A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 2 2 5 as tensile strength, compression and shear strength, moduli, and Poisson’s ratio. Therefore, the material requirements of the working surface need to be carefully considered. In general, plastics should be avoided as they can easily scrape or break from tools being dropped or heavy loads being applied. Instead, the cover should be made of a tough material that does not easily damage or crack during use. Composite testing often requires high force test systems that sit on the floor instead of on a table. Floor model systems present ergonomic challenges to operators that should be mitigated whenever possible with an optional base extension that raises the test space to a comfortable height. Improving ergonomics with a tall base reduces physical strain on operators when changing out fixtures or loading test specimens, and also improves endurance during extended periods of testing. Another benefit of an extended base is the ability to store tools, specimens, or fixtures below the test space. The addition of a contoured front will reduce the reaching distance when loading specimens or lifting fixtures from storage to the test space. Keep in mind that a facility with low ceiling height may make this solution challenging; so the tall base option needs to be carefully considered within the context of a laboratory’s interior space limitations. Temperature chambers for testing below or above ambient temperature are a common accessory for composite testing systems. This setup requires tensile grips with long extender rods leading the grip heads into the chamber. The grips are not easily interchangeable, as lifting equipment is needed to disassemble the load string, and the risk of damaging equipment during removal is high. Furthermore, when load strings with extended grips are assembled, an alignment verification is performed to ensure accurate results from testing. Removing these grips after installation would invalidate any alignment verification such as Nadcap. This poses a challenge for composites testing, which requires multiple different fixtures in order to fully evaluate the different bulk properties of the material. To overcome this challenge and increase the types of tests that can be performed with these grips, a piggybacked load string can be utilized to increase the versatility of a system. Grips can be designed to accept adapters that allow them to connect compression platens, smaller grips, and other specialized test fixtures, or allow direct connection of compression platens onto the grip surface. In addition to these hardware solutions for high shock loads, ingress protection, test frame ergonomics, and piggybacking capabilities, there are also software features that can be especially helpful for users when conducting composite tests. SOFTWARE AND SAFETY As previously mentioned, composite testing systems must be versatile to accommodate the various test fixtures needed to evaluate the bulk properties of test coupons. However, when numerous load strings are being used, the risk of damaging fixtures or load cells increases significantly because the parts become vulnerable as the operator jogs the crosshead to uninstall and install accessories. To mitigate this risk, modern test systems have the ability to detect unexpected loads during jogging or automatic return of the crosshead and immediately stop the system if two fixtures begin to make contact. This feature is helpful when changing out fixtures and when using sensitive equipment such as small grips and load The height of the test space is an important ergonomics consideration. Precision grips with an adapter for piggybacking a lower capacity load cell and grips for testing at lower forces.
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