Functionally graded materials (FGMs) gradually change composition throughout their volume, allowing for areas of a part to be optimized for specific performance requirements. While additive manufacturing (AM) process types such as material jetting and directed energy deposition are capable of creating FGMs, design guidelines for varying the material composition in an FGM do not exist. This article presents a novel design solution for FGMs: creating the material gradient by varying the mesostructural size and thickness of bicontinuous, multi-material geometries. By using a bicontinuous structure, such as Schoen's gyroid surface or Schwarz's P and D surfaces, each component material exists as a continuous discrete structure, which allows FGMs to be fabricated by a wider range of AM processes. The gradient is created by varying the volume fraction occupied by the surface structure inside the part volume. This article explores the use of this technique to create FGMs with material extrusion AM. Properties of these bicontinuous structures are experimentally characterized and shown to outperform typical material extrusion FGMs.

Purpose The continued improvement of additive manufacturing (AM) processing has led to increased part complexity and scale. Processes such as electron beam directed energy deposition (DED) are able to produce metal AM parts several meters in scale. These structures pose a challenge for current inspection techniques because of their large size and thickness. Typically, X-ray computed tomography is used to inspect AM components, but low source energies and small inspection volumes restrict the size of components that can be inspected. This paper aims to develop digital radiography (DR) as a method for inspecting multi-meter-sized AM components and a tool that optimizes the DR inspection process. Design/methodology/approach This tool, SMART DR, provides optimal orientations and the probability of detection for flaw sizes of interest. This information enables design changes to be made prior to manufacturing that improve the inspectabitity of the component and areas of interest. Findings Validation of SMART DR was performed using a 40-mm-thick stainless-steel blade produced by laser-based DED. An optimal orientation was automatically determined to allow radiographic inspection of a thickness of 40 mm with a 70% probability of detecting 0.5 mm diameter flaws. Radiography of the blade using the optimal orientation defined by SMART DR resulted in 0.5-mm diameter pores being detected and indicated good agreement between SMART DR’s predictions and the physical results. Originality/value This paper addresses the need for non-destructive inspection techniques specifically developed for AM components.