Primary Calibration of Shock Transducers Influence of the Laser Spot Position

Transcription

1 Primary Calibration of Shock Transducers Influence of the Laser Spot Position Dr. Martin Brucke, Philipp Begoff, Michael Mende, Frank Schulz

2 Introduction Shock Exciters according to ISO (1) 1. Shock machine based on rigid body motion of an anvil (Hammer Anvil exciter) Barrel Anvil DUT p +/- Projectile (Hammer) Back-to-Back Reference Sensor APMP Conference

3 Introduction Shock Exciters according to ISO (2) 2. Shock machine based on wave propagation inside a long thin bar (Hopkinson-Bar exciter) F Displacement u(x,t) a t MP 1 MP 2 MP n t Barrel DUT p +/- Hopkinson - Bar Laser Vibrometer Projectile (Hammer) APMP Conference

4 Introduction Shock Exciters according to ISO (3) 2. Shock machine based on wave propagation inside a long thin bar (Hopkinson-Bar exciter) APMP Conference

5 Introduction Influence of the Laser Spot Position? APMP Conference

6 Shock Exciter with controlled shock duration Influence of the Laser Spot Position! ISO (section 4.3) In general the longitudinal displacement in the bar will vary as a complicated function of radial position and frequency depending on the material properties and diameter of the bar. This can introduce a frequency-dependent base strain to the transducer under test, increase the uncertainty in the calibration or both. SAVE Conference

7 Shock Exciter with controlled shock duration Special Hopkinson-Bar F Reaction Force F Input Force Hopkinson-Bar DUT Reaction Mass Piezoelectric Actuator Laservibrometer (reference standard) SAVE Conference

8 Shock Exciter with controlled shock duration Special Hopkinson-Bar F Reaction Force F Input Force Hopkinson-Bar DUT Reaction Mass Piezoelectric Actuator Laservibrometer (reference standard) SAVE Conference

9 Shock Exciter with controlled shock duration Special Hopkinson-Bar F Reaction Force F Input Force Hopkinson-Bar Reaction Mass Piezoelectric Actuator La (re APMP Conference

10 Shock Exciter with controlled shock duration Special Hopkinson-Bar F Reaction Force F Input Force Hopkinson-Bar Reaction Mass Piezoelectric Actuator La (re APMP Conference

11 Shock Exciter with controlled shock duration Special Hopkinson-Bar APMP Conference

12 Shock Exciter with controlled shock duration Special Hopkinson-Bar APMP Conference

13 Influence of the Laser Spot Position! Measurement Results Transducer B Diameter 13.7 mm Weight 13.5 gram HOP-Bar Diameter 20 mm Material Titan APMP Conference

14 Influence of the Laser Spot Position! Measurement Results Transducer B Diameter 13.7 mm Weight 13.5 gram HOP-Bar Diameter 20 mm Material Titan APMP Conference

15 Influence of the Laser Spot Position! Measurement Results Transducer A Diameter 10.7 mm Weight 6 gram HOP-Bar Diameter 20 mm Material Titan APMP Conference

16 Influence of the Laser Spot Position! Conclusions Shock duration > 100 µs measured DUT sensitivity deviation < 0.5% independent from the laser spot position. At shorter the shock durations, high deviations of the measured DUT sensitivity can occur. Repeat the calibration with the laser spot positioned at different spots around and close to the DUT and average the determined sensitivities. Currently more investigations are on the way Can these effects be reproduced well? How do material and diameter of the bar influence the results? How big is the impact on the measurement uncertainty? APMP Conference

17 Influence of the Laser Spot Position! Conclusions Thank You! APMP Conference