1 / 16

Strain Gauges

Strain Gauges. Hooke’s Law. Example: Bone has a Young’s modulus E of about 100,000 psi. 10 psi of stress will stretch a 20 inch femur. Compare to F = K* Δ x …. stress-strain curve: stiffness, yield strength, fracture. www.tpub.com/doematerialsci/materialscience22.htm.

davidharvey
Download Presentation

Strain Gauges

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Strain Gauges Hooke’s Law Example: Bone has a Young’s modulus E of about 100,000 psi. 10 psi of stress will stretch a 20 inch femur Compare to F = K*Δx …

  2. stress-strain curve:stiffness, yield strength, fracture www.tpub.com/doematerialsci/materialscience22.htm

  3. Transverse Strain and Poisson’s ratio Consider incompressible material (constant volume…)

  4. What to expect on the strain gauge quiz: Given stress, Young’s modulus, gain, Vex, Poisson’s ratio, calculate Vout… www.solware.co.uk/blog

  5. Another deformation: torsional twist http://home.gna.org/getfem/shots.html

  6. What about the piezoresistivity term?It is normally not zero. In fact for some semiconductors it dominates the expression on the right of the equation. For metals, with a Poisson ratio around 0.3, nonzero piezoresistivity of 0.4*ε basically results in approx: In the Strain Gage Quiz the gauge factor will be 2.

  7. from www.sensorland.com from www.natmus.dk

  8. Unknown material properties vs strain gauge material properties: Gauge factor: of the strain gauge Poisson’s ratio: of the unknownstrain: of the unknownYoung’s modulus = Ym… Young’s modulus: of the unknown > Ym of SG Next consider a Wheatstone bridgemade with 4 strain gauges… Two voltage dividers to consider:

  9. That is the term to finish the expression for Vout = G*Vex*ΔR/4R for one longitudinal strain gauge in a "positive" location in the bridge.

  10. Sign of influence on Vout given SG placement: Table reads: if R1 is the LG strain gauge then how does Vout change? *dR/4R …

  11. SG web links: • http://me.queensu.ca/courses/MECH215/documents/MECH215-Week06Lecture1-StrainMeasurement-Introduction.pdf • http://www.eidactics.com/Downloads/Refs-Methods/NI_Strain_Gauge_tutorial.pdf • http://www.thorlabs.com/images/TabImages/Strain%20Tutorial.pdf

  12. FINAL REPORT TO THE NATIONAL OPERATING COMMITTEE ON STANDARDS FOR ATHLETIC EQUIPMENT (NOCSAE) 1999 “THE USE OF SHOE ORTHOTICS TO REDUCE BONE STRAIN RATE” http://www.nocsae.org/research/rep/Burr_final.htm

More Related