Metaklett-steel grips, Biomimicry and Shape Memory Alloy meanders

One rarely gets a chance, when talking of innovations in the very mature steel industry, to slip in such recent fields such as:

A. Biomimicry, ‘Learning from Nature’, whereby scientific and engineering innovations are inspired by performances and functionalities observed in Nature, its models, systems, processes, and elements— and emulates them to solve human problems and meet human requirements.

B. Shape Memory Alloys the metallurgists contribution to the overall field of so called ‘intelligent or smart materials’ and


This opportunity, rife with menace, arose and matured following the public announcement on 3-Sep-2009 by the Technical University of Munich, (TUM.) of their new clip and close, pull and open, hook and loop fastener steel strips. The news was rapidly up-taken by several of the main science magazines cf. Acknowledgements below.

The new invention, called "Metaklett", uses the same hook-and-loop fastening system as Velcro but can support loads of up to 35 tonnes per square metre at temperatures as high as 1,472F (800C) thus earning the coined denomination of Steel 'Velcro®'.

Like the popular fabric fastener, Metaklett is designed to be peeled apart and reused, making it a potentially useful and cost-effective engineering component.

Strips of the 'super-strength adhesive' are just 0.2mm thick, with the delicate steel hooks capable of attaching themselves to the loops at almost any angle.

The fastener has been developed by a team at the Institute of Metal Forming and Casting at TUM.

“The unbeatable advantage of a hook and loop fastener is that it is easy to close and open again, and just like everyday 'Velcro® like materials, it can be opened up without specialised tools and used again." reports Josef Mair, a scientist at the Institute,

In addition to bearing heavier loads, the invention has advantages over synthetic fasteners in that it can withstand both high temperatures and corrosive chemicals, claim the research team.

[Effectively high-temperature and corrosion resistance coupled with workability,and cost effectiveness of a mature industry are just a few of the very important properties only currently found in steels and alloys.-JA]

“Things can get very hot, for example, in the automotive sector. A car parked in direct sunlight can reach temperatures of 80 °C, and temperatures of several hundred degrees centigrade can arise around the exhaust manifold," quoting Mair. [still not the upper limit of 800°C or red hot-JA]

"Aggressive disinfectants are used for cleaning purposes in hospitals, and traditional hook, and loop fasteners are too weak for use in the construction of building façades. Metaklett has been developed for use in car construction and air-conditioning systems, but its creators claim that it could be turned to any number of applications.

These fasteners are resistant to chemicals and can withstand a tensile load of up to 35 tonnes per square meter, their mechanical advantage-(cf.definition on Wikipedia) at temperatures as high as 800°C. [from memory that's red hot!-JA ]

BIOMIMICRY:

Biomimicry’s most famous example which incidentally helps date contemporary biomimicry science:

A fairly good account of the Velcro biomimicry invention may be found on Wikipedia search Velcro History. cf. also "How a Swiss invention hooked the world" on swissinfo,by Thomas Stephens.

In 1941, not in 1948 as is often quoted. apparently, de Mistrals was inspired to create the hook and loop fastener after taking his dog out for a walk. Upon returning home from the walk, he noticed that his dog and his pants were covered with Cockle-burrs or abbreviated often to burrs.

Intrigued, he discovered that the cockleburrs had tiny hooks all around it which allowed them to stay attached to both the hair of his dog and the fabric of his pants.


The cockleburrs inspired de Mestral to create a fastener of his own. After a few years, he was able to perfect his idea and he created the Velcro® brand hook and loop fastener. He originally patented his invention in Switzerland in 1951.

Velcro hook and loop fasteners can be made of many things—the first sample was made of cotton, which proved to be impractical.[3] Nylon and polyester[4] are the fibers most commonly used now. Velcro fasteners made of Teflon loops, polyester hooks, and glass backing are used on space shuttles.[4] [3,4 cf. Wikipedia]

It is worth recalling to inventors-innovators that there are variations on the standard Velcro hook and loop fasteners: one of which, for example, includes hooks on both sides. However these are not common. Alternatives to Velcro brand fasteners are buttons, zippers, laces and buckles.

Metaklett claim to carry this a couple of steps further, combining high temperature strength coupled with corrosion resistance properties.

More on Inventor Strategies... and scroll to list of famous inventors.


Metaklett claim to carry this a couple of steps further, combining high temperature strength coupled with corrosion resistance properties.

What materials are involved?

"The researchers opted to use spring steel,as the material for their fastener in order ensure high ductility with high strength. They created various three-dimensional models for the optimum interlocking of the fastener elements on the computer. They then built the most promising candidates as prototypes and subjected them to comprehensive tests. Around 40 variations of the geometry referred to as "Flamingo" alone were tested on the computer. The researchers studied its adhesive strength and reaction to extreme temperatures to establish the limits of its resilience.

[Normally high-temperature materials must be tested for creep and corrosion resistance for atmospheric corrosion degradation? Here is a new selector steel data site LINK - cf. 18Cr-10Ni, 304 stainless steel, for example - JA]

Two of the tested models ultimately made the grade: a spring lock, the Flamingo, and a hook and loop system known as the Entenknopf (duck's head). Both consist of 0.2-mm-thick hook tape and loop or perforated tape of the same thickness. The "duck's head" model is based on the traditional synthetic hook and loop system. Numerous delicate steel hooks can attach at any angle to the loops in the perforated metal loop tape.

A very full account of the hook and loop design geometry including virtual motion images of both fasteners operating principles Eurekalert LINK

Far less technical information is available online concerning the "selected spring steel materials" which are likely to respond to high-temperature, corrosion resistant steels and refractory alloys nor the durability of 0.2mm steel strip with intricate geometries and for what duration?

Are "Spring Steels" or "Metaklett" Shape Memory Alloys SMA's?

By asking this rather "out of the box" question, some interesting ideas for future consideration arise.

Strictly speaking conventional metallurgical knowledge returns a definate no to the lead question above. Spring steels depend rather on elastic deformation represented by a linear relationship between stress (force/unit area) and strain (deformation or displacement ie. elongation) They do not undergo structural phase transformation. In other words they obviously undergo cyclic stretching and relaxation of the interatomic bonds and groups-networks of bonds called crystals-lattices. They do not undergo or depend on for their shape memory function on cyclic structural phase change. Nevertheless many steel grades depending on the heat treatment have a structure called Martensite which is part of the common denominator of most if not all SMA's.

An excellent hyperlinked introductory source illustrating both spring steels,martensite and shape memory alloys link

hysteresis property whereby a given shape at a given temperate may be "memorised" and cycled between two shapes.


With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at As (austenitic transformation start temperature) and is completed at Af (finish) (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). As is determined by the alloy type and composition. It can be varied between −150 °C and maximum 200 °C.


The two-way shape memory effect is the effect that the material remembers two different shapes: one at low temperatures, and one at the high temperature shape. This can also be obtained without the application of an external force (intrinsic two-way effect). The reason the material behaves so differently in these situations lies in training. Training implies that a shape memory can "learn" to behave in a certain way. Under normal circumstances, a shape memory alloy "remembers" its high-temperature shape, but upon heating to recover the high-temperature shape, immediately "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the deformed low-temperature condition in the high-temperature phases. There are several ways of doing this.
LINK

Here is a 45s video demonstrating the Shape Memory effect. LINK


Lou Reade, in Materials World 01 Aug. 9 reports on one high safety requirement SMA

“In the case of the diving helmet, Nitinol and Aramid fibre are joined together using an automated technique called warp knitting. A high-energy collision forces the material to change between two different sold states, giving rise to energy dissipation that improves impact resistance.

The programmed shape, to which the SMAs revert to, is set by heating the material to 400ºC. One challenge for researchers was reducing this level for hybrid materials. 'At these temperatures, most conventional textiles will burn,’ notes Rehm of The Institute of Physics at the Academy of Sciences of the Czech Republic who have developed a heat treatment technique for SMAs that works below 200ºC, and whose patent is pending.”
cf. Materials World 01 Aug. 9 for the full news item.

Returning to Metaklett.
One can expect further developments, judging by the industrial and early financial support for these innovations,

Industrial Project Partners
Reinz global automotive supplier
in the fields of metallic gaskets, including head gaskets, thermal and acoustic shielding valve covers.
Stamping and Precision Engineering
Koenig Connection Ltd.,a series supplier of fasteners in the automotive industry.
R&D.

Financial Backing
This research project is / was supported by funds from the Federal Ministry for Education and Research (BMBF) within the "Research for the production of tomorrow" by the developer and the Forschungszentrum Karlsruhe, Production and Manufacturing Technologies

Link:MetaKlett-Website(German)
I used Google's Translator to get a reasonable understanding.

NB
35 tonnes per square meter when tensile force is applied parallel to the fastener surface. When it is applied perpendicular to the fastener surface, Metaklett can still withstand a force of seven tonnes per square meter
New Steel 'Velcro' -
-3.5kg/ square cm or 35tonnes/m^2 ie. 3.5 kg/cm^2 in horizontal tension or pull.
-0.7kg/ sq cm or 7tonnes/m^2 ie. 0.7kgs/cm^2 in ‘shear’_vertical position
Cf. Old industrial grade velcro comment on New Scientist.
- 3.1 kgs/ square cm
And again Velcro on Wikipedia
- 175lbs /in^2 roughly 3kg/cm^2


Temperature is therefore a critical factor in projected applications.

Sources: New Scientist comments below and Wikipedia.

References and Acknowledgements:

How a Swiss invention hooked the World_George de Mestral

Eurekalert LINK

MetaKlett-Website (German)

Spring Steel summary with typical grades and Heat-Treatment structural changes outlined via TTT - Time-Temperature-Transformation Diagrammes with when available, Environmental Data
'conventional spring steel on a new site Matbase'

Martensite

spring steels,martensite and shape memory alloys link

SMA mechanism LINK for structure and shape change between higher temperature austenite and lower temperature martensitic phase.

Materials World 01 Aug. 9

Acknowledgements .
1. New Scientist NB Comments.
2.The Telegraph, UK. 8 Sept.09