State of the art of fatigue strength of materials & structures from additive manufacturing – The pivot, A CETIM development.

Abstract

Additive manufacturing is a subject at the heart of innovation in many fields of mechanics. It allows, through different techniques, to produce increasingly complex parts. It also offers greater design freedom, often with shorter times than conventional manufacturing. These techniques having a multitude of parameters and finishing methods, Cetim wishes to study their influence on fatigue resistance through tests on standardized samples and on mechanical parts.The pivot is an example of study part developed at CETIM. It is at the crossroads of technical art and technological developments. This part, resulting from a mechanical assembly of cable reels for industry, has been specially developed for additive manufacturing. It incorporates all the constraints and advantages of current technology. This part is stressed in fatigue during operation in combined rotations. It is subjected to alternating loads linked to centrifugal forces.The design optimizes the constraints and design opportunities linked to additive manufacturing (topological optimization, supports optimizations). It also integrates metallurgical considerations and geometric constraints necessary for the finish. A specific range of surface finishes was produced for this part, driven by the reduction of two key roughness values, the Ra and Rz of the surfaces.The validation of the mechanical properties was carried out on several production batches characterize the alloy behavior (metallurgically, mechanically and in fatigue). The parameters obtained during the first test phase (static and Manson-coffin) were incorporated into the simulations and dimensioning of the fatigue tests of the part. The pivot had several metrological checks with no-contact methods (tomography, scan, CMM, etc.) to check the dimensions and whether any defect was present. Then, the part was placed under a test bench to validate its mechanical performance and industrial expectations.This study therefore proposes a direct correlation between the difficulties linked to the development of parts of additivemanufacturing structures. The various technical problems from the microstructure to the structure of the part were removed step by step.