of the PSDs (power spectrum density) of the variable exciting the system, whereas if the loads are deterministic the time domain based approaches are usually preferred. As the finite element (FE) Method is becoming the most popular tool for materials modeling, in structural dynamics the modal and harmonic analyses are the starting point for studying system properties and deriving transfer functions (FRF). The transfer functions are key to evaluating the spectral moments of Stress or Strain PSDs and building probability density functions (PDF) to evaluate damage. Dirlik's method has been very successful in modeling both narrow and broad band processes. Recent researches have endeavored to address residual and mean stresses in the frequency domain and cover the gaps in Dirlik’s approach. The present paper is mostly dedicated to provide further details on a particular method known as Tovo and Benasciutti method (T&B). A case study is presented where a brake chamber has been analyzed. The brake chamber has both functions of a brake pneumatic actuator and parking brake, therefore playing a vital role in Safety. The numerical results are compared with laboratory and field tests, where we had a life error of 43%, justified by the high complexity of modeling and calibration of the brake chamber assembly numerical model. The novelty of the method is the application of various numerical modeling techniques to achieve an acceptable experimental numerical correlation, using frequency domain fatigue, weld joint characterization, residual stresses and 3 materials involved in structural analysis, all with experimental calibrations to have an accurate numerical model