Many manufacturers provide material test reports (also known as technical reports or specification sheets) as a service to aid their customers. These reports show the performance of a cured rubber compound when subjected to a variety of standardized ASTM tests. Provided these tests mirror the anticipated service conditions, you can use them to make an informed decision regarding the compound’s suitability for your application.

To help you better understand just how much test reports can tell you, let’s take a closer look at a sample report whose subject is the same 70 (Shore A) durometer nitrile compound that we dealt with in “Understanding ASTM D 2000 / SAE J200.” As we go through the report line by line, you’ll find references to many of the most commonly used ASTM tests. Keep in mind, however, that not every report you see will (or should) cover all of these tests. We’re including them here simply to help you get better acquainted with as many tests as possible.

A. This first line tells you the absolute basics: you are looking at a test report of “N470,” a nitrile compound that has a durometer hardness of 70 (Shore A).

B. The next item lists all of the ASTM specifications to which the N470 material conforms. Each of these are defined individually during the course of the report, but for now, just recall from “Understanding ASTM D 2000 / SAE J200” that each line call-out entry corresponds to a particular test. For example, “EA14” is an ASTM D 471 70-hour water resistance test conducted at 100° C.

C. “Original properties” are the initial attributes of the material. Information in this and all subsequent entries is broken into two columns: the “specification” (what is required to be acceptable) and the properties (or response) of the “N470” nitrile. There are six different original properties on this report: 1) Hardness, 2) Tensile Strength, 3) Elongation, 4) Modulus at 100%, 5) Tear Resistance, and 6) Specific Gravity. Note that specific gravity (SG) is not specified on the report; rather, it is a reported figure to be used as a quality control criterion. The SG of N470 (1.25) is understood relative to water’s SG of 1.00. Compound N470 is 25% heavier than water.

D. The first test on this report is “heat resistance” (also known as heat aging or air aging). Per the line call-out, our nitrile is a Grade 2 “BG” compound. This would normally send you to the D 2000 or J200 documents, where you would turn to the “BG Materials” section of Table 6 and see data similar to that shown in Table 22. You’ll see that “A14” is the suffix designation for “heat resistance” as gauged by ASTM D 573, a 70-hour test conducted at 100° C.

Why, then, is A14 not listed among the additional suffix requirements in this material’s line call-out? It is omitted from the call-out because there are no A14 specifications for Grade 2 BG compounds. In Table 22, the Grade 2 column across from row A14 is empty, so the heat resistance specifications column in our sample report is blank. When there are no specifications, a material cannot be said to “conform” to a given test, and the corresponding suffix designation is not listed in the call-out. We’ve chosen to include heat resistance on this report because it is a common test used to gauge resistance to oxidation and thermal attack over time. You’ll no doubt see it regularly on test reports, and it will likely be specified in three properties: 1) Hardness Change, 2) Tensile Change, and 3) Elongation Change.

E. The second test is “compression set” (B14 in the line call-out) as determined by ASTM D 395, a 22-hour test conducted at 100° C. This report lists one property specification related to compression set: Percent of original deflection, which is specified at a 25% maximum. In this instance, the N470 test specimen takes a 14% set. Be aware that a number of factors other than the compound itself can greatly affect compression set results, including the test temperature and the sample thickness.

F. The third test is “water resistance” (EA14 in the line call-out) as determined by ASTM D 471, a 70-hour test conducted at 100° C. This report lists two property specifications related to water immersion: 1) Hardness Change and 2) Volume Change.

G. The next four tests gauge fuel and oil resistance (EF11, EF21, EO14, and EO34 in the line call-out). In each case, there are four property specifications: 1) Hardness Change, 2) Tensile Change, 3) Elongation Change, and 4) Volume Change. Per J200 / D 2000, EF 11 is the suffix designation for ASTM D 471, a 70-hour test conducted at 23° C using Reference Fuel A. That’s good to know, but you’re probably wondering what EF11 and the other fluid resistance tests can really tell you about a compound.

Put simply, fluid resistance tests give you an indication of how the compound will react when brought in contact with fuels and oils. In most cases, the primary concern is swelling, though compound degradation is also common. Recall that volume changes (either swell or shrinkage) are typically accompanied by changes in physical properties, including hardness, tensile strength, modulus, elongation, tear resistance, and compression set.

ASTM Reference Fuels A through K (see Table 17) have been specifically selected to test compounds in contact with gasolines or diesel fuels. Which tests are called for depends on which fluid(s) the seal will encounter. For example, Reference Fuel A (used in the EF11 test) is a 100% isooctane fluid which mirrors the shrinking or low-swell effects of gasolines composed primarily of straight-chain aliphatic (rather than ringed aromatic) hydrocarbons. If the compound in question will be used around gasolines with a very high aliphatic content, then an EF11 test is a good idea. Reference Fuel B (used in the EF21 test) is a 70% isooctane-30% toluene mixture. The toluene content lends the mixture a level of aromaticity, enabling Reference Fuel B to more closely approximate the swelling effects of commercial gasolines.

The other two fluid resistance tests on this report are based on shrinking or swelling in lubricating oils rather than fuels. EO14 is the suffix designation for another ASTM D 471 test, this one lasting 70 hours and conducted at 100° C using Number 1 Oil. EO14 is commonly used to gauge elastomer shrinkage. The time and temperature requirements for EO34 are identical to EO14, with the exception that Industry Reference Material (IRM) 903 is used rather than Number 1 Oil. EO34 is a common tool for gauging elastomer swell. As with the Reference Fuels, the choice of oils in testing is not arbitrary. Rather, Number 1 Oil and IRM 903 are used because they have an aniline point similar to the aniline point of a fluid to be found in service.

The aniline point is the lowest temperature at which equal volumes of aniline (an oily, colorless, and poisonous organic liquid derived from benzene) and the oil will completely dissolve in one another. The aniline point is actually a good measure of the aromatic content, or the amount of unsaturated hydrocarbons present in the oil. The higher the level of unsaturants, the more easily the organic aniline can “step in” to combine with the oil, and thus the aniline point will be low. A low aniline point is important because it translates to a higher potential for swelling certain rubber compounds.

Number 1 Oil has the highest aniline point (124° C ± 1°) of the ASTM test oils, meaning it typically causes the least amount of rubber swell. As is clear by looking at the EO14 volume change specification (-10% to +5%), Number 1 Oil actually has the potential to cause more shrinkage than swell. Testing with Number 1 Oil is thus a common tool for gauging oil-induced shrinkage due to plasticizer extraction. IRM 903, on the other hand, has the lowest aniline point (70° C ± 1°) among the test oils and typically causes the greatest swell. Be aware that IRM 903 is used in lieu of the now-obsolete Number 3 Oil for EO34 testing.

H. The eighth test is “impact brittleness” (also known as low-temperature brittleness; Z1 in the line call-out). Note that this is a three-minute test conducted at -25° C. Per ASTM D 2137 (Method A), low temperature tests are normally conducted at -35° C, -40° C, or -55° C. For example, if this test had been conducted at -40° C, F17 would have been noted in the line call-out. Because this test was conducted at a non-standard temperature (-25° C), it is noted in the line call-out using a special “Z” suffix. (Per D 2000 / J200, special suffix requirements begin with a “Z” and must be specified in detail, including test methods.) Our report has one specification related to Z1, which is conducted on a pass-fail basis only: No cracks in the material after it is struck once. N470 passes this test.

On some reports, you may also see a “temperature retraction” TR-10 listing. Though TR-10 is not covered by a D 2000 suffix, ASTM D 1329 does detail TR-10 as a way to gauge a compound’s crystallization and visco-elastic properties at low temperatures. In this case, specification is for the material to remain viable at -25° C. N470 passes this test. For more on TR-10 testing, see Quality Assurance: Low Temperature Effects.

I. The ninth test is another special stipulation required by the user of the material (Z2 in the line call-out). In our example, “Z2” is “resistance to marking.” There is one specification related to this test, which is conducted on a pass-fail basis only: Non-marking by the material. That is, the compound should not leave any mark when wiped on white paper with a 0.03 MPa contact pressure. N470 passes this test.

In some instances, a Z suffix may be used for something as basic as a hardness reading, as with the specification for a 75 (Shore A) durometer fluorocarbon. Because the line call-out system only allows three digits for both durometer and tensile strength (as with “714” indicating a 70 durometer material with a tensile strength of 14 MPa), it is not possible to specify a 75 durometer material in this way. A special Z suffix would be needed.