Issue 76

H. Houri et alii, Fracture and Structural Integrity, 76 (2026) 238-264; DOI: 10.3221/IGF-ESIS.76.15

f=0

f=0.1

f=0.2

f=0.3

(b) Figure 16: Equivalent plastic strain contours for polyamide during the 2-ECAE process using a 105° die at φ = 15° for different friction coefficients, with lengths: (a) L = 30 mm and (b) L = 50 mm. Evolution of the variation factor Fig. 17 presents the evolution of the variation factor for different friction coefficients in the case of the 105° 2-ECAE die. The results clearly demonstrate that friction has a significant impact on the homogeneity of the equivalent plastic strain distribution. The numerical values of the variation factor and the average equivalent plastic strain are summarized in Tab. 5. It can be observed that the average plastic strain varies between 1.45 and 1.64 across all studied cases, indicating a relatively high level of deformation. However, the variation factor, which reflects the degree of strain heterogeneity, exhibits its maximum values when friction is absent (f = 0) for all channel lengths. This outcome suggests that, in the absence of interfacial resistance, the material flow is less constrained, leading to uneven strain localization. Conversely, a moderate friction coefficient, particularly f = 0.2, appears to promote better strain homogenization, as evidenced by the lowest value of the variation factor obtained for L = 20 mm. This behavior can be explained by the fact that a controlled amount of friction enhances shear transfer between the die and the billet, thereby redistributing deformation more uniformly across the sample cross-section. Nevertheless, excessive friction (f = 0.3) tends to elevate strain levels but at the expense of introducing localized heterogeneities and potential risks of surface defects. These findings highlight the dual role of friction in the ECAE process: while a complete absence of friction induces non-uniform strain fields, a moderate coefficient can improve homogeneity, whereas excessive values may degrade material quality.

10 12 14 16 18

f=0,0 f=0,1 f=0,2 f=0,3

14,4 14,4

13,9

13,4

12,8

12,6 12,3

12,4

11,8

11,3

11,3

11,3

10,7

10,4

7,71

0 2 4 6 8

6,14

Variation factor ( V % )

f=0,1

f=0,1

f=0,1

f=0,1

f=0,2

f=0,0

f=0,2

f=0,3

f=0,3

f=0,0

f=0,3

f=0,0

f=0,2

f=0,3

f=0,2

f=0,0

L=20

L=30

L=40

L=50

Figure 17: Illustration of the variation factor in the case of the 105° die 2-ECAE with the effect of friction.

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