On the contact domain method: a comparison of penalty and Lagrange multiplier implementations

This work focuses on the assessment of the relative performance of the so-called contact domain method, using either the Lagrange multiplier or the penalty strategies. The mathematical formulation of the contact domain method and the imposition of the contact constraints using a stabilized Lagrange multiplier method are taken from the seminal work (as cited later), whereas the penalty based implementation is firstly described here. Although both methods result into equivalent formulations, except for the difference in the constraint imposition strategy, in the Lagrange multiplier method the constraints are enforced using a stabilized formulation based on an interior penalty method, which results into a different estimation of the contact forces compared to the penalty method. Several numerical examples are solved to assess certain numerical intricacies of the two implementations. The results show that both methods perform similarly as one increases the value of the penalty parameter or decreases the value of the stabilization factor (in case of the Lagrange multiplier method). However there seems to exist a clear advantage in using the Lagrange multiplier based strategy in a few critical situations, where the penalty method fails to produce convincing results due to excessive penetration

A new approach in computational contact mechanics: The contact domain method

This first part of the work presents the theoretical aspects of a new approach to solve two-dimensional large-strain problems in computational contact mechanics. The basic elements of the proposed metod are: 1) the use of an updated Lagrangean approach to describe the motion of the contacting bodies, 2) consideration of a two-dimensional aontact domain, where the contact/friction restrictions are imposed, and construction of a one layer triangulation in this domain, 3) resorting to a Lagrange multiplier method to impose the contact/friction contraints, 4) an interior penaltyprocedure, allowing condensation of the Lagrange multipliers, ensuring the stability of the discretized problem and 5) an active set strategy, for determining the subsets of the contact domain were contact/friction conditions have to be applied, based on the concept domain were contact/friction conditions have to be aaplied, based on the concept of effective gaps as suitable entities for extrapolation and prediction purposes

Numerical modeling of crack formation in powder forming processes

This paper presents a constitutive model describing the mechanical behavior of metal powders during (uniaxial) cold die compaction processes, placing special emphasis on the modeling of cracks formed during the ejection stage. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield condition is determined by three surfaces intersecting non-smoothly in stress space, namely, an elliptical cap and the classical Von Mises and Drucker–Prager yield surfaces. The distinct irreversible processes are described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to characterize the plastic flow on the linear Drucker–Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate the softening modulus to fracture energy values obtained experimentally on Distaloy AE powder specimens. The predictive capability of the constitutive model is checked by simulating three representative cases: a diametral compression test, the ejection of an over-densified thin cylindrical part and the compaction of an axially symmetric multilevel part in an advanced CNC press machine. These simulations demonstrate the ability of the model to detect evidence of macroscopic cracks, clarify and provide reasons for the formation of such cracks, and evaluate, at least qualitatively, the influence of variations in the input variables on their propagation through the green compac

A contact domain method for large deformation frictional contact problems. Part 1: Theoretical basis

In the first part of this work, the theoretical basis of a frictional contact domain method for two-dimensional large deformation problems is presented. Most of the existing contact formulations impose the contact constraints on the boundary of one of the contacting bodies, which necessitates the projection of certain quantities from one contacting surface onto the other. In this work, the contact constraints are formulated on a so-called contact domain, which has the same dimension as the contacting bodies. This contact domain can be interpreted as a fictive intermediate region connecting the potential contact surfaces of the deformable bodies. The introduced contact domain is subdivided into a non-overlapping set of patches and is endowed with a displacement field, interpolated from the displacements at the contact surfaces. This leads to a contact formulation that is based on dimensionless, strain-like measures for the normal and tangential gaps and that exactly passes the contact patch test. In addition, the contact constraints are enforced using a stabilized Lagrange multiplier formulation based on an interior penalty method (Nitsche method). This allows the condensation of the introduced Lagrange multipliers and leads to a purely displacement driven problem. An active set strategy, based on the concept of effective gaps as entities suitable for smooth extrapolation, is used for determining the active normal stick and slip patches of the contact domain

A contact domain method for large deformation frictional contact problems. Part 2: Numerical aspects

This second part of the work describes the numerical aspects of the developed contact domain method for large deformation frictional contact problems. The theoretical basis of this contact method is detailed in the first part of this work. Starting from this, the present contribution focuses on describing important algorithmic details that go along with the finite element implementation for two-dimensional problems. Important aspects are the construction of the contact domain mesh, via a constraint Delaunay triangulation, the linearization of the discretized contact contributions and some important technical aspects about the extrapolation procedure used for the predictive active set strategy. Finally a set of numerical examples is presented to demonstrate the performance of the developed contact strategy. Demanding static and dynamic contact problems in the context of large deformations, including frictional effects as well as self contact, show the wide applicability and the robustness of the proposed metho

Strategic Alliances In Public Accounting Firms

The decade of the 1990s saw the emergence of the concept of the strategic alliance and its significant growth in both numbers and diversity of alliance areas as well as its impact on business performance in terms of new service or product introductions and/or increases in revenue, profit, volume or market share.  Public accounting (CPA) firms have participated in such alliances especially during times of staffing shortages and seasonal peak periods, but their participation has not been well reported in the literature.  This study examines the state of strategic alliances in public accounting firms.  The topic is particularly relevant now in light of the greater responsibilities placed on management since the passage of the Sarbanes-Oxley Act, and the issuance recently of two Statements of Financial Accounting Standards (SFAS No. 157 in 2006 and SFAS No. 159 in 2007) which give companies the option to report certain financial assets and liabilities at fair value.  These additional responsibilities may include the restructuring and restatement of financial reports to more accurately reflect the financial position and results of operations of a business.  This has resulted in a greater demand for accounting services which some CPA firms were not able to provide.  The findings reveal that participation in strategic alliances enables accounting firms to pool their resources, increase revenues, build a larger knowledge support system to serve a wider clientele, and compete with larger firms both nationally and on a global basis

Head and neck region consolidation radiotherapy and prophylactic cranial irradiation with hippocampal avoidance delivered with helical tomotherapy after induction chemotherapy for non-sinonasal neuroendocrine carcinoma of the upper airways

Background: Non-sinonasal neuroendocrine carcinomas (NSNECs) of the head and neck are considered an unfrequent clinico-pathological entity. Combined modality treatment represents an established therapeutic option for undifferentiated forms where distant metastasis is a common pattern of failure.Methods: We report on a case of NSNEC treated with sequential chemo-radiation consisting of 6 cycles of cisplatin and etoposide followed by loco-regional radiation to the head and neck and simultaneous prophylactic cranial irradiation to prevent from intracranial spread, delivered with helical tomotherapy with the 'hippocampal avoidance' technique in order to reduce neuro-cognitive late effects.Results: One year after the end of the whole combined modality approach, the patient achieved complete remission, with no treatment-related sub-acute and late effects.Conclusions: The present report highlights the importance of multidisciplinary management for NSNECs of the head and neck, as the possibility to achieve substantial cure rates with mild side effects with modern radiotherapy techniques. © 2012 Franco et al; BioMed Central Ltd

On urban re‐arrangements: a suite in five movements

This movement introduces the ethos of the collective project: its conceptual and practical preoccupations. It focuses on our concern with urban processes on the cusp of change, in the midst of being re-arranged, and thus homes in on the various polyrhythms of intersections, how things come together and diverge, how possibilities open and close in urban contexts of continuously shifting horizons

Movement 5. Sensing the affective lives of arrangements

This final movement explores whether thinking with re-arrangements can help us account for that which is hidden, unseen or nested in the recesses and folds of urban practices. And if so, how we might then talk about and account for elusive parts of an arrangement that both exert an influence and are influenced. This essay uses sensibilities as an entry point into the intangible interactions between subjects and (re)arrangements

Movement 4. Breath sigh tempest: On the temporal dimensions of re‐arrangements

The fourth movement explores the temporal relationship between arrangements and re-arrangements, addressing the question of how an obdurate and ‘sticky’ temporal order may give way to palpable re-arrangement of the ways in which subjects experience time. Eschewing a concern with linear homogenous time, it addresses the processes of re-arrangement by understanding the dynamics of grave events, hauntings of the past, subtly changing rhythms of everyday life, and the force of potential futures in synchrony