Grzegorz Robak

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.

The Fictitious Radius as a Tool for Fatigue Life Estimation of Notched Elements

In this paper, the fictitious radius - according to Neuber’s method for determination of stresses at the notch root was used. Next, the fatigue lives of elements of the ring notches were calculated, and then compared with results of experimental tests of S235JR steel samples. However, the obtained fatigue lives did not bring satisfactory results. It has been demonstrated that the fictitious radius strongly depends on the expected fatigue life

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.

Test Stand for Analysis of Fatigue Crack Propagation under Bending with Torsion

The paper presents a test stand for measurements of fatigue crack propagation. The stand includes a fatigue machine MZGS–100 and a device for registration of the crack length. The test stand is equipped with a stereoscopic microscope with fluent magnification of 7× – 67.5×. The microscope can be applied for observation of fatigue crack development. The microscope is also equipped with a digital camera, which enables continuous observation of fatigue crack development on the computer monitor and it is not necessary to stop the machine. The test results obtained at this stand can be used for determination of fatigue life and fatigue crack propagation rate.

Application of Fictitious Radius to Fatigue Life Calculations of Bending Notched Specimens

The paper contains an application of Neubers fictitious radius methods to fatigue life calculations for elements with geometrical notches. FEM analysis for notched specimen with fictitious radius were performed, then results of simulations and experimental tests for smooth and notched specimens made of S355J2G1W structural steel were compared by each other. Based on simulation results, function dependence of micro structural length was determined, both for linear-elastic and elasto-plastic calculation.

Determining Effective Length for 40 HM-T Steel by Use of Non-Local Line Method Concept

Abstract In the paper, the concept of non-local line method is presented and used for determining the effective length for notched elements. Experimental tests and calculations were performed for 40 HM-T (42CrMo4+QT) steel made specimens of two types, i.e. smooth specimens, and notched specimens with notch radius equal to 0.2 mm, 0.5 mm, 0.8 mm, and 1 mm. The performed FEM calculations took into account the multi-linear hardening model and cyclic material properties. The concept of the presented non-local line method bases on finding the position of critical plane and determining the effective length, meant as the fracture process zone. During numerical stress gradient simulations, also the weight function was implemented. It was observed that the effective length increases as the load increases.

Equivalent Fatigue Zone in a Notched Elements Determined by Use of Non-Local Line Method with Weight Function

The work presents non-local line method by which the equivalent fatigue zones were designated. These zones are one-dimensional efficient lengths in which operating stress variables cause initiation of fatigue cracks. The algorithm of the presented method considers the issues of multi-axial stress state, critical plane and weighting function. Calculations of stresses in the test element were performed by using the FEM assuming cyclic material properties, which are described with the model for multi-linear hardening. The empirical lifetime of elements with a notch was assumed to define length of the crack amounting to 0.1 mm. As the result of calculations, the dependence of effective length on nominal stress and radius of the notch was determined.

Application of the fictitious radius for the calculation of the fatigue life using the elastic-plastic body model

In this paper, the fictitious radius - according to Neuber’s method for determination of stresses at the notch root was used. Next, the fatigue lives of elements of the ring notches were calculated, and then compared with results of experimental tests of S235JR and 42CrMo4+QT steel samples. It has been demonstrated that the fictitious radius strongly depends on the expected fatigue life.