OBRABOTKAMETALLOV technology Vol. 25 No. 3 2023 As shown in figs. 6 and 7, the flow of materials at the stage I of bond deformation is quite different from the idealized representation: plastic deformation of both D16 alloy and harder AMg3 alloy begins almost simultaneously. An analysis of the deformation of representative volumes shows that the asperities of both materials crumble simultaneously. This is primarily due to the closeness of the strain resistances of the alloys, whose ratio is close to 0.8. By the end of critical stage II, unfilled sections of cavities remain at the interface between materials due to insufficient applied pressures, while plastic deformation begins to propagate deep into the bulk of both materials (stage III). As the work hardening of both materials increases and the pressure at the interlayer boundary increases, the cavities on AMg3 alloy surface are filled up. When the maximum value of the effective stress of the D16 alloy is reached, unfilled cavities remain at the interlayer boundary (residual pores). A further increase in pressure is required to fill it. Thus, despite the differences at the first stage of joint plastic deformation, the final stages proceed in accordance with the proposed theoretical mechanism. At stage III of the accumulative roll bonding micromodel, the relative penetration depth hl/H and the reduced normal stress at the contact of materials σ/k were evaluated and compared with the theoretical model [18] (Table 2). As can be seen from Table 2, the relative penetration depth of asperities hl/H of the FE micromodel differs significantly from the results of calculation by the theoretical model. The discrepancy is primarily due to significant differences between the actual profiles of material surfaces from the theoretical ones, as well as the closeness of strain resistances of materials, which resulted in almost simultaneous materials’ deformation. The discrepancies in the reduced normal stresses σ/k, obtained through the FE micromodel and the theoretical model, are also noticeable, which is explained by the closeness of the strain resistances of the material and its almost simultaneous transition to the plastic state. As a result, the theoretical model [18] gives only approximate values of the stress-strain state indicators for the processes under consideration. An important practical aspect of FE microsimulation was the determination of areas of the most probable fracture of surface oxide layers. As a criterion for assessing the probability of fracture, the well-known Cockcroft-Latham criterion was used 1 0 ð d ε σ ε σ ∫ , where σ1 is the principal stress, σ is the effective stress, and dε is the accumulated plastic strain increment. Fig. 8 shows the contact surface on the side of D16 alloy at the beginning of stage III of accumulative roll bonding with highlighted contact points with AMg3 surface and without contact points. Fig. 8 demonstrates that the highest values of damage of the surface layers are observed in areas free from contact with the opposite material. Fig. 6. Stages of joint plastic deformation of AMg3 and D16 alloys preliminary grinded with a 40 grit band Fig. 7. Stages of joint plastic deformation of AMg3 and D16 alloys preliminary grinded with a 120 grit band
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