In our latest paper, soon to appear in a special issue of ASME Journal of Applied Mechanics dedicated to the mechanics of architectured materials, we present new results regarding the computational modelling of 3D auxetic lattices. ( https://doi.org/10.1115/1.4044542 )
These results have been obtained by Frédéric Albertini, in collaboration between PIMM and Monash University (Dr. Andrey Molotnikov).
The auxetic effect could lead to improved mechanical properties such as acoustic damping, indentation resistance, or crashworthiness. In this work, two 3D auxetic lattices are introduced. Auxeticity is achieved by design through pre-buckling of the lattice struts. The influence of geometrical parameters on the effective elastic properties is investigated using computational homogenization method with periodic boundary conditions. Effective Young’s modulus is 3D mapped to reveal anisotropy and identify spatial orientations of interest. The effective Poisson ratio is computed for various geometric configurations to characterize auxeticity. Finally, the influence of effective elastic properties on energy dissipation under compression is explored for elastoplastic lattices with different loading directions, using finite element simulations. Results suggest that loading 3D auxetic lattices along their stiffest direction maximizes their crashworthiness.
PhD scholarship in materials science available (36 months)
An ANR-funded scholarship is available at PIMM laboratory to work on the material architecturation of metallic sheets by localized laser treatment. The successful candidate should have obtained a Master’s degree (or equivalent) with a strong background in computational mechanics, materials science, mechanical engineering or any related field; although prior knowledge of the French language is not mandatory, spoken and written English proficiency is needed. See the file attached for more information: A4 advertisement
In the past year, a new materials engineering curriculum was designed and developed at Cnam in the Paris campus. This curriculum will be supervised by Justin Dirrenberger, starting in September 2018. The program is proposed within a 3-year fully co-operative education framework, combining classical academic teaching with on-hand professional experience. More information on this program can be found in the attached documents (in French).
I was recently invited to give a keynote lecture on architectured materials within the context of EDTAS Symposium on Advanced Materials and Manufacturing, organised by the Australian Defence Science & Technology Group and the University of Melbourne. The event was live-streamed on YouTube and my presentation can be seen on the following link: https://youtu.be/DPiwN5O40YQ?t=4h38m57s
Our new paper titled Design of Space Truss Based Insulating Walls for Robotic Fabrication in Concrete as part of the Humanizing Digital Reality book. Romain Duballet has been working on the on the design of ultra-light concrete walls for individual or collective housing, the normative context being constrained masonry. A robotic manufacturing technique based on mortar extrusion that allows producing more efficient walls is used. He made use of optimisation and genetic algorithms in order to design a structure optimised for robotic construction. Romain is also a founding member of XtreeE, a startup company specialised in developing large-scale 3D printing equipment.
Our new paper titled Classification of building systems for concrete 3D printing was just published in the journal Automation in Construction. Congratulations to Romain Duballet who has been working on a classification method for building systems making use of large-scale additive manufacturing. Our aim with this paper is to set a nomenclature and classification system that will be hopefully be adopted by the scientific community in the large-scale additive manufacturing field. The classification we propose also allows to determine the minimal robotic complexity necessary for a given application. Romain is also a founding member of XtreeE, a startup company specialised in developing large-scale 3D printing equipment.
Specific parameters are highlighted – concerning scale, environment, support, and assembly strategies – and a classification method is introduced in the paper. The objective is to explicitly characterise construction systems based on 3D printing processes. A cartography of the different approaches and subsequent robotic complexity is proposed. The state of the art gathered from the literature is mapped thanks to this classification. Here is a depiction of the variations associated with the external support parameter:
Our new paper titled Isogeometric shape optimization of smoothed petal auxetic structures via computational periodic homogenization was just published in Computer Methods in Applied Mechanics and Engineering. The aim of this research is to develop and apply isogeometric analysis to the shape optimization of 2D auxetic lattice materials. This work was lead by Zhen-Pei Wang, currently an associate researcher in the group of Prof. Leong Hien Poh at National University of Singapore. This is a collaboration between NUS, Mines-ParisTech, and our group in Paris.
On the figure hereafter, subfigure a depicts 3 different cases of shape optimization with a radius of curvature constraint; subfigure b shows the polar plot of the effective in-plane Poisson ratio; subfigure c is a plot of the convergence of negative Poisson’s ratio with respect to the iteration steps of the optimization scheme.
Our new paper titled Correlation of the high and very high cycle fatigue response of ferrite based steels with strain rate-temperature conditions is published in Acta Materialia. Congratulations to Noushin Torabian, who will defend her PhD in two weeks, and co-authors for an interesting take on very high cycle fatigue behaviour of dual-phase steel. The paper is available online here.
The following map, taken from the paper, depicts the transition between athermal regime and thermally-activated regime for screw dislocations, which are indicated as Region I and Region II, respectively. The solid line representing the transition boundary between these two deformation regimes was obtained from the empirical equation proposed by Rosenfield and Hahn (Trans. Am. Soc. Mater, 1966) for low carbon steels. These different regimes will be attained depending on testing parameter and variable such as loading frequency and temperature, hence explaining the discrepancies (or the lack of) in the response of body-centered cubic Fe-based materials between conventional and ultrasonic fatigue testing.
Justin Dirrenberger joins the newly created board of editors for the Springer Series in Adaptive Environments, which presents multidisciplinary research around spatial constructs and systems that are specifically designed to be adaptive to their surroundings and to their inhabitants. The creation and understanding of such adaptive Environments spans the expertise of multiple disciplines, from architecture to design, from materials to urban research, from wearable technologies to robotics, from data mining to machine learning and from sociology to psychology.