On prediction of residual stresses for additive manufacturing of Ti-6Al-4V

Brachetta, Vincenzo ORCID: 0009-0008-3553-0163 (2024). On prediction of residual stresses for additive manufacturing of Ti-6Al-4V. University of Birmingham. Ph.D.

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Abstract

The study of the mechanical performance of components produced via laser additive manufacturing presents several challenges. High thermal gradients lead to the formation of residual stresses, which can contribute significantly to the overall stress experienced by the components under service conditions, ultimately reducing their fatigue life. Drawing from the analogy between additive manufacturing and welding, a process model for Ti-6Al-4V based on finite element analysis has been explored. Using high-performance computing, it is possible to estimate the magnitude of residual stresses within the typical process window. The predicted residual stresses range from 300 to 1000 MPa for speeds between 200 and 1400 mm/s. The numerical studies indicate that they can be significantly reduced using a laser speed of approximately 800 mm/s, while the hatch spacing has minimal influence. Additional considerations and the experimental characterisation of the martensitic phase, a by-product of the process, are also discussed. The numerical results are validated using the Carlsson-Larsson theory, incorporating its most recent advancements, and by comparison with the existing literature. Lastly, a fatigue analysis incorporating residual stresses, surface roughness, and the width of martensitic laths is conducted, revealing a reduction in stress amplitude of approximately 200 MPa under very high load cycles.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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