Abstract
In this article the statical and cyclical strength investigations of austempered ductile cast iron (ADI) are presented. ADI material becomes more and more popular. Ductile iron is lighter than steel and its mechanical properties are better. ADI has good resistance to fatigue, high tensile strength, toughness and ductility. The fatigue crack initiation generally occurs in the graphite matrix. In the work the kinetic fatigue diagrams, longevity distributions laws and the mathematical model of crack growth ratio are described. The blanks of material were cut from a tooth of gear. Structure of the material consists of bainite and spherical graphite. The mechanical properties of ADI were obtained with assessment of chemical composition. The detennined statical mechanical properties of two different ADI materials are presented. The compact specimen was produced in order to detennine a threshold stress intensity factor. According to the investigations the stress intensity factor (threshold) is ΔK th = 9,8 MPa√m for the ADI 6.2.02 and ΔK th = 8,6 MPa√m for the ADI 9.4.02. The carried out investigations are insufficient for the complete evaluation of austempered ductile iron for the production of transport equipment elements.
Highlights
Assurance of longer service life and increase of reliability both for machinery used in transport sectors and for various constructions are associated with many factors making their impact on limit states and playing a decisive role in defming the strength of separate members of a stmcture as well as of the structure, as a whole
Austempered ductile iron becomes more popular in the production of various dimensions transport machines
Experimental investigation was fulfilled in the Laboratory of Strength Mechanics at Vilnius Gediminas Technical University using a set of testing machines to produce static and cyclic loading effects
Summary
Assurance of longer service life and increase of reliability both for machinery used in transport sectors and for various constructions are associated with many factors making their impact on limit states and playing a decisive role in defming the strength of separate members of a stmcture as well as of the structure, as a whole. Austempered ductile iron (ADI) has an ausferrite matrix of bainite and retained austenite They have good resistance to fatigue and wear and possess a combination ofhigh tensile strength, toughness and ductility. The maximum fatigue resistance in ductile irons occurs at intermediate strength This coincides with increased ductility due to a maximum of retained austenite obtained in austempered materials. In material with a fatigue endurance limit all initiated cracks may not arrest, propagation rates may become very slow in the vicinity of microstructure barriers. This behavior is typical of microstructure short cracks, which have a size of the same order as the spacing of microstructure barriers. The interaction with microstructure decreases as the crack grows, and its behavior as a long crack becomes treatable using Elastic-Plastic (EPFM) and Linear Elastic (LEFM) fracture mechanics continuum models
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