Assessment of Fatigue Life of 3D-Printed Aluminum Components in Automotive Brakes under Real Driving Conditions

Thesis Abstract

The rapid adoption of additive manufacturing for brake components promises weight reduction and design freedom but raises concerns about fatigue performance under real driving conditions, where variable loads, thermal cycles, and environmental factors interact to influence component longevity. This study addresses the gap in empirically validated fatigue life data for 3D-printed aluminum brake components operated in authentic vehicle duty cycles. The aim is to quantify fatigue life and identify dominant factors governing failure under real-world usage, with objectives to (i) characterize the microstructural features arising from selective laser melting (SLM) of A356 aluminum alloy used in caliper and bracket geometries, (ii) assess the fatigue behavior under representative driving profiles, (iii) develop a predictive fatigue life model incorporating printing parameters, surface finishing, residual stress, and in-service thermal exposure, and (iv) propose design and process recommendations to enhance reliability. A mixed-methods, empirical field-lidelity approach is employed. The population comprises 3D-printed aluminum brake components produced via standardized SLM procedures and installed on instrumented test vehicles that traverse urban, highway, and mixed-duty routes. A stratified sampling scheme yields 60 specimens distributed across three component geometries (caliper brackets, adaptors, and mounting plates) and five printing parameter sets (build orientation, laser power, scan speed, hatch spacing, and post-processing) to capture variability. Data collection integrates non-destructive evaluation (NDE) and in-service monitoring (i) laser-ultrasound and X-ray computed tomography to quantify porosity, microvoids, and residual stress; (ii) strain gauges and brake torque sensors to log cyclic loading and thermal profiles over a 20,000-km field trial; (iii) accelerated fatigue tests on a servo-hydrostatic test rig with stochastic loading sequences derived from the collected in-service profiles, supplemented by thermography to map thermal transients. Anisotropy and defect-sensitive statistical analyses guide the interpretation of fatigue behavior. Analytical methods include reliability-based regression modeling and survival analysis to estimate Wöhler (S-N) curves under variable amplitude loading, with a multi-factor ANOVA to assess the influence of printing parameters, surface finish, and thermal exposure. Finite element analysis (FEA) with cohesive zone modeling evaluates crack initiation and propagation paths, incorporating measured residual stresses as boundary conditions. A Bayesian updating framework integrates field data with laboratory results to refine fatigue life predictions and quantify uncertainty. The study tests hypotheses that (H1) print orientation and porosity significantly affect high-cycle fatigue life, (H2) thermal cycling during braking reduces endurance limits due to residual stress interactions, and (H3) predictive models incorporating post-processing improvements (peening, HIP, and surface finishing) significantly extend service life compared to baseline specimens. Expected findings indicate that 3D-printed components display distinct S-N behavior with lower fatigue limits in specimens exhibiting higher porosity and tensile residual stresses, but achieving comparable performance to wrought counterparts through optimized post-processing and orientation. The integrated model is anticipated to predict fatigue life within ±15% accuracy for 95% of anticipated service scenarios, with thermal exposure identified as a critical modifier of crack initiation resistance. The contribution to knowledge lies in providing the first comprehensive, field-validated fatigue life framework for additively manufactured brake components subjected to authentic driving loads, bridging the gap between lab-based testing and real-world performance, and offering design-for-fatigue guidelines and process controls for industry adoption. The study concludes that carefully controlled printing parameters, rigorous post-processing, and fabrication-aware design substantially mitigate fatigue risk, enabling safer deployment of 3D-printed aluminum brake components. Recommendations include standardized field-data collection protocols, incorporation of residual-stress-aware design libraries, and industry-ready validation campaigns to extend the approach to other critical braking parts and aluminum alloys.