Investigation of Bursting Stress and Spalling Stress in Post-tensioned Anchorage Zones

Over the past decades, considerable efforts have been made to quantify the bursting forces in the post-tensioned anchorage zones based on the simplified model or fitting formulas, however reproducing the transverse stress distribution is still a challenging topic, which is also important to detail the reinforcing details in the anchorage zones, especially for cracking control. To address this issue, this paper is devoted to seeking an elasticity solution for transverse stresses in the anchorage zones, and providing a more rational equation for transverse distribution in anchorage zones. The sum function of normal stresses is employed to solve the stresses filed in the anchorage zones with concentric load and two eccentric loads. The bursting stresses in the concentric anchorage zones and spalling stresses in the eccentric anchorage zones are verified by the photoelastic tests. The transverse stresses along the symmetry axis of the eccentric anchorage zones can be handled as a concentric single anchorage zone with equivalent bearing plate width. Moreover, according to the concept of force stream tube, the profiles of isostatic line of compression (ILCs) are determined and validated, which confirms the existence of ILCs.

Cosmological Milestones and Gravastars - Topics in General Relativity

<p>In this thesis, we consider two different problems relevant to general relativity. Overthe last few years, opinions on physically relevant singularities occurring in FRWcosmologies have considerably changed. We present an extensive catalogue of suchcosmological milestones using generalized power series both at the kinematical anddynamical level. We define the notion of “scale factor singularity” and explore its relationto polynomial and differential curvature singularities. We also extract dynamicalinformation using the Friedmann equations and derive necessary and sufficient conditionsfor the existence of cosmological milestones such as big bangs, big crunches, bigrips, sudden singularities and extremality events. Specifically, we provide a completecharacterization of cosmological milestones for which the dominant energy conditionis satisfied. The second problem looks at one of the very small number of seriousalternatives to the usual concept of an astrophysical black hole, that is, the gravastarmodel developed by Mazur and Mottola. By considering a generalized class of similarmodels with continuous pressure (no infinitesimally thin shells) and negative centralpressure, we demonstrate that gravastars cannot be perfect fluid spheres: anisotropcpressures are unavoidable. We provide bounds on the necessary anisotropic pressureand show that these transverse stresses that support a gravastar permit a higher compactnessthan is given by the Buchdahl–Bondi bound for perfect fluid stars. We alsocomment on the qualitative features of the equation of state that such gravastar-likeobjects without any horizon must have.</p>

Calculation of lateral stresses for uniaxial compression of geomaterial samples

A method is proposed for calculating the transverce stresses during uniaxial compression of geomaterial samples from the measured load and mutually perpendicular deformations. Analytical expressions connecting the indicated parameters are obtained. The dependences of the change in the calculated transverse stresses on time are plotted for various values of Poisson’s ratio. The difference in transverse stresses demonstrates a much greater sensitivity to mechanical stress than each transverse stress separately. Sharp changes in the values of the difference in transverse stresses are observed, which coincide with bursts of AE activity.

Cosmological Milestones and Gravastars - Topics in General Relativity

<p>In this thesis, we consider two different problems relevant to general relativity. Overthe last few years, opinions on physically relevant singularities occurring in FRWcosmologies have considerably changed. We present an extensive catalogue of suchcosmological milestones using generalized power series both at the kinematical anddynamical level. We define the notion of “scale factor singularity” and explore its relationto polynomial and differential curvature singularities. We also extract dynamicalinformation using the Friedmann equations and derive necessary and sufficient conditionsfor the existence of cosmological milestones such as big bangs, big crunches, bigrips, sudden singularities and extremality events. Specifically, we provide a completecharacterization of cosmological milestones for which the dominant energy conditionis satisfied. The second problem looks at one of the very small number of seriousalternatives to the usual concept of an astrophysical black hole, that is, the gravastarmodel developed by Mazur and Mottola. By considering a generalized class of similarmodels with continuous pressure (no infinitesimally thin shells) and negative centralpressure, we demonstrate that gravastars cannot be perfect fluid spheres: anisotropcpressures are unavoidable. We provide bounds on the necessary anisotropic pressureand show that these transverse stresses that support a gravastar permit a higher compactnessthan is given by the Buchdahl–Bondi bound for perfect fluid stars. We alsocomment on the qualitative features of the equation of state that such gravastar-likeobjects without any horizon must have.</p>

Experimental and Finite Element Analysis of the Tensile Behavior of Architectured Cu-Al Composite Wires

The present study investigates, experimentally and numerically, the tensile behavior of copper-clad aluminum composite wires. Two fiber-matrix configurations, the conventional Al-core/Cu-case and a so-called architectured wire with a continuous copper network across the cross-section, were considered. Two different fiber arrangements with 61 or 22 aluminum fibers were employed for the architectured samples. Experimentally, tensile tests on the two types of composites show that the flow stress of architectured configurations is markedly higher than that of the linear rule of mixtures’ prediction. Transverse stress components and processing-induced residual stresses are then studied via numerical simulations to assess their potential effect on this enhanced strength. A set of elastic-domain and elastoplastic simulations were performed to account for the influence of Young’s modulus and volume fraction of each phase on the magnitude of transverse stresses and how theses stresses contribute to the axial stress-strain behavior. Besides, residual stress fields of different magnitude with literature-based distributions expected for cold-drawn wires were defined. The findings suggest that the improved yield strength of architectured Cu-Al wires cannot be attributed to the weak transverse stresses developed during tensile testing, while there are compelling implications regarding the strengthening effect originating from the residual stress profile. Finally, the results are discussed and concluded with a focus on the role of architecture and residual stresses.

DETERMINATION OF THE POISSON’S RATIO IN CONCRETE BY USING DITIGITAL IMAGE CORRELATION

The article presents the results of the experimental investigation of concrete prismsand determination of the Poisson's ratio using the method of digital image correlation (DIC). Toachieve the goals and objectives of the research, a concrete prism measuring 100x100x400 mm ofclass C50 / 60 was formed. The surface of the prism was cleaned and levelled to a smooth surfacewith a mechanical device and grinding stone. The surface of the prism is then cleaned with a solventto remove dust residues. After that, speckles were applied to determine the strain using the DICmethod. For determine the strain, by using digital image correlation, were used Two FlirGrasshopper 3 cameras with a Computar F25 / 2.8 lens and a Sigma 70-200 mm f2.8 APO EX DGHSM Macro II lens. Stains for image correlation were recorded at a speed of 250 ms. 2 LED lampswere used for lighting. Since the press is not able to record the load in time, to record the load useda camera at a speed of 50 frames/sec. The load was applied evenly at the same rate to the physicaldestruction of the test samples. As a result, the images were processed using VIC-2D software toobtain vertical and transverse strains. The advantage of the image correlation method is the abilityto obtain deformations and, accordingly, the stress of the full surface of the sample. Thus, if weanalyse the horizontal (transverse) stresses for a prism with a concrete strength of C50 / 60, it ispossible to see the appearance of internal cracks in the sample before it occurs outside, at a timewhen cracks cannot be visually fixed. As a result of work the technique of testing of concrete sampleswith use of digital correlation of the image is developed and presented. The Poisson's ratio from thebeginning of loading to the destruction of the sample was determined experimentally by the developedmethod.

Faserschonende Carbonfaserproduktion durch innovatives Galetten-Oberflächen-Design - CarboGerd

While carbon fibres can easily absorb forces in the fibre direction, they are extremely sensitive to transverse stress due to their anisotropic material behaviour. During the manufacturing process, unavoidable transverse stresses are induced in the fibre by the drive and deflection godets, which can damage or destroy individual filaments of the roving. The demand for a surface that is gentle on the fibre is offset by the static friction required between the fibre and the godet in order to drive the fibre. The aim of the CarboGerd research project is therefore to develop and validate an optimal godet coating for fibre-protecting and quality-assuring carbon fibre production. For this purpose, both typical coatings (ceramic, Topocrom coatings) and unconventional solutions (elastomer, PACVD coatings) are being tribologically investigated on a laboratory scale and validated on a prototype system.

Constitutive Modelling of Polylactic Acid at Large Deformation Using Multiaxial Strains

Sheet specimens of a PLLA-based polymer have been extended at a temperature near to the glass transition in both uniaxial and planar tension, with stress relaxation observed for some time after reaching the final strain. Both axial and transverse stresses were recorded in the planar experiments. In all cases during loading, yielding at small strain was followed by a drop in true stress and then strain hardening. This was followed by stress relaxation at constant strain, during which stress dropped to reach an effectively constant level. Stresses were modelled as steady state and transient components. Steady-state components were identified with the long-term stress in stress relaxation and associated with an elastic component of the model. Transient stresses were modelled using Eyring mechanisms. The greater part of the stress during strain hardening was associated with dissipative Eyring processes. The model was successful in predicting stresses in both uniaxial and planar extension over a limited range of strain rate.

Investigation of residual stress in butt-welded plates considering phase transformation

This paper presents a new approach to predict the residual stresses caused by welding in a butt-welded specimen. Based on the developed three-dimensional finite element model, both the process of material filling and the effects of phase transformation are considered through the material properties which depend on both the temperature and temperature history. For simulating the change in volume caused by phase transformation, a linear model is proposed to relate the start temperatures with the peak temperatures. A comparison of the computational and experimental results verifies the applicability of the proposed approach for welding involving material filling and phase transformation. Four models were built to analyze the influence of the material-filling process and phase transformation. The results demonstrated that without the use of material filling process, the residual stress is underestimated. In addition, without phase transformation, the transverse stress in the weld region is underestimated, while the longitudinal and transverse stresses in the weld region and HAZ, respectively, are overestimated.