Gradient Smoothing in Finite Elasticity: near-incompressibility

Report (2015)

Error Controlled Adaptive Multiscale Method For Fracture Modelling in Polycrystalline materials

in Philosophical Magazine (2015)

In this paper an adaptive multiscale method is presented in an attempt to address the lack of separation of scales in simulation of fracture. This method is set in the context of FE2 [20] for which ... [more ▼]

In this paper an adaptive multiscale method is presented in an attempt to address the lack of separation of scales in simulation of fracture. This method is set in the context of FE2 [20] for which computational homogenisation breaks down upon loss of material stability (softening). The lack of scale separation due to the coalescence of microscopic cracks in a certain zone is tackled by a full discretisation of the microstructure in this zone. Polycrystalline materials are considered with cohesive cracks along the grain boundaries as a model problem. Adaptive mesh refinement of the coarse region and adaptive initiation and growth of fully resolved regions are performed based on discretisation error and homogenisation error criteria, respectively. In order to follow sharp snap-backs in load-displacement paths, a local arc-length technique is developed for the adaptive multiscale method. The results are validated against direct numerical simulation. [less ▲]

Interfacial shear stress optimization in sandwich beams with polymeric core using non-uniform distribution of reinforcing ingredients

in Composite Structures (2015)

Core shearing and core/face debonding are two common failure states of sandwich beams which are mainly the result of excessive shear stresses in the core. Generally, the core made of homogeneous Fiber ... [more ▼]

Core shearing and core/face debonding are two common failure states of sandwich beams which are mainly the result of excessive shear stresses in the core. Generally, the core made of homogeneous Fiber Reinforced Polymer (FRP) shows better shear resistance in comparison with that made of pure polymer. Usually, this enhancement is however somewhat limited. This paper proposes a methodology to decrease interfacial stresses by presenting the optimal distribution of reinforcing ingredients in the polymeric matrix. For this purpose, a Non-Uniform Rational Bspline (NURBS) based reinforcement distribution optimizer is developed. This technique aims at the local stress minimization within any arbitrary zone of the design domain. In our methodology, optimization and model analysis (calculation of the objective function and the design constraints) have common data sets. The quadratic NURBS basis functions smoothly define the reinforcement distribution function as a NURBS surface. The core and face sheets are modeled as multi-patches and compatibility in the displacement field is enforced by the penalty method. An adjoint sensitivity method is devised to minimize the objective function within areas of interest defined over arbitrary regions in the design domain. It is also used for efficient updating of design variables through optimization iterations. The method is verified by several examples. [less ▲]

Probabilistic multiconstraints optimization of cooling channels in ceramic matrix composites

in Composites. Part B, Engineering (2015), 81

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal ... [more ▼]

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal cooling capacity of all channels (which directly minimizes the amount of coolant needed). In the first step, available uncertainties in the constituent material properties, the applied mechanical load, the heat flux and the heat convection coefficient are considered. Using the Reliability Based Design Optimization (RBDO) approach, the probabilistic constraints ensure the failure due to excessive temperature and deflection will not happen. The deterministic constraints restrict the capacity of any arbitrary cooling channel between two extreme limits. A “series system” reliability concept is adopted as a union of mechanical and thermal failure subsets. Having the results of the first step for CMC with uniformly distributed carbon (C-) fibers, the algorithm presents the optimal layout for distribution of the C-fibers inside the ceramic matrix in order to enhance the target reliability of the component. A sequential approach and B-spline finite elements have overcome the cumbersome computational burden. Numerical results demonstrate that if the mechanical loading dominates the thermal loading, C-fibers distribution can play a considerable role towards increasing the reliability of the design. [less ▲]

Shape optimisation with isogeometric boundary element methods

Presentation (2014, December)

Isogeometric locking-free plate element: a simple first order shear deformation theory for functionally graded plates

in Composite Structures (2014), 118

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first ... [more ▼]

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first-order shear deformation theory (S-FSDT), which was recently presented in Thai and Choi (2013) [11], is naturally free from shear-locking and captures the physics of the shear-deformation effect present in the original FSDT, whilst also being less computationally expensive due to having fewer unknowns. The S-FSDT requires C1-continuity that is simple to satisfy with the inherent high-order continuity of the non-uniform rational B-spline (NURBS) basis functions, which we use in the framework of isogeometric analysis (IGA). Numerical examples are solved and the results are compared with reference solutions to confirm the accuracy of the proposed method. Furthermore, the effects of boundary conditions, gradient index, and geometric shape on the mechanical response of functionally graded plates are investigated. [less ▲]

Multiscale fracture across scales and time

Scientific Conference (2014, November 11)

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a ... [more ▼]

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a clinical error than from an air crash. This is probably the consequence of over a century of experience building, starting with the Wright brothers at the beginning of the 20th century to the most recent aerospace developments culminating in technological giants such as the Airbus A380 and the Boeing Dreamliner, through the enlightening catastrophic events of the "Comet Aircraft”, ``Liberty Ships'' and many others. Yet, with the increasing urge to increase flight efficiency, decrease costs and Carbon emissions, airlines have been pushed to drive down the weight of aircraft, whilst guaranteeing their safety. This push for lighter aircraft has progressively seen a reduction in the use of metallic components which have been slowly replaced by composite materials. Such composite materials are made up of two or more phases of which they exploit the mechanical complementarity. For some applications, such as thermal barrier coatings, thermal complementarity is also leveraged. Yet, these novel materials, and especially their failure mechanisms and durability have proven difficult to understand, both through physical and virtual, in silico, experiments. One of the reasons for this is the large ratio between the size of the smallest constituent relevant in the description of failure mechanisms (e.g. 5-10 micron diameter carbon fibres) and the size of the structure (79m wingspan A380). In this presentation, we will briefly review advances in modeling and simulation of failure across the scales. We will discuss non exhaustively some of the recent advances in this field, ranging from adaptive atomistic modeling of fracture to algebraic model reduction methods for severely non-linear problems, including homogenization. We will also discuss the relevance of such simulations in daily engineering practice and claim that devising interactive simula- tors able to let engineers interact with the composite structure of interest and thus develop intuition about these advanced and complex materials. We will conclude by making a parallel between the difficulties encountered in modeling complex aerospace components and those met in personalized medicine, by discussing briefly the concept of Digital Twin. [less ▲]

Cardiff/Luxembourg Computational Mechanics Research Group

Poster (2014, November)

Discrete Multiscale Modelling and Future Research Plans concerning Metals (presentation)

Presentation (2014, October 14)

Shape optimisation directly from CAD: an isogeometric boundary element approach

Report (2014)