196 research outputs found
Near tip stress and strain fields for short elastic cracks
Recent experimental fatigue crack growth studies have concluded an apparent anomalous behavior of short cracks. To investigate the reasons for this unexpected behavior, the present paper focuses on identifying the crack length circumstances under which the requirements for a single parameter (K(sub I) or delta K(sub I) if cyclic loading is considered) characterization are violated. Furthermore, an additional quantity, the T stress, as introduced by Rice, and the related biaxiality ratio, B, are calculated for several crack lengths and two configurations, the single-edge-cracked and the centrally-cracked specimen. It is postulated that a two-parameter characterization by K and T (or B) is needed for the adequate description of the stress and strain field around a short crack. To further verify the validity of this postulate, the influence of the third term of the Williams series on the stress, strain and displacement fields around the crack tip and in particular on the B parameter is also examined. It is found that the biaxiality ratio would be more negative if the third term effects are included in both geometries. The study is conducted using the finite element method with linearly elastic material and isoparametric elements and axial (mode I) loading. Moreover, it is clearly shown that it is not proper to postulate the crack size limits for 'short crack' behavior as a normalized ratio with the specimen width, a/w; it should instead be stated as an absolute, or normalized with respect to a small characteristic dimension such as the grain size. Finally, implications regarding the prediction of cyclic (fatigue) growth of short cracks are discussed
Using cool paving materials to improve microclimate of urban areas e Design realization and results of the flisvos project
The present paper deals with the application of 4500 m2 of reflective pavements in an urban park in the greater Athens area. The aim was to improve thermal comfort conditions, reduce the intensity of heat island and improve the global environmental quality in the considered area. To our knowledge, this has been the largest application of cool pavements in urban areas in the world. To evaluate the thermal impact of cool paving materials, specific and detailed measurements of the climatic conditions in the park have been performed before and after the installation of the new materials. Validated computerized fluid dynamics techniques have been used to homogenize the boundary conditions occurring during the
two experiments and to perform direct comparisons of the climatic quality in the park. It was estimated that the use of cool paving materials contributes to the reduction of the peak ambient temperature during a typical summer day, by up to 1.9 K. At the same time, the surface temperature in the park was decreased by 12 K, while comfort conditions have been improved considerably. It is concluded that the use of reflective paving materials is a very efficient mitigation technique to improve thermal conditions in urban area
On a multiscale strategy and its optimization for the simulation of combined delamination and buckling
This paper investigates a computational strategy for studying the
interactions between multiple through-the-width delaminations and global or
local buckling in composite laminates taking into account possible contact
between the delaminated surfaces. In order to achieve an accurate prediction of
the quasi-static response, a very refined discretization of the structure is
required, leading to the resolution of very large and highly nonlinear
numerical problems. In this paper, a nonlinear finite element formulation along
with a parallel iterative scheme based on a multiscale domain decomposition are
used for the computation of 3D mesoscale models. Previous works by the authors
already dealt with the simulation of multiscale delamination assuming small
perturbations. This paper presents the formulation used to include geometric
nonlinearities into this existing multiscale framework and discusses the
adaptations that need to be made to the iterative process in order to ensure
the rapid convergence and the scalability of the method in the presence of
buckling and delamination. These various adaptations are illustrated by
simulations involving large numbers of DOFs
Critical Buckling Loads of the Perfect Hollomon's Power-law Columns
In this work, we present analytic formulas for calculating the critical
buckling states of some plastic axial columns of constant cross-sections. The
associated critical buckling loads are calculated by Euler-type analytic
formulas and the associated deformed shapes are presented in terms of
generalized trigonometric functions. The plasticity of the material is defined
by the Hollomon's power-law equation. This is an extension of the Euler
critical buckling loads of perfect elastic columns to perfect plastic columns.
In particular, critical loads for perfect straight plastic columns with
circular and rectangular cross-sections are calculated for a list of commonly
used metals. Connections and comparisons to the classical result of the
Euler-Engesser reduced-modulus loads are also presented.Comment: 15 page
Buckling of sandwich wide columns
Abstract The paper deals with the theoretical prediction of buckling loads for sandwich columns with metallic and laminated facings and foam or honeycomb core. The loading is a uniform axial compression, applied statically (very slowly) and suddenly with constant magnitude and inÿnite duration (step loading). The e ect of length and boundary conditions is assessed and results are presented for the following cases: for a cantilever column, a simply supported column and a clamped column, for several lengths. Several ÿber materials are used in the laminated facings. Two types of core were examined: alloy-foam or hexagonal glass=phenolic honeycomb. The facings are Boron=Epoxy, Graphite=Epoxy and Kevlar=Epoxy laminates with 0 • orientation with respect to the column axis and a metallic one made out of aluminum. These various materials are employed to provide comparative data that can be used in design. Results, for the static case are generated by computer codes as well as by the use of closed form theoretical solutions. For the dynamic case, results are generated by the DYNA3D code.
Degradation and healing in a generalized neo-Hookean solid due to infusion of a fluid
The mechanical response and load bearing capacity of high performance polymer
composites changes due to diffusion of a fluid, temperature, oxidation or the
extent of the deformation. Hence, there is a need to study the response of
bodies under such degradation mechanisms. In this paper, we study the effect of
degradation and healing due to the diffusion of a fluid on the response of a
solid which prior to the diffusion can be described by the generalized
neo-Hookean model. We show that a generalized neo-Hookean solid - which behaves
like an elastic body (i.e., it does not produce entropy) within a purely
mechanical context - creeps and stress relaxes when infused with a fluid and
behaves like a body whose material properties are time dependent. We
specifically investigate the torsion of a generalized neo-Hookean circular
cylindrical annulus infused with a fluid. The equations of equilibrium for a
generalized neo-Hookean solid are solved together with the convection-diffusion
equation for the fluid concentration. Different boundary conditions for the
fluid concentration are also considered. We also solve the problem for the case
when the diffusivity of the fluid depends on the deformation of the generalized
neo-Hookean solid.Comment: 24 pages, 10 figures, submitted to Mechanics of Time-dependent
Material
Fracture mechanism simulation of inhomogeneous anisotropic rocks by extended finite element method
The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores, grain sizes or different mineralogical compounds in different locations, they are often classified as inhomogeneous materials. In such materials, stress intensity factors (SIFs) at the crack tip, which control the initiation of failure, strongly depend on mechanical properties of the material near that area. On the other hand, crack propagation trajectories highly depend on the orthotropic properties of the rock mass. In this study, the SIFs are calculated by means of anisotropic crack tip enrichments and an interaction integral are developed for inhomogeneous materials with the help of the extended finite element method (XFEM). We also use the T-stress within the crack tip fields to develop a new criterion to estimate the crack initiation angles and propagation in rock masses. To verify and validate the proposed approach, the results are compared with experimental test results and those reported in the literature. It is found that the ratio of elastic moduli, shear stiffnesses, and material orientation angles have a significant impact on the SIFs. However, the rate of change in material properties is found to have a moderate effect on these factors and a more pronounced effect on the failure force. The results highlight the potential of the proposed formulation in the estimation of SIFs and crack propagation paths in inhomogeneous anisotropic materials
From the Sum of Near-Zero Energy Buildings to the Whole of a Near-Zero Energy Housing Settlement: The Role of Communal Spaces in Performance-Driven Design
Almost a century ago Modernism challenged the structure of the city and reshaped its physical space in order to, amongst other things, accommodate new transportation infrastructure and road networks proclaiming the,nowadays much-debated ‘scientificated’ pursuit of efficiency for the city. This transformation has had a great impact on the way humans still design, move in, occupy and experience the city. Today major cities in Europe, such as Paris
and London, are considering banning vehicles from their historic centers. In parallel, significant effort is currently underway internationally by designers,
architects, and engineers to integrate innovative technologies and sophisticated solutions for energy production, management, and storage, as well as for
efficient energy consumption, into the architecture of buildings. In general, this effort seeks for new technologies and design methods (e.g., DesignBuilder
with EnergyPlus simulation engine; Rhicoceros3D with Grasshopper plugin and Ecotect, Radiance and EnergyPlus tools) that would enable a holistic approach to the spatial design of Near-Zero Energy buildings, so that their
ecological benefits are an added value to the architectural design and a building’s visual, and material, impact on its surrounding space. The paper inquires how the integration of such technological infrastructure and performance-orientated interfaces changes yet again the structure and form of cities, and to what extent it safeguards social rights and enables equal access to common
resources. Drawing from preliminary results and initial considerations of ongoing research that involve the construction of four innovative NZE settlements
across Europe, in the context of the EU-funded ZERO-PLUS project, this paper discusses the integration of novel infrastructure in communal spaces of these settlements. In doing so, it contributes to the debate about smart communities and their role in the sustainable management of housing developments and settlements that are designed and developed with the concept of smart territories
- …