
One Stop Shopping of High Speed Testing

One Stop Spin Testing

Introduction

One of the difficulties customers have in outsourcing spin testing programs is often the need for several different vendors to satisfy the varied program requirements. These requirements can include designing and fabricating the spin tooling at the beginning of a program to inspection services and failure analysis at the end. Juggling the different vendors is similar to what you may hear from people who have handled subcontracting of their own house. It can be very time consuming and frustrating.

Realizing customers do not have the time to spend coordinating project stages with several vendors, Test Devices has developed a group of strategic partners. Over a twenty plus year time period, TDI has developed relationships with expert and dependable vendors who provide adjunct services to spin testing. Test Devices, together with its strategic partners, enables customers to produce a single purchase order to Test Devices and avoid the micro management responsibility. Additionally, since Test Devices has established relationships with vendors, customers can benefit from seamless project management.

Some of the services offered by Test Devices in addition to tooling design/fabrication, balancing, and spin testing are outlined below.

Inspection Services

Fluorescent Penentrant Inspection (FPI)

FPI is a nondestructive inspection method used to detect cracks and other flaws at the surface of components. FPI can be performed on any non-porous material, and is particularly helpful for detecting flaws in non-magnetic aerospace super-alloys (Inconel®, Waspalloy®), where MPI is not an option. Fluorescent penentrant inspection can be an invaluable segment of low cycle fatigue test programs, as well as other spin tests.

The process includes: cleaning the component to remove any residue (oil, dirt, etc.), applying the penetrant and allowing dwell time, removal of penentrant, applying developer, and finally inspection with a black light. Flaws are evident by a glowing bright indication when viewed under black light.

American Society for Non-Destructive Testing (ASNT) certified technicians perform the inspections. Components inspected range from simple geometry components to jet engine rotor parts which can be much more complex including bolt holes, blade routes, and rotor bores.

Magnetic Particle Inspection (MPI)

MPI is a nondestructive inspection method used to detect surface and subsurface cracks and other flaws in ferrous (magnetic) components.

The process includes: cleaning the component to remove any residue (oil, dirt, etc.), installing a magnetic connection, energizing the component through the connection, applying magnetic particles to the component, and finally inspection. Flaws are evident by the collection of particles in areas of “magnetic leaks” on the surface of the component.

American Society for Non-Destructive Testing (ASNT) certified technicians perform the inspections.

Eddy Current Inspection (EC)

Eddy current is a nondestructive inspection method used to detect surface and subsurface cracks and other flaws in ferrous (magnetic) components, and is also used for measurement of flaw size. Eddy current inspection is based on inducing electron flow (eddy currents) in electrically conductive materials.

The eddy current inspection procedure involves calibration of the probe (eddy current sensor). Representative defects (similar to expected flaws) are installed in to material having similar composition and geometry as the component to be inspected. Instrumentation settings are optimized during the calibration process to ensure that all artificial defects are detected.

Following successful calibration, the eddy current probe(s) are traced over the sections of the component which are susceptible to development of defects. Detected flaws show up as spikes in impedance on graphs.

Instrumented Blades

Figure 1 - Instrumented Blades

X-Ray Inspection

X-Ray inspection is used to find anomalies in alloy components caused by porosity, inclusions, or abusive machining practices. X-Ray inspection is often used by Test Devices to ensure raw material is homogeneous for the rigorous requirement of spin tooling, where failing a spin arbor is not an option. Additionally, X-Ray is offered to customers who require internal inspection of rotating components.

Ultrasonic Inspection (UT)

Ultrasonic inspection is a nondestructive inspection method used to detect surface and subsurface cracks and other flaws in ferrous (magnetic) components. UT uses sound waves to detect flaws and measure material thickness. UT inspection is often used by Test Devices to ensure raw material is homogeneous for the rigorous requirement of spin tooling, where failing a spin arbor is not an option.

Additionally, UT is offered to customers who require internal inspection of rotating components.

Dimensional Inspection

Dimensional inspection is typically performed for a couple of reasons. The most common reason for dimensionally inspecting machined components is to verify or determine dimensions.

Another reason for precise dimensional measurements is to determine whether the rotating component has undergone plastic growth. Often customers ask TDI to precisely measure rotor ID’s and OD’s pre and post spin test to determine part growth due to centrifugal force.

For simple geometry components Test Devices can provide dimensional inspection services in house. Dimension inspections can be either performed by using calibrated mechanical measuring equipment or by a calibrated digital measurement machine with a precision of 0.0001 inch.

For complex geometry components requiring a coordinate measurement machine (CMM) TDI has established a relationship with an expert inspection vendor. This vendor is able to precisely measure components of complex geometry, including: airfoils and rotor blade roots (blade attachments). It is often more convenient for customers who have already performed a pre-spin test CMM inspection to have TDI handle to post or interim spin test inspection by utilizing this vendor.

Bench Testing

As part of a pre-spin test operation Test Devices has joined together with a facility to offer “bench testing”. Bench testing includes the items outlined below and is a key predecessor to the high cycle fatigue testing offered at TDI. The bench testing identifies the optimum location for gage placement for excitation testing.

Holography

The holography process defines hardware mode shapes and frequencies under excitation. This is typically done on turbomachinery airfoils to map mode shapes. This allows for frequency correlation with the computer model.

Holographic Image

Figure 2 - Holographic Image

Stress Pattern Analysis by Thermal Emission (SPATE)

The SPATE technique provides a full field stress analysis by recording the minute changes in temperature of structures under excitation. Areas under highest stress show (node or anti node?) warm to hot colors while the low stress (node or anti node?) areas display cool colors. This is particularly important for placement of strain gages for fatigue (bench or spin test) testing.

SPATE Images

Figure 3 - SPATE Images

Fatigue Testing

After strain gages are applied per locations determined during the SPATE process, the airfoil is mounted to an electro dynamic or piezo-electric shaker system to determine fatigue life. The blades are step loaded until failure which is characterized with fluorescent penenetrant inspection.

Sensors on blades

Figure 4 - Instrumented blades

Instrumentation

Instrumentation in spin testing usually refers to strain gages, thermocouples, and RTD’s (resistance temperature detectors). For spin tests requiring data be recorded from the rotating assembly, Test Devices uses a vendor with over 30 years of experience in static and dynamic strain measurement. This vendor specializes in the installation of strain gages and ancillary sensors (thermocouple, RTD and heat flux). Instrumentation is expertly installed by Sensor Application Technicians with many years of experience, taking great care that the instrumentation and lead wires are installed to survive the high “g” field spin testing environment to which they will be exposed. Proper instrumentation installation is critical to a successful instrumented spin test, and TDI’s instrumentation vendor has demonstrated time and again why they are world renowned.

Surface Treatments

Surface treatments are often done to make components more durable (plating, painting). One method commonly used in the aerospace industry to increase component life is shot peening. Shot peening involves bombarding a component with shot material, typically steel, ceramic or glass bead spheres, 0.010 inch diameter. As the shot media contacts the component it imparts small indentations, which is caused by yielding of the component material. The surface compressive stress increases component resistance to fatigue failures, lengthening component life, by lowering the mean stress under cyclic conditions and eliminating the detrimental effects of abusive machining and other forms of processing. Shot peening typically is effective to a depth of 0.006 to 0.008 inch.

Through its shot peening vendor, Test Devices offers this service to customers who need to decrease the potential initiation of cracks due to abusive machining or material flaws.

For more information, please contact one of our sales engineers at: