How Do You Calculate Strain in a Faulty T-Delta Rosette Configuration?

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Discussion Overview

The discussion revolves around calculating the strain recorded by gauge A in a faulty T-delta rosette configuration, where one gauge's data is missing. Participants explore the relationships between the strains measured by the other gauges and the implications of the configuration on the calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • The initial problem involves a T-delta configuration with four strain gauges, where gauge A's data is missing, and the measured strains in gauges B, C, and D are provided.
  • Some participants propose that the relevant equation for calculating strain needs to be corrected, as the current formulation does not account for the angles between the gauges accurately.
  • There is a suggestion to swap the positions of eB and eA based on their perpendicular relationship with gauge D.
  • Another participant emphasizes the need for additional equations related to strain in the context of the gauges, indicating that the current approach is incomplete.
  • Hints are provided regarding the angles between the gauges, suggesting that the angle from gauge A to gauge D is 90 degrees, which may influence the calculations.

Areas of Agreement / Disagreement

Participants express differing views on the correct formulation of the equations needed to solve for the strain in gauge A, indicating that the discussion remains unresolved with multiple competing approaches being suggested.

Contextual Notes

There is uncertainty regarding the appropriate equations to use, the relationships between the gauges, and the implications of the angles involved. The discussion highlights the complexity of the problem and the need for careful consideration of the gauge configuration.

jcurtis
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Homework Statement

For experimental validation of a design based on FEA, a prototype was tested using strain gauge rosettes at critical locations in a typical t-delta configurations, consisting of 3 gauges: A, B, C and fourth (extra) gauge D. D normally serves as a check on the strains recorded by the rosette arms. In this instance due to a fault in the measuring circuit, the strain response in gauge A could not be recorded the measured strains in the other three gauges were: eB = (-)135x10-6, eC=227x10-6 and eD= (-)63 x 10-6.
What would have been the strain recorded by gauge A?

Homework Equations


I found that J=eXX + eYY = eA + eC = eB + eD


The Attempt at a Solution

I've looked in my notes that my lecturers put online and I've been searching on google all day and I can't find anything. I know it has something to do with the fourth gauge, but there's no information on the web about it that I could find. The equation I found seemed too simple as the question is worth 8 marks. Or is it more simple than I'm making out? Can anyone help please?
 
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jcurtis: As I currently see it, you have four equations and four unknowns. Your relevant equation is currently incorrect; eB and eD are not mutually perpendicular. Try it again. And, you need to list three more equations, for strain in a strain gauge leg. You must list relevant equations yourself. The angle from gauge A to gauge D is 90 deg; but I think you knew that, right? Hint: thetaA = 0 deg.
 
Thanks for replying. So you're saying I should swap eB and eA around because a and d are perpendicular?
I can't find any other strain equations that aren't to do with resistance. other than principle strain equations which I need the value of A for, however I know it has to just do with the values of B, C and D as that's all they've given me.. Sorry I'm being a bit dense here, I'm just very confused.
 
Yes, swap eB and eA, then omit eB + eC from your above equation, because gauges B and C are not mutually perpendicular.
 
Hint 2: thetaYY = 90 deg. Do you have anything else at 90 deg? What does that tell you about the value of eYY?
 

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