Calculating the strain in three different ways - experimental error?

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SUMMARY

The discussion focuses on an experiment measuring strain in a channel section beam using a strain gauge and dial gauges to assess deflections under various loading conditions. The strain calculated from deflections and experimental stiffness showed a maximum error of 10%, while the strain gauge readings exhibited a higher error of approximately 30%. The participant questions the significant discrepancy between experimental and theoretical results, particularly regarding the orientation of the strain gauge during measurements.

PREREQUISITES
  • Understanding of strain measurement techniques, specifically using strain gauges.
  • Knowledge of beam bending theory and deflection calculations.
  • Familiarity with experimental error analysis and its implications.
  • Basic principles of material mechanics, particularly related to stiffness and curvature.
NEXT STEPS
  • Investigate the effects of strain gauge orientation on measurement accuracy.
  • Explore advanced techniques for minimizing experimental error in strain measurements.
  • Learn about the relationship between deflection and strain in beam theory.
  • Examine case studies involving strain measurement discrepancies in similar experiments.
USEFUL FOR

Mechanical engineers, materials scientists, and researchers involved in experimental mechanics or structural analysis will benefit from this discussion.

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I've recently done an experiment where I've obtained the strain of a channel section beam in bending. I used a strain gauge to get the strain from the midspan and also used dial gauges to get the deflections of the beam under different loading conditions.

Along with the readings I've obtained from the strain gauge, I have also used the deflections to calculate the strain in two other ways. I've done this through the deflections (curvature) and the experimental stiffness. The strain for deflections and experimental stiffness are virtually alike (highest error is 10%) however, in comparison to the strain gauge readings, there is a greater error (highest error ir around 30%).

I ensured that I performed the experiment correctly and given my raw results, they do seem correct. So, I'm wondering why do the experimental and theoretical results vary so much?
 
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uhm, I can't put my finger on it but have you calculated the strain in the same direction in which the strain gauge is oriented?
 

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