3D printed elastomeric polyurethane: Viscoelastic experimental characterizations and constitutive modelling with nonlinear viscosity functions

Digital Light Synthesis (DLS) technology creates ample opportunities for making 3D printed soft polymers for a wide range of grades and properties. In DLS, a 3D printer uses a continuous building technique in which the curing process is activated by an ultra-violet (UV) light. In this contribution, EUP40, a recently invented commercially available elastomeric polyurethane (EPU) printed by the DLS technology, is experimentally characterised. For characterizing the mechanical properties, an extensive viscoelastic experimental study on the digitally printed EPU taking the strain rate-dependence are conducted. The study reveals a significant time-dependency on its mechanical responses. Moreover, the material demonstrates noticeable nonlinear viscosities that depend on strain and strain rates. Based on the experimental findings for the printed elastomer, a large strain viscoelastic model is devised where evolution laws are enhanced by strain and strain rate-dependent nonlinear viscosities. Following identifications of relevant material parameters, we validate the model with the experimental data that show its good predictability. Such an extensive experimental study along with a constitutive model will help in designing and simulating more complex cellular and structured metamaterials using 3D printed elastomeric polyurethanes

On the Performance of Different Architectures in Modelling Elasto-Plasticity with Neural Network

Constitutive models have been utilized to study the mechanical behaviors of solid material. The formulation of constitutive relations is difficult and could be associated with limiting hypothesis. This work proposes neural network-based approaches to reproduce the complex nonlinear constitutive relations of solid materials including elastic behavior and plastic deformation. It is shown that the proposed history-based and internal variable-based strategies can represent exactly the von Mises elasto-plastic material model in uni-axial stress state. Furthermore, close investigation suggests that the internal variable-based approach is most suitable

Uticaj količine azota na prinos i kvalitet odabranih genotipova soje

The aim of the study was to analyze the effect of different amounts of nitrogen on seed yield and quality of selected varieties with different length of vegetation period, specific corn characteristics and from different breeding Institutes. Trials were conducted on tchernozem soil type on the experimental field in the Maize Research Institute in Zemun Polje. Based on the results obtained it can be concluded that all fertilization variants increased the seed yield from 3.6% (P60K60 variant) to 12.2% (N90P60K60 variant). Fertilization variants had lower positive effect by increasing the seed protein content and was from 0.4% (P60K60 variant) to 4.0% (N90P60K60 variant). Negative correlation between seed protein and oil content was determined.U radu je prikazan uticaj različitih količina azota na prinos i kvalitet sorata soje, različite dužine vegetacionog perioda i specifičnih svojstava zrna, iz različitih selekcionih kuća. Istraživanja su obavljena na zemljištu tipa černozem na oglednom polju Instituta za kukuruz u Zemun Polju. Dobijeni rezultati pokazuju da su sve varijante đubrenja povećale prinos zrna soje u intervalu od 3,6% (varijanta đubrenja P60K60) do 12,2%(varijanta N90P60K60). Slabiji efekat varijante đubrenja imale su u pogledu povećanja sadržaja proteina u zrnu soje. Kretao se u intervalu od 0,4% (varijanta đubrenja P60K60) do 4,0%(varijanta N90P60K60). Utvrđena je negativna korelacija između sadržaja proteina i ulja u zrnu soje

On large deformations of thin elasto-plastic shells: implementation of a finite rotation model for quadrilateral shell element

A large-deformation model for thin shells composed of elasto-plastic material is presented in this work. Formulation of the shell model, equivalent to the two-dimensional Cosserat continuum, is developed from the three-dimensional continuum by employing standard assumptions on the distribution of the displacement field in the shell body. A model for thin shells is obtained by an approximation of terms describing the shell geometry. Finite rotations of the director field are described by a rotation vector formulation. An elasto-plastic constitutive model is developed based on the von Mises yield criterion and isotropic hardening. In this work, attention is restricted to problems where strains remain small allowing for all aspects of material identification and associated computational treatment, developed for small-strain elastoplastic models, to be transferred easily to the present elasto-plastic thin-shell model. A finite element formulation is based on the four-noded isoparametric element. A particular attention is devoted to the consistent linearization of the shell kinematics and elasto-plastic material model, in order to achieve quadratic rate of asymptotic convergence typical for the Newton-Raphson-based solution procedures

On implementation of a nonlinear four node shell finite element for thin multilayered elastic shells

A simple non-linear stress resultant four node shell finite element is presented. The underlying shell theory is developed from the three dimensional continuum theory via standard assumptions on the displacement field. A model for thin shells is obtained by approximating terms describing the shell geometry. In this work the rotation of the shell director is parameterized by the two Euler angles, although other approaches can be easily accomodated. A procedure is provided to extend the presented approach by including the through-thickness variable material properties. These may include a general non-linear elastic material with varied degree of orthotropy, which is typical for fibre reinforced composiotes. Thus a simple and efficient model suitable for analysis of multilayered composite shells is attained. Shell kinematics is consistently linearized, leading to the Newton-Raphson numerical procedure, which preserves quadratic rate of asymptotic convergence. A range of linear and non-linear tests is provided and compared with available solutions to illustrate the approac

Mechanical experimentation of the gastrointestinal tract: a systematic review

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in literature (n=247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include i) more human data, allowing for more accurate modelling for applications within medicine, ii) an increase in time-dependent studies, and iii) more sophisticated in vivo testing methods which allow for both the layerand direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies which investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented