ETEK Technology FAQ

What is the difference among ETEK, iETEK and RiETEK products?

The ETEK is the original ultrasonic laboratory instrument for measuring all the independent elastic and engineering constants of a friction material. This is a destructive test and the results are typically used as property data input to CAE simulation models (SAE J2725) for development of new friction material formulations. Measurements are made at ambient and elevated temperature and using different pre-loads.
The iETEK uses the same ultrasonic technology as the ETEK. The iETEK measures the dynamic modulus in the out-of-plane direction in as-manufactured pads. The measurement is rapid and non-destructive. Data is primarily useful for QC applications (SAE J3175) for checking batch to batch consistency and spatial uniformity within a pad.
The RiETEK also uses the same ultrasonic technology as iETEK. The RiETEK units are designed for use by systems integrators and automation companies for on-line measurements in a manufacturing environments. Using this units dynamic modulus can be measure in less than 200 milliseconds. Units are supplied with ModBus TCP communication software to facilitate automation.

What is the highest temperature?

The highest temperature measured for the ETEK is 325°C. The iETEK and RiETEK measurement are limited to temperatures less than 50°C.
Contact IMS for custom instrumentation if higher temperature measurement capabilities are needed. We have custom options for measurement capabilities up to 2000°C.

What is the sample size?

ETEK: The samples are cut to approximately 20mm x 15mm x 8mm
iETEK: Brake pads of all sizes can be measured on the iETEK in multiple positions. The diameter of the sensor is 15mm which typically allows for 2-8 measurements per pad. Measurements cannot be made over the spigot holes or over raised areas on the backing plate.

What is the lowest temperature?

Low temperature measurements are made on the ETEK using “dry ice” for cooling. This instrument has no active cooling.

How fast can we make measurement on the iETEK?

The iETEK measurement for a single position takes approximately 0.2 seconds. Manually moving the pad to another position and applying pre-load may take several seconds but this time can be reduced significantly when automated. Measurement time less than 2 seconds/pad has been achieved. The RiETEK modules allow simultaneous measurements of multiple positions using multiple pairs of sensors. Production line speeds of 2 seconds per pad with 4 positions each and included thickness measurements have been reported.

What are the limits on the pre-load?

Force used for loading the samples ranges from 100 N to maximum of 900 N. For test samples used in the ETEK this force creates a maximum pressure of 5.5 MPa in the sample.

Why do I need to supply pre-load?

Many friction materials are highly non-linear and the modulus is dependent upon the pre-load.

What is the size of the sensors?

The most commonly used sensor is ~15 mm in diameter. Sensors as small as 7.5 mm diameter have been used in special applications.

Why are multiple sensors needed for ETEK measurements?

For anisotropic materials measurements of both longitudinal and shear waves propagating along different directions are needed in order to determine all of the independent elastic properties. For friction materials which have transversely isotropic symmetry with 5 independent elastic constants 5 measurements are needed. The measurement process and analysis is dictated by Hooke’s law.

How many sensors are needed for an iETEK measurement?

The iETEK measures only the out-of-plane modulus in friction material. Dynamic Young’s modulus is estimated from historical data obtained using SAE J2725. Only one sensor pair is needed.

How do we make measurements on the ETEK?

Once the samples are prepared, the ETEK software interface steps the user through the process of creating the sample files, entering sample dimensions and selecting different measurements using shear or compressional sensors at various loads and temperatures and generating a final report. Algorithms for converting the measured velocities into elastic constants and engineering constants, Young’s modulus, shear modulus and Poisson’s ratio’s are incorporated into the ETEK software.

Can I measure materials other than friction materials?

Yes, other materials such as ceramics, composites and metals may be measured using the ETEK. However, the frequency response of the sensors may not be appropriate. The sensors included with the ETEK have been specifically selected to work best with friction materials in terms of signal amplitude and resolution. A different frequency (generally higher) may be appropriate for other materials. A high frequency sensor package option is available for purchase with an ETEK.

Why is it important to control pre-load?

For most materials pre-load is not important, but friction materials are unique in that the modulus increases as load is applied. We have observed some friction material’s modulus change by as much as 60% as a function of pre-load.

What is the maximum pre-load?

The maximum pre-load we typically apply in a Load measurement is 5.5 MPa or 55 Bar. Using a higher pre-load could cause damage to the load measuring device and ultrasonic sensors.

How are the instruments calibrated?

The ultrasonic timing, Time-of-flight (ToF) is the primary measurement in these instruments and calibration. Calibration is done at the start of each iETEK program initialization and performed daily on the ETEK. The calibration is accomplished using a certified steel gage block that has a specific thickness and is measured independently for thickness and ultrasonic transit time using both shear and compressional waves. Any variation in the certified gage block ToF value is subtracted from all ToF measurements in the form of an offset value calculated with each calibration.