We are specialists in High Cycle Fatigue (HCF) testing of engine airfoils for service life limit analysis for our aerospace clients.
High vibrations conditions of airfoils during operation can impact the structural integrity of a test specimen which makes HCF testing indispensable. Individual metallic and future advanced material turbine blades or segments of a bladed disk are tested in the natural resonance frequency range until crack initiation. Our equipment allows us to run a very high number of cycles in a short amount of time simulating a components' service life. Our HCF testing service portfolio also includes the ability to carry out strain gauge calibration on instrumented airfoils.
HCF Test Excitation Methods
- Constant Airjet
- Chopped Air
- Sonic Fatigue (Hot/Cold)
Key HCF Testing Facts
- 9 Test Chambers
- Specimen sizes from smallest compressor airfoils up to FAN Blades
- Frequencies up to 20kHz
- Up to 1200°C
- More than 15.000 airfoils tested
Chopped Air Testing
Exciting high frequencies of larger and relatively stiff specimens requires more specialist testing methods, especially for higher modes. To do this we have put dedicated chopped air testing facilities in place, using a pulsed air flow for aero-dynamical excitation. This world class and unique capability enables Element to handle everything from the smallest to the very largest aeroengine FAN Blades in service today.
Hot High Cycle Fatigue (HCF) Testing
For the analysis of service life limits, individual turbine blades or segments of a bladed disk are tested in the natural resonance frequency range until a crack occurs. In addition, turbine blades are subjected to a realistic temperature load up to 1200°C to take for example creep processes into account.
Airfoil Clamping and Holding Block Design
Depending on the type of airfoil, different clamping conditions can occur which need to be considered for HCF testing in order to recall these influences on the system behavior and to chose the proper excitation method. Element can provide all possible conditions like free-free, fixed-free and fixed-fixed can be covered by solid experience gained from the last decades.
Not less important to achieve stable testing conditions and representative results is the know-how to design holding blocks that are an accurate counterpart to the airfoils' root but still flexible enough to allow assembly and adjusting the clamping. With more than 15.000 airfoils successfully tested, Element developed best practices in this discipline to ensure stable test and representative failure conditions.
Holography (Frequency Check and Modeshape Analysis)
Determining the behavior of a component, in terms of its reply characteristics after excitation, is essential to state if it can meet operational requirements. With this specific analysis eigen values and damping factors can be obtained and used in advance of HCF testing to identify relevant modeshapes at various frequencies, nodal patterns and/or validate finite element method (FEM) simulations.
Advanced graphical analysis systems based on a touchless sensor system (EPSI & SLDV) detect the smallest deformations via sine-step procedure which helps to identify and interpret these in a standardized way correctly and quick. These results are used by our experienced engineers to run following fatigue test properly, in an appropriate way and in the desired test mode.
How pre-damaged components respond during fatigue is very important when appraising their operational resilience. This is traditionally tested using manual hammer impact techniques. Our Engaged Experts have established a new, more modern method which enables reproducibility and more precise impacts (e.g. exact location, notching depth and angle) to take place. This enables us to compare results of multiple sets that are tested.