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"Structural mechanics"
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Effect of prestrain on ductility and toughness in a high-strength line pipe steel
Fracture properties of a mother plate for API grade X100 line pipe after pre-straining up to 6% are investigated using tensile notched bars and CT pre-cracked specimens. The material has an anisotropic plastic and damage behavior due to the thermo-mechanical control rolling process. Experiments evidence a decrease in both ductility and toughness for both rolling and long transverse direction with increasing prestrains. This effect is however more pronounced at low prestrain levels (
0
→
2
%
) than at higher levels (
2
→
4
→
6
%
). The modified GTN model proposed by Shinohara et al. (Int J Fract 197:127–145, 2016) is used to represent the database. A good agreement is obtained provided some damage model parameters are modified so as to obtain a slightly higher damage rate for the prestrained materials. This represents the fact that void growth tends to be faster for materials with a lower work hardening rate as evidenced by unit cell calculations. In addition, stress/strain distributions in test specimens are modified for reduced hardening so that stress triaxiality is increased at failure initiation points. This further lowers measured mechanical properties.
Journal Article
Modelling Friction-Induced Dynamic Instability Dedicated for Isogeometric Formulation
Flutter-type dynamic instability induced by friction is a highly nonlinear phenomenon and computationally expensive to model through transient analysis. An efficient way to make inference of such instabilities in a dynamical system is through analyzing the first-order effect of a perturbation at one of its equilibrium with eigenvalue analysis. The contact characteristics of such dynamical systems are typically modelled through the normal compliance approach with inference from experiments. In this case, the dynamical response of the system is implied to be sensitive to the contact stiffness modelled through the normal compliance approach. Typically, with the normal compliance approach, the continuum of the contact interface is approximated through a set of nonlinear springs which can be interpreted as a collocation method. Such approximations or the numerical implication of contact formulations in general for such problems is not largely studied. We focus on a variational formulation-based contact formulation without domain decomposition which is computationally efficient with small sacrifice in accuracy, where we imply that the dynamical response can be robustly modelled with the given accuracy. Further, we expose the inadequacy of the collocation method for such problems, where the dynamical system is observed to be sensitive to the extent of inaccuracy as a result of collocation for low values of contact stiffness. The inferences numerically imply the characteristics of the dynamical system for variation in contact stiffness.
Journal Article
Scaling of structural strength
This book is concerned with a leading-edge topic of great interest and importance, exemplifying the relationship between experimental research, material modeling, structural analysis and design. It focuses on the effect of structure size on structural strength and failure behaviour. Bazant's theory has found wide application to all quasibrittle materials, including rocks, ice, modern fiber composites and tough ceramics. The topic of energetic scaling, considered controversial until recently, is finally getting the attention it deserves, mainly as a result of Bazant's pioneering work. In this new edition an extra section of data and new appendices covering twelve new application developments are included.
* The first book to show the 'size effect' theory of structure size on strength* Presents the principles and applications of Bazant's pioneering work on structural strength * Revised edition with new material on topics including asymptotic matching, flexural strength of fiber-composite laminates, polymeric foam fractures and the design of reinforced concrete beams
eBook
Meeting the Contact-Mechanics Challenge
This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adhesion between indenter and substrate, were specified so that diverse quantities of interest, e.g., the distribution of interfacial stresses at a given load or the mean gap as a function of load, could be computed and compared to a reference solution. Many different solution strategies were pursued, ranging from traditional asperity-based models via Persson theory and brute-force computational approaches, to real-laboratory experiments and all-atom molecular dynamics simulations of a model, in which the original assignment was scaled down to the atomistic scale. While each submission contained satisfying answers for at least a subset of the posed questions, efficiency, versatility, and accuracy differed between methods, the more precise methods being, in general, computationally more complex. The aim of this paper is to provide both theorists and experimentalists with benchmarks to decide which method is the most appropriate for a particular application and to gauge the errors associated with each one.
Journal Article
Model order reduction methods for geometrically nonlinear structures: a review of nonlinear techniques
This paper aims at reviewing nonlinear methods for model order reduction in structures with geometric nonlinearity, with a special emphasis on the techniques based on invariant manifold theory. Nonlinear methods differ from linear-based techniques by their use of a nonlinear mapping instead of adding new vectors to enlarge the projection basis. Invariant manifolds have been first introduced in vibration theory within the context of nonlinear normal modes and have been initially computed from the modal basis, using either a graph representation or a normal form approach to compute mappings and reduced dynamics. These developments are first recalled following a historical perspective, where the main applications were first oriented toward structural models that can be expressed thanks to partial differential equations. They are then replaced in the more general context of the parametrisation of invariant manifold that allows unifying the approaches. Then, the specific case of structures discretised with the finite element method is addressed. Implicit condensation, giving rise to a projection onto a stress manifold, and modal derivatives, used in the framework of the quadratic manifold, are first reviewed. Finally, recent developments allowing direct computation of reduced-order models relying on invariant manifolds theory are detailed. Applicative examples are shown and the extension of the methods to deal with further complications are reviewed. Finally, open problems and future directions are highlighted.
Journal Article