Tensile Strength of Leather: Standards and Testing

The tensile strength test measures how much force leather can handle when stretched. This test shows how durable the leather is under stress. This ensures that leather products resist tearing or breaking during actual use. Testing helps manufacturers learn about leather’s physical properties.
This information matters for:
Ensuring quality
Choosing materials
Designing products
Evaluating performance
This article explains the testing methods and key information on leather’s tensile strength.

1 Related International Standards 

ISO 3376:2020 (IULTCS/IUP 6) – Leather — Determination of tensile strength and elongation

This standard specifies methods for measuring the tensile strength and elongation of leather.

ISO 3377-2 (IULTCS/IUP 8) – Leather Tests – Tear Load Measurement – Part 2: Double-Edge Tear

This standard explains how to test the tear strength of leather. It uses the double-edged tear method.

ISO 2418 – Leather — Chemical, Physical, and Mechanical Fastness Tests — Sampling Locations

This standard defines the correct sampling locations on leather for various laboratory tests.

ISO 2419 – Leather — Physical and Mechanical Tests — Sample Preparation and Conditioning

It provides guidelines on how to prepare and condition leather specimens before testing.

ISO 2589 – Leather — Physical and Mechanical Tests — Determination of Thickness

This standard outlines the procedure for the precise measurement of leather thickness.

ISO 7500-1—Metallic Materials: Checking Static Uniaxial Testing Machines. Part 1 is about Tension/Compression Testing Machines. It looks at how to verify and calibrate the force-measuring system.

2 Equipment and Materials

The table below lists the instruments and consumables used:

2.1 Tensile Testing Machine

Accuracy: Class 1.0 (largest error within ±1%)
The grips move at a constant speed of (100 ± 20) mm/min.
During the test, the sample slippage between the grips will not exceed 1% of the initial gauge length.

2.2 Elongation Measuring Device

You can measure elongation by observing the grip separation. You can also use sensors to measure the distance between two fixed points on the specimen.
In most cases, the machine now uses the displacement between grips. It’s usually built into the testing machine.

2.3 Thickness Gauge

The instrument should follow the requirements of QB/T 2709.

2.3.1 Dial Gauge

Smallest scale: 0.01 mm
Accuracy: ±0.02 mm across the entire measuring range.

2.3.2 Test Platform

A level cylindrical surface with a diameter of (10.00 ± 0.05) mm and a height of (3.0 ± 0.1) mm.
Mounted on a coaxial circular base with a diameter of (50.0 ± 0.2) mm.

2.3.3 Presser Foot

A circular flat surface with a diameter of (10.00 ± 0.05) mm, positioned in line with the test platform.
Capable of vertical movement
The load applied when the presser foot contacts the test platform should be (393 ± 10) cN.
The dial gauge (3.1) provides a direct reading of the displacement of the presser foot.
Note: The combination of the presser foot’s weight and dimensions creates a pressure of 49.1 kPa (500 g/cm²).

2.3.4 Rigid Frame

Used to support the dial gauge (3.1), test platform (3.2), and presser foot (3.3).

2.4 Cutting Die

The cutting die must meet QB/T 2707 standards. It should cut specimens into the shape shown in Figure 1 and the sizes listed in Table 1.
An illustration of the die appears in Figure 1. The inner surface must be perpendicular to the surface of the cut material. At the cutting edge, the angle between the inner and outer surfaces should be 20°, forming a wedge shape. The depth (d) of the wedge must be greater than the thickness of the leather.
Note: The hardness grade of the die material must be suitable for use as a cutting die.

Figure 1: Sample Shape

Table 1: Sample Dimensions

Unit: mm

Specification	L	L1	L2	B1	B2	R
Standard Size	110	50	30	10	20	5
Large Size	190	100	45	20	40	10

Figure 2: Die Cutter

2.5Vernier Caliper

Accuracy: 0.1 mm

3 Testing Principle

The test measures how much force and stretching the specimen can handle. It stretches at a set rate until it hits a specific force or breaks.

4 Sampling

4.1 Sampling

The requirements of QB/T 2706 will dictate the taking of samples.

4.2 Sample Preparation

Using a cutting die by QB/T 2707, cut six samples from the grain surface. Position three samples with their long edges parallel to the backbone (longitudinal samples). Place the other three samples so their long edges are perpendicular to the backbone. These are the transverse samples.
Use a larger die to cut new samples if earlier tests show slippage between the sample and the grips.

4.3 Sample Conditioning

Sample conditioning will follow the rules of QB/T 2707.

5 Testing

5.1 Measurement of Dimensions

5.1.1 For each sample, measure the width at three points.

Do this on both the grain and flesh sides with a vernier caliper (accuracy: 0.1 mm).
For each group of 3 measurements, select a midpoint (E), as shown in Figure 1. Position the other two points between the midpoint (E) and the lines AB and CD.
The researchers will take the average of the six measurements to find the width (w) of each sample.
Note: You can use the width of the cutting die as the sample width for soft leather.

5.1.2 Measure the thickness of each sample under QB/T 2709.

Measure at 3 points: the midpoint (E) and the other two points positioned between (E) and the lines AB and CD.
The team will find the thickness of each sample by using the average of the three measurements.

5.2 Tensile Strength Measurement

5.2.1 Set the distance between the upper and lower grips of the tensile testing machine to (50 ± 1) mm for standard samples. For larger samples, set it to (100 ± 2) mm. Clamp the specimen. Make sure the grip edges line up with the AB and CD lines. Also, check that the grain side of the specimen is level. The long axis of the specimen should be parallel to the direction of tension.
5.2.2 Start the tensile testing machine and continue until the specimen breaks. Record the maximum force at the moment of rupture as the breaking force (F).

5.3 Measurement of Elongation at Specified Load

5.3.1 Following the procedure in 2.1, clamp the specimen and measure the distance between the upper and lower grips. Record this distance as L (accurate to 0.5 mm), which will serve as the initial length for the test.
5.3.2 Start the tensile testing machine. As the force goes up, watch the distance between the grips. You can either use sensors or allow the machine to record and plot a force-elongation curve by itself.
5.3.3 Record the distance between the grips (L) when the specified load is first reached. This represents the elongation of the specimen under the applied force. Do not stop the test before completing steps 2 or 4.

5.4 Measurement of Elongation at Break

• Follow the procedure in 3.1.
• Operate the tensile testing machine until the specimen breaks.
• Record the distance between the grips or the sensor reading at the moment of specimen rupture. This will be the length of the specimen at break.

5.5 Slippage Deviation

Slippage between the specimen and grips in steps 2-4 makes the test results invalid. This is true if the slippage distance is more than 1% of the initial length. In such cases, use a larger cutting die to get a new specimen and retest.

6 Results

6.1 Tensile Strength

6.2 Specified Load Elongation Rate

6.3 Breaking Elongation Rate

Use these formulas to find tensile strength, load elongation rate, and breaking elongation rate. These are crucial properties for testing materials like leather and textiles.

7 Applicability of Tensile Strength

Testing the tensile strength of leather is key for assessing its physical properties. It’s standard to check the quality and performance of leather products. Below are some common leather products and their applications for tensile strength testing:

7.1 Footwear Industry

• Upper Leather: Shoes’ upper leather faces stretching from walking, running, and other activities. Tensile strength testing checks whether the leather can withstand tension. This helps keep the shoes durable and looking good.
• Sole Leather: Leather soles need to be tough. They should resist bending and stretching while walking. This helps avoid cracks and keeps the sole in shape.
  We must test insole leather for tensile strength. This keeps it elastic. It won’t break from repeated compression and stretching over time.

7.2 Apparel Industry

• Leather Jackets and Pants: Wearing leather makes it stretch, bend, and resist friction. Tensile strength testing checks if leather will tear or change shape under pressure. This helps ensure the garment lasts longer and looks good.
• Leather Accessories: Items such as belts, bags, and gloves must be strong. This strength helps them resist damage from stretching or tearing while in use. A belt must handle stretching forces during physical activity. Also, the handles of leather bags need to resist pulling forces when lifting heavy items.

7.3 Furniture Industry

• Sofa Leather: Leather on sofas must cope with stretching and the weight of sitting or lying down. Tensile strength testing checks that the leather stays strong. It won’t crack or tear even after stretching it many times over its lifespan.
• Leather Seats: Leather on car seats and office chairs must be strong. It needs to resist damage from friction and stretching while in use.

7.4 Luggage Industry

• Travel Bags and Handbags: These bags need strong leather. It should handle heavy luggage and pulling forces during transport. Tensile strength testing checks whether leather will tear or change shape when pressed.
• Wallets and Key Cases: These small leather items aren’t used as much, but we still test their strength. This ensures they last and can handle everyday use.

7.5 Sports Goods Industry

• Sports gloves: Baseball gloves and boxing gloves need to be strong. They must resist stretching and friction during sports to avoid damage.
• Sports Shoes: Pro shoes like soccer cleats and basketball shoes have tough leather tops. This strength helps them resist stretching and friction during tough games.

7.6 Automotive Interior Industry

• Car Seat Leather: Leather in car seats faces constant movement and driving vibrations. Tensile strength testing makes sure the leather won’t crack or tear when it faces these forces.
• Car Door Trim Leather: The leather in car door trims needs to be strong. It should resist stretching when the doors open and close.

8 Leather-Related Standards

8.1 Chinese National Standards

General Technical & Sampling

• GB/T 38412-2019: General technical specifications for leather products
• GB/T 39376-2020: Leather – Sampling – Sample size for batch sampling
• GB/T 39364-2020: Leather – Chemical, physical, mechanical, and color fastness tests – Sampling locations

Physical & Mechanical Tests

• GB/T 39374-2020: Determination of bending strength
• GB/T 39371-2020: Determination of softness
• GB/T 39375-2020: Determination of dimensional change
• GB/T 17928-2023: Determination of puncture tear strength
• GB/T 40938-2021: Determination of water permeability pressure
• GB/T 22889-2021: Determination of surface coating thickness
• GB/T 39372-2020: Determination of elongation
• GB/T 39370-2020: Determination of surface reflectance
• GB/T 39369-2020: Determination of water vapor permeability
• GB/T 39452-2020: Determination of coating adhesion strength
• GB/T 39365-2020: Determination of dry heat resistance
• GB/T 40927-2021: Determination of patent leather heat resistance
• GB/T 22891-2008: Waterproof performance of heavy leather
• GB/T 40936-2021: Waterproof evaluation for clothing leather
• GB/T 22888-2021: Low-temperature cracking of surface coatings
• GB/T 39368-2020: Fold durability: Shoe upper bending method
• GB/T 43818.1-2024: Abrasion resistance – Taber method
• GB/T 39507-2020: Abrasion resistance – Martindale method
• GB/T 39500-2020: Apparent density and unit area mass
• GB/T 4689.21-2008: Measuring static water absorption

Water Resistance Testing

• GB/T 22890.1-2024: Water resistance – Line compression method
• GB/T 22890.2-2024: Water resistance – Angle compression (Mezze method)

Color Fastness

• GB/T 42949-2023: Rotating friction color fastness

Product-Specific

• GB/T 42167-2022: Leather for clothing
• GB/T 16799-2018: Leather for furniture

Chinese Industry Standards

Mechanical & Physical Testing

• QB/T 2710-2018: Tests for strength and stretch
• QB/T 2714-2018: Fold durability testing
• QB/T 2707-2018: Sample preparation and conditioning
• QB/T 5253.1-2018: Soiling performance – Martindale method
• QB/T 2726-2005: Abrasion resistance test
• QB/T 2711-2005: Tear strength – Double tear method
• QB/T 2712-2005: Grain strength and stretch – Spherical bursting
• QB/T 2728-2005: Atomization performance test
• QB/T 2713-2005: Shrinkage temperature test
• QB/T 4198-2011: Tear strength – Single tear method

Product-Specific

• QB/T 5796-2023: Chrome-free shoe upper leather
• QB/T 2540-2023: Leather straps
• QB/T 1873-2023: Chrome-tanned shoe upper leather
• QB/T 2703-2020: Leather for automotive decoration
• QB/T 1615-2018: Leather garments
• QB/T 5245-2018: Leather clothing with down-filled linings
• QB/T 5087-2017: Leather for luggage
• QB/T 1872-2004 / 1993: Leather for clothing
• QB/T 1873-1993: Leather for shoe uppers
• QB/T 2709-2005: Determination of thickness
• QB/T 2001-1994: Leather for shoe soles
• QB/T 2680-2004: Leather for shoe linings
• QB/T 2704-2005: Leather for gloves
• QB/T 2288-2004: Transfer film leather

Terminology & Support Standards

• QB/T 1582-1992: Leather hardware industry terminology
• QB/T 2262-1996: Leather industry terminology
• QB/T 5054-2017: Release paper for synthetic leather

SN/T Inspection & Testing Standards

• SN/T 5230-2019: Weathering test for automotive leather interiors
• SN/T 3704.3-2013: Leather garment inspection rules for import/export
• SN/T 3474-2014: Compliance assessment of leather garments and products