Issue 36

M. Ouarabi et alii, Frattura ed Integrità Strutturale, 36 (2016) 112-118; DOI: 10.3221/IGF-ESIS.36.11 118 Figure 8 : Experimental ( ) da f Keff dN   curve in mode I under R=-1, for CP1000 (at 20 kHz) with air cooling and at room temperature. C ONCLUSION n this work, the procedures for testing thin steel sheets in fatigue against crack initiation and crack propagation have been developed. Flat specimens of 1.2 mm thickness were used. It has been shown that it is possible to obtain appropriate results by using high frequency resonant fatigue testing machine in tension-compression. Fatigue endurance tests have shown fatigue strength in the gigacycle regime for CP1000 ferritic-martensitic steel around 352 MPa under fully reversed tension. For the crack propagation test on CP1000, the threshold value of the mode one effective stress intensity factor range is around 7 MPa√m in laboratory air. The proposed computing methodology is consistent since frequencies for each specimen geometry are practically the same in experimentation. Flat specimens must be perfectly designed to avoid any problem with bending deviation of the stress amplitude or stress intensity factor. A CKNOWLEDGEMENTS he authors thank the European Commission for the financial support of the FREQTIGUE (CECA) project and all the partners of this project: ARCELOR MITTAL, FIAT, GERDAU, Karlstadt University, Karlsruhe Institute of Technology, Aachen University, University Paris Ouest Nanterre La Defense. R EFERENCES [1] Bathias, C., Paris, C., Gigacycle fatigue in mechanical practice, Marcel Dekker, New York, (2005) [2] Bathias, C., Piezoelectric fatigue testing machines and devices, International Journal of Fatigue, 28 (2006) 1438-1445. [3] Palin-Luc, T., Perez Mora, R., Bathias, C., Dominguez, G., Paris, P.C., Arana, J., Fatigue crack initiation and growth on a steel in the very high cycle regime with sea water corrosion, Engineering Fracture Mechanics, 77-11 (2010) 1953- 1962. [4] Perez-Mora R., Palin-Luc T., Bathias C., Paris, P.C., Very high cycle fatigue of high strength steel under sea water corrosion: a strong corrosion and mechanical damage coupling, Int. J. Fatigue, 74 (2015) 156-165. [5] Wang, C., Microplasticité et dissipation en fatigue à très grand nombre de cycles du fer et de l’acier, PhD Thesis Université Paris Ouest Nanterre – La Défense, (2013). [6] Wu, T.Y., Modelisation de la fissuration en fatigue vibratoire à haute temperature; applications aux alliages à base de nickel, PhD Thesis Ecole Centrale de Paris, (1992). I T