AIRFRAME
Visual Inspection Criteria For elastomeric isolators, there are several methods used to assess the life of a part. This may depend on whether or not the elastomeric element is visible in the assembly. When the elastomer is hidden, physical measurements are often taken to check for excessive compression set or drift of the system. In some cases, visual indicators can be used to eliminate the actual measuring process. When the elastomer material is accessible, visual inspections look for de- bonding, elastomer cracks, tears or crumbling. Elastomer tears or cracks do not necessarily mean the mount no is longer viable to perform its function. Comparing the crack width and depth against the supplier’s fatigue test criteria will estimate the life status of the part.
Accelerated Testing Fatigue testing is used to establish the life cycle criteria followed during inspections. Accelerated life testing is commonly done to reduce the test time by elevating the input levels. The goal is to accurately predict and represent degradation and failure modes of the system under normal life expectations. This is usually acceptable with materials having well-known stress versus fatigue characteristics. However, with increased hysteresis of elastomers, this is
not necessarily the case. Accelerating a test too much often results in premature failure which does not accurately represent the actual failure mode of what would happen at normal levels. This is most commonly due to overheating of the elastomer as it is exercised at greater defl ections. The damping energy does not have time to distribute as it would normally, causing the elastomer to overheat, revert, crack or tear abnormally. Because of this, it is reasonable to add cooling fans on the test units and/or pause testing to allow the test unit to cool. Recording the test unit surface temperature and monitoring for excessive temperature rise is advised. Remember that the point of the test is to accurately represent real-world degradation and identify indicators leading to future failure.
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The industry expert in Air Data Test Sets & NDT Inspection Technologies
Designing for End Use Keeping the end user in mind is not only a good consideration in the mount design process, but a mandatory one. Communicating these needs to a mount supplier will allow them to be creative and will often result in a better product to install, monitor or replace. For example, anti-torque can be built directly into the isolator to prevent damage during installation. In addition, if the elastomer does tear, it can still be removed. Other proactive solutions include quick-attach features to reduce assembly time, or sage markers and/or limiters, allowing visual inspectors to identify product end of life and recommend replacement or maintenance. The options are endless with ongoing communication from the people who assemble and service the equipment.
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Conclusion Proactively designing and testing elastomeric mounts will ensure optimal product performance and life. Reactive designs often result in limited product space and, therefore, lower fatigue life. Proper testing will accurately identify the fatigue indicators to be evaluated during routine inspections. With better fatigue resistance, products will require fewer inspections and less maintenance, saving time and money. Suppliers can also off er opportunities to make the product easier to install, inspect and replace by working with and understanding end user needs.
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