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Fatigue Testing with Interface Load Cells

Engineers rely on fatigue testing to ensure the safety and reliability of their product designs and structures. By understanding how materials behave under repeated loading, engineers can design components resistant to fatigue failure.

Fatigue testing requires accurate and reliable force measurement. Interface uses ‘fatigue-rated’ as an exact specification that defines a special class of load cell design and construction. Interface fatigue-rated load cells are designed to withstand the rigors of repeated loading, which makes them ideal for even the most demanding high cycle count fatigue testing applications.

In a typical fatigue testing setup, Interface fatigue-rated load cells are attached to the test specimen or the test machine, and the cyclic loading is applied according to the test protocol. The load cells continuously record the applied forces or stresses, allowing engineers and researchers to monitor how the material responds to repeated loading.

By analyzing the data from Interface load cells, researchers and material engineers can determine the material’s endurance limit, fatigue life, and stress-strain behavior. This information is invaluable for optimizing material selection, design, and manufacturing processes to enhance product performance and reliability while identifying fatigue and potential failure risks.

The use of fatigue-rated load cells and data logging instrumentation is necessary for most test and measurement applications, particularly when materials, parts, or assemblies are tested for destruction. This is true because an accurate record of the forces at every moment of the tests is the only way an engineer can analyze the stresses that occurred in the moments just before the ultimate failure. Read more about fatigue testing in our Interface’s Technical Library.

Interface Fatigue-Rated Load Cells

1000 Fatigue-Rated LowProfile® Load Cell

1000 High Capacity Fatigue-Rated LowProfile® Load Cell

1500 Low Capacity LowProfile® Load Cell

1208 Flange Standard Precision LowProfile® Load Cell

Profile of a Fatigue-Rated Load Cell

  • Design stress levels in the flexures are about one-half as high as in a standard LowProfile load cell.
  • Internal high-stress points, such as sharp corners and edges, are specially polished to avoid crack propagation.
  • Extraneous load sensitivity is specified and adjusted to a lower level than in a standard LowProfile load cell.
  • All Interface fatigue-rated load cells have a specified service life of 100 million fully reversed, full-capacity loading cycles.

No one can accurately predict exactly when the failure will occur, nor which part of an assembly will be the weakest link that eventually will fail. This is why high cycle count testing is the best way to measure fatigue life. To read more about fatigue testing and fatigue theory, consult Interface’s Load Cell Field Guide.

Fatigue Testing Applications

Interface fatigue-rated load cells are used in various industries, including aerospace, automotive, civil engineering, and manufacturing. They are used to test various products, from aircraft wings and landing gear to furniture and industrial machinery.

How Interface fatigue-rated load cells are used in fatigue testing:

  • Aerospace: Interface fatigue-rated load cells test the durability of aircraft wings, landing gear, and other aerospace components. This helps to ensure that aircraft can withstand the rigors of repeated takeoffs, landings, and flights. These load cells test the materials used for structures and even rockets.
  • Automotive: Interface fatigue-rated load cells test the fatigue life of engine components, chassis, and suspension systems. This helps to ensure that vehicles are safe and reliable and that they can withstand the stresses of everyday driving.
  • Civil engineering: Interface fatigue-rated load cells test the fatigue resistance of bridges, buildings, and critical infrastructure. This helps to ensure that these structures can withstand the loads they are designed to carry and are safe for the public.
  • Manufacturing: Interface fatigue-rated load cells test the fatigue life of industrial machinery, tools, and consumer products. This helps to ensure that these products are reliable and can withstand the demands of everyday use.

Watch how Interface load cells are used in this bike frame testing application.

Interface has specialized in fatigue-rated load cells and their applications since our founding in 1968. Our LowProfile® fatigue-rated load cells provide up to 100 million duty cycles, and the gaged sensors in every load cell are individually inspected, tested, and certified to meet our rigid performance standards.

It is imperative to choose the right load cell for your fatigue testing application. Load cells come in various sizes and capacities, so it is vital to choose one that is right for your fatigue testing application. Ensure you know the maximum load that will be applied to the load cell, the type of loading, the accuracy requirement, and the environmental conditions for testing. Consult with Interface application engineers to find the suitable load cell for your testing requirements.

ADDITIONAL APPLICATIONS AND RESOURCES

CPG Bike Handlebar Fatigue Testing

Interface Specializes in Fatigue-Rated Load Cells

Prosthetics Load and Fatigue Testing App Note

Furniture Fatigue Cycle Testing App Note

Aircraft Wing Fatigue App Note

 

Interface Plays a Role in Testing Bicycles

Interface sensors are used in a never-ending list of products, from heavy machinery to miniature medical devices. In the spirit of the Olympics, we thought we would share how our force and torque technologies are used in the test and measurement of bicycles, whether used for extreme off-road racing or speeding around the track. Interface has a role in helping to get bikes on the road and performing at optimum speeds.

Road, mountain and e-bikes present a fantastic use case for our products because everything from the force a rider puts on a bike’s suspension, shocks and frame when sitting on it, to the torque of the pedals and tires need to be carefully tested before a bike is ready for action. In the application notes below, we outline different parts and kinds of bikes that utilize measurement testing in design and actual use, along with the specific Interface force sensors used in each case.

Mountain Bike Shock Testing

In this application example, when a manufacturer wanted to test the durability of the forks on the front of their bikes, the rear shocks, front suspension, and ensure that the bikes shocks absorption is working properly for bike riders, we had a solution. Interface suggested installing the 1000 High Capacity Fatigue-Rated LowProfile™ Load Cell in a fatigue frame using the company’s bike forks. The forks undergo a fatigue test for several hours. Test results from the 1000 High Capacity Fatigue-Rated LowProfile™ Load Cell will be sent to the INF-USB3 Universal Serial Bus Single Channel PC Interface Module where the customer can view, log, and graph the results on their PC computer or laptop with provided software. Using this solution, the customer was able to test the bike’s front and rear shocks using Interface’s products. They determined if there were any weak spots in the forks or if it was working properly.

E-Bike Torque Measurement

e) manufacturer needed to test the torque on their electronic bicycles. They also needed a torque sensing system that measures how much force the bike rider is pedaling onto the pedals, because this determines how much electric power the bike’s motor generates. To address this challenge, Interface suggested installing the Model T12 Square Drive Torque Transducer where the pedal assist sensor would normally be. The T12 Square Drive Torque Transducer’s results could then be recorded, graphed, and logged using the SI-USB4 4 Channel USB Interface Module when connected to the customer’s PC. This allows the e-bike manufacturing company to successfully test the torque on their electronic bicycles with Interface’s products and instrumentation.

Bike Power Pedals

For a bike manufacturer testing the functionality of its power pedals, Interface supplied a full wireless system solution to measure how much force the cyclist pushes down onto the bike pedals. The solution included four Model SML Low Height S-Type Load Cells installed within the bike’s pedals. The four SMLs were paired with our Wireless Telemetry System components, two WTS-AM-4 Wireless Strain Bridge Transmitter Modules, which transmit the force data from the cyclist to the WTS-BS-6 Wireless Telemetry Dongle Base Station Dongle connected to the customer’s PC or laptop. Interface also provided the software needed with their wireless products. Using this system, the bike manufacturer was able to measure the pedal power applied by the cyclist. The customer was also able to measure and log the data wirelessly transmitted to their PC computer.

Bike Load Testing

In this example, another mountain bike manufacturing company wanted a system that measures their bike frames load capacities and vibrations on the frame, and to ensure the bike’s high quality and frame load durability during the final step of the product testing process. Interface suggested installing Model SSMF Fatigue Rated S-Type Load Cell, connected to a WTS products, the WTS-AM-1E Wireless Strain Bridge, between the mountain bike’s seat and the bike frame. This measured the vibrations and load forces applied onto the bike frame. The results are then captured by the WTS-AM-1E and transmitted to the customer’s PC using the WTS-BS-6 Wireless Telemetry Dongle Base Station. Using this solution, the mountain bike manufacturing company was able to gather highly accurate data to determine that their bikes met performance standards through this final testing.

Bike Frame Fatigue Testing

Fatigue testing is critical for bike design engineers. Our customer wanted to perform a fatigue test on their bike frames and analyze the strength of their bike frames in order to ensure durability and high-quality standards, turned to Interface for a solution. We suggested installing Model 1000 Fatigue-Rated LowProfile™ Load Cell to the customer’s bike frame fatigue tester. This load cell provides the customer with highly accurate results through the fatigue cycling. These results are collected using the INF-USB3 Universal Serial Bus Single Channel PC Interface Module and displayed on the customer’s PC or Laptop with Interface’s provided software. With this solution, the bike manufacturing company successfully had their bikes undergo fatigue frame testing, receiving highly accurate results with Interface’s load cell and instrumentation.

This deep dive into bicycle testing is just the beginning in demonstrating how many applications of Interface products can be used to improve the quality and reliability of the final design. When you consider bicycles, testing is critical whether it’s being used in the Olympics, for recreation or even transportation. Bicycle safety is fundamental to any design. Testing the performance and durability are essential before any bicycle is approved to be used on the road.

For a preview of all the application we have and can possibly work on, continue following the Interface IQ Blog at http www.interfaceforce.com/blog/. Each month we provide analysis and insight on new and interesting use cases and application examples.