Formation Of Cracks
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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.


2022 ◽  
Author(s):  
Bassem Andrawes ◽  
◽  
Ernesto Perez Claros ◽  
Zige Zhang ◽  
◽  
...  

The deterioration of bridge decks is a problem typically associated with the corrosion of the reinforcing steel. This issue was partially controlled during the 1970s with the incorporation of the epoxy-coating protection system. However, research later demonstrated that the smooth surface resulting from the epoxy-coating application reduces most of the friction between the rebar and the surrounding concrete. Consequently, forces acting on the rib faces are reconfigured in such a way that the radial components increase, triggering the early development of cracks. To mitigate both the reduction of bonding and the formation of cracks, the Illinois Department of Transportation proposed a new type of coated bars: textured epoxy-coated (TEC) bars. Over the last few years, different projects have been executed to understand and improve the characteristics of TEC rebars. This report is a continuation of research performed at the University of Illinois Urbana-Champaign to evaluate the bond behavior of TEC bars. The experimental program starts by characterizing, qualitatively and quantitatively, the roughness of the TEC rebars. Next, their bond-slip interaction embedded in concrete is evaluated through pull-out tests. Finite element models of these tests are developed to validate the behavior observed as the textured reinforcement loses anchorage with concrete. Based on these results, the experimental program then aims to study the impact of the drying shrinkage, temperature change, and flexural demands on two large-scale bridge deck specimens reinforced, individually, with TEC and standard epoxy-coated bars. The results collected from both specimens using digital image correlation and strain gauges are compared to explore the differences exhibited by the traditional and the new type of reinforcement coatings in terms of stress distribution in bridge decks. Finally, given the specialized equipment and time-consuming procedure needed to calculate the roughness parameters of TEC bars, an empirical, weight-based approach is developed as a rapid method for assessing the rebars’ roughness on-site.


2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Bo Wu ◽  
Hualong Li ◽  
Guowang Meng ◽  
Shixiang Xu ◽  
Jinglong Zhang ◽  
...  

Rock mass blasting is a complex process that involves the coupling of both discontinuous and continuous media. This paper aims to reveal the dynamic failure process between adjacent boreholes under an elliptical bipolar linear charge structure using the SPH-FEM (smooth particle hydrodynamics and finite-element method) coupling algorithm numerical simulation method. The numerical simulation results are compared with the existing experimental results, which proves the rationality of the algorithm. According to the numerical simulation results, the shaped jet will first shock the hole wall and form a stress concentration zone that will guide the formation of cracks during the stress wave propagation process. In the case of double-hole blast loading, there is a tendency for cracks coalescence to develop between adjacent boreholes due to the superposition of stresses between the double holes and the increase in damage and plastic strain. The best blasting results will be achieved with this structure when the distance between adjacent holes is 110 cm. Finally, the superiority of elliptical bipolar linear blasting in engineering blasting was verified through field experiments. The results of this study provide a reference for subsequent applications of elliptical bipolar structures in the field of rock blasting.


2021 ◽  
Vol 6 (1) ◽  
pp. 5
Author(s):  
Tim Richter ◽  
Marcel Giese ◽  
Michael Rhode ◽  
Dirk Schroepfer ◽  
Thomas Michael ◽  
...  

Multi-element systems with defined entropy (HEA—high entropy alloy or MEA—medium entropy alloy) are rather new material concepts that are becoming increasingly important in materials research and development. Some HEA systems show significantly improved properties or combinations of properties, e.g., the overcoming of the trade-off between high strength and ductility. Thus, the synthesis, the resulting microstructures, and properties of HEA have been primarily investigated so far. In addition, processing is crucial to achieve a transfer of potential HEA/MEA materials to real applications, e.g., highly stressed components. Since fusion welding is the most important joining process for metals, it is of vital importance to investigate the weldability of these materials. However, this has rarely been the subject of research to date. For that reason, in this work, the weldability depending on the surface preparation of a CoCrFeMnNi HEA and a CoCrNi MEA for TIG welding is investigated. The fusion welding of longer plates is described here for the first time for the CoCrNi alloy. The welds of both materials showed distinct formation of cracks in the heat affected zone (HAZ). Optical and scanning electron microscopy analysis clearly confirmed an intergranular fracture topography. However, based on the results, the crack mechanism cannot be conclusively identified as either a liquid metal embrittlement (LME) or hot cracking-like liquid film separation.


2021 ◽  
Author(s):  
Zhi-xiong Bi ◽  
Xue-jiao Li ◽  
Ting-zhao Zhang ◽  
Quan Wang ◽  
Kai Rong ◽  
...  

Abstract In order to study the interface characteristics and microstructure formation of Ti-Al composite plate, explosive welding was carried out with TA2 titanium as the fly plate and 5083 aluminums as the base plate. Optical microscope and electron microscope were used to analyze the microstructure of intermetallic compounds. SPH method was used to simulate the welding process of composite plates. The formation conditions and initial defects of intermetallic compounds were analyzed. The results show that most of the melted metal in the wave-front stays in the wave-waist region, and there was a relative velocity difference between the vortex and the titanium tissue, which led to the existence of small pieces of fragmentation. The outer layer of the vortex had higher velocity than the inner layer. The formation of Ti3Al, its antioxidant capacity wound lead to the formation of cracks. The temperature of outer vortex was higher than that of inner vortex, and the vortex has a transition layer of 5 μm, which is thinner than the transition layer of 8 μm between cladding plate and substrate. The jet was mostly composed of aluminum metal, and the interface jet velocity reaches 3000 m·s-1 and the interface temperature reaches up to 2100 K. Compared with the molten metal in the wave-back vortex, the jet temperature at the interface was higher, resulting in a thicker transition layer at the bonding surface. The residual stress at the interface wound cause the density of the material to increase.


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 1197 (1) ◽  
pp. 012017
Author(s):  
Rajat Mohan ◽  
Aakash Gupta ◽  
Kshitij Gaur

Abstract With continuous wear and tear actions of rubber tyre on roads, a pile of waste rubber gets accumulated every year and it is posing severe threats to the environment. Due to high temperature in the summers, the road tends to become brittle, which may cause separation of binder in the bituminous road causing heavy cracks, so usage of wax tends to reduce the formation of cracks and improve the flexibility of road. This study aims to examine the effects on properties of the bitumen-aggregate mixture when the aggregates are partially replaced by similar sizes of waste rubber tyre particles and bitumen in the mix are partially replaced by a crumb waste rubber tyre, with partial addition of wax content in the bituminous samples. For this purpose of testing the suitability of using rubber waste in road pavement, Marshall Stability test is conducted on several bituminous mixtures. Varying percentages of rubber tyre, such as 0%, 5%, 10% and 15%, are used with different percentages of bitumen content (4.0, 4.2, 4.4, and 4.6), and varying percentages of paraffin wax (0-5%) is also added in the specimen with rubber and bitumen. This is utilized in obtaining the optimum content of bitumen required for best suitability of flexible pavement as well as to assess the durability and strength of a pavement. This study is performed on various mixtures, for the values of bulk density, air voids, stability value and flow value. The studies show that bitumen content corresponding to the maximum stability value and maximum bulk specific gravity in bituminous mixture, indicating the optimum bitumen percentage that can be replaced with crumb rubber tyre. This paper discusses the partial replacement of both aggregate and bitumen in the bituminous mixture, containing some percentages of paraffin, which can help in improving the serviceability level and assists in enhancing the flexibility and cohesion of road to resist heavy loadings of vehicle.


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.


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