Abstract: In the work presented here an elastic-plastic crystalline finite element method is used to
simulate the cyclic behavior of 316L austenitic stainless steel single crystals and polycrystal. The
evolution of the back stress on each slip system is described using a non linear kinematics hardening
law to account for the hardening induced by long range dislocation interactions. As the contribution
of short range interactions is assumed to be negligible, the value of the friction stress is kept
constant. Three dimensional finite element calculations are performed to simulate the cyclic stress
strain curves in the case of a single crystal oriented for multiple slips, as well as for the case of the
polycristal. Simulations are compared to experimental data. They seem to be satisfactory for low
strain values (εp\2 <10-3) whereas, for εp\2 >10-3, they underestimate the hardening observed
Abstract: High fatigue threshold values of duplex ferritic-martensitic steels are interpreted by using
a unified model of roughness- and plasticity induced crack closure. Complex metallographical and
fractographical analysis was performed in order to obtain characteristics of tortuous crack paths
produced by crack deflection and branching mainly at austenite/ferrite interfaces. Calculated values
of effective thresholds are in a good agreement with experimental data. The total level of extrinsic
toughening (closure + shielding) induced by the duplex microstructure was determined to be as
much as 70% of measured fatigue threshold values. This is the main reason for the high resistance
to propagation of long fatigue cracks in the near-threshold region.
Abstract: This paper deals with an analysis of the possible causes of a transversal crack in a steel
slab with a l300×l45 mm cross-section using results from two models. Samples were taken from
and around the crack in order to analyze the concentration (i.e. chemical heterogeneity) of the
relevant elements. Simultaneously, the concentration of elements at the surface of the crack was
measured after the crack was opened. The chemical heterogeneity of elements was analyzed with
the aid of the JEOL JXA 8600/KEVEX analytical equipment. The measurement results were
processed using mathematical statistics procedures. The results proved that there was an internal
crack initiating immediately below the curve of the solid-state temperature and consecutively
Abstract: An original three-dimensional (3D) model of solidification is used to describe the process
of solidification and cooling of massive 500x1000x500 mm cast-iron castings in sand moulds. The
calculated model of the kinetics of the temperature field of the casting is verified during casting
with temperature measurements in selected points. The following dependences are later determined
according to the experimental and calculated data: the average size of the graphite spheroids rg,
graphite cells Rb and the average distances among the particles of graphite Lg – always as a function
of the local solidification time θ [xi, yi, zi]. Furthermore, it has been found that the given basic
characteristics of the structure of the cast-iron (rg, Rb and Lg) are a linear function of the logarithm
of the local solidification time θ. The original spatial model of solidification can therefore be used
in its first approximation for the assessment of the pouring structure of massive cast-iron castings.
Abstract: Most families of S-N curves determined at various temperatures present certain general
regularities on whose basis the Basquin equation describing finite-life S-N curves can be
generalized for various temperatures. This equation can be represented by straight lines with
common slope if log-log fit for stress vs. temperature dependence is used. Deviations from these
straight lines (anomalies) are evidence that additional degradation mechanisms are effective besides
fatigue, whose temperature dependences differ from the mentioned temperature dependence of
fatigue strength. In high-temperature region it is most often cyclic creep, in low-temperature region
athermal processes of plastic deformation can play significant role in fatigue failure.
Abstract: Ordered alloys and intermetallides are important constructional materials, because they
have a unique property – positive temperature dependence of yield stress. It is known that antiphase
boundaries and washing effects of order, structures and concentrations of components near the
boundaries are of great impotence in the appearance of positive temperature dependence. But
superstructures have not only APB but also APB tubes, APB stripes. Their role is also important in
physical and physics-mechanical properties of ordered alloys and intermetallides. The paper
presents the classification of all the types of planar defects and their local properties for some alloys
of different superstructure types.
Abstract: The development of the volume fraction of cumulated persistent slip bands (PSBs) in
cyclically deformed nickel polycrystals was investigated in dependence on the number of cycles
using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was shown that
there is a large scatter of the volume fraction of PSBs from grain to grain. Three different tendencies
for the development of the volume fraction with increasing number of cycles were distinguished. It
was shown that there is a correlation of the orientation of the primary slip systems with the volume
fraction of cumulated PSBs and the activation of PSBs during half-cycle deformation.
Abstract: Texture of a fatigue crack surface is strictly related to crack growth rate. Cracks in
specimens from aluminum alloy were studied. Two types of information were used: SEM images of
fracture surfaces, and 3D reconstructions of fracture surface morphologies. Sets of equidistantly
focused images obtained by an optical microscope served as the basis for 3D reconstruction.
Multiparametric fractal analysis was applied to characterize crack surfaces. A vector of fractal
features represented each image or 3D reconstruction of selected locations of fracture surfaces. For
estimating fractal characteristics, the box-counting method in 3D was used in all cases, .
Multilinear regression was used to express the relation between crack growth rate and feature
vectors, with satisfactory results for both crack surface representations.
Abstract: A 3D time-harmonic problem for an infinite elastic matrix with an arbitrarily located
interacting rigid disk-shaped inclusion and a penny-shaped crack is analyzed by the boundary
integral equation method. Perfect bonding between the matrix and the moving inclusion is assumed.
The crack faces are subjected to time-harmonic loading. The boundary integral equations (BIEs)
obtained are solved numerically by the implementation of regularization and discretization
procedures. Numerical calculations are carried out for a crack under tensile loading of constant
amplitude, where an interacting inclusion is perpendicular to the crack and has the same radius.
Both the normal crack-opening-displacement and the mode-I stress intensity factor are investigated
for different wave numbers and distances between the crack and the inclusion.
Abstract: The evaluation of the generalized stress intensity factor (GSIF) and T-stress for the case
of the surface crack terminating perpendicular to the interface between two orthotropic materials is
considered. The combination of the discretization, numerical and analytic methods is used. The
discretization method, such as common finite element method (FEM), is served to include the
boundary condition to the GSIF solution and to describe the remote stress and displacement field
region with the low influence of the singularity of the crack tip. The Lekhnickii-Eshelby-Stroh
(LES) formalism is used to derive the approach solution for the near stress field of the crack tip and
the singularity problem in an orthotropic 'trimaterial' using the Schwartz-Neumann's alternating
technique. The problem of the stress singularity is treated as a non-linear eigenvalue problem, which
leads to the characteristic equation for the stress singularities of the form rδ −1 , 0 <δ <1. Two ways
of the evaluation of the GSIF are presented, using the reciprocal theorem ψ -integral) and the crack
model by means of continuous distribution of dislocations. Both results are compared for a specific
material. The continuous distribution of dislocations technique is also used for determination of the