LCF Testing Services
Low cycle fatigue testing determines how many operational cycles a rotating component can survive before a crack initiates – a critical data to determine the components durability and maintenance schedule for the equipment. Test Devices is the global leader and the expert in rotor LCF testing, has performed LCF testing on turbine discs, advanced motor rotors for Evs and eVTOLs, and other high-speed components for decades.
Rotor LCF testing involves cycling the actual part or a geometrically representative specimen through a specified speed range, so the centrifugal load produces the representative complex stress field the component sees in service. That distinction from other test methods, such as tensile coupon testing, matters, because the initiation site and the propagation path of a fatigue crack is influenced by the interplay between the test environment and rotor geometry, material, and manufacturing processes of the parts that are not easy to replicate in test coupons.
What LCF Testing Measures
Low cycle fatigue damage is driven by repeated large stress excursions, and in a rotating machine those excursions primarily come from speed changes. Every startup, shutdown, throttle change, and mission segment loads and unloads the rotor. Over thousands of these cycles, plastic strain accumulates at the stressed features until a crack forms and grows.
High speed rotating components such as turbine and compressor wheels are carefully designed and meticulously analyzed, yet they remain subject to rigorous low cycle fatigue testing Modern advanced analytical models can predict the components fatigue life, typically conservatively, but a prediction is not a validation. Cyclic fatigue testing gives engineers the empirical cycle counts – a key data needed to certify the life limit, calibrate a fatigue damage model, or plan an inspection interval.
Ask an Expert
Talk through your fatigue program with an engineer who has run thousands of LCF tests on rotating hardware.
How Test Devices Approaches LCF Testing
We perform LCF tests across the complete component speed range inside spin chambers built to contain a high-energy failure. Our largest pit accepts parts up to 54 inches in diameter and is equipped with 9.5 inch thick high-strength steel containment rings inside test cells. The spin pit is installed within a 20 inch double-reinforced concrete walls to ensure safety of operators during the high risk tests. We operate seven spin test facilities and our drives cover the speed range up to 160,000 rpm.Below are the key variables typically govern the quality of LCF tests:
- Speed accuracy & control. If maximum cycle speed drifts high, the component sees more stress than intended and it could fatigues prematurely. If it drifts low, the test could reports an unrealistically longer fatigue life. We understand the importance of speed control accuracy and consistency.
- Cycle rate: Fatigue programs run to thousands of cycles, so throughput drives cost. Our high-power drives are designed for accelerated fatigue testing, cycling the part in the shortest possible time to maximize cycles per day.
- Schedule Management: Our spin pit are equipped to run the LCF test 24-7 unsupervised. In addition, the use of our Real-Time Crack Detection System (RT-CDS), a patented and proprietary technology, allows continuous monitoring of the test rotor and eliminates the need for interim damage inspections – eliminating the time-consuming test interruptions.
- Cycle Quality Audit: We audit every single cycle data from LCF tests. We developed a cycle check software to generate the key statistics to quantify the quality of our LCF test data – reporting any cycle speed deviations as well as the event logs.
- Cycle profile: A cyclic controller runs simple minimum to maximum profiles as well as complex mission profile cycles that mirror an actual duty cycle.
Real-Time Crack Detection During Fatigue Testing
The traditional way to end an LCF test is to run the part to a predefined cycles, typically defined based on the analysis result. This approach often result in a conservative and premature termination of the LCF test or a rotor burst which often result in a destroyed the test specimen and risks damaging tooling and the rig. Subsequent efforts in failure investigation into understanding the crack initiation location of the rotor require careful collection of fragments, cleaning and examination – very laborious and time consuming effort. Test Devices’ Real-Time Crack Detection System offers an economical and better quality test result – It continuously monitors the rotating part and identifies crack initiation and propagation, halting the test at the onset of fatigue crack emergence – an ideal result for this type of testing. Based on our historical data, RT_CDS offers 80 to 90 percent detection accuracy.
The capability to monitor and detect the crack rather than waiting for the burst changes the economics of a fatigue program. Engineers get the cycle count all the way to initiation, usually the actual number the life analysis wants, and the test part is preserved in a condition ideal for sectioning and metallurgical examination. If the customer decides, a follow-on cycles to study crack propagation becomes a deliberate continuation of the same test rather than a separate program. The use of RT-CDS also allows customer to shorten the test schedule by eliminating the need for interim inspections. Our overview of LCF testing and crack detection systems and our other test innovations go into further detail.
Elevated Temperature and Complex Test Conditions
Some rotors, such as jet engine turbine discs are designed to operate in a very hot and arduous conditions. The temperature affects the material behavior as well as the type of damage mechanisms that could lead to fatigue cracking. Our LCF capability includes elevated temperature fatigue testing with controlled thermal gradients that reproduce the radial temperature distribution of a running engine. Combining thermal effect on to centrifugal cycling produces a far more realistic evaluation of the rotor behavior in an operating conditions.
Components and Industries We Test
LCF spin testing applies to any part where centrifugal load cycles are the governing fatigue durability. Common test articles include turbine and compressor discs, integrally bladed rotors, seals and spacers, impellers, high-speed fans, flywheels, electric motor rotors, and centrifuge rotors.
- Aerospace and defense
Turbine engine rotating hardware and life-limited parts requiring certified cycle limits. - Electric vehicles and electric propulsion
Motor rotors subjected to aggressive speed cycling, covered further in our introduction to LCF testing for electric motors. - Energy and power generation
Industrial gas turbine components, turbochargers, and flywheel energy storage rotors. - Medical and laboratory
High-speed centrifuge rotors where a burst would endanger operators.
Speed, temperature, vibration, and all out test data are recorded on a state-of-the art digital data acquisition system. We offer engineering services to post-process, analyze and prepare a full reports. Testing is performed at our AS9100 and ISO 9001 certified facility in Hudson, Massachusetts, which is ITAR registered and holds ISO 14001, ISO 45001, and Joint Certification Program approvals.
When planning for your low cycle fatigue spin test, it is worth a conversation with our experts. We can will help you scope the objective, cycle profile, and instrumentation your analysis requires to fit your budget and schedule. Once the approach is settled, submit a Request for Quote and we will return a defined program with pricing and schedule. You can also review the broader value of fatigue testing or explore our full range of spin testing services.
