Design and Structural Optimization in Additive Manufacturing - From Isotropy to Anisotropy

Lead Research Organisation: Imperial College London
Department Name: Dept of Aeronautics

Abstract

This research aims to investigate ways to combine design and structural optimization with anisotropic considerations for additive manufacturing (AM) of lightweight parts with minimized compliance.
The scope of this PhD encompassed two major themes: numerical analyses and computational modelling as well as experimental testing and manufacturing. The following three objectives will be the subject of this work:

Objective 1: Isotropic topology with orthotropic reinforcement derived from medial axis transformation (MAT)
-Content/Numerical Approach: It is envisaged to develop a novel method which combines continuous fibre reinforcement (C-FR) i.e. an effective fibre trajectory planning with topology optimization in an iterative process under the consideration of AM-specific manufacturing constraints. Preliminary investigations and methods on this topic have been published recently (SFF Symp 2018)
-Experimental Verification: In order to fabricate these novel AM-designs with tailored fibre paths, a custom multi-material 3D printer enabling fibre reinforced AM (FRAM) was developed and will be further improved.
-Potential Applications and Value: This novel approach aims to enhance the performance of AM-parts in terms of stiffness and weight, making them more viable for a wider range of industries. Besides this development towards end-use parts, we seek to gain valuable findings that help streamline the product and development cycles for engineers and designers employing AM processes.
Objective 2: Multiscale modelling of mixed architectures with representative volume elements (RVEs) realizing light multifunctional AM-parts
-Content/Numerical Approach: This objective aims to develop bio-inspired, light, stiff and robust sandwich structures for AM (see Figure 1). The development of a method which effectively combines topology optimization, C-FR and functionally graded cellular structures will be hereby pursued. From a computational point of view this will include multiscale modelling with dissimilar architectures using RVEs to replicate heterogeneous material characteristics.
-Experimental Verification: It is envisaged to employ the above-mentioned custom 3D printer. For the evaluation of the robustness it is intended to conduct for variable loading scenarios.
-Potential Applications and Value: This objective aims to combine the two topics in structural optimization for AM which are currently undergoing intense study, namely topology optimization and the employment of cellular structures. This enables the realization of multi-objective structures for AM, which combine e.g. stiffness and strength (fibre reinforced shell) with improved thermal conduction or impact resistance (cellular structure). Possible application can be found in the automotive, the medical engineering and the aerospace sector.
Objective 3: Mapping functionally graded lattices to specific mechanical performance
-Content/Numerical Approach: The actively researched topic of functionally graded lattices exploits the inherent design freedom of AM for tailored and locally varying material properties. However, in polymer-based AM, certain microstructural grading schemes have not been thoroughly studied yet. For this purpose multiscale modelling approaches using RVEs will be developed helping for a better understanding of these materials and aiding their wider application and adoption.
-Experimental Verification: Among others, our custom multi-material 3D will be employed to manufacture advanced microstructurally and compositionally grading cellular structures. Mechanical tests shall help optimizing the computational model.
-Potential Applications and Value: These findings will help different industries, which are increasingly adopting cellular structures for the design of their products, to better predict and understand the mechanical characteristics of different cell topologies and therefore enable them to fabricate more efficient structures.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 30/09/2021
2091639 Studentship EP/N509486/1 01/11/2017 30/04/2021 Janos Plocher
 
Description Generally, the work covers design and structural optimisation for additive manufacturing of lightweight structures. Firstly, the state-of-the art lightweighting strategies (latticing and topology optimisation) were analysed in an extensive review from an academic and industrial standpoint, highlighting their capabilities and potential for shaping the new era of manufacturing (industry 4.0) and design. Moreover, the work discovered current shortcomings, identified future trajectories worth exploring in additive manufacturing and hence constitutes pivotal groundwork for future research. Secondly and more specifically, the work provides novel insight into the manufacturing and performance of fibre-reinforced structures. This includes the first ever investigation into the properties of functionally graded fibre-reinforced lattice structures, delivering valuable information for engineers how the severity of grading, cell type and build direction affect stiffness, energy absorption, structural response, etc. which will ease the design choices for lightweight multi-functional parts in the future and harness the potential of additive manufacturing. This includes a research outcome related to additively manufactured nature-inspired structures shedding light on the prospect for parts with a structural and functional purpose. At last, together with an investigation into topology optimisation with orthotropic considerations and a novel manufacturing strategy for fibre-reinforced materials in conjunction with manufacturing rules and guidelines, this research has successfully shown how to further reduce the weight of e.g. automotive, aerospace or consumer parts while maintaining or even improving their performance, which can result in more sustainable products due to substantial savings in energy and resources.
Exploitation Route These findings serve a wide range of industries employing additive manufacturing by:
1. Helping to improve today's manufacturing strategies, to increase part performance
2. Enhance current software solutions for additive manufacturing, especially for applications with cellular structures and material orthotropy
3. Informing about manufacturing rules and guideline vital for efficient design with fibre-reinforcement and lattices
4. Work can be advanced towards a full-fleshed slicing software for gcode generation
5. Theoretical material models can be established based on the experimental data
Sectors Aerospace, Defence and Marine,Education,Transport

URL https://scholar.google.com/citations?user=W8pi7-AAAAAJ&hl=de
 
Title Data set on the software landscape of today's topology optimization and latticing tools and their capabilities 
Description The supplementary data provided with our open access review article on "Review on design and structural optimisation in additive manufacturing: Towards next-generation lightweight structures" provides a unique summary of the specific software used for additive manufacturing making use of topology optimization and latticing. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact This research has sparked interest in industry (contact and interest was expressed through first contact) as it provides a comprehensive comparison of capabilities 
URL https://doi.org/10.1016/j.matdes.2019.108164
 
Title Experimental data set of a variety of short-fibre reinforced functionally graded lattices with dissimilar relative density, density and unit cell size gradation 
Description In the context of the work on functionally graded lattices (FGLs), we have established an extensive data-set revealing the effect of the severity of both density and unit cell size grading as well as build direction on the stiffness, energy absorption and structural response of fibre-reinforced FGLs. The data-set allowed us to derive semi-empirical functions that predict the energy absorption capability as a function of the severity of grading and unit cell type. Thus we were able to categorize of the performance of FGLs with respect to other engineering materials and with regards, as proposed by Gibson-Ashby models. This insights will better harness the potential additive manufacturing has on offer for functional lightweight structures and guide engineers towards more informed design decisions for future manufacturing. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact This experimental research constitutes the basis for validating the computational finite element models and serves as baseline for subsequent studies. As a consequence international companies like Mantis Composites (http://www.mantiscomposites.com/) got in touch for potential collaborations, elucidating the impact and interest in industry. 
 
Description "The future of additive manufacturing" with the Institute for Molecular Science and Engineering 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Contribution of a poster showcasing my research activities in the context of my PhD and engaging in discussions with attendees on related subjects.
Year(s) Of Engagement Activity 2017
URL https://www.imperial.ac.uk/news/183592/the-future-additive-manufacturing/
 
Description Composites Research Showcase Event of the Department of Aeronautics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Contributed a poster with my current research topics and outcomes to spark interest in the industry for additive manufacturing of composite materials and to engage in disucussion with my colleagues about my research.
Year(s) Of Engagement Activity 2018
URL http://www.imperial.ac.uk/composites-centre/research-showcase-event/