美国麻省理工大学：《Engineering Design and Rapid Prototyping》Lecture 7 Structural Testing

16810(16682) Engineering Design and Rapid Prototyping Lecture 7 a1n Structural Testing Instructor(s) Prof, olivier de weck January 21, 2004 Massachusetts Institute of Technology

  (QJLQHHULQJ'HVLJQDQG5DSLG3URWRW\SLQJ (QJLQHHULQJ'HVLJQDQG5DSLG3URWRW\SLQJ /HFWXUH 6WUXFWXUDO7HVWLQJ ,QVWUXFWRUV 3URI2OLYLHUGH:HFN 3URI2OLYLHUGH:HFN -DQXDU\

IGa10 Outline Structural Testing Why testing is important Types of Sensors, procedures Mass, Static Displacement, Dynamics Test protocol for 16810 Explain protocol Sign up for time slots 16.810(16682) Massachusetts Institute of Technology

2XWOLQH „ 6WUXFWXUDO7HVWLQJ „ :K\WHVWLQJLVLPSRUWDQW „ 7\SHVRI6HQVRUV3URFHGXUHV« „ 0DVV6WDWLF'LVSODFHPHQW'\QDPLFV „ 7HVW3URWRFROIRU „ ([SODLQSURWRFRO „ 6LJQXSIRUWLPHVORWV  

Data Acquisition and Processing al0 for Structural Testing (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 16.810(16682) Massachusetts Institute of Technology

'DWD$FTXLVLWLRQDQG3URFHVVLQJ 'DWD$FTXLVLWLRQDQG3URFHVVLQJ IRU6WUXFWXUDO7HVWLQJ IRU6WUXFWXUDO7HVWLQJ 6HQVRU2YHUYLHZ $FFHOHURPHWHUV/DVHUVHQVRUV6WUDLQ*DJHV )RUFH7UDQVGXFHUVDQG/RDG&HOOV*\URVFRSHV 6HQVRU&KDUDFWHULVWLFV '\QDPLFV )5)RIVHQVRUVEDQGZLGWKUHVROXWLRQSODFHPHQWLVVXHV 'DWD$FTXLVWLRQ3URFHVV ([FLWDWLRQ6RXUFHV1RQOLQHDULW\$QWL$OLDV)LOWHULQJ6LJQDO &RQGLWLRQLQJ 'DWD3RVW3URFHVVLQJ ))7')7&RPSXWLQJ36' VDQGDPSOLWXGHVSHFWUD VWDWLVWLFDOYDOXHVRIDVLJQDOVXFKDV506FRYDULDQFHHWF ,QWURGXFWLRQWR6\VWHP,GHQWLILFDWLRQ (7)('\QD0RG0HDVXUHPHQW0RGHOV  

IGAl0 Why is Structural Testing Important? M Example: Ground vibration Testing Product Qualification Testing Performance assessment a System Identification Design verification Damage assessment Aerodynamic Flutter Testing Operational Monitoring Material Fatigue Testing stimulus A Structural response Ref:http://www.af.mil/photos/may1999/19990518f2235.html System (imAgeistakenfromU.s.AirForceWebsitehttp://www.af.mill) vibration tests at edwards air N DAQ H DSP Force Base, calif. in april 1999 DAQ=data acquisition DSP =digital signal processing 16.810(16682) Massachusetts Institute of Technology

:K\LV6WUXFWXUDO7HVWLQJ,PSRUWDQW" „ 3URGXFW4XDOLILFDWLRQ7HVWLQJ ([DPSOH*URXQG 9LEUDWLRQ7HVWLQJ ([DPSOH*URXQG9LEUDWLRQ7HVWLQJ „ 3HUIRUPDQFH$VVHVVPHQW „ 6\VWHP,GHQWLILFDWLRQ „ 'HVLJQ9HULILFDWLRQ „ 'DPDJH$VVHVVPHQW „ $HURG\QDPLF)OXWWHU7HVWLQJ „ 2SHUDWLRQDO0RQLWRULQJ „ 0DWHULDO)DWLJXH7HVWLQJ VWLPXOXV UHVSRQVH 5HIKWWSZZZDIPLOSKRWRV0D\IKWPO XW [W )5DSWRUGXULQJJURXQG )5DSWRUGXULQJJURXQG YLEUDWLRQWHVWVDW(GZDUGV$LU YLEUDWLRQWHVWVDW(GZDUGV$LU )RUFH%DVH&DOLILQ$SULO )RUFH%DVH&DOLILQ$SULO '$4 GDWDDFTXLVLWLRQ '63 GLJLWDOVLJQDOSURFHVVLQJ 6WUXFWXUDO 6\VWHP '$4 '63   (Image is taken from U.S. Air Force Web site: http://www.af.mil.)

IGA10 I. Sensor Overview This sensor morphology is useful for classific of typical sensors used in structural dynamics Sensor Morphology Table Type Linear Rotational Bandwidth Low Medium High DerivativePosition Rate Acceleration Reference Absolute Relative Quantity Force/Torque Displacement Impedance Low High Example: uniaxial strain gage Need units of measurement [m], [Nml[)[rad]etc 16.810(16682) Massachusetts Institute of Technology

,6HQVRU2YHUYLHZ 7KLV6HQVRUPRUSKRORJ\LVXVHIXOIRUFODVVLILFDWLRQ RIW\SLFDOVHQVRUVXVHGLQVWUXFWXUDOG\QDPLFV 6HQVRU0RUSKRORJ\7DEOH 6HQVRU0RUSKRORJ\7DEOH 7\SH %DQGZLGWK 'HULYDWLYH 5HIHUHQFH 4XDQWLW\ ,PSHGDQFH /LQHDU 5RWDWLRQDO /RZ 0HGLXP +LJK 3RVLWLRQ 5DWH $FFHOHUDWLRQ $EVROXWH 5HODWLYH )RUFH7RUTXH 'LVSODFHPHQW /RZ +LJK ([DPSOHXQLD[LDOVWUDLQJDJH 1HHGXQLWVRIPHDVXUHPHQW >P@>1P@> µVWUDLQ@>UDG@HWF«  

a10 Sensor EXamples for Structural Dynamics Example: fixed-fixed Goal: Explain what they measure and how they work beam with center load laser sensors excitation accelerometers gyroscopes strain gages m load cells inductive sensors shaker EI ground First flexible mode frequency: 0=14 F(m+0.375m) 16.810(16682) assachusetts Institute of Technology

6HQVRU([DPSOHVIRU6WUXFWXUDO'\QDPLFV ([DPSOHIL[HGIL[HG *RDO([SODLQZKDWWKH\PHDVXUHDQGKRZWKH\ZRUN EHDPZLWKFHQWHUORDG VKDNHU ODVHUVHQVRUV DFFHOHURPHWHUV OV LYH VHQVRUV )L O ( )    Q E (, OP P ω = + PE P O VWUDLQJDJHV J\URVFRSHV ORDGFHO JURXQG LQGXFW H[FLWDWLRQ UVWI H[LEOHPRGHIUHTXHQF\  

GG.aln Strain Gages Strain △ Strain gages measure strain differential displacement over a finite area via a change in electrical resistance R=lp[Q2 Current Nominal length io: I( With applied strain: I (+△)p implementation Wheatstone bridge iaY ni balance circuit bond to test article strain gages feature polyimide-encapsulated GND constantan grids with V+ copper-coated solder tabs Mfg Ref:http://www.measurementsgroup.com 16.810(16682) assachusetts Institute of Technology Ui

6WUDLQ*DJHV 6WUDLQ ∆O 6WUDLQJDJHVPHDVXUHVWUDLQGLIIHUHQWLDO GLVSODFHPHQWRYHUDILQLWHDUHDYLDD ε = FKDQJHLQHOHFWULFDOUHVLVWDQFH5 Oρ >Ω@ OR &XUUHQW1RPLQDOOHQJWKO  , = 9LQ R R ORρ OR :LWKDSSOLHGVWUDLQ ,ε = 9LQ OR + ∆Oρ ,PSOHPHQWDWLRQ :KHDWVWRQHEULGJH FLUFXLW ERQGWRWHVW VWUDLQJDJHVIHDWXUH DUWLFOH SRO\LPLGHHQFDSVXODWHG *1' FRQVWDQWDQJULGVZLWK FRSSHUFRDWHGVROGHUWDEV 9 0IJ 5HIKWWSZZZPHDVXUHPHQWVJURXSFRP  

IG aln Accelerometers Accelerometers measure linear acceleration in one, two or three ￥()→s2X(s-3 axes. We distinguish (generally neglect initial conditions) single Vs. multi axis accelerometers mag +40db/dec DC versus non-DC accelerometers rolloff Recorded voltage response to base motion 1(t)=K(t)+V out Can measure: linear, centrifugal and gravitational acceleration Use caution when double-integrating acceleration to get position(drift) Single-Axis C1 Accelerometer must be aligned with sensing axis C2 Example: Kistler Piezobeam (not responsive at Dc Example: Summit capacitive Manufacturers: Kistler. Vibrometer Summit accelerometer Dc capable) 16.810(16682) Massachusetts Institute of Technology

$FFHOHURPHWHUV $FFHOHURPHWHUVPHDVXUHOLQHDU DFFHOHUDWLRQLQRQHWZRRUWKUHH D[HV:HGLVWLQJXLVK ‡VLQJOHYVPXOWLD[LVDFFHOHURPHWHUV ‡'&YHUVXVQRQ'&DFFHOHURPHWHUV   → V ; V − V[ − G[ [ W  GW JHQHUDOO\QHJOHFWLQLWLDOFRQGLWLRQV PDJ $FFHOHURPHWHU UHVSRQVHWR EDVHPRWLRQ G%GHF UROORII 5HFRUGHGYROWDJH 9 W  = .[W   +9 ω RXW D  &DQPHDVXUHOLQHDUFHQWULIXJDODQGJUDYLWDWLRQDODFFHOHUDWLRQ 8VHFDXWLRQZKHQGRXEOHLQWHJUDWLQJDFFHOHUDWLRQWRJHWSRVLWLRQGULIW 6LQJOH$[LV & $FFHOHURPHWHUPXVWEH DOLJQHGZLWKVHQVLQJD[LV & ([DPSOH.LVWOHU3LH]REHDP QRWUHVSRQVLYHDW'& ([DPSOH6XPPLWFDSDFLWLYH 0DQXIDFWXUHUV.LVWOHU9LEURPHWHU6XPPLW DFFHOHURPHWHU'&FDSDEOH D  

in Laser Displacement sensors sensor Records displacement directly x()→>X(s) via slant range measurement TVDC cal Settings 1: 2um-60 ms II: 15um-2ms target l:50m0.15ms0 Resolution tradeoff patlal vs temporal Distance x is recorded via triangulation . 7 between the laser diode(emitter), the target and the receiver range. (position sensitive device -PSD) Advantages Vibrometers include advanced processing contact-free measurement and scanning capabilities Disadvantages Manufacturers: Keyence, MTI Instruments need reflective, flat target limited resolution 1 g 16.810(16682) Massachusetts Institute of Technology Ui

/DVHU'LVSODFHPHQW6HQVRUV 5HFRUGVGLVSODFHPHQWGLUHFWO\ GLVSODFHPHQWGLUHFWO\ YLDVODQW UDQJH YLDVODQWUDQJHPHDVXUHPHQW WDUJHW [W ; V     → 9RXW [>P@ >9'&@ 'LVWDQFH[LVUHFRUGHGYLDWULDQJXODWLRQ EHWZHHQWKHODVHUGLRGHHPLWWHUWKH WDUJHWDQGWKHUHFHLYHU [ VHQVRU    &/ UDQJH 7\SLFDO6HWWLQJV , µPPV ,, µPPV ,,, µPPV 5HVROXWLRQWUDGHRII VSDWLDOYVWHPSRUDO SRVLWLRQVHQVLWLYHGHYLFH 36' $GYDQWDJHV 9LEURPHWHUVLQFOXGHDGYDQFHGSURFHVVLQJ FRQWDFWIUHHPHDVXUHPHQW DQGVFDQQLQJFDSDELOLWLHV 'LVDGYDQWDJHV 0DQXIDFWXUHUV.H\HQFH07,,QVWUXPHQWV QHHGUHIOHFWLYHIODWWDUJHW OLPLWHGUHVROXWLRQa µP  

IGA10 Force Transducers/ Load cells Force Transducers/Load Cells are capable of measuring Up to 6 dOF of force on three orthogonal axes, and the moment (torque)about each axis, to completely define the loading at the sensor's location The high stiffness also results in a high resonant frequency allowing accurate sensor response to rapid force changes Load cells are electro-mechanical transducers that translate force or weight into voltage Mz My They usually contain strain gages internally F Manufacturers: JR3, Transducer techniques Inc 16.810(16682) Massachusetts Institute of Technology 10

)RUFH7UDQVGXFHUV/RDG&HOOV )RUFH7UDQVGXFHUV/RDG&HOOVDUHFDSDEOHRIPHDVXULQJ 8SWR'2)RIIRUFHRQWKUHHRUWKRJRQDOD[HV DQGWKHPRPHQWWRUTXHDERXWHDFKD[LVWR FRPSOHWHO\GHILQHWKHORDGLQJDWWKHVHQVRU VORFDWLRQ 7KHKLJKVWLIIQHVVDOVRUHVXOWVLQDKLJKUHVRQDQWIUHTXHQF\ DOORZLQJDFFXUDWHVHQVRUUHVSRQVHWRUDSLGIRUFHFKDQJHV /RDGFHOOVDUHHOHFWURPHFKDQLFDOWUDQVGXFHUV WKDWWUDQVODWHIRUFHRUZHLJKWLQWRYROWDJH 7KH\XVXDOO\FRQWDLQVWUDLQJDJHVLQWHUQDOO\ 0DQXIDFWXUHUV-57UDQVGXFHU7HFKQLTXHV,QF )[ )] )\ 0[ 0] 0\