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 4 As composite materials become more complex, materials testing equipment must evolve in order to keep up. Testing composites on a coupon or fiber level continues to be a challenge for manufacturers of testing machines due to the high shock and debris output yielded by composite breaks. This article discusses how testing equipment can be designed to better accommodate these materials. Fiber reinforced composite specimens exhibit high stiffness when compared to other high-strength materials such as metals. When a unidirectional composite coupon undergoes tensile testing, energy is released abruptly upon failure, causing high shock loads that the test frame needs to absorb. This is complicated by the fact that test frames contain sensitive electronics, which are highly susceptible to damage. Designers of testing equipment should consider replacing sensitive components with more durable parts or minimizing the risk of failure by eliminating these components altogether when possible. Moreover, designers need to think about strategies to isolate the vibration and shock away from the electronics. PROTECTION FROM DEBRIS AND WATER Debris generated by specimen breaks also poses a threat to testingmachine electronics. Debris from carbon fiber and other materials can degrade and damage electronic components due to their potential conductivity as particles disperse during testing. In addition to debris, precipitation from an environmental chamber will also damage electronics if it is able to ingress into the base of the frame. During subambient testing, water vapor from the air freezes to the chamber and forms a layer of ice. When the chamber returns to ambient temperature after testing, the melting ice can drip onto— and potentially into—the base of the frame. Cleaning and maintenance of electronic components is not enough to prevent machine downtime and costly repairs—it is critical that the system is designed with the goal of sheltering the electronics. Test system manufacturers must keep in mind that every opening on the machine has the potential to let in debris particles that could harm internal components; frame designs should limit rod access holes, provide additional gasketing for insulation, and consolidate cabling. BASE DURABILITY AND ERGONOMICS The front cover of a testing system’s base beam is often overlooked as a source of durability issues. Many operators use this as a working surface to rest heavy fixtures during the installation of different load strings. This is especially true for composite testing, which requires various fixturing to assess the different bulk properties such OVERCOMING COMPOSITES TESTING CHALLENGES A look at how the high energy breaks, conductive debris, and ergonomic issues unique to composites testing can be resolved with proper equipment set up. TECHNICAL SPOTLIGHT Precision grips in an environmental chamber with strain gauged specimen for load string alignment.
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