M. Fulland

A new criterion for the prediction of crack development in multiaxially loaded structures

In many cases the lifetime of technical structures and components is depending on the behaviour of cracks. Due to the complex geometry and loading situation in real-world structures cracks are often subjected to a superposition of normal, in-plane and out-of-plane loading. In this paper a new criterion for 3D crack growth under multiaxial loading, that means superposition of the fracture modes Mode I, II and III, is described. The criterion allows the prediction of three-dimensional crack surfaces advancing from arbitrary 3D crack fronts with the help of the two deflection angles φ0 and ψ0. The underlying theory for the development of this new criterion is described in detail.

Finite-Elemente-Simulation im Vergleich zur Realität

Kurzfassung Im vorliegenden Beitrag werden spannungsanalytische und bruchmechanische Untersuchungen zum ICE-Radreifenbruch beschrieben. Das Risswachstum beim ICE-Rad begann am Innenrand des Radreifens. Der Riss wuchs zunächst mehr in die Tiefe des Radreifens, um sich später in halbelliptischer Form auszubreiten. Erst als der Radreifenquerschnitt zu etwa 80% durch das Risswachstum geschädigt war, trat der Bruch des Radreifens ein. Die Bruchfläche weist Farbeffekte und Bruchflächenstrukturen auf, die auf ein sehr diskontinuierliches Risswachstum hindeuten. Es wird aufgezeigt, dass sich das Risswachstum mittels Finite-Elemente-Simulationen und experimenteller Untersuchungen erklären lässt.

Comparison of Computational Crack Path Predictions with Experimental Findings for a Quarter-Circular Surface Crack in a Shaft under Torsion

In this paper the rather complex 3D fatigue crack growth behaviour in a shaft with a quarter-circular crack under torsion is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-model of the shaft are in good agreement with experimental findings for the development of two anti-symmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the free surface of the cylindrical laboratory test-specimens. Consequently, also for this case with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3Dprogramme and the validity of the proposed 3D fracture criterion can be stated.

Finite-Element-Based Fatigue Crack Growth Simulation in Real Structures

In the following paper at first general concepts are introduced, whi ch ave to be considered for the accomplishment of a 3D fatigue crack propagation si mulation by the FE-method in real structures. In doing so numerical aspects concerning the necessary mesh ge neration as well as fracture mechanical issues will be discussed. Furthermore the 3D crack simulation program ADAPCRACK3D, which has been developed at the Institute of Applied Mecha nics t University of Paderborn, is presented in its general functionality. The simulation e xample of the crack propagation in a shutter ring of a hydraulic press shows the practica l usability of both the implemented algorithms and fracture mechanical concepts. Introduction The prediction of crack growth in structures and components is of increa sing relevance in industrial practise due to economic as well as ecologic reasons. In order to s upport this process, the development of eligible simulation tools becomes more and more important . The method of Finite Elements is especially suited for this purpose, as it already i s widely accepted in industry in the field of “classical” stability calculations. Besides the choice of t he appropriated numerical method a reliable simulation of crack growth in a structure requires the know ledge of the general fracture mechanical parameters of the particular material that is under consideration. Those parameters, which especially include the crack growth rate curve in dependence of the local cyclic loading situation, can be obtained by experiments with test specimen. Reasonable approach for crack growth simulations for real structures The accomplishment of a crack growth simulation might generally be carried out by two different approaches. In the first approach it can be attempted to reasonably si mplify the originally complex three-dimensional problem. On the one hand side this could mean, that the probl em is reduced to a 2D one, which has the advantages, that a lot of different 2D-simulation codes are available for such kind of problem and also the calculation time is notably smaller than for full 3D-problems. On the other hand side it also is possible for each problem to refer to a c ert in library, which possibly consists of 3D-crack problems, but of course is restricted by its e xtent, so that an approximation of the real geometry has to be carried out anyway. This strategy e.g. is embarked on by the program NASGRO [1], which is widely spread in aeronautical industries. Whene ver this approach of simplification does not deliver any proper results in terms of a re liabl crack growth prediction, it is necessary to perform a full 3D-simulation, which maintains the orig inal geometrical complexity. However, for this far more complicated approach only very few simula tion programs do exist, e.g. the code ADAPCRACK3D, which recently has been developed at Institute of Applied Mechanics at University of Paderborn. Independently from the simulation code, that is used for a 3D crack cal ulation, there are some general demands and strategies, that have to be taken into considerati on for a simulation by means Key Engineering Materials Online: 2003-10-15 ISSN: 1662-9795, Vols. 251-252, pp 79-84 doi:10.4028/www.scientific.net/KEM.251-252.79

Numeric Simulation of Fatigue Crack Growth in a Material Graded Structure

This article deals with the development of functional graded materials which is pursued by the collaborative research centre Transregio 30. The functional gradation is produced by a thermo-mechanical production process and is characterized by different fracture mechanical specific values. Because cracks are by all means responsible for failure of structural elements crack growth has to be considered during the development of these materials. In this contribution simulations of crack growth which were carried out with the system ADAPCRACK3D are presented to illustrate the influence of a material gradation on crack growth.

Fatigue Crack Growth Simulations and Experimental Findings for SEN-Specimens under Different Loadings

In this paper the rather complex 3D fatigue crack growth behaviour in a SEN-specimens under anti-plane shear or torsion loading is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-models of the specimens are in good agreement with experimental findings for the development of two antisymmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the free surfaces of the laboratory SEN test-specimens. Consequently, also for these cases with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3D-programme and the validity of the proposed 3D fracture criterion can be stated.

Experimental and Numerical Investigation of 3D Mixed-Mode Crack Problems in Structures

Fracture processes in real structures are in many cases of a three dimensional (3D) character. In this paper some basic problems of 3D-fracture processes are considered and discussed, in particular for general mixed-mode loading conditions, when modes I and II and III are superimposed. For experimental investigations an AFM-specimen is under consideration, while numerical simulations are carried out with the program ADAPCRACK3D.