Michal Krzyzanowski

Titanium alloys, due to their exceptional mechanical properties and biocompatibility, are commonly used to produce medical implants nowadays. However, the presence of such elements as aluminium and vanadium can be harmful to human health. One of the possible solutions could be replacing the titanium alloys with ultrafine-grained commercially pure titanium (cpTi). The yield and also the ultimate strength of cpTi can exceed 1000 MPa. One of the most promising methods in manufacturing medical implants with improved biological fixation is laser cladding in which bioactive glass coatings are imposed on metallic substrates. The aim of this work is development of a 3D numerical model of the above mentioned additive manufacturing process. The obtained model is able to predict the stress-strain and temperature distributions during the processing. A sequentially coupled finite element (FE) model of laser cladding has been developed by applying element birth and death technique to calculate the transient temperature fields used in the stress analysis. The concentrated volumetric heat source from the laser beam moving along the metal surface has been represented by the Gaussian distribution in the radial and exponential decay in the depth direction. The developed FE based numerical model is capable to support the optimal design of such advanced multi-layered structural materials using the laser cladding technique.

The paper is devoted to development of the modelling approach based on 3D finite-element (FE) analysis of the transient temperature fields and the thermally induced phase transformations as a way towards residual stress management in large size forgings. Heating, holding and cooling stages are under consideration and modelling of both the austenite formation and decomposition are taken into account. The thermal-mechanical FE model capable of taking into account changes in the specific volume during ferrite/austenite transformation is coupled with the relevant phase transformation model in order to allow simulation of the transient stresses due to both thermal contraction and the dilatometric effect. The model is capable of taking into account different boundary conditions for the heat transfer problem based on the available data. To improve the predictive abilities, the following two commercial FE codes, such as MSC Marc 2013.1.0 and Abaqus/Standard6.12, are used for solving the non-steady state 3D problem of the metal expansion/contraction during consecutive heating, holding and cooling stages. Although all the mentioned process steps are considered, the model is dedicated to be used for modelling the cooling stages of large forgings and castings.

The complex analysis of the interface behaviour has been performed during constrained compression testing of 316L steel plates as a way towards processing of the multilayered metallic materials. The approach is based on a combination of experiments under appropriate operating conditions and computer modelling based on finite element (FE) methodology for interpretation of the test results. Multilayered metallic structure was successfully obtained using the applied constrained compression testing technique. The specially designed die and compression specimens allowed for joining of the steel plates together even at room temperatures. The performed numerical analysis using the ABAQUS/Standard FE software revealed the strain and stress localisation areas within the multilayered structure among other features that are described in the paper. The results are in agreement with experimental observations.