All Positions

Research
Mechanics

Mechanics in additive manufactured structures under dynamic loadings

DC-42
ENSAM and UNSW
Bordeaux (France) and Canberra (Australia)

Proposed projects

Option 1

Bio-Inspiration: Effect of the density gradient on the mechanical behaviour of an architectural material under dynamic loadings

The development of new additive manufacturing processes has changed the way we consider process/microstructure/properties relationships of materials. Furthermore, the architectured structures obtained by additive manufacturing can be specifically designed to be used as energy absorbers in the case of an impact, shock or ballistic loading. The light-weighting of these structures, and their capability to dissipate energy are advantageous for the development of components for crashworthiness or other protective applications.
To conceive more efficient structures, it is possible to draw inspiration from nature. Over the millennia, lightweight natural structures have developed heterogeneous architectures to cope with quasi-static, cyclic or impact mechanical loading conditions. One of the features observed in many biological structures is the density gradient. Such feature has been shown to improve the mechanical properties of architectural structures. The aim of this project is to establish how a bioinspired density gradient affects energy absorption of such an engineered structure. There is a current lack of detailed understanding of the underlying strain mechanisms of biological and bio-inspired structures during mechanical loading and their dependence on strain and strain rate.
A methodology will be developed to (1) characterize the density gradient in biological structures using SEM and microtomography; (2) conceive and produce by metallic additive manufacturing architectured samples with a bioinspired density gradient; and (3) identify experimentally the mechanical behaviour of the architectured material at different strain rates with high-speed jack, Hopkinson bars and high-velocity gas gun. The final step of this study is to correlate and model the effect of the density gradient on the response of the 3D printed material to mechanical loading.

Option 2

Multiscale Architectural Materials: The Effect of Porosities on Mechanical behaviour under Dynamic Loadings

The development of new additive manufacturing processes has changed the way we consider process/microstructure/properties relationships of materials. Furthermore, the architectured structures obtained by additive manufacturing can be specifically designed to be used as energy absorbers in the case of an impact, shock or ballistic loading. The light-weighting of these structures, and their capability to dissipate energy are advantageous for the development of components for crashworthiness or other protective applications.
In the design of these new parts, the structure is alveolar, mainly to reduce the mass. The walls of these materials can also be considered as a cellular material due to the level of porosity introduced during the manufacturing process. It is therefore possible to obtain a multi-scale architectural material by additive manufacturing. The objective of this project is to study the influence of the porous multi-scale structure on the mechanical behaviour of these architectured materials under complex dynamic loading. The aim is to consider the macroscopic behaviour of the 3D printed geometry of the part obtained by SLM additive manufacturing but also that of its porous microstructure formed during the manufacturing process.
An experimental methodology has to be developed to (1) model and print porous architectured materials; (2) characterize their microstructure by SEM and multiscale microtomographic observations; and (3) identify experimentally the mechanical behaviour of the material at different strain rates with high speed jack, Hopkinson bars and high-velocity gas gun. The final step in this study will be to correlate and model the effect of porosities and architecture on the response of the 3D printed material.

Option 3

Methodology for characterising the mechanical behaviour of an architectural material under dynamic loadings

There have been relatively few studies on the behaviour of metallic architectured structures subjected to high strain rates. This is probably due to the challenges in understanding and modelling the damage mechanisms induced by dynamic loading. Further, the use of classical experimental apparatus in dynamics such as the Split Hopkinson Pressure Bar (SHPB) must be reconsidered for identifying the dynamic behaviour of these materials.
Hopkinson bars are a classical experimental apparatus for identifying the mechanical response of dense -metallic or polymeric- materials at high strain rates. This experimental SHPB setup has also been modified to study the behaviour of cellular materials with low impedances. In any case, the use of Hopkinson bars to identify the mechanical behaviour of a material under dynamic loading requires assumptions concerning wave propagation in the sample.
The SHPB assumptions cannot be verified in the case of architectured materials. During a dynamic compressive loading using Hopkinson bars, the propagation of waves, their multiple reflections in the structure of the material must be analyzed.
In this research project, it is proposed to model and develop Hopkinson bars adapted for the mechanical characterization of architectured materials. An experimental methodology coupled with numerical simulations is proposed to (1) design and print a representative metallic structure of an architectured material; (2) model and simulate its behaviour under propagation of waves during an SHPB test; and (3) improve the identification of the mechanical behaviour of architectured material by experimental/simulation comparison in using complementary observations by high-speed camera and digital image correlation techniques (DIC). The final step of this study is to validate the material behaviour identified with a high-velocity gas gun.

Research Areas

Mechanics, Materials