Experiments,modelling and simulation of adhesive curing processes in bonded three dimensional curved piezo metal composite structures

This contribution deals with the modelling and simulation of curing phenomena in adhesively bonded piezo metal composites which consists of a piezoelectric module enclosed by an adhesive layer which in turn is surrounded by two metal sheets. A short survey on the neccessary experimental investigations to characterise the adhesive's material behaviour is given and important aspects on the corresponding phenomenological modelling approach are presented. Both steps take into account the curing reaction, changes of volume, like chemical shrinkage, and inelastic mechanical behaviour which is temperature and curing dependent. Finally, the simulation strategy for the modelling within a finite element environment is depicted. By this, residual stresses, secondary deformations and loads on the piezo modules can be predicted, which is exemplified by a comparative study verifying a novel manufacturing strategy. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A general modelling framework and specific mechanical approaches to simulate curing phenomena in polymers

Polymers are employed as adhesives, filling or sealing materials, among others. Within these applications, a chemical reaction (e.g. polymerization) leads the materials to cure from a liquid to a solid. In this contribution, first a general continuum mechanical modelling framework for the simulation of curing phenomena is highlighted. It takes into account the main chemical, thermal and mechanical phenomena of polymeric curing processes. Secondly, different mechanical models to capture the mechanical behaviour of polymeric curing processes are regarded. It is shown that elastic, viscoelastic and viscoplastic models at large deformations can be employed. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

FE-simulation of spatially graded gelation during adhesive's curing

In this contribution main aspects of material characterization and modelling of a curing adhesive are denoted. It is pointed out how to deal with the exothermic heat generation during curing, both, how to obtain it experimentally as well as how to account for it in the continuum mechanical an FE-modelling framework. Furthermore, a strategy to simulate spatially graded gelation processes in ANSYS® is presented. An academic simulation example completes this work. By the help of this simulation tool a better understanding of a novel manufacturing process of smart semi-finished light weight structures is ensured. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Sensitivity of Residual Stresses of Cross-Ply Laminates to Manufacturing and Material Parameters

By using a finite-element model elaborated, the sensitivity of residual stresses of polyester/glass cross-ply laminates to manufacturing and material parameters is investigated. The development of residual stresses in the laminates and the significance of the parameters for the problem are discussed. It is found that the main attention in calculating residual stresses should be focused on the properties of resin, which must be measured with care. The most important parameters related to the resin are, of course, its stiffness, thermal expansion, and chemical shrinkage, while the properties of fibers can be obtained from material handbooks with a sufficient accuracy. In curing a thin laminate in an autoclave, the simulation of chemical reactions and the parameters needed in thermal analysis are quite insignificant, because, in practice, the autoclave temperature and the properties of the mold determine the laminate temperature history.     

Carbon Fibre Prepregs: Simulation of a Thermo-Mechanical-Chemical Coupled Problem

In automotive industry research is done to replace high strength steel by combinations of steel and carbon-fibre prepregs (pre-impregnated fibres). It is planned to form both steel and uncured prepregs in one step followed by the curing process under pressure in the forming die. The ability to simulate the mechanical behaviour during forming and curing would allow more economical processes. The simulation of prepregs must regard highly anisotropic, viscoelastic and thermal- chemical properties. For this the model is split into an anisotropic elastic part, which represents the fibre fraction and an isotropic, viscoelastic part, representing the matrix. This part also contains curing, causing a dependency on time and temperature. During deep-drawing large deformations are occurring, so a large strain model regarding anisotropy, viscoelasticity and curing has been developed. Also experiments were made to validate this model. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Degree of cure-dependent modelling for polymer curing processes at small strains

In this paper, a thermodynamically consistent small strain constitutive model is formulated that is directly based on the degree of cure, a key parameter in the curing (reaction) kinetics. The new formulation is also in line with the earlier proposed hypoelastic approach, cf. Hossain et al., 2010. The curing process of polymers is a complex phenomenon involving a series of chemical reactions which transform a viscoelastic fluid into a viscoelastic solid during which the temperature, the chemistry and the mechanics are coupled. Some representative numerical examples conclude the paper and show the capability of the newly proposed constitutive formulation to capture major phenomena observed during the curing processes of polymers. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical investigations on the fixation of cemented and uncemented endoprostheses

In this contribution, a constitutive model adopted from the computational plasticity-models of Drucker-Prager and von Mises is presented. This model captures the material behavior of osseointegration and the curing-process of bone cement. With this basic model, both simulations of bone-ingrowth of uncemented implants and simulations of the curing process of bone cement for cemented implants are carried out in a bone-implant interface. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Homogenization of fibre composites using X-FEM

A successful material design process for novel textile reinforced composites requires an integrated simulation of the material behaviour and the estimation of the effective properties used in a macroscopic structural analysis. In this context the Extended Finite Element Method (X-FEM) is used to model the behavior of materials that show a complex structure on the mesoscale efficiently. A homogenization technique is applied to compute effective macroscopic stiffness parameters. This contribution gives an outline of the implementation of the X-FEM for complex multi-material structures. A modelling procedure is presented that allows for the automated generation of an extended finite element model for a specific representative volume element. Furthermore, the problem of branching material interfaces arising from complex textile reinforcement architectures in combination with high fibre volume fractions will be addressed and an appropriate solution is proposed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A one-dimensional approach to the chemical and thermo-mechanical coupled modeling of curing adhesives including plasticity

The modeling and simulation of curing adhesives is of great importance for industrial applications, mainly for the automotive industry. The one-dimensional model proposed here combines known viscoelastic models for curing material with effects of plasticity. To describe these plasticity effects, a yield stress with isotropic hardening is formulated as an equation of temperature and degree of cure. The proposed model therefore includes viscoelastic properties, thermo-chemical shrinkage and the aforementioned plasticity characteristics, all as functions of temperature and degree of cure. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Towards Modeling the Curing Processes of Thermosets

This contribution presents a newly developed phenomenological model to describe the curing processes of thermosets undergoing small strain deformations [1]. The governing equations are derived from a number of physical and chemical assumptions. Some numerical examples demonstrate the model's capability to correctly represent the evolution of elastic and inelastic material properties as well as the volume shrinkage taking place during the curing process. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parallel multigrid method for finite element simulations of complex flow problems on locally refined meshes

We present a parallel multigrid solver on locally refined meshes for solving very complex three‐dimensional flow problems. Besides describing the parallel implementation in detail, we prove the smoothing property of the suggested iteration for a simple model problem. For demonstration of the efficiency and feasibility of the solver, we show a chemically reactive flow simulation for a Methane burner using detailed chemical reaction modeling. Further, we give the results of an ocean flow simulation. All described methods are implemented in the finite element toolbox Gascoigne. Copyright © 2010 John Wiley & Sons, Ltd.     

The inverse estimation of kinetic parameters of composite materials without using DSC data

Determining the kinetic parameters of a chemical model of the curing process in polymer composites plays an important role in the design of proper cure conditions. The employment of data obtained from the differential scanning calorimetry (DSC) is the main method to estimate the parameters. In this paper, the kinetic parameters are estimated utilizing an inverse heat transfer algorithm and the temperature obtained from a one-dimensional model of cure process without resorting to DSC. The six constants of the Kamal and Sourour model are estimated simultaneously for a composite material by using the Levenberg-Marquardt algorithm. The results of this study agree well with those obtained by experimental methods. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 547–558, July–August, 2008.     

Time and frequency domain finite element implementation of a fully anisotropic linear visco-elastic model

Consistent time and frequency domain formulations for a fully anisotropic, linear visco-elastic material model are presented. The finite element implementation leads to a complex valued stiffness matrix in the frequency domain. A homogenisation procedure based on unit-cell analyses in the frequency domain is presented to derive input parameters for the material model. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wave simulations of Gray‐Scott reaction‐diffusion system

In this work, we study the numerical simulation of the one‐dimensional reaction‐diffusion system known as the Gray‐Scott model. This model is responsible for the spatial pattern formation, which we often meet in nature as the result of some chemical reactions. We have used the trigonometric quartic B‐spline (T4B) functions for space discretization with the Crank‐Nicolson method for time integration to integrate the nonlinear reaction‐diffusion equation into a system of algebraic equations. The solutions of the Gray‐Scott model are presented with different wave simulations. Test problems are chosen from the literature to illustrate the stationary waves, pulse‐splitting waves, and self‐replicating waves.     

Transport of Mass,Momentum and Energy through Periodic Open Cell Metal Foams Applied in Catalysis

An ODE model to predict the temperature field of periodic open cell metal foams applied in catalysis as carrier structures is presented. The catalytic and highly endothermic reaction takes place in a porous layer which surround the struts of the foam and releases gas from a fluid. The one-dimensional model includes dependencies of the foam structure (strut radius, shape of strut), process conditions (surrounding velocity, surrounding fluid: liquid and/or gas), chemical conditions (reaction enthalpy, activation energy) and material parameters (thermal conductivity, density, viscosity). This makes it possible to estimate optimal parameters, that are able to provide sufficient heat to the reaction. The advantage of this model is the substantial time saving in contrary to three dimensional finite volume simulations. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling of bainitic phase transformation

In this work, we present a macroscopic material model for simulation of austenite to bainite and of austenite to martensite transformations accompanied by transformation-induced plasticity (TRIP), which is an important phenomenon in metal forming processes. In order to account for the incubation time the model considers nucleation of the bainite phase. When this quantity attains a barrier term, growth of bainite volume fraction is started. The model formulation allows for individual evolutions of upper and lower bainite. Furthermore, the numerical implementation of the constitutive equations into a finite element program is described. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Object-oriented dynamic supply-chain modelling incorporated with production scheduling

In this paper we present a new modelling approach for realistic simulation of supply-chains. It is based on an object-oriented architecture, which enables flexible specification of the supply-chain configuration along with its operational decisions and policies.A model of a generic supply-chain node is developed to capture the features present in all supply-chain entities. The generic node models in detail activities such as inventory control, manufacturing processes and order handling. The supply-chain model is constructed by linking generic nodes and specifying the physical and business attributes of each supply-chain member. The generic-node model may also be linked to external software for greater accuracy, e.g., detailed production scheduling or optimisation.The model provides a fully dynamic simulation of the supply-chain and the effect of various uncertainties can be evaluated through Monte Carlo simulation and other, more efficient, sampling techniques (not described here).A case study is presented to illustrate the applicability of the model. The case study demonstrates how the effect of policy changes on the supply-chain performance under uncertainty can be evaluated before implementation.