SAMPE Journal - March/April 2022 - 40
FEATURE / ADHESIVE-FREE THERMOPLASTIC SANDWICH PANELS
certain point of time and depends on the processing
parameters such as pressure, temperature and
time and material parameters such as viscosity and
surface roughness.
The second mechanism, healing, is referred to
diffusion of molecular chains across the contact
interface and based on the reptation theory
proposed by de Gennes6
. When two surfaces contact
each other at the temperature above the glass
transition or melting, the polymer chains diffuse
across the interface. Once the molecular chain
completely exits its original tube, the reptation
time is achieved and the interface becomes fully
healed (Figure 3).
Degree of healing is defined as ratio of the
autohesive strength at a certain point of time
to the cohesive strength, which represents the
maximum strength of material. It is governing by
the temperature and time.
Figure 3. Molecular movement based on reptation theory7
defined as proportion of the deformed core wall to
the width of the unit cell (Figure 4).
MANUFACTURING
Materials
In this research project, the thermoplastic polymer
Polycarbonate (PC) was used as core and skin
matrix material. In order to fulfill the flammability
requirements, the Polycarbonate was modified by
added halogen-free flame retardants.
The sandwich face sheet consists of two PC
fiber
glass
These two mechanisms occur simultaneously.
To define the effective degree of bonding, the
coupled model was developed4,8
. At any time t
during the fusion bonding, an additional intimate
contact surface,
The healing for this additional surface at the final
bonding time is defined as Dh
(tf-t), while tf
describes the healing time.
is created at interface.
-t
reinforced fabric
plies, which have
a satin textile weave. As core structure, the PC
honeycomb tubus core is used. For the purpose of
the recyclability, the same polymer for the core and
the skin matrix was applied.
Manufacturing Process
For the manufacturing of the thermoplastic monomaterial
sandwich structure, two approaches were
defined: isothermal and non-isothermal. The
process is called isothermal, when the heating
and bonding are performed simultaneously. Once
these two processes are separated, it is referred as a
non-isothermal case10
.
Core Flow Model
In order to investigate the bonging
of the thermoplastic sandwich
panel with the honeycomb core, the
core flow model was developed9
.
It describes the flow of the melted
honeycomb core material. Upon
applying pressure and heat, the
melted part of the core spreads over
the face sheet, thereby increasing
the degree of bonding.
The degree of intimate contact is
.
Figure 4. Schematic illustration of flow at skin-coreinterface
during molding9
.
40 | SAMPE JOURNAL | MARCH/APRIL 2022
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SAMPE Journal - March/April 2022
Table of Contents for the Digital Edition of SAMPE Journal - March/April 2022
Contents
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