Tomasz Łodygowski

The Numerical Analysis of the Intrinsic Anisotropic Microdamage Evolution in Elasto-Viscoplastic Solids

The objective of the present article is to show the formulation for elastic-viscoplastic material model accounting for intrinsic anisotropic microdamage. The strain-induced anisotropy is described by the evolution of the intrinsic microdamage process — defined by the second-order microdamage tensor. The first step of the possibility of identification procedure (calibration of parameters) are also accounted and illustrated by numerical examples.

Interaction of deformation waves and localization phenomena in inelastic solids

Abstract The main objective of this paper is the investigation of the interaction and reflection of elastic–viscoplastic waves which can lead to localization phenomena in solids. The rate type constitutive structure for an elastic–viscoplastic material with thermomechanical coupling is developed. An adiabatic inelastic flow process is considered. The Cauchy problem is investigated and the conditions for well-posedness are examined. Discussion of fundamental features of rate-dependent plastic medium is presented. This medium has dissipative and dispersive properties. Mathematical analysis of the evolution problem (the dynamical initial-boundary value problem) is presented. The dispersion property implies that in the viscoplastic medium any initial disturbance can break up into a system of group of oscillations or wavelets. On the other hand, the dissipation property causes the amplitude of a harmonic wavetrain to decay with time. In the evolution problem considered in such dissipative and dispersive medium, the stress and deformation due to wave reflections and interactions are not uniformly distributed, and this kind of heterogeneity can lead to strain localization in the absence of geometrical or material imperfections. Since the rate-independent plastic response is obtained as the limit case, when the relaxation time T m tends to zero, the theory of viscoplasticity offers the regularization procedure for the numerical solution of the dynamical initial-boundary value problems with localization of plastic deformation. Numerical examples are presented for a steel bar axisymmetric specimen subjected to tension, with the controlled displacements imposed at one or two opposite sides with different velocities. Two cases of the initial-boundary conditions are considered; (A) symmetric (double side) tension of the specimen which results in symmetric pattern of deformations; (B) asymmetric (single side) tension of the specimen with the opposite side fixed, which leads to non-symmetric deformation. For both cases of boundary conditions a set of examples is computed with different initial velocities changing between 0.5 and 20 m/s. The final states are defined by prescribed value of the total elongation of a specimen. In the numerical examples the attention is focused on the investigation of the interactions and reflections of waves and on the location of localization of plastic deformation. The distribution of plastic equivalent strain, temperature and vector plots of velocities represents the results. The computations are performed using the industrial finite element program ABAQUS (explicit method).

Thermal Stresses in Metallic Materials Due to Extreme Loading Conditions

The role of thermal stresses, understood as stresses introduced by a uniform or nonuniform temperature change in a body which is somehow constrained against expansion or contraction, in metallic materials due to extreme loading conditions is under consideration. The thermomechanical couplings (thermal expansion and thermal plastic softening phenomena) have a fundamental impact on damage and localization phenomena due to their influence on the propagation and interaction of the deformation waves. Such processes include strain rates over 107s-1 and temperatures reaching the melting point. It should be emphasized, that apart from thermal effects, the anisotropy of damage (both initial and induced by deformation) plays a central role in the overall process. The aforementioned dynamic events are described in this paper in terms of the Perzynas type viscoplasticity model recently developed by the authors, including the anisotropic damage. The discussed constitutive structure has a deep physical interpretation derived from the analysis of a single crystal and polycrystal behaviors.

Tooth-Implant Life Cycle Design

Dental restorations with the application of implants are very effective and commonly used in dental treatment. However, for some percent of patients, diverse complications can be observed. These problems can be caused by mechanical reasons such as loosening of the retaining screws or fracture and cracking of the dental implant components. These problems suggest the need for permanent modernization and development of dental implants. This paper describes selected aspects of the life cycle design process of the tooth-implant system Osteoplant. The authors would like to present what they mean by implant life cycle design as one part of the whole Digital Product Development (DPD) process. The sequential stages of this process are described and the tools and methods are discussed. The attention is focused on numerical simulations the mechanical behavior of dental implants and genetically based optimization algorithms. The tools and methodology of FE simulations of implant behavior are described. The whole process of optimization of a dental implant system is explained, and a self-developed optimization tool based on a genetic algorithm is presented. These processes are crucial for modern design procedure beyond the life sciences industry.

Designing of Multilayered Protective Panels Against Improvised Debris

This paper presents the design process of multilayered protective panels used to protect people and property from debris resulting from the explosion. A series of numerical analysis were conducted, which allowed to find the number of aluminium sheets to fill the barrier and to determine their shape in order to stop penetration. In this work not only the design process, that employs the most current engineering tools, is presented, but also behaviour of metallic materials under extreme dynamic loading.

Computer estimation of plastic strain localization and failure for large strain rates using viscoplasticity

The problem of modelling extreme dynamic events for metallic materials including strain rates over 107 s-1 and temperatures reaching melting point is still vivid in theoretical, applied and computational mechanics. Such thermomechanical processes are highly influenced by elasto-viscoplastic wave effects (their propagation and interaction) and varying initial anisotropy caused by existing defects in metals structure like microcracks, microvoids, mobile and immobile dislocations densities being together a cause of overall induced anisotropy during deformation (from the point of view of meso-macro continuum mechanics approach). It should be emphasised, that the most reliable way for estimation of such processes needs nowadays a complex phenomenological models due to limitations of current experimental techniques (it is still not possible to measure the evolution of crucial quantities e.g. temperature for extreme dynamic processes) and computational capabilities.

Safety of Concrete and Masonry Structures under Unusual Loadings

In the paper the behavior of selected brittle materials and structures (concrete and masonry) subjected to explosive loadings is discussed. For concrete the accepted Cumulative Fracture Criterion (CFC) is exposed. It describes the degradation of the material under fast dynamic processes accompanied by the strong waves propagation phenomenon and large strain rates of deformation. To overcome the computational difficulty in the analyses of such complex problems, the sub-modeling technique as well as splitting of the calculations into two separate parts: analysis of acoustic wave in the air and the propagation of stresses in structures, were used. Some instructive numerical examples of concrete and masonry walls are in focus of the presentation. The numerical tools and computer simulations allow for proper estimation of the structures safety and for taking the design decisions on how to ensure their expected strength.

Selected Constitutive Relations in Practical Computations

The paper presents some numerical applications of the problems in which constitutive difficulties influence significantly the complexity of the models. In particular, the examples are focused on three domains. There are: the analysis of localization of plastic deformations in ductile materials as well as the estimation of speed of its development and fracture, biomechanical complexities for fatigue analysis of tooth implants and the analysis of spine segment and finally, the failure of brittle materials (concrete) and structures under fast explosive loading.