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Physics with Industry – website & flyer & poster invitation text
Where is the out-of-the-box thinking physicist, who dares to compete with a
2000 years old seemingly established industrial idea ?
DSM Dyneema (www.dyneema.com) is the manufacturer of Dyneema®, The World’s Strongest Fiber™.
This ultra-strong, superlight weight high tenacity fiber is made from UHMWPE resp. HMPE (ultrahigh
molecular weight polyethylene resp. high modulus polyethylene) .
With its tenacity of at least 3,5 N/tex, this synthetic fiber is on weight-to-weight basis fifteen times
stronger than steel with it’s typical tenacity of 0,2 N/tex only.
Therefore Dyneema® fiber is replacing steel since twenty years in weight critical applications such like
heavy marine mooring ropes for oil tankers, in armor panels for police cars and in heavy duty lifting
slings for offshore wind park installation, for example.
On its path to innovation, DSM Dyneema has defined a new ambitious project: replacement of heavy
steel link chains by synthetic link chains made with Dyneema® fiber. The world market for steel link
chains is about 3 Billion Euro large and still growing fast.
With our idea we dare to compete against heavy metal chains that were already used by the Romans.
On our way forward, together with our customer www.loadsolutions.no , we are already providing
synthetic link chains for heavy marine lashing tasks, that are up to six times lighter than the lightest steel
chains from the best steel grades available in the market.
But our ambition reaches further towards even more efficient, much smarter designed synthetic link
chains, that are up to ten times lighter than the best existing steel chains !
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For that huge step change , we need world class physicists like you to help us with your latest know how
in classical mechanics, in fluid – and hydro dynamics, material sciences and polymer physics, solid state
physics, aerodynamics, kinematics and 3D-finite element methods.
We seek a team of out-of-the-box thinkers, who know their theories of course, while being hands on,
street smart nerds with fine noses for feasible mass manufacturing technologies and commercial hearts !
We like to welcome you in our DSM Dyneema Technical Center Europe in Heerlen (The Netherlands) to
show you breathtaking experiments with our super fiber Dyneema®, while training and preparing you
for winning the Physics with Industry Contest 2014 in Leiden, The Netherlands !
Background
Dyneema® SK75 (and SK78) fibers have a tensile strength of about 3.4 GPa. This is as strong as the
strongest steel types. However, steel with such a strength is extremely hard and brittle and therefore
often unpractical. Dyneema® is still flexible and tough and highly useful. Moreover, the density of
Dyneema® is only 1/8 of that of steel. Thus the specific strength (also denoted as tenacity) of Dyneema®
is about 10 times that of steel. Dyneema® as well as steel are often used in cables. Cables are typical
tension members. An alternative tension member is a chain. The tenacity of chains is lower than that of
cables. Yet, chains are often preferred, because the chain links allow hooking-in all along the chain
length. This practical feature can be of large importance. Thus, recently Dyneema® is also used for
chains. Again, the chain tenacity is considerably lower than that of a cable. Improving the tenacity will
make the use of Dyneema® chains more attractive. Before discussing this problem in more detail, some
introduction to Dyneema® is useful, because material characteristics as well as geometrical conditions of
the final product may be important.
Introduction to Dyneema®
Dyneema® fibers are made from linear polyethylene molecules. Polyethylene is the most simple
polymer consisting of repeated CH2 grous. However, for this application the molecules are extremely
long, about 10 microns (for molecules this is giant), The gel-spinning process developed by DSM causes
aligning of these molecules along the fiber axis. Thus the fiber tensile strength is dominated by the
strength of those long molecules. Yet, the strength in other directions is low. Transverse, or compressive
loading of the fibers does not result in fracture, but in plastic deformation at low stress levels. So
Dyneema® is mechanically a very asymmetric material showing high tensile strength and stiffness, but
low strength and high ductility in all other loadings than tension. This behavior has consequences for
applications. The open access paper “Design with ultra strong polyethylene fibers”, can be downloaded
free at: http://www.scirp.org/journal/PaperDownload.aspx?paperID=4772&returnUrl=http%3a%2f% it
discusses the properties of Dyneema® and the consequences for applications in more detail.
Dyneema® chains
The tenacity of Dyneema® chains is about a factor 2 lower than the tenacity of the Dyneema® fibers.
Fracture is typically observed at the interface of two links. Thus it is assumed that the load transfer from
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link to link is sub optimal. The stress system at this location is very complex and will be far from optimal.
One reason for a strength reduction is that the inside of a link has a smaller length than the outside. Yet
the displacements are nominally identical, so the tensile strain and the resulting stress at the link inside
is higher and failure starts at this inner side. This problem has already been reduced by shaping the links
as Möbius rings. A Möbius ring has no real inner and outer side anymore. See the picture below:
Another improvement was to preload the chain at elevated temperature. The Dyneema® fibers show
increased creep at higher temperature and most creep occurs at the locations with the highest fiber
stress, thus relaxing the stress peaks and causing a more homogeneous stress distribution in the fibers.
And improving the strength.
Adding some textile material in-between of the links (so at the interface) also causes a small
improvement. However, at the penalty of adding non-load carrying mass and it is an elaborate handling
and production complication.
Combining wide thick links with narrower long links yields a structure where the critical narrow links are
in contact with a wider link at the interface, thus the stress concentration in the critical link is lower and
the effective strength is improved. However, production of such chains is very complicated, thus it is
hardly attractive.
In spite of the above mentioned improvements, the Dyneema® chains still show a tenacity of about half
the fiber tenacity. The obtained improvements support the hypothesis that the irregular stress
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distribution is an important factor. However, so far only the tensile stress distribution is considered. Yet,
the chain interface also comprises large contact stresses. These contact stresses are transverse to the
fiber axis and occur simultaneous to the tensile stresses. The influence of those contact stresses on the
tensile strength at simultaneous loading is unknown, nor is the contact stress distribution. It may be of
large importance or of no importance at all.
Summary of the problem
Dyneema® chains exploit about only half of the tenacity of the fibers. The hypothesis is that this is
related to a complex inhomogeneous stress distribution over the fibers at the link-link interfaces. Some
improvements were already obtained, but still a factor of 2 improvement could potentially be possible.
Technical measures resulting in a strength improvement towards that factor 2 are highly desired.
It should be noted that the above hypothesis stems from people responsible for designing the
Dyneema® synthetic chains. So there is a serious risk for a designer “tunnel vision”. The hypothesis is
inly supported by experimental evidence, but far from proven. Team members should not “blindly”
adopt this hypothesis and thus limit their view on possible solutions. Original solutions towards the
factor 2 improvement are highly appreciated.