Legislation regarding greenhouse gases has increased the demand for lightweight materials within several industrial sectors. According to the European Commission [1], GreenHouse Gas (GHG) emissions must be reduced by 60% by the middle of the century to meet the long-term goals of the 2011 Transport White Paper. Since the 1990’s GHG emissions from road transport, international aviation and international shipping have increased by 23%, 129% and 32%, respectively.
Lightweighting is a widespread method for reducing vehicle mass with maintained performance, allowing a low emission mobility. A material solution with great lightweight potential is a sandwich material. By optimal material combinations, the best characteristic of each constituent is utilised, resulting in components with excellent properties. Traditionally, thicker sandwich panels have been used, offering poor formability. In recent years, more studies have investigated the so-called micro-sandwich for various applications.
Hybrix™ is an advanced multilayer lightweight material with good formability properties and a micro-structural core with several essential components. It has been shown that all the best in class manufacturers utilise CAE in the design phase to develop better products with accurate prediction failure and performance; see Formable Sandwich Material Hybrix™.
However, the accuracy of the CAE results is highly dependent on several key elements, e.g., input data in form of mechanical properties of the material, constitutive model, discretization grades and solver precision, etc. The case becomes more complicated when it comes to multi-layer material with a complex core.
A characterisation method combining X-ray microtomography and FE simulation shows promising results
A method for material characterisation of the core using high-resolution X-ray microtomography (XCT) in combination with the FE method [2][3] has shown a promising approach to be able to map the material’s complex mechanical properties.
This approach provides a detailed geometrical description of the microstructure of Hybrix™-core, and a digital twin will be generated, see Figure 1. With proper descriptions of the constituents of the micro-sandwich, the method allows for virtually evaluating product performance using Hybrix™ material without costly and time-consuming experiments, reducing the environmental footprint of the material.
Figure 1: Left: Conceptual image of the Hybrix™ and micro scanned core. Right: X-ray microtomography system at Lulea University of Technology
It is relevant to consider the complexity of the core geometry of the Hybrix™ material. To create a full-scale digital model, where the entire microstructure is discretised, is not feasible and time consuming. Instead, representative volume element (RVE) techniques [4] will be adopted. From a subset, i.e., Volume Element (VE), of the detailed geometry generated by the XCT, a detailed FE model will be generated, containing all micro-sandwich constituents; see Figure 2.
Figure 2: Generation of Artificial RVE for Hybrix™ material: RVE 2 mm x 2 mm x 2.5. A part of results from a German-Swedish R&D project. The picture illustrates the scanning results performed by Technische Hochschule Mittelhessen within a German-Swedish R&D project.
The numerical studying VEs of various sizes and in random locations, allows the investigation of spreading in mechanical characteristics and determination of effective properties[5][6]. Furthermore, it is possible to estimate the mechanical properties of the XCT-segment, estimate fibre orientation, modify the digital twin, and estimate the mechanical properties of the digital twin.
The method suggested gives a better understanding of the Hybrix™ micro-sandwich by providing a full description of the core, utilizing XCT scanning in combination with the FE method. Moreover, the method is not only limited to Hybrix™, but can be adopted to anisotropic materials in general.
References
[1] European Commission, “Communication from the commission to the european parliament, the council, the european economic and social committee and the committee of the regions”, 07/2016.
[2] M. Neikter et al., “Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography”, Aeronautics and Aerospace Open Access Journal, ISSN: 2576-4500, 2, 3, 139-145 (2018)
[3] P. S. Semsari et al., “Characterization of ore texture crack formation and liberation by quantitative analyses of spatial deformation”, Minerals Engineering, 157 (2020)
[4] Z. Liu et al., ”Multiscale simulations of material with heterogeneous structures based on representative volume element techniques”, 15th International LS-DYNA Users Conference.
[5] Hammarberg, et al., “Ultra high strength steel sandwich for lightweight applications,” SN Applied Sciences, vol. 2(6), (2020).
[6] Hammarberg, et al., “Numerical Evaluation of Lightweight Ultra High Strength Steel Sandwich,” SN Applied Sciences, accepted.
Dr. Ramin Moshfegh, CTO at Lamera AB (Sweden):
Ramin Moshfegh is CTO at Lamera AB since 2016. Skilled in Industrial Engineering, Sheet Metal Forming, CAE, Manufacturing Engineering, and technical sales support. He has a Doctor of Philosophy (Ph.D.) focused on Solid Mechanics from Linköping University, Sweden.
Email: ramin.moshfegh@lamera.se
View his LinkedIn profile
Jörgen Kajberg, Associate Professor, Luleå University of Technology (Sweden):
Email: Jorgen.kajberg@ltu.se
View his LinkedIn profile
