Using multiaxial testing to ensure seismic survivability of energy equipment

From biaxial to triaxial testing

For over 70 years, Sopemea has been a leading provider of testing solutions for products, equipment, systems and infrastructure for high-end industries such as aeronautics, defense, automotive, railways and energy, collaborating with customers to test the resiliency of their products.

As Sopemea has grown, it has acquired companies that use a variety of control systems for modal analysis, data acquisition and control. By 2019 they had 30 systems, and the group decided it wanted to consolidate this into one solution.

Previously, Sopemea only had single axis and biaxial vibration test rigs and decades of experience in testing components for shock and vibration for different industries, especially aerospace, defense and energy. To expand their testing capabilities and fulfill the increase in demand for energy components, they decided to invest in a 6-axis shaking table. “This type of test bench is largely used in the automotive industry,” explains Lisbeth Marty, mechanical testing engineer at Sopemea. “But we wanted to use it for seismic testing to verify that energy equipment is sturdy enough to withstand earthquakes.”

Traditional shaker testing replicates stresses on objects or materials, typically exciting them sequentially in perpendicular directions. However, in an earthquake, objects are often subjected to stresses that develop simultaneously in all three directions. This can only be fully replicated by triaxial testing.

After evaluating various options, Sopemea chose Siemens Digital Industries Software’s Simcenter™ Testlab™ software for dynamic environmental testing to develop a solution that would best meet these requirements. Simcenter is part of the Siemens Xcelerator business platform of software, hardware and services.

Preventing overengineering

Umberto Musella, product manager for shock and vibration products, says manufacturers tend to be conservative so they perform sequential single axis testing instead of opting for multiaxial testing. This may force them to overengineer products to ensure safety and yet implicitly accept some risk.

“Simultaneous multiaxial testing leads to more realistic replications that have the potential to reduce margins for the design of critical equipment,” he says. “These improved test practices also mean that designs can be simplified and at the same time ensure safe operations and resistance to shock and vibrations. Manufacturers will save development time and costs without compromising the quality of their products.”

Marty worked closely with Musella and the Simcenter Testlab development team to implement the latest version of Simcenter Testlab Dynamic Environmental Testing Shock and MIMO Shock control. The goal was to find a solution that could drive the multi-axis test rigs at Sopemea in the most accurate and efficient way. Sopemea and Siemens together reinvented how to specify and derive shocks from multiple shock response spectra (SRS) for earthquake qualification to accurately replicate seismic events.

The system includes new control modes that increase the user control over the safety of the test article, the safety of the excitation hardware and the accuracy of the replicated environment. It also allows engineers to define an under-testing avoidance factor to ensure the right level of testing and limit unexpected failures after deployment. The software guides the user from initial setup to final reporting. This includes a new safe and accurate multiple-input multiple-output (MIMO) control algorithm, enabling the definition of a multi-axis shock set from multiple SRS. With a few clicks, the user can find an optimal set of shocks that fulfill a specific maximum cross-correlation requirement and minimize SRS errors.

Close collaboration leads to streamlined processes

Marty says the ability to work closely with Siemens was vital to the project. “We knew that Simcenter Testlab could control time histories and sine tests but couldn’t run the seismic tests the way our customers required,” she explains. “But once we spoke to Siemens, we were confident we could work with their engineers to implement the multiple-input multiple-output testing we needed.

”To share results with customers, Sopemea needed accurate and efficient reporting tools, so they took advantage of the active picture feature. This supports editing graphs in Microsoft Office without a Simcenter Testlab license. “Active picture makes it very easy to export data,” says Marty. “When we run tests, we must choose some resonance frequencies, but we can’t choose all of them. Rather than going back and forth with the customer, we can send them the active picture and they can change the parameters themselves to get the data they want. They don’t need any extra licenses, and this makes the process more convenient for everyone.

“We’re really happy with our collaboration with Siemens and the technical support from them in developing the MIMO solution,” says Marty. “They came to our lab several times: first, we explained how we run seismic tests, the plus/minus of the software used so far. Then Siemens came to show us the first implementation of their solution and to test it in lab conditions. Siemens’ support helped us to configure our test bench and get the most out of it. Their technical expertise was superb, and they were very professional and easy to work with.”

Using the 3-axis tests in seismic tests provides significant savings to customers. Typically, test run times are reduced by 60 percent, making the entire testing process cheaper and faster.

Marty also cites the new control system as a significant benefit. “Previously, we had separate control systems for each axis – they were running at the same time but not taking into account what the other was doing. Now we have a real 3-axis control system that knows what is happening and accounts for any transverse behavior that wasn’t set up on the test bench. This is helpful in setting the right conditions and reducing testing errors. Most importantly, we can now replicate seismic events more accurately to ensure the equipment will withstand it in the real world.”

Xavier Caron, a Sopemea test engineer, has seen immediate advantages since switching to Simcenter Testlab. “Simcenter Testlab is very intuitive,” he says. “I found it easy to set up tests and it’s much quicker than other controller systems. For instance, one test that would previously have taken half a day to set up can now be configured in just 20 minutes.”

Extending triaxial testing beyond the energy industry

Marty is confident the new test bench and control system will bring more business to Sopemea. “This type of triaxial test bench has not been commonly used in this sector so far,” she says. “But now we’ve developed it so we can use it across a wider range of customers. Sopemea is well known for its work with environmental testing, but we want to show how the combination of hexapod and Siemens solutions improve testing, helping to avoid over- and under-engineering and reduce the cost of materials, products and qualification.”

Musella believes the project will have a wider impact too. “Sopemea is doing critical work in investigating and establishing the standards for multi-axis testing,” he says. “This will be pivotal to the market across Europe in the coming years.”