PSI - Issue 2_B

G. La Rosa et al. / Procedia Structural Integrity 2 (2016) 2140–2147 G. La Rosa et al./ Structural Integrity Procedia 00 (2016) 000 – 000

2147

8

Table 7. Mean ratios of the strain measured by D.I.C. Hole [mm] ( ) 8 2,473

( ) 1,467 1,387

( ) 1,625 1,402

( ) 3,581 2,899

5,5

2,256 1,702

4

1,233

1,285

2,376

Comparing the results shown in Tables 6 and 7, it can be observed that, in general, the average ratios of the strains are closer to the average ratios of temperature changes, confirming the validity of the proposed methodology.

4. Conclusions

The tests conducted have shown that D.I.C. is a valuable methodology in measuring deformations and absolute displacements of the points during the test. It allows following the position of the point of measurement in the thermal image, moving because of deformation and, consequently, it is able to correct the static curve of temperature, obtaining more reliable values of the thermal behavior, especially in the notched zones. The main feature of the methodology is to be able to operate in full field, thus allowing a correction in real time of the whole zone and, in particular, of the measuring points. The results of the analysis of D.I.C.-T.A. correlation, performed on drilled PVC specimens, showed an actual deviation between the profiles of correlated thermal curves and those relating to the fixed spot, especially in areas where there is a high deformation gradient. Refer to the correlated thermal curve allows to better characterize the mechanical state of the material and avoid underestimating the stresses. The comparison among the D.I.C. and the thermographic stress concentration factors (as ratios between temperature or strain in notched and unnotched zones) shows how the effect of following the point and correcting the thermal curves can significantly improve the reliability of the measures. References Chrysochoos, A., Huon, V., Jourdan, F., Muracciole, J.M., Peyroux, R., Wattrisse, B., 2010. Use of full-field digital image correlation and infrared thermography measurements for the thermomechanical analysis of material behaviour. Experimental Mechanics, 46(6), 117 – 130. Clienti, C., Fargione, G., La Rosa, G., Risitano, A., Risitano, G., 2010. A first approach to the analysis of fatigue parameters by thermal variations in static tests on plastics. Engineering Fracture Mechanics , 77 (11), 2158-2167. Geraci, A., La Rosa, G., Risitano, A., 1995. 7th International Conference on Mechanical Behaviour of Materials, The Hague, The Netherlands, 783-784. La Rosa, G., Risitano, A., 2014. Evaluation of the fatigue limit of materials in static test using thermal analysis: Effect of the cross-head speed. Key Engineering Materials . 577-578, 69-72. Orteu, J.J., Rotrou, Y., Sentenac T., Robert, L., 2008. An Innovative Method for 3-D Shape, Strain and Temperature Full-Field Measurement Using a Single Type of Camera: Principle and Preliminary Results. Experimental Mechanics, 48:163 – 179. Risitano, A., Risitano, G., Clienti, C., 2010. Fatigue limit by thermal analysis of specimen surface in mono axial traction test. EPJ Web of Conferences, 14th International Conference on Experimental Mechanics, ICEM 2014; Poitiers; France. Risitano, A., Clienti, C., Risitano, G., 2011. Determination of fatigue limit by mono-axial tensile specimens using thermal analysis. Key Engineering Materials . 452-453, 361-364. Risitano, G., Clienti, C., 2012. Experimental study to verify the fatigue limit found by thermal analysis of specimen surface in mono axial traction test. Key Engineering Materials, 488-489, 795-798. Risitano, A., Risitano, G., 2013. Determining fatigue limits with thermal analysis of static traction tests. Fatigue and Fracture of Engineering Materials and Structures. 36, 7, 631-639. Risitano, A., La Rosa, G., Geraci, A., Guglielmino, E., 2015. The choice of thermal analysis to evaluate the monoaxial fatigue strength on materials and mechanical components. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 229, 7, 1315-1326. Rossi, M., Broggiato, G.B., Papalini, S., 2008. Application of digital image correlation to the study of planar anisotropy of sheet metals at large strains. Meccanica, 43, 2, 185-199. Vergani, L., Colombo, C., Libonati, F., 2014. A review of thermographic techniques for damage investigation in composite. Frattura ed Integrita Strutturale, 8, 27, 1-12.