Foam Industry Guide for Material Testing
Foam is a type of polymer that has been mixed with a blowing agent to create a cellular structure. Once the foam bun has cured, it can be cut into pieces and used for a myriad of different applications.
Foam has once again become popular in the bedding and furniture industry. In the past, the manufacturing process used rubber and included the addition of harmful carcinogenic chemicals. This foam was also difficult to recycle and the industry was a . However, with recent advances in technology and material science, manufacturing foam products has become both better for the environment and for the end customer. Foam is now rapidly becoming the industry favorite as the base material for pillows, mattresses, and furniture. Performance foams and rigid foams are also used as structural material for lightweighting purposes in the automotive and aerospace industries.
One interesting thing about the foam industry that is different from all other industries has to do with shipping costs. Foam can consist of up to 95% or even 98% air. For this reason, foam products are expensive to ship relative to their base material costs. Most manufacturers are either small, privately owned enterprises, or consist of larger businesses with multiple, regional production facilities. In some cases the foam can be compressed for shipping, however the foam can be permanently damaged if it gets too cold and enters its glass transition temperature phase, or if it is compressed for too long.
Indentation Force Deflection (IFD) - also known as Indentation Load Deflection (ILD), is the measure of a foam material's resistance to a compression force. This measure is used to determine the "firmness" or "softness" of the foam. IFD is the amount of force it takes to compress a sample to a specified amount of deflection. A common IFD measurement could be 30 lbs. at 25% deflection, or 60lbs. at 65% deflection. Almost all IFD measurements are communicated assuming ASTM D3574 testing methods.
Stiffness Factor - also known as the sag factor, is the ratio of the IFD at 65% to the IFD at 25%. Using the previous example, the stiffness factor would be 60/30 or 2. Stiffness factor values are almost always somewhere between 3 and 1. A stiffness factor closer to 1 would mean that the foam is more susceptible to bottoming out.
Introduction to ASTM Testing for Foam
ASTM D3574 - How to Configure a Universal Testing Machine for Foam Compression Testing
Almost any dual column universal testing machine can be retrofitted to test ASTM D3574 on foam samples. Other companies may recommend a specially designed system for foam testing, however this is not necessary unless you are performing high speed, dynamic testing. If you are only looking to static testing for IFD, a regular H sytle frame can be used as long as there is enough space (16"+) Between the columns.
By configuring the system with the correct grips and fixtures, the machine can test according to the D3574 standard. The bottom compression plate should measure slightly more than 16 x 16" inches. This works out to about 404 x 404 mm. This bottom plate should have 6mm holes drilled into it and spaced out at a distance (center to center) of 20mm. The top compression platen should have a beveled edge and measure 8" in diameter. This top compression platen should be attached to a universal joint, which is also known as a swivel joint or cardan joint. This special joint allows the platen to dynamically adjust as it is compressing down onto the sample. The standard foam testing sample is 16 x 16 by 4" thickness.
ASTM D3574 - Foam Tensile Testing can be performed by switching out the compression plates for tensile grips. Self-tightening Scissor Grips are ideal for this type of testing, but roller grips and vise grips can also be used.
ASTM D3574 - Tear Testing is a trouser style tear procedure. The same type of tensile grips should work fine for this test.
Tensile Testing Fixture - Self Tightening Roller Grips
Compression Fixtures for Foam
Test on a sub-standard size sample
Software for Foam Testing
Universal grip offers the Graphwork 6 software for Galdabini's full line of tensile and compression testing machines. The software can be delivered with pre-loaded ASTM D3574 testing procedures. UGC and Galdabini's engineers will ensure that you are testing according to the appropriate ASTM standard. The software also has database tools for exporting results to Laboratory Information Management Systems (LIMS). Software training and well-documented manuals are available with every machine. Remote support is offered through the TeamViewer screen-sharing software.