What is Fabric Testing?
Fabric is the principle raw material in garment production, making up about 70% of the total cost and covering nearly 100% of the garment’s visible surface. All the other materials like trimmings, accessories, closures, and packaging materials are generally arranged on or around the fabric utilized in the garment. Since fabric has the biggest impact on cost, it goes through the most quality checks during production. Fabric testing plays a key role in the textile and apparel industry. It helps make sure that fabrics are suitable for their intended use, meet quality standards, and will be durable over time. A faulty fabric, isn’t identified early—right when it’s received— it can lead to extra costs during cutting, sewing, finishing, and packing. Early detection also saves time and transportation expenses. Another common practice, in local purchase, is to inspect the fabric right after it is received in the warehouse of an apparel manufacturing facility. A third party inspection may be involved where the prepared fabric has to be shipped to other countries.
In apparel, a fabric can be subjected to various mechanical/physical (e.g. tensile, bending, rubbing and flexing) actions and chemical actions, which lead to changes in appearance and functionality of the fabric, and ultimately to the garment no longer being acceptable, either from an appearance or functional point of view. If fabric durability and wear performance are to be reliably estimated in the laboratory, testing would need to measure (or simulate) and appropriately weight all the components of wear and durability, such as abrasion resistance, strength (tensile, tear, bursting), pilling, etc. It is important that the tests subject the fabric to relatively low and random abrasive forces, so including one or more laundering cycles as well usually improves actual wear prediction.
The finished fabric may involve raw material irregularities that may become more apparent after dyeing and finishing. It also includes yarn defects like thick and thin places. In addition weaving or knitting imperfections occur, such as miss picks, broken ends, and miss stitches. Dyeing and printing process irregularities also impart adverse effects to finished fabric. Other testing requirements relate to shrinkage, skewness, strength, elasticity, pilling and abrasion, stiffness, weight of fabric, fabric quality, among others. Therefore, it is necessary for garment manufacturing that the provided fabric is free of all previous processing irregularities and that it complies with garment performance standards.
Testing is important, mainly for customer satisfaction of the textile product as well as to ensure product quality for the market in which the textile manufacturer competes. Testing is also important in order to control the manufacturing process and cost. In this article different types of testing methods for fabric are discussed.
Different Types of Fabric Testing Techniques:
Normally, a fabric undergoes the following testing methods:
- Physical Testing
- Chemical Testing
- Performance Testing
- Comfort Testing
- Durability Testing
Here are some common fabric testing methods used in the textile industry:
Visual Inspection and Grading of Fabric:
This is the most common test for deciding whether the fabric lot should be accepted or not and is based on visual inspection of the finished fabric. The fabric roll is loaded on one side of the inspection table that is equipped with the appropriate type and intensity of light. The fabric runs across the inspection table at a certain speed and an expert checks visually for predefined faults.
A certain number of points are allocated, depending on the dimension, severity, and nature of the faults, for a single meter of the fabric being inspected. More than one standard grading system exists. A four-point system, for example, is one in which the inspector allocates a maximum of four points to an individual meter inspected, according to predefined criteria. The total points are then counted over the roll length.
The procedure is repeated for all rolls taken in a selected sample from the whole population of the fabric lot. At the end, the total points and total length inspected are calculated. The results are then expressed in points per 100 square units (square yards or square meters) or per 100 linear units (meters or yards) of fabric. The decision to accept a fabric lot is made on the basis of the pre-settled mutual understanding of supplier and customer. For example, a result of 30 points per 100 linear meters will result in the rejection of the lot, if the supplier agreed to provide fabric at 20 points per 100 linear meters. The reference standard for inspection and grading of fabrics is ASTM-D5430.
Fabric Color Test:
A standard way for testing fabric color is to check the Pantone color reference number as described by the customer. The dyed fabric is matched to the relevant Pantone reference to decide on whether to accept the prepared fabric lot. Garment manufacturers usually check fabric color against preapproved fabric swatches supplied by the customer. The fabric swatches are developed in the pre-production phase, according to the Pantone number given by the customer. Once the color swatches have been approved after multiple trials the supplier is asked to follow those approved. The supplier is expected to follow the same recipe as was used in dyeing the swatch fabrics.
In reality, however, process variations occur, which put the relevant stakeholders in a decision-making situation. All variations, though minor, are sent to the customer for approval. The approved shades are given to the person checking fabric color. The inspector then decides on whether to accept on the basis of all the shades approved. If the provided roll matches with any of the approved shades, it will be considered valuable for further use, and vice versa. In addition the shade may vary within the roll.
Therefore, it is more appropriate to check the fabric shade at first, last, and inner points of a single roll. Another common fault relating to color shade is the variation across fabric width. This fault typically arises when dealing with wider width fabrics like home textiles. Checking the shade from the left, center, and right of the fabric width gives appropriate information regarding variations.
Bursting Strength Test of Fabric:
A common consideration for strength parameters of textile fabrics is their bursting strength. This test is well known within the textile trades. The ball burst test is used to test the bursting strength of fabrics. A specimen of fabric taken from either a fabric roll or garment is placed between grooved plates of the testing equipment and fastened by means of screws. A polished and hardened steel ball attached to a pendulum actuating clamp of the machine is forced through the fabric, at right angles to the fabric plane, until the rupture occurs. The force reading gives the bursting strength of the fabric.
Two standard methods exist for this test: one with a constant rate of traverse, whose reference standard is ASTM-D3787, and another with a constant rate of extension (CRE), whose reference standard is ASTM-D6797.
Tensile Strength and Elongation Test of Fabric:
Fabric in garments has to bear a number of forces throughout its performance life. A fabric, therefore, must satisfy the minimum level of strength to satisfy customer needs. The standard test involves checking more than one parameter of the fabric. For testing tensile properties, a test specimen of the fabric is clamped in the jaws of a tensile testing machine and a force is applied until the specimen breaks. The maximum amount of force exerted by the machine, recorded from the machine scale, gives the breaking force. A tensile tester is depicted in Figure-2.
Subtract the specimen’s initial length from its length at breaking point. The difference expressed in percentage gives the elongation measurement. The method is applicable to most woven and nonwoven fabrics, knitted and stretch fabrics being an exception. The test should be performed as directed in standards ASTM-D5035 (strip method) and ASTM-D5034 (grab method).
Tearing Strength Test of Fabric:
Tearing strength is defined (ASTM D1682) as the force required to start or to continue to tear a fabric, in either weft or warp direction, under specified conditions. A tear in a fabric or garment generally occurs progressively along a line, and can be initiated by a moving fabric being caught on a sharp object. Several methods are used to measure tear strength, e.g. double tongue rip (tear) test, trapezoid tear test, (ASTM D5587) and single tongue tear test (ASTM D2661, BS 4303).
There are three methods to test the tearing strength of a fabric. The first method uses a falling pendulum (Elmendorf) type tester, which is shown in Figure-3. The tester includes a stationary clamp, a clamp carried on a pendulum that is free to swing on a bearing, and a mechanism to level, hold, then instantly release the pendulum to measure the force. The test specimen with a precut central slit is held between two clamps and the specimen is torn through a fixed distance.
The resistance to tearing is then calculated using Equation-1. The reference standard is ASTM-D1424.
………….Rs x Cs
Ft = ——————— ………………………. (1)
…………..100
Where,
Ft is the tearing force in cN (centi-Newton)
Rs is the scale reading
Cs is the full scale capacity in cN or lbf
In the second method, the tensile testing machine with a CRE is used. It is named the tongue procedure. A rectangular specimen with a cut in the short side is prepared. One tongue of the specimen is gripped in the upper jaw while the other is gripped in the lower jaw of the machine. The jaws are continuously moved apart with the application of force to propagate the tear.
At the same time the instantaneous force is recorded and graphed. The average of the highest peaks in the graph gives the value of the tearing strength. The standard reference method is ASTM-D2261.
The third type of test is known as the trapezoid procedure. An outline of a trapezoid is marked on a rectangular fabric specimen. A slit is made on the smallest base of the trapezoid to start the tear. The nonparallel sides of the marked trapezoid are gripped in the parallel jaws of the machine. Force is applied to increase separation continuously, between the jaws, to propagate the tear. At the same time the instantaneous force is recorded and graphed.
The average of the highest peaks in the graph gives the value of the tearing strength. The standard reference method is ASTM-D5587.
Yarn Slippage Test:
One of the major issues in sewn fabrics is the yarn slippage. The fabrics in garments and other sewn products should exhibit sufficient resistance to yarn slippage along the seams. The test exists to determine the resistance to slippage of warp yarn over filling yarns, or filling yarns over warp yarns, using a standard seam.
For testing the slippage of warp yarns over weft yarns a specimen is cut from the fabric with its larger side along the fabric weft. The specimen is then folded and a standard seam, parallel to the warp yarn, is made at a particular distance from the folded edge of the specimen. The specimen is then clamped between the two jaws of the tensile tester in a standard way such that the seam ideally stays at the center of the jaws. The load–elongation curve of the fabric is superimposed over a load–elongation curve of the same fabric with a standard seam sewn parallel to the yarns being tested. The resistance to yarn slippage is reported as the load at which a slippage of a specified size is seen. The test should be performed as directed in standard ASTM-D434.
Fabric (weight) Areal Density Test:
Fabric mass per unit area is a very important consideration in the selection of fabric for a particular end use. Garments made of fabric with higher areal densities are not used in the summer season, and vice versa. To determine the mass per unit area of a certain fabric a standard specimen is prepared first. This is weighed and the results are expressed in mass per unit area. The standard test method is ASTM-D3776.
A common approach is to use a grams per square meter (GSM) cutter, as shown in Figure-4. The cutter prepares a circular specimen of diameter 113 mm. The weight of this specimen in grams, multiplied by a factor of a hundred, gives the weight (in grams) of the fabric in a square meter.
Bowing and Skewness Test of Fabric:
Bowing is the displacement of filling yarns (woven) or courses (knitted) from an imaginary line perpendicular to the fabric selvage. When the same displacement is in angular form, it is regarded as skewness. Bowing and skewness disturbs the grain line of the garment patterns and causes discomfort and improper functioning of the final garment. In addition, it also diminishes the aesthetics of the garment. These measurements are equally important for accepting a fabric lot.
To measure the bowing a steel tape may be used. The straight edge of the steel tape is placed across the fabric width to measure the distance between the two points where a selected weft yarn or course of fabric meets the two edges or selvages, denoted by “BL” in Figure-5. The greatest distance between the straight line and the marked filling or course line is measured parallel to the fabric selvage, as indicated by “D” in the diagram.
The fabric bow is then calculated by
………………………..D
Bow (%) = 100 (———) ………………………………. (2)
……………………….BL
Where,
D is the bow depth
BL is the base length or the straight distance between the points of the marked filling yarn/course.
To measure skewness the straight line distortion of the marked filling or course, from a line perpendicular to the selvage, is measured. Figure-6 shows the measurement of skewness in fabric.
Equation-3 is used to calculate the skewness.
……………………….AB
Skew % = 100 —————- ………………………………. (3)
………………………BC
Where,
AB is the fabric width, perpendicular to the selvage
BC is the skew depth
The reference standard test method is ASTM-D3882.
Air Permeability Test:
This is the ability of a fabric to allow air passage perpendicular to the fabric plane. This is an important testing requirement regarding the acceptance/ rejection of commercial shipments. It is also important for garment manufacturing as the fabric with too little air permeability will not allow sweat to evaporate and hence create body irritation and odor along with the accumulation of perspiration. Therefore, fabric may be required to pass a certain level of air permeability before it is accepted to make a certain garment.
The rate of air flow passing perpendicularly through a known fabric area is adjusted to obtain a prescribed air pressure differential between the two fabric surfaces. From this rate of air flow, the air permeability of the fabric is determined. The scale provides a reading in cm3/s/cm2 or ft3/min/ft2.
An air permeability tester is illustrated in Figure-7. The reference standard test method is ASTM-D737.
Dimensional Changes after Home Laundering:
Fabric shrinkage is one of the prime considerations for the selection of fabrics in apparel manufacturing. If the appropriate shrinkage is not considered the garment may run short on the wearer’s body after washing. For that purpose, the shrinkage along both warp and weft is calculated and adjusted in garment specifications in the cutting room. The stitched garment may appear enlarged in some dimensions, but it adapts to the original customer requirements after washing. Similarly, it is important to measure fabric elongation.
To calculate fabric shrinkage, a square of a particular size is cut from the individual fabric roll. A further square is marked inside at a certain distance from the edges, as shown in Figure-8. This is done because the fabric may experience fraying in washing and run short on dimensions, which will not represent the true shrinkage percentage. The marked sample is then washed and dried as per standard conditions. Sample preparations for dimensional change testing.
The difference in measurements is used to calculate shrinkage by,
………………………………………………………Change in dimension
Percentage dimensional change (%) = ————————————- x 100
……………………………………………………….Original dimension
The reference standard is AATCC TM 135.
Conclusion
Fabric testing is essential for quality control, safety, and customer satisfaction. By using these methods, manufacturers can produce reliable, high-performance textiles for different needs. Whether it’s strength, comfort, or safety, proper testing ensures fabrics meet industry standards.
