Zeitschriftenartikel: „Roll Spallings“

1

Hager, Izabela, und Katarzyna Mróz. „Role of Polypropylene Fibres in Concrete Spalling Risk Mitigation in Fire and Test Methods of Fibres Effectiveness Evaluation“. Materials 12, Nr. 23 (23.11.2019): 3869. http://dx.doi.org/10.3390/ma12233869.

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The explosive behaviour of concrete in fire is observed in rapidly heated concrete. The main factors controlling the occurrence of spalling are related to the material’s low porosity and high density as well as the limited ability to transport gases and liquids. Thus, for high-strength, ultrahigh-strength, and reactive powder concrete, the risk of spalling is much higher than for normal-strength concrete. The paper presents the discussion on the leading hypothesis concerning the occurrence of concrete spalling. Moreover, the methods for spalling prevention, such as polypropylene fibre application, which has been found to be an effective technological solution for preventing the occurrence of spalling, are presented. Various tests and testing protocols are used to screen concrete mixes propensity toward spalling and to evaluate the polypropylene fibres’ effectiveness in spalling risk mitigation. The most effective testing methods were selected and their advantages were presented in the paper. The review was based mainly on the authors’ experiences regarding high performance concrete, reactive powder concrete testing, and observations on the effect of polypropylene fibres on material behaviour at high temperature.

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2

Miah, Md Jihad, Francesco Lo Monte, Roberto Felicetti, Hélène Carré, Pierre Pimienta und Christian La Borderie. „Fire Spalling Behaviour of Concrete: Role of Mechanical Loading (Uniaxial and Biaxial) and Cement Type“. Key Engineering Materials 711 (September 2016): 549–55. http://dx.doi.org/10.4028/www.scientific.net/kem.711.549.

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Fire poses one of the most severe environmental conditions that can act on concrete structures as an external load and can induce severe damages (cracks, spalling) or even lead to collapse. Fire spalling of concrete is a complex phenomenon, which might occur due to pressure build-up in the pores, thermal and load-induced stresses. In this context, ordinary concrete specimens (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to standard fire curve (ISO 834-1), while a constant uniaxial or biaxial compressive load was applied. Six different levels of uniaxial compressive stress on cubes and four different levels of biaxial compressive stress on slabs have been investigated. The test results showed that loaded specimens are more susceptible to spalling than unloaded specimens, with increasing amount of spalling for higher values of applied load. It has been found that biaxially loaded specimens are more prone to spalling than uniaxially loaded specimens. B40-II concrete (3% of slag) exhibited higher spalling than the B40-III concrete (43% of slag).

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3

Zhao, Jie, Jian Jun Zheng und Gai Fei Peng. „Modeling of Vapor Pressure Build-Up in Heated High-Performance Concrete“. Applied Mechanics and Materials 204-208 (Oktober 2012): 3691–94. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.3691.

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Under high temperature conditions, such as fire, high-performance concrete will undergo material degradation or even spalling. Spalling is the most detrimental to concrete structures. To prevent concrete from spalling, the mechanism should be understood. Since the build-up vapor pressure in concrete is supposed to play a dominant role in spalling, a vapor pressure prediction model is proposed in this paper to quantitatively analyze the vapor pressure, which can be used for the spalling mechanism study.

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Tian, Kai Pei, Yang Ju, Hong Bin Liu, Jin Hui Liu, Li Wang, Peng Liu und Xi Zhao. „Effects of Silica Fume Addition on the Spalling Phenomena of Reactive Powder Concrete“. Applied Mechanics and Materials 174-177 (Mai 2012): 1090–95. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.1090.

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The explosive spalling of high-strength concrete due to fire is a problem that has garnered increasingly widespread attention, particularly the explosive spalling of reactive powder concrete (RPC). For years, based on the vapor pressure mechanism, the addition of fibers has been demonstrated to be somewhat effective in protecting against spalling. However, relevant experiments indicate that fibers are not effective for dense concrete, which is a challenge for the simple vapor pressure mechanism in providing spalling resistance for RPC. The authors found that silica fume plays an important role in the explosive spalling of RPC. Thus, four classes of RPCs with different ratios of silica fume were prepared, and the spalling phenomena and the inner temperature distribution during heating were investigated. The results show that silica fume content has a prominent effect on the spalling process of RPC.

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OHKOMORI, Yoshihiro, Ikuziro KITAGAWA, Keigo SHINOZUKA, Ritsuzo MIYAMOTO, Seiichi YAZAKI und Mutsuhiko INOUE. „Study on Spalling of Hot Strip Mill Backup Roll“. Tetsu-to-Hagane 73, Nr. 6 (1987): 691–98. http://dx.doi.org/10.2355/tetsutohagane1955.73.6_691.

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6

Zhang, Wenge, Christian Krempaszky und Ewald Werner. „Work-roll surface degradation due to spalling of oxide layer“. PAMM 7, Nr. 1 (Dezember 2007): 4030041–42. http://dx.doi.org/10.1002/pamm.200701045.

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7

Dong, Zhong Qi, Jun Suo Li und Jin Chen. „Research on CSP Work Roll Defect Causes and Improvement Measure“. Advanced Materials Research 652-654 (Januar 2013): 1388–92. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.1388.

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It was analysed that the causes for the poor wear resistance of roller, fracture of roller and the surface of the roller flaking off were researched. Introducing CSP plant carried through technical and improved works about work roll material and using system in order to improve strip quality and decrease producing costs. It’s effective to resolve wear and breakage and spalling of the work roll and improve profile control and so on.

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8

Mottahedi, Ali Akbar. „Investigation of Phase Transformation of Forged Steel Cold Rolls due to Heat Affecting and Prevent its Failure“. Defect and Diffusion Forum 289-292 (April 2009): 219–24. http://dx.doi.org/10.4028/www.scientific.net/ddf.289-292.219.

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In rolling Industries, cold rolls are chosen of low alloy steel heat treated to about 60 RC in 50 millimeter depth on surface. Troostite phase which happens in some cases in tempered martensite has lower fracture toughness, although its ductility is a little more. In rolling process, some technological problems seldom take place, and the roll might be locally heated accidentally. In cold rolling technology, this effect may cause a phase change in metallurgical structure on the surface of the cold work forged steel rolls, named Troostite. However, the rolls which subjected to this problem have no mechanical defect to be detected by NDT, but these kinds of affected rolls may be failed in working (rolling) by fracture, spalling or cracks. So Troostite is a harmful phase for rolls and causes lots of losses for rolling companies. The following paper is a practical industrial approach to show and follow thermal instability of roll surface and metallurgical change of the surface from sorbite to troostite by diffusion mechanism, due to any improper mill usage.

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OHKOMORI, Yoshihiro, Chu SAKAE und Yukitaka MURAKAMI. „Analysis of Mode II Crack Growth Behavior in Spalling Failure of Backup Roll.“ Journal of the Society of Materials Science, Japan 50, Nr. 3 (2001): 249–54. http://dx.doi.org/10.2472/jsms.50.249.

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10

Yoo, S. H., S. W. Shin und I. K. Kim. „Optimum Dosage of PP Fiber for the Spalling Control of High Strength Reinforced Concrete Columns“. Key Engineering Materials 348-349 (September 2007): 621–24. http://dx.doi.org/10.4028/www.scientific.net/kem.348-349.621.

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Spalling is defined as damages to concrete exposed to high temperature during fire, causing cracks and localized bursting of small pieces of concrete. As the concrete strength increases, the degree of damage caused by spalling becomes more serious due to impaired permeability. It has been reported that polypropylene(PP) fiber has an important role in protecting concrete from spalling, and the optimum dosage of PP fiber is 0.2%. However, this result was based on the fire test of non-reinforced concrete specimens. The high-temperature behavior of highstrength reinforced concrete columns with various concrete strength and various quantity of PP fibers is investigated in this study. The results revealed that the ratio of unstressed residual strength of columns increased as the concrete strength increased and as the quantity of PP fiber increased from 0% to 0.2% the residual strength of columns increase. However, the effect of PP fiber quantity on residual strength of column was barely above 0.2%.

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11

Galek, Artur, Harald Moser, Thomas Ring, Matthias Zeiml, Josef Eberhardsteiner und Roman Lackner. „Mechanical and Transport Properties of Concrete at High Temperatures“. Applied Mechanics and Materials 24-25 (Juni 2010): 1–11. http://dx.doi.org/10.4028/www.scientific.net/amm.24-25.1.

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When concrete structures are subjected to fire loading, temperature-dependent degradation of the material properties as well as spalling of near-surface concrete layers has a considerable effect on the load-carrying capacity and, hence, the safety of these structures. Spalling is caused by interacting thermo-hydro-chemo-mechanical processes with both mechanical and transport properties playing an important role. Within experimental research activities at the IMWS, these properties are subject of investigation, i.e., (i) the strain behavior of concrete under combined thermal and mechanical loading and (ii) the permeability increase of temperature-loaded concrete and cement paste.

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12

Pantazopoulos, G., und A. Vazdirvanidis. „Fractographic and Metallographic Study of Spalling Failure of Steel Straightener Rolls“. Journal of Failure Analysis and Prevention 8, Nr. 6 (16.09.2008): 509–14. http://dx.doi.org/10.1007/s11668-008-9170-5.

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13

Ne´lias, D., M. L. Dumont, F. Champiot, A. Vincent, D. Girodin, R. Fouge´res und L. Flamand. „Role of Inclusions, Surface Roughness and Operating Conditions on Rolling Contact Fatigue“. Journal of Tribology 121, Nr. 2 (01.04.1999): 240–51. http://dx.doi.org/10.1115/1.2833927.

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Tests have been performed on a two-disk machine in order to evaluate the role of inclusions, surface roughness and operating conditions on rolling contact fatigue of AISI 52100 and M50 bearing steels. Important parameters—such as nature and location of inclusions, small and large wavelengths of surface roughness, normal loading or sliding conditions—on crack initiation and propagation stages have been identified. The operating conditions have been selected to encompass typical jet engine applications. Tests have been carried out up to 4.2 GPa, for two different surface finishes. Surface distress and sub-surface damage which could result in catastrophic failure have been observed. Indeed, surface initiated deep spalling (observed at 3.5 GPa for unpolished surfaces and under rolling plus sliding conditions) as well as sub-surface initiated deep spalling (at 4.2 GPa for polished specimens) have been observed. Sub-surface micro-cracks were detected early and followed during some interrupted tests by the means of an ultrasonic echographic device. Results of our experiments are analyzed and discussed in relation to the rolling contact fatigue theories.

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Rohden, Abrahão Bernardo, Jessica Regina Camilo, Rafaela Cristina Amaral, Estela Oliari Garcez und Mônica Regina Garcez. „Effects of Plastic Waste on the Heat-Induced Spalling Performance and Mechanical Properties of High Strength Concrete“. Materials 13, Nr. 15 (23.07.2020): 3262. http://dx.doi.org/10.3390/ma13153262.

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This paper investigates a potential application of hard-to-recycle plastic waste as polymeric addition in high strength concrete, with a focus on the potential to mitigate heat-induced concrete spalling and the consequent effects on the mechanical properties. The waste corresponds to soft and hard plastic, including household polymers vastly disposed of in landfills, although technically recyclable. Mechanical and physical properties, cracking, mass loss, and the occurrence of spalling were assessed in high strength concrete samples produced with either plastic waste or polypropylene fibers after 2-h exposure to 600 °C. The analysis was supported by Scanning Electron Microscopy and X-Ray Computed Tomography images. The plastic waste is composed of different polymers with a thermal degradation between 250 to 500 °C. Polypropylene (PP) fibers and plastic waste dispersed in concrete have proved to play an essential role in mitigating heat-induced concrete spalling, contributing to the release of internal pressure after the polymer melting. The different morphology of plastic waste and polypropylene fibers leads to distinct mechanisms of action. While the vapor pressure dissipation network originated by polypropylene fibers is related to the formation of continuous channels, the plastic waste seems to cause discontinuous reservoirs and fewer damages into the concrete matrix. The incorporation of plastic waste improved heat-induced concrete spalling performance. While 6 kg/m3 of plastic increased the mechanical performance after exposure to high temperature, the incorporation of 3 kg/m3 resulted in mechanical properties comparable to the reference concrete.

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15

Ghosh, Soma, Pankhuri Sinha, Shivanandan Indimath, Goutam Mukhopadhyay und Sandip Bhattacharya. „Ribbon Fatigue Spalling of a Forged Work Roll Used at a Cold Rolling Mill“. Journal of Failure Analysis and Prevention 14, Nr. 6 (31.10.2014): 707–14. http://dx.doi.org/10.1007/s11668-014-9885-4.

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16

Zhou, Jing Ling, Xiao Yang Chen, Guo Qing Wu und Jian Chun Chen. „Fatigue Failure of Silicon Nitride Ceramic Balls“. Advanced Materials Research 148-149 (Oktober 2010): 774–77. http://dx.doi.org/10.4028/www.scientific.net/amr.148-149.774.

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Silicon nitride ceramic ball surface is examined after failure with scanning electron microscopy. The profile of the fatigue spalling takes the shape of an ellipse. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material, and propagate, to form fatigue spalls under the action of principal tensile stresses. The contours of equal tensile stress of Oxy plane underneath surface are elliptical. Subsurface cracks are shape of ellipses and spall is also of the elliptic shape. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life.

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17

OHKOMORI, Yoshihiro, Ikujiro KITAGAWA, Keigo SHINOZUKA, Ritsuxo MIYAMOTO, Seiichi YAZAKI und Mutsuhiko INOUE. „Cause and Prevention of Spalling of Backup Rolls for Hot Strip Mill“. Transactions of the Iron and Steel Institute of Japan 28, Nr. 1 (1988): 68–74. http://dx.doi.org/10.2355/isijinternational1966.28.68.

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18

Tseng, A. A., S. X. Tong, S. H. Maslen und J. J. Mills. „Thermal Behavior of Aluminum Rolling“. Journal of Heat Transfer 112, Nr. 2 (01.05.1990): 301–8. http://dx.doi.org/10.1115/1.2910376.

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Proper roll cooling has been identified as a critical factor in the problems of excessive roll spalling and poor thermal crowning in modern, high-speed rolling mills. In this paper, an analytical model has been developed to determine the temperature profiles of the roll and the strip. This model uses basic heat transfer theory and provides the capability of studying the influence of operating parameters on both the work-roll and workpiece temperatures. Examples on cold and hot rolling of aluminum alloys are given to demonstrate the feasibility and capability of the model developed. Previous work on thermal modeling of rolling processes is also briefly reviewed.

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19

Wang, X. D., F. Li, B. H. Li, G. S. Zhu, B. Li und B. H. Zhang. „VCR back-up roll and negative work roll contour design for solving roll spalling and transfer bar profile problems in hot strip mill“. Ironmaking & Steelmaking 37, Nr. 8 (November 2010): 633–40. http://dx.doi.org/10.1179/030192310x12700328925949.

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20

Korentz, Jacek. „Methods of analysis of a reinforced concrete section under bending with axial force in the post-yield range“. Budownictwo i Architektura 13, Nr. 3 (11.09.2014): 119–26. http://dx.doi.org/10.35784/bud-arch.1787.

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Predicting the behaviour of plastic hinges subjected to large inelastic deformations caused by extreme loads such as earthquakes plays an important role in assessing maximum stable deformation capacities of framed concrete structures. This paper presents the analytical procedure for analysing the behaviour of a reinforced concrete section under bending with axial force in the post-yield range. The following stages of section behaviour are defined: the uncracked, first cracked, yielding, cover crushing, cover spalling, buckling of bars and limit stages. The relationship between the moment and curvature in these stages, including the effects of concrete confinement, the spalling of the concrete cover, and the inelastic buckling of the reinforcing bars, is considered. The presented method makes it possible to estimate the ductility of reinforced concrete members with various longitudinal and transverse reinforcement.

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Sarma, B. Y., und M. M. Mayuram. „Some Studies on Life Prediction of Thermal Sprayed Coatings Under Rolling Contact Conditions“. Journal of Tribology 122, Nr. 3 (13.10.1999): 503–10. http://dx.doi.org/10.1115/1.555393.

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Design of engineering components is concerned with their strength and durability characteristics. While design for strength is influenced by the bulk material characteristics, the design for durability is dependant on the surface characteristics. Majority of the component failures are surface originated. Surface engineering could play a vital role in minimizing such failures. Thermal sprayed coatings, one of the versatile surface coating techniques, can be applied to components of machinery surfaces to avoid such failures. The present paper presents a methodology for contact stress evaluation of surface coated elements, adopting a layered structure approach, and thereby analytically predict their spalling life. Further data on cycles to single pit formation, and spalling of spray fused coatings obtained from experimental testing are presented for assessing the applicability of life prediction models to layered structures such as sprayed coatings. Experimental investigations were conducted on spray fused coatings using a twin disk RCF test setup. The surface and subsurface contact stress distribution have been obtained analytically by Smith–Liu equations along with first order model perturbation method (FOMP), to account for the variation of elastic modulus constants of the layered structure. Applying Lundberg-Palmgren and Tallian life prediction models, the spalling life of these coatings has been predicted analytically and compared with experimental life values. [S0742-4787(00)02502-9]

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22

Qiong, Wu, Sun Da-le, Liu Chang-sheng und Li Chun-guang. „Analysis of surface and sub-surface initiated spalling of forged cold work rolls“. Engineering Failure Analysis 15, Nr. 4 (Juni 2008): 401–10. http://dx.doi.org/10.1016/j.engfailanal.2007.01.009.

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23

Prasad, M. S., S. K. Dhua, C. D. Singh und Amitava Ray. „Genesis of spalling in tandem mill work-rolls: Some observations in microstructural degeneration“. Journal of Failure Analysis and Prevention 5, Nr. 6 (Dezember 2005): 30–38. http://dx.doi.org/10.1361/154770205x76349.

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24

Dong, Qiang, Jian-guo Cao und Dun Wen. „Spalling Prevention and Wear Improvement of Rolls in Steel Strip Hot-Rolling Process“. Journal of Failure Analysis and Prevention 15, Nr. 5 (04.09.2015): 626–32. http://dx.doi.org/10.1007/s11668-015-0011-z.

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25

Korentz, Jacek. „The method of analysis of a reinforced concrete section under bending in the post-yield range“. Budownictwo i Architektura 12, Nr. 1 (11.03.2013): 123–30. http://dx.doi.org/10.35784/bud-arch.2182.

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Predicting the behavior of plastic hinges subjected to large inelastic deformations caused by extreme loads such as earthquakes plays an important role in assessing maximum stable deformation capacities of framed concrete structures. This paper presents an analytical procedure for analysing the behaviour of a reinforced concrete section under bending in the post-yield range. The following stages of section behaviour are defined as the uncracked; first cracked; yielding; cover crushing; cover spalling; buckling of bars; and limit stages. The relationship between the moment and curvature in these stages, including the effects of concrete confinement, the spalling of the concrete cover, and the inelastic buckling of the reinforced bars, are considered. The results obtained from analytical calculations have are compared to the results obtained from a computer analysis. The presented method makes it possible to estimate the ductility of reinforced concrete members with various longitudinal and transverse reinforcement.

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26

SANO, Yoshikazu, und Kazuo KIMURA. „Statistical Analysis about Crack and Spalling on Work Roll for Hot Strip Mill Finishing Rear Stands“. Tetsu-to-Hagane 73, Nr. 9 (1987): 1154–61. http://dx.doi.org/10.2355/tetsutohagane1955.73.9_1154.

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27

Mennicke, C., M. Y. He, D. R. Clarke und J. S. Smith. „The role of secondary oxide inclusions (“pegs”) on the spalling resistance of oxide films“. Acta Materialia 48, Nr. 11 (Juni 2000): 2941–49. http://dx.doi.org/10.1016/s1359-6454(00)00081-1.

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28

Kolari, Kari. „Modeling Splitting and Spalling of Columnar Ice Compressed Biaxially: The Role of Crack Nucleation“. Journal of Geophysical Research: Solid Earth 124, Nr. 4 (April 2019): 3271–87. http://dx.doi.org/10.1029/2018jb017032.

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29

Di Schino, Andrea, und Paolo Di Nunzio. „METALLURGICAL ASPECTS RELATED TO CONTACT FATIGUE PHENOMENA IN STEELS FOR BACK-UP ROLLS“. Acta Metallurgica Slovaca 23, Nr. 1 (28.03.2017): 62. http://dx.doi.org/10.12776/ams.v23i1.852.

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<p>The need of even longer rolling sessions is driving the improvement of back up rolls in terms of wear resistance. This is also aimed to reduce costs. In this paper the effect of steel chemical composition on contact fatigue phenomena, bringing to the macroscopic damage named spalling is reported. Results show that the removal by grinding operations of damaged portion of rolls surface should be not sufficient to restore the initial performances of material. Experimental tests showed that a portion of material below the damaged one keeps memory of the last fatigue cycle, and has to be removed.</p>

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Mazzucco, G., und G. Xotta. „Fire Spalling Prevention via Polypropylene Fibres: A Meso- and Macroscale Approach“. Modelling and Simulation in Engineering 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/8639545.

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A deep understanding of concrete at the mesoscale level is essential for a better comprehension of several concrete phenomena, such as creep, damage, and spalling. The latter one specifically corresponds to the separation of pieces of concrete from the surface of a structural element when it is exposed to high and rapidly rising temperatures; for this phenomenon a mesoscopic approach is fundamental since aggregates performance and their thermal properties play a crucial role. To reduce the risk of spalling of a concrete material under fire condition, the inclusion of a low dosage of polypropylene fibres in the mix design of concrete is largely recognized. PP fibres in fact evaporate above certain temperatures, thus increasing the porosity and reducing the internal pressure in the material by an increase of the voids connectivity in the cement paste. In this work, the contribution of polypropylene fibres on concrete behaviour, if subjected to elevated thermal ranges, has been numerically investigated thanks to a coupled hygrothermomechanical finite element formulation. Numerical analyses at the macro- and mesoscale levels have been performed.

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Ray, Amitava, M. S. Prasad, S. K. Dhua, S. K. Sen und S. Jha. „Microstructural Features of Prematurely Failed Hot-Strip Mill Work Rolls: Some Studies in Spalling Propensity“. Journal of Materials Engineering and Performance 9, Nr. 4 (01.08.2000): 449–56. http://dx.doi.org/10.1361/105994900770345854.

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32

Ray, Amitava, M. S. Prasad, P. K. Barhai und S. K. Mukherjee. „Microstructural Characteristics of Prematurely Failed Cold-Strip Mill Work-Rolls: Some Observations on Spalling Susceptibility“. Journal of Materials Engineering and Performance 14, Nr. 2 (01.05.2005): 194–202. http://dx.doi.org/10.1361/10599490523283.

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33

Lu, Qiao Qiao, Min Li und Xiao Jing Wang. „Source Location of Cracks in a Working Roll of the Temper Mill with Acoustic Emission Technology“. Advanced Materials Research 572 (Oktober 2012): 343–47. http://dx.doi.org/10.4028/www.scientific.net/amr.572.343.

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The application of the temper mill is mainly to improve the mechanical property of strip and to rectify the shape of strip. The working roll of a temper mill is often running with alternating load that prone to lead to faults such as wear, crack and spalling, which cause severe quality problems in the production of strip steel. In order to gain the information of crack's location and depth, the proposed method employs two circles of AE sensors along the direction of the roll body and use static pressure as external loads together with time-of-arrival localization method to detect the exact location of the roll cracks. The positioning results confirmed the validity of the proposed method with the post-repair grinding data. The advantage of this detection method is not requiring the full roll body scan point by point. With only one layout of the sensors, the method can detect the crack location with high efficiency and good real-time property.

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Zhao, Jian Chuang, Jian Dong Hu, Fan You Meng und Yao Min Wang. „Machinability and Material Removal Mechanism of Face Centred Cubic (FCC) Conductive Ceramic TiBCN in EDM Processing“. Key Engineering Materials 680 (Februar 2016): 147–51. http://dx.doi.org/10.4028/www.scientific.net/kem.680.147.

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Fcc-TiBCN powder synthesized by boronizing of Ti was pressured into monolithic block by hot pressing (HP) method. Then the block material was machined by wire-cut EDM. The machinability and the material removal mechanisms were discussed of Fcc-TiBCN block in wire-cut EDM. Results show that the machinability of Fcc-TiBCN is satisfying. The discharge current has little relationship on surface roughness in the range of factory-adjusted optimum settings. The discharge duration and pulse interval time play an important role on the quality of machined surface and EDM machining efficiency. In order to obtain excellent quality of the machined surface, the number of power tube turned on can not exceed 6, and the pulse interval time must be as long as possible. The mini roughness of machined surface is 0.4μm～0.6μm as the number of power tube turned on is 5, the pulse interval time and discharge duration is set in the range of 20～22μs and 65～75μm, respectively. There are three material removal mechanisms of TiBCN conductive ceramic in the EDM machining process: spalling, melting and evaporation. Spalling is the main mechanism resulted by thermal stress superposing.

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Dong, Qiang, Jian-guo Cao, Hong-bo Li, Yun-song Zhou, Tan-li Yan und Wu-zhou Wang. „Analysis of Spalling in Roughing Mill Backup Rolls of Wide and Thin Strip Hot Rolling Process“. steel research international 86, Nr. 2 (19.04.2014): 129–36. http://dx.doi.org/10.1002/srin.201300476.

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36

Cofiño-Villar, Alberto, Jose Alvarez-Antolin und Juan Asensio-Lozano. „Enhanced Fracture Strength in the Working Layer of Rolls Manufactured in Ni-Hard Cast Iron Alloyed with Mo, Nb and Mg“. Metals 8, Nr. 9 (15.09.2018): 725. http://dx.doi.org/10.3390/met8090725.

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One of the main in-service failure mechanisms of the work-rolls used in hot strip mill finishing stands is surface spalling. The indefinite chill double-poured rolls usually comprise of a peripheral working layer made of crushed Ni-hard cast iron and a grey cast iron core, mostly pearlitic matrix with spheroidal graphite. To enhance its wear resistance, the working layer can be alloyed with Mo and Nb. The possible cracking and spalling of the surfaces of these work-rolls is strongly influenced by the presence of carbides and the continuity of their network. The flexural and impact toughness tests are reliable testing methods to assess these properties. The aim of this paper is to identify those manufacturing factors that have a significant effect on the flexural strength and toughness of this material, correlating the results with the volume fraction of precipitated carbides. It is worth highlighting, among the analysed factors are the liquidus temperature, the %Si, the use of an inoculant with traces of Lanthanum, and inoculation with different amounts of FeB, SiCa and Mg. Inoculation with SiCa is found to have a positive effect on the toughness of the material, breaking up the continuity of the carbide network, while FeB is found to act as a heterogeneous nucleant for NbC precipitation. However, high FeB contents reduce flexural strength and do not have a significant effect on the hardness of the material. To enhance the fracture toughness of the working layer, a liquidus temperature in the 1270–1275 °C range is recommended, as well as inoculating the ladle with Mg, 3 kg/T FeB and 0.6 kg/T SiCa.

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37

Kodur, Venkatesh. „Properties of Concrete at Elevated Temperatures“. ISRN Civil Engineering 2014 (13.03.2014): 1–15. http://dx.doi.org/10.1155/2014/468510.

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Fire response of concrete structural members is dependent on the thermal, mechanical, and deformation properties of concrete. These properties vary significantly with temperature and also depend on the composition and characteristics of concrete batch mix as well as heating rate and other environmental conditions. In this chapter, the key characteristics of concrete are outlined. The various properties that influence fire resistance performance, together with the role of these properties on fire resistance, are discussed. The variation of thermal, mechanical, deformation, and spalling properties with temperature for different types of concrete are presented.

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Wang, Yang, Manchao He, Dongqiao Liu und Yubing Gao. „Rockburst in Sandstone Containing Elliptic Holes with Varying Axial Ratios“. Advances in Materials Science and Engineering 2019 (01.04.2019): 1–17. http://dx.doi.org/10.1155/2019/5169618.

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Rockburst disaster is one of the prominent problems faced by deep underground engineering. In this study, rockburst in four elliptical holes with different axial ratios in sandstone under biaxial loading is studied as an analogue for underground roadways. Video and acoustic emission (AE) equipment is used to monitor the biaxial loading tests. Experimental results indicate that each of the elliptical holes goes through four stages: quiet period, small particle ejection, spalling, and rockburst. The duration of quiet and spalling periods increased with increasing axial ratio of ellipse. The duration of the ejection and rockburst periods remains unchanged. All the four elliptical holes have V-shaped pits after rockburst occurs. The fragments produced during rockburst are divided into coarse, medium, fine, and micro grains. The quantity of coarse and medium grains increases with increasing axial ratio. The mass ratio of coarse and medium grains increases and that of fine and micro grains decreases. The depth, angle, and area of the V-shaped pits decrease with increasing axis ratio. Tensile cracks play an important role in rockburst failure. Tensile cracks are the dominant crack types formed during rockburst and account for over 70% of all cracks in the samples. The number of tensile cracks increased and the number of shear cracks decreased. This paper has some reference value for practical engineering design and prevention of rockburst.

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Zinszner, Jean-Luc, Benjamin Erzar und Pascal Forquin. „Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, Nr. 2085 (28.01.2017): 20160167. http://dx.doi.org/10.1098/rsta.2016.0167.

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Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 10 3 to 10 4 s −1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual–Forquin–Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’.

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Yang, Guang Hui, Jie Zhang, Hong Bo Li, Jian Guo Cao und Sheng Hui Jia. „Taper Roll Contour Design for Edge Drop Control of Non-Oriented Electrical Steel on Tandem Cold Rolling Mill“. Applied Mechanics and Materials 166-169 (Mai 2012): 670–73. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.670.

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The taper work roll of the 1700 mm tandem cold rolling mills had some problems in the course of using, and the taper roll contour was ground difficultly and the difference between the designed contour and grinding contour was very big, and the work roll and backup roll had very serious and non-uniform roll wearing and even often had roll spalling, and above those problems affected the stability of rolling process seriously. After analyzing the structure and contour of the taper work roll, it was found that the work roll contour was designed unreasonably and the straight line part and the edge drop control part of roll contours were not connected smoothly, and so it lead to the local stress concentration easily in the transition region and a bigger contacting pressure peak between work roll and backup roll appeared. On basis of decreasing the contacting pressure peak and taking the width of rolled strip and the grinding contour length change into consideration, the design method of the edge control contour part of the taper roll was put forward. The finite element model was built with the software ANASYS9.0 to analyze the mill shape adjusting characteristics, and the simulation result showed that the newly-designed taper roll contour could improve the mill shape adjusting ability. It was shown in the rolling trial that the strip edge drop average was decreased from 14.9μm to 7.5μm and the edge drop fluctuation of strip was restrained to some extent and controlled within ±3μm.

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Huang, Kexin, Xindan Zhang, Dong Lu, Ning Xu, Yingxin Gan und Xin Han. „The Role of Iron Tailing Powder in Ultra-High-Strength Concrete Subjected to Elevated Temperatures“. Advances in Civil Engineering 2021 (15.03.2021): 1–11. http://dx.doi.org/10.1155/2021/6681429.

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Iron tailing powder (ITP) is considered to have the potential to replace cement to manufacture ultra-high-performance concrete (UHPC). However, the performance of UHPC with the addition of ITP after exposure to high temperatures is more complex. This investigation prepares seven UHPC formulations by introducing different contents of ITP and investigates the mechanical behavior (residual strength), bound water content, and microstructural properties (crystalline and amorphous phases, chemical structure, and morphology) of UHPC subjected to elevated temperatures. The experimental results show that the addition of ITP postpones the spalling of concrete when exposed to high temperatures. The concrete incorporating 15% ITP maintains 53.8% of its original strength at 800°C, unlike the concrete without ITP that maintains 31.6% of its original strength. The addition of ITP increases the number of micropores/cracks in concrete and helps release the vapor pressure caused by water evaporation. The findings of this investigation highlight the potential application of ITP for future UHPC design and manufacture.

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NAKAGAWA, Yoshihiro, Takashi HASIMOTO, Hiroaki KATAYAMA und Hajime MORIKAWA. „Development of High-Cr Roll for Hot Strip Mill with Superior Resistance to Surface Deterioration and to Spalling of Outer Shell“. Tetsu-to-Hagane 74, Nr. 10 (1988): 1993–2000. http://dx.doi.org/10.2355/tetsutohagane1955.74.10_1993.

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Gavini, Vikram. „Role of the defect core in energetics of vacancies“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 465, Nr. 2110 (05.08.2009): 3239–66. http://dx.doi.org/10.1098/rspa.2009.0136.

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Electronic structure calculations at macroscopic scales are employed to investigate the crucial role of a defect core in the energetics of vacancies in aluminium. We find that vacancy core energy is significantly influenced by the state of deformation at the vacancy core, especially volumetric strains. Insights from the core electronic structure and computed displacement fields show that this dependence on volumetric strains is closely related to the changing nature of the core structure under volumetric deformations. These results are in sharp contrast to mechanics descriptions based on elastic interactions that often consider defect core energies as an inconsequential constant. Calculations suggest that the variation in core energies with changing macroscopic deformations is quantitatively more significant than the corresponding variation in relaxation energies associated with elastic fields. Upon studying the influence of various macroscopic deformations, which include volumetric, uniaxial, biaxial and shear deformations, on the formation energies of vacancies, we show that volumetric deformations play a dominant role in governing the energetics of these defects. Further, by plotting formation energies of vacancies and di-vacancies against the volumetric strain corresponding to any macroscopic deformation, we find that all variations in the formation energies collapse on to a universal curve. This suggests a universal role of volumetric strains in the energetics of vacancies. Implications of these results in the context of dynamic failure in metals through shock-induced spalling are analysed.

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Bennett, James P., Kyei Sing Kwong, Hugh Thomas und Rick Krabbe. „A New Generation of Refractories to Enable Gasifier Fuel Flexibility“. Advances in Science and Technology 70 (Oktober 2010): 179–92. http://dx.doi.org/10.4028/www.scientific.net/ast.70.179.

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Gasification is used by industry to convert low cost carbon into materials for producing electricity and chemical products such as fertilizer, plastics, and Fischer-Tropsch liquids. It is considered a critical technology in the success of the DOE’s Near Zero Emissions Advanced Fossil Fuel Power Plants, could play a key role in defining long-term energy security in both power and liquid fuels, and is considered a leading candidate for H2 production in a hydrogen based economy. Molten slag originating from mineral impurities in the carbon feedstock is of concern to slagging gasifier operation, with some gasifiers generating over 100 tons per day. Molten slag attacks and wears away the internal lining of the gasifier vessel by two major mechanisms, chemical dissolution and spalling. The main component in current refractory linings is chrome oxide. NETL is researching new types of refractory materials as an alternative to the high chrome oxide refractories currently used, with the goal of improving performance and providing a predictable service life. It has previously developed and patented the use of phosphate additives to improve the wear and spalling resistance of high chrome oxide refractories, and is exploring chrome and non-chrome oxide materials through laboratory testing and the use of thermodynamic modeling. In this paper, the results of a different additive (carbon) was evaluated by laboratory testing and found to improve slag penetration resistance. Data on this evaluation will be presented, and is proposed as a means of improving the molten slag wear resistance of the refractory. The use of it as a means of improving refractory service life in the field is patent pending.

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Matusikova, Anna, Petra Rozehnalova, František Girgle, Vojtěch Kostiha und Petr Štěpánek. „An Engineering Heat and Mass Transport Model Utilized for Concrete at Fire“. Key Engineering Materials 738 (Juni 2017): 58–68. http://dx.doi.org/10.4028/www.scientific.net/kem.738.58.

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Mathematical models which can sufficiently describe processes proceeding in concrete during fire play an important role when assessing a load bearing capacity of concrete structures. In this paper a coupled heat and mass transport model based on principles of conservation of mass and energy is presented. A 2D computational solver using FEM was created to find three unknowns – a temperature, an amount of free water and a magnitude of pore pressure in concrete cross section during rapid heating. These variables, mutually connected through state equation, are necessary not only for determination the load bearing capacity of concrete element but also for prediction of concrete spalling. A parametric study of numerical results influenced by material properties of concrete (e.g. permeability, thermal conductivity) and initial conditions (e.g. relative humidity, temperature) is introduced and discussed in the end.

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Liu, Hua Li, Fei Gao, Wan Hua Nong und Rong Fu. „Effect of Incremental Copper Powders Third Body on Friction Properties of Q235 Steel“. Applied Mechanics and Materials 148-149 (Dezember 2011): 1567–71. http://dx.doi.org/10.4028/www.scientific.net/amm.148-149.1567.

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To understand the effects of the third body of copper in the copper-based composite materials on the friction properties, the effect of copper powders on the friction properties of Q235 steel is studied by using the pin-on-disk tester and adding copper powders third body. The results show that when the friction speed at 500-3000 r/min, due to the incremental copper powders, the depth of the furrows on the friction surface was reduced and the adhesion and spalling process of surface third body were intensified, which results that the frictional coefficients of the Q235 steel are increased 0.2-0.35 comparing with that of without adding copper powders. The reason is that incremental copper third body plays the role of increasing the meshing of the asperity and the actual friction area.

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Schiffer, Michael Brian, James M. Skibo, Tamara C. Boelke, Mark A. Neupert und Meredith Aronson. „New Perspectives on Experimental Archaeology: Surface Treatments and Thermal Response of the Clay Cooking Pot“. American Antiquity 59, Nr. 2 (April 1994): 197–217. http://dx.doi.org/10.2307/281927.

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This paper examines pottery technology and change through the eyes of the experimental archaeologist. A new vision is presented of experimental archaeology and the role its findings can play in archaeological explanation. It is argued that the most useful results of experimental archaeology are best obtained with long-term research programs. This perspective is illustrated by a case study of the relations between surface treatments (interior and exterior) and thermal performance in cooking pots. The experiments indicate that surface treatments like texturing, organic coatings, and smudging have marked impacts on thermal shock cracking and on thermal spalling in simulated cooking. It is emphasized that the findings of experimental archaeology, expressed as correlates, can be employed in explanations of prehistoric technological change, but only when embedded in more inclusive correlate theories and coupled with the requisite contextual information.

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Rosenbaugh, Scott K., Jennifer D. Schmidt, Harald P. Larsen, Ronald K. Faller und Andrew Pankratz. „Development and Testing of the Manitoba Constrained Width Tall Wall Barrier“. Transportation Research Record: Journal of the Transportation Research Board 2638, Nr. 1 (Januar 2017): 55–64. http://dx.doi.org/10.3141/2638-07.

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This project in Manitoba, Canada, developed a single-slope concrete barrier system with a height of 1,250 mm and a base width of no more than 600 mm. Configurations for bridge rail, roadside, and median barrier applications were developed and optimized to minimize installation costs while satisfying the AASHTO Manual for Assessing Safety Hardware (MASH) Test Level 5 performance standards. Additionally, a bridge deck was developed for the overhang portion of the deck supporting the bridge rail. To evaluate the new barrier system, a 45.7-m-long section of the bridge rail was constructed on a simulated bridge deck and subjected to a full-scale crash test according to MASH Test 5-12. During the test, the 36,000-kg vehicle was safely redirected with minimal roll to the cab and trailer. Damage to the barrier and deck was minor, consisting of concrete gouging, hairline cracks, and some spalling to the top of the barrier. Thus, the Manitoba constrained width tall wall was deemed crashworthy to MASH Test Level 5 standards.

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Fan, Lei, Hua Hui Chen, Wan Ting Mao und Jing Jing Cao. „Friction and Wear Behavior of CaO-MgO-Al₂O₃-SiO₂ Glass-Ceramics Prepared by Waste Casting Sands“. Applied Mechanics and Materials 217-219 (November 2012): 1251–56. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.1251.

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CaO-MgO-Al2O3-SiO2 glass-ceramics were produced by using waste casting sands as a main raw material. Friction and wear tests for the glass-ceramics were conducted with M-200 wear tester against GCr15 steel wheel. The worn morphologies, wear mechanisms and compositions of the glass-ceramics were observed and analyzed with scanning electron microscope (SEM) and energy diffraction spectrum (EDS). The results show that under the dry friction sliding the glass-ceramics present high wear rate and friction coefficient, with wear mechanisms are dominantly brittle spalling and some with adhesive wear. By an addition of 10% pure aluminum, the density of the glass-ceramics and wear resistance can be improved with their friction coefficient being lowered. Under oil lubrication sliding, the friction coefficient of glass-ceramics decreases and their wear resistance increases extremely, whose reason is that small pores within the glass-ceramics play an role on oil storage.

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Lin, Wen Song, Ning Xiang Fang und Liang He. „Wear Properties of Reaction Sintered B₄C Composites“. Advanced Materials Research 152-153 (Oktober 2010): 883–86. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.883.

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B4C/CNTs and B4C/Ccomposites were prepared by reaction-sintering technique. The density and porosity of the samples were determined and three-points bending strengths of the composites were measured. Wear resistance tests were performed using a HT-500 pin-on-disc tribometer with the sample placed horizontally on a turning table. The morphology of the worn surfaces and fracture of the composites were examined by means of scanning electron microscopy so as to explore the wear mechanisms. The results indicate that B4C/CNTs composites show improved friction and wear properties as compared with B4C/C composites. It is found that CNTs in the specimens play important role in improving the wear properties of the composites. The wear mechanism of the B4C/CNTs composites is characterized by micro-cutting and plowing at ambient temperature, and sub-surface cracking and the resultant localized spalling on the worn surface at the temperatures higher than 500°C.

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