3 PhDs in computational mechanics of composites and 3D printed materials @ Ghent University (Belgium)

The three PhD vacancies are part of a large research program “Macro-level predictive modeling, design & optimization of advanced lightweight material systems (MacroModelMat)", that is funded by the Flemish funding organization SIM (Strategic Initiative Materials – http://www.sim-flanders.be/). The coordinator of this research program is the company LMS (part of Siemens PLM Software –http://www.lmsintl.com/). There is also a strong interaction with the Catholic University of Leuven (KUL-MTM research group) and the Free University of Brussels (VUB-MeMC research group) in this program. Below, the content of the three PhD's is listed:

• 1 PhD on predictive simulation of structural composites under variable-amplitude multi-axial fatigue loading

  Fatigue damage in composite structures leads to stiffness degradation, and hence to stress redistribution during fatigue life. For correct evaluation of those stress redistributions, the simulation should be performed at discrete cycle numbers, where fatigue damage has progressed sufficiently to cause a change in load distribution. This progressive damage approach is feasible for small structures under uniaxial constant-amplitude fatigue loading, but is far more difficult under multi-axial variable amplitude loading. A methodology will be developed to simulate progressive fatigue damage in larger structures under multi-axial variable-amplitude fatigue loading, based on the cycle-jump approach developed earlier by UGent-MMS and the long term experience of LMS (part of Siemens PLM Software – http://www.lmsintl.com/). LMS also has pending patents in this area, which combine their hysteresis operators with the cycle jump approach developed by UGent-MMS. 
  Delamination is an important fatigue damage type that can be induced by accidental impact, and develop further under fatigue loading. This interlaminar damage type cannot be included in the meso-scale simulation of one single unit cell. A modeling framework will be developed to include delaminations into this scheme for progressive fatigue damage. Focus will be mainly on time adaptive integration schemes for predicting their growth under multi-axial variable-amplitude fatigue loading. In order to quantify and to increase the credibility in the numerical models being developed, model verification and validation through dedicated experiments is mandatory. The experiment should accurately reflect the real in-service conditions and should be carried out on specimens/subcomponents which are relevant for industry. During testing the specimen/subcomponent will be fully instrumented (strain gages, acoustic emission, digital image correlation, thermography ...) in order to monitor the effect of fatigue damage on the overall macroscopical mechanical performance (stiffness, strength and fatigue life). The expected outcome of this validation procedure is a quantified level of agreement between the obtained experimental data and the model prediction.

   

• 1 PhD on predictive simulation of crashworthiness of structural composites under impact loading

  Existing crash simulation tools are most often empirical and are generally applied on the full (homogenized) laminate level; they do not/cannot take into account stacking sequence, occurrence of multiple delaminations, or effect of strain rate. This PhD aims at the development of predictive crash simulation methods for composite plates and shells, designed to keep structural integrity. The main research questions address the possibility of extending current practices to the inclusion of extensive interply delaminations, and the possibilities of the combined use of refined and more detailed local (but yet “macro’) modelling of the areas being damaged, with rougher modelling of the (large) non-damaged areas. For the inclusion of interply delaminations, extensive use will be made of (zero thickness) cohesive elements, which are generated between consecutive plies. The research group has already been successful in doing so in smaller scale simulations. The appropriate stiffnesses of the cohesive elements (which are known to inevitably lower the global stiffness to some extent) will be determined, and appropriate damage laws (to simulate delaminations) in traction and in shear) will be set up. 
  In the macro-scale crash simulations, continuum damage mechanics (CDM) models will be used to predict the developing damage under impact loading in every single ply. In today's practice, the material constants in these CDM models are calibrated from impact experiments on coupon level. It will be investigated if the material constants can be calibrated from meso-scale simulations, predicting the development of impact damage at ply level. This approach would reduce the number of impact experiments to calibrate the models. Validation should finally apply to the macro-scale and cover both UD, NCF and textile composites. The PhD can build further on long-lasting experience with similar models at UGent and LMS (part of Siemens PLM Software –http://www.lmsintl.com/).

   

• 1 PhD on basic mechanical properties simulation of 3D printed lightweight materials through CAE

  "3D printing" is a popular term for the layerwise manufacturing of metals or polymers with a printing head, that builds up the component with droplets of molten polymer or metal into a 3D shape. The geometries that can be realized with this technique, can be very complex, and this with a minimum of material usage, because no material has to be milled away. Further, very lightweight materials can be achieved. Flanders region plays a leading role in Europe in this 3D printing sector, with important industrial players such as Materialise, Layerwise and Melotte. In this PhD project, UGent is working together with Materialise, the worldwide leader in software for 3D printing (http://www.materialise.com/), and with LMS (part of Siemens PLM Software –http://www.lmsintl.com/). The purpose is to develop finite element simulation tools for 3D printed lightweight structures. The focus will be on lattice structures, defined as cellular materials that are built up from a three-dimensional network of struts (as opposed to other cellular materials such as foams and honeycombs). The struts do not necessarily have to be straight, but can also have varying cross-sectional dimensions or can consist of several curved segments. These lattice structures can make up a whole component on their own, can be covered with a thin solid skin or can be integrated into solid parts to form a complete component. The lattice structures that are considered here have typically a few thousand to a few tens of thousands of lattices. The typical length of the lattices ranges from 1 mm to 10 mm. Cross-sections are typically circular with a diameter ranging from 0.2 to 3 mm. Because of the layerwise manufacturing, the elastic and strength properties of the individual struts are anisotropic, and the length axis of the struts is typically not aligned with the building direction. This makes the finite element modelling a big challenge, especially because detailed meshes with continuum elements will be computationally impossible for real-size lattice structures. The simulation of the (nonlinear) elastic response must be feasible for 3D printed parts with up to 100 000 individual lattices.

   

For all three PhD's, a profound background in computational mechanics is required. It is certainly an advantage if the candidate is familiar with the mechanics and typical damage phenomena of structural composites.

How to apply ?

• you write a detailed Curriculum Vitae in Dutch or English, containing:
  • your personal details (name, address, date of birth, nationality,...)
  • your education, subject of master thesis and degrees
  • your work experience (previous jobs)
  • additional skills (finite element software, programming languages, communication skills, ...)
  • mastered languages (Dutch, English, French)
  • references (previous projects in the domain, published papers,...)

     

• you send the C.V. by post or e-mail to the following person:
  Prof. Wim VAN PAEPEGEM
  Ghent University
  Mechanics of Materials and Structures
  Technologiepark-Zwijnaarde 903
  9052 Zwijnaarde
  Belgium
  Tel.: +32-(0)9-331.04.32
  Fax: +32-(0)9-264.58.33
  E-mail: Wim.VanPaepegem@UGent.be

Additional information ?

• Visit http://www.composites.ugent.be/PhD_job_vacancies_PhD_job_positions_composites.html for the full description of the vacancies
• More information on the achievements of the research group can be found on http://www.composites.ugent.be/.