Unified Calibration and Standardization of Friction Measuring Equipment Systems
II. RESEARCH NEEDS STATEMENT
During the past two decades new modern and updated friction measurement technologies have been developed as well as a number of advancements and improvements have been built into existing measurement systems and brought to market. The devices are targeting both the highway and the aviation friction community. Whilst the measurements from these devices correlate with each other to a degree, it has not proved possible to develop relationships that are sufficiently precise, across the range of surface types and measurement speeds encountered during normal operation, for the different devices to be regarded as interchangeable. The difficulty of correlating these friction measurement systems as well as successfully harmonizing existing devices has led to a lack of faith on the part of both governmental state concerns as to the viability of high quality harmonized measurements collected by the large array of devices. Coupled with a lack of standardization of requirements and the large variety and actual differences of designs and technical specifications of devices and their subcomponents, there is a need to develop:
1. General technical specifications and performance criteria for device components by standardizing portions of the systems to eliminate some of the measurement system’s variability. Variations in the performance and the quality of even standardized measurement tires, the water delivery amount and process, loading and slip ratio are four of the major differences affecting the friction measurement equipment and their measured results. The development of standard performance requirements of test tires, standard water nozzles, flow rates, test tire loading and slip ratio are primary deliverables.
2. New unified calibration specification that incorporates the targeted static calibration of device subcomponents and both static and dynamic calibration of the friction measurement systems on certified calibration sites incorporating a laboratory based calibration site surface quality assurance.
3. New calibration site requirements including the technology to implement calibration site quality assurance.
The results of this research will enable manufacturers of the devices to build equipment that can be more easily correlated with higher fidelity of correlation results. The research also will develop and recommend a multi-step new unified calibration technology applicable to all types of devices and to all segments of use including highway and aviation. The developed calibration process and requirements for the calibration sites will include performance criteria and technology to ensure calibration site quality assurance providing more accurate and closely matched harmonized data with high confidence levels.
III. RESEARCH OBJECTIVE
The objectives of this project are to:
· Review the current state of designs for different friction measurement devices and systems and identify how:
o the measurement tire-type performance compared to applicable standards,
o sub-systems of water delivery,
o measurement tire loading,
o and the applied percentage slip could be standardized or relevant performance and quality requirements for these effectively established.
· Develop model(s) to counter the remaining differences in measurement principles, designs and subcomponents of the different devices with a substantial and semi-empirical/physical model. The ASTM E1960 model developed and available will be examined extended and tested.
· Develop unified calibration procedures, including practice, surfaces, and static device calibration. The ASTM E556 and E2793 and the newly developed and currently balloted ASTM harmonization standard E1890 will be used as a basis for the development of the unified calibration procedure.
· Develop new technology to utilize highly controlled laboratory made surfaces and a pair of highly repeatable portable devices that can be dynamically calibrated in the lab and then taken to field to establish check standard measurements of large test surfaces for calibration sites to guarantee calibration site surface quality assurance. The ASTM E1911 and E2157 standards will be used as starting point and basis.
The key tasks to accomplish the objective of this research are listed below. These tasks are intended to provide a framework for conducting the research. The objective is to develop a research plan that demonstrates consideration of the issues raised in the objective, an understanding of the problem, and a description of the research effort that can realistically be conducted within constrains of available funds and contract time.
Task 1. Perform review of the current designs for different friction measurement devices and systems including:
a) Identify the range of test tires in use and review the existing controls on their consistency
b) Identify the range of nozzle designs and water delivery systems in use
c) Identify the loading or range of loading required for accurate testing and what the limits are under both summer and winter conditions.
d) Identify and review the effect of changes in Slip ratio on Friction values under both summer and winter conditions.
Task 2. Develop proposals for those elements of the design of friction measurement devices that can be standardized
Task 3. Interim report and Phase II work plan.
Task 4. Propose specifications for those elements of the friction measurement devices recommended in Phase I, for example:
a) Determine a standard test tire
b) Determine a standard load on the test tire and the range of acceptable limits on the dynamic variation of this load during testing
c) Identify a standard nozzle design and flow rate to provide the required amount of water film, currently 1.0mm, under the test tire.
Task 5 Develop equipment and procedures for checking the calibration and performance of measurement devices against the above specifications, for example:
a) Design and build a water flow/distribution test device that is both accurate and portable
b) Determine appropriate procedures and equipment for testing the calibration of the vertical and horizontal load measurement systems
c) Development of additional controls on the variability of tyres in addition to any controls in current standards
Task 6. Based on research results of task 3 develop models to counter the remaining differences in measurement principles, designs and subcomponents of the different devices. Test developed models through actual measurements at a candidate calibration site using a sample of the different measurement systems that meet the proposed specifications. Recommend possible changes and improvements for the corresponding ASTM E1960 standard or develop draft new ASTM standard based on developed model.
Task 7. Using the results of the measurements from task 4 and the verified physical models together with the ASTM standard procedures develop a unified calibration procedure and recommend possible changes to the applicable ASTM standards.
Task 8. Develop and test at least three different sets of controlled manufactured surfaces with at least five (5) different friction and texture levels. Test the durability of these surfaces regarding the retention of their frictional and textural characteristics with extended usage. Test the reproducibility of the manufacturing of these surfaces regarding their frictional and textural characteristics. Deliver a draft ASTM standard for the requirements of the production, storage, and use of the best performing surface set to be used in the calibration process.
Task 9. Develop procedure and standard for the use of the new check-standard laboratory surfaces in device calibration and calibration site quality assurance.
Task 10. Final Report
IV. ESTIMATE OF FUNDING AND RESEARCH PERIOD
An estimate of the recommended funding levels to accomplish the objectives stated in item III is $300,000.
An estimate of the number of months to complete the research effort, including three months for preparation of a draft report to accomplish the research objectives identified in item III is 18 months.
(Note: These estimates may be changed by the AASHTO Standing Committee on Research to fit the problem into the broad program.)
V. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION
The importance and urgency of this research is supported by the recent developments in the aviation community regarding the use of friction measurement devices. Due to the lack of available harmonization and the loss of confidence in the quality and accuracy of the measured frictional values on runways and taxiways regulatory bodies in the US & Canada, The EU and the ICAO countries are developing policies that removes CFME devices from winter operations. The same reasons had prompted a number of highway agencies in the EU and also in the US develop very costly quality assurance procedures that are varying greatly in their scope and adequacy as well as proven to be unique to the specific agency; The lack of adequate, objective and accurate assessment of runway conditions will present substantially increased risk in inclement weather operations and could potentially severely limit airport operations causing substantial cost increase for airport and airline operations and severe congestion. In the highway community the lack of adequate quality control of the measurement device calibrations lead to costly and unnecessary surface repairs or lack of necessary maintenance actions producing hazardous conditions increased accident rates with associated costs according to FHWA “70% of wet pavement crashes can be affected by pavement friction improvements”. The development of the standardized practices, components and a unified quality and technical performance requirement would provide the basis for the continued and increased use of high quality devices preventing the above described potential safety, financial and traffic management ramifications from occurring!
This research will result in improved data collection and lead to a standardized design for friction measurement devices used at highways and airports throughout the US and around the world. Results of the design research will be included to ASTM standards for fixed slip devices.
The expected documents to be affected by this research are:
· ASTM E556
· ASTM E2793
· ASTM E1890
· ASTM E1911 and
· ASTM E2157