## Saturday, February 5, 2011

### BURSTING STRENGTH

The machines used for this test tend to give a value which is the sum of the strength warp way and weft way. The test is particularly useful for knitted fabrics, which have no warp and weft and are extremely difficult to test by the usual fabric machines. It is also important for such fabrics as parachute silk, which in actual use are subjected to stresses of equal value both warp and weft way simultaneously. (see B.S.I. handbook No.11 (1949),P143.)
In one form of ball-bursting machine the fabric is clamped tightly between two annular rings, of 1.75-in .internal diameter , and a steel ball of 1-in .diameter is pressed down upon the fabric until it bursts under the pressure, which is then read , The main recommendation for this type of machine is that it can be designed to replace the jaws on an ordinary fabric testing machine. The ball burst strength in this type of machine is about 33% greater then the strip test strength of a woven fabric in the weaker direction .
In the bydraulic burst tester a rubber dia phragm is placed over an annular ring , the fabric is placed upon the rubber diaphragm, a second annular ring is clamped down , and hydraulic pressure (using water or glycerine)  is exerted against the rubber diaphragm. The bursting strength is read on a pressure gauge at the point when rupture of either warp or weft direction occurs.  The machine has to be calibrated for the pressure required to stretch the rubber diaphragm.  In the mullen machine of this type the diameter of the cloth circle tested is 1.2 in , but it is advisable to use circles of much larger diameter in order to obtain a more average result, and to eliminate errors due to the lack of fibre slippage with circles of 1-2 ins. diameter . In all textile testing it is advisable to have the length of specimen tested as least as long as the mean fibre length in the specimen , and preferable of such a length that 90% of the fibres are held only at one end.