SATRA research update

A review of some of the footwear projects which have recently engaged the members of SATRA’s innovation and development team.

by Zach Armitage

SATRA is not just a test house – it has been a research facility for the footwear industry for over 100 years. During this time, we have been at the forefront of many technical developments and innovations, including the development of nearly 460 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 by ISO, BSI, ASTM and other standards committees.

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.

Further information is available in the article ‘The development of SATRA test methods’, published in the October 2021 issue of SATRA Bulletin, and the video presentation ‘An insight into test method development’, which can be accessed through the members-only section of www.satra.com/resources

Contract research

Contract research is carried out in the form of consultancy for a specific member, often to help develop a product or design 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.

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 SATRA 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 SATRA’s facilities as required. So, for example, if prototype parts are designed at the workshop, they can be three-dimensionally (3D) 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 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 with which SATRA is involved. For example, these include 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 considerable amount of fundamental research in order to ensure that current test methods and guidelines are still correct. This is especially conducted where there is a chance that a particular new technology, material or process may be disadvantaged by a specific method. Test methods are written very carefully in order to ensure that they are not design restrictive. However, even with great hindsight, this occasionally happens and must be addressed. A good example is in the testing of components such as toe posts (straps or thongs) which traditionally would have been made from inelastic materials such as leather. With the prevalence of synthetic materials, straps and toe posts may be made of materials with a lower modulus of elasticity that may require a low force to stretch. In toe post attachment strength tests, materials that can stretch pose a problem to a simple force to detachment test. Taking elasticity into consideration makes this test more relevant to modern materials and can identify alternative failure modes.

This is where fundamental research is required. 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.

Recent fundamental research

An example of fundamental research currently under way at SATRA is the expansion of the modern foot dimensions database. SATRA collected several thousand adult’s and children’s foot scans using 3D scanning technology. While a number of measurements have been analysed and disseminated from this project, the fact that the original foot scans are available means that new dimensions can be extracted beyond the scope of the original project. SATRA has recently coded scripts to assess these scans for ankle dimensions, long heel girth and toe heights, which are important additions to the original project. Furthermore, scripts for shapes analysis have been developed that allow greater insight into the form of the foot and average contour lines to be predicted. This can be used to establish, for instance, the typical toe shape or arch and heel curve.

Closely related to the foot dimensions project is SATRA’s development of artificial foot forms that provide a useful tool to fit assessors. These artificial feet have been idealised using SATRA global foot dimensions data to feature the typical dimensions for their given size. When assessing fit, size and comfort of footwear, the standard procedure is to use a fitting model – or, ideally a panel of models – to try on the footwear. A skilled fit assessor then evaluates the fit in comparison to the foot dimensions of the models. However, it is not always easy to find models with the correct foot dimensions, particularly with children whose feet will grow and change. These SATRA artificial feet provide a standardised foot form with specific, unchanging dimensions that can be used when human models are unavailable. Being a standardised model also means that fit assessment can be carried out in multiple locations and the same assessment made of the sizing and comfort of footwear.

Last assessment has been a service offered at SATRA for many years, in which a physical last is sent to SATRA and precisely measured. From this, comments can be made on the suitability of the size marking and the likely comfort of shoes made on that last. SATRA has invested in digitising this process, so that rather than requiring a physical last, a digital last file can be emailed instead. The digital last assessment programme then identifies the last, orientates it appropriately for its heel pitch and insock allowance, and takes the same precise measurements that a skilled last assessor would have taken of a physical last. These measurements are automatically reviewed against guidelines and comments generated on fit and comfort, which allows last assessment to be performed much faster and with less chance for error. Moreover, the last dimensions can be compared to foot dimensions statistics so that a prediction of likely population coverage can be calculated, with comments on dimensional changes that may improve the last. These last modifications can be performed by our in-house CAD specialists to provide a complete last assessment and adjustment service.

Investigating new ideas

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 subject areas. This is done with a view to developing much larger projects on those subject areas if needs and interest justifies them.

One such project was the investigation of alternative pre-treatments for adhesion. Typical pre-treatments for adhesion use volatile organic compounds (VOCs) to chemically attack the surface of a material in order to make bonding easier. Once applied, the VOC attacks the surface of the material, making more points for chemical and physical adhesion. It then evaporates in to the atmosphere, leaving the treated material behind. Unfortunately, VOCs are harmful to humans and the environment, and limiting the release of VOCs can reduce the environmental cost of footwear production. With this in mind, SATRA has investigated a pre-treatment that utilises ultraviolet (UV) light and ozone to create the roughing needed for adhesion. It has been found that this new process can offer as good, and in many cases, a better bond than achieved with traditional VOC treatments.

One major project during the last year has been the evaluation of applied loads in footwear testing. In order to accurately predict the lifecycle of footwear products, realistic testing needs to be performed. The SATRA STM 528 Pedatron replicates a natural gait pattern and applies forces typical of a 95 kg individual. The average weight for men in the UK and US is around 85 to 90 kg. A new gait cycle has been developed for the Pedatron that allows greater loads to be applied, which is more reflective of an individual in the 90th percentile weight category. In addition to this, a new test machine has been developed that allows heel impacts of up to 300 kg to be emulated in order to test underfoot products to the extremes that they may be expected to experience in real wear.

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 10 of the March 2022 issue of SATRA Bulletin.

Other articles from this issue »

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