111,862 research outputs found
An experimental and numerical investigation of concrete dam joints
No full textThis communication summarises the results of a comprehensive investigation aimed at improving the understanding of the cyclic behaviour of concrete dam joints, covering both experimental and numerical aspects.
In the laboratory work, a jointed concrete block is subjected to reversed cyclic slip at imposed normal stress. The specimen is intended to represent a portion of either a lift joint or the dam-foundation interface. Aspects of novelty can be found in the test setup and in the specimen size (90×70×30 cm). The tests performed so far, though limited in number, have allowed to assess and approximately quantify for concrete the characteristic influence of joint roughness on the observed shear strength and dilatancy.
A generalised interface model is proposed in order to describe the joint behaviour, including all the phenomena commonly accounted for in mixed mode fracture of cohesive quasi-brittle materials and the effects of surface roughness. This result has been obtained by combining a fracture-mechanics based interface model for concrete with a cyclic one for rock joints. Simulations carried out so far evidence a good qualitative agreement with results available in literatur
Non linear finite element analysis and size effect study of a metal-reinforced ceramic composite
No full textFracture of concrete under variable amplitude fatigue loading
No full textThe fracture response of concrete under low-cycle variable amplitude loading at frequencies up to 10 Hz was investigated. The applied loading history, selected to reflect earthquake loads on concrete dams, consisted of a basic sinusoidal oscillation interrupted by occasional spikes. Test results of specimens with different sizes and loading histories are reported. It was determined that the induced damage is both size and loading history-dependent; further, it was found that spikes in the loading history are likely to accelerate crack growth. On the basis of the experimental results, a fracture mechanics-based empirical law for crack propagation under variable amplitude cyclic loading is proposed
A Fracture Mechanics Based Model for Joints Under Cyclic Loading
No full textA generalized interface model for joints and cracks in quasi-brittle materials is formulated. The proposed model marries an existing fracture mechanics based one developed for monotonic loading of concrete with another frictional based model developed for the cyclic response of rock joints to address the (reverse) cyclic response of rough surfaces in the presence of cohesive stresses. The properties of the model and its capability to capture several experimentally observed behaviors are shown by the numerical simulations performed. This joint constitutive model is particularly suitable to simulate the seismic response of dam/rock joints subjected to seismic excitation, or of concrete joints under reverse cyclic loading
Numerical simulation of thermal residual stress in Mo- and FeAl-toughened alumina
No full textMicrostructure-level residual stresses occur in composite ceramics during processing, mainly as a result of thermal expansion anisotropy. The magnitude of these stresses can be sufficiently high to cause spontaneous microcracking when cooled from the processing temperature. They are also likely to affect where cracks initiate and propagate under macroscopic loading. Alumina-based composites containing different amount of second phase particles with lower (Mo) and higher thermal expansion coefficient (FeAl) were prepared. Fluorescence spectroscopy was used to measure the residual stress distribution due to thermal expansion anisotropy in these composites. A finite element model was also established for two-phase ceramics. The residual stress distribution in the model was analyzed, and the variation regularity of internal stress along with the second phase particle’s volumetric proportion was given
Fracture Mechanics of Composite Solid Rocket Propellant Grains: Material Testing
No full textFollowing a detailed literature survey on the fracture-mechanics properties of solid rocket propellants, this paper reports on an innovative set of fracture tests performed on a composite solid propellant based on ammonium perchlorate hydroxyl-terminated polybutadiene. After a short summary on standard linear–viscoelastic mechanical characterization, results on both linear–elastic fracture-mechanics (characterized by the fracture toughness KIC) and nonlinear fracture-mechanics (characterized by GF) tests are reported. Test results for linear–elastic fracturemechanics simulations have been obtained using middle-tension specimens. A practical methodology to separate the
amount of strain energy lost through viscous processes from other sources is given and provides an effective method to apply the toughness-test validity criteria of the American Society for Testing and Materials E399 norm to propellants and other thermoviscoelastic materials. Measurements to determine the linear fracture-mechanics properties of the propellant have been carried out applying the wedge-splitting test methodology. Master curves for the toughness, the critical crack-opening displacement, and the fracture energy have been generated to correlate test
data. Results are coherent with Shapery’s theory of fracture for viscoelastic materials. Results can be used within finite element simulations to assess the safety and integrity of a solid-propellant rocket motor under various loads, such as thermal cycling and ignition, assuming stationary conditions
Random lattice particle modeling of damage localization in concrete members under compression
No full textThe ability to predict the localization of damage in concrete members subject to uniaxial
compression is investigated by means of a recently developed random lattice particle model. Such
capability is of great interest in the modeling of concrete structures, since most of the existing mod els rely on the a-priori definition of a zone in which the nonlinear behavior is concentrated. Lattice
particle models, by explicitly representing the mesoscale structure of the material, are capable of sim ulating the localization of damage. Herein, aggregate particles are represented by poly-sized spheres
embedded in a cementitious matrix. The connectivity among particles is defined by a Delaunay tetra hedralization of the sphere centers; the resisting areas of the lattice struts are evaluated by a graph that
is dual to the tetrahedralization. The mesoscale mechanical properties used in the simulations were
measured as part of a multiscale experimental campaign, which also served to validate the numerical
macroscopic response of concrete elements subjected to uniaxial compression
author-bios-SRD-19-0063.R1 – Supplemental material for The Network Structure of Police Misconduct
No full textSupplemental material, author-bios-SRD-19-0063.R1 for The Network Structure of Police Misconduct by George Wood, Daria Roithmayr and Andrew V. Papachristos in Socius</p
Effect of Post-Fire Curing on the Residual Mechanical Properties of Fire-Damaged Self-Compacting Concrete
No full textConcrete is recognized for being a fire-resistant construction material. At elevated temperatures concrete can, however, undergo considerable damage such as strength degradation, cracking, and explosive spalling. In recent decades, reuse of fire-damaged concrete structures by means of developing techniques to repair the degraded material has gained interest amongst researchers. Autogenic self-healing methods such as re-curing in water has proven to partly restore the strength of concrete. The extent of restoration is dependent upon various parameters such as concrete type, exposure temperature, and post-fire curing conditions for example. The use of selfcompacting/ consolidating concrete (SCC) has become common in the construction industry due to its high workability and low permeability. This paper presents the results of an experimental study aimed at investigating the improved mechanical properties of high temperature exposed SCC concrete by the autogenic self-healing phenomenon resulting from water re-curing. The residual mechanical properties including strength, modulus of elasticity and ultimate strain of the material upon application of different post-fire curing regimes are presented herein with special emphasis on the effect of thermal profile including exposure time, temperature and cooling rate. The experimental results confirm that the recovery of material properties in fire-damaged SCC concrete is contingent on the post-fire water curing conditions.Materials and Environmen
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