M. Leonavičius

SHAKEDOWN OF BOLTS WITH A ONE-SIDED PROPAGATING CRACK

Abstract Cyclic strains of joints may cause formation of a crack or cracks in a bolt thus changing its loading conditions. After crack appearance in a bolt it can be used if its length does not exceed a critical one. Modification of the shakedown theorem—the method of additional load—was applied in the investigation. The results—the analytical expressions of shakedown conditions are in a sufficiently good agreement with those achieved by other methods. Differences occur due to failure to get an accurate analytic expression. Solution of the shakedown problem plays an essential role in determining the safety factor of bolts subjected to cyclic strains.

THE INVESTIGATION AND PECULIARITIES OF CALCULATION OF TRANSPORT MACHINE ELEMENTS MADE OF AUSTEMPERED DUCTILE IRON

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...

The High Cyclic Failure Analysis of Welded Joints of CT Specimens

The results of failure process of welded joints subjected to high-cyclic loading are presented. Analysis of the microstructure of welded joints, indexes of mechanical properties are provided and failure mechanism in the area of fatigue and static fracture is analyzed. The fractographic analysis of CT specimens was performed by means of optical and scanning electron microscopes.

Evaluating the fracture strength of welded joints based on their limit states under high-cycle stresses

The research presented here aims at evaluating the strength of the welded joints of spheroidal cast iron of large mineral crushers based on the limit states under very high-cycle loading. Several experiments were performed using semi-natural and standard specimens. This study derived the summary fracture process diagram, including the test results for compact tension specimens and semi-natural specimens, for all fracture process stages. A method for evaluating the strength of these welded joints based on safety factors, when the number of loading cycles exceeds 108, is proposed.

Cyclic Fracture Analysis of Semi-Natural Cast Iron Plate with Metallurgical Defects Layer

Fatigue fracture of the semi-natural cast iron plate with dross and carbon float defects was analyzed. Crack formation and propagation were traced under the programmable cyclic load of the pure bending. The focuses of the crack and their consistent pattern up to the total fracture were determined. Fracture analysis was performed by using optical and electronic microscopy methods. High-cycle fracture mechanism was established when the number of the cycles exceeded 108. The influence of the microstructure upon fracture process was investigated.

STRENGTH OF MINING AND BUILDING EQUIPMENT MATERIALS SUBJECTED TO GIGACYCLE LOADING

High-strength cast iron is used for manufacturing the supporting elements of minerals and cement clinker grinding machines. The dross layer remains inside large dimension castings after manufacturing. It has worse mechanical properties and resistance to fatigue crack formation and propagation. In this paper, the results of an experimental investigation of cyclic bending strength of semi-natural specimens from cast iron with a dross layer of 10-11 mm thickness are presented. The mechanical properties and structures of the base and dross layers differed considerably. Before testing the methods of defectoscopy were applied to detect technology defects. The stress ratio was r = -0,62 and the stress alternating range varied from 70 to 280 MPa. To 1·10 8 cycles, crack growth was insignificant. Further crack propagation was controlled. The 1 st specimen was broken after 3·10 8 and the 2 nd one after 2·10 8 cycles. The dependencies of crack propagation on cycle number and stress intensity factor range were estimated. The dross layer stops crack propagation, when crack front passes from dross to base metal.

PECULIARITIES OF CALCULATING THE CYCLIC STRENGTH OF IMPORTANT THREADED JOINTS

Abstract The calculation of the strength of important threaded joints is started by defining the minimum size of the cross-section of bolts (studs). Then the static and cyclic strength is tested. The studs of the demountable joints of nuclear power equipment are calculated in accordance with the norms of the Russian Federation and the ASME Code. The calculation methods coincide in essence, they are based on similar limit states; however, there also some differences exist. The authors investigate and compare both methods in their work. There is a brief analysis of calculation methods in the article. For closer definition of standards and their substantiation the authors used experimental and theoretical investigations performed at Laboratory of Strength Mechanics of Vilnius Gediminas Technical University. In order to develop a uniform cyclic strength and shakedown calculation procedure for critical threaded joints, a completely new calculation of a progressive profile change is recommended to be performed ...

ANALYSIS OF EXPERIMENT AND CALCULATION OF THE THREADED JOINTS UNDER TENSION AND CYCLIC BENDING

Summary The effect of individual elements of the system “bolt-nut” under tension and bending on the cyclic strength is a complicated and insufficiently clear subject. The data presented in the works of the laboratories of strength mechanics and those of the present authors have been obtained when the ratio of bending and tension stress caused by eccentrically applied tension force was from 0 to 1.5. If stresses caused by bending account for 0.25 σ y of tension stresses, the strength to low-cycle fatigue somewhat increases. When σ m = 1.5σ n , the decrease in longevity is observed. The results obtained, however, differ insignificantly from the longevity of threaded joints under cyclic tension as long as bending stresses do not exceed 0.5. σ y . A comprehensive experimental study of these problems and the analysis are presented in the works of the present authors. One of the main factors determining the cyclic strength of the system “bolt-nut” is the distribution of internal resultants. The distribution of ...