Using thermal imaging to predict footwear problems

How infrared thermography can assist shoemakers to assess where their product may fail.

Infrared (IR) light is electromagnetic radiation with a wavelength longer than visible light (between 0.75 and 1,000 micrometres), beyond the spectrum visible to the human eye. Infrared radiation is produced by all objects with temperatures above absolute zero (-273.15°C or -459.67°F). Even ice cubes emit some infrared radiation.

It is generated by the rotation and vibration of atoms and molecules – the higher the temperature of an object, the more motion there is and, therefore, the greater amount of infrared energy that is emitted.

The technology to view and measure infrared radiation was originally developed in the 1950s for military applications, to allow soldiers to see an enemy through battlefield smoke, fog or in complete darkness.

Thermal imaging was adopted by many firefighting services around the world. This began with the British Royal Navy, which used it to locate shipboard fires, before the technology was taken up by a variety of industries and organisations to remotely view and measure heat.

Infrared thermography

An infrared camera produces pictures from thermal radiation, allowing for the assessment of variations in temperature across an area. It is a non-contact device that produces a graphic display of the infrared energy emitted and reflected by an object. In-built software calculates and displays accurate temperature measurements.

Why measure it?

The properties that have made infrared detection valuable to military services around the world also make it very useful to industry, public services and scientific research. Any system that measures infrared energy can be used to reveal otherwise obscured objects. Thermal cameras allow temperature measurements by non-invasive and non-destructive means, and are used by wildlife researchers to study mammals in their natural habitat at night. They are regularly used to perform diagnostic body scans, since injured or diseased parts of the body often exhibit a different temperature to surrounding tissue.

Advanced navigational technology (now found in some luxury cars) relies on sensing infrared emissions from the surroundings, and space satellites use infrared devices to study meteorological conditions on Earth.

During the 2009 Swine Flu outbreak, infrared thermography was used to detect suspected cases at airports, since victims showed an elevated body temperature. Infrared cameras continue to be indispensible to firefighting services, where they are used to find the unseen sources of combustion and to look for survivors in smoke-filled buildings.

Building engineers and inspectors use infrared thermography to find poorly-insulated areas of buildings, detect unseen water ingress and to look for gas leaks or draughts.

Uses in testing and research

The areas of a material or component under constant stress are more prone to failure. When a material comes under stress – for example, during flexing – the forces involved generate heat. The heat detected by an infrared camera during product durability testing can, therefore, be indicative of stress points that may eventually fail in wear.

The ability to see heat and to be able to map changing temperatures across a surface will be invaluable in wear trials. This is especially so with comfort testing of garments, because the measurement process is not intrusive and the task or test need not be interrupted. As well as measuring temperatures across the whole of a scene, it is possible to focus on measuring temperature changes within a very small range. Where changes in body temperature are the object, assessing a narrow range of temperatures (such as a 4-5° band around regular body temperature) is more beneficial than a wider view, and allows the thermal properties of any background to be discounted.

Like all systems, infrared thermography has its limitations. Generally speaking, it is not as accurate as direct contact methods of temperature measurements. A figure of ± 2 per cent accuracy is fairly standard for the specifications of newer cameras, they are usually of a lower resolution than conventional digital imaging devices, and are still relatively expensive.

Using the SATRA equipment

As one of the latest additions to SATRA’s arsenal of research tools, the infrared camera provides the capability to record and analyse both thermal images and videos. Post-analysis software allows us to process the data recorded by the camera and to take further temperature readings from different areas of a recorded scene.

There are a considerable number of areas of testing and research that stand to benefit from the use of infrared thermography. Any test or assessment that examines either the build-up or movement of heat around a subject can be further scrutinised by pointing an infrared camera at it.

In the same way that structural engineers use infrared cameras to check the insulation of a house and to look for escaping heat, we can use infrared imaging to look for heat escaping from footwear or cold-weather garments. Where the insulation properties of a garment are under test, escaping heat is clearly undesirable but, in instances where the footwear claims to disperse heat or humidity, escaping heat could be seen as beneficial. Monitoring this process with an infrared camera could help validate manufacturers’ claims in this regard.

Infrared thermography also offers the opportunity to examine the operation of machines like heat-setters used in footwear production, where it could be used to look at the distribution of heat throughout the working area. Hotspots can quickly be identified, and shoes that have passed through the setter could then be tracked to monitor which areas of the footwear stay hot longest.

Publishing Data

This article was originally published on page 16 of the March 2018 issue of SATRA Bulletin.

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