JEC COMPOSITES MAGAZINE - Issue #113 - June 2017 - 62

TECHNOLOGY mechanics
isotropic damage theories and their coupling with plasticity
and other phenomena related to multiple physics (oxidation,
water absorption...).

mesh, and therefore easily integrated with industrial FE solvers, or on a NURBS description. This means that it can also
be easily integrated with CAD software programs.

With the growing performance of computers, simulating
more complex materials and structures became possible. A
hybrid micromodel describing explicitly each transverse
crack and delamination was developed in the late 2000s. The
objective was to set up a reference model that could replace
many tests on structural details in order to better understand
the degradation scenarios and their interactions, and thus
to improve and enrich the mesomodel. A dedicated numerical code was developed on the basis of the Latin multiscale
method for that purpose as standard finite element tools
were not powerful enough for such computations. A cluster
of 1000 cores is available at LMT for these types of computations.

The heart and the art of LMT
Comprehensive physics-based simulations need rich constitutive models and powerful numerical methods. Rich constitutive models require rich experimental data in term of
multi-axial loading and measurements. The main objective
of LMT is to develop fundamental research in these different
areas to handle industrial challenges. While numerical and
experimental developments have been conducted in parallel
for several decades, high-performance computing and fullfield measurements are now leading to more integrated approaches. A significant consequence is the new emphasis that
needs to be put on the "mechanical content" of each developed technique: this is the heart and the art of LMT.

Rich experiments for rich models
To provide material parameters for these models and validate these simulations, LMT developed strong knowledge in
experimental mechanics, focusing on two different aspects:
dedicated loading setups (uniaxial or multi-axial) and fullfield measurement techniques. While standard tests are well
suited for industrial needs, this is usually not the case for
research studies. Therefore, many dedicated setup and test
principles were developed or adapted to characterize composite materials. For example, the Climbing Drum Peel test
was recently adapted to study delamination propagation in
a CFRP under an oxidizing atmosphere, as this setup makes
it possible to fix the mechanical energy available for crack
propagation.

Last but not least, in 2019 the LMT, together with the ENS
Paris-Saclay, will move to a new building designed by the
Renzo Piano Building Workshop in Saclay to be fully integrated in Université Paris-Saclay. This huge educational and
research cluster (65,000 students, including 9000 preparing
a PhD and 9000 researchers) will reinforce the interactions
between different world-class research entities in France.

Unfortunately, uniaxial tests are generally not sufficient to
fully characterize complex materials such as CMCs. In 1990,
LMT and Schenck developed a tri-axial testing machine
called ASTREE. Using this machine, complex multi-axial
and non-proportional loading paths can be applied to dedicated coupons to study the influence of such loads on damage development and to identify damage models that take
into account coupled loads. It was the case for C/C for example, for which a 2D cross-shaped specimen was used in
conjunction with full-field digital image correlation (DIC).
Using this technique, it is possible to extract the displacement field of a coupon surface from optical observations, but
also of a specimen volume from tomographic 3D images. By
combining DIC with constitutive modelling, it is possible to
identify the model parameters within an integrated procedure. For this purpose, a tension-torsion mechanical testing
machine was developed to work in the tomograph recently
acquired by LMT. Note that, contrary to commercial DIC
software programs, the DIC technique developed at LMT
uses a global approach for the kinematic representation. In
particular, it can be based on an underlying finite element

jec composites magazine / No113 June 2017

More information:
www.lmt.ens-cachan.fr
References
Ladevèze, P., LeDantec, E. (1992). Damage modelling of the
elementary ply for laminated composites. Composites science and technology, 43(3), 257-267.
Abisset, E., Daghia, F., & Ladevèze, P. (2011). On the validation of a damage mesomodel for laminated composites
by means of open-hole tensile tests on quasi-isotropic laminates. Composites Part A: Applied Science and
Manufacturing, 42(10), 1515-1524.
Ladevèze, P., Lubineau, G., & Violeau, D. (2006). A computational damage micromodel of laminated composites.
International Journal of Fracture, 137(1), 139-150.
Périé, J. N., Calloch, S., Cluzel, C., & Hild, F. (2002). Analysis
of a multiaxial test on a C/C composite by using digital
image correlation and a damage model. Experimental
Mechanics, 42(3), 318-328.
Hild, F., & Roux, S. (2006). Digital image correlation: from
displacement measurement to identification of elastic properties - a review. Strain, 42(2), 69-80.
Dufour, J. E., Schneider, J., Hild, F., & Roux, S. (2016). IGMU:
A Geometrically Consistent Framework for Identification
from Full Field Measurement. In Residual Stress,
Thermomechanics & Infrared Imaging, Hybrid Techniques
and Inverse Problems, Volume 9 (pp. 17-21). Springer
International Publishing.

http://www.lmt.ens-cachan.fr

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