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Safeguarding Test Articles During Structural Testing

MTS aerospace product manager Dr. Christoph Leser discusses advanced technology for managing loads while keeping test articles free from harm.

Q: What safety considerations are unique to aerospace structural testing?

Leser:
Beyond the obvious objectives of protecting staff and test data, labs running full-scale structural tests must make certain that the test article itself is safeguarded from sustaining physical damage.

These tests involve many channels of load applied through dozens, often hundreds, of hydraulic actuators that are often cross-coupled in complex ways. In the event of a power outage or mechanical malfunction, dangerous amounts of energy may remain within the test article, which can unload in unpredictable ways if left unmanaged.

You only get one chance when testing full-scale structures. A damaged test article can set a test program back months and millions of dollars. In an industry where time-to-market and cost containment are paramount, even the most remote chance of sustaining specimen damage cannot be tolerated. It must be reduced to as close to zero as possible.

Q: What technology is available to meet these safety demands?

Leser:
Multiple measures exist at both the test software and hardware levels. On the software side, safety features include an A/B compare capability, which compares two measurements per each load channel of control to ensure load feedback integrity. Shutdown recorders also record all test activity after a test gets aborted, ensuring that all test data remain safe, too.

Control system safety features include an ability to automatically cease test activity the instant a loss of power is detected, along with watchdog timers that ensure incoming and outgoing signals are valid, synchronized and in constant communication with one another.
But these software and hardware measures alone will not provide adequate protection. At the point of system interlock, it is essential to remove the loads from the test article.

This critical process can be accomplished using cutting-edge active load abort system technology, which requires a specially designed hydraulic manifold to be installed between each test actuator and servovalve. The instant a failure or test interlock gets sensed on the control side, this manifold prompts the redundant unloading control system to instantaneously and uniformly remove the load present in the test.

Q:  Haven't load abort manifolds been around for quite some time?

Leser:
Yes. Constant-velocity, or ‘passive,’ load abort manifolds have been in use for decades, and still provide a sufficient means of energy removal for many structural testing applications. These passive manifolds protect test articles from damage by incorporating an adjustable orifice that controls the flow rate of hydraulic fluid from each actuator.

Q:  Why do some test labs choose 'active' instead of 'passive' abort load technology?

Leser:
Driven by shorter development cycles, more complex tests and more expensive test articles than ever, certain test labs opt for the more expensive active technology because it involves less setup time and ensures the most even removal of energy from the test article.

Passive load abort technology successfully manages the unloading of hydraulic pressure, but does not guarantee the achievement of zero load levels for all actuators across the test article simultaneously.

In contrast, active load abort systems enable all actuator loads to reach a neutral state at precisely the same time, regardless of varying pressures and positions of individual actuators. A separate control system runs parallel to the load control system, and takes the state of the entire test into account when removing hydraulic pressure from the test article. The system senses a failure on the control side, and then works to immediately and evenly remove the load from the article, protecting the test article from harm.

Active abort load module technology is more costly and complex than passive technology, but some test labs justify this expense with the additional layer of safety the technology provides. In addition, certain manufacturers are requiring test labs to have active abort load measures in place when working with their test articles.
 
Protecting your test program from every angle
MTS offers a full suite of the latest aerospace testing software; hardware and system safety capabilities to best protect your staff, test articles and test data, including both passive and active abort load module technology. Contact us today to learn more about how MTS can help optimize the safety of your structural testing, based on your unique needs.


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MTS Systems

14000 Technology Drive
Eden Prairie, MN USA
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Tel: 952.937.4000
Tel: 800.328.2255
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Email: info@mts.com