Methods of Obtaining Magnitude and Direction of Principal Stress (Rosette Analysis)

Generally, if the direction of principal stress is uncertain in structure stress measurement, a triaxial rosette gage is used and measured strain values are calculated in the following equation to find the direction of the principal stress. (The following equation is only for specified angle triaxial rosette gages.)

Precautions in Analysis

  1. Regard εa→εb→εc as the forward direction.
  2. Angle θ is:
    • Angle of the maximum principal strain to the εa axis when εcb
    • Angle of the minimum principal strain to the εa axis when εac
    • Comparison between εa and εc in magnitude includes plus and minus signs.

Max. principal strain

Min. principal strain

Direction of principal strain (from εa axis)

Max. shearing strain

Max. principal stress

Min. principal stress

Max. shearing stress

ν:Poisson's ratio
E:Young's modulus