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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

 

Examining Interface Aerospace Industry Solutions

Among the many industries Interface serves, the aerospace industry is one of the fastest growing users of our precision force measurement solutions. This is because ultra-accurate force, weight and torque measurements and data are critical to testing, performance and safety for airplanes, helicopters, and rockets.

Aerospace engineers and manufacturers of commercial, industrial, and military aerospace vehicles and associated components must measure multitudes of factors such as fatigue, structure durability, materials, weight distribution, drag, effects of inclement weather, velocity changes, thrust, and center of gravity to name a few.

Interface is synonymous with high performance sensors used for all types of test and measurement applications. For more than five decades, aerospace innovators and industrial giants have relied upon Interface to provide precision products and services they can trust.  Our test and measurement solutions are designed for use in the aerospace industry to withstand extreme conditions, whether they are for testing wings on commercial airplanes or used to measure the force of an intergalactic vessel launch.

Interface showcases products and use cases in our new aerospace solutions brochure detailing many the products and custom solutions we provide to the industry. We provide an overview of our accurate and reliable lineup of force measurement products, as well as highlighting various application examples to outline different ways we have long served the makers, builders, testers and engineers across the diverse aerospace industry.

To work in the aerospace industry, you have to meet the highest quality industry requirements in manufacturing and calibration. We take our commitment towards quality assurance very seriously and guarantee our products meet or exceed the quality clauses outlined by the International Organization of Standardization (ISO). We test and calibrate all products we build in a certificated lab based in Arizona that holds A2LA, International Standard ISO/IEC 17025:2017 and ANSI/NCSL Z540-1- 1994 accreditations. The strict adherence to these standards demonstrates our technical competence for a defined scope and the operation of a laboratory quality management system. Every Interface manufactured sensor goes through rigorous testing and calibration before it’s released to our customers.

The sensors, instrumentation, and accessories we supply to aerospace equipment manufacturers and testing labs range from mini to jumbo load cells, torque transducers, multi-axis sensors, and various wireless, digital and analog instrumentation devices. Interface sensors have been used regularly in the engineering and testing of military aircraft, missiles, space, commercial airliners, and for general aviation components as demonstrated in this aerospace and defense industry case study.

One aerospace use case of our force sensors is for structural testing. Interface LowProfile™ Load Cells are utilized for structural static and fatigue testing. Our moment and temperature compensated load cells use proprietary alloy strain gages for extreme accuracy and reliability. Using eight proprietary strain gages per sensor, our 4mV/V output well exceeds the performance. These load cells are offered in single, dual, and triple bridge configurations for different data acquisition and control requirements in aerospace vehicle production.

The range of aircraft and space vehicles that use Interface solutions include all types from unpowered gliders to commercial and military aircraft, as well as rockets, missiles, drones, launch vehicles, and spacecraft. These vehicles go through extensive and rigorous test and measurement programs and processes requiring the reliability and accuracy of Interface made products. Here are a few types of aerospace applications using Interface measurement solution:

Aircraft Wing Fatigue

Before any of the U.S. Navy’s F/A-18 twin-engine supersonic fighter jets can be put into operation, the wings of the aircraft must undergo fatigue testing in a controlled environment to ensure that they are capable of withstanding the forces that will be encountered during real-world flight throughout the lifetime of the aircraft. Highly accurate measurements must be recorded in order to make sure that a near-exact replication of in-flight conditions are being achieved. During fatigue tests, Interface’s 1248 Standard Precision Flange LowProfile Load Cells are installed in line with the hydraulic cylinders, which apply back-and-forth loading forces to the aircraft. This is carried out over the course of 18 months to simulate in-flight stresses and strains on the wings. Load cells are connected to indicators, which record output. Capable of withstanding more than 100 million (1×108) fully reversible load cycles, Interface’s LowProfile Fatigue-Rated Load Cells have performed flawlessly in F/A-18 wing testing with zero recorded failures in the many years that testing facilities around the world have been using them.

Rescue Helicopter Hoist Test

When a customer wanted to test the strength of the cable line used in the hoist of their helicopter during rescue missions and situations, see if both the cable and the hoist can withstand a heavy load safely, and for long periods of time while the helicopter is in flight, they turned to Interface. We supplied a WTSSHK-D Wireless Crosby™ Load Shackle, which is attached to each mooring cable in use. Results are sent to the customers through the WTS-BS-4 USB Industrial Base Station when connected to the customer’s supplied computer. Data can also be transmitted to the WTS-BS-1-HS Handheld Display for Single Transmitters, giving the customer the option to view mooring cable line tension. Using this solution, the customer was able to add a heavy load to the end of the helicopter hoist, to ensure it is strong and safe enough to carry both rescue personnel and objects while being in midair.

The aerospace industry is responsible for some of the greatest inventions and innovation in our global history. The engineering and manufacturing of a single rocket engine design, using handwritten calculations and with less computing power than a modern smartphone, took us to the moon. The aerospace industry is an assembly of researchers, design houses, test labs and manufacturing companies that engineer and build vehicles to travel within and beyond Earth’s atmosphere using Interface products. Whether you need a million-pound jumbo load cell, custom load pin, or wireless instrumentation, we understand aerospace requirements and our engineers are on stand-by to assist. Get your copy of our new Aerospace Solutions Brochure here.

Additional Resources

Solutions Provider for Aerospace & Defense

Exploring Aerospace Force Measurement Solutions

Interface Displays Force Measurement Aerospace Applications at Space Tech Expo

Aerospace and Defense Industry Solutions

Interface Recognized as Contributor to Human Flight Success

Interface Specializes in Fatigue-Rated Load Cells

Often test protocols require a fixed load plus a dynamic load to be applied to a test sample simultaneously. Interface Fatigue-Rated Load Cells are well suited for this requirement. Fatigue-rated is a specification that defines a special class of load cell design and construction used for repetitive cycle and fatigue testing.

Interface has specialized in fatigue-rated load cells and their applications since our founding in 1968.  The stringent discipline that is necessary to produce true fatigue-rated load cells, with consistency, is why Interface is known for this specialized load cell design and construction.

Manufacturing these special types of load cells, we can proudly state there is no record of reported fatigue failure for Interface Fatigue-Rated Load Cells used within their specified ratings. Interface fatigue-rated load cells have a given service life of 100 million fully reversed, full capacity loading cycles. It’s why reliability, durability, and quality rank these types of load cells as best-in-class for fatigue and cycle testing.

The use of fatigue-rated load cells and data logging instrumentation are used for testing materials, parts, or assemblies for weakness, and often ultimately to destruction. These types of fatigue tests are valuable to have an accurate record of the forces applied at every moment of a test to analyze stresses, identify fatigue and potential failure risks.

INTERFACE FATIGUE-RATED LOAD CELLS:

  • 1000 Fatigue-Rated LowProfile® Load Cell Model 1000 series is a fatigue-rated low profile load cell with 300% safe overload, extremely low moment sensitivity of 0.1%/in and a higher fatigue life. Capacities give you options to measure 1 pound (4.45N) and up to 1 million pounds (4500kN) of force.
  • 1000 High Capacity Fatigue-Rated LowProfile® Load Cell With many variants and configurations our fatigue-rated load cells provide up to 100 million fully rendered cycles. The gaged sensors in every load cell are individually inspected, tested, and certified to meet our rigid standards.
  • 1500 Low Capacity LowProfile® Load Cell – The Interface Model 1500 is a fatigue-rated unique LowProfile Load Cell designed for low capacity applications where low sensitivity to eccentric load is important.

Each fatigue-rated load cell model grouping also has numerous capacities and variations, including additional bridge options. All product variations, capacities, customization options and availability are online. There are possibilities to have engineered-to-order made products and customized solutions, as with all Interface manufactured load cells.

When passing fatigue testing is critical to the success of an assembly, piece of equipment or product, engineers and manufacturers rely on Interface Fatigue-Rated Load Cells. Our fatigue-rated load cells are used by most manufacturers of test machines, aircraft, spacecraft, auto and transportation vehicles, and various devices and industrial systems.

Here are a few fatigue-rated applications that demonstrate different use cases:

Furniture Fatigue Cycle Testing App Note

Bike Frame Fatigue Testing App Note

Aircraft Wing Fatigue App Note

Prosthetics Load and Fatigue Testing App Note

Additional reading on this subject can be found here in the post, Considerations for Fatigue-Rated Load Cells. If you are exploring fatigue-rated load cells or products for cycle testing, contact our application engineers to answer questions and ensure you get the right product for your testing needs.

Exploring Aerospace Force Measurement Solutions

The aerospace industry is responsible for some of the greatest inventions and innovation in our global history. The engineering and manufacturing of a single rocket engine design, using handwritten calculations and with less computing power than a modern smartphone, took us to the moon.

The NASA Parker Solar Probe is the culmination of some of the most impressive technology ever developed by mankind, journeying through the skies and beyond earth’s atmosphere with the ability to reach a top speed of 430,000 miles per hour.

The aerospace industry is an assembly of researchers, design houses, test labs and manufacturing companies that engineer and build vehicles to travel within and beyond Earth’s atmosphere. The range of aircraft and space vehicles include all types from unpowered gliders to commercial and military aircraft, as well as rockets, missiles, launch vehicles, and spacecraft. The term aerospace comes from the combination of the words aeronautics and spaceflight. All of these vehicles go through extensive and rigorous test and measurement programs and processes.

For more than half a decade, Interface has served some of the most prominent aerospace organizations in the nation including NASA, Boeing, Northrop Grumman and more. Our sensor technology has been used to design, test and manufacture airplane frames, wings, landing gear, rocket engines and even the machines that build the components for these products. These projects require the most precise data available, not only to ensure that the airplane or spaceship can fly and land, but more importantly to guarantee its safety for the pilot, crew and passengers.

Interface is humbled and proud to provide critical force measurement solutions and technology to the aerospace industry, in support of science, innovation and exploration.

Interface is often selected by our aerospace customers over the competition because we offer the most accurate and reliable force measurement products on the market. In this blog, we will be outlining how Interface serves the aerospace industry in validating designs, improving performance and maintain the highest safety possible.

AIRCRAFT

One of the most important tests to run in aircraft development is static and fatigue testing on the frame of the aircraft and the wings. Engineers will often simulate the effects of various forces on the aircraft and wings with actuators which act as of wind, weather, debris and more. Hundreds of Interface load cells are used to measure those forces to either validate the simulations or find errors in order to adjust the simulation and design accordingly. Load cells are also used on the machines controlling these forces in the test environment to ensure the actuators are simulating the right amount of force.

READ THIS APP NOTE FOR AIRCRAFT WING FATIGUE TESTING

ROCKETS

For a spacecraft that can weigh up to 1,000 tons, you need a lot of force to get it off the ground and safely out of the earth’s atmosphere. One of the ways that engineers test the thrust force of a rocket engine is with load cells. During these tests, the engine is attached under the mounting plate, which is part of a test stand. Interface load cells are installed between the plate and test stand and when the rocket thrust pushes up on the plate, the load cells relay the force data to the engineers. These tests help engineers make adjustments to the engine to use the precise amount of force to lift the craft into space, but not too much so that it doesn’t burn up too much fuel.

READ THIS CASE STUDY: LAUNCHING INTO ORBIT WITH INTERFACE

AEROSPACE MANUFACTURING

Before the air and spacecrafts are even assembled, the components need to be manufactured in a plant. There are hundreds of machines that are used on the production line for the hundreds of thousands of components needed to complete the craft. Interface load cells and torque transducers can be found on many of these machines. Not only are they used to help test the machines, they are also used to measure various forces on the machines in real-time. Our products are used to provide a wealth of insight to tell the manufacturers if the machine is working properly, needs to be recalibrated or needs repairs.

READ THIS APP NOTE FOR ROCKET STRUCTURAL TESTING

For more information on the numerous applications of Interface products in the aerospace and space industry, visit our solutions page at www.interfaceforce.com/solutions/aerospace/. Here you can read application notes and browse the various products we offer for our customers.

To watch an actual aircraft structural, check out this great Airbus video of an actual test.

Contributor: Randy White, Regional Sales Director at Interface

Considerations for Fatigue-Rated Load Cells

There are many products that are made to serve a single or limited use. Needs for these types of products, often consumable, are immediate and buying decisions usually require limited research or comparisons. On the other end of the spectrum, there are products that need to be extremely reliable, durable, and built to last a long time. The buying decisions for these types of products often require more research to make certain they are highly rated, safe, and made from sturdy and reliable materials.

How do original equipment manufacturers (OEMs) determine how long a product should last with consistent use? What design decisions need to be made to improve product reliability? The answer is often found in the defined fatigue requirements of a product. In the test and measurement and design phase of a product, answers to these questions frequently require product and component testing with fatigue-rated load cells.

Fatigue is the weakening of a material caused by repeatedly applied loads. Similar to if you repeatedly bend a paper clip, it will eventually weaken and then break. The only way to test fatigue is to put prototypes of the product through stress tests for long periods of time or use an apparatus that tests the lifetime “wear and tear” in a few hours. The tool that reports the data gathered from stress tests is the load cell.

With Interface fatigue-rated load cells, designers and engineers can predict the time and force it will take for wear and tear to take its toll on their products. They can then create safety instructions for customers or redesign the product for better results.

Interface Model 1000 series is a portfolio of fatigue-rated low profile load cells with 300% safe overload, extremely low moment sensitivity of 0.1%/in and higher fatigue life. If you need to measure 1 pound (4.45N) or 1 million pounds (4500kN) of force, Interface fatigue-rated load cells are built for this type of testing.

Interface fatigue-rated load cells are designed for an operational life of in excess of 100 million fully reversed cycles.

It’s also important to note that Interface fatigue-rated load cells are based on fully reversed load cycles, which means they are rated for two directions. This type of loading cycle is considerably more stringent than unidirectional loading. It is the more common application of load cells. If a fatigue load cell is repeatedly loaded in only one direction, it can be loaded to about 133% of the bidirectional fatigue-rated capacity with no degradation of its fatigue rating.

Interface works with customers to provide our fatigue-rated load cells for products that can’t fail. It is our mission to ensure precision products are safe, reliable and durable. If they do fail, it could result in significant harm.

Two examples of products dependent on fatigue-rated load cells for testing are aircraft wings and furniture stability. In aircraft wing testing, load cells test the materials used to build the wings to ensure they are strong and lightweight. The load cells are also used in wind tunnels to test the stress of high winds on the wings over time. Safety protocols manufacturing for furniture products require fatigue testing, seat testing, shock testing, and proof testing. These tests must be rigorously performed before entering the marketplace.

Force testing simulations using fatigue-rated load cells help the manufacturer define max loads in order to protect manufacturers from liability due to damages resulting in the misuse or overloading of their products. These types of applications require the most accurate data available provided by our load cells to ensure that testing results produce a quality product that lasts.

Fatigue-rated load cells are one of the many Interface force measurement tools available to help customers develop quality products. For information on all of the load cells we provide, please visit www.interfaceforce.com/product-category/load-cells/.

Contributor:  Jay Bradley, Sr. Electrical Engineer, Interface