Procedure of Fabric Seam Slippage Test

Seam Slippage:
Seam slippage is a fabric problem especially for fabrics that contain slippery yarns or that have an open structure or where the number of warp and weft interlacings is low. Such factors mean that one set of yarns may be easily pulled through the other. Seam slippage is the condition where a seam sewn in the fabric opens under load. Some of this gap may close on removal of the load but some of it may be a permanent deformation.

Seam Slippage Test:
This test method is used to determine the resistance to slippage of filling yarns over warp yarns , or warp yarns over filling yarns, using a standard seam.

There are three different types of seam slippage test in existence, each of which has its drawbacks. Firstly there is the type where a standard seam is put under a fixed load and the seam gape is measured. In second type a load extension curve is plotted with and without a standard seam and the difference between the two curves is taken as the slippage. The third type does away with a sewn seam and measures the force required to pull a set of pins through the fabric. A variant of the first type is to measure the load required to give a fixed seam opening.

Procedure of Seam Slippage Test:
The British Standard test for seam slippage is a test of the second type. Five warp and five weft specimens each 100mm X 350mm are used. Each sample is folded 100mm from one end and a seam is sewed 20mm from the fold line using the special sewing thread and sewing machine settings which are detailed in the standard. The layout of the sample is shown in Fig. After sewing the folded part of the fabric is cut away 12mm from the fold line leaving the seam 8mm from the cut edge. A standard strength tester equipped with 25mm grab test jaws is used, the gauge length being set to 75 mm.
Fig
Just before the test the sample is cut into two parts one with the seam and one without but with each part containing the same set of warp or weft threads. The sample without a seam is first stretched in the tensile tester up to a load of 20ON and a force elongation curve drawn. The matching sample with the seam is then tested in the same way making sure that the force elongation curve starts from the same zero position.

In order to find the force required to open the seam a given distance, the separation of the curves at a force of 5 N is measured and this distance is added to the seam opening specified (usually 6mm but some specifications require 5 mm) making appropriate allowance for the horizontal scale of the chart. Next the point on the curves where there is a separation of this distance is located and the value of load at this point is read off the chart. If the curves do not reach the specified separation below 20ON then the result is recorded as 'more than 20ON'.

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