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1

Nonlinear static analysis of truss core sandwich beams in three-point bending test

Wesolowski Miroslaw, Ruchwa Mariusz, Rucevskis Sandris

Archives of Civil Engineering

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2023

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Vol. 69, nr 4

459--475

EN

An analysis of sandwich beams with truss core is an important issue in many fields of industry such as civil engineering, automotive, aerospace or maritime. The objective of the present study is a nonlinear static response of sandwich beams subjected to the three-point bending test configuration. The beams are composed of two parent components: upper and lower laminated face sheets (unidirectional tape) and a pyramidal truss core manufactured by means of 3D printing. A polyamide filament strengthened with chopped carbon fibres – CF-PA-12 is used for the core development. The both, experimental and numerical analyses are presented. A detailed numerical model of the sandwich beam was developed in Abaqus software. The numerical model considers modelling of the adhesive joint with an additional layer of material placed between the parent components of the beam. A continuum hybrid solid shell elements were used to model the adhesive layer. In addition, a special care was taken to use an appropriate material model for the CF-PA-12 filament. To do so, the uniaxial tensile tests were performed on 3D printed samples. Having acquired the test data, a hyperelastic material model was evaluated based on a curve fitting approach.

PL

Kompozytowe struktury przekładkowe z wypełnieniem kratownicowym (typu sandwich) są wytwarzane w postaci płyt, belek, oraz powłok cylindrycznych. Kompozyty te zbudowane są głównie z dwóch materiałów macierzystych, tj. okładzin zewnętrznych w postaci cienkich płyt lub taśm oraz wypełnienia wewnętrznego o geometrii przestrzennej kratownicy. Struktury te mogą być traktowane jako elementy konstrukcyjne ze względu na ich znakomite wskaźniki sztywności i wytrzymałości w stosunku do masy. Ponadto, ich komórkowa budowa poprawia możliwości wentylacyjne oraz umożliwia prowadzenia instalacji pomiędzy poszczególnymi komórkami całej struktury. Powoduje to, że oprócz funkcji nośnych, struktury te stanowią również elementy funkcjonalne. Zalety struktur przekładowych przyczyniły się do zintensyfikowania badań naukowych w zakresie analiz statycznych. Jako, że struktury te stanowią kompozyt, ich właściwości mechaniczne przyjmują różnorodne cechy w zależności od schematu obciążenia. Pociąga to za sobą dodatkowe trudności w procesie modelowania takich konstrukcji ze względu na bardzo szeroki zakres materiałów stosowanych do ich budowy oraz połączeń między nimi. Różnorodność ta przejawia się już w doborze okładzin zewnętrznych, które są wykonywane z trzech grup materiałów, tj. metali lub ich stopów (np. aluminium), laminatów warstwowych (np. laminaty włókniste), materiałów organicznych (np. sklejka). Kolejną kwestią jest materiał stosowany na budowę komórkowej warstwy wypełnienia. Ograniczając się do jednej geometrii tej warstwy, tj. do postaci przestrzennej kratownicy, materiałami stosowanymi do ich budowy, poza wyżej wspomnianymi, są polimery wytwarzane techniką przyrostową. Niestety zdecydowana większość opracowań naukowych pozostawia bez komentarza kwestie modelowania oraz nośności połączeń adhezyjnych w powyższych strukturach. W bieżącej pracy założono przeprowadzenie analizy statycznej wg schematu trzypunktowego zginania. W procesie budowy modelu numerycznego uwzględniono połączenia klejone pomiędzy elementami macierzystymi belki poprzez wprowadzenie dodatkowego materiału adhezyjnego. Do modelowania polimerowego wypełnienia kratownicowego (CF-PA-12) zastosowano hipersprężysty model materiału. Parametry sprężyste modelu materiałowego oszacowano na podstawie statycznej próby rozciągania próbek wytworzonych techniką przyrostową. Weryfikacja poprawności opracowanego modelu MES przeprowadzona została na podstawie porównania obliczeń numerycznych z przeprowadzonymi pomiarami laboratoryjnymi, uzyskując dużą zbieżność wyników. Przeprowadzone badania pozwoliły na opracowanie modelu numerycznego belki przekładkowej z uwzględnieniem warstwy adhezyjnej. Wykony model numeryczny belki może służyć do prognozowania jej odpowiedzi statycznej. Zastosowanie kontynualnych elementów skończonych pozwoliło na znaczną redukcję ilości elementów po grubości warstwy adhezyjnej.

2

Bio inspired salamander robot with Pneu-Net Soft actuators – design and walking gait analysis

Natarajan Elango, Chia Kwang Y., Faudzi Ahmad Athif Mohd, Lim Wei Hong, Ang Chun Kit, Jafaari Ali

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

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Vol. 69, nr 3

art. no. e137055

EN

The research was attempted to mimic the locomotion of the salamander, which is found to be one of the main animals from an evolutionary point of view. The design of the limb and body was started with the parametric studies of pneumatic network (Pneu-Net). Pneu-Net is a pneumatically operated soft actuator that bends when compressed fluid is passed inside the chamber. Finite Element Analysis software, ANSYS, was used to evaluate the height of the chamber, number of chambers and the gap between chambers for both limb and body of the soft mechanism. The parameters were decided based on the force generated by the soft actuators. The assembly of the salamander robot was then exported to MATLAB for simulating the locomotion of the robot in a physical environment. Sine-based controller was used to simulate the robot model and the fastest locomotion of the salamander robot was identified at 1 Hz frequency, 0.3 second of signal delay for limb actuator and negative π phase difference for every contralateral side of the limbs. Shin-Etsu KE-1603, a hyper elastic material, was used to build the salamander robot and a series of experiments were conducted to record the bending angle, the respective generated force in soft actuators and the gait speed of the robot. The developed salamander robot was able to walk at 0.06774 m/s, following an almost identical pattern to the simulation.

3

Identifying the Poly Methyl Methacrylate behavior during free thermoforming using experimental tests and numerical simulation

Sattarian Mansour, Ghassemi Aazam

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 4

909--921

EN

Thermoforming is one of the new methods for forming of polymer sheets. Free thermoforming is one of the thermoforming methods in which shaping is done with air pressure or vacuum without the plug mold. In this paper, free thermoforming of Poly Methyl Methacrylate (PMMA) has been investigated by experimental tests and finite element simulation. The main purpose of this article is the identification of the real behavior of PMMA during free thermoforming to achieve maximum workable air pressure with respect to initial thickness. For this, at first, tensile and relaxation tests have been done in working temperature (160◦C). Then the process was simulated by Abaqus software with considering four types of the material property: three hyperelastic models (Ogden, Mooney-Rivlin, and Marlow) and a hyperviscoelastic model. After that, experimental tests were done, and the samples final shape were compared with simulation results. Accordingly, the simulation results obtained based on the Marlow hyperelastic model showed the best agreement with the experiments compared to others. After that, maximum workable air pressure versus plate initial thickness and minimum thickness of the deformed plate were achieved by finite element simulation.

4

Digital materials – evaluation of the possibilities of using selected hyperelastic models to describe constitutive relations

Mańkowski J., Lipnicki J.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 3

601--612

EN

The authors tried to identify the parameters of numerical models of digital materials, which are a kind of composite resulting from the manufacture of the product in 3D printers. With the arrangement of several heads of the printer, the new material can result from mixing of materials with radically different properties, during the process of producing single layer of the product. The new material has properties dependent on the base materials properties and their proportions. Digital materials tensile characteristics are often non-linear and qualify to be described by hyperelastic materials models. The identification was conducted based on the results of tensile tests models, its various degrees coefficients of the polynomials to various degrees coefficients of the polynomials. The Drucker’s stability criterion was also examined. Fourteen different materials were analyzed.

5

Elastic constants influence on the L4-L5-S1 annuli fibrosus behavior, a probabilistic finite element analysis

Jaramillo H. E., Garcia J. J.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 4

3--12

EN

A probabilistic finite element (FE) analysis of the L4-L5 and L5-S1 human annulus fibrosus (AF) was conducted to obtain a better understanding of the biomechanics of the AF and to quantify its influence on the range of motion (ROM) of the L4-L5 and L5-S1 segments. Methods: The FE models were composed of the AF and the upper and lower endplates. The AF was represented as a continuous material composed of a hyperelastic isotropic Yeoh matrix reinforced with two families of fibers described with an exponential energy function. The caudal endplate was fully restricted and 8 Nm pure moment was applied to the cranial endplate in flexion, extension, lateral flexion and axial rotation. The mechanical constants were determined randomly based on a normal distribution and average values reported. Results: Results of the 576 models show that the ROM was more sensitive to the initial stiffness of the fibers rather than to the stiffening coefficient represented in the exponential function. The ROM was more sensitive to the input variables in extension, flexion, axial rotation and lateral bending. The analysis showed an increased probability for the L5-S1 ROM to be higher in flexion, extension and axial rotation, and smaller in lateral flexion, with respect to the L4-L5 ROM. Conclusions: An equation was proposed to obtain the ROM as a function of the elastic constants of the fibers and it may be used to facilitate the calibration process of the human spine segments and to understand the influence of each elastic constant on the ROM.

6

Corneal hyper-viscoelastic model: derivations, experiments, and simulations

Su P., Yang Y., Song Y

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 2

73--84

EN

Purpose: The aim of this study is to propose a method to construct corneal biomechanical model which is the foundation for simulation of corneal microsurgery. Methods: Corneal material has two significant characteristics: hyperelastic and viscoelastic. Firstly, Mooney–Rivlin hyperelastic model of cornea obtained based on stored-energy function can be simplified as a linear equation with two unknown parameters. Then, modified Maxwell viscoelastic model of the cornea, whose analytical form is consistent with the generalized Prony-series model, is proposed from the perspective of material mechanics. Results: Parameters of the model are determined by the uniaxial tensile tests and the stress-relaxation tests. Corneal material properties are simulated to verify the hyper-viscoelastic model and measure the effectiveness of the model in the finite element simulation. On this basis, an in vivo model of the corneal is built. And the simulation of extrusion in vivo cornea shows that the force is roughly nonlinearly increasing with displacement, and it is consistent with the results obtained by extrusion experiment of in vivo cornea. Conlusions: This paper derives a corneal hyper-viscoelastic model to describe the material properties more accurately, and explains the mathematical method for determination of the model parameters. The model is an effective biomechanical model, which can be directly used for simulation of trephine and suture in keratoplasty. Although the corneal hyper-viscoelastic model is taken as the object of study, the method has certain adaptability in biomechanical research of ophthalmology.

7

Simulation of Energy Dissipation During Impacts with Hyperelastic Elements

Osiński J., Rumianek P.

Machine Dynamics Research

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2012

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Vol. 36, No. 2

64-75

EN

The aim of this article is to analyze the possibility of energy dissipation during the impact a pedestrian by a vehicle. The energy created during the impact will be dissipated by element of protection made of a hyperdeformable material. Energy intensive structures are able to take over the kinematic energy during impact, which is equivalent to the work of their destruction (crushing, breaking). This has the effect of increasing pedestrian safety during the accident to fulfillment of the regulation of the European Parliament and Council Regulation (WE) No 78/2009 of 14 January 2009 with all amendments. Ensuring the safety and reduce pedestrian injuries during an accident is very important. Presented in work method of analysis of polyurethane materials, hyperdeformable with using the Finite Element Method can demonstrate how important it is to conduct researches to increase security. Exercising studies of materials using the FEM can verify used materials, and thus, drawing conclusions and present proposals for the use of new materials with improved properties. To describe the properties of the foam will be used previously known theories: hyperelstic materials and properties of elastic-plastic materials, including volumetric plastic deformations. The results of experimental studies will enable determine the model of to the foam and use it in calculations using the Finite Element Method of ABAQUS system. Explicit calculation of the dynamic module of the ABAQUS system is used to simulate impact of a bumper with protective element in the under-bumper beam to the pedestrian, will be analyzed the degree of energy dissipation. Simulation will allow an assessment of the effectiveness pedestrian protection - the operation of protection element.

8

Application of Modified Ogden’s Model for Describing Features of Composites with Gas Phase

Osiński J., Rumianek P.

Machine Dynamics Research

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2012

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Vol. 36, No. 2

76-83

EN

In modem technology, more widely are used the composites with the gas phase - porous structures with pores closed, filled the gas. Can find here polymeric materials: EPP polyurethanes used in automobile bumpers, CELLASTO polyurethane in suspension systems. To the same group may also include gazars - composites reinforced by gas, and thus structure, in which the gas in the closed pores is subjected to initial pressure. Gazars are made as the structure of metal, usually copper, carbon dioxide or a mixture of gases. The aim of this work is to develop methods of describing the properties of such materials based on knowledge of: basic materials, technologies (gas pressure formed during foaming) using the theory of hyperplastic materials, in particular using Ogden’s model and its modifications. The resulting description can be used for the applicability of hyperelstic models, and therefore in the whole range of deformation of the polymer-based composites and elastic composites of metals (not included plasticity). Verification of the method is carried out through the execution of experimental EPP foam polyurethane derived from car bumpers, enabling a better understanding of materials and will be able to better modify structures, and thus, improve the mechanical properties.

9

Method and device for in-vivo measurement of elasto-mechanical properties of soft biological tissues

Vuskovic V., Kauer M., Dual J., Bajka M.

Machine Graphics and Vision

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1999

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Vol. 8, No. 4

637-654

EN

We present a method to determine elasto--mechanical properties of soft biological tissues, and a device able to perform the required measurements in-vivo. The device permits the controlled application of vacuum to small spots of organic tissue and registers the small deformation caused, during the whole measurement process. Deformation is measured with a vision based technique and the grabbed images are processed in real-time to avoid storage problems. We model biological tissue with a hyperelastic quasilinear viscoelastic material law and determine the unknown material parameters via inverse finite element methods.