Martindale sock abrasion testing
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This article follows the EN 13770 Martindale sock abrasion testing method. The structure of this method is based on the ISO 12947-1 abrasion standard, which is considered the benchmark for nearly all textile abrasion tests, though it has some very key differences in several areas, which are detailed here.
What is it?
Unlike ISO 12947-1, EN 13770 recognises that knitted footwear behaves fundamentally differently. Socks are highly elastic, cylindrical, and experience abrasion while stretched over a 3-dimensional form. They undergo flexing and tension patterns entirely different from that of flat fabrics.
It is for this reason why EN 13770 introduces two separate test methods designed specifically to recereate how socks are used. Firstly there is the Modified Martindale Method for Socks, and secondly there is the Abrasion on Leg Forms. For the purposes of this article we will focus only on the first part of this method as it is the only part that relates to testing using the Martindale.
The EN 13770 sock abrasion method, much like in the standard tests, still requires a Martindale tester, fabric specimens, test materials, and a grading environment for final assessments.
Why it matters
As with any other physical textile test, we are trying to determine how durable the textile product is, to ensure it can fulfil a suitable lifespan as expected by the consumer.
Why it matters to perform this specific sock abrasion test over simply testing according to the standard ISO 12947-1, is because flat testing cannot replicate real or realistic wear for a sock. This type of knitted garment is designed and constructed to contour against the foot, and so a more realistic test must be performed to be able to better replicate real-life conditions, such as walking and playing sports.
How it works
This method retains the core principles of abrasion testing on the Martindale, such as:
- 16 point Lissajous motion
- Controlled contact pressure (using a weight)
- Defined test materials (abradant)
…there are however some key differences. EN 13770 introduces a special abrasion holder assembly, replacing that of the typical holder, and it includes:
- A needle ring – for gripping the knitted specimen
- A rubber sphere – with a small flat test surface
- A holder nut and body – designed to compress the specimen onto the sphere
- A spring-loaded tightening block – to ensure consistent mounting
The set-up of this head is designed as such so as to create a curved and uniformly tensioned specimen, that replicates the contour and extension seen during real-life wear. Circular samples are taken from the sock specimen, and then mounted into the sock abrasion holders.
The number of samples per sock/ specimen is a minimum of 4 (per the EN 13770 standard). Two from the heel, and another two from the base of the sock. For additional samples, additional socks will need to be used.
The Martindale itself is ‘dressed’ as usual with the relevant test materials for abrasion, (wool felt pads and wool abradant as per ISO 12947-1). The other significant difference with this test, is that we are required by the standard to use the 12kPa weight. Once this is set-up, the test is then initiated.
(Pictured below is the sock abrasion test holder in its’s full set-up. In addition, see the suggested sample preparation guide as detailed on a sock).
What you’ll see
The endpoint criteria for the sock abrasion test is assessed from two angles.
Firstly, as we would expect, we would wait to see a hole formation, a breakthrough of the structure. As we are testing knitted specimens, we won’t be seeing a ‘thread break’ as such, as the construction of the fabric typically allows only for a hole formation, triggered by a broken loop/thread.
Secondly, we are looking for areas of thinning. Many cotton and nylon yarns for instance have the propensity to lose spun area and mass, which results in ‘thin’ looking patches where the specimen has been tested.
For inspection, it is detailed in the standard to remove any pills from the specimen with a pair of small, sharp scissors, as the presence of pills can distract from the viewing and eventual grade of the abrasion. The endpoint criteria is to be noted on the report, with either or both the hole formation and/ or thinning where appropriate, and at what rub count the specimen achieved at either point.
The untested sock fabric specimen (pictured left). On the tested specimen (pictured right), we can see a moderate degree of wear.
Quick takeaway
The Martindale sock abrasion test is a lot more common than you might suspect, and has a great deal of similarity to the standard textile abrasion test, though the EN 13770 is very specifically designed to test knitted socks on a Martindale tester, only.
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