Simulation of crack generation on a concrete wall

Abstract

One of the applications using computer graphics is landscape simulation, which evaluates the scenery changed by constructing new buildings. The scenery is built with models generated by computer graphics modelling software or image based modelling techniques. The models generated by computer graphics modelling software is beautiful without stains or cracks on the building walls so that some sceneries are built by mapping real images of real buildings onto the walls of the buildings in order to improve the reality. However, even if real images are mapped onto the building walls, the scenery remains the same unless the images change as time passes. Many researchers have been trying to represent stains or cracks on the surfaces of objects built in a virtual space. Cracks on buildings or roads affect the landscape simulation very much so that this paper considers how cracks are generated and how to represent them. A crack is generated by fatigue of materials that construct objects such as buildings or roads in a virtual space, and also the heat at the vertex of a crack affects the process of crack generation. In order to represent cracks on building walls, it is necessary to simulate the process of crack generation, and there are many methods for the simulation. The simplest method is the Mass-Spring model that has some vertices having masses, which are located at several points on the target material, and are connected with springs. FEM (Finite Element Method) is also generally used in the simulation, which divides the target material into finite small elements and calculates the stress in the material. These physically based simulations can generate detailed crack patterns; however, it takes a lot of time for the simulation so that some patterns are generated using leaf venation or Voronoi diagram. In addition, some patterns can be generated by NPR (Non-Photorealistic Rendering). Previous works generated many kinds of crack patterns; however, those were generated on free surfaces on an object and stresses caused by the surrounding materials were not considered. In fact, a concrete wall that constructs a building is surrounded by reinforcing bars, and the crack is generated by the stress due to the reinforcing bars in addition to the gravity. Previous researches also did not consider the change of crack width. The crack can be elongated as time elapses; however, the width did not change even if time passed. Therefore, this paper proposes a simulation method of crack generated on a reinforced-concrete wall with physically based simulation, which method changes the width of crack as time passes. In this paper, we adopt RBSM (Rigid Body Spring Model) for the simulation, which can calculate the inner stress faster than FEM and generate more precise patterns than Mass-Spring model. In addition, we use Delaunay triangulation to generate a variety of crack patterns with small number of elements, and change the crack width by referring to the experimental results of crack on a reinforced-concrete wall. As the result of the simulation, we have succeeded in generating crack patterns on a reinforced-concrete wall, where the crack grew with the width change as time passed. Figure 1 shows the result of the simulation and a real concreate wall. By comparing them, we can see that some parts surrounded by circles are similar.