Mastering Fatigue Testing with Force Measurement Webinar Recap
Interface has nearly six decades of experience engineering precision force measurement solutions for various forms of fatigue testing. Our ForceLeaders webinar, Mastering Fatigue Testing with Force Measurement, delves into the intricacies of fatigue testing, fatigue-rated sensors, engineering tips, best practices, and frequently asked questions.
The comprehensive and fast-paced discussion details fatigue principles, standard testing techniques, and sensor-related equipment for practical fatigue analysis using force measurement data. Interface force measurement experts answer critical questions like, can you use a load cell that is not fatigue-rated for fatigue testing? What is the highest cycle count recommended for a single load cell? How can load cells fail in fatigue? And what is the recommendation for mounting load cells for fatigue testing?
TIP: If you missed the live event, the full webinar recording is now available at your convenience. This recap will highlight the key takeaways. The recording also allows you to note the material that interests you most.
Why Fatigue Testing Matters
The webinar kicked off by emphasizing the crucial role of fatigue testing in various industries. Fatigue testing validates a product’s life span, demonstrates structural safety, and ensures liability compliance. The data available in fatigue testing helps refine FEA models and optimize maintenance schedules. An accurate force record over the testing period provides proof of analyzing the stresses before and during the ultimate failure.
Fatigue Testing Webinar Topics
#1 Fatigue Test Basics
Predicting exactly when failure will occur or defining which part of an assembly will be the weakest link can be difficult. Implementing load cells and a data logging system is necessary where materials, parts, or assemblies are fatigue tested for verification of life cycle or destruction. When designing a test protocol, serious thought should be given to the possibility that some test parameters will need to be changed based on information learned in the early test cycles. The two types of fatigue failure are high-cycle and low-cycle. High-cycle fatigue refers to relatively low-stress loads acting on a mechanical component that lead to fatigue failure over millions of load cycles. Low-cycle fatigue relates to higher stress loads that lead to failure over fewer cycles.
TIP: Use equipment that can accommodate some range of alteration without significantly redesigning fixtures.
#2 Design and Material Characterization
Load cells provide critical data for fatigue life prediction, damage accumulation analysis, and material characterization. Understanding how material properties like composition, microstructure, ductility, and hardness are valuable. Fatigue testing helps define failure in materials, and the materials used for designing load cells also play a role. In this presentation, Brian Peters and Peter Baldwin highlight the critical role of S-N curves and the importance of selecting the proper load cells for fatigue testing. The S-N curve represents the allowable load cycles versus cyclic stress levels to predict material fatigue life and avoid material failure. Many materials have a stress level that allows for infinite life. Components in a fatigue test should be designed for safe operation under the S-N curve endurance limit.
#3 Fatigue Testing Sensors
Since its founding, Interface has specialized in fatigue-rated load cells. Fatigue rating is a distinct specification that guarantees the customer a load cell with a service life of 100 million fully reversed loading cycles at full-rated capacity. Fatigue-rated flexures are about one-half as high as in a standard Interface LowProfile load cell.
Interface Fatigue-Rated Load Cells
- 1000 Fatigue-Rated Universal LowProfile® Load Cell
- 1208 Flange Standard Precision Universal LowProfile Load Cell
- 1700 Flange LowProfile Load Cell
- 1500 Low Capacity Universal LowProfile Load Cell
- SSMH Sealed Hazardous Environment Intrinsically Safe S-Type Load Cell
Most Interface load cells can provide high-accuracy measurements for fatigue testing. Please consult with our Application Engineers to learn which sensor best fits your test requirements. One of the most critical topics for discussion includes details about mechanical set-up and mounting. Learn about fixturing, load string, impact loads, cable influence, and installation tips.
#4 High-Frequency Fatigue Testing
We addressed the complexities of predicting fatigue life and the importance of considering flexure and strain gage failures. Controlled tests on the simplest configurations of test specimens can result in a wide scatter band of results. Analysis is even more difficult with complex structures. We review dynamic considerations, including natural frequency and cycle frequency. There are system frequency limits. For example, the best practice for minimal underdamping error is to target ~10% of the load cell’s natural frequency. Your data acquisition system (DAQ) is an important consideration. Amplifier and instrument filtering must be greater than the cycle frequency of the operation
#5 Mechanical Limits and Considerations
The session highlighted the importance of understanding mechanical limits, uncertainty considerations, and instrumentation challenges. We emphasized the need for appropriate sample rates, filtering, and bandwidth for accurate data capture. Mechanical limits in fatigue testing refer to the limitations and constraints imposed by the mechanical aspects of the testing set-up and equipment. These limits can affect the accuracy, validity, and scope of fatigue testing. This is a key topic to review in fatigue testing with load cells.
#6 Testing Configurations and Data Interpretation
We covered many testing set-ups, from basic configurations like rotating bending and axial loading to advanced techniques like multiaxial and thermo-mechanical fatigue. We also delved into data interpretation methods, including S-N curves, hysteresis loops, and strain-life analysis. The configuration considerations include sensor selection, load isolation, and multi-axis loading.
#6 Instrumentation Challenges and Solutions
We discussed the importance of sample rates, filtering, bandwidth, sensor compensation, and dynamic considerations, including the load cell’s natural frequency versus the operation’s cycle frequency. Sample rates must be fast enough to capture peak values. It is essential to check that filters are not limiting data. We highly recommend using instrumentation triggers and set point relays or limit switches. Learn about the instrumentation checks you should consider when testing fatigue, particularly speed-related ones.
#8 Use Cases and Applications
The diverse fatigue testing applications showcase real-world examples, such as prosthetics, aircraft wings, furniture, and bike frames, to give a sense of the range of fatigue testing and how Interface products support this type of testing.
Interface offers online resources and consultation with our experts to help you with fatigue testing projects. Learn more by watching the presentation. Whether you’re a seasoned engineer or new to the field, this webinar provides valuable insights into fatigue testing. We encourage you to watch the full recording to understand these critical concepts better and discover how Interface can support your testing needs.
