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By Fanny Herrera, David Reaño, Luis Chahua, Elio Murrugara

El crecimiento del depósito de desmonte Pampa Verde es altamente dependiente de las siguientes restricciones: (1) opciones limitadas para extender lateralmente los contrafuertes existentes; (2) la necesidad de satisfacer tanto la estabilidad estática como la sísmica; (3) la necesidad de seleccionar adecuadamente materiales de alta resistencia para el refuerzo; (4) la importancia de realizar pruebas específicas del material geosintético de refuerzo para caracterizar su interacción con el suelo; y (5) la compleja geometría del sistema en conjunto, particularmente para su estabilidad global. El dique de contención existente fue estabilizado mediante su reforzamiento con geosintéticos, el cual consistió en un relleno de suelo compactado con una talud de 2,1H:1V sobre un muro de suelo estabilizado mecánicamente (MSE o suelo reforzado). La estructura MSE involucra dos muros (superior e inferior) con una banqueta horizontal entre ambos. El muro superior está reforzado con geomallas, mientras que el muro inferior consiste en un sistema Terramesh de gaviones reforzados con geomallas. El enfoque general del diseño consideró el diseño de un talud de suelo reforzado con geosintéticos (TSR) que usaría geomallas de alta capacidad de tracción. Las guías de diseño para el TSR propuesto son las emitidas por la Administración Federal de Carreteras de EE. UU. (FHWA-NHI-10-024). Un aspecto clave a considerar en el diseño propuesto fue la adecuada evaluación de la interfase del suelo contra la geomallama, por lo que se consideró un total de cinco productos de geomalla para su posible uso en la construcción del talud de suelo reforzado con geosintéticos.

Sep 20, 2019

By Ryan G. Wade, Mark K. Larson

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are studying the time-dependent response of rock stressed along weakness planes. The objective is to improve mine safety by reducing the number of roof falls that cause injuries and fatalities to miners. Researchers conducted direct-shear tests on mudstone overcored from a coal mine roof. Results showed frictional strength weakens with displacement along the shearing planes. Results of direct-shear creep tests also showed time-dependent deformation. Test measurements were compared to classical analytical models. Results suggest that risk of roof collapse may be decreased through layout and support design to reduce creep rates and thus slow progression toward failure.

By M. K. Larson, R. G. Wade

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are studying the time-dependent response of rock stressed along weakness planes. The objective is to improve mine safety by reducing the number of roof falls that cause injuries and fatalities to miners. Researchers conducted direct-shear tests on mud-stoneovercored from a coal mine roof. Results showed frictional strength weakens with displacement along the shearing planes. Results of direct-shear creep tests also showed time-dependent deformation. Test measurements were compared to classical analytical models. Results suggest that risk of roof collapse may be decreased through layout and support design to reduce creep rates and thus slow progression toward failure.

Jan 1, 2000

By Albert Smith

THE creep properties of metals have as-sumed increasing importance in recent years and many investigations have been made on various phases of the problem. In the past year the annual lectures of the Insti-tute of Metals Division1 and the Iron and Steel Division2 were concerned with this subject, and are excellent reviews. For many years the creep properties of lead and lead alloys have been investigated at the Central Research Laboratories of the American Smelting and Refining Co., and it is hoped that the present paper will contribute knowledge of some of the factors that influ-ence creep. Lead, being a metal that recrys-tallizes readily at room temperature, is an excellent material upon which to investi-gate creep phenomena because of the sim-plicity of the apparatus needed, and it might be expected that results would apply to some extent to elevated-temperature tests of other metals.

Jan 1, 1940

By Richard Miller

RECENT studies of creep have made it apparent that plastic deforma-tion may occur in metals under stresses less than the elastic limit as deter-mined from short-time tests. In summarizing conclusions drawn from creep tests by various investigators, Tapsell1 said: "It is evident that if a material has a true elastic range, the elastic limit must represent the maximum stress for no creep." The presence of a. definite elastic limit, represented in single crystals by a critical or threshold shearing stress, is claimed by Schmid2, Elam3 and others who have investigated the plastic deformation of single crystals. However, this "law of critical shearing stress" was deter-mined2 from short-time tests, and the measurement of the deformation was made with apparatus primarily designed to observe large amounts of plastic deformation, not to detect elastic changes. Experimental data recently obtained with highly sensitive instru-ments by A. W. Hanson4 on zinc and by Podaschowsky5 on rock salt indicate that the elastic range in single crystals is considerably narrower than formerly was supposed. Moreover, a theoretical possibility of permanent deformation, under the influence of even the smallest shear stress in single crystals above a certain temperature (Td), has been developed by G. I. Taylor6. This evidence seemed to warrant an examination of the elastic limit in large single crystals by means of creep tests. The first metal chosen for examination was zinc.

Jan 1, 1936

By Levi de Oliveira Bueno

Constant stress testing was used for characterization of creep behavior of a 1Cr0.5Mo steel plate in the virgin condition. The tests were performed on creep machines equipped with Andrade-Chalmers type profiles, high sensitivity SLVC transducer extensometry, high stability temperature controllers, and facilities for monitoring the creep curves with an automatic data logging system. Ten creep machines of this type were used in this research, in an experimental work that lasted for one year. Three temperature levels were selected: 538, 565 and 593°C, with stress in the range from 69 to 258 MPa producing rupture times varying from 8 to about 4908 h. The creep curves were all followed with great scrutiny using data logger scanning rates which enabled storing thousands of readings in each case. The experimental analysis involved measurements of minimum creep rate, rupture time and final elongation at rupture. The data were analyzed according to the classical phenomenological / physical relations (Norton, Arrhenius, Zenner-Hollomon, Monkman-Grant) and also considering five traditional parameterization methodologies (Larson-Miller, Orr-Sherby-Dorn, Goldhoff-Sherby, Manson- Haferd and Manson-Succop). Comparisons are presented among the possibilities of data extrapolation from five different methodologies. Comparison is also made with creep results mentioned in literature for the same material in the virgin condition.

Aug 16, 2017

By Levi de Oliveira Bueno

Constant stress testing was used for characterization of creep behavior of a 1Cr0.5Mo steel plate in the ex-service condition. The tests were performed on creep machines equipped with Andrade-Chalmers type profiles, high sensitivity SLVC transducer extensometry, high stability temperature controllers, and facilities for monitoring the creep curves with an automatic data logging system. Ten creep machines of this type were used in this research, in an experimental work that lasted for one year. Three temperature levels were selected: 538, 565 and 593°C, with stress in the range from 52 to 224 MPa producing rupture times varying from 5 to about 3950h. The creep curves were all followed with great scrutiny using data logger scanning rates which enabled storing thousands of readings in each case. The experimental analysis involved measurements of minimum creep rate, rupture time and final elongation at rupture. The data were analyzed according to the classical phenomenological / physical relations (Norton, Arrhenius, Zenner-Hollomon, Monkman-Grant) and also considering five traditional parameterization methodologies (Larson-Miller, Orr-Sherby-Dorn, Goldhoff-Sherby, Manson- Haferd and Manson-Succop). Comparisons are presented among the possibilities of data extrapolation from five different methodologies. Comparison is also made with creep results obtained on a similar plate of the same material in the virgin condition.

Aug 16, 2017

By Jinqian Zhao, Jiarong Li, Shizhong Liu

"Creep cavitation of in single crystal (SX) superalloy was investigated. The constant load creep tests, in single crystal superalloys DD6, were conducted at the conditions of 800°C/700MPa, 850°C/550MPa and 900°C/450MPa, respectively. It was found that there were square facets on the stress fracture surface, and microscopic cavities in the ruptured specimens in the vicinity of the fracture surface. Both the square facets on the fracture surface and microscopic cavities in the section of the ruptured specimens show the morphology of the same thing at the different views, namely creep cavities, which are take the form of flatten cuboid. In fact, creep cavities are the longitudinally tensiled creep cracks slowly growing during the stress tensiling. The factors of creep cracks nucleation and growth conditions include: (a) enough high temperature to activate diffusion (b) casting pores as nucleation origination (c) high strains and strain rates. Eventually, the instantaneous fracture mechanism of creep specimen is cleavage fracture.IntroductionFor the materials used in elevated temperature service, creep behavior has to be accounted for. It is well recognized that creep rupture in polycrystalline materials at high temperature occurs principally by the nucleation and growth of microscopic cavities at grain boundaries, followed by microscopic cavities linkage to form micro- and eventually macro-intergranular cracks[l,2]. Without the usual grain boundaries, SX superalloys have superior capabilities at high temperatures to polycrystalline superalloys, and have become an established feature of gas turbine technology where they are commonly employed in the manufacture of high performance blades[3]. A considerable amount of work has been done over the past tens of years, and many models for nucleation and growth of creep cavities have been proposed, however, those are mainly for polycrystalline materials.In order to improve creep resistance that single crystal superalloys, in which grain boundaries are removed, have been developed. Because there don't exist grain boundaries in SX superalloy, the mechanism of nucleation and growth of creep cavities must be different from that in polycrystalline materials.Understanding the formation and characteristics of creep cavitation is crucial to model the lives of single crystal superalloys.M. Marchionni and L.G. Zhao et al. found that there were square facets on the stress fracture surface [4,5]. Roger C. Reed pointed out creep cavities lie in the necked region[6]. In this paper, the effects on the formation of creep cavities are discussed, as well as the morphology of creep cavities and fracture mechanism of SX superalloys."

Jan 1, 2013

By Y. FUJII, E. CHANDA, J. KODAMA, D. FUKUDA, M. NISHIHARA, Y. NAKAYAMA, P. SINKALA

This paper describes a creep damage model that was proposed to clarify the rockburst mechanism for the Mufulira underground copper mine in Zambia. Cumulative rock damage was evaluated for the edge elements of each sidewall of the mining drives based on normal stresses by the 3-D displacement discontinuity method (DDM) (Crouch and Fairhurst, 1973). The rockburst occurrences were well hindcasted.

Jan 1, 2023

By Y. FUJII, E. CHANDA, J. KODAMA, D. FUKUDA, M. NISHIHARA, Y. NAKAYAMA, P. SINKALA

For over 40 years, Mufulira underground copper mine has been recording incidents of rockburst. Laboratory tests and numerical analyses were carried out to understand the rockburst mechanism at the Mufulira mine. Rockburst did not occur in the chain pillars or at the mining face, but mainly in the mining drives along diminishing pillars or ahead of the mining face. RQD suggested that the rock mass in the rockburst areas was relatively intact. Laboratory tests confirmed that the rock at Mufulira mine is very strong and brittle. Elastic stress analyses for the rockburst sites by 3D displacement discontinuity method (DDM) indicated very high stress in the chain pillars and low-stress concentration at the sites of rockburst during the initial mining stages. However, there was no apparent positive correlation between the elastically calculated normal stress values and the occurrences of rockbursts. The 2D elastic FEM analysis was conducted under the concentrated stress by DDM and indicated that some stress increase with face advance for the rockburst in the vicinity of the mining face. However, stress severity indicated almost no increase, and the rockbursts cannot be explained as an instantaneous rock mass failure due to stress increase by mining. Therefore, a creep damage model was proposed to clarify the mechanism of the rockbursts. Cumulative rock damage was evaluated for the edge elements of each sidewall of the mining drives, based on the normal stresses by 3D DDM. The rockburst occurrences were well hindcasted. A method to estimate the volume of the rockburst source was proposed, and a likely result was obtained.

Aug 12, 2022

By M. Kunst

The creep behavior of three AJ62 alloys was investigated in a wide range of stresses and temperatures. Multi-level tensile creep tests revealed a distinct primary creep stage and a high stress exponent up to a value of 10. The threshold stress concept which is commonly used in combination with high stress exponents was utilized in the analysis of creep behaviour. This resulted in an effective stress exponent for the AJ alloys indi¬cating dislocation climb as the dominating creep mechanism. In addition, microstructural observations of the lamellar eutectic and of the a-Mg-matrix were carried out using opti¬cal microscopy, SEM and TEM. The creep properties of the alloys are discussed in the context of microstructural parameters such as phase volume-fraction, stability and solute supersaturation.

Jan 1, 2006

By C X. Zhang, W K. Ru, S C. Hu

To study the creep properties and the energy evolution characteristics of the weakly cemented rock (WCR) in western China, the creep deformation damage law of weakly cemented mudstone (WCM) under graded loading and the energy evolution characteristics of each creep stage were analysed based on the triaxial graded loading creep test of WCR. The results showed that as the confining pressure increased, the creep failure strength of the WCM increased from 9.5 to 24.8 MPa, and the relative displacement of the mineral particles in the mudstone increased gradually, resulting in a reduction in the fracture angle from 79.7° to 58.3°. At the same stress level, the strain energy Ue, the total energy U, and the dissipation energy Ud all increased as the confining pressure increased, but the growth rates of U and Ud decreased gradually, while the growth rate of Ue remained high. At the end of the stable creep stage, Ue increased slowly with the confining pressure, while U and Ud increased rapidly with the confining pressure, and their growth rates were basically the same. At the end of the accelerated creep stage, the growth trends of these three energies were all positively correlated with the confining pressure, Ue was significantly lower than that at the end of the stable creep stage, and Ud and U were further increased. These results revealed the unique creep properties and energy evolution characteristics of the WCR, providing a theoretical basis for long-term stability control of roadways that are built with WCR.

Nov 29, 2022

By Adriano Gonçalves dos Reis

In the development of the structural materials for the advanced applications, as in the aerospace industry, there is a constant strive to increase both strength and toughness. Maraging steels are iron-nickel alloys designed to combine both properties that are achieved through the age-hardening of low carbon martensite. This alloy have a metastable martensitic structure that can revert to austenite when heated in temperatures close to the aging temperature, and this effect can be enhanced with the temperature increasing and time of treatment. Therefore, the study of creep behavior in elevated temperatures has technological importance to the development of this material. In this work the creep behavior of a maraging 300 steel solution annealed is evaluated by carrying out creep tests at 650ºC and in a stress of 200, 300 and 500 MPa. Creep parameters, such as steady state creep rate (?????), final creep time (tf), and stress exponent from secondary creep (n) are determined, considering that they are important to evaluate the creep resistance of the material.

Aug 7, 2018

By N. Bakhshizadeh

In this investigation, the aging effect on creep behavior of A12024-10%SiC composite fabricated by powder metallurgy was studied. P/M bars were manufactured by hot powder extrusion method at 450°C with a ratio of 16 to 1. Creep specimens were over-aged at 187 ºC for 43 h. It was found that almost full density composite with relatively homogenous distribution of reinforcing particles throughout the aluminum alloy matrix could be attained by direct powder extrusion process. Creep tests were conducted at temperatures from 275 to 325°C under stresses from 25 to 60 MPa. The analysis of the creep mechanism determined that dislocation glide was the predominant mechanism of plastic deformation. The activation energy of the creep process was found to be higher than that of lattice self-diffusion in pure aluminum.

Jan 1, 2007

By James S. Redpath

"The ways of the world be many and most of the ways be tried, you follow in the footsteps of others till you come to the great divide". These words, written by Robert Service a long time ago, come to mind when I think of our original attitude upon entering into a contract with the International Nickel Company to sink the deepest shaft in the world outside of the Union of South Africa. This shaft was to be sunk to a depth of 7,137 feet from surface, and while it was recognized by all concerned to be a somewhat unusual undertaking in our part of the world, the fact that quite a few shafts had already been sunk to this depth in South Africa probably gave us the feeling that we were following in the footsteps of others. In retrospect, because this shaft was being sunk under entirely different conditions than those existing in South Africa, we were in fact venturing into an entirely new area of endeavour without properly recognizing this fact. It has occurred to me that others considering a similar type of job could benefit from our experience, especially in an assessment of the risks involved and how they compare to those encountered in an ordinary shaft. For comparison purposes, I would define an ordinary shaft as being sunk to a depth of 5,000 ft or less, and a deep shaft as one being sunk to a depth of between 5,000 ft and 8,000 ft. The sinking of the Creighton No. 9 Shaft has been de-

Jan 1, 1997

By Cresap P. Watson

ABOUT the time this magazine reaches its readers, Cresap P. Watson will celebrate his 53d birthday. If he spends that birthday at his West Los Angeles home, he won't be far, as distance is measured today, from Santa Barbara, where he was born on July 8, 1895. He is truly a member of a petroleum family; one brother, N. O. Watson, managed Royal Dutch Shell interests in Venezuela for years and is now general manager of the Caribbean Petroleum Co. at. Maracaibo; another brother, Rex, is vice-president of the Drilling and Exploration Co., while brother-in-law Ben Belt is an executive of Gulf Oil. His own life has centered in the petroleum industry since his first job in 1913 as camp cashier for a Mexican oil field at Tampico. Down on the isthmus of Tehuantepec he advanced to tool dresser and' production foreman for the company. The first World War interrupted his Mexican experience by transforming him into an artillery officer in France. Once the Army ceased to demand his services¬by then it was 1919-he returned to the task of furthering his professional career as agent for the Amerada Petroleum Corp. By 1927 he had reached the position in which he could be called an executive in the petroleum industry, having organized and become president of the Federal Royalties Co. His activities in local and national legislation affecting the petroleum industry increased as has his advocacy of the development of oil and gas fields under sound engineering and conservation principles through unitization or other co-operative forms of operation. Considerable amounts of his time go to the promotion of industry public relations.

Jan 1, 1948

By Rômulo Albertini Rigueira

A fratura por fadiga é a forma mais comum de falha estrutural e, atualmente, é um problema desafiador no projeto de componentes mecânicos. O objetivo desta pesquisa foi modelar matematicamente as curvas de crescimento de trinca por fadiga em função do fator de intensidade de tensão de uma junta de aço 1016 obtida pelo processo de soldagem GMAW. Os resultados obtidos no estágio II da curva de propagação de trinca por fadiga mostraram que o material respeita a equação de Paris para solicitação no sentido longitudinal. No entanto, verificou-se uma correlação linear entre os parâmetros. Esta correlação deixa de existir quando se trabalha com o modelo de Bergner. Não houve variação no crescimento de trinca por fadiga na direção TL, analisado segundo o modelo de Bergner e na região fundida.

Aug 16, 2017

By Fabiane Leocádia da Silva

Cristais da família cristalográfica do sal de Tutton A2B(XO4)2.6H2O, A=K, NH4, Rb, Cs, Tl, B=Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, V, Cr, X=S e Se tem sido investigados por diversas técnicas experimentais com o objetivo de compreender suas propriedades físicas e potenciais aplicações tecnológicas. Investigações sobre o comportamento estrutural têm sido realizadas por difração de raios-x a fim de compreender suas propriedades estruturais, principalmente a distorção Jahn-Teller presentes nos cristais com cromo e cobre. Soluções sólidas destes sais na forma A2B'xB”(1-x)- (SO4)2.6H2O, têm sido relativamente pouco investigadas embora possam apresentar distorção Jahn-Teller. A estrutura dos cristais desta série à temperatura ambiente é monoclínica, grupo espacial P21/a com duas moléculas por célula unitária. Bons monocristais da série (NH4)2NixCu(1-x)(SO4)2.6H2O com 0

Aug 16, 2017

By William R. Yernberg

The Cripple Creek & Victor Gold Mining Co.(CC&V) celebrated completion of a two-year, $168.5-million expansion and capital improvement program. An open house celebration was held in the historic mining town of Victor, CO on Oct. 4, 2002. Hundreds of townspeople, the press and other invited guests from the mining industry joined the employees of CC&V in the celebration. The event included mine tours, company displays and a barbecue picnic, complete with a country and western band. The Cresson Mine is located about 40 km (25miles) west of Colorado Springs, CO between the towns of Cripple Creek and Victor. The mine is the only large-scale gold mining operation in Colorado and now employs about 300 (ME, October 2001, pp.21-28). The operation is a joint venture between Anglo-Gold (Colorado) (67%), based in Greenwood Village, CO, and Golden Cycle Gold (33%), based in Colorado Springs. CC&V is managed by AngloGold North America. AngloGold North America is the U.S. subsidiary of AngloGold, the world’s second largest gold mining producer. AngloGold is based in Johannesburg, South Africa.

Jan 1, 2002

By Jeffrey A. Pontius

The Cresson gold deposit is in the southcentral portion of the Cripple Creek mining district in central Colorado (Fig. 1). The deposit is hosted by a series of 32 Ma (Kelley, 1995) felsic to mafic, alkaline volcanic rocks that were deposited in a diatremal environment. Mineralization in the Cresson deposit is structurally con-trolled. It occurs as disseminated and vein type. Gold deposition is closely associated with potassium-pyrite metasomatism and quartz-telluride vein development(Pontius, 1992). The Cresson deposit is owned by the Cripple Creek and Victor Gold Mining Co. (CC&V), a joint venture between Pikes Peak Mining (67%) and Golden CycleGold (33%).

Jan 1, 1996