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Item type:Publication, Access status: with files , Strength and ductility loss of Magnesium-Gadolinium due to corrosion in physiological environment: Experiments and modeling(Elsevier, 2023-08-01); ; ; Luczak, MonikaWe propose a computational framework to study the effect of corrosion on the mechanical strength of magnesium (Mg) samples. Our work is motivated by the need to predict the residual strength of biomedical Mg implants after a given period of degradation in a physiological environment. To model corrosion, a mass-diffusion type model is used that accounts for localised corrosion using Weibull statistics. The overall mass loss is prescribed (e.g., based on experimental data). The mechanical behaviour of the Mg samples is modeled by a state-of-the-art Cazacu–Plunkett–Barlat plasticity model with a coupled damage model. This allowed us to study how Mg degradation in immersed samples reduces the mechanical strength over time. We performed a large number of in vitro corrosion experiments and mechanical tests to validate our computational framework. Our framework could predict both the experimentally observed loss of mechanical strength and the ductility due to corrosion for both tension and compression tests.Publicationtype: Journal ArticleScopus© Citations 2 44 106 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combining peridynamic and finite element simulations to capture the corrosion of degradable bone implants and to predict their residual strength(2022-04-15); ; ; ; This paper proposes a computational framework to describe the biodegradation of magnesium (Mg)-based bone implants. It is based on a sequential combination of two models: an electrochemical corrosion model to compute the mass loss of the implant over several weeks combined with a mechanical model to assess its residual mechanical strength. The first model uses a peridynamic (PD) corrosion model to tackle the complex moving boundary of the corroding material in an efficient manner. The results of this corrosion simulation are mapped to a finite element (FE) model by way of a damage variable. Subsequently, the FE model is used for mechanical analysis. To use PD for such a complex problem, we proposed three innovative improvements compared to state-of-the-art PD models: (1) application of an adaptive multi-grid discretization in space and an implicit time-stepping algorithm enabling an efficient simulation of the complex implant geometry over prolonged periods, (2) novel non-local Dirichlet absorbing boundary conditions to truncate the simulation domain in the close neighborhood of the implant of interest without prohibitive losses of accuracy, and (3) selection of suitable non-local kernel functions and parameter calibration on the basis of experimental data by an evolutionary algorithm. We demonstrate that this framework can capture the loss of implant mass due to corrosion for typical alloys such as Mg-5Gd and Mg-10Gd. Moreover, we point out how this framework can be used in the future to predict the declining mechanical strength of bone screws subject to biocorrosion over several weeks.Publicationtype: Journal Article69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Grain-scale investigation of the anisotropy of Portevin-Le Chatelier effect in Mg AZ91 alloy(2019-01-07); ; ; An aspect of Portevin-Le Chatelier (PLC) type plastic instability that is yet to be understood is its orientation dependence. Such knowledge is crucial in view of its implications for texture weakening and, by extension, improvement in formability in Mg–based alloys. In this work, insight into the micromechanisms that govern PLC and its orientation dependence in single grains of Mg AZ91 is achieved using a combination of spherical nanoindentation, local orientation image analysis and crystal plasticity based finite element simulations, which was specifically used to identify the anisotropy in slip activity for the investigated orientations. Moreover, a statistical thermal activation model that is based on the distribution of load jumps between consecutive displacement bursts in the load vs. displacement response is presented. The paper demonstrates the ability of the model to predict the thermal activation parameters for PLC effect. On the basis of the results, we propose a mechanistically sound model for PLC effect that explains the underlying micromechanisms, the role of Al and Zn atoms, and the origin of the orientation dependence of the phenomenon. We also highlight the influence of the PLC effect on formability in Mg–based alloys.Publicationtype: Journal Article214 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Finite element damage analysis of an underwater glider–ship collision(Springer, 2015-11-06); ; ; ; Underwater gliders, which are profiling autonomous underwater vehicles designed to make oceanographic measurements, are increasingly used in the coastal ocean. As they regularly surface for data transmission, gliders increasingly pose a risk for fast ships. In order to estimate the extent of damage due to collision, 3D finite element simulations of collisions between a glider and a high-speed craft with a glass-fiber reinforced plastic hull are performed. Different collision scenarios such as impact locations, angles of attack and speeds are examined. The results are compared to an analytical solution based on simplifying assumptions. Although both methods reveal consistent results, it is shown that finite element simulations are required to account for the 3D shape of the ship. The results indicate that at ship velocities exceeding 7.5 m/s (14.6 kt) the glider penetrates the ship’s hull causing severe damage to its structure.Publicationtype: Journal ArticleScopus© Citations 8 381 280 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Crashworthiness of magnesium sheet structures(Trans Tech Publications, 2013-07); ; ; ; A hollow rectangular profile, as an example of a typical structural component made of magnesium alloy sheets has been built, tested and evaluated in order to assess its behaviour during axial crushing. The profiles were joined from plane sheets of AZ31 and ZE10, respectively, by laser beam welding and were then tested in compression. Numerical simulations have been conducted to understand the complex interplay between hardening characteristics of the materials under investigation, profile cross-section variation and energy absorption. The results from the compression testing of the profiles show that the welds are not the source of damage initiation and failure. The performance of the magnesium profiles in terms of dissipated specific energy is confirmed for small and intermediate displacements to be comparable to that of aluminium profiles. For large displacements, however, the shear-type failure mode of magnesium causes a sharp drop of the crushing force and thus limits the energy absorption. These findings demonstrate the requirement for an alloy and wrought magnesium process development specifically for crash applications which aims at progressive hardening along with high ductility for improving the bending and shear behaviour.Publicationtype: Conference Paper265