Wyniki wyszukiwania - BazTech

1

The fatigue life estimate by the LEFM concept of the tube joints exposed to axial load

Djoković J. M., Nikolić R. R., Bujňák J., Hadzima B.

Roczniki Inżynierii Budowlanej

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2017

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z. 17

35--41

EN

In the tube joints the crack growth usually appears along the weld’s edge, i.e. at the spot where the chord and the brace are connected. The semi-elliptical crack the most frequently develops from the initial flaw that originated during the welding. The abrupt change in the material’s structure and response to loading are increasing the normal stresses in the lateral tube at certain spots around the crossing of the main and lateral tubes, producing the “hot spot” stress. Sensitivity to fatigue depends on combination of the cyclic loading, initial defects, environmental influences and the “hot spot” stresses which are the result of the tube walls bending during the loading of the structure. The principles of the Linear Elastic Fracture Mechanics (LEFM) are applied in this paper to analysis of the crack propagation behavior of a thin tube joints. Influence of various parameters was investigated individually and independently, and the share of the fatigue crack growth and subsequently the working life of the welded joint were estimated.

2

Buckling of variable cross-sections columns in the braced and sway plane frames

Nikolić R. R., Djoković J. M., Bujňák J.

Roczniki Inżynierii Budowlanej

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2016

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z. 16

31--39

EN

Columns of the variable cross-sections are used in order to decrease the costs of the structure, for the purpose of easier maintenance, or for architectural reasons. Buckling of such columns is a problem that could appear in many steel structures, and could cause the loss of the structural stability. The critical buckling loading and the effective buckling lengths of such columns are analyzed in this paper for the cases of columns in the braced frame with the fixed and the sway frame with the movable nodes. Results are presented on corresponding diagrams what enables pinpointing the exact moment at which the particular column would lose its stability. The comparison of obtained results for the two types of frames are presented, as well.

3

Comparison of analytical and the FEM method for deriving the Mode I stress intensity factor of thin-walled beams containing a crack

Djoković J. M., Vulović S. D., Nikolić R. R., Živković M. M., Bujnak J.

Roczniki Inżynierii Budowlanej

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2015

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z. 15

43--51

EN

The problem considered in this paper is of the cracked thin-walled beams. They are subjected to combined loading by the bending moment and the axial force. The profiles with the I (H), T and U cross-sections were analyzed. The analytical method is based on application of classical expressions for Mode I SIF of such beams with taking into account the cross sections' warping. The classical expressions for SIF for the thin plate are adapted by including the reduced forces and moments characteristic for the thin-walled beams. The numerical simulation for calculating the stress intensity factor of the cracked thin-walled beams consisted of application of the Finite Element Method (FEM) by use of the J-EDI method. It is found that the Mode I SIF of cracked thin-walled beams increases with crack length increase. The conducted comparison of results obtained by application of the two methods confirms the validity of the proposed analytical expressions only for the small crack lengths.

4

Analysis of the LEFM concept for interfacial cracks application to coating buckling delamination in terms of substrate elastic characteristics

Djoković J. M., Nikolić R. R., Miletić I. M., Mićunović M. V.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 1

61--69

EN

In this paper the buckling delamination of a coating on a flat substrate in form of a straightsided blister with special attention paid to the influence of elastic characteristics of the substrate is considered. Conditions for the buckling initiation are analyzed as well as the energy release rate and mode mixity of the interface crack as functions of the difference in elastic characteristics of the coating and the substrate. The problem is discussed from the aspect of application of the linear elastic fracture mechanics (LEFM) concept for the interfacial crack. The real angle function ! of the Dundurs parameters and and the ratio of thicknesses of the two layers are used for determination of the energy release rate and the load phase angle. Both the energy release rate along the sides of the blister and the average energy release rate at the front of the blister were calculated. The results thus obtained justify the application of the LEFM concept for interfacial cracks to the considered problem.

5

Optimal plates with prismatic cores

Bujnak J., Djoković J. M., Nikolić R. R.

Roczniki Inżynierii Budowlanej

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2013

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z. 13

13--20

EN

In this paper the multifunctional sandwich plates with prismatic cores were optimized with respect to their dimensions and mass. The comparison of those plates to plates with honeycomb cores was performed. The two loading directions, longitudinal and transversal, were considered. The plates with prismatic cores have best performances when loaded longitudinally, since the plate characteristics are restricted by buckling of a plate and not of a beam. Plates with the honeycomb cores are more efficient related to weight, than the plates with the prismatic cores for smaller loads. This advantage diminishes with load increase. Based on this analysis a conclusion can be drawn that the sandwich plates with the prismatic cores are the most efficient from the aspect of the optimal mass, for structures which are simultaneously used for load carrying and cooling.

6

Optimization of sandwich plates with truss cores

Nikolić R. R., Djoković J. M., Bujnak J.

Roczniki Inżynierii Budowlanej

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2012

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z. 12

5--10

EN

Sandwich plates with truss core have many advantages with respect to other structures, including the plates with the honeycomb cores. Besides the architectural possibilities, which are the consequence of their favorable appearance, these structures can carry equal or even higher loads than other similar structures. In this paper is presented an attempt to optimize the mass of the sandwich plate's structure, which is subjected to simultaneous action of loads due to the transversal shear force and the bending moment. In comparison to the corresponding sandwich plate with the honeycomb cores, the plate with the truss core is almost equally efficient form the aspect of the mass decrease.