ADVANCED MATERIALS & PROCESSES | JANUARY 2026 30 the former example, the load is applied to the band to secure it around the pulleys and is sustained as a result of the pulleys maintaining their position. Over time, the applied load on the band will reduce due to deformation, while the elongation of the rubber band remains the same. In the latter case, the weight/load applied to the rubber band remains constant, so creep comes in the form of increased elongation. As deformation forms in the band, it can no longer support the weight at its current position, so to compensate, the weight’s position should drop to increase the stress in the material to support it. In laboratory testing, ideal operating conditions must be maintained, such as temperature, air quality, and any other aspects that would be considered standard conditions for the final product. For accurate results, these properties must be as consistent as possible throughout the testing duration. These conditions can be varied to see the effect of different environmental conditions on the behavior of products while in use, and can be instrumental for determining the longevity of rubber products in varying environments. When running a creep test, rubber samples have the benefit of greater the extensometer rather than the positional changes of the tensile tester. Important for rubber and elastomer applications, a long-range extenso- meter is an easy-to-use, practical fixture providing long travel distance. Some models of test stands, such as in the Starrett line, also offer built-in options for extensometers that are designed to run the full length of the machine’s testing space, eliminating the need for secondary storage when the extenso- meter is not in use (Figs. 1 and 2). CREEP TESTING In both compression and tensile testing of materials, there is deformation in the sample. For many materials, when kept within a certain range, they will return to their original shapes after the applied forces are removed. This is most notable in metals such as various steels used in tool manufacturing or spring manufacturing. How- ever, if these materials are left under the load application for a significant period, they will exhibit an overall change in either the material shape or supported load. In materials testing, this is often referred to as a stress-relaxation test, where the material deforms because of sustained loads rather than solely applied loads. For rubber, this creep testing can be informative regarding the longevity of these materials when intended to be designed for sustained loads. “Creep” can be observed in two aspects in the testing of materials—the reduction of applied forces when a deformation is applied relative to distance (either through elongation or compression), or the change in elongation as a result of sustaining a fixed load. An example of either instance would be a rubber band, either serving as a belt between two fixed pulleys, or as a support for a free-hanging weight. In Fig. 3 — Data reflecting the elongation and break of a rubber sample. The elongation is measured from the extensometer rather than machine movement. Fig. 4 — Comparison of two data sets in elongation and break testing.
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