Project FitforAM - Design concept for additive manufacturing

30/11/2020

• Challenge
• Objectives
• Methods
• Partners

In the case of additive-manufactured components, inhomogeneities may occur. These can be caused by local and temporally varying energy input during the manufacturing process. As a result, the microstructure within an additive-manufactured component varies and with it its mechanical properties. Inhomogeneous material properties are difficult to map. It can be assumed that the mechanical characteristics obtained e.g. from accompanying samples are not representative for the critical points in the component.

A design concept for additive manufactured components shall be developed. This concept is to be based on a fracture-mechanical calculation of the locally achievable lifetime of the highest loaded area of a component. The approach shall allow a statement about the maximum defect sizes that are allowed at these locations.

A central task is the simulative calculation of the temperature history of components and a transfer to test piece geometries. The material characteristics are to be determined on specimens that represent the local temperature history of a component area. The IBESS method developed at BAM will be applied to additive specimens for the first time.

The FitForAM project is a BAM-funded project and is carried out in cooperation between the Division of Welding Technology and the Division of Welded Joint Integrity.

The challenge of component design

Additive-manufactured metallic components are increasingly used in industries such as aerospace and power engineering. However, due to the lack of design criteria up to now, their use has only been possible after a costly and time-consuming qualification process for each individual component. The broad use of additive-manufactured components is significantly hindered by this.

Mechanical properties can vary locally in the case of additively manufactured components. This can be caused by a local and temporally uneven energy input, the selected build-up strategy or different geometric characteristics. The microstructure, defects within the component and the resulting mechanical properties can vary locally. The inhomogeneity of the material properties cannot yet be adequately reproduced by accompanying test specimens. The resulting mechanical properties are sometimes not representative for the actual component.

Life cycle prediction using the IBESS method

The objective of the FitForAM project is to develop a design concept for additively manufactured components that is based on the fracture mechanics calculation of the component's lifetime. The basis is the material data of the areas classified as relevant to failure. This will be done specifically for the additive manufacturing process Selective Laser Melting (SLM) and the stainless material AISI 316L. The IBESS method developed at BAM will be applied for the first time to additive samples for the calculation of the lifetime. If the calculated lifetime under load is too low, the design can be adapted locally on the basis of the information thus obtained. Part of the approach is a statement about which maximum defect sizes are allowed at these locations. This provides an important target value for quality assurance by means of non-destructive testing.

Simulation of the temperature history for representative test specimens

The material characteristics are to be determined on samples that simulate the local temperature history of the damage-relevant areas. For this purpose, the simulative calculation of the temperature history of real components by means of Finite Element Method (FEM) and a transfer to test specimen geometries is planned. Due to the dimensions of real components and the local energy input, differences in scale arise, which represent a great challenge for an FEM calculation. Therefore a multi-scale approach is to be used. The validation of the calculated temperature curves shall be done by using thermography in the build-up process. BAM has already been able to gain experience in current projects.