Spin 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 potential danger associated with rotating component failure, governing authorities such as the Federal Aviation Administration (FAA) often require spin burst testing in order to establish margins of safety above maximum rated operating speeds (burst margins) for critical rotating components.

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Why it Matters

If not contained, the fragments projected 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 fatal threat to anyone within the event sphere. Any product that does not protect the public in such cases exposes the manufacturer to litigation and added costs related to insurance and regulation. Aside from safety considerations and the value in determining effective containment designs, spin burst testing is also used to confirm the ultimate limits to which a rotating system can be operated.

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What You Can Do

Rotational testing to the point of burst offers manufacturers valuable information about the ultimate strength of a component part or material. Test Devices has expertise and experience in the specialized techniques of spin burst testing, strain measurement, failure analysis, and the design of burst containment measures. Our Spin Tests are capable of conducting spin burst testing to contain fragments that are projected or deflected in both rotational in-plane and out-of-plane projectiles directions. This is an important feature since the energy that is not absorbed by the spin rig walls will be deflected upwards towards the lid – a result that has been often documented in practice; sometimes with serious consequences. We have invested in top-flight equipment, instrumentation processes, data recording, and personnel to provide our customers with the critical information they require while safeguarding against property damage and personal injury.

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Advantages of Spin Burst Testing

Design Validation: Spin burst testing provides hard data that rotating component design and performance is within safe operating limits. 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 inconsequential, without testing there is no way to know the impact of a substitute material or change in processing procedures. Spin 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 spin burst testing during production can also validate that materials are within specifications and manufacturing processes are being adhered to.

Failure Analysis: Spin 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. Test Devices can also include a ring of material around the test component known as Soft Containment. This material captures burst fragments while preserving the condition of the fracture surfaces, enabling further analysis into the initiation and propagation of cracking.

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 spin 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 Spin 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

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Spin Burst Testing

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 spin 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 containment 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 80 mph than a locomotive at 80 mph). 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.

Spin Burst Test Options

Figure 1 - Post-test disk fragments reassembled for review — Figure 1 – Post-test disk fragments reassembled for review

Standard Spin Burst Test

Test components are accelerated in a spin test chamber until the rotating assembly fails under increasing centrifugal stress.

Data Includes

Speed at burst

Return of burst fragments

Elevated Temperature

Isothermal Option

Test Devices offers customers the option of performing spin burst tests at elevated temperatures. Spin 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. More info »

Cooled

Cryogenic Temperature Option

Test Devices also provides spin 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. More info »

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. More info »

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. Figure 2 – Normal spin, initial crack formation and test article bursting More info »

Containment

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.

Spin Burst Testing

The Issue

Why it Matters

What You Can Do

Advantages of Spin Burst Testing

Some Applications for Spin Burst Testing

Spin Burst Test Options

Standard Spin Burst Test

Data Includes

Elevated Temperature

Isothermal Option

Elevated Temperature

Axial and Radial Thermal Gradient Option

Cooled

Cryogenic Temperature Option

Strain

Strain Measurement Option

Growth

Elastic/Plastic Growth Measurement Option

Video

High-Speed Video Option

Containment

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