S erviceability, W ear and A brasion

Serviceability:

An article which is serviceable is capable of performing useful service; its serviceability ceases

when it can no longer do so.

To a lady of fashion, her last season’s outfit is unserviceable as far as being in the fashion is

concerned even though the cloth may still be in as the new condition.

Purposes of Serviceability testing:

1. To determine validity and suitability of application of fibre, yarn or fabric objectively

and precisely.

2. To ensure the reasonable prospects of commercial success as a long term proposition.

3. To compare a number of different fibers, yarns, or fabrics.

4. To determine the influence of cloth structure and finishing on performance.

5. To assess suitability of the fabric or article that is considered as ‘borderline’ by

laboratory testing against a performance specification.

6. To determine suitability for making up e.g. seaming properties, pleating and creasing

properties and other tailoring requirements.

7. To assist in establishing criteria for laboratory testing and standards of performance.

Wear:

Wear is the net result of a number of agencies which reduce the serviceability of an article.

Some of the more important agencies are –

Bending and stretching

Tearing

Abrasion

Laundering

Clearing

Abrasion:

Abrasion is one aspect of wear and is the rubbing away of the component fibers and yarns of

the fabric.

Abrasion may be classified as follows-

1. Plane or flat abrasion-A flat area of material is abraded.

2. Edge abrasion-This kind of abrasion occurs at collars and folds.

3. Flex abrasion-In this case, rubbing is accompanied by flexing and bending.

Factors affecting abrasion resistance:

Fibre type:Nylon is generally considered to have the best abrasion resistance. Polyester and polypropylene are also considered to have good abrasion resistance. Blending either nylon or polyester with wool and cotton is found to increase their abrasion resistance.Viscose and acetates are found to have the lowest degree of resistance to abrasion. Fibre properties:A fabric made up with longer fibres gives better abrasion resistance than short fibres because they are harder to remove from the yarn. For the same reason filament yarns are more abrasion resistant than staple yarns made from the same fibre. Increasing fibre diameter up to a limit improves abrasion resistance.

Yarn twist:An optimum amount of twist in a yarn gives the best abrasion resistance. At low-twist factors, fibres can easily be removed from the yarn so that it is gradually reduced in diameter. At high twist levels, the fibres are held more tightly but the yarn is stiffer so it is hard abrade under pressure.

Fabric structure:The crimp of the yarns in the fabric affects whether the warp or the weft is abraded the most. Fabrics with the crimp evenly distributed between warp and weft give the best wear because the damage is spread evenly between them.

Points to be consider before abrasion testing / Factors affecting abrasion

tests:

1. Condition of specimen: The fabric should be conditioned and tested in a standard

testing atmosphere.

2. Choice of testing instrument: The choice of testing instrument may be dependent upon

the character of the testing desired, e .g-flat abrasion, flexing abrasion, etc.

3. Choice of abrasive motion: The rubbing movement may be reciprocating, rotary or

multi-directional.

4. Direction of abrasion: The direction of abrasion can be at angles to the warp and weft

directions.

5. Choice of abradant: The severity of the abrasion will vary with the nature of abradant.

For example: steel and silicon carbide give constant abrasive qualities. A standard

worsted or canvas fabric, emery cloth of various grade are also used as abradant.

6. Backing the specimen: The hardness of the backing of the specimen may affect the

results. In some testes a hard backing is used, in others a felt or foam rubber.

7. Cleanliness of the specimen and instrument: The region to be abraded should be

handled as little as possible and be free from foreign matter such as graphite of pencils.

The accessories of the instrument which may rub the fabric must be spotlessly clean

and free from grease.

8. Tension on the specimen: Standard method of mounting the specimen should be used

to avoid errors due to variation in the tension used.

9. The pressure between abrading and specimen: The severity of the abrasion will be

affected by the pressure applied. So suitable standard must be set up.

10. The end point of the test: The test should be frequently stopped as soon as the hole

appeases or the specimen breaks by automatic stop motion.

Assessment of abrasion damage:

Several methods are used to judge the amount of damage. Some are mentioned below:

i. The difference in appearance between an abraded and unabraded specimen.

ii. The number of cycles required to produce a hole, broken threads or broken strip.

iii. Loss in weight often plotted against the number of cycle.

iv. Change in thickness e.g. loss of pile height.

v. Loss in strength, e.g. tensile, bursting or tearing strength, expressed in percentage of

unabraded strength.

vi. Change in some other properties like lustre, air permeability etc.

vii. Microscopic examination of damage of yarns and fibres.

Method of assessment:

Two approaches have been used to assess the effects of abrasion:

1. Abrade the sample until a predetermined end-point such as a hole, break of fabric and

record the time or number of cycles to this.

2. Abrade for a set time or number of cycles and assess some aspect of the abraded fabric such

as change in appearance, loss of mass, loss of strength, change in thickness or other relevant

property.

Martindale Abrasion Tester:

Description of the machine:

1. This apparatus gives a controlled amount of abrasion between fabric surfaces.

2. Abrasion is given at comparatively low pressures in continuously changing directions.

3. In this test, circular specimens are abraded under known pressure.

4. This abrasion is given by a motion that is the resultant of two simple harmonic motions

at right angles to one another.

5. The fabric is abraded against a standard fabric.

6. Abrasion resistance is estimated by visual appearance or by loss in mass of the

specimen.

Fig: The Martindale abrasion tester

Fig: A standard holder for the Martindale abrasion test

Fig: One station of a Martindale abrasion tester

Method:

1. Four specimens each 38mm in diameter are cut using the appropriate cutter.

2. They are then mounted in the specimen holders with a circle of standard foam behind the fabric being tested. The components of the standard holder are shown in Figure. It is important that the mounting of the sample is carried out with the specimens placed flat against the mounting block.

3. The test specimen holders are mounted on the machine with the fabric under test next to the abradant.

4. A spindle is inserted through the top plate and the correct weight (usually of a size to give a pressure of 12kPa but a lower pressure of 9kPa may be used if specified) is placed on top of this. Figure shows the sample mounted in a holder.

5. The standard abradant should be replaced at the start of each test and after 50,000 cycles if the test is continued beyond this number.

6. While the abradant is being replaced it is held flat by a weight as the retaining ring is tightened.

7. Behind the abradant is a standard backing felt which is replaced at longer intervals.

Assessment:The specimen is examined at suitable intervals without removing it from its holder to see whether two threads are broken. In the Table, it is shown that, for the time lapse between examinations. If the likely failure point is known the first inspection can be made at 60% of that value. The abrading is continued until two threads are broken. All four specimens should be judged individually. Inspection intervals for Martindale abrasion test

The individual values of cycles to breakdown of all four specimens are reported and also the average of these.

3. The test specimen holders are mounted on the machine with the fabric under test next to the abradant.

4. A spindle is inserted through the top plate and the correct weight (usually of a size to give a pressure of 12kPa but a lower pressure of 9kPa may be used if specified) is placed on top of this. Figure shows the sample mounted in a holder.

5. The standard abradant should be replaced at the start of each test and after 50,000 cycles if the test is continued beyond this number.

6. While the abradant is being replaced it is held flat by a weight as the retaining ring is tightened.

7. Behind the abradant is a standard backing felt which is replaced at longer intervals.

Assessment:The specimen is examined at suitable intervals without removing it from its holder to see whether two threads are broken. In the Table, it is shown that, for the time lapse between examinations. If the likely failure point is known the first inspection can be made at 60% of that value. The abrading is continued until two threads are broken. All four specimens should be judged individually. Inspection intervals for Martindale abrasion test

The individual values of cycles to breakdown of all four specimens are reported and also the average of these.