The DN 55 High Temperature Dry Sliding & Fretting Machine comprises a special short stroke, minimum trapped oil volume, servo hydraulic actuator, mounted vertically on a massive cast iron base. The actuator incorporates hydrostatic bearings, which, in combination with the minimized oil volume, allows high frequency and short stroke operation.
The test assembly is located vertically above the actuator and comprises two fixed specimen arms supported on flexural pivot bearings, which are in turn mounted on linear flexure assemblies. Motion in a vertical direction is restrained by piezo force transducers. As each arm reacts against its own independent transducer, the friction between the each moving specimen and each fixed specimen is monitored independently. This allows two different material pairs to be tested simultaneously under identical conditions of load and temperature.
The actuator is driven by a Moog super high response servo valve, connected to a high frequency analogue controller, which derives its set points via a 16 bit control and data acquisition card from a standard PC running COMPEND 2020 software. Real time adaptive control features provided within the software allows high precision control of the actuator when working against highly non-linear loads. Sine, square, triangular and random waveforms may be programmed and, depending on the physical capabilities of the hydraulic system, oscillating frequencies up to 500 Hz may be controlled.
The servo actuator, when enabled, is always, for safety reasons, operated under closed loop analogue displacement control with positional feedback from an integral LVDT. An analogue open loop set point is provided to the servo amplifier by the signal generator, which in turn receives an open loop digital set point from the computer control and data acquisition system.
The displacement control loop is subsequently closed in software using a single error correction adaptive control algorithm. This control action operates each time high-speed data acquisition is triggered. The process involves sampling the measured displacement signal and analysing both the peak amplitude and the mid-stroke position. A proportion of the resulting error is added to or subtracted from the digital set point to the signal generator, thus making a single adjustment to both the peak value of the amplitude and the mid-stroke position. Subsequent repeat high-speed data acquisition cycles make further adjustments with the resulting displacement progressively converging on the required value.
Depending on the stroke length, the displacement signal for high-speed data acquisition and adaptive displacement control may be taken either from the LVDT (long stroke applications) or from the capacitance probe (short stroke applications).
Frequency Control and Waveform
The frequency is set digitally either manually from the on-screen display or from the test sequence file. Similarly, uniform waveforms (sine, triangular or square) may be toggled from the screen or set within the test sequence file. Pre-recorded random waveforms may also be toggled, but under these circumstances, the adaptive control functions must, for obvious reasons, be disabled.
Signal Processing and Data Acquisition
Low-speed data, such as temperature, load and r.m.s. parameters, may be stored to hard disk. At the end of a test this data may be manipulated for calculation or graphical presentation using standard spreadsheet software.
High-speed data acquisition may be triggered either manually from the computer screen or automatically from a test sequence file. The operator may select the number of channels to be recorded, the sampling frequency and the number of samples. Each burst of high-speed data is stored in an independent data file. If triggered automatically through a test sequence file, each burst of high-speed data is stored into a new file, which is automatically time stamped, with a hyperlink automatically generated between the appropriate point in the low-speed data file and the corresponding high-speed data file.
Impact Sliding and Impact Fretting Tests
For impact sliding and fretting tests, the standard fixed specimens are replaced by wedge shaped specimens. The moving specimen is withdrawn from contact and the fixed specimens are loaded against a stop with a pre-set force applied by means of the pneumatic bellows. To perform a test, the moving specimen is brought into contact with the fixed specimens under velocity control. Adaptive control functions in the software allow peak to peak tuning of the displacement in order to achieve either a required displacement or a required impact force.
Impact and Hertzian Fretting Tests
For impact and Hertzian fretting tests, to twin fork tooling is replaced by a single fixed specimen mounting system. Impact tests are performed with the fixed and moving specimens coming in and out of contact. Hertzian fretting tests are performed with the specimens in continuous contact.
DN 55/1 Small Perturbation Signal Generator
This optional additional signal generator and signal analysis system allows combined sliding motion with co-axial vibration to be generated. The standard servo amplifier incorporates a summing junction on the input stage with dual inputs. This means that with the addition of a second signal generator, two separate signal inputs, one low frequency and long stroke and one high frequency and short stroke, can be combined, thus producing reciprocating motion with superimposed vibration from a single servo hydraulic actuator.
Type of contact: Ball/Flat Flat/Flat Line/Flat Maximum Specimen Diameter: 20 mm Type of Movement: Sine, Square, Triangular and Random Maximum Load: 2000 N Maximum Friction Force: +/-2000N Stroke – continuously variable: 10 microns to 20 mm Frequency: 0.1 Hz to 200 Hz Environment: Dry Temperature: Ambient to 1200°C Super High Response Servo Valve: 12 l/min Actuator Bearings: Hydrostatic Dynamic Load: 5.7 kN Static Load: 8.6 kN Hydraulic Power Pack: 12 l/min at 250 bar High Speed Interface: PCI bus Resolution: 16 bit Number of Input Channels: 1 to 16 Maximum Data Rate: One channel at 250 kHz Interface: Phoenix Tribology USB micro-controller interface Software: COMPEND 2020 DN 55/1 Small Perturbation Signal Generator Type of Movement: Sinusoidal sliding stroke with co-linear superimposed sinusoidal perturbation Sliding Motion: Maximum Stroke: 20 mm (Amplitude: 10 mm) Type of Movement: Sinusoidal Frequency (FS): 0 to 5 Hz Vibration Motion: Stroke/Frequency: 200 microns (Amplitude 100 microns) @ 0 to 200 Hz 100 microns (Amplitude 50 microns) @ 0 to 300 Hz Frequency (FP): 0 – 300 Hz Control Requirements: FP must be greater than FS x 20 Controlled Parameters Frequency Stroke Load Temperature Test Duration Measured Parameters Frequency Stroke Load Friction Temperature Services Electricity: 220/240V, single phase, 50 Hz, 7.5 kW 110/120 V, single phase, 60 Hz, 7.5 kW Mains water and drain: 10 l/min (typical)
aerospace materials ball on plate ceramics fretting fretting wear high temperature testing impact sliding multi-station oxidative wear reciprocating sliding severe oxidative wear sliding line contact
Paper # 278 An Experimental Investigation on Composite Fretting Mode Zhu M H, Zhou Z R, Kapsa P, Vincent L, Tribology International, 34 (2001) 733-738. Paper # 281 The Prediction of Fretting Fatigue Resistance of Various Surface Modification Layers on 1045 Steel: Role of Fretting Maps Xu G Z, Liu J J, Zhou Z R, Tribology International, 34 (2001) 569-575. Paper # 286 Radial Fretting Fatigue Damage of Surface Coatings Zhu M H, Zhou Z R, Kapsa P, Vincent L, Wear 250 (2001) 650-657. Paper # 634 A practical methodology to select fretting palliatives: Application to shot peening, hard chromium and WC-Co coatings K Kubiak, S Fouvry, AM Marechal Wear Volume 259, Issues 1-6, July-August 2005, p. 367-376 Paper # 635 A quantitative approach of Ti–6Al–4V fretting damage: friction, wear and crack nucleation S Fouvry, P Duóa, P Perruchaut Wear Volume 257, Issues 9-10, November 2004, p. 916-929 Paper # 640 High-load fretting of Ti–6Al–4V interfaces in point contact X Huang and RW Neu Wear Volume 265, Issues 7-8, 20 September 2008, p. 971-978 Paper # 641 Fretting Behavior of AISI 301 Stainless Steel Sheet n Full Hard Condition M R Hirsch Thesis presented to the Academic Faculty Georgia Institute of Technology August 2008 Paper # 728 Fretting damage in thin sheets: Analysis of an experimental configuration MR Hirsch, RW Neu 6 th International Symposium on Fretting Fatigue, Chengdu, China, April 19-21, 2010 Paper # 729 Fretting behaviour of AISI 301 stainless steel sheet in full hard condition in contact with AISI 52100 steel MR Hirsch, RW Neu Tribology – Materials, Surfaces & Interfaces 2008 VOL 2 NO 1 Paper # 780 Relationships between the fretting wear behavior and the ball cratering resistance of solid lubricant coatings DB Luo, V Fridrici Surface and Coatings Technology 2010 Volume 204, Issue 8, p. 1259-1269 Paper # 784 Selecting solid lubricant coatings under fretting conditions DB Luo, V Fridrici Wear 2010 Volume 268, Issues 5-6, p. 816-827 Paper # 788 Surface property enhancement of Ni-free medical grade austenitic stainless steel by low-temperature plasma carburising J Buhagiar, L Qian Surface and Coatings Technology 2010 Volume 205, Issue 2, p. 388-395 Paper # 870 Influence of temperature on the fretting response between AISI 301 stainless steel and AISI 52100 steel MR Hirsch, RW Neu Tribology International – Available online 14 November 2012 Paper # 909 A simple model for friction evolution infretting MR Hirsch, RW Neu Wear Volume 301, Issues 1–2, April–May 2013, Pages 517–523 Paper # 910 A new multicontact tribometer for deterministic dynamic friction identification JL Dion, G Chevallier, O Penas, F Renaud Wear Volume 300, Issues 1–2, 15 March 2013, Pages 126–135 Paper # 1311 Coefficient of friction evolution with temperature under fretting wear for FeCrAl fuel cladding candidate T Winter, RW Neu, PM Singh, LE Kolaya Journal of Nuclear, 2019 – Elsevier Paper #1348 Validation of a dry sliding wear simulation method for wastegate bearings in automotive turbochargers AA Schmidt, J Plánka, T Schmidt, O Grabherr, D Bartel Tribology International – 2020 – Elsevier
Honeywell Inc Czech Republic SNECMA France Mitsubishi Heavy Industries Japan National Physical Laboratory UK Georgia Tech USA
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