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Design methodology of vessel produced by L PBF stainless steel using representative specimens
(2022)
This work presents the preliminary results of an ongoing project with a double objective: on the one hand, the characterisation of the mechanical properties against fatigue damage of an additively manufactured 316 stainless steel produced by laser powder bed-based (L-PBF) technology; on the other hand, the implementation of numerical simulation techniques able to predict the mechanical behaviour of the material in order to optimise and reduce the design costs of vessels used in the chemical sector. The current state of the work developed in this research framework allows showing the first batch of experimental results of crack propagation rate (FCGR) and high cycle fatigue (HCF) tests. The geometry of the vessels studied presents three clearly differentiated regions, either in terms of thickness (11-15 mm) or concerning the inclination of the walls to the direction of manufacturing (0º - 45º). The experimental campaign carried out so far allows identifying the differences in behaviour when comparing different extraction locations around the vessel. This is due to the variations in thermal cycles that the deposited material undergoes during the manufacturing process. Therefore, this causes variations in the microstructure which lead to changes in the response of the material. In this work, these differences are analysed qualitatively and quantitatively from the results of FCGR and HCF, thus allowing to locate the regions with the highest risk in terms of structural integrity against fatigue. This preliminary phase together with the numerical simulation of the additive manufacturing process are key to achieving a reliable description and modelling of the material. The latter will make it possible to address the priority aim of this project, involving the manufacture of independent samples whose properties are representative of the original material extracted from the reference vessels. It is, therefore, a comprehensive methodology for the design of additively manufactured components based on the localised fatigue mechanical properties of representative specimens.
The presentation provides a discussion and damage tolerant assessment of metallic AM components. In the focus are problems of the determination of representative material data, the effect of material defects and residual stresses. Starting with the actual state-of-the-art in the field, options and possibilities of a damage tolerant design for AM are discussed.
The Topic of the presentationis a discussion on defects which can cause failure in cyclically loaded metallic components. Although also touching Features such as material defects such as pores or micro-shrinkages, etc. and geometric defects such as surface roughness and secondary notches (which are not considered in the design process) which origin in manufacturing, and others the presentation concentrates on non-metallic inclusions. It is prefaced by an introduction to the life cycle of a fatigue crack from initiation up to fracture. Special emphasis is put on the fact that only cracks which are not arrested during one of their distinct Propagation stages can grow to a critical size.