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Analysis of Inorganic Binder Bridges Destruction after Thermal Load

Vaskova I., Conev M.

Archives of Foundry Engineering

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2019

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iss. 2

25--28

EN

Recently, the use of inorganic binders cured by heat as a progressive technology for large scale production of cores is widely discussed topic in aluminium foundries. As practical experiences show, knock-out properties of inorganic binders were significantly increased, although they cannot overcome organic based binder systems. This paper contains information about hot curing processes based on alkali silicate and geopolymer binder systems for core making. Main differences between hot cured geopolymers and hot cured alkali silicate based inorganic binders are discussed. Theory of geopolymer binder states, that binder bridge destruction is mainly of adhesive character. The main aim of this research paper was to examine binder bridge destruction of alkali silicate and geopolymer binder systems. In order to fulfil this objective, sample parts were submitted to defined thermal load, broken and by using SEM analysis, binder bridge destruction mechanism was observed. Results showed that geopolymer binder system examined within this investigation does not have mainly adhesive destruction of binder bridges, however the ratio of adhesive-cohesive to cohesive destruction is higher than by use of alkali silicate based binder systems, therefore better knock-out properties can be expected.

2

Effect of induced temperature field on development of curvilinear crack with bonds between the faces in end zones

Mirsalimov V. M., Mustafayev A. B.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 3

765--778

EN

Temperature changes near the end of a curvilinear cohesive crack and their influence on crack growth are investigated. The problem of local temperature changes consists in a delay or retardation of the cohesive crack growth. The bonds between the curvilinear crack faces in the end zones are modeled by application to the crack surface cohesive forces caused by the presence of bonds. The boundary value problem of equilibrium of the curvilinear crack with interfacial bonds in the end zones under action of external tensile loads, induced temperature field and tractions in the bonds preventing to its opening, is reduced to a system of singular integral equations with a Cauchy-type kernel. From the solution of this equation system, normal and tangential tractions in the bonds are found. Analysis of the limit equilibrium of the crack using the end zone model is performed on the basis of a criterion of bonds limiting stretching and includes: 1) establishment of tractions depending on opening of the crack faces; 2) evaluation of the stress state near the curvilinear crack with taking into account tensile loads, induced temperature field, tractions in the bonds; 3) determination of the critical external tensile loads.

3

Crack nucleation in circular disk under mixed boundary conditions

Mirsalimov V. M., Kalantarly N. M.

Archives of Mechanics

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2015

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Vol. 67, nr 2

115--136

EN

A model of crack nucleation in a circular disk, based on consideration of cracking process zone is suggested. It is assumed that the cracking process zone is a finitelength layer containing a material with partially disturbed bonds between separate structural elements. Existence of bonds between the pre-fracture zone faces (the area of weakened interparticle bonds of the material) is simulated by application of cohesive forces caused by the existence of bonds to pre-fracture area surfaces. Analysis of limit equilibrium of the pre-fracture zone in a circular disk with mixed conditions on the boundary are fulfilled on the basis of ultimate stretching of material’s bonds and includes: 1) setting up the dependence of cohesive forces on opening of pre-fracture area faces, 2) estimation of stress state near the pre-fracture zone with regard to external loads and cohesive forces, 3) determination of dependence of critical external loads on geometrical parameters of the disk, under which the crack appears.