PSI - Issue 57

4

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Jacopo Pelizzari et al. / Procedia Structural Integrity 57 (2024) 817–823

820

Table 1. Static tensile properties of EN-GJS-500-7 derived from the two tested specimens taken from the trumpet of the off-highway axle.

Material

Specimen

E s [MPa]

n [MPa]

 p0.2 [MPa]  R [MPa] A [%] Z [%] K [MPa]

EN-GJS-500-7 EN-GJS-500-7

1 2

165200 175600

360 360

605 610

8.1

7.8 9.7

914.9 889.2

0.159

10.4 0.155 The strain-controlled fatigue tests have been performed by applying fully reversed cyclic loading (R  = -1) with strain amplitudes between 1.45·10 -3 and 1·10 -2 . The fatigue loadings have been applied adopting a sinusoidal wave form with loading frequencies ranging between 0.1 Hz and 2 Hz. The testing time relevant to fatigue tests performed in the high-cycle region, up to 2·10 6 , has been reduced by switching to load-controlled mode after the stabilized material behavior has been reached. The frequencies adopted in the load-controlled tests range from 5 Hz to 21 Hz. The test datum has been considered run-out when 4 million reversals were achieved without specimen failure; with this limit set, one specimen out of nine resulted run-out. Fig. 4b shows the stabilized cyclic stress-strain curve (SCC) fitted over eight experimental data coming from the strain-controlled fatigue tests. The SCC curve has been defined according to the Ramberg-Osgood equation, Eq. 1, where the coefficients K and n have been substituted with the coefficients K’ and n’, to distinguish the coefficients relevant to the static and cyclic material behavior. The coefficients of the SCC curve are reported in Table 2 along with the Young’s modulus E assumed equal to the average value obtained from the static tensile tests. The tested material showed a hardening behavior (see Fig. 4b) typical of pearlitic cast iron as reported also in previous investigations [1,10].

700

700

SCC fitted curve Experimental data

600

600

Specimen 1 - static test Specimen 2 - static test

500

500

100 Engineering stress,  [MPa] 200 300 400

400

Stress,  [MPa]

300

200

100

Specimen 1 Specimen 2

(a)

(b)

0

0

0

0.005

0.01

0.00 0.02 0.04 0.06 0.08 0.10 Engineering strain,  [m/m]

Strain ,  [m/m]

Fig. 4. (a) Static curves derived from static tensile tests and (b) comparison with the stabilized cyclic stress-strain curve (SCC) of the EN-GJS 500-7 cast iron obtained by strain-controlled fatigue tests. The cyclic stress-strain curve (SCC) is expressed in terms of stress range  /2 against strain amplitude  a . Table 2. Fatigue coefficients of the cyclic stress-strain curve and the Manson-Coffin fatigue design curve of EN-GJS-500-7 fitted over the data derived from strain-controlled fatigue tests on specimens with R  =-1 . Material Procedure E [MPa] K ' [MPa] n '  ' f [MPa] b  ' f c EN-GJS-500-7 Curve fitting 170400 927.6 0.123 909.3 -0.0973 0.284 -0.701