Crack Paths 2012

The beginning of the crack propagation stage with striations occurrence (stage II) has

been studied previously by the temperature recording on the specimen surface during

the test [9-10], which allows the determination of the number of cycles at crack

initiation. In this paper, from the temperature recording on the specimen surface of an

Armcoiron during fatigue tests, the intrinsic dissipation profile along the specimen gage

part was calculated using a local expression of the heat diffusion equation. Besides,

fractographic observations were performed on the specimen surface and fracture

surface.

M A T E R I A L

The studied material is a polycrystalline D iron whose chemical composition is given in

Table1.The carbon content is 80ppm. The microstructure is ferrite with equiaxe grains.

The inclusion size is less 1.5Pm. The ferrite grain size is included in 10 to 40 Pm. No

specifically orientation was observed by EBSD.Yield Stress is 240 M P aand Ultimate

Tensile Stress is 300MPa.

Table 1: Chemical composition of studied material

C P Si

M n S Cr Ni M o Cu Sn Fe

0.008 0.007 0.005 0.048 0.003 0.015 0.014 0.009 0.001 0.002 Balance

E X P E R I M E N TPARLO C E D U R E

Mechanical and Thermal Procedure

Tests were performed on a piezoelectric fatigue machine designed by C. Bathias and co

workers [11].

An infrared camera was used to record the temperature evolution during the test.

For the reason of surface observation condition by IR camera, a new design of 1 m m

flat specimen (Fig. 1) was used to carry out fatigue tests. Specimen, special attachment

and piezoelectric fatigue machine constituted the resonance system working at 20kHz.

The cyclic loading is tension-compression (R = -1).

Figure 1: Design of flat specimen (unit: m m )

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