Fringe order of one appeared when a load of 1755 newtons was applied The load

Fringe order of one appeared when a load of 1755

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created was observed and analyzed to determine the fringe value, fσ. Fringe order of one appeared when a load of 175.5 newtons was applied. The load was increased to 356.6 newtons and fringe order two appeared. At 578.8 newtons fringe order three appeared. The load was increased to 794.0 newtons and fringe order four appeared. Fringe orders five and six appeared at 940.8 and 1165.0 newtons respectively. These values were then graphed in Figure 3. Using the equation Fσ = ( 8 /( PI D ) ¿ ∗( P / N ) , the material fringe value (Fσ) was solved for to be 6280 newtons. For part two, a plate with a hole was loaded to 700 lbs and the resulting fringe pattern was compared to the provided one. The pattern provided in the lab appeared to display the plate under more pressure than was tested in the lab as evident by the higher order fringes. The stresses appeared to match the direction of the stresses in the example and a similar fringe pattern was presented in the experiment. The stresses along the boundary of the hole were as expected. High fringe orders along the top, bottom, and sides of the hole represent the tension and compression on the boundary due to the load. The resenting graph displays that max stress occurs on the sides of the hole which are under compression measuring at 2283 psi. The fringes are parallel to the side of the plate along the horizontal axis of symmetry indicating that there are no shear stresses. The stress concentration factor is calculated with the ratio of the hole diameter to the width of the plate. The fringe numbers are labeled in Figure 4 depicting the isochromatic fringe patterns of the plate under the given load. For part three, a cracked specimen was placed under load and the stress intensity factor from the loads was solved for and compared with theory. The experimental stress intensity factor for each load is obtained by estimating the distance and angle from the crack to the apogee of the fringe loops surrounding the crack tip. The experimental intensity factors are much smaller than estimated by the theory under the given conditions. This discrepancy is likely to have due to the quality of the pictures making it difficult to create an accurate estimation. Even so, the stress intensity factor increases as load increases just as presented by the theory. 18
6 Conclusions and Recommendations The principle of photoelasticity was introduced and the setup of circular polariscope was described. The load-phase stepping method was used to extract the photoelasticity parameters in this report. A photo elastoplastic investigation was also conducted to determine the stress concentration factors in two specimens of polycarbonate material. The stress during loading was found by loading by the materials under known intervals and watching the elastic process. The results contained in this report are experimental and could be useful in verifying any analytical results. It is proposed for future work to study the same problem in models made of other materials. The results could provide a relation between the extent of increase of fatigue life and the percentage of overloading in the materials.

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• Fall '17
• YI
• Instron

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