SATRA’s research update

Reviewing some of the footwear projects which have recently engaged the members of SATRA's research team.

by Tom Bayes

SATRA is not just a test house – it has been a research facility for the footwear industry for over 95 years. During this time, SATRA has been at the forefront of many technical developments and innovations, including the development of nearly 450 test methods which address all aspects of testing with respect to footwear and leathergoods. These methods are often regarded as industry standards. Not only have they been adopted by footwear manufacturers, but also most international standards have SATRA test methods at their core. Nevertheless, many members are probably unaware that this tradition still continues. SATRA is still very active in the production of new test methods and test equipment, as well as revising older methods to ensure that they are fit for the requirements of the 21st century footwear industry. Research and development activities at SATRA can be divided into two subsets – contract research and authorised research. These are not distinct, and there is considerable overlap, with members often having a role to play in new developments.

Contract research

Contract research is carried out in the form of consultancy for a specific member, often to help develop a product or to develop new innovative methods of testing the product and to provide scientific evidence to verify performance. In its simplest form, this can mean modifying existing test methods – for example, those to be carried out in different environments. Often, however, contract research requires the development of new testing techniques and/or machinery in order to verify the performance of a product. For most contract research, the customer pays fully for the consultancy and developments. As a result, the customer will retain the intellectual property, although this is not a fixed model. There are many cases where SATRA has already made developments in an area, and customers create the need and motivation required to develop the ideas further. In this event, (and working closely with the customer), SATRA is able to fund the developments to varying degrees, thus quite significantly reducing the costs to the member. Clearly in the development of new methods of testing, members that are close to the developments have an industry advantage – especially if the test methods then go on to become international standards.

Contract research for an individual member is, of course, completely confidential as it frequently involves products and ideas that are not yet on the market. Once the customer’s requirements have been defined, one of the more successful methods of progressing this process is to hold focused workshops at SATRA’s facilities. These typically last between one and three days, with groups of individuals from the customer’s development team meeting at SATRA with an appropriate team of the Technology Centre’s consultants to develop, for instance, prototype products or test methods. Fees are based on a single day rate for consultancy that also includes access to SATRAs facilities as required. So, for example, if prototype parts are designed at the workshop, they can be 3-D printed and appropriately tested at the time. These events have proved to be very successful, and often reduce the time it takes to bring a product to market.

Authorised research

SATRA authorised research is for the development of projects that are funded internally. Due to the unique way SATRA operates, we have always developed a comprehensive annual research programme for the benefit of our members. Every year, projects are proposed – some new, others continuations of previous years – and funding levels are decided. The project topics vary considerably, with a blend of fundamental research and new, innovative thinking. Some of the projects are also planned to give technical support to the various international standards committees that SATRA is involved with. These include, for example, the European Technical Committee TC161 and International Standards Organisation Committee ISO/TC94/SC3, as well as a number of ASTM committees responsible for safety footwear standards.

SATRA carries out a large amount of fundamental research in order to ensure that current test methods and guidelines are still correct. This is especially where there is a chance that a particular new technology, material or process may be disadvantaged by a particular method. Test methods are written very carefully in order to ensure that they are not design restrictive. Even with great hindsight, this occasionally happens and must be addressed. A good example is in the testing of components such as box toes, which have traditionally been cut from sheet material. New developments allow components to be formed by a sintering process (compacting and forming a solid mass of material by heat and/or pressure without melting it to the point of liquefaction), dusting a layer of powder using a template and sintering the compound directly onto the upper. Clearly, test methods must evolve to allow components made in this fashion to be tested effectively.

This is where fundamental research comes in. The original work is re-assessed, to include perspectives on modern technology, production techniques, design and materials. If necessary, further work is initiated to confirm current guidelines or, in the case of any discrepancy, to modify guidelines and – most importantly – be able to present the evidence if challenged. This makes SATRA rather unique, as we have access to the original work carried out that was used to justify tests (research that is taken for granted by other test houses). More importantly, if the evidence is found lacking – for instance, with the availability of new methods of measurement, we initiate research to address the concerns.

An example of fundamental research currently under way at SATRA is its global foot dimension survey. Running over several years and with a considerable financial investment, this project is unique in that rather than manually collecting key dimensions, every single subject has had their feet scanned to create detailed 3-D models. The survey has currently covered both the east and west coast of the USA (over 2,000 subjects), the UK (in excess of 1,000 subjects) and China (more than 3,000 subjects). This has provided over 12,000 digitised foot scans, including data from children and the senior population. The collection of so many foot scans is extremely time consuming. However, it has the great advantage of allowing future researchers full access to the whole foot, so that measurements not yet defined can be determined. Initial statistical results are based around the common measurements that are made, and the data also includes calf girths at different heights for the female subjects.

Measurement of slip is another area of fundamental research that is active year-on-year. During 2014, a programme of gait analysis work was undertaken to further our understanding and knowledge of this subject. The availability of modern measurement techniques such as force platforms, underfoot pressure mapping and high-speed videography (as well as the ease with which these techniques can be used) has now allowed some of the fundamentals to be re-examined and confirmed as valid. This also included children’s gait and adults in high-heeled footwear, in addition to parallel, bare foot gait for comparison. It was as a result of this work – together with some materials tests – that the guidelines for top-piece friction were modified in accordance with our findings.

Water resistance is, of course, an ongoing sequence of projects, as it is an important subject area for many of our customers. New machines are developed, as well as modifications and improvements to existing machines such as the SATRA STM 505 Dynamic Water Resistance Tester. During 2014, automatic leak detection was added to our STM 505 capabilities, along with a prototype of a much improved foot form. In order to make automatic leak detection effective and reliable, the behaviour of the humidity and temperature within the footwear must be monitored. Footwear normally has a heat source (the foot) inside, and this creates a gradient that aids breathability. Of course, there is no foot present in the test.

This allows the humidity in a water resistance test to build up very rapidly and causes the dew point to align very close to the ambient air temperature. The subsequent electrical resistance can be measured. This allows sensible limits to be placed on the minimum resistance, which would indicate a physical leak rather than the machine responding with a false indication due to the rise in humidity within the footwear.
One of the most interesting projects comes under the umbrella title of ‘Investigative’. Such a project is usually split into several distinct and small sub projects, in order to evaluate new ideas and subjects areas. This is done with a view to developing much larger projects on those subject areas if needs and interest justifies them.

During 2014, one of these projects was the need to develop a method of measuring torsional slip/grip of footwear on different surfaces (including artificial sports surfaces mimicking turf). There has been increased importance placed on this due to the number of lower leg injuries that occur as a result of high torsional forces being transmitted up the leg. A biomechanically correct test would also allow improved designs for footwear soling, especially where the particular activity involves sudden change of direction and/or a swivelling motion. Early results have demonstrated that this is achievable and the torsional forces can be measured during the gait cycle.

Thermal properties of footwear – particularly with respect to breathability – have also been at the forefront of developments during 2014. Breathability of whole footwear and materials is commonly measured at ambient conditions of 23ºC/50 per cent relative humidity (rh). Two questions commonly asked are, ‘how do materials breathe at different climatic conditions?’ and ‘how much moisture do they absorb?’ Two of our popular breathability tests – SATRA TM376:2009 – ‘Advanced moisture management test’ and SATRA TM47:2002 – ‘Water vapour permeability and absorption’ were adapted so that they could be carried out in our climatic chamber. As a result, they now include situations where the ambient temperature is greater than the foot and the ambient humidity is higher than inside the footwear. In this circumstance, moisture tends to enter the footwear rather than be driven out. Until these developments, selection of materials for extreme conditions was largely based on anecdotal evidence and experience. The development of these new tests allows the performance of materials to be measured empirically.

Prioritising the subject areas for the research programme comes largely through engagement with members. Members are encouraged to contribute ideas to these programmes, both while visiting SATRA’s facilities or through our many seminars and events where current work is disseminated. Surprisingly, some of the best ideas come from quite casual conversations with members, where it becomes clear that there is a common problem to be solved. This is an important member benefit that may lead to a project being funded.

Publishing Data

This article was originally published on page 40 of the July/August 2015 issue of SATRA Bulletin.

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