formation of cracks
Recently Published Documents


TOTAL DOCUMENTS

206
(FIVE YEARS 65)

H-INDEX

15
(FIVE YEARS 2)

2022 ◽  
Vol 334 ◽  
pp. 04015
Author(s):  
Daria Vladikova ◽  
Blagoy Burdin ◽  
Asrar Sheikh ◽  
Paolo Piccardo ◽  
Milena Krapchanska ◽  
...  

This work aims at development of Accelerated Stress Tests for SOFC via artificial aging of the fuel electrode applying chemical and electrochemical (hydrogen starvation) redox cycling. In principle the degradation processes follows that of calendar aging (Ni coarsening and migration), but in addition it can bring to irreversible damages caused by the development of cracks at the interface anode/electrolyte due to the expansion/shrinkage of the Ni network. The challenge is to introduce conditions which will prevent the formation of cracks which can be done by partial oxidation. The advantage of the proposed methodology is that a mild level of oxidation can be regulated by direct impedance monitoring of the Ni network resistance changes during oxidation/reduction. Once the redox cycling conditions are fixed on bare anode and checked on anode/electrolyte sample for eventual cracks, the procedure can be introduced for AST in full cell configuration. The developed methodology is evaluated by comparative impedance analysis of artificially aged and calendar aged button cells. The results for 20 redox cycles which can be performed for 24 hours are comparable with those obtained for about 1600 hours operation in standard conditions which ensures more than 50 times acceleration.


Author(s):  
Gustavo Sipp ◽  
Guilherme Aris Parsekian

Abstract This study aims to evaluate the adherence between clay blocks and grouts. For this purpose, push-out and pull-out tests were performed to assess the adherence presented by different combinations of five types of clay blocks and two types of grouts. The results demonstrated that the geometry of the cells of the clay blocks has a preponderant role in their adherence with grout, as the extent of the contact area between grout and block depends on the geometry of the cell. The shrinkage of the grout can cause the formation of cracks at the interface between block and grout, reducing the adherence between the materials. The shrinkage formed inside each type of block can be estimated based on the testing procedure developed in this research and used in conjunction with the geometric characteristics of the cells of the blocks to estimate the maximum load in the push-out tests. The test procedure developed to estimate the percentage of contact area lost due to grouts shrinkage shows to be promising, since its results were used in the equation to estimate the bond strength between blocks and grouts and shown good correlation. However, more study must be done because there are other variables that can affect the results. These results show that it is possible to use different characteristics of blocks and grouts to increase the adherence between these materials and provide a better behavior for reinforced masonry structures. However, it looks like if block types with a grooved hollow cell are used, a bigger contact surface is produced, and a higher bond strength appears to be assured.


2021 ◽  
Vol 105 (1) ◽  
pp. 431-440
Author(s):  
Pavel Šafl ◽  
Jana Zimáková ◽  
Tomáš Binar

The aim of this work is to study the climatic influences on 3D printed materials. This study focuses on the HIPS material, which was chosen as the starting material for further studies. The material in the field of 3D printing is known for its rapid photooxidation, which results in the formation of cracks in the final product. A climatic chamber was used for degradation, in which UV light, heat and increased humidity were applied to the material. The degree of degradation was then checked by tensile test and electron microscope.


2021 ◽  
Vol 903 ◽  
pp. 197-202
Author(s):  
Ruta Švinka ◽  
Visvaldis Švinka ◽  
Maris Rundans ◽  
Inta Timma ◽  
Laila Petersone

Clay of the deposit Liepa is used for the production of ceramic building and finishing bricks in the factory “Lode” in Latvia. In the present work different types of these clays were investigated and “quartz effect” was determined using quartz sand as a leaning material. The substitution of quartz sand with milled E-glass fibre from Valmiera Glass was investigated and the changes in the magnitude of the quartz inversion effect were analysed. Thermal expansion was the main method for the determination of possible formation of cracks during technological process. Powder of milled glass fibre in amount of 5–10 % affects such properties as water uptake, porosity and apparent density and provides the required material properties at a lower firing temperature.


2021 ◽  
Vol 2094 (4) ◽  
pp. 042030
Author(s):  
O A Maykov ◽  
E A Kokhonkova ◽  
T N Baturin

Abstract The paper deals with the issue of diagnostics of main pipelines by the vibration method, exploring the influence of the formation of cracks in the walls of the pipeline on the change in the frequency characteristics of the pipeline. By analyzing the difference in the natural oscillation frequency of a pipe with a crack and without it, it is possible to assess the location of the defect with a certain accuracy. The issue of the possibility of reading the natural oscillations of the main pipeline from the surface of the soil located above the pipeline is also being studied.


2021 ◽  
Vol 2094 (4) ◽  
pp. 042037
Author(s):  
A M Khakimov ◽  
K V Nikitin ◽  
S S Zhatkin

Abstract This paper presents the development of stable modes of additive technology of direct laser growing, using the starting material - a metal powder made of heat-resistant EP648 alloy of Russian production. The subsequent heat treatment of the manufactured samples was tested in order to avoid the formation of cracks in the structure of the material formed as a result of the presence of internal stresses after surfacing. Recommendations for further research are given.


2021 ◽  
Author(s):  
Pedro Navarrete-Segado ◽  
Mallorie Tourbin ◽  
Christine Frances ◽  
David Grossin

In this paper, the tailoring of hydroxyapatite powders properties for the preparation of highly hydroxyapatite-loaded photocurable organic slurries was discussed. A methodical study was conducted to investigate suspensions properties and processability to find the most outstanding formulation for the production of hydroxyapatite scaffolds by stereolithography-based additive manufacturing technique. A debinding-sintering process was designed to avoid the formation of cracks during the pyrolysis of the resin and sintering of the ceramic part. A total porosity of 35 vol. % was observed for the scaffolds with an interconnected macroporosity, which could facilitate the flow transport of nutrients necessary to maintain living cells. A compression strength of 4.9±0.3 MPa was obtained for the specimens printed diagonally (45º to the printing stage surface). A slow degradation rate was shown for the printed parts mainly due to the high degree of crystallinity and the intrinsic stability of the hydroxyapatite phase. Our findings indicate that the tailoring of hydroxyapatite powders is needed for better processability as filler in photocurable suspensions. Moreover, it was demonstrated the feasibility of printing hydroxyapatite parts showing promising results for their application in surgery in the case of minor or non-load bearing implants requiring slow resorption properties.


2021 ◽  
pp. 53-60
Author(s):  
V.A. Zharkov

The theory and calculation of the parameters of the strain-stress state at the stages of pre-bending, calibration, straightening, bending of a straightened section and bending of the subsequent sections, taking into account the hardening of the billet on a roller machine, is developed. Deformations, stresses and forces acting on the billet from the rolls were investigated by CAD/CAE-modeling. Criteria for the formation of cracks, low accuracy and excessive springback of the part after these stages of processing are determined. Recommendations for the elimination of these defects are given. Keywords: sheet stamping, billet, bending, roller machine, pre-bending, calibration, straightening, CAD/CAE modeling. [email protected]


2021 ◽  
Vol 15 (58) ◽  
pp. 33-47
Author(s):  
Ahcene Arbaoui ◽  
Abdeldjalil Ouahabi ◽  
Sebastien Jacques ◽  
Madina Hamiane

This paper proposes an efficient methodology to monitor the formation of cracks in concrete after non-destructive ultrasonic testing of a structure. The objective is to be able to automatically detect the initiation of cracks early enough, i.e. well before they are visible on the concrete surface, in order to implement adequate maintenance actions on civil engineering structures. The key element of this original approach is the wavelet-based multiresolution analysis of the ultrasonic signal received from a sample or a specimen of the studied material subjected to several types of solicitation. This analysis is finally coupled to an automatic identification scheme of the types of cracks based on artificial neural networks (ANNs), and in particular deep learning by convolutional neural networks (CNNs); a technology today at the cutting edge of machine learning, in particular for all applications of pattern recognition. Wavelet-based multiresolution analysis does not add any value in detecting fractures in concrete visible by optical inspection. However, the results of its implementation coupled with different CNN architectures show cracks in concrete can be identified at an early stage with a very high accuracy, i.e. around 99.8%, and a loss function of less than 0.1, regardless of the implemented learning architecture.


2021 ◽  
Author(s):  
Iqra Bashir ◽  
Zafar Iqbal Shams ◽  
Syed Ehteshamul-Haque ◽  
Faizah Urooj ◽  
Hafiza Farhat

Abstract The present study aims at identifying the ability of nine fungal species, which were isolated from garbage of different sites to degrade commonly used polymers, viz. polyethylene, polystyrene, and polyurethane when treated with four methods separately, viz., sterilized and unsterilized drench methods, sterilized and unsterilized mulching methods for four months. All the species considerably degraded the polymers by the above-mentioned methods. However, polystyrene demonstrated the greatest degradation compared to the other two polymers, particularly by sterilized and unsterilized drench methods. Seven fungal species caused greater than 50% weight loss of polystyrene when treated with the above-mentioned methods. Aspergillus flavus instigated the greatest weight loss (74.78 ± 2.85%) by the unsterilized drench method. Of nine, three species caused more than 50% weight loss of polyurethane by the unsterilized drench method. A. niger divulged greater than 50% weight loss of the polymer by sterilized drench method. In this study, polyethylene was found least degraded compared to polystyrene and polyurethane by the selected fungal species. Of nine, only two species, viz. Aspergillus flavus and A. niger caused a higher than 50% weight loss of polyethylene only by sterilized drench method. Scanning Electron Microscopy (SEM) images of six elevated degraded polymer samples were taken to reveal the formation of spores and hyphae on the surface of the plastic. The images demonstrated the formation of cracks and crevices on the surface of different polymers by spores and the fungal hyphae.


Sign in / Sign up

Export Citation Format

Share Document