l9 - 16.810 16.810 Engineering Design and Rapid Prototyping...

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16.810 16.810 Engineering Design and Rapid Prototyping Engineering Design and Rapid Prototyping Instructor(s) Structural Testing January 18, 2005 Prof. Olivier de Weck Prof. Olivier de Weck Lecture 9
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16.810 2 Outline ! Structural Testing ! Why testing is important ! Types of Sensors, Procedures …. ! Mass, Static Displacement, Dynamics ! Test Protocol for 16.810 (Discussion) ! Application of distributed load ! Wing trailing edge displacement measurement ! First natural frequency testing
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16.810 3 (1) Sensor Overview : Accelerometers, Laser sensors , Strain Gages , Force Transducers and Load Cells, Gyroscopes (2) Sensor Characteristics & Dynamics : FRF of sensors, bandwidth, resolution, placement issues (3) Data Acquistion Process : Excitation Sources, Non-linearity, Anti-Alias Filtering, Signal Conditioning (4) Data Post-Processing : FFT, DFT, Computing PSD's and amplitude spectra, statistical values of a signal such as RMS, covariance etc. (5) Introduction to System Identification ETFE, DynaMod Measurement Models Data Acquisition and Processing Data Acquisition and Processing for Structural Testing for Structural Testing
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16.810 4 Why is Structural Testing Important? ! Product Qualification Testing ! Performance Assessment ! System Identification ! Design Verification ! Damage Assessment ! Aerodynamic Flutter Testing ! Operational Monitoring ! Material Fatigue Testing F-22 Raptor #01 during ground 22 Raptor #01 during ground vibration tests at Edwards Air vibration tests at Edwards Air Force Base, Calif., in April 1999 Force Base, Calif., in April 1999 Example: Ground Vibration Testing Example: Ground Vibration Testing Structural System stimulus u(t) DAQ DSP response DAQ = data acquisition DSP = digital signal processing x(t)
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16.810 5 Type Linear Rotational Bandwidth Low Medium High Derivative Position Rate Acceleration Reference Absolute Relative Quantity Force/Torque Displacement Impedance Low High I. Sensor Overview This Sensor morphology is useful for classification of typical sensors used in structural dynamics. Example: uniaxial strain gage Need units of measurement: [m], [Nm],[ µ strain],[rad] etc… Sensor Morphology Table Sensor Morphology Table
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16.810 6 Sensor Examples for Structural Dynamics strain gages shaker laser sensors accelerometers gyroscopes load cells ground inductive sensors Example: fixed-fixed beam with center load excitation First flexible mode frequency: () 3 14 0.375 n b EI lm m ω= + m b m l Goal: Explain what they measure and how they work
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16.810 7 Strain Gages Current Nominal length l o : in o o V I l ρ = Strain: o l l ε = GND V+ l o With applied strain: () in o V I ll = +∆ Strain gages measure strain (differential displacement) over a finite area via a change in electrical resistance R=l ρ [ ] strain gages feature polyimide-encapsulated constantan grids with copper-coated solder tabs. bond to test article Implementation: Wheatstone bridge circuit Mfg:
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16.810 8 Accelerometers Single-Axis Accelerometer must be aligned with sensing axis.
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This note was uploaded on 11/08/2011 for the course AERO 16.810 taught by Professor Olivierdeweck during the Winter '07 term at MIT.

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l9 - 16.810 16.810 Engineering Design and Rapid Prototyping...

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