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1

Novel rheological modelling of thermosets and unidirectional monotropic fibre-reinforced thermoset matrix composites

Klasztorny Marian, Nycz Daniel B.

Composites Theory and Practice

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2023

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R. 23, nr 1

3--21

EN

A refined, fully analytical rheological modelling of thermosetting polymers and unidirectional monotropic fibre-reinforced thermoset matrix (UFRT) composites is presented. New polymers and composites under normal conditions, fully relaxed from curing and post-curing stresses, are modelled. The theory includes quasi-static short-term/medium-term/long-term reversible rheological processes. Thermosets are isotropic materials exhibiting linearly viscoelastic shear strains and linearly elastic bulk strains. Fibres are monotropic (transversely isotropic) and linearly elastic materials. A generic function well reproducing the viscoelastic characteristics of thermosets and UFRT composites is a Mittag-Leffler fractional exponential function in an integral form. Coupled/uncoupled standard/inverse constitutive equations of linear rheology are formulated for thermosets and UFRT composites. The equations are mutually analytically transformable. New rheological models (coded H-R/H) for thermosets and UFRT composites are described by the smallest possible number of material constants. The thermoset is described by two independent elastic constants and three independent viscoelastic constants. The homogenized UFRT composite is described by five independent elastic constants and four independent viscoelastic constants, whereby two visco-elastic constants are common to the matrix and the composite. An improved homogenization theory of UFRT composites, based on analytical solutions of the selected tasks of the theory of linear elasticity, is formulated for monotropic fibres and positively validated experimentally. The viscoelastic constants of the thermoset are calculated analytically in an iterative loop using a long-term unidirectional tension creep experimental test. The viscoelastic constants of the UFRT composite are calculated analytically employing H-R/H shear/quasi-shear storage compliances and VECP (the viscoelastic-elastic correspondence principle) shear/quasi-shear storage compliances. The H-R/H rheological model was validated numerically for selected UFRT composites. The validation tests were performed on the enhanced reliability UFRT composites reported by Soden, Hinton, and Kaddour (Composites Science and Technology, 1998, 2002).

2

Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

Xiao Wenchao, Wang Baoyu

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 1

134--143

EN

The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300–450 °C and stamping speeds of 13–40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.

3

Thermal Properties of Functionally Graded Fibre Material

Turant J., Radaszewska E.

Fibres & Textiles in Eastern Europe

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2016

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Vol. 24, no. 4 (118)

68--73

EN

In this paper the problem of modelling graded materials in the form of a fibre composite with varying fibre diameter is considered. The aim of modelling was to determine the micro and macroscopic thermal properties of this type of material, in which the average thermal conductivity in relation to fibre saturation changes was calculated at any point of fibre FGM, and then the effective thermal conductivity of a whole layer of the material was determined. To do that, a unit cell of the material of given structure was isolated and the onedimensional heat flux passing through it was considered. As an effect of the investigation, the procedure of effective thermal conductivities calculation was presented and illustrated with a numerical example. Additionally the discrete and continuous approach to the effective thermal conductivities calculations were analysed and compared.

PL

W pracy zajęto się problemem modelowania włóknistych materiałów gradientowych o zmiennej średnicy włókien. Celem modelowania było określenie mikro i makro własności termicznych tego typu materiałów. Konsekwentnie, w dowolnym punkcie materiału gradientowego obliczono średni współczynnik przewodzenia ciepła w kierunku zmian nasycenia kompozytu włóknami a następnie określono efektywną przewodność cieplną całej warstwy materiału. W tym celu wyodrębniono elementarną komórkę materiału o określonej strukturze i rozpatrzono dla niej jednowymiarowy przepływ ciepła. Zaprezentowaną metodologię obliczania zastępczych współczynników ciepła zilustrowano numerycznym przykładem. Dodatkowo przeanalizowano i porównano dyskretne i ciągłe podejście do obliczenia zastępczych współczynników przewodzenia ciepła.

4

New open-source ANSYS-SolidWorks-FLAC3D geometry conversion programs

Bock S.

Journal of Sustainable Mining

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2015

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Vol. 14, iss. 3

124--132

EN

Numerical calculations are used increasingly often to obtain a stress-strain state in many engineering problems. A popular program for this type of calculation which makes use of the finite difference method (a continuous method) is Itasca's FLAC3D. However, an important limitation of FLAC3D is the difficulty of geometry creation. This paper presents new open-source programs allowing the preparation of numerical models in a third-party software (ANSYS, SolidWorks) and their conversion to internal FLAC3D geometry files. The converters have been written in BASH-scripting language and published under the terms of the GNU General Public License, which allows the free distribution and/or modification of the software with some limitations.

5

Numerical modelling of a void behind shaft lining using FDM with a concrete spalling algorithm

Bock S.

Journal of Sustainable Mining

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2014

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Vol. 13, iss. 2

14--21

EN

Purpose: The aim of the research presented in this paper was to determine the impact of voids behind the lining on shaft stability. Methods: This paper presents an example of extending the FLAC3D with the possibility of the simulation of concrete detachment and separation under specific conditions by means of a developed FISH routine. Results: The appearance of voids and cavities behind the lining has been repeatedly observed in active shafts in Polish coal mines and can lead to the emergence of tensile forces in the lining. The study included 366 models of shafts using the rock mass properties of typical shale stone, coal, and sandstone found in the Upper Silesian Coal. Practical implications: The presented concrete spalling algorithm may be used, especially, for the stability evaluation of locally damaged shaft lining or when there is a suspicion of void behind the lining. Originality/ value: An important limitation of all continuous methods is the inability (except when using some additional tools) to simulate the rotations of predefined elements (blocks) and their separation from the rest of the object. The concrete spalling algo-rithm presented extends the capabilities of FLAC3D with the possibility of simulating the detachment and separation of destroyed lining fragments.

6

ANN constitutive material model in the shakedown analysis of an aluminum structure

Potrzeszcz-Sut B., Pabisek E.

Computer Assisted Methods in Engineering and Science

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2014

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Vol. 21, no. 1

49--58

EN

The paper presents the application of artificial neural networks (ANN) for description of the Ramberg-Osgood (RO) material model, representing the nonlinear strain-stress relationship of ε(σ). A neural model of material (NMM) is a feed-forward layered neural network (FLNN) whose parameters were determined using the penalized least squares (PLS) method. A FLNN performing the inverse problem: σ(ε), using pseudo empirical patterns, was developed. Two models of NMM were developed, i.e. a standard model (SNN) and a model based on Bayesian inference (BNN). The properties of the models were compared on the example of a reference truss structure. The computations were performed by means of the hybrid FEM/NMM program, in which NMM developed previously described the current model of the material, and made it possible to explicitly build a tangent operator Et = dσ/dε. The neural model of material was applied to the analysis of the shakedown of load carrying capacity of an aluminum truss.

7

On Finite Element Modelling of Architectural Fabrics for Ganging Roofs

Ambroziak A., Kłosowski P., Woźnica K.

Machine Dynamics Problems

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2006

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Vol. 30, No. 2

7-17

EN

This paper deals with the constitutive modelling and identification of coated woven fabrics properties. The authors give brief characterization of the constitutive models used for the material modelling and discuss in details the fundamental equations of the dense net model. The special identification method of the non-linear elastic properties of the coated fabric is presented. The material parameters are determined on the base of uniaxial tensile tests in the warp and weft directions. For the identification process, techniques using the least squares method are applied. Additionally, the results of the uniaxial tension tests are compared with biaxial tension tests.

8

Material modelling for structures subjected to impulsive loading

Cichocki K., Adamczyk R., Ruchwa M.

Computer Assisted Mechanics and Engineering Sciences

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1999

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Vol. 6, No. 2

231-244

EN

The main results of numerical analyses of a possible design configuration of a submerged structure subjected to impulsive loading due to explosion, performed for various material models assumed for a plain concrete are presented and discussed. Three different models were considered - the modified Drucker-Prager plasticity model, brittle cracking model and the elastoplastic model with damage. The present study suggests problems and possible solutions to be applied into numerical analysis of such structures by means of available finite element computer codes.