Definitions
- Burst Contingency & Repair
As discussed earlier, rotating parts store large amounts of energy and, by definition, all that energy will be released during a burst. While our test systems are very robust, there will be some minor damage by the very nature of the test. Damage to the turbine or other equipment due to burst testing is assessed on a time and materials basis up to the limit of the burst contingency. The burst contingency should be accounted for in the testing budget and indicated on the purchase order.
- Burst Debris
Burst debris is a more generic term and includes not only burst fragments, but also other material such as pieces of probes, sensors, ovens, etc. destroyed during the burst and which accumulates at the bottom of the containtment vessel (spin test chamber).
- Burst Fragments
Burst fragments are pieces of the original test specimen that remain after the test has been performed. Test Devices can also supply special proprietary capture systems to preserve the rotor fracture surfaces during burst, however, some of the smaller parts will become embedded in other materials inside the pit simultaneously so 100% recovery is rare. Nevertheless, we will recover the vast majority of the original test part pieces. We will remove these pieces from the spin pit chamber, package and return them for failure analysis review
- Containment Vessel
An apparatus that will prevent the shrapnel from leaving the immediate area of the burst and protects both people and equipment nearby that would be subject to damage. There are numerous technologies to accomplish this and which can be tested in addition to the rotating part in our test chambers. Currently, there are no computer programs that accurately model potential failures in containment.
- Documentation
Includes all information agreed upon for the test plan and could include plots, certifications, videos, TIF files, photographs, etc. Test Devices, Inc. provides a formal certification document for each article or lot as required. All test documentation and report material are archived at Test Devices, Inc. and available for inspection or duplication.
- Rim Peel
Rather than the entire test specimen disintegrating, a portion of the outer diameter comes off while the hub section remains intact. Less energy is dissipated, as a result, and therefore less dangerous (as in: it is less dangerous to stand in front of a SUV at 80mph than a locomotive at 80mph). If this were the failure mode, less containment would be required
- Rotor
Any rotating part. Usually refers to the Customer’s part submitted for testing. Used interchangeably with DUT.
- Tri-Hub Burst
This is when the entire test specimen disintegrates and releases all of its energy. Typically, a part will decompose into 3 major pieces which carry about 1/3 of the energy in the part which containment vessels are designed to contain. While more numerous pieces are possible, they are easier to contain, especially for penetration of the containment vessel
Rotor Spin Testing:
Burst Testing
The Issue
High speed rotating machinery stores huge amounts of kinetic energy. When one or more rotating components burst, that energy is released. For example, a rotor weighing 272 kg (600 lbs), having a diameter of 76 cm (30 in) and spinning at 14,000 rpm has an energy equivalent of 2.1 x 107 Joules. This is equivalent to the power of some bombs. Even small rotors spinning at high speed can cause catastrophic damage during a burst.
Because of the danger associated with rotating component failure, governing authorities such as the Federal Aviation Administration (FAA) often require burst testing in order to establish margins of safety above normal operating speeds (burst margins) for critical rotating components.
Why it Matters
If not contained, the projectiles liberated during a burst can penetrate a machine housing, aircraft fuselage, etc., causing catastrophic damage to equipment. More importantly, a burst can pose a significant and potentially mortal threat to anyone within the event's sphere of influence. Any product that does not protect the public in such cases exposes the manufacturer to litigation and added costs related to insurance and regulation.
What You Can Do
Overspeed centrifugal stress testing to the point of burst offers manufacturers valuable information about the ultimate strength of a part or material. Additionally, rigorous strain surveys and temperature control can provide critical data right up to the point of failure that helps improve the predictability of life and the modes of failure. Test Devices has expertise and experience in the specialized fields of burst testing, strain surveys, failure analysis, and containment systems. Our Spin Test systems perform burst testing at designed energy levels for in-plane and out-of-plane projectiles. We have invested in top-flight equipment, instrumentation processes, data recording, and personnel to provide our customers with the crucial information they require while safeguarding against property damage and personal injury.
Advantage of Burst Testing
- Design Validation: Burst testing, combined with rigorous environmental control and strain surveys, provides hard, empirical evidence that design parameters were reasonable and that all considerations have been investigated. If the speed at which a rotor bursts is within a predicted failure range for a given temperature and/or temperature gradient, the resulting data validates design intent and subsequent engineering.
- Materials Validation: While slight changes in materials and processing may seem harmless, without testing there is no way to know the impact of a substitute material or change in processing procedures. Burst testing validates the best choice of materials and processes to meet all safety considerations at the most economical cost.
- Reduction of Manufacturing Costs: By evaluating failure modes using good data, equipment designers can optimize design of both rotating equipment and static containment systems. Periodic burst testing during production can also validate that materials are within specifications and manufacturing processes are being adhered to.
- Failure Analysis: Burst testing a component provides customers with data regarding the component mode of failure that can be used to evaluate failure risk and to design appropriate containment. If Test Devices' High Speed Video is employed, additional clues as to the origin and mode of failure can be ascertained.
- Containment Evaluation: Failing a high speed component provides an opportunity to test the capability of the real-world containment structure. Spin test chambers provide a safe environment to evaluate the capability of containment designs. Should the containment fail, the robust spin chamber is there to prevent component fragments from endangering other equipment or personnel.
- Establish Safety Margin: A burst test establishes the speed at which a rotating component fails and allows customers to calculate the safety margin between the operational speed and the speed at which the component fails.
Some Applications for Burst Testing
| Jet engine components | Gears | Compressor rotors |
| Turbine rotors | Centrifuge rotors | HVAC fans |
| Turbofans | Impellers | Metallic flywheels |
| High speed fans | Turbochargers | Composite flywheels |
| High speed machine tools | Electric motor rotors | Grinding wheels |
Standard Burst Test
Test components are accelerated in a spin test chamber until the rotating assembly fails due to increasing centrifugal stress.
Data includes
Speed at burst
Return of burst fragments
Elevated Temperature
Isothermal Option
Test Devices offers customers the option of performing burst tests at elevated temperatures. Burst tests can be run at isothermal temperatures up to 1500°F (815°C), with special applications to 1600°F (871°C). Tests performed at operational temperatures better simulate the conditions the rotor will actually experience during use, producing a more realistic scenario for the component during testing.
Elevated Temperature
Axial and Radial Thermal Gradient Option
Controlling the temperature of individual sections (axial), or radial gradients of a rotating assembly allows for better correlation with finite element stress models and real world conditions. Temperature gradient simulation during testing adds additional stress on rotating components. Differences in temperature (non-isothermal), both radial and axial, create stresses in an assembly that rival centrifugal stresses.
Cooled
Cryogenic Temperature Option
Test Devices also provides burst testing services at cryogenic temperatures. Spin tests of rocket components often require test temperatures well below ambient, and Test Devices has developed techniques to test components at cryogenic operating temperatures below -300° F..Cryogenic testing can also be used to validate remaining life of a component that was pulled from service.
Strain
Strain Measurement Option
Sensors mounted to the test component are used to monitor the strain resulting from the centrifugal stress. Customers are able to select specific high stress areas of interest on the test component and obtain strain data at speed..The strain data is most often used to validate CAE analysis.
Growth
Elastic / Plastic Growth Measurement Option
Proximity sensors are used to measure the growth of a component bore and/or rim at speed. This is particularly important when component growth becomes plastic. Growth measurements provide customers with the ability to determine a component's position on the stress/strain curve during a test.
Video
High Speed Video Option
Recording burst events with high speed video equipment provides immediate data with regard to the component failure locations. Knowledge of the failure location can greatly simplify failure analysis.
Containment Evaluation Option
Evaluation of high speed component containment systems is effectively done in a spin chamber. Typically containment tests require rotors to be failed at a specific speed, which presents a known amount of energy to the containment system. Test Devices has developed unique methods of failing test components at pre-determined speeds to satisfy this requirement.
Contact
Please contact Christine Murner (+1-978-562-4930) in our sales department for more information and to learn how we can help you.