Dogleg Calculation

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  • Published : July 13, 2011
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Connection Development & Evaluation Centre
Prepared by: Alief Taufiqurrahman
Test Engineer

Dogleg Calculation Using strain DAQ

1 Purpose
To compare dogleg value between strain DAQ and theoretical results, during combine loading axial and bending. 2 Problem Statement Dogleg values between strain DAQ reading and theoretical results is not showing a good agreement during combine loading (i.e. Tension and Bending). The strain DAQ could not show the actual dogleg values, it shows the artificial and actual dogleg. Artificial dogleg occurred due to variation of material properties throughout the cross-section. 3 Method of Calculations 3.1 Strain DAQ V3 Uni-axial Strain method was used to calculate the dogleg, thus 4 uni-axial strain gauges were installed on each section of the specimen (total 2 sections). The setup will give 8 strain signals which eventually the strain DAQ software will calculate the dogleg values. However, the values indicate by the software is not the actual value due to variation of strain signal during tension (caused by variation of material properties on cross section). The dogleg values are shown on Figure 1. 3.2 Theoretical Values Theoretical results were obtained from the raw data generated by strain DAQ. The following formulae (see Annex E of strain DAQ manual for further detail) were used to calculate the dogleg values :

a) Determine the Bending Strain in the 0° plane for each section :

b) Determine the Bending Strain in the 90° plane for each section :

c) Calculate the Dogleg value at 0° plane for each section :

D = Specimen OD (inch)

d) Calculate the Dogleg value at 90° plane for each section :

D = Specimen OD (inch)

e) Calculate the specimen vector sum dogleg :

Theoretical Dogleg values and Strain DAQ results are shown on Figure 1 below :

Figure 1. Dogleg Comparison

Figure 1 indicates 2 different cases, case #1 is combine loading of Tension and Bending, case #2 is pure bending load applied on the...
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