ACM Transactions on Graphics

We present a boundary element based method for fast simulation of brittle fracture. By introducing simplifying assumptions that allow us to quickly estimate stress intensities and opening displacements during crack propagation, we build a fracture algorithm where the cost of each time step scales linearly with the length of the crackfront. The transition from a full boundary element method to our faster variant is possible at the beginning of any time step. This allows us to build a hybrid method, which uses the expensive but more accurate BEM while the number of degrees of freedom is low, and uses the fast method once that number exceeds a given threshold as the crack geometry becomes more complicated. Furthermore, we integrate this fracture simulation with a standard rigid-body solver. Our rigid-body coupling solves a Neumann boundary value problem by carefully separating translational, rotational and deformational components of the collision forces and then applying a Tikhonov regularizer to the resulting linear system. We show that our method produces physically reasonable results in standard test cases and is capable of dealing with complex scenes faster than previous finite- or boundary element approaches

High-resolution brittle fracture simulation with boundary elements

We present a method for simulating brittle fracture under the assumptions of quasi-static linear elastic fracture mechanics (LEFM). Using the boundary element method (BEM) and Lagrangian crack-fronts, we produce highly detailed fracture surfaces. The computational cost of the BEM is alleviated by using a low-resolution mesh and interpolating the resulting stress intensity factors when propagating the high-resolution crack-front. Our system produces physics-based fracture surfaces with high spatial and temporal resolution, taking spatial variation of material toughness and/or strength into account. It also allows for crack initiation to be handled separately from crack propagation, which is not only more reasonable from a physics perspective, but can also be used to control the simulation. Separating the resolution of the crack-front from the resolution of the computational mesh increases the efficiency and therefore the amount of visual detail on the resulting fracture surfaces. The BEM also allows us to re-use previously computed blocks of the system matrix

Example-Based Fractured Appearance

International audienceA common weathering effect is the appearance of cracks due to material fractures. Previous exemplar-based aging and weathering methods have either reused images or sought to replicate observed patterns exactly. We introduce a new approach to exemplar-based modeling that creates weathered patterns on synthetic objects by matching the statistics of fracture patterns in a photograph. We present a user study to determine which statistics are correlated to visual similarity and how they are perceived by the user. We then describe a revised physically-based fracture model capable of producing a wide range of crack patterns at interactive rates. We demonstrate how a Bayesian optimization method can determine the parameters of this model so it can produce a pattern with the same key statistics as an exemplar. Finally, we present results using our approach and various exemplars to produce a variety of fracture effects in synthetic renderings of complex environments. The speed of the fracture simulation allows interactive previews of the fractured results and its application on large scale environments

Efficient Collision Detection for Brittle Fracture

International audienceIn complex scenes with many objects, collision detection plays a key role in the simulation performance. This is particularly true for fracture simulation, where multiple new objects are dynamically created. In this paper, we present novel algorithms and data structures for collision detection in real-time brittle fracture simulations. We build on a combination of well-known efficient data structures, namely distance fields and sphere trees, making our algorithm easy to integrate on existing simulation engines. We propose novel methods to construct these data structures, such that they can be efficiently updated upon fracture events and integrated in a simple yet effective self-adapting contact selection algorithm. Altogether, we drastically reduce the cost of both collision detection and collision response. We have evaluated our global solution for collision detection on challenging scenarios, achieving high frame rates suited for hard real-time applications such as video games or haptics. Our solution opens promising perspectives for complex brittle fracture simulations involving many dynamically created objects

Point Primitives Based Virtual Surgery System

In order to achieve a high degree of visual realism in surgery simulation, we present a virtual surgery system framework, which is based on point primitives for the virtual surgery scene rendering and the biomechanical calculation of the soft tissue. To embody the superiority of this framework, two virtual surgery systems based on point primitives we developed are exhibited in this paper. Six critical functional modules were selected as representative of basic and advanced virtual surgery skill. These modules were: 1) point-based texture mapping; 2) deformation simulation; 3) cutting simulation; 4) tearing simulation; 5) dynamic texture mapping; and 6) 3-D display. These modules were elaborated by including working principle, execution process, and the performance of the algorithm. The experimental results have shown that point primitives-based virtual surgery systems obtained higher performance in terms of computational efficiency and rendering effect than traditional meshes-based virtual surgery system

A Materials Science Driven Pattern Generation Solution to Fracturing Computer Generated Glass for Films and Games

Believably and realistically fracturing computer generated glass for visual effects has been previously solved through various methods such as algorithmic approaches, utilizing texture maps, or finite element analysis. These solutions can achieve some believable results but often at the cost of one or more of the following: simulation time, preparation time, art directability, consistency with materials science research, or the requirement of creating or utilizing fixed assets or maps. In this thesis I present a novel method that draws from the appropriate literature and focuses on quickly generating accurate fracture patterns. The method takes inputs such as the artist’s animation of an impact and desired object properties, and outputs fracture patterns used for breaking objects apart based on input values, materials science literature, and fracture mechanics. After determining all of the fracture pattern variables such as the number of radial and concentric cracks, the artist is able to override the computed parameters to retain control and art directability. Implementation of this method was performed using MAXScript, the built-in scripting language for Autodesk 3ds Max. The result is a computationally fast and mechanically accurate tool while retaining art directability to fulfill film storyboards or game design

IST Austria Thesis

This thesis describes a brittle fracture simulation method for visual effects applications. Building upon a symmetric Galerkin boundary element method, we first compute stress intensity factors following the theory of linear elastic fracture mechanics. We then use these stress intensities to simulate the motion of a propagating crack front at a significantly higher resolution than the overall deformation of the breaking object. Allowing for spatial variations of the material's toughness during crack propagation produces visually realistic, highly-detailed fracture surfaces. Furthermore, we introduce approximations for stress intensities and crack opening displacements, resulting in both practical speed-up and theoretically superior runtime complexity compared to previous methods. While we choose a quasi-static approach to fracture mechanics, ignoring dynamic deformations, we also couple our fracture simulation framework to a standard rigid-body dynamics solver, enabling visual effects artists to simulate both large scale motion, as well as fracturing due to collision forces in a combined system. As fractures inside of an object grow, their geometry must be represented both in the coarse boundary element mesh, as well as at the desired fine output resolution. Using a boundary element method, we avoid complicated volumetric meshing operations. Instead we describe a simple set of surface meshing operations that allow us to progressively add cracks to the mesh of an object and still re-use all previously computed entries of the linear boundary element system matrix. On the high resolution level, we opt for an implicit surface representation. We then describe how to capture fracture surfaces during crack propagation, as well as separate the individual fragments resulting from the fracture process, based on this implicit representation. We show results obtained with our method, either solving the full boundary element system in every time step, or alternatively using our fast approximations. These results demonstrate that both of these methods perform well in basic test cases and produce realistic fracture surfaces. Furthermore we show that our fast approximations substantially out-perform the standard approach in more demanding scenarios. Finally, these two methods naturally combine, using the full solution while the problem size is manageably small and switching to the fast approximations later on. The resulting hybrid method gives the user a direct way to choose between speed and accuracy of the simulation

Approches de remplissage automatique de trous à l'intérieur d'images et de séquences vidéo

À notre époque, les images et les séquences vidéo destinées au cinéma ou à la télévision sont fréquemment altérées durant l’étape de postproduction afin d’effectuer le remplissage de régions indésirables. Par exemple, les graffitis à caractères haineux présents dans une image sont supprimés. Pour produire un résultat de qualité, il est important que le remplissage ait une apparence réaliste et qu’il présente des signes d’usure. Les méthodes actuelles traitant de ce problème ne sont pas adaptées puisqu’elles utilisent des paramètres peu intuitifs et qu’elles traitent généralement d’un seul effet de détérioration. Le remplissage peut aussi se faire sur une séquence vidéo dans laquelle la perche de son a malencontreusement été filmée. Le remplissage de régions manquantes dans une séquence vidéo pose des défis additionnels, comme la cohérence spatio-temporelle et la grande quantité d’information à traiter, et les approches actuelles sont inadaptées. En effet, la plupart des méthodes, dont celles basées sur les champs aléatoires de Markov, ne peuvent traiter directement la haute résolution dans un délai raisonnable. De plus, les méthodes actuelles sont limitées par le type de mouvement de caméra, la taille des régions indésirables et la variation de l’intensité lumineuse. Un objectif de cette thèse est de développer un système de remplissage qui permet la génération d’effets de détérioration basé sur une image échantillon contenant un exemple de l’effet voulu. Pour y arriver, une approche de synthèse de textures par remplissage de trous qui ne comporte aucun paramètre complexe à manipuler par l’artiste et qui permet de reproduire de nouveaux effets similaires est introduite. Un deuxième objectif est l’élaboration d’un système de remplissage de régions manquantes de séquences vidéo de haute définition. Un algorithme de synthèse de textures par remplissage de trous est adapté en tirant profit du principe de la cohérence et d’une recherche locale. De plus, le dernier volet de la thèse présente une approche de remplissage basée sur le suivi de caractéristiques invariantes permettant de compléter de très grandes régions manquantes provenant de séquences vidéo filmées avec des mouvements de caméra non-triviaux. Les résultats obtenus à partir des différentes contributions du projet de recherche montrent un réalisme accru lors du remplissage de régions manquantes d’images et de séquences vidéo. Les différentes méthodes sont faciles d’utilisation et intuitives puisqu’elles ne possèdent aucun paramètre complexe à spécifier par l’artiste. De plus, elles s’intègrent bien dans le processus itératif de création de ce dernier. Finalement, les petits temps de calculs rendent faciles leur intégration dans le pipeline de production des studios

Real-Time Simulation of Brittle Fracture using Modal Analysis

We present a novel physically-based approach for simulating realistic brittle fracture of impacting bodies in real-time. Our method is mainly composed of two novel parts: (1) a fracture initiation method based on modal analysis, (2) a fast energy-based fracture propagation algorithm. We propose a way to compute the contact durations and the contact forces between stiff bodies to simulate the damped deformation wave that is responsible for fracture initiation. As a consequence, our method naturally takes into account the damping properties of the bodies as well as the contact properties to simulate the fracture. To obtain a complete fracture pipeline, we present an efficient way to generate the fragments and their geometric surfaces. These surfaces are sampled on the edges of the physical mesh, to visually represent the actual fracture surface computed. As shown in our results, the computation time performances and realism of our method are well-suited for physically-based interactive applications