Analysis of creep process in two-layer metallic Al-Zn composite

Robert Uścinowicz Politechnika Białostocka, Wydział Mechaniczny, Katedra Mechaniki i Informatyki Stosowanej, ul. Wiejska 45 C, 15-351 Białystok, Poland

Quarterly No. 3, 2008 pages 262-268

DOI:

keywords: clad metal, composite, creep, mechanical properties, hardening, isochronous curves

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abstract Analysis of the deformation occurring during creep process of two-layer aluminium-zinc composite in conditions of fixed uniaxial stresses and the temperature was presented. The composite to tests made by gluing metal strips of aluminium and zinc with using of CX-80 glue based on epoxy resin. Tests were also independently carried out on components of bimetal, and on the specimens which layers did not permanently joined itself on the final gauge length. The mathematical description of deformation while monotonic loading and creep processes used an adapted model of deformational orthotropic body, widely applied for composites of the laminates type - so-called isostrain model. First tests carried out using monotonic increasing deformation rate gave possibility to determination basic mechanical properties, it means: values of stress limits and elongations, elastics constants, Ramberg-Osgood’s parameters describing characteristics of tensile. It was found that for short-lived temporary tests realized at the monotonic increasing load the mixtures law correctly described mechanical properties in the range of great plastic strains of two-layer composite metal. The creep tests were carried out at the constant stress in the range of 110121 MPa and at the 273 K temperature at the identical samples which were used in initial tests. The creep curves received from tensile tests served for determination the dependence stationary creep rate on stress, for the tested material in the two separate stages of creep process. The formulas which described the relation among deformation creep rate and stresses for aluminium and Al-Zn composite during second period of creep were linear or quasi-linear form. Created empirical model of relation among creep strain rate and stress in the stationary creep period for Al-Zn composite contained rheological properties of components. Correctness of the worked out equation was verified using data held from experiment. During the study, the analysis of the similarity of tested materials to the model of the linear viscoelasticity body was executed. The reciprocal similarity of isochronous creep curves and non-linearity of form for Al-Zn composite was identified. In the tensile tests an effect of characteristic bending of specimen was observed in direction perpendicular to the plain of flat sample at the side of the aluminium layer. It could be explained by effect of the significant difference of the Poisson coefficients values of composite layers in the elastic range (Zn = 0.25; Al = 0.35) and suiting diversified values of contraction coefficient in the plastic range.