Sponge Fatigue Hardness Measurement Test and Method According to ISO 3385 Standard

The Sponge Fatigue Test is a mechanical test method applied to determine the hardness and fatigue resistance properties of flexible cellular polymer materials (especially polyurethane-based foams). Hardness and fatigue resistance are among the most important parameters of elastic materials such as foam in terms of user comfort, durability, and performance.

The test measures the deformation of the foam under a certain load to evaluate its load-bearing capacity. In addition, the fatigue behavior of the material is examined through repeated loading. This test is widely used in industries where comfort and durability are critical, such as automotive, furniture, bedding, packaging, and cushioning materials.

ISO 3385 Standard

ISO 3385 defines an internationally recognized test method that determines the fatigue behavior and hardness change of flexible cellular polymers under repeated load.

  • Scope: Flexible cellular polymers, primarily polyurethane foams used in the automotive, furniture, bedding, and packaging industries.

  • Test Parameters: Repeated loading cycles are applied at certain compression ratios, and the change in the foam’s hardness value is measured.

  • Validity: Published by the International Organization for Standardization (ISO) and accepted worldwide.

Test Application Method

1. Sample Preparation

  • Samples are prepared in specific dimensions before testing.

  • Prior to the test, foams are conditioned for at least 16 hours at 23°C ± 2°C and 50% ± 5 relative humidity.

2. Test Equipment Features

  • Fatigue and hardness testing device equipped with a compression plate

  • Sensitive load cell for force measurement (in Newtons)

  • Compression mechanism operating at a defined speed (e.g., 100 mm/min)

3. Application Steps

  1. The sample is placed on the test table.

  2. The compression plate applies a certain compression to the foam.

  3. The foam is subjected to repeated loading cycles (e.g., 80,000 or 100,000 cycles).

  4. The hardness of the foam is measured at the beginning and at the end of the test.

  5. The change in hardness after fatigue is recorded.

Hardness Measurement Principle

Foam hardness and fatigue resistance are based on the relationship between applied force and resulting deformation. According to ISO 3385:

  • The initial hardness of the sample is measured.

  • After the specified loading cycles, hardness is re-measured.

  • The change in hardness indicates the comfort life and durability of the material.

This method reveals not only the initial hardness of the foam but also the performance loss during long-term use.

Application Areas

  • Automotive Industry: Comfort and long-term durability testing of car seats

  • Furniture Production: Fatigue resistance control of seating groups

  • Mattress and Bedding Products: Maintaining comfort and support performance throughout service life

  • Packaging and Cushioning Materials: Evaluation of impact absorption performance after repeated use

Interpretation of Results

The Sponge Fatigue Test conducted according to ISO 3385 determines both the initial hardness value of the foam and the loss of hardness after fatigue.

  • High Durability: Low hardness loss indicates long-lasting material.

  • Low Durability: Significant hardness loss indicates early deformation.

  • Optimum Values: Materials providing both comfort and durability are preferred for quality products.

Therefore, this test is an essential part of quality control in mass production.

Frequently Asked Questions (FAQ)

1. When is the Sponge Fatigue Test performed?
It is performed during product design, quality control processes, and to verify fatigue resistance and hardness after production.

2. Are there other standards besides ISO 3385?
Yes. Standards such as ASTM D3574 are also used for foam fatigue and hardness testing.

3. How does hardness and fatigue value affect product quality?
They directly determine product comfort, service life, and long-term customer satisfaction.

4. Is the ISO 3385 test internationally valid?
Yes, since it is published by ISO, it is globally recognized.

5. How long does the test take?
Excluding conditioning, the duration depends on the number of cycles and may range from several hours to several days.