Fully automated fabric stiffness testing serves as a critical method for evaluating a fabric's resistance to bending (stiffness and softness), widely applied in quality control for textiles such as cotton, wool, synthetic fibers, and home textiles. Its core principle involves automatically measuring the bending deformation of fabric samples under specific conditions via mechanical devices to calculate stiffness values. This method offers advantages including high precision, excellent repeatability, and reduced human error. The following details the fully automatic fabric stiffness testing method across six dimensions: testing principle, standard basis, instrument structure, operational procedure, data processing, and precautions.

I. Testing Principle

Fabric stiffness fundamentally represents a fabric's resistance to bending deformation, closely related to fiber type, yarn structure, fabric weave, and finishing processes (such as coating or calendering).

Fully automated testing employs the “cantilever beam method” (the mainstream approach): one end of the fabric specimen is fixed as a “cantilever,” while the other end is allowed to hang freely. The instrument automatically applies a small external force (or relies solely on the sample's own weight) to bend the sample to a specific angle (e.g., 45°, 30°, 15°). The bending length (L) or bending moment (M) at the free end is recorded at this angle. This value is then combined with the sample's mass per unit area (g/m²) to calculate the stiffness index.

Bending Length (L): The horizontal distance the free end extends beyond the fixed end when the specimen is bent to a specified angle, measured in cm.

Stiffness Value (S): Commonly expressed as “bending length × mass per unit area” (unit: mg·cm). Higher values indicate greater fabric stiffness.

II. Reference Standards

Testing standards in different countries/regions specify requirements for specimen dimensions, bending angles, environmental conditions, etc. Common standards include:

GB/T 18318-2009 Textiles—Determination of bending length of fabrics—Cantilever method

ISO 9073-7:1998 Textiles—Test methods for nonwovens—Part 7: Determination of bending length and bending stiffness

AATCC 124-2020 Evaluation of fabric appearance smoothness and stiffness

JIS L1096:2020 Test methods for textiles

III. Test Procedure

Using GB/T 18318-2009 (45° bend angle) as an example:

1. Sample Preparation

Randomly select at least 5 specimens from different areas of the fabric sample. Each specimen should measure 25mm (width) × 150mm (length). Test 5 specimens each in the warp and weft directions to evaluate stiffness differences between warp and weft.

Avoid fabric edges (≥10cm from edge) and defects (e.g., holes, oil stains). Sample edges must be straight (cut with a dedicated cutter to avoid frayed edges).

Environmental Conditioning:

Balance samples in standard temperature and humidity conditions for at least 24 hours (20±2°C, 65±4% RH). Maintain stable conditions throughout testing (prevent airflow interference with specimen bending).

2. Instrument Calibration

Before testing, calibrate the instrument using a standard calibration block (metal strip with known bending length):

Secure the calibration block in the fixture and set the bending angle to 45°;

Initiate the test. If the displayed bending length deviates ≤0.1mm from the calibration block's standard value, the instrument is functioning correctly; otherwise, adjust the optical sensor or mechanical precision.

3. Parameter Setting and Testing

Power on the instrument and its software, select the test standard (e.g., GB/T 18318-2009), and set parameters:

Bending angle: 45°;

Test direction: Warp (or weft);

Sample quantity: 5 pieces (per set);

Movement speed: 5 mm/s (standard recommendation).

Clamping the specimen:

Place one end (lengthwise) of the specimen into the fixture, ensuring it lies flat against the fixture without tension or slack. After clamping, the free end of the specimen should hang naturally downward.

Initiate Test:

The instrument automatically drives the fixture to move, gradually extending the free end of the specimen to initiate bending;

An optical sensor continuously monitors the bending angle. When 45° is reached, the fixture stops moving, and the software automatically records the “Bending Length (L)”;

Repeat the operation to complete testing for all warp and weft specimens.

4. Data Processing and Reporting

Software automatically calculates:

Stiffness value of a single specimen:

S = L×m (where m is the fabric mass per unit area, g/m², pre-measured using an electronic balance with 0.01g precision);

The average (Sˉ), standard deviation (SD), and coefficient of variation (CV% = SD/Sˉ × 100%) for the sample group. CV% must ≤5% (otherwise, resampling is required to eliminate sample non-uniformity effects).

Report Generation:

The report must include: sample name, fabric composition, test standard, temperature/humidity, warp/weft bending length, warp/weft stiffness value, average value, CV%, and be signed for confirmation.

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