Nonlinear deformations of a cylindrical pipe with pre-stressed thin coatings

The paper presents an exact solution for the problem of large deformations of torsion, axial tension–compression, and radial expansion or shrinkage of an elastic hollow circular cylinder equipped with pre-stressed elastic coatings. Surface coatings are modeled using the six-parameter nonlinear shell theory. The constitutive material of the cylinder is described by a three-dimensional nonlinear model of the isotropic incompressible body of the general form. Special boundary conditions describe the interaction of this material with thin coatings on the inner and outer surface of the pipe. Based on the solution obtained, numerical calculations were performed on the effect of preliminary stresses in coatings on the stress–strain state of a cylindrical pipe.

Implementation of qualia structures provided by relative adjectives and composites in German

The present paper deals with the semantic representation of attributive elements in the nominative group − relative adjectives and composites. The aim of the present study is to analyze the semantic representation of a predominantly noun in an attributive group with reference to Qualia structures, as applied in J. Pustejovsky’s theory of generative lexicon, and their realization through relative adjectives and composites, which are direct explicators of the semantic structure of predominant words (nouns). The study is based on the 150 most frequent relative adjectives identified on the basis of the electronic corpus of the German language. Relative adjectives qualify as Qualia structures and can denote objective constitutive (material and origin), formal (physical parameters, colour, time, place), telic (purpose and function of an object) and agentive (information about the creator, artifact, natural genus and causal chain) properties. The system of relative adjectives demonstrates a wide range of semantic meanings that are expressed in German by other linguistic means, e.g. composites. When describing the possibility of implementing Qualia structures in the noun group, other correlative linguistic units, such as composites, are analyzed. The variation in the use of nouns in composites and relative adjectives formed from them helps to actualize the presence of a feature in a particular situation, to give the nominal groups a terminological character and to make the transition from one qualification group to another.

Odontological Drugs and Their Action on Some Biological Organisms

Odontology is the study of teeth, of theirs diseases and treatment of these. Many odontological drugs are commonly used in dental practice. Antibiotics are indicated for the treatment of odontogenic infections, oral non-odontogenic infections, as prophylaxis against focal infection, and as prophylaxis against local infection and spread to neighboring tissues and organs. In addition to antibiotic, antifungals (drugs for classes azoles, imidazoles and polyenes), antiviral such as antimicrobial mouthwashes and nucleases inhibitors are also indicated for the treatment. These drugs prescription is almost invariably associated with the prescription of Nonsteroidal Antiinflammatory Drugs (NSAIDs), topical corticoids, local anaesthesic for odontological pain and/or Sodium Fluoride for dental caries. Odontalogical drugs act on several levels of metabolism either of microorganisms’ constitutive material (e.g. wall, membrane, cytoplasm and nuclear materials for antibiotics, antivirals, antifungals and oxidizing substances) to destroys them or of humans system cells (receptors, enzymes, hormones for painful, inflammation, local anaesthesic and dental building drugs) to inhibit or stimulate them for the best functioning.

Identification of the LLDPE Constitutive Material Model for Energy Absorption in Impact Applications

Current industrial trends bring new challenges in energy absorbing systems. Polymer materials as the traditional packaging materials seem to be promising due to their low weight, structure, and production price. Based on the review, the linear low-density polyethylene (LLDPE) material was identified as the most promising material for absorbing impact energy. The current paper addresses the identification of the material parameters and the development of a constitutive material model to be used in future designs by virtual prototyping. The paper deals with the experimental measurement of the stress-strain relations of linear low-density polyethylene under static and dynamic loading. The quasi-static measurement was realized in two perpendicular principal directions and was supplemented by a test measurement in the 45° direction, i.e., exactly between the principal directions. The quasi-static stress-strain curves were analyzed as an initial step for dynamic strain rate-dependent material behavior. The dynamic response was tested in a drop tower using a spherical impactor hitting a flat material multi-layered specimen at two different energy levels. The strain rate-dependent material model was identified by optimizing the static material response obtained in the dynamic experiments. The material model was validated by the virtual reconstruction of the experiments and by comparing the numerical results to the experimental ones.

Identification of LLDPE Constitutive Material Model for Energy Absorption in Impact Applications

Current industrial trends bring new challenges in energy absorbing systems. Polymer materials as the traditional packaging material seem to be promising due to their low weight, structure and production price. Based on the review, the linear low-density polyethylene material was identified as the most promising material for absorbing impact energy. The current paper addresses the identification of the material parameters and the development of a Constitutive material model to be used in future design by virtual prototyping. The paper deals with the experimental measurement of the stress-strain relations of the linear low-density polyethylene under static and dynamic loading. The quasi-static measurement is realized in two perpendicular principal directions and is supplemented by a test measurement in the 45 degrees direction, i.e. exactly between the principal directions. The quasi-static stress-strain curves are analyzed as an initial step for dynamic strain rate dependent material behavior. The dynamic response is tested in the drop tower using a spherical impactor hitting the flat material multi-layered specimen at two different energy levels. The strain rate dependent material model is identified by optimizing the static material response obtained in the dynamic experiments. The material model is validated by the virtual reconstruction of the experiments and by comparing the numerical results to the experimental ones.

A nonlinear rotation-free shell formulation with prestressing for vascular biomechanics

We implement a nonlinear rotation-free shell formulation capable of handling large deformations for applications in vascular biomechanics. The formulation employs a previously reported shell element that calculates both the membrane and bending behavior via displacement degrees of freedom for a triangular element. The thickness stretch is statically condensed to enforce vessel wall incompressibility via a plane stress condition. Consequently, the formulation allows incorporation of appropriate 3D constitutive material models. We also incorporate external tissue support conditions to model the effect of surrounding tissue. We present theoretical and variational details of the formulation and verify our implementation against axisymmetric results and literature data. We also adapt a previously reported prestress methodology to identify the unloaded configuration corresponding to the medically imaged in vivo vessel geometry. We verify the prestress methodology in an idealized bifurcation model and demonstrate the significance of including prestress. Lastly, we demonstrate the robustness of our formulation via its application to mouse-specific models of arterial mechanics using an experimentally informed four-fiber constitutive model.

A Methodology for the Statistical Calibration of Complex Constitutive Material Models: Application to Temperature-Dependent Elasto-Visco-Plastic Materials

The calibration of any sophisticated model, and in particular a constitutive relation, is a complex problem that has a direct impact in the cost of generating experimental data and the accuracy of its prediction capacity. In this work, we address this common situation using a two-stage procedure. In order to evaluate the sensitivity of the model to its parameters, the first step in our approach consists of formulating a meta-model and employing it to identify the most relevant parameters. In the second step, a Bayesian calibration is performed on the most influential parameters of the model in order to obtain an optimal mean value and its associated uncertainty. We claim that this strategy is very efficient for a wide range of applications and can guide the design of experiments, thus reducing test campaigns and computational costs. Moreover, the use of Gaussian processes together with Bayesian calibration effectively combines the information coming from experiments and numerical simulations. The framework described is applied to the calibration of three widely employed material constitutive relations for metals under high strain rates and temperatures, namely, the Johnson–Cook, Zerilli–Armstrong, and Arrhenius models.