Ron Peerlings

On the influence of delamination on laminated paperboard creasing and folding

Laminated paperboard is used as a packaging material for a wide range of products. During production of the packaging, the fold lines are first defined in a so-called creasing (or scoring) operation in order to obtain uncracked folds. During creasing as well as folding, cracking of the board is to be avoided. A mechanical model for a single fold line has been proposed in a previous study (Beex & Peerlings 2009 Int. J. Solids Struct. 46, 4192–4207) to investigate the general mechanics of creasing and folding, as well as which precise mechanisms trigger the breaking of the top layer. In the present study, we employ this modelling to study the influence of delamination on creasing and folding. The results reveal the separate role of the cohesive zone model and the friction model in the description of delamination. They also show how the amount of delamination behaviour should be controlled to obtain the desired high folding stiffness without breaking of the top layer.

Extended modelling of dislocation transport-formulation and finite element implementation

In the past decade, several higher-order crystal plasticity models have been developed to properly capture size effects, dislocation pile-up and patterning. Here we consider a formulation which accounts for the presence and behavior of both positive and negative dislocations in terms of densities. We derive an implicit finite element implementation for the continuum crystal plasticity model including dislocation transport, using a generalised continuum expression for the short-range dislocation interactions, by discretizing the two governing non-linear transport equations in time and space. The resulting non-linear algebraic equations are solved by an incremental-iterative solution scheme. We compare the resulting numerical solutions with discrete dislocation simulations. This analysis shows the capabilities of the implicit FEM framework to solve continuum dislocation transport in crystal plasticity with the added energetic dislocation interactions.

Predicting conducting yarn failure in woven electronic textiles

Smart, electronic textiles are often exposed to tensile stress which can lead to fracture of the interwoven conducting yarns. In this study, a model is proposed to relate the extensibility of the conducting yarns to the weaving pattern of the textile – in particular to the thickness and pitch of the textile yarns. The model is validated by simultaneous mechanical and electrical tests on bare yarns extracted from several textiles. The results show that mechanical failure precedes electrical failure. Thus, a lower and conservative bound for electrical failure can be obtained from the extensibility prediction as a function of the structure of the weave.

Advances in Delamination Modeling of Metal/Polymer Systems: Continuum Aspects

Adhesion and delamination have been pervasive problems hampering the performance and reliability of micro- and nano-electronic devices. In order to understand, predict, and ultimately prevent interface failure in electronic devices, development of accurate, robust, and efficient delamination testing and prediction methods is crucial. Adhesion is essentially a multi-scale phenomenon: at the smallest scale possible, it is defined by the thermodynamic work of adhesion. At larger scales, additional dissipative mechanisms may be active which results in enhanced adhesion at the macroscopic scale and are the main cause for the mode angle dependency of the interface toughness. Undoubtedly, the macroscopic adhesion properties are a complex function of all dissipation mechanisms across the scales. Thorough understanding of the significance of each of these dissipative mechanisms is of utmost importance in order to establish physically correct, unambiguous values of the adhesion properties, which can only be achieved by proper multi-scale techniques.

Micromorphic computational homogenization for mechanical metamaterials with patterning fluctuation fields

Abstract This paper presents a homogenization framework for elastomeric metamaterials exhibiting long-range correlated fluctuation fields. Based on full-scale numerical simulations on a class of such materials, an ansatz is proposed that allows to decompose the kinematics into three parts, i.e. a smooth mean displacement field, a long-range correlated fluctuating field, and a local microfluctuation part. With this decomposition, a homogenized solution is defined by ensemble averaging the solutions obtained from a family of translated microstructural realizations. Minimizing the resulting homogenized energy, a micromorphic continuum emerges in terms of the average displacement and the amplitude of the patterning long-range microstructural fluctuation fields. Since full integration of the ensemble averaged global energy (and hence also the corresponding Euler–Lagrange equations) is computationally prohibitive, a more efficient approximative computational framework is developed. The framework relies on local energy density approximations in the neighbourhood of the considered Gauss integration points, while taking into account the smoothness properties of the effective fields and periodicity of the microfluctuation pattern. Finally, the implementation of the proposed methodology is briefly outlined and its performance is demonstrated by comparing its predictions against full scale simulations of a representative example.

FFT-based interface decohesion modelling by a nonlocal interphase

In this paper, two nonlocal approaches to incorporate interface damage in fast Fourier transform (FFT) based spectral methods are analysed. In FFT based methods, the discretisation is generally non-conforming to the interfaces and hence interface elements cannot be used. This limitation is remedied using the interfacial band concept, i.e., an interphase region of a finite thickness is used to capture the response of a physical sharp interface. Mesh dependency due to localisation in the softening interphase is avoided by applying established regularisation strategies, integral based nonlocal averaging or gradient based nonlocal damage, which render the interphase nonlocal. Application of these regularisation techniques within the interphase sub-domain in a one dimensional FFT framework is explored. The effectiveness of both approaches in terms of capturing the physical fracture energy, computational aspects and ease of implementation is evaluated. The integral model is found to give more regularised solutions and thus a better approximation of the fracture energy.

Integrated Modelling of Damage and Fracture in Sheet Metal Forming

A framework for finite element simulations of ductile damage development and ductile fracture during metal forming is presented. The damage evolution is described by a phenomenological continuum damage model. Crack growth and fracture are treated as the ultimate consequences of the damage process. Computationally, the initiation and growth of cracks is traced by an adaptive remeshing strategy, thereby allowing for opening crack faces. The application of the method to the fabrication of food‐can lids demonstrates its capabilities, but also some of its limitations.

Damage localisation in computational homogenisation of masonry and its incorporation in a two-scale computational framework.

This paper presents a multi-scale framework for the computational study of damage development in masonry walls, based on computational homogenisation techniques.

A Coupled Computational Framework for Ductile Damage and Fracture

Metal forming processes generally introduce a certain amount of damage in the material being formed. Predictions of the damage formation and growth in a series of forming steps may assist in optimising the individual operations and their order. This is particularly true for operations such as cutting and blanking, which rely on the nucleation of damage and cracks in order to separate material. The precise moment and location of crack initiation and the trajectory followed by the crack(s) have an important influence on the quality of the products resulting from these processes. Since the nucleation and growth of cracks may be influenced by damage induced in previous forming steps, simulations require an integral approach towards damage and fracture. For this purpose we have developed a coupled damage-fracture framework, which uses a nonlocal continuum damage approach to model the evolution of material damage and full remeshing to trace the crack growth.

A gradient-enhanced plasticity-damage approach towards modelling of forming processes

This chapter presents a gradient-enhanced coupled damage-plasticity framework, which is used to model damage development and growth in metal forming operations. The constitutive model is based on a hyperelasto-plasticity formulation in which the yield stress is degraded by a ductile damage variable. The evolution of damage depends on the effective plastic strain through an additional partial differential equation, which precludes pathological localization. To allow for realistic simulations of forming processes, the finite element implementation of the model is extended with an adaptive remeshing scheme. Particular attention is given to the robustness of the remeshing and accompanying transfer of state variables. To be able to perform fully, coupled finite element analyzes crack growth in a robust way. The chapter develops the remeshing-transfer algorithm and shows the final finite element discretization obtained with the algorithm for more or less academic problem geometry.