UC th Users Conference on BiAxial Fatigue Testing November 11 th, 2015

Transcription

1 UC th Users Conference on BiAxial Fatigue Testing November 11 th, 2015 UC Robert Keplin M.Sc. Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

2 LOAD FILE DEVELOPMENT page 2

3 Content Load file fundamentals Specification of a load file Basic load file development process Load file development for 3 axle semi-trailer application Used wheel end instrumented with strain gauges Local strain measurements for transformation of wheel loads to test rig loads Process for load file development of used wheel end Summary Outlook page 3

4 Specification of a load file for a LBF BiAxial fatigue test machine LBF load file is specified by: Combination of different actuator load sequences (vertical and lateral direction) in kn Defined drum speed for each load sequence in km/h Defined length of time for each load sequence in sec Seq Fv Fh v t [kn] [kn] [km/h] [sec] By means of a test load file a correct correlation between the LBF design spectrum and the BiAxial time reduced test spectrum shall be given in terms of loading, stress and damage content page 4

5 Basic load file development process (I) Results of experimental stress analysis on LBF flat track are input for the load file development Load assumptions Determination of local peak stresses by measurements of local strains on LBF flat track Derivation of the LBF design spectrum and calculation of RFS values Required Fatigue Strength for the relevant locations page 5

6 Basic load file development process (II) Transformation of wheel loads to test rig loads by means of damage accumulation on the basis of local strain measurements in BiAxial test rig Accurately stress reproduction for all design load cases Measurements of local strains in BiAxial test rig for complete period of load sequences Comparison of measured BiAxial test spectrum to LBF design spectrum via RFS value concept Load file / load sequence adjustment until required analogy is given in terms of damage content page 6

7 Basic Design Spectrum for 500,000 km of Service and Test Spectrum for heavy duty trucks (front axle) Test duration for heavy duty truck application front axle Steel wheels and castiron hubs: 16,000 km

8 Load file development for 3 axle semi-trailer application Seq Fv Fh v t [kn] [kn] [km/h] [sec] page 8

9 Wheel end for 3 axle semi-trailer European usage 11.75x22.5 inset120 steel wheel typical semi-trailer wheel for European usage Rated wheel load: kg Tire size: 385/65 R 22.5 No. of studs: 10 Pitch circle: ø335 mm Stud hole diameter: ø26 mm No. of ventilation holes: 10 aligned to area between stud hole center Ventilation hole design: oval Valve hole: aligned to ventilation hole center mating flange thickness: ca. 13 mm Hub system w/ brake disk typical semi-trailer hub system for European usage Rated wheel load: kg Hub system consist of: Hub flange (cylindrical cast-iron) Brake disk Hub-unit No. of studs / stud size:10 / M22x1.5 Brake disk: screwed w/ wheel studs Hub-unit: screwed w/ flange screws M18x1.5 No. of flange screws: 12

10 Wheel end instrumented w/ strain gauges SGs used at different locations on the wheel and the hub flange 23 SGs on wheel 4 on wheel flange outside 2 on mating flange 3 on disc radius inside 4 on ventilation hole inside 3 on ventilation hole outside 2 close to welding line 1 close to valve hole 2 on drop center 1 on rim well 1 on inner rim flange exemplary cross section wheel exemplary cross section wheel end 9 SGs on hub flange 3 on radius behind wheel bolt head inside 3 on radius wheel centering outside 2 on casting skin inside 1 on casting skin outside

11 Wheel end instrumented w/ strain gauges Most important SGs used for the measurement of local strains in LBF BiAxial test rig 6 SGs on wheel 1 on wheel flange outside, close to wheel nut contour (screwing area) 1 on mating flange, pretty close to the hub flange contour 1 on ventilation hole inside (peak stress area) 1 on ventilation hole outside 1 close to valve hole (rim well area) 1 on inner rim flange exemplary cross section wheel exemplary cross section wheel end 2 SGs on hub flange 1 on radius wheel centering outside 1 on casting skin inside (close to wheel bolt head peak stress area)

12 Local strain measurement w/ 8 channel telemetry system Using of high-precision telemetry system by datatel for the wireless transmission of the measured strains 6 measuring channels used for wheel structure 2 measuring channels used for hub flange structure Sample rate: 200 hz Operable temperature range of transmitter: 0 to 85 C page 12

13 BiAxial fatigue testing Realistic wheel loads while testing Straight driving Cornering Rough road Different actuator forces are needed for generation of equivalent wheel forces/local stresses by tilting and running against sidewalls of inner drum system page 13

14 Transformation of wheel loads to test rig loads Accurately stress reproduction for design load cases Design load cases Actuator load combination Cornering Vertical wheel load [kn] Lateral wheel load [kn] page 14

15 Transformation of wheel loads to test rig loads Accurately stress reproduction iteration loops Inner rim flange Ventilation hole inside Strain gauges on wheel structure Mating flange inside Ventilation hole outside Wheel flange outside Valve hole Design load case cornering Vertical Lateral Stresses for design load case Wheel loads MPa in % MPa in % MPa in % MPa in % MPa in % MPa in % kn in % kn in % Measured stresses Actuator loads 1. iteration 92,0 85,0 93,0 87,0 86,0 94,0 100,0 100,0 Relative deviation [%] -9,00-15,00-8,00-13,00-14,00-7,00 0,00 0,00 Absolute deviation [MPa] -12,00 25,00-9,00-20,00-15,00-6,00 0,00 0,00 2. iteration 95,0 92,0 96,0 93,0 93,0 96,0 105,0 110,0 Relative deviation [%] -5,00-8,00-4,00-7,00-7,00-4,00 5,00 10,00 Absolute deviation [MPa] -7,00-13,00-5,00-10,00-8,00-3,00 4,00 3,00 X. iteration 102,0 99,0 103,0 101,0 102,0 104,0 110,0 120,0 Relative deviation [%] 2,00-1,00 3,00 1,00 2,00 4,00 10,00 20,00 Absolute deviation [MPa] 3,00-2,00 4,00 2,00 3,00 3,00 8,00 6,00 Many iteration loops needed until measured stresses are reproduced in an adequate way for all design load cases and each strain gauge page 15

16 Final load file development Transformation of wheel loads to test rig loads by means of damage accumulation Measurements of local strains on BiAxial test rig for complete period of load sequences Damage accumulation Analysis: BiAxial test spectrum vs. LBF design spectrum Load file development/ adjustment until required analogy is given in terms of damage content page 16

17 Developing of an adequate wheel load file for 3 axle semitrailer application Specification of the wheel test load file Test load file consists of 99 load sequences Driven distance of one period 99 load sequences: ca. 65 km Test duration: 16,000 km ca. 246 repetitions Matched to a drum speed of 73 km/h and an inner drum size of 1.8 m Load sequences mixed for good drivability Cover new LBF design spectrum for 3 axle semi-trailer application (500,000 km) in a good way Seq Fv Fh v t [kn] [kn] [km/h] [sec] page 17

18 Results overview Load file adjustment by means of RFS value concept 1,1 1,0 0,9 RFS value normalized to maximum value 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 Inner rim flange Ventilation hole inside Mating flange inside Ventilation hole outside Wheel flange outside Valve hole RFS LBF design Spectrum RFS Load File Semi-Trailer page 18

19 LBF design spectrum vs. test spectrum Strain gauge on ventilation hole inside page 19

20 Load file comparison by means of RFS value concept Load file front axle vs. new load file semi-trailer 1,1 1,0 RFS value normalized to maximum value front axle 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 +2% +3% +4% +1% +7% +1% 0,1 0,0 Inner rim flange Ventilation hole inside Mating flange inside Ventilation hole outside Wheel flange outside Valve hole RFS Load File Front Axle [16,000 km] RFS Load File Semi-Trailer [16,000 km] page 20

21 Summary Up to now an adequate wheel test load file has been developed for typical 11.75x22.5 IS120 steel wheels for 3 axle semi-trailer application New load file for trailer axle application is in all relevant locations of the wheel structure more severe than the basic load file for front axle application, especially in the wheel screwing area Validity for hub: There is a deviation between the wheel and the hub due to the different lateral load transmission on BiAxial test rig for the hub higher actuator loads are necessary According to the current load file status the RFS value for the most critical location is about 6% too low extended test duration is needed Validity for aluminum wheels: Until now not enough measurements have been done for verification of the load file for aluminum wheels page 21

22 Outlook Current load file, which is valid for steel wheels, will be most likely available in the final version within 1. Quarter 2016 Outlook for hub More measurements still need to be done for final conclusion According to current status mixed test strategy could solve the deviation between wheel and hub e. g. test the wheel at first and continue hub testing w/ increased test parameters (c v and c h ) Outlook for aluminum wheels With SGs instrumented typical 11.75x22.5 IS120 aluminum wheel as well an accurate regression model is already available More measurements still needed for final validation page 22

23 Thank you for your attention. we will keep your wheels running