Mechanical Hysteresis

December 10, 2020 Cadence PCB Solutions

Key Takeaways

  • Mechanical hysteresis is a common engineering problem that can cause unexpected results in mechanical systems.

  • Mechanical hysteresis affects many materials and industries in a variety of ways, including through friction and wear and tear of components.

  • Accurately predicting mechanical hysteresis is a complex, ongoing issue in mechanical engineering.

Mechanical Hysteresis

Car tire experiencing friction

Car tire experiencing friction, a type of mechanical hysteresis.

When designing an electronics project, designers can usually assume a negligible time delay between input and its resulting output within a mechanical system. This assumption is essential to the proper functioning of many electronics. However, it does not always hold true, either because of unexpected input or unanticipated physical variations in the system. The delays caused by these situations, called mechanical hysteresis, can cause unexpected behavior in a mechanical system. This unexpected behavior can range from mild friction to severe vibrational problems that could threaten the structural integrity of a project.  Mechanical hysteresis is notoriously difficult to predict and minimize in many areas of engineering.

What is Mechanical Hysteresis?

Hysteresis is a broad term that can be applied to mechanical and biological systems, among others. In a general sense, hysteresis describes a situation in which input to a system causes a delayed result, and the system has changed significantly during the delay. In electronics, mechanical hysteresis refers to system changes on the physical level. Since the system changes between receiving input and generating the associated output, mechanical hysteresis is often described as a physical state that depends upon its history. This doesn’t happen because the system is actively saving knowledge of its previous states, but because the cumulative effect of unexpected forces causes larger-scale changes.

There are two different types of mechanical hysteresis: rate-independent and rate-dependent. Rate-independent hysteresis has the potential to permanently change the properties of a mechanical system. Rate-dependent hysteresis, by contrast, depends on how long unexpected inputs continue and eventually levels off to zero when unexpected inputs end. The effects of rate-independent hysteresis can persist after unexpected inputs end. Both types of mechanical hysteresis can cause physical changes to a system, but those created by rate-dependent hysteresis may take much longer to alter the system’s functionality in a significant way.

Mechanical hysteresis is usually characterized as an engineering problem, which is how the rest of this article will describe it. However, it is important to note that there are also specific instances where mechanical hysteresis can be helpful to engineers. For example, there are often spaces left at the places where gears meet to allow them “wiggle room.” The gears lose efficiency, but they’re less prone to breakage and deformation if they don’t engage perfectly.

How Does Mechanical Hysteresis Impact Engineering?

Mechanical hysteresis can come from many sources and can have a broad effect on mechanical and electrical systems. Two of the most easily recognizable are deformation and friction. Deformation can be the product of many forms of hysteresis, including mechanical and voltage hysteresis. Mechanical hysteresis promotes deformation once it starts. Once a component is deformed, it dissipates energy at an increasing pace as its deformation continues, rather than converting energy into work as intended. This is partially due to friction but can be affected by many other factors, including the integrity of materials and the environment in which energy dissipation happens. Engineers and designers can calculate how much energy is being lost by estimating the amount of mechanical hysteresis in a system.

The Bouc-Wen model is a common equation for measuring mechanical hysteresis in engineering and electronics. It was directly inspired by vibrations caused in physical systems, a problem that is common in electrical engineering. The model involves complicated math and can measure the impacts of mechanical hysteresis caused by multiple inputs, allowing designers finer control over the amount of hysteresis in a project. As mentioned earlier, hysteresis may be useful in some contexts, so amplifying useful mechanical hysteresis while breaking the loop of dangerous vibrations are both essential priorities. New models derived from the Bouc-Wen model have found use in recent years for both specific and general applications, allowing further fine-tuning of hysteresis control.

Electromagnetic circuit

Electromagnetic circuit, which can experience mechanical hysteresis.

Why is Mechanical Hysteresis an Ongoing Problem?

Despite multiple models available to predict it, mechanical hysteresis is often unpredictable. The forces caused by potential deformation and friction are not easy to predict ahead of time. Predicting mechanical hysteresis is different from estimating the amount of mechanical hysteresis that already exists in a system. Models like Bouc-Wen have limitations because they can’t easily model highly dynamic systems.

Artificial intelligence has led to some new ideas for predicting mechanical hysteresis. Neural networks may be able to predict mechanical hysteresis by learning how hysteresis works in a way that humans cannot directly observe. The accuracy of current mechanical hysteresis models depends on them being used in the proper engineering field, and universal prediction of mechanical hysteresis has remained elusive. Neural networks can model many hysteresis loops at once, allowing granular refinement of predictions with increased input.

Gears with gaps

Gears with gaps, a potential source of mechanical hysteresis.

The  PCB Design and Analysis overview page at Cadence Design Systems provides tools ideal for minimizing mechanical hysteresis, including the Allegro PCB Editor. Learn what's new in Allegro so your CMP processes stay efficient and up-to-date. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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