Abstract: The solidification models basing on the Fourier equation with the additional term
controlling the kinetics of phase transition are discussed. The different approaches to this term
definition lead to the different solidification models, in particular the macro and the macro/micro ones
can be taken into account. In the case of macro description the equation in which the parameter called a
substitute thermal capacity is considered, while in the case of macro/micro approach the linear or
exponential models of crystallization can be introduced. The solution of the problem can be found
using the numerical methods. In this paper the boundary element method using discretization in time is
applied, the examples of numerical simulations are also shown.
Abstract: Recent studies indicate that the austenite(γ)-to-ferrite(α) transformation kinetics in low
alloyed steels is solely controlled by the intrinsic mobility of the interface at least in the initial stages
of ferrite growth. Then, diffusion processes in the interface significantly retard ferrite growth, so that
bulk diffusion of the fast diffusing interstitial component carbon becomes relevant. Two series of
dilatometer tests, one from a low to ultra-low carbon steel  (alloy A) and the other from an Fe-Mn
steel  (alloy B), are considered. In case of alloy A the first stage of the transformation kinetics is
apparently controlled by the intrinsic interface mobility, whereas in the second stage carbon diffusion
in the interface and in the bulk material comes into play. The transition region can be modeled by an
effective mobility, which depends on the interface velocity. In the second stage the interface mobility
depends on the temperature only. In case of alloy B a hierarchical model allows for a direct estimation
of the intrinsic mobility. The numerical results indicate that the interface mobility also changes from
an intrinsic mobility at the initial stage of the transformation to an effective mobility due to solute
drag during the transformation process.
Abstract: It has frequently been observed that the ductility or elongation of a material can
significantly be affected by its grain size. Poor ductility with low elongation has been found in
ultrafine-grained (UFG) steels when their grain size is smaller than a critical value. The so called
instability of plasticity is a well known drawback for UFG steels and has greatly prevented them from
wider application. Although the instability has been attributed to the lack of strain hardening capacity
of ultrafine-grained materials, its mechanism is still unclear. In this paper, a newly developed model
for predicting the dependence of uniform elongation on grain size is described, using which the
instability of plasticity in UFG steels can be explained. The model is based on a strain hardening
model for polycrystalline metals that was previously developed by the present author and was
modified in the present study to take the grain size effect into account. The uniform elongation
calculated using the model is in good agreement with that experimentally measured in two steels. It
was found that the elongation begins to decrease rapidly when the grain size is reduced to below 2μm
- a clear sign of the occurrence of the instability of plasticity.
Abstract: A physically-based multi-scale model for martensitic transformation induced plasticity is
presented. At the fine scale, a model for one transforming martensitic variant is established based on
the concept of a lamellae composed of a martensitic plate and an austenitic layer. Next, the behaviour
of 24 potentially transforming variants is homogenized towards the behaviour of an austenitic grain.
As a simple example, the model is applied to deformation and transformation of a single austenitic
grain under different deformation modes.
Abstract: The apparent shear strength of rock discontinuities is lower than that of small scale
samples. At the same time, the sliding behavior is characterized, in situ, by marked instabilities.
Numerical algorithms permit to calculate contact forces at any point, and to describe the stick-slip
transition. On the other hand, the critical aspects are not captured by classical theories. Multiscale
simulations show that the contact domain between rough surfaces is a lacunar set. This explains the
size-dependence of the apparent friction coefficient. By applying an increasing tangential force, the
regime of partial-slip comes into play. However, the continuous and smooth transition to fullsliding
predicted by the Cattaneo-Mindlin theory is not occurring in real situations. We implement a
numerical renormalization group technique, taking into account the redistribution of stress
consequent to partial-slip. This permits the critical value of the tangential force to be found. The
critical force is less than the one predicted by Coulomb’s theory, and depends on the specimen size
and on the topology of the interface.
Abstract: For semicrystalline materials, a stacked lamellar morphology gives rise to a strongly
anisotropic mechanical response. A multiscale numerical model is used to simulate the effect of a
stacked lamellar microstructure on the macroscopic behaviour. The constitutive properties of the
material are identified separately for the crystallographic and amorphous domains. The averaged
fields of aggregates of individual phases, having different preferential orientations are determined.
The anisotropy of preferentially oriented material is investigated in different deformation modes.
Abstract: The paper presents a nonlocal elastic damage-frictional interface model. The reason to
introduce nonlocal mechanical features inside the constitutive relations is justified by the fact that
there are several circumstances, in which the interface displays inside an extended process zone with
microstructural spatial interactions. Typically, spatial bridging mechanical effects can be effectively
modeled by integral (strongly nonlocal) stress-strain relations. The paper develops an elastic nonlocal
model with local isotropic damage and the relations are constructed following a thermodynamical
Abstract: This paper deals with the problem of decohesion in composite structures containing
interfaces of similar/dissimilar materials. The analysis of the tractions transmitted between opposite
faces into contact as well as of the initiation and propagation of delamination zones is studied with
reference to plane structures with adhesive joints under shear stresses. A simplified monodimensional
structural model is formulated and applied to develop basic understanding of the
standard adhesion test. The analytical results obtained are used to optimize the performance of
single-lap adhesive joints in practical applications.