Wyniki wyszukiwania - BazTech

1

Inżynieria powierzchni betonu a trwałość napraw konstrukcji betonowych

Garbacz A.

Ochrona przed Korozją

|

2015

|

nr 6

218--222

PL

Podstawowym kryterium doboru materiału do napraw konstrukcji betonowym jest zapewnienie kompatybilności wszystkich komponentów układu naprawczego oraz odpowiednie przygotowanie podłoża betonowego. W pracy przeanalizowano wpływ uszorstnienia powierzchni, mikrozarysowanie wynikające z obróbki powierzchniowej oraz zwilżenie podkładu na kształtowanie przyczepności. Wysoka adhezja zwiększa tolerancję na możliwe różnice we właściwościach fizyko-chemicznych materiału naprawczego i podkładu betonowego.

EN

The main criterion for the selection of material for the repair of concrete is to ensure compatibility of all components of the repair as well as proper preparation of concrete substrate. In this work the effect of surface roughness, microcracking resulting from surface treatment and substrate wetting on an adhesion is discussed. High adhesion increases tolerance to possible differences in the physical and chemical properties of the repair material and the concrete substrate.

2

Ultrasound monitoring for evaluation of damage in reinforced concrete

Rucka M., Wilde K.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2015

|

Vol. 63, nr 1

65--75

EN

The paper deals with automated monitoring of damage evolution in concrete elements subjected to three-point bending tests. The monitoring is based on the nonlinear interactions of traveling ultrasonic waves with micro-crack zones inside the concrete specimens and surface-breaking cracks. The developed procedure assumes semi-continuous ultrasonic testing during the element full loading cycle and generation of the power spectral density maps for the on-line assessment of the degradation process. Two damage indicators are introduced to evaluate micro- and macro-damage. The preliminary experimental results show that the proposed automated monitoring system provides an effective method for the evaluation of progressive damage in concrete.

3

A surface engineering approach applicable to concrete repair engineering

Garbacz A., Courard L., Bissonnette B.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2013

|

Vol. 61, nr 1

73-84

EN

The objective of the paper is to analyze the effect of substrate roughness and superficial microcraking upon adhesion of repair systems using concrete surface engineering approach. The results presented in this paper have been obtained within the framework of research projects performed to develop a better understanding of the factors affecting the adhesion of repair materials through a surface engineering approach. Based on the results of investigations, the authors showed that the durability and quality of concrete repairs depend to a large degree on the characteristics of the substrate. Mechanical preparation and profiling of the concrete surface to be repaired has to be balanced with potential co-lateral effects such as superficial cracking, too often induced as a result of inappropriate concrete removal method selection, and the loss of benefits due to better mechanical anchorage. The results obtained confirm also that Concrete Surface Engineering, as a scientific concept, will definitely contribute to shed more light on how to optimize repair bond, taking into account interactions between the materials at different observation scales.

4

Application of Acoustic Emission Method to Determine Critical Stress in Fibre Reinforced Mortar Beams

Ranachowski Z., Jóźwiak-Niedźwiedzka D., Brandt A. M., Dębowski T.

Archives of Acoustics

|

2012

|

Vol. 37, No. 3

261-268

EN

The objective of this investigation was to test the effectiveness of the Acoustic Emission (AE) mea- surements in determining the critical stresses during four-point bending of mortar beams. Within the measuring procedure the parameter σcr/σ300 was calculated and analysed. Additionally, the influence of cement replacement by high calcium fly ash (HCFA) on the process of crack healing was discussed. Mortar beams with different content of HCFA and reinforced by steel microfibres were prepared for tests. After curing in standard conditions the beams were subjected to four-point bending test in order to introduce the pre-cracking. Thereafter the beams were cured in the lime water and loaded after 56 and 112 days in the same way as for the first time. Additionally the microstructure of mortars was studied in a stereo optical microscope as well in an electron scanning microscope including the Energy Dispersive X-ray analysis (EDX). The results of microstructural characterization of mortar containing HCFA from lignite combustion are presented. The applied load level slightly exceeded the critical stress, producing intense crack growth processes however did not significant affected the load capacity of the beams. During the consecutive loading the decreasing tendency of σcr/σ300 ratio was noted. The obtained results confirm that the latter parameter can be applied as a measure of the composite degradation level for the elements carrying the repeated loads of amplitude close to the critical stress of the structure and also that the cement replacement with HCFA influences the process of crack healing.

5

Effectivness of dispersion strengthening in the NiAl intermetallic alloy produced by self-sustaining high-temperature synthesis

Witczak Z., Dymek S.

Archives of Metallurgy and Materials

|

2009

|

Vol. 54, iss. 3

747-753

EN

The stoichiometric NiAl intermetallic alloy strengthened by nano-particles of Al2O3 was produced by self-sustaining high-temperature synthesis (SHS). The particles, in the volume quantity of 2.5 and 5%, were introduced into the material at the stage of mechanical mixing of elemental nickel and aluminium powders. Two methods of mechanical mixing of powders were employed: a conventional one, where the powders were mixed in a ball rotational mixer (in air) and the ultrasonic method, where the powders were mixed by high intensity ultrasound in a liquid (acetone) or gaseous (helium) medium. The mixed powders were subjected to the SHS process. All synthesised materials were densified by hot hydrostatic extrusion (hydroextrusion) at the same conditions (1000C, 4:1 reduction ratio). The effectiveness of the applied technological procedure was estimated from the mechanical properties of the produced materials. Mechanical properties were measured by means of uniaxial compression tests. Beside the as-received materials, the materials after high-temperature annealing were tested. This permitted evaluation of the thermal stability of the materials. Strength and plastic properties of the materials were determined from an acoustic emission being monitored during the test. As a measure of the quality of the synthesized alloys, the product of the yield strength and the maximal true plastic strain was proposed. Using this measure, it was established that the ultrasonic method of doping nano-particles is more effective, and that the most desireable quantity of the Al2O3 dispersoid in the NiAl matrix is less than 5% by volume.

PL

Zbadano wpływ technologii wprowadzania nanocząstek Al2O3 do osnowy stechiometrycznego związku międzymetalicznego NiAl na efektywność procesu dyspersyjnego umacniania stopu. Nanocząstki, w ilosci 2,5 i 5% obj., były wprowadzane mechanicznie do materiału na etapie mieszania proszków wyjściowych niklu i aluminium przed procesem samopodtrzymującej się wysokotemperaturowej syntezy (SHS). Zastosowano dwie procedury mieszania: tradycyjna, w mieszalniku kulowym (w powietrzu) oraz ultradźwiękowa w ośrodku ciekłym (aceton) i gazowym (hel). Po procesie syntezy wszystkie materiały były dogęszczane przez wyciskanie hydrostatyczne na goraco (1000 C, współczynnik wyciskania 4) w jednakowych warunkach. Efektywność całego procesu technologicznego oceniano na podstawie własności mechanicznych wytworzonych materiałów, bezpośrednio po hydroekstruzji oraz, w celu oszacowania ich stabilności termicznej, po wysokotemperaturowym wyżarzaniu. Własności mechaniczne mierzone były w próbie jednoosiowego ściskania. Dzięki monitorowaniu, metodą emisji akustycznej, całego procesu odkształcania materiału można było okreslić nie tylko jego wytrzymałościowe, ale również plastyczne własności. Zaproponowano używanie iloczynu granicy plastyczności i odkształcenia plastycznego w próbie ściskania jako miare jakości materiałów półkruchych, takich jak związki międzymetaliczne. Przy użyciu tego wskaźnika stwierdzono, że metodą ultradźwiękowa jest efektywniejsza od tradycyjnej, oraz, że pozadana zawartość cząstek umacniajacych Al2O3 w osnowie NiAl mieści się w przedziale 0-5% objętościowych.

6

Random hydrogen-induced stresses and effects on cracking

Hołobut P., Sobczyk K.

Archives of Mechanics

|

2007

|

Vol. 59, nr 6

559-579

EN

The paper presents a method for quantitative characterization of random hydrogen-induced stresses. The method is based on randomized diffusion-elasticity equations. Also a stochastic parametric model, suitable for representing relevant empirical data, is outlined. The general considerations are illustrated by two particular examples. The first one concerns the effect of random hydrogen concentration on material failure time in a half-space, whereas the second one shows its effect on the ModeI stress intensity factor for a crack in a circular cylinder.

7

Damage modelling framework for viscoelastic particulate composites via a scale transition approach

Nadot C., Dragon A., Trumel H., Fanget A.

Journal of Theoretical and Applied Mechanics

|

2006

|

Vol. 44 nr 3

553-583

EN

The aim of this paper is to pursue, in the wake of the work by Nadot-Martin et al. (2003), a non-classical micromechanical study and scale transition for highly filled particulate composites with viscoelastic matrices. The present extension of a morphology-based approach due to Christoffersen (1983), carried forward to the viscoelastic small strain context by Nadot-Martin et al. (2003), consists here in introducing a supplementary mechanism, namely damage by grain/matrix debonding. Displacement discontinuities (microcracks) on grain/matrix interfaces are first incorporated in a compatible way within geometric and kinematic hypotheses regarding the grains-and-layers assembly of Christoffersen. Then, local field expressions as well as homogenized stresses are established and discussed for a given state of damage (i.e. for a given actual number of open and closed microcracks) and using the hypothesis of no sliding on closed crack lips. A comparison with the results obtained for the sound viscoelastic composite by Nadot-Martin et al. (2003) allows to quantify the damage influence on local and global levels. At last, the basic formulation of the model obtained by scale transition is completed by the second stage leading to a thermodynamically consistent formulation eliminating some superfluous damaged-induced strain-like variables related to open cracks. This second stage is presented here for a simplified system where delayed (viscoelastic) effects are (tentatively) neglected. It appears as a preliminary and crucial step for further generalization in viscoelasticity.

PL

Celem tej publikacji jest sformułowanie wieloskalowego modelu mikromechanicznego dla granulowanych kompozytów o wysokim stopniu upakowania inkluzji w osnowie lepkosprężystej. Przedstawiony model, będący rozwinięciem morfologicznego podejścia Christoffersena (1983) i Nadot-Martin i in. (2003) w zakresie małych odkształceń lepkosprężystych, polega na wprowadzeniu do analizy dodatkowego mechanizmu uszkodzenia - mikropękania na granicy inkluzji i osnowy. Mikroszczeliny na granicy inkluzji i osnowy uwzględniono w hipotezie geometrycznej i kinematycznej metody Christoffersena. Następnie, wyznaczono lokalne oraz uśrednione pola naprężenia dla zadanego stanu uszkodzenia (tzn. dla zadanej liczby otwartych i zamkniętych mikroszczelin przy pominięciu poślizgów na powierzchniach mikroszczelin zamkniętych). Porównanie z wynikami uzyskanymi przez Nadot-Martin i in. (2003) dla nieuszkodzonego kompozytu lepkosprężystego pozwoliło na określenie wpływu uszkodzenia na poziomie lokalnym i globalnym. Na koniec, podstawowy model wieloskalowy uzupełniono o drugą część sformułowania, która pozwoliła usunąć pewne nadmiarowe odkształcenia związane z mikroszczelinami otwartymi, czyniąc cały model termodynamicznie spójnym. Ta druga część modelu wieloskalowego jest przeprowadzona przy założeniu upraszczającym, polegającym na (tymczasowym) pominięciu efektów lepkosprężystych.

8

On the problem of crack propagation in porous ceramic materials

Sadowski T., Samborski S.

Folia Societatis Scientiarum Lublinensis

|

2000

|

vol. 9

135-141

EN

In the paper two types of porosity were considered: distributed inside grains and along grain boundaries. The pores distributed along grain boundary lead to significant crack resistance reduction in that part of the materiał. These b-cal weakening places create preferential conditions for microcracks growth, which are responsible for internal damage process in macroscale. The proposed theory was illustrated by uniaxial compression loading process of polycrystalline MgO sample.

PL

W pracy rozważono dwa rodzaje porowatości: wewnątrz-ziarnową i między-ziarnową. Pory rozsiane wzdłuż granic ziaren polikryształu powodują znaczny spadek odporności materiału na pękanie w miejscu ich występowania. Stwarzają one bowiem dogodne warunki dla rozwoju mikropęknięć, odpowiedzialnych za wewnętrzny proces uszkodzenia widziany w skali globalnej. Zaproponowany model teoretyczny zobrazowano przez proces jednoosiowego ściskania próbki polikrystalicznego tlenku magnezu (MgO).