EXPERIMENTAL STRESS ANALYSIS AND THE PERSONAL COMPUTER

Abstract

Because of its small size, versatility, and comparatively low cost, the personal computer (PC) provides specific advantages for experimental stress analysis. Programs can be written and stored to perform the calculations for a variety of stress-analysis methods. Correction factors can be easily included for best accuracy. Least-squares methods can be used in a straightforward manner to include excess data and information. Graphics can be used to show functional relationships and vividly display the results. This presentation will show how the PC can be used to determine the state of strain and stress from strain gages as shown in Fig. 1. Two-, three-, or four-gage rosettes are used. Calculations are general for the gages with different gage factors and transverse sensitivities for the rosette elements. General rosette-element angles are also used. Leastsquares is used for the four-element rosette. Stress calculations include the solution for safety factor using the Tresca and von Mises failure (yield) criteria. Principal strain directions are shown with respect to the rosette elements and the state of stress is shown graphically with respect to the yield surfaces for the two different failure criteria. Stress analysis is described using brittle coatings. Coating failure is shown in Fig. 2 for different combinations of surface stress. State of stress is determined using brittle coatings. Specimen loading and coating failure are shown graphically. Birefringent coatings are used for analysis of surface stress. Oblique incidence is included, as is the factor of safety. Correction factors for coating thickness are included for plane loading, as well as for torsion, bending and pressure vessels. Calculations include solutions for optimum coating thickness. Treatments of correction factor for coating thickness and of factor of safety include graphics. Calculations are described for photoelastic stress analysis. The state of stress is determined in a region of interest in a photoelastic model. Stress-optical equations are used together with the stress-equilibrium equations and the static-equilibrium conditions. An excess of information is used to find a “best” solution with the assistance of leastsquares. Results are displayed graphically. A booklet will be available at the session entitled, “Calculations for Experimental Stress Analysis (Using the Personal Computer),” which will contain the notes for the presentation.