Foams test specimens

The hydraulic crush point of a foam is also important in determining to what maximum hydrostatic pressure it can be subjected without rapid failure via high water absorption. Water absorption is another important factor. A high-quality syntactic foam displayed less than 3% water absorption after six weeks of exposure to its ultimate hydrostatic strength for 1-in-diameter by 2-in-long test specimens. The test pressure employed should be not greater than 75 to 80% of the crush point. 

ASTM D 3574 - Test G is another method used for air flow of flexible foams. The test measures the ease with which air passes through a cellular structure. The test consists in placing a flexible-foam core specimen in a cavity over a chamber and creating a specified constant air-pressure differential. The rate of flow of air require to maintain this pressure differential (125 Pa) is the air-flow value. The results are reported in cubic decimeters per second (dm /sec). Tests are usually carried out in two directions parallel to foam rise and perpendicular to foam rise. 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

BS 4370, Part I. Method 3 [8], which is related to ISO 844, I985 [9], gives a result for either the compressive strength or the compressive stre,ss at 10% compression of the foam. The test specimen should where possible be a cube of 50 mm side, and this material is subjected to increasing compression at a fixed rate of I0% of the thickness per minute until the specimen is reduced to 90% of the original thickness. 

Three to four specimens were produced for any given set of conditions. Four test specimens were die-cut from each foam pad and evaluated for each physical property listed in subsequent data tables. All results were included in calculating averages and standard deviation. Each test was carried out as specified in ASTM D3574 [5]. 

Standardized methods cover tests of rigid self-supporting specimens, flexible films, and expanded materials with a bulk density not lower than 100 kg/m. Types of specimens laid down by the standard ISO/DIS 4589-1983 are listed in Table 3.5. Specimens for other standards are essentially identical to these except for ASTM D 2863-1977 in which specimens I, II and III are not involved instead, the oxygen index of rigid solids is determined on specimen IV, while specimens with cross section of 12.5 mm square are used for testing plastic foams. Testing flexible films is the same for all standards. 

The first and hitherto most wide-spread standard flammability test for plastics foams, ASTM D 1692 has been withdrawn. The practically identical ISO 3582-1978 prescribes a test specimen of 150 mm x 50 mm with a thickness between 5 and 13 mm, placed on a horizontal wire gauze of 215 mm x 75 mm. 13 mm of the length of the gauze is bent upwards to a right angle as shown in Figure 3.60. The specimen is marked 125 mm from the end to be ignited then placed in a holder (Fig. 3.61). 

Compressive strength n. The load at which a test specimen fails in compression, divided by the original cross-sectional area perpendicular to the load. For rigid plastics, ASTM test D 695 is used for rigid foams, D 1621. These tests also prescribe procedures for estimating compressive moduli. The actual mode of failure of a stiff material in a test of compressive strength is usually by diagonal shear. 

Fourteen commercially available organic foam insulations were examined to determine their suitability for insulating liquid hydrogen tanks of subsonic hydrogen fueled aircraft. Materials investigated were polyurethane, polymethacryllmide, polyisocyanurate, polymetric isocyanate, polybenzamidazole, toluenedi isocyanate, and isocyanate foam. The test specimens included foams with chopped fiberglass reinforcements, flame retardants, and vapor barriers. 

Resilience ri- zil-yan(t)s n (1824) (1) The degree to which a hody can quickly resume its original shape after removal of a deforming stress. When the body is a standard test specimen, the resilience, expressed as the percentage recovery from a stated maximum strain, may be attributed to the material from which R the specimen was made. ASTM Tests D 926 and D 945 (section 09.01) describes compression and shear tests for resilience of rubber and foam rubber. 

The top housing of the apparatus was insulated by foamed-in-place polyurethane. The lower housing and transfer line were vacuum jacketed. The vent line was insulated by 4 feet of block polyurethane foam from the top of the test chamber. The static heat leak resulted in vaporization of less than 1/2 liter of liquid nitrogen per hour. In operation, however, the vaporization was primarily a result of friction heat from the test specimens and the shaft seals, A 100-liter dewar of liquid nitrogen was usually sufficient for up to four 1-hour runs or one 5-hour run. 

Since the mechanical properties of foamed plastics are functions of their densities, however, and since test specimens cut from the same large sample will show variations in density, comparison of the properties of different specimens can only be made after accounting for this variation. Manufacturers literature gives mechanical properties of different types of plastic foams either as an exponential function or as... 

The steam autoclave test consists of exposing the foam specimens to a low-pressure steam autoclave at a prescribed temperature and time, and observing the changes in the physical properties of the specimen. The test specimens are exposed to steam following specified preconditioning. After the exposure period, specimens are properly dried in a dryair oven. The compression load deflection is obtained before and after exposure and percent change from original value is reported. The steam autoclave compression set value is also calculated. 

The heavier material tends to foam, therefore the operator must exercise considerable care. Overheating must be avoided so that neither the test specimen nor the dish are heated to a red hot appearance, as this can result in loss of ash. Likewise, the flame must never be higher than the rim of the dish to avoid superheating the crust, thereby producing sparks that can result in considerable loss of ash. 

Note 16 Warning—After 20 min at ambient temperature, the temperature of the test specimen will be approximately 50 C. The vapor pressure at that temperature may still exceed 100 kPa. Under these circumstances, inattentive opening of the pressure vessel may induce foaming with resultant loss of sample and possible injury to personnel. 

There are several ways to measure a material s resistance to tearing. In these tests, the applied force is not distributed over the entire specimen but is concentrated on a slit or notch and the tear strengtii is reported as the force required to propagate a tear from this point. For urethane elastomers and foams, the most... 

We prepare force versus compression plots in a similar fashion to force versus elongation plots. We generally perform compressive testing over a much more limited range of strain than tensile testing. Samples typically take the form of thick pads, which do not break in the same manner as tensile specimens. The limit of compressive strain can approach 100% for low density foams, but is much less for other samples. The most common property that we obtain from this mode of testing is compressive modulus. 

PU foam crumb must also have been made from PU foam block which meet the relevant requirements. Polystyrene foam beads are considered to have passed the test if the beads cascading from the specimen consistently extinguish the gas flame (Table Vil). 

POLYURETHANE FOAM SHEETS OR BLOCKS. These are required to resist ignition source 5 (17 gram wood crib) of BS5852 Part 2 except that the flames may penetrate the full depth of the specimen and that the mass loss (due to burning and liquid residues falling from the test rig) shall not exceed 60 grams. 

Although the ignition resistance of upholstered furniture, mattresses and bed assemblies are specified by tests on the final composite specimen, filling materials and foams are additionally required to conform to the 1988 regulations (Table IX). 

---