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 Pattern Languages of Program Design 3
, 1997
"... c. 360 BC original What is knowledge? How do we know that those who profess to have knowledge actually have it? How can one inquire into anything one does not know? Is knowledge the same as the arts and sciences? How does knowledge relate to perception, belief, and truth? What kinds of account can w ..."
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c. 360 BC original What is knowledge? How do we know that those who profess to have knowledge actually have it? How can one inquire into anything one does not know? Is knowledge the same as the arts and sciences? How does knowledge relate to perception, belief, and truth? What kinds of account can we expect from someone who has knowledge? Is there any formal way to represent and criticize scientific reasoning and explanations? How do general principles of scientific knowledge relate to specific sciences, such as mathematics, psychology, and biology? We will examine these fundamental epistemological issues as they arise for the first time in the writings of Plato and Aristotle. We will begin by reading three aporetic dialogues of Plato concerned with knowledge: Euthyphro, Meno, and Theaetetus. We will then read fragments from a popular dialogue by Aristotle entitled Exhortation to Philosophy, and from several of his technical works, including his dialectical account of the history of science in the Metaphysics, followed by methodological books of Aristotle’s physics, psychology, and biology.
Approximate Models for Ductile Metals Containing Nonspherical Voids—Case of Axisymmetric Prolate Ellipsoidal Cavities,"
 J. Mech. Phys. Solids,
, 1993
"... The aim of this paper is to extend the classical I Introduction Metals often contain microvoids which significantly alter their mechanical behavior. The growth of such microvoids was studied in the pioneering works of The choice of axisymmetric ellipsoids can serve to model a wide range of void s ..."
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The aim of this paper is to extend the classical I Introduction Metals often contain microvoids which significantly alter their mechanical behavior. The growth of such microvoids was studied in the pioneering works of The choice of axisymmetric ellipsoids can serve to model a wide range of void shapes, ranging from pennyshaped cracks to needles. Such a choice was made in several recent papers. In a recent paper (Gologanu et al., 1993), we proposed a constitutive model for idealplastic materials containing aligned or randomly oriented prolate ellipsoidal cavities. This model was obtained by extending The aim of the present work is to extend this analysis to the case of oblate cavities. Two fresh difficulties will be encountered. The first one is that while in the prolate case, both of Gurson's classical models for spherical and cylindrical voids could be used as references, only the first one is relevant to the oblate case. The second difficulty arises when one looks for an approximation of the twofield criterion leading to an analytic, Gursonlike expression. While in the prolate case it was possible to neglect the "crossed term" proportional to the product of the two velocity fields in the expression of the plastic dissipation without significantly altering the accuracy of the estimate, the same approximation reveals impossible for oblate voids, as will be detailed below. As in the prolate case, we shall consider an ellipsoidal cavity embedded in a finite volume (this allows to study arbitrarily great porosities), namely, a confocal ellipsoid. Such a geometry is primarily chosen because of mathematical tractability, but it is not a completely unreasonable approximation of an elementary cell in a periodic medium, just as Gurson's hollow sphere. Attention will be restricted to idealplastic behavior and axisymmetric loadings. Conditions of homogeneous boundary strain rate (v = D.x, where v denotes the velocity, D the overall strain rate and x the current position) will be enforced on the outer surface. The reason for imposing a homogeneous strain rate rather than a homogeneous stress is that the space of admissible velocity fields is smaller in the former case, so that the search for an
Development of the local approach to fracture over the past 25 years: theory and applications. Int J Fract 2006;138(1):139–66
"... This review paper is devoted to the local approach to fracture (LAF) for the prediction of the fracture toughness of structural steels. The bases of this relatively newly developed methodology are first presented. The LAF has been considerably developed over the past two decades, not only to provide ..."
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This review paper is devoted to the local approach to fracture (LAF) for the prediction of the fracture toughness of structural steels. The bases of this relatively newly developed methodology are first presented. The LAF has been considerably developed over the past two decades, not only to provide a better understanding of the fracture behaviour of materials, in particular the failure micromechanisms, but also to deal with loading conditions which cannot easily be handled with the conventional LEFM and EPFM global approaches. Both ductile rupture and brittle cleavage fracture micromechanisms are considered. The ductiletobrittle transition observed in ferritic steels is also briefly addressed. Two types of LAF methods are presented: (i) those assuming that the material behaviour is not affected by damage (e.g. cleavage fracture), (ii) those using a coupling effect between damage and constitutive equations (e.g. ductile fracture). The micromechanisms of brittle and ductile fracture investigated in elementary volume elements are briefly presented. The emphasis is laid on cleavage fracture in ferritic steels. The role of second phase particles (carbides or inclusions) and grain boundaries are more thoroughly discussed. The distinction between nucleation and growth controlled fracture is made. Recent developments in the theory of cleavage fracture incorporating both the effect of stress state and that of plastic strain are presented. These theoretical results are applied to the crack tip situation to predict the fracture toughness. It is shown that the ductiletobrittle transition curve can reasonably be well predicted using this approach. Additional applications of the LAF approach methods are also shown, including: (i) the effect of loading rate and prestressing; (ii) the influence of residual stresses in welds; (iii) the mismatch effects in welds; (iv) the warmprestressing effect. An attempt is also made to delineate research areas where large improvements should be made for a better understanding of the failure behaviour of structural materials.
Multiscale constitutive model and computational framework for the design of ultrahigh strength, high toughness steels. Computer Methods in Applied Mechanics and Engineering
, 2004
"... Abstract A multiscale hierarchical constitutive model is developed for establishing the relationship between quantum mechanical, micromechanical, and overall strength/toughness properties in steel design. Focused on the design of ultrahigh strength, high toughness steels, a twolevel cell model is ..."
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Abstract A multiscale hierarchical constitutive model is developed for establishing the relationship between quantum mechanical, micromechanical, and overall strength/toughness properties in steel design. Focused on the design of ultrahigh strength, high toughness steels, a twolevel cell model is used to represent two groups of hard particles (inclusions) in an alloy matrix which is characteristic of such Febased alloys. Primary inclusion particles, which are greater than a micron in size, are handled by a microcell. Secondary inclusion particles which are tens of nanometers in size are modeled by a submicrocell. In the submicrocell, the matrix constitutive behavior is given by quantum mechanics computation of bcciron calibrated according to experiments. In the microcell, the matrix constitutive behavior is given by the stressstrain response of the submicrocell, characterized by a plastic flow potential based on the numerical simulation of the representative cell. In turn, the plastic flow potential generated by the stressstrain response of the microcell is used as the constitutive response at the continuum macro level for simulation of ductile fracture and for the assessments of toughness. The interfacial debonding between the matrix and the primary and the secondary inclusion particles are modeled using decohesion potentials computed through quantum mechanics calculation together with a mechanical model of normal separation and gliding induced dislocation, which also provides quantitative explanations why practice strength of a steel is much lower than the atomic separation force and how plasticity occurs in steels. The ductile fracture simulations on an ASTM standard center cracked specimen lead to the generation, for the first time, of a toughness, strength, adhesion diagram based on computer simulation and which establishes the relationship between alloy matrix strength, interfacial decohesion energy, and fracture toughness.
Evaluation of ductile fracture models for different metals in blanking
, 2000
"... This study is focussed on the evaluation of ductile fracture methodologies, which are needed to predict product shapes in the blanking process. In an earlier publication [Goijaerts et al., J. Manuf. Sci. Eng., Trans. ASME 122 (2000) 476], two approaches were elaborated using local ductile fracture m ..."
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This study is focussed on the evaluation of ductile fracture methodologies, which are needed to predict product shapes in the blanking process. In an earlier publication [Goijaerts et al., J. Manuf. Sci. Eng., Trans. ASME 122 (2000) 476], two approaches were elaborated using local ductile fracture models. The first strategy incorporates the characterisation of a ductile fracture model in a blanking experiment. The second methodology is more favourable for industry. In this approach, instead of a complex and elaborate blanking experiment, a tensile test is used to characterise a newly proposed criterion, which was shown to predict accurately the ductile fracture for different loading conditions. In this paper, finite element simulations and experiments are performed on both tensile testing and blanking to evaluate the validity of both approaches with corresponding criteria for five different metals. In the blanking process, different clearances as well as different cutting radii of the tools are considered. In conclusion, it can be stated that the first approach gives very good results close to, or within the experimental error for all five materials. The second approach, the more favourable one for industry, yields good results that deviate slightly more over the range of metals. # 2001 Published by Elsevier Science B.V.
TESTING AND SIMULATION OF ULTRALOW CYCLE FATIGUE AND FRACTURE IN STEEL BRACES
"... Preliminary experimental and simulation results are presented for the first phase of testing for a Network of Earthquake Engineering Simulation Research (NEESR) project to investigate UltraLow Cycle Fatigue (ULCF) in largescale steel bracing members. The tested members represent braces in Special ..."
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Preliminary experimental and simulation results are presented for the first phase of testing for a Network of Earthquake Engineering Simulation Research (NEESR) project to investigate UltraLow Cycle Fatigue (ULCF) in largescale steel bracing members. The tested members represent braces in Special Concentrically Braced Frame (SCBF) systems that undergo severe cyclic inelastic deformations accompanied by global and local buckling eventually leading to ULCFinduced fracture. The experimental findings are complemented by detailed continuumbased FEM and lineelementbased OpenSEES analyses. The ULCF process itself is simulated through micromechanicsbased models that capture the fundamental processes of void growth, collapse, and damage responsible for ULCF. The paper briefly describes existing models for base metals and ongoing efforts to develop models for weld metals. The paper concludes with a commentary on the methodology of utilizing micromechanicsbased fracture models for largescale structural components where modeling of phenomena such as local and global buckling may need explicit attention. Future experiments and research directions are discussed.
Fast estimation of localized plasticity and damage by energetic methods
 International Journal of Solids and Structures
"... Structural failure often follows the initiation of cracks occurring at corners, free edges or interfaces. Continuum damage mechanics gives quantitative information about such cracking. But when used in a fully coupled manner (with elasticity and plasticity), it leads to costly computations. In order ..."
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Structural failure often follows the initiation of cracks occurring at corners, free edges or interfaces. Continuum damage mechanics gives quantitative information about such cracking. But when used in a fully coupled manner (with elasticity and plasticity), it leads to costly computations. In order to obtain helpful results for a fine and fast design, we propose to determine localized plasticity and damage by use of local postcalculations, which follow a simple elastic finite element computation. Energetic methods such as Neuber’s, such as the strain energy density or as the complementary energy density methods, are justified for small scale yielding by use of pathindependent integrals. They are extended to cyclic loading inducing fatigue and the case of thermal stresses is considered. For plane problems, these methods are completed by the analytical determination of the stress triaxiality along free edges or rigid inclusions. The crack initiation conditions are then quickly estimated by the timeintegration of Lemaitre’s damage law. Cal
Modeling of Glass Fracture Damage Using Continuum Damage
 Mechanics – Static Spherical Indentation, International Journal of Damage Mechanics
, 2004
"... ABSTRACT: The response of sodalime glass subjected to the stress field induced by the static indentation of a spherical indenter is studied using continuum damage mechanics (CDM). An anisotropic damage tensor with linear damage evolution law is chosen to model the cracking damage. An axisymmetric f ..."
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ABSTRACT: The response of sodalime glass subjected to the stress field induced by the static indentation of a spherical indenter is studied using continuum damage mechanics (CDM). An anisotropic damage tensor with linear damage evolution law is chosen to model the cracking damage. An axisymmetric finite element model is generated to simulate the static indentation process. The damage pattern and zone size are predicted for both the loading cycle and the unloading cycle, and the comparison between the predictions and the experimental results reported in the open literature serves as a validation of the CDM model and the modeling procedure. KEY WORDS: continuum damage mechanics, glass fracture damage, spherical indentation, damage pattern.