Spin Testing Services

The reliability and accuracy of Test Devices Production Proof Testing has become essential for those who manufacture and repair high-speed components. Whether it is a test for mechanical integrity or radial growth, the results are carefully recorded and documented in accordance with the customer's specifications. Detailed certification and test documentation is provided. The key to efficient and accurate production testing is to design and fabricate arbors that will accommodate repetitive change-outs with minimum effort. Arbors are analyzed, designed and built to ensure speed, accuracy and safety for each customer's component. (See detail page)

Low Cycle Fatigue Testing

Low Cycle Fatigue (LCF) tests are critical to assure safety and adequacy of economic life (for life management). Only spin testing gives program managers data needed to validate models and assure nothing is overlooked. Our LCF spin testing provides this critical information early enough in a development program to allow the necessary modifications and improvements to shorten the design cycle and reduce program risk.

Test Devices is uniquely qualified to offer the most economical life management test program possible. High cycle rates and high test security reduce the time to achieve results and the overall cost of life management programs to a minimum, allowing appropriate testing within tight time and cost constraints.
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Burst Testing

Over-speed centrifugal stress testing to the point of burst offers, valuable information on the ultimate strength of a part or material. However, the energy of high-speed parts poses a unique challenge regarding safety and containment. The practice of bursting at energy levels that have been underestimated or misunderstood can end with disastrous results. Test Devices imposes the highest level of safeguard from personal injury.

Test Devices performs numerous burst tests on a wide variety of parts and materials including energy storage flywheels, conventional automotive flywheels, high-speed centrifugal compressors, impellers, jet engine components, fans, blowers, etc. Many of the tests are to measure the containment capability of various systems. These tests can be burst speed investigations only or can involve substantial instrumentation including video (high-speed and normal), accelerometers, strain gauges, thermocouples, proximity probes, pressure measurements, etc.

Test Devices is co-chair of the Flywheel Containment Working Group; a DARPA and industry sponsored program dedicated to developing safe containment for flywheels. The working group is organized under the Southern Coalition for Advanced Transportation (SCAT), and members include Trinity Flywheel Power, US Flywheel, the University of Texas at Austin (Center for Electromechanics), Lawrence Livermore National Labs, Argonne National Labs, Oakridge National Labs and Test Devices.

High Cycle Fatigue Testing

Recreating the elusive phenomenon of High Cycle Fatigue (HCF) on bladed rotors has become a signature testing technology at Test Devices. We can generate sufficient excitation to study all engine order frequencies to provide data to support corrective designs by the OEM. Our technical staff can advise on selection from among several forms of excitation developed by our engineering staff for the specific purpose of replicating engine order frequencies and amplitudes. Choosing the method of excitation is only part of performing a successful HCF test program. In addition, Test Devices provides high quality data acquisition, recording, data reduction and formal reporting. Our engineering, technical and production staff are equipped to perform to the level necessary for the most sophisticated HCF testing.

Test Devices is heavily involved in high cycle fatigue testing programs using a variety of excitation schemes on different components of jet engines. Test Devices has pioneered the use of spin pits as cost effective HCF test vehicles. HCF testing has been a driving force in the development of high power drives and excitation schemes that have produced superior results at a fraction of the cost of a full-up engine test.

Test Devices has pioneered the use of flow-fence excitation in HCF tests as an alternative to air jets. Spin pit testing is substantially cheaper than rig testing or full-up engine testing, and problems can be resolved early, on a component by component basis, before parts get into the field. Flow fence tests are conducted in a reduced vacuum, with the component inside an enclosure that has the number of flow interrupters (flow fences) installed that equate to the desired order of excitation.

Fan component inside special shroud containing flow interrupters that excite required modes. Shroud is attached to underside of spin pit lid; cooling air is supplied to center of system.

An excitation test recently completed compared the resonant response of a shrouded vs unshrouded fan blisk. In this test a special enclosure was built to house the part, and flow interrupters were developed to provide excitation of specific modes of interest.

In most HCF testing strain gages are applied to critical areas of the part, signals are run through a slip ring, and data is recorded as speed and pressure are varied. When found, a resonance can be held until failure occurs (if required).

Technical challenges of aerodynamic excitation include the development of the flow interrupters to provide excitation of the modes of interest, and management of aerodynamic heating that occurs from the high losses and low mass of air involved.

Aerodynamic heating problems were overcome through the injection of cryogenic liquids into the test section, taking advantage of the heat of vaporization to balance the aero-mechanical heat input. Improved methods for cooling, excitation and rig drive are under continuous development. Further work is also under way to develop a more detailed understanding of the forcing function created by the flow fences.

The flow interrupters used in the tests completed to date have been very successful in exciting the modes of interest. In particular, it has been possible to excite several different n-nodal diameter modes by judicious placement of the flow barriers.

Test Devices offers a wide variety of Design and Engineering Services to compliment and support all of our processes. We have on staff some of the industries leading Engineers and Designers using the latest technologies and equipment. We can design, analyze, manufacture, assemble, provide drawings and ensure your project or test gets completed on time with predictable results.

48 Jet Assembly Design

Figure 5

48 Jet Assembly in Spin Pit

Figure 6

From Design (fig 5) to Finished Test Assembly (fig 6)

High Speed Video (see sample)

Test Devices uses a Kodak EKTAPRO-HS Motion Analyzer System (Model 4540) to capture very high-speed events that occur during spin testing. The EKTAPRO-HS is a digital video camera that uses a laser illuminator to take pictures at rates up to 40,000 frames/sec. Unlike a film camera, the digital camera takes pictures continuously and merely overwrites its memory when it gets to the end of its picture buffer. In addition, the test engineer can trigger the system anywhere in memory, instructing the camera to save the last N frames before continuing to the end of the picture buffer. This allows the test engineer to capture and save visual history PRIOR to the trigger event.

Test Devices uses an Oxford Laser system as an illuminator for high-speed photography, instead of relying on a mechanical shutter. Resolution of the camera ranges from 256 x 256 (8-bit pixels) to 64 x 64, depending on the frame rate. The camera and the associated view-port are situated at the bottom of the spin pit, which sits atop a concrete channel specifically designed for this purpose. The entire spin pit is then enclosed inside a reinforced concrete test cell.
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Real-Time Crack Detection

As part of the process of instrumenting and conducting a Low Cycle Fatigue spin test, Test Devices has developed a novel method to monitor and evaluate the integrity of a spinning disk, or an assembly of disks. The method uses a simple and readily available non-contact probe to measure the vibration vector of the part, then compares the amplitude and phase of this vibration to a baseline that has been previously established. Any distortion in the strain field of the disk, or any relative movement of the components that make up the assembly will cause a minute unbalance and will appear as a distinct amplitude and phase change. The vibration vector change usually indicates that a crack has developed, but sometimes discloses some other important change in the assembly such as a loose tie bolt, etc. In the spin pit this signal is used as an early warning of a crack to determine when the part should be taken out for inspection, or as a diagnostic tool to determine if there has been some slipping, fretting or movement between the pieces of the assembly. Monitoring the raw vibration data is not helpful in detecting signals of interest here, since the changes in vibration are very small vector quantities and often have no observable effect on the overall vibration level of a rotor.

Without this instrumentation a spin test engineer is "flying blind", and relies only upon experience and luck to select the correct time to remove a part for inspection. Much the same thing happens in a real engine. Components are removed at fixed intervals and are inspected, but there is no on-line indication of a potential problem

The graphs shown below give a good feeling for the indications of cracks seen during an actual test. At the end of this test of a bladed power turbine assembly there were sixteen (16) cracks in the part, all approximately 0.2" in size. The first graph shows the relative size of the crack compared to an initial baseline. The first solid indication of a crack in this test came at approximately cycle 15,000 where the amplitude had increased (which is a sign that an unbalance has occurred), and the phase (see next graph) had settled out to a straight line (which is a sign that the unbalance has moved away from the baseline location).

Phase is the angular location of the crack or mechanical slippage measured from a fixed reference point.

The technique developed can detect cracks at least as small as 0.34" and has the potential to detect cracks even smaller. This is much smaller than the cracks that have caused air transport fatalities in the recent past from disks that have burst due to cyclical centrifugal stress fatigue, so the system has great potential to show direct benefit immediately as a flight safety enhancement.

With this unique technology it is possible to terminate tests just prior to disk burst, preserving the entire disk for analysis. Preventing a burst allows the metallurgist an opportunity to view the disk with no collateral damage and to determine the crack initiation site with complete certainty. Preventing a burst also reduces the cost of the test by eliminating the high costs associated with facility repair after a failure; and further savings are realized by preserving arbors, blade sets, and other associated tooling and attachments.

The method has been proven to be reliable and allows a significant reduction in the need for interrupting the test for interim inspections. The benefits of the system include early warning of the existence of cracks, the ability to have intact hardware available for full metallurgical analysis, and a significant reduction in test program cost and duration.

This patented crack detection system is also the subject of a Small Business Innovative Research grant aimed at moving the system on-wing to give early warning to maintenance technicians of potential problems in the engine.
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Precision Tooling & Machining

Test Devices offers Precision Machining services to our customers and to support our testing and manufacturing operations. This allows us maximum flexibility to solve problems and make same day modifications to equipment, arbors, tooling and even customers parts if necessary. We also offer inspection services for pre and post test dimensioning for radial growth and part deformation. Material Certifications, Dye Penetrate Inspection, Heat Treating and Chemical Etching Services.

Testing Services @ Hudson, MA

Production and Over-speed Proof Testing