JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014 - 48

damage

Damage modelling of composites: validation
of an interlaminar damage model at the element
level in an industrial application
In this paper, the LMS Samtech Samcef finite
element code is used to assess the damage
tolerance of composite structures. Delamination (ply separation), which is one of the most
dangerous and predominant failure modes in
laminated composites, is addressed. Two methods are used. The first one is based on a pure
fracture mechanics approach, namely VCE (virtual crack extension), while the second method
relies on cohesive elements and on continuum
damage mechanics. These methods are implemented in the commercial version of LMS
Samtech Samcef . This means that, besides the
commercial FE solver, no additional (and costly)
plug-ins providing such capabilities are required
to solve the problem. Another advantage is that
the user does not have to implement academic
methods or models that may be described in the
literature. Even if the openness of LMS Samtech
Samcef is available via material user routines, a
native implementation in a commercial software
program always provides a more reliable solution.

igure 1 illustrates the damage in a laminated structure
resulting from an impact at different energy levels. When
the impact energy is low, that is for a quasi-static loading,
flaws (and especially delaminations) appear inside the part but
this damage is invisible (or barely visible) from the outside.
Although the user is not aware of it, initial damage is present
in the structure. As such an initial damage will penalize the
mechanical performance of the composite material, it must be
taken into account in the design of the part. This situation is
studied here.
In this paper, the authors assess the dangerousness of initial
interlaminar cracks and predict the non-linear mechanical response and the propagation of delamination in a composite part
submitted to a quasi-static loading and including initial defects.

Fig. 1: Flaws in an impacted laminated composite structure

Here, we concentrate on the element level of the pyramid of
tests illustrated in Figure 2. Additional validations of the LMS
Samtech Samcef damage laws for damage tolerance of composites at the coupon and component levels can be found in [1-4].

By
Michael Bruyneel, R&D Team Manager (1) & Lecturer (2),
Jean-Pierre Delsemme, Product Manager (1),
Philippe Jetteur, Scientific Advisor (1),
Fabrice Germain, Team leader, Engineering Services (1),
Nourrédine Boudjemaa, Composite Material Stress Analysis Expert (3)
(1) SAMTECH s.a.
(2) Aerospace and Mechanical Engineering Department,
University of Liège
(3) LATECOERE

48 jec composites magazine / No90 June - July 2014

Fig. 2: Building block approach including the composite structure and virtual and
experimental material testing. With courtesy of Airbus Innovations Works.

JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014