scholarly journals Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 319
Author(s):  
Grzegorz Ludwik Golewski ◽  
Damian Marek Gil
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fly Ash ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Early Age ◽  
Strength Parameters ◽  
Cement Binder ◽  
Mineral Additives

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor—KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

scholarly journals Determination of fracture toughness for steel 22k from the results of tests of different types specimens

2021 ◽  
pp. 20-25
Author(s):  
Andriy Kravchuk ◽  
Ievgen Kondriakov
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fracture Energy ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
J Integral ◽  
Heat Resistant Steel ◽  
Impact Tests

Nowadays, in various industries, in particular in nuclear energy, to determine the fracture toughness, along with standard tests of compact specimens, which are quite expensive and complex, methods are developed to determine these characteristics by impact tests of Charpy specimens using different correlations between Charpy impact fracture energy (CVN) and critical stress intensity factor (J-integral). The paper analyzes correlation and analytical methods, the authors of which consider them universal for a certain class of steels. Correlation methods are divided into one-stage and two-stage. One-stage methods allow to obtain the value of the critical stress intensity factor by the known fracture energy. Two-stage methods in the first stage offer the calculation of the dynamic critical stress intensity factor, in the second the temperature shift and obtaining a static critical stress intensity factor. Analytical methods according to the іmpact fracture diagram of the specimen allow to construct a J-R curve and calculate the value of the J-integral. A series of fracture tests of CT specimens made of heat-resistant steel 22K was carried out, the reference temperature T0 was determined according to the single-temperature method of the ASTM-1921 standard and the Master curve was constructed. A series of standard Charpy specimens impact tests in the temperature range -50…+100°С was performed using an instrumented drop-weight impact testing machine equipped with a high-speed registration system. According to the results of Charpy specimens impact tests, the fracture toughness were determined using different methods. It is established that both analytical and correlation methods cannot be universal and can be used to determine the fracture toughness of 22K steel. Therefore, a new exponential correlation was proposed between the fracture energy of the Charpy specimens and the critical stress intensity factor for heat-resistant steel 22K.

Effect of Grain Size on the Fracture Toughness of Bimodal Nanocrystalline Materials

2014 ◽  
Vol 936 ◽  
pp. 400-408 ◽  
Author(s):  
Ying Guang Liu ◽  
Xiao Dong Mi ◽  
Song Feng Tian
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Grain Size ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Cohesive Zone ◽  
Critical Stress ◽  
Crack Tip ◽  
Critical Stress Intensity Factor ◽  
Coarse Grain

To research the effect of grain size on the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials by considering a typical case where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, the cohesive zone size is assumed to be equal to the grain sizedof the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It was found that the critical stress intensity factor increases with the increasing of grain sizedof the NC matrix as well as the coarse grain sizeD. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size rather than that of NC matrix.

Effects of Electric Field on the Fracture Toughness (KIC) of PZT Ceramics

2011 ◽  
Author(s):  
Sam Goljahi ◽  
David Pisani ◽  
John Gallagher ◽  
Christopher S. Lynch
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Electric Field ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Field Application ◽  
Four Point Bending ◽  
Dc Electric Field

Ceramic PZT with a controlled crack was subjected to combined four point bending and longitudinal electric field loading to determine the fracture toughness (KIC) as a function of electric field. Application of a positive DC electric field (in the polarization direction) during mechanical loading was observed to reduce the critical stress intensity factor and application of a negative electric field increased the critical stress intensity factor.

scholarly journals Increasing the crack resistance of high-strength self-compacting concrete

2021 ◽  
Vol 1 (1(57)) ◽  
pp. 17-24
Author(s):  
Vyacheslav Troуan ◽  
Bogdan Kindras
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Silica Fume ◽  
Critical Stress ◽  
High Strength ◽  
Critical Stress Intensity Factor ◽  
Self Compacting Concrete ◽  
Mineral Additive ◽  
Mineral Additives ◽  
Positive Effect

The object of research is high-strength self-compacting concrete, which does not require additional vibration during laying. One of the most problematic issues of high-strength self-compacting concretes is increased cracking, associated with large shrinkage deformations of such concretes and their fragile destruction. A decrease in shrinkage deformations of concrete was established when part of the cement was replaced to mineral additives. This effect is explained by a decrease of the cement content and, accordingly, a decrease of the chemical component of the autogenous shrinkage of concrete, and an increase of the adsorptive binding of capillary moisture by mineral additives, with reduces the physical drying shrinkage of concrete. In this case, the type and dispersion of the used mineral additive can affect to the shrinkage deformations of concrete. A significant decrease in shrinkage deformations when using metakaolin is explained by an increase the amount of ettringite as a result of the reaction of active metakaolin Al2O3 with two-water gypsum of cement. It was found that the replacement of cement to 10 % of mineral additives leads to a decrease in the value of the critical stress intensity factor (SIF), which is compensated by a decrease of the fragility of concrete fracture (an increase of the area of microplastic deformations). At the same time, the type of mineral additive used does not affect to the value of the critical stress intensity factor, but significantly affects to the fragility of fracture of concrete samples. The introduction of 10 % mineral additives (to replace cement) had a positive effect on the retention of flow of self-compacting concrete mixes; the best results according to this criterion were observed when using silica fume, fly ash and limestone. All mineral modifiers, except for silica fume, led to a decrease of the compressive strength of high-strength concretes on all terms of hardening. In the case of the tensile strength of concrete at bending and splitting, with the introduction of silica fume, metakaolin and fly ash, a positive effect was observed compared to the base composition without additives. Comprehensive accounting of the results obtained will allow a reasonable approach to the design of high-strength self-compacting concretes with increased crack resistance.

Fracture Toughness of Nanomodified-Epoxy Systems

2013 ◽  
Vol 393 ◽  
pp. 206-211 ◽  
Author(s):  
Aidah Jumahat ◽  
Constantinos Soutis ◽  
Ahmad Nurulnatisya ◽  
Wan Mazlina Wan Mohamed
Keyword(s):  
Carbon Nanotubes ◽  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Release Rate ◽  
Critical Stress ◽  
Critical Energy ◽  
Critical Stress Intensity Factor ◽  
Critical Energy Release Rate

The effect of nanosilica, multiwalled carbon nanotubes (MWCNT) and montmorillonite (MMT) nanoclay on critical stress intensity factor and critical energy release rate of Epikote 828 epoxy polymer was studied. Fracture toughness tests were conducted on three types of nanocomposites which contain 5-25 wt% nanosilica, 0.5-1 wt% MWCNT and 1-5 wt% MMT nanoclay. The compact tension specimens of 9 mm initial crack length were fabricated and tested in tension. It was found that, the load at crack growth initiation FQfor all nanomodified polymer systems was higher than that of the neat epoxy. Hence, the presence of nanosilica, carbon nanotubes and nanoclay improves the critical stress intensity factor and critical energy release rate of the polymer. For the nanoclay-modified epoxy system, the degree of enhancement depends on the morphology of the nanocomposites. At high nanoclay content (> 3 wt%), a detrimental effect on the fracture toughness was observed. This is due to a weak nanomer/epoxy interfaces in a highly intercalated structure nanocomposite.

Fractography of Dense Metal-Like Carbides Sintered with Carbon

2009 ◽  
Vol 409 ◽  
pp. 287-290 ◽  
Author(s):  
Agnieszka Gubernat ◽  
Ludosław Stobierski
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Periodic Table ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Carbon Powder ◽  
Carbon Compounds ◽  
The Way

Metals belonging to groups 4-6 of periodic table of elements form with carbon compounds named metal-like carbides (WC, TiC1-x, NbC, TaC, CryCz). It was established that is possible to achieve dense sintered bodies of this carbides at temperatures near 2000oC using only carbon powder as an additive. Its role consists in reduction of oxide impurities. Presented paper summarized investigations on sintering of metal-like carbides with carbon. Dense WC, TiC1-x, NbC, TaC and CryCz bodies were characterized by KIc factor value. A special care was taken on microstructure and the way of fracture description in relation to the critical stress intensity factor (KIc). It was established that the way of fracture and the finally fracture toughness depend on type of microstructure and degree of nonstoichiometry.

scholarly journals The use of fractal geometry in determination of fracture toughness of metakaolinite modified concrete

2013 ◽  
Vol 12 (3) ◽  
pp. 177-184
Author(s):  
Janusz Konkol
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Compressive Strength ◽  
Fractal Dimension ◽  
Stress Intensity ◽  
Fractal Geometry ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Independent Variables

The aim of the paper is to present the results of experiments on concretes after 180 days of hardening with metakaolinite addition. Measurements of compressive strength fc, critical stress intensity factor KIcS and fractal dimension Dm were performed. The plan included nine measurement points. Water/binder ratios ranging from 0.35 to 0.54, and the metakaolinite additives in the amount ranging from 2.1 to 14.9 % relative to the mass of binder were used as independent variables. Statistically significant correlations were given. The proposed solutions can be used in designing the concrete with metakaolinite, which enables the prediction of KIcS after 180 days of hardening concrete with no need for destructive tests.

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