SAMPE Journal - March/April 2016 - 26
Feature Article
Within this first level of testing, tests at laminate
level were also envisaged mainly to characterise the
mechanical performance of the skin (i.e., lay-up of
±45 at 1.4 mm thickness). These included tension,
compression and compression after impact at Barely
Visible Impact Damage (BVID) level.
For the purposes of this research and development
programme only one environmental condition (i.e.,
room temperature dry - RTD) was considered and
only one batch of material was tested at all levels of
the building block approach. The limitations imposed
by this restriction were treated at the allowable
development phase by implementing a suitable
reduction of specific material properties, equivalent
to 60%. This was based on 80% knockdown for worst
environment conditions, 80% for material scatter
effect, 65% BVID strength reduction. Altogether these
factors result in a combined value of 41.6% of the
original allowable value, thus it was rounded to 40%.
Level 2 Testing
Level 2 testing was divided into (a) tests on critical
laminates, (b) tests on critical joints and (c) tests on
details and particular features of the design.
Test on critical laminates aimed to demonstrate
that the classical laminate theory will predict the
strength and stiffness of these laminates with input
from the material test programme and to provide
certification data for failure modes not predicted
by accepted analysis methods (i.e., strength after
impact damage, flaw growth from impact damage,
etc). For this programme the critical laminates were
considered to be the skin and the ribs. As most of the
skin (±45 laminate) and ribs (unidirectional laminate)
related properties were defined in the previous
block, the focus in Level 2 was on investigating the
performance of the actual ribs and correlating that
26
back to the manufacturing process. Besides critical
laminates, joints and splices must be shown to be
capable of carrying ultimate loads under applicable
environments. In this programme the micro-pin joints
for the floor attachment were found to be of critical
importance to the design of the structure and hence
they were tested to evaluate their adhesion to the
base laminate.
Critical details other than the joints included: (a)
the intersection of spiral and hoop ribs (with and
without skin attached - Type 1 & 2 components in
Figure 4); (b) the attachment frame details (with and
without skin attached - Type 3 & 4 components in
Figure 4). Representative loading (i.e., compressive)
was applied to these components and the resulting
strain field and load carrying ability were compared
to numerical analysis.
In particular, the deformation of Type 1 and Type 2
components at the point of failure is illustrated in the
photographs in Figure 5. For Type 1 components there
was significant out-plane deformation of the skin at
the edges of the component as well as in the middle
(upper triangular area) also indicated by the local
strain measurements. The measured deviation from
strain linearity above 20 kN was attributed solely to
the local buckling of the skin. The ribs continued to
carry load in a linear manner up to failure. The local
buckling of the skin had a detrimental effect on the
failure of the component. This could be described
as a combination of skin-to-ribs debonding and
local compressive failure of the ribs. The behaviour
of the Type 2 components was somehow different
as the omission of the skin led to the instability of
the ribs at a much lower load level. Deviation from
strain linearity occurred just after 10 kN and the ribs
continued to deform substantially prior to failing
locally in compression.
Figure 4. Geometry of the various types of critical components considered.
SAMPE Journal, Volume 52, No. 2, March/April 2016
Table of Contents for the Digital Edition of SAMPE Journal - March/April 2016
Contents
SAMPE Journal - March/April 2016 - Cover1
SAMPE Journal - March/April 2016 - Cover2
SAMPE Journal - March/April 2016 - Contents
SAMPE Journal - March/April 2016 - 2
SAMPE Journal - March/April 2016 - 3
SAMPE Journal - March/April 2016 - 4
SAMPE Journal - March/April 2016 - 5
SAMPE Journal - March/April 2016 - 6
SAMPE Journal - March/April 2016 - 7
SAMPE Journal - March/April 2016 - 8
SAMPE Journal - March/April 2016 - 9
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SAMPE Journal - March/April 2016 - Cover3
SAMPE Journal - March/April 2016 - Cover4
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