An adaptive space-time phase field formulation for dynamic fracture of brittle shells based on LR NURBS

We present an adaptive space-time phase field formulation for dynamic fracture of brittle shells. Their deformation is characterized by the Kirchhoff–Love thin shell theory using a curvilinear surface description. All kinematical objects are defined on the shell’s mid-plane. The evolution equation for the phase field is determined by the minimization of an energy functional based on Griffith’s theory of brittle fracture. Membrane and bending contributions to the fracture process are modeled separately and a thickness integration is established for the latter. The coupled system consists of two nonlinear fourth-order PDEs and all quantities are defined on an evolving two-dimensional manifold. Since the weak form requires C1-continuity, isogeometric shape functions are used. The mesh is adaptively refined based on the phase field using Locally Refinable (LR) NURBS. Time is discretized based on a generalized-α method using adaptive time-stepping, and the discretized coupled system is solved with a monolithic Newton–Raphson scheme. The interaction between surface deformation and crack evolution is demonstrated by several numerical examples showing dynamic crack propagation and branching

Crack propagation in thin shells by explicit dynamics solid-shell models

A computational technique for the simulation of crack propagation due to cutting in thin structures is proposed. The implementation of elastoplastic solid-shell elements in an explicit framework is discussed. Finally, in the case of crack propagation, the issue of the selection of a propagation criterion is briefly discussed. Crack propagation is modelled making use of a so called “directional” cohesive approach

Numerical product design: Springback prediction, compensation and optimization

Numerical simulations are being deployed widely for product design. However, the accuracy of the numerical tools is not yet always sufficiently accurate and reliable. This article focuses on the current state and recent developments in different stages of product design: springback prediction, springback compensation and optimization by finite element (FE) analysis. To improve the springback prediction by FE analysis, guidelines regarding the mesh discretization are provided and a new through-thickness integration scheme for shell elements is launched. In the next stage of virtual product design the product is compensated for springback. Currently, deformations due to springback are manually compensated in the industry. Here, a procedure to automatically compensate the tool geometry, including the CAD description, is presented and it is successfully applied to an industrial automotive part. The last stage in virtual product design comprises optimization. This article presents an optimization scheme which is capable of designing optimal and robust metal forming processes efficiently

Tools for quantitative form description : an evaluation of different software packages for semi-landmark analysis

The challenging complexity of biological structures has led to the development of several methods for quantitative analyses of form. Bones are shaped by the interaction of historical (phylogenetic), structural, and functional constrains. Consequently, bone shape has been investigated intensively in an evolutionary context. Geometric morphometric approaches allow the description of the shape of an object in all of its biological complexity. However, when biological objects present only few anatomical landmarks, sliding semi-landmarks may provide good descriptors of shape. The sliding procedure, mandatory for sliding semi-landmarks, requires several steps that may be time-consuming. We here compare the time required by two different software packages ('Edgewarp' and 'Morpho') for the same sliding task, and investigate potential differences in the results and biological interpretation. 'Morpho' is much faster than 'Edgewarp,' notably as a result of the greater computational power of the 'Morpho' software routines and the complexity of the 'Edgewarp' workflow. Morphospaces obtained using both software packages are similar and provide a consistent description of the biological variability. The principal differences between the two software packages are observed in areas characterized by abrupt changes in the bone topography. In summary, both software packages perform equally well in terms of the description of biological structures, yet differ in the simplicity of the workflow and time needed to performthe analyses

Multiscale computational first order homogenization of thick shells for the analysis of out-of-plane loaded masonry walls

This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic brick-masonry walls. The proposed method is designed for the analysis of shells whose micro-structure is heterogeneous in the in-plane directions, but initially homogeneous in the shell-thickness direction, a structural topology that can be found in single-leaf brick masonry walls. Under this assumption, this work proposes an efficient homogenization scheme where both the macro-scale and the micro-scale are described by the same shell theory. The proposed method is then applied to the analysis of out-of-plane loaded brick-masonry walls, and compared to experimental and micro-modeling results.Peer ReviewedPostprint (author's final draft

Textile hybrid kinetic adaptive structures: a case study

Dissertação de mestrado integrado em Engenharia CivilThis thesis has the main objective to study three distinct typologies of structures. These structures are, form-active structures, in particular membrane structures, bending-active structures and the integration of both concepts with a kinetic principle, therefore adaptive hybrid structures. Both membrane and bending-active are structures that require form finding, since the form of these structures is dependent on the loading and boundary conditions, thus only known a posteriori. These structures are subject to large deformations and thus, geometric nonlinearities must be considered during the calculation. Additionally, the flexibility of membrane structures conjugated with the elastic behaviour of bending-active structures creates the perfect conditions for the development of hybrid kinetic structures that adapt according to the external loading conditions present. This study intends to elaborate an exploratory approach on these concepts, thus bringing forward the main problems that originate when analysing a structure of this type. Therefore, firstly a study on membrane, bending-active, hybrid and kinetic structures is presented, containing the most relevant knowledge that currently exists regarding these topics. Then, the structural aspects that are inherent to these structures are exposed. Three routines are developed in Sofistik® in order form find and calculate the above-mentioned structures. Validations are made on these routines and software analysis. The structural feasibility of an architectural concept proposed by Costa (2017) of a hybrid adaptive concept is studied by applying these routines, and the kinetic hybrid concept is simulated in Sofistik®. The adaptive principle is also extended to function structurally, by taking advantage of the bending prestress implied by the bending-active elements. Finally, external wind loads are applied to this structure, in order to test the effectiveness of the structural adaptive concept. It was concluded that there is significant importance of the bending adaptive movement in the loadbearing capacity of the overall system. Additionally, the choice of the initial shape of the structure defines a crucial step on the definition of the structure, since it affects the process of form finding, that latter affects the structural performance.A presente dissertação tem como objetivo principal estudar três tipologias distintas de estruturas. Estas estruturas são as estruturas de forma ativa, particularmente as estruturas em membrana, as estruturas de flexão ativa e a integração de ambos os conceitos com um princípio cinético, ou seja, estruturas hibridas adaptativas. Tanto as estruturas de membranas como as estruturas de flexão ativa são estruturas que requerem determinação da forma pois, como a forma destas estruturas é dependente das condições de tensão e de fronteira, apenas é conhecida a posteriori. Estas estruturas estão sujeitas a grandes deformações e, portanto, as não linearidades geométricas devem ser consideradas durante o cálculo. Para além disto, a flexibilidade das estruturas de membrana conjugada com o comportamento elástico das estruturas de flexão ativa geram condições perfeitas para o desenvolvimento de estruturas cinéticas hibridas que se adaptam de acordo com as condições de carregamento presentes. Este estudo pretende elaborar uma aproximação exploratória a estes conceitos, trazendo para primeiro plano os principais problemas originários da análise deste tipo de estruturas. Desta forma, primeiramente é apresentado um estudo sobre estruturas de membrana, flexão ativa, hibridas e cinéticas, contendo a informação mais relevante que existe atualmente sobre estes assuntos. De seguida, os aspetos estruturais inerentes a estas estruturas são expostos. Três rotinas são desenvolvidas no Sofistik® de forma a determinar a forma e calcular as estruturas anteriormente mencionadas. São realizadas validações destas rotinas e da análise preconizada pelo software. A viabilidade estrutural de um conceito de arquitetura proposto por Costa (2017) sobre uma estrutura hibrida adaptativa é estudada através da aplicação destas rotinas, e o princípio cinético hibrido é simulado através do Sofistik®. O princípio adaptativo é alargado de modo a funcionar estruturalmente, tirando partido da pretensão implícita pelos elementos de flexão ativa. Finalmente, são aplicadas cargas externas de vento à estrutura, de forma a testar a eficácia do principio adaptativo estrutural. Foi concluído que o movimento adaptativo de flexão tem uma importante significância ao nível da carga admissível na estrutura. Adicionalmente, a escolha da geometria inicial da estrutura define uma etapa fundamental na definição da estrutura, pois afeta o processo de form finding, que mais tarde afeta o desempenho estrutural