ASTM D3574 describes a range of tests used to characterize the properties of flexible polyurethane foams. These foams are most commonly used by the furniture, bedding, and automotive industries for the creation of seats and mattresses that will improve consumer ergonomics and maximize comfort. In order to form a complete picture of a material's mechanical properties, extensive testing to ASTM D3574 is required. This guide is designed to introduce you to the basic elements of ASTM D3574 testing, including an overview of the equipment, software, and specimens needed. However, anyone planning to conduct testing to this standard should not consider this guide an adequate substitute for reading the full standard.
What Does it Measure?
ASTM D3574 includes 18 different mechanical tests that are designed to evaluate the compressive, tensile, and tear resistant properties of foam. The most commonly performed tests are the compressive tests, which have the greatest impact on product performance. Though not all of the 18 tests require the use of a universal testing machine, the following ones do:
- Test B1 - Indentation Force Deflection Test (IFD) *Most Common
- Test B2 - Indentation Residual Gauge Length Test (IRGL)
- Test C - Compression Force Deflection Test *Most Common
- Test D - Constant Deflection Compression Set Test
- Test E - Tensile Test
- Test F - Tear Resistance Test
While static tests provide valuable information regarding the initial foam properties and limitations, long-term dynamic testing provides manufacturers insight into the durability of the product. An end user expects foam products to feel supportive not only on the first use, but the one thousandth and millionth use as well. The following tests are capable of being performed on ElectroPuls dynamic systems:
- Test I2 - Dynamic Fatigue Test, Roller Shear
- Test I3 - Dynamic Fatigue Test, Constant Force Pounding
- Test I4 - Dynamic Fatigue Test, Carpet Cushion
- Test I5 - Dynamic Fatigue Test, Constant Deflection Pounding
Is ASTM D3574 the Right Standard for You?
There are many different testing methods which apply to various types of foams, including rigid polyurethane foams. ASTM D3574 applies only to flexible polyurethane foams: the technical definition between flexible and rigid is explicitly defined within the standard. ASTM D3574 testing is ideal for performing comparative testing between different foam samples, often differentiated by chemical composition, density, and porosity. This standard is often performed in conjunction with more sophisticated pressure analysis to mimic the loading applied by the human body.
Materials Testing System
Most ASTM D3574 compression testing is performed on a dual-column universal testing machine like Instron's 5960 series systems. The size of the specimen and related fixtures requires the use of a dual column system, while the tensile and tear resistance tests can be performed on either a dual column or a single column system, such as Instron's 5940 series. A 5kN or 10kN (1125 or 2250 lbf) system is the most common, capable of applying the vast majority of compressive and tensile forces produced during ASTM D3574 testing.
Fixtures and Grips
The ASTM D3574 standard requires the use of a specialized compressive fixture that minimizes the variability between labs when performing tests B1 and B2. The fixture has a perforated base with set hole diameters and spacing, which allows air to flow through the foam while under compression. The anvil utilizes a spherical seat to self-align during a test, minimizing any off-center loading.
For tests C and D, standard, non-perforated rigid platens can be used. For these tests, the size of the platens is dependent on the required specimen geometry. Because both tests recommend a specimen size of 50 mm x 50 mm x 25 mm, a standard 6 inch diameter platen is suitable.
Performing the tensile and tear tests require the use of side action grips. Advanced screw action grips are ideal because of their ability to manually adjust the clamping pressure and distance between the jaw faces. The foam specimens are very compliant, and most pneumatically-driven grips impart too much clamping pressure and cause the specimen to fail prematurely. Serrated faces are typically used to prevent the specimen from slipping out of the jaw face.
The test procedures outlined in the standard for compressive properties include complex series of ramps and holds to evaluate the material. For example, the Indentation Force Deflection Test (IFD) requires pre-cycling of the specimen and multiple ramps and holds which cannot be programmed with a standard method template. Bluehill Universal’s TestProfiler allows the user to create complex test sequences with ease. The software interface uses intuitive icons and effortless workflows to simplify the process, minimizing the amount of time operators needs to spend on method creation. The following is an example of a TestProfiler sequence in accordance with the standard as well as the subsequent curve produced from the test:
For labs with high-volume testing needs, the machine setup can be modified in several ways, up to and including full automation, in order to speed up the testing process. Fully automated systems such as Instron's AT3 are designed to incorporate specimen measurement, specimen loading, testing, and removal, and are able to run for hours without operator interaction. These systems help to reduce variability due to human error and can be left running unattended after lab operators have gone home for the night.