JEC COMPOSITES MAGAZINE - Issue #93 - December 2014 - 55

substrate, the temperature rises, melting the polymer material and
deforming the rivet head as it becomes anchored in the polymer.
Overmoulding
Macroscopic texturing processes are under development to improve shear strength at the interface of a metal part that is overmoulded with a polymer. Surfi-SculptTM is a surface treatment
developed by The Welding Institute (TWI) in 2004. The treatment
consists in bombarding a surface with an electron gun to create a
good bonding surface, then overmoulding with the polymer matrix
(ComeldTM process).

Fig.6: Screw assemblies

"intelligent" screwing system (fig 6).
The fasteners can be optimized through a controlled increase of the
friction coefficients (texturing, dedicated coatings) at the interfaces
of the parts to be joined; the minimum prestressing force required
for a screw assembly (for example), will decrease.
For non-structural assemblies, developments are under way to
apply the mechanical assemblies without predrilling that are used
in the automotive industry to metal-metal joints. Here is a nonexhaustive list of these:
- Self-pierce riveting without pre-drilling is being developed by
suppliers of automotive fasteners for metal/composite joining.
- Friction riveting (developed by S. Amancio [4] and patented in
2005 by HZG), which consists in pushing a rotating rivet through
a pre-drilled metal plate. When the rivet penetrates the polymer

Fig.7: Designed using Abaqus FEA software

There is also:
- texturing using a cold metal transfer (CMT) process (arc welding) to create extrusions on a stainless steel surface before overmoulding (Ucsnik, 2010[5]);
- the Teufelberger process, involving positioning pins on the metal
part, then overmoulding using RTM (T-IGEL Process).

Scale 1 demonstrators
Composite lifting jibs
As part of an Cetim in-house project, a Scale 1 demonstrator was
developed and prevalidated in cooperation with Terex Cranes
France. A crane can have up to 3-4 telescopic elements, at the end
of which the user has the option of adding another one or two
extensions. The goal of the project was to reduce the weight of the
jib's top-most element by shifting from steel to a composite material.
The composite jib and the bolted/adhesive-bonded assemblies
were designed using Abaqus FEA software to meet the criteria for
the composite's torsional and bending stiffness, deformation (or
deflection), buckling and damage (fig 7).
The chosen solution was an infused carbon/
epoxy matrix material, with unidirectional
(for bending stiffness) and +/- 45° (for
torsional stiffness) orientations, which made
it possible to reduce the weight from 150 kg
(steel solution) to about 90 kg. To create the
prototype, three preforms were used for the
part: a U-shaped one, a UD insert, and then a
second U-shaped one. Co-injection was used
to assemble these elements, producing a part
of constant thickness around the perimeter.
Full-scale tests were conducted to validate the
calculations (among others). The tests consisted of attaching the composite jib directly
on the end of a telescopic crane boom and
measuring the displacement under load. A
contactless measuring method was used with
a survey-type sighting technique, and the jib
was equipped with acoustic emission sensors
to enable monitoring (NDT department -
Cetim-Senlis).
No93 December 2014 /

jec composites magazine 55

JEC COMPOSITES MAGAZINE - Issue #93 - December 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #93 - December 2014