When a customer reported that one of the three fixtures connecting an
instrument panel to a headlamp mounting unit had failed in service, CCM
Motorcycles brought in an analysis consultant to investigate the
possibility that the unit may have been subjected to an abnormally high
loading
Up until 1998, CCM specialised in competition motorcycles, but saw its
position eroded as lightweight engines were introduced into the
competition market. Now the company has established a range of Trail and
Supermoto models, based on its competition models, which are designed to
appeal to the fast growing on-road/off-road leisure market. But there
seemed to be a problem with the structural integrity of an instrument
panel mounting on the new models, which had been brought to CCM's notice
by one of its customers.
According to the customer, one of three fixtures that connect the
instrument panel to the headlamp mounting unit had failed in service.
CCM, convinced that it had got the design right and that the unit must
have been subjected to forces beyond the design specification, brought in
consultant, IDAC UK to investigate the issue. In order to prove that the
fixture had indeed been correctly designed and rated, CCM requested that
a full stress analysis be performed, to determine whether or not the unit
had been subjected to an abnormally high loading.
The stress analysis was performed by IDAC in Ansys finite element
analysis (FEA) simulation software. An axi-symmetric model was created
and subjected to two loading conditions, the first being a 'torquing-up'
of the connector to the 'as-assembled' condition, the second being the
application of the 'pull-out' load. The FE model comprised 2D
axi-symmetric solid elements and encompassed the connector and a finite
length of the instrument panel and headlamp housing, determined from
physical measurements of the assembly.
The first loading condition was the pre-loading (or torquing-up) of the
connector. To simulate this process, the bolt was modelled in two
separate pieces, the gap between the two being the axial length through
which the well-nut connector was torqued-up.
The torquing-up process itself consisted of a vertical displacement load
on the lower half of the bolt that brought the two halves into contact. A
bonded contact surface was described between the two halves of the bolt,
such that, when they came into contact, the bolt became one solid
component. The second loading condition was the application of the
pull-out load on the headlamp housing. This was modelled by applying a
vertical displacement load to the outer diameter of the headlamp housing.
The analysis tested the equivalent (or Von Mises) stress distribution at
the final pull-out load, which far exceeded the normal service load. Even
at this excessive pull-out load, the connector did not fail. As a result
of this analysis, CCM Motorcycles was able to show that its original
design was more than adequate and that it was indeed capable of
supporting a load far in excess of that which would be expected in normal
service.
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