Aleksander Karolczuk

Critical Planes in Multiaxial Fatigue

The paper includes a review of literature on the multiaxial fatigue failure criteria based on the critical plane concept. The criteria were divided into three groups according to the distinguished fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the applied the critical plane position. The multiaxial fatigue criteria based on two critical planes seem to be the most promising. These two critical planes are determined by different fatigue damage mechanisms (shear and tensile mechanisms).

Residual Stresses in Steel-Titanium Composite Manufactured by Explosive Welding

The main aim of the paper is determination of residual stresses in explosively welded steel-titanium bimetal. The analysis considers two bimetallic specimens: before and after the heat treatment. In residual stress determination the hole drilling method along with finite element analysis were applied. The results show different residual stress states depending on the heat treatment. The obtained results are confirmed by thermal stress calculation.

Fatigue Life According to Cyclic Strain Characteristics Determined from Variable-Amplitude Loading*

Abstract The paper includes the analysis of influence of cyclic stress-strain curve parameters on the fatigue life estimation. The parameters of cyclic stress-strain curve, described by the Ramberg-Osgood relation, were determined by a new method from the variable-amplitude loading histories. The variable-amplitude stresses were used to calculate strain courses based on different values of cyclic stress-strain curve parameters. The calculated and experimental strain courses were applied to calculate fatigue life with use of damage accumulation hypothesis by Serensen-Kogayev.

Structural and Fatigue Properties of Titanium-Steel Bimetallic Composite Obtained by Explosive Welding Technology

Structure of bimetallic composite obtained during explosive welding process exhibits strong heterogeneity in the vicinity of interface. The interface usually has a wavy shape with characteristic increase of hardness and largely deformed grains. Recently obtained fatigue tests for titanium-steel bimetal specimens under fully reversed push-pull loading show ratcheting phenomenon. In order to investigate this phenomenon mechanical testing and structural observations of titanium-steel bimetal and titanium before cladding have been performed. Fatigue characteristics in the form of relation between strain amplitude and fatigue life for titanium (Grade 1), steel (S355J2+N) and bimetal will be presented.

Identification of Efficient Material S-N Curve for Steel Welded Joints

The paper presents results of simulation and experimental tests carried out in order to identify the S-N curve introduced for the evaluation of fatigue life for various types of steel welded joints. Such curve is explicitly defined through the corresponding values of Cf and mf parameters. The identification process involved finite element analysis, undertaken for different discrete models varying in notch radius. The obtained results served as an input into iterative calculations carried for different values of Cf and mf parameters. Such calculations were aimed at minimization of the estimator in the form proposed for the process of identification.

The Effect of the Detonation Velocity in Explosively Welded Steel-Zirconium Bimetal on the Residual Stresses Determined by the Hole-Drilling Method

As a result of the explosion welding, residual stresses are generated in the cladded material which can affect the properties of the bimetallic composite. This paper analyses the value of residual stresses in the steel-zirconium bimetal sheets, for which the detonation velocities were 1,0V0 (where V0 = 2200m/s); 1,3V0 and 1,6V0 with constant others welding parameters.

Modelling of Titanium-Steel Bimetallic Composite Behaviour under Mechanical Cyclic Loading

The aim of the paper is to analyse how different mechanical properties of bonded metals influence the cyclic behaviour of bimetallic components. The simulations also include different initial state of stress since one of the methods for manufacturing bimetals is explosive welding which introduces residual stresses into bonded materials. The analysed cyclic behaviour concerns cyclic stress-strain relation in elastic-plastic strain state. The multi-surface plasticity model of Mróz-Garud was applied. Results shows that depend on residual stresses the ratchetting phenomena could occur.

Modelling of Stresses in Welded Joints Under Consideration of Plastic Strains in Fatigue Life Calculations

Abstract Welded joints submitted to variable loadings are, by their nature, experiencing a stress concentration resulting from the presence of a complex notch effect relating to geometrical and structural features of the joint. In the finite element method, modelling of the weld toe as a sharp notch reveals a non-linear relation of stresses dependent on the mesh density. In this paper, an approach for determination of the notch radius in a welded part was proposed, based on the application of finite element calculations with a non-linear elastic-plastic body model under employment of the linear hardening rule. The derived stresses are used in calculations of fatigue life, carried out according to algorithms provided for structural elements without the presence of welds.

Analysis of correlation between stresses and fatigue lives of welded steel specimens based on real three-dimensional weld geometry

Abstract Welded joints are areas of increased stresses in construction. The reason for this phenomenon is associated with the nonhomogeneous mechanical, structural and geometrical properties of the weld. In the article the correlations between locally raised stresses due to real geometry and fatigue lives of non-load carrying cruciform joints made from S355J2+N steel are analysed. Stresses were computed using Finite Element Method (FEM) based on real three-dimensional weld geometry obtained by 3D scanning. The specimens were experimentally tested under cyclic push-pull loading with a zero mean value of applied force. The correlation was analysed using Pearson’s correlation coefficient and statistical hypotheses. It was shown that statistically significant correlation exists between maximum values of normal stresses and fatigue lives.

Ratcheting Simulation in a Titanium-Steel Bimetallic Plate Based on the Chaboche Hardening Model

Abstract The paper presents the results of fatigue loading simulation applied to bimetallic model using the Chaboche kinematic hardening rule. Three cases of simulations were performed: (i) without residual stresses; (ii) considering residual stresses and (iii) considering asymmetrical geometry of bimetal, i.e. cross area reducing under tension period of loading. Experimental results exhibit the ratcheting phenomenon in titanium-steel bimetallic specimens. The observed ratcheting phenomenon could be explained by the third case of simulation which is supported by detection of microcracks in the vicinity of welded area.