Paul Wood, Senior Application Engineer
MTS Systems Corporation
MTS High-force load frames feature numerous design refinements derived from decades of meeting real-world needs.
Reduced-mass high-force grips provide test engineers the widest possible range of frequency and maximum force.
Meeting the Challenges of High-Force TestingPaul Wood has more than 20 years of experience in materials testing. He has managed a wide range of software development, custom product development and application engineering programs. He specializes in understanding customers’ test requirements and translating customer needs into highly usable mechanical test solutions. In this Q&A, Wood discusses the challenges and nuances of high-force materials and components testing.
Q: What defines a high-force test? What kinds of specimens require high-force testing?
Wood: In general, any test that requires more than 1 Meganewton (MN), or 224,800 lbf, qualifies as a high-force test. High-force mechanical testing is critical for determining the performance and durability properties of materials, components and sub-assemblies in many industries, including construction materials like concrete and steel; civil structures, such as beams, columns and rebar; and large components for aerospace, oil and gas, rail and wind turbines. Essentially, if you make a specimen large enough it will require a high-force test.
Q: What applications are most common in high-force testing?
Wood: High-force applications can range widely from static strength characterization to complex, dynamic life studies. This is where MTS focuses a great deal of attention, particularly on fracture mechanics and fatigue crack growth. These are dynamic tests that help determine the life of components, failure rates and crack growth rates. Also, product developers and manufacturers prefer to test full-scale components due to volumetric effects – as a material sample or specimen gets larger, its behavior may change. This is especially true for new materials, such as aluminum or polymer composites. If you have a material with a one-and-a-half-inch round cross-section, you will need a 1 MN load frame to break it.
Q: How are data from high-force tests used?
Wood: High-force test data is vital for developing reliable structures, components and products that perform as expected. High-force tests investigate and determine maximum stresses for materials, which can be difficult to predict due to the volumetric effects mentioned in the previous answer. Specimen size can greatly influence a material’s fatigue curve, which is used in product design. Engineers use high force testing to determine whether a material’s failure mechanisms vary according to specimen sizes, and then create models that accommodate for these variances. For some materials, such as polymer composites, the data from high-force dynamic testing helps engineers understand how the weave and angle of the reinforcing fibers affect the ultimate strength and life of the material.
Q: What kind of systems does MTS offer for high-force testing applications?
Wood: MTS offers a complete portfolio of standard high-force test systems and often provides custom-engineered solutions. For the lower end of high-force testing, from 1-5 MN (224,800 lbf - 1,124,000 lbf), the solution starts with an ultra-stiff, four-column standard servohydraulic load frame, to which we add SilentFlo™ Hydraulic Power Units (HPUs) and other hydraulic features, state-of-the-art digital FlexTest® controllers, MTS TestSuite™ software and a full complement of high-force grips, fixtures and platens. All of these components are designed to work together and engineered with a great deal of application knowledge derived from real-world experience and thousands of customer installations around the world.
Q: What differentiates a custom-engineered from a standard high-force solution?
Wood: Force capacity is typically what drives a custom solution. For these instances, MTS works directly with customers to design and build, for example, a 10 MN (2,248,000 lbf) system for conducting bend tests of structural steel beams, or a 30 MN (6,744,000 lbf) system for running compression tests of reinforced concrete columns. In both cases, the resulting system is the product of decades of collective MTS application engineering expertise.
Q: What differentiates MTS high-force load frames from other high-force solutions on the market?
Wood: Numerous design refinements derived from decades of meeting real-world needs put MTS systems in a category of their own. For example, the system actuator is integral to the frame cross-head. The welded cross-head has a “bathtub” design inside which the actuator sits to minimize the distance between the bearing and the test base. Basically, the front end of the actuator rod is shorter than what you might expect. We have hydraulic service manifolds (HSMs) mounted directly on the frame and we employ local close-coupled accumulation. We use smooth columns with clamps integral to the crosshead, which allows fast and infinite adjustment of crosshead height. All of this manifests in the unmatched utility and ruggedness of the system, and its ability to run fatigue tests to the full force rating of the frame for very long periods of time.
Q: How does MTS ensure proper alignment in high-force test solutions?
Wood: Alignment is critical because any bending in the specimen will compromise data quality. Our load frames exhibit superior system alignment, which minimizes bending strain to enhance test accuracy and reduce data scatter. In addition, we offer alignment fixtures for our standard 1 MN solutions that make it easy to detect whether any part of the load train for a fully instrumented specimen is out of alignment.
Q: Does high-force testing involve special grips?
Wood: Yes. Our grips are sized and engineered to reduce mass for high-force dynamic testing. They are designed to be light to improve performance and give customers the widest possible range of frequency and maximum force. Light grips help avoid wasting a great deal of energy to get the same results.
Q: How long has MTS provided high-force solutions? Where have they been deployed?
Wood: MTS has been solving high-force testing problems for many industries for nearly 50 years. We were a pioneer in these applications. We were the first to use hydraulics for cyclic materials testing and the first to use them for high-force testing. What that means for customers is that our team understands the implications of all the decisions that must be made before you get a solution that delivers the data you need. Application knowledge is built into the design of every component. We have seen what works and what doesn’t and how to avoid problems before they begin. We have deployed these systems extensively throughout North America, Europe and Asia, in university research labs and for some of the world’s biggest manufacturers.
Q: Do high-force load frame systems present unique facilities challenges?
Wood: Yes, it can be very challenging. Recently we had to remove the roof from a building and move the system in on a crane. In another instance, we delivered a 30 MN system to a facility in Taiwan where we integrated components designed in Minneapolis and manufactured by suppliers from across the globe. Even for smaller high-force systems, facility design plays a very important role. The base plate of the system often must be integrated with the floor of the building, for example. We have the experience to guide customers through the process so they understand how to prepare the facility for a successful installation and test operations.
Contact MTS today and learn how you can benefit from decades of MTS high-force testing expertise.
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