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By C. Ringas

Pipelines are used extensively in industry to convey various products. Internal corrosion of pipelines can lead to perforation and leakage of the product. A growing problem, not often accurately recognized, is internal corrosion of pipelines caused by bacteria. Microbiologically-induced corrosion (MIC) refers to corrosion caused by a variety of micro-organisms. This form of corrosion is not widely recognized in many industries, although it is widespread and causes many corrosion problems in pipelines, both internal and external. Sulphate-reducing bacteria (SRB) are responsible for the bulk of the corrosion problems caused by MIC. Corrosion caused by SRB is found extensively in water pipelines conveying raw, potable and waste water, as well as in pipelines conveying slurries. This problem also occurs in pipelines conveying crude oil. This paper describes internal corrosion problems of slurry pipelines caused by bacteria and outlines mitigation methods to improve slurry pipeline integrity, thereby extending the life of such pipelines.

Jan 1, 2007

By C. Ringas

Pipelines are used extensively in industry to convey various products. Internal corrosion of pipelines can lead to perforation and leakage of the product. A growing problem, not often accurately recognized, is internal corrosion of pipelines caused by bacteria. Microbiologically-induced corrosion (MIC) refers to corrosion caused by a variety of micro-organisms. This form of corrosion is not widely recognized in many industries, although it is widespread and causes many corrosion problems in pipelines, both internal and external. Sulphate-reducing bacteria (SRB) are responsible for the bulk of the corrosion problems caused by MIC. Corrosion caused by SRB is found extensively in water pipelines conveying raw, potable and waste water, as well as in pipelines conveying slurries. This problem also occurs in pipelines conveying crude oil. This paper describes internal corrosion problems of slurry pipelines caused by bacteria and outlines mitigation methods to improve slurry pipeline integrity, thereby extending the life of such pipeline

Jan 1, 2007

By R. R. Mankowski

The work described in this paper is an attempt to increase present-day knowledge of fatigue in mine hoisting cables, particularly the internal energy loss arising from interwire/strand friction in a cable undergoing periodic non-planar transverse vibration. Such frictional energy loss is known to be one of the major influences limiting useful working life of hoisting cables in use today, and is responsible for the large capital outlay required to maintain the high safety factors prescribed by the mining industry. The experimental method employed identifies two mechanical characteristics of cables that are independent of amplitude and frequency, and are primarily attributed to the type of cable construction. Interest is focused the time rate of change of curvature as the major parameter influencing the internal damping mechanism. Empirical results confirm that amplitude and mode number play an important role in quantifying the internal losses, and also reveal that a critical radius of curvature exists below which damage due to vibration fatigue rises exponentialy to potentially high levels.

Jan 1, 1988

By W. Jacobi, K. Eisfeld

The primary objective of dosimetric modelling for the inhalation of radon daughters is the evaluation of the dose distribution and of the mean dose to sensitive cells or target tissues in the respiratory tract which are assumed to be responsible for the initiation of lung cancer. The results of such dosimetric models are influencing the practice of radiation protection in a twofold manner: Firstly, they enable us to identify appropriate operational quantities for air monitoring and for the surveillance of individual exposures to radon daughters. Secondly, they can be used to derive secondary and operational limits for these radionuclides from the basic dose limits. The dose to target tissues in the lung from inhaled radon daughters depends on various physical and biological parameters: The unattached fraction of daughter atoms, the AMAD of the carrier aerosol for attached atoms, the geometry of the respiratory airways, the breathing conditions, the parameters for the retention and translocation of daughter atoms in the different lung regions, and the location of the target cells or target tissues, respectively. Therefore, dosimetric modelling for radon daughters has to include a sensitivity analysis showing the influence of these parameters. To meet these objectives we have recently described in a comprehensive report an improved dosimetric model for the inhalation of 222Rn, 22ORn and their short lived daughters (Jacobi and Eisfeld, 1980). In the following this model is shortly described and the main results are summarized. DOSIMETRIC MODEL [Model Structure]. For the geometry of the bronchial airways the model A of Weibel (1963) was used. Each bronchial generation i (i =0.1 .... 16) was considered as a separate compartment i, for which the following transfer pathways for radon daughter atoms were taken into account (see fig. 1): (1) the uptake by deposition (deposition probability wi); (2) the translocation by ciliary clearance (rate constant [A]i); (3) the transfer to blood by diffusion through the bronchial epithelium (rate constant [A]b). To distinguish between attached (Index a) and free (index f) daughter atoms each bronchial generation was divided in two subcompartments (i.a and if) with a transfer rate constant [a]s (ia- if) characterizing the desorption or dissolution rate of attached atoms in the mucus fluid. Thus for daughter atoms primarily deposited in attached form the transfer to blood is a twostep process with the rate constants [a]s and [A]b which were assumed to be independent of the generation number i. [Deposition]. The deposition probabilities wi in each bronchial generation were calculated on the basis of the laminar diffusion model of Gormley et al. (1949); however the deposition in the upper airways was corrected for turbulent air flow, taking into account the results of our deposition experiments (Martin et al., 1972). Figure 2 shows the resulting deposition probabilities per unit surface area of the bronchial generations for nose breathing at a rate of 20 1/min. The values for attached daughter atoms refer to an AMAD of 0.2 - 0.3 µm ([O]g =3) for the carrier aerosol; the deposition values for free atoms were derived with a diffusion coefficient of 0.05 cm2/s, assuming a prefiltration of 50% in the naseopharyngeal region.

Jan 1, 1981

By Lin Li, Wen Shi, Hua Wang

"Specimens of the ultra-low carbon bake hardening steel were soaked for 1 min to 5 min, and then cooled by water quenching. The internal friction experiments were carried out to detect the spectra of the specimens. Results show that Snoek peaks are present in all the specimens, however, an obvious Snoek-Koster peak is found only in the 5 min-annealed specimen. Besides, tensile results indicate that the bake hardening values increase with the annealing time prolonging from 1 min to 3 min, but decrease as the annealing time prolongs further to 5 min. The solute distributions in the specimens were characterized by three dimensional atom probe. Some segregated C and V are found in the 1 min-annealed specimen, and the C and V contents decrease as annealing time prolongs to 5 min.1. IntroductionAs an excellent member of automotive body panel materials, various types of bake hardening (BH) steels have been developed since 1980s. Bake hardening property, as one of the most important mechanical properties, has been studied by many researchers [ 1-5]. As is known, BH phenomenon is generally controlled by the interaction between solute C and dislocations. The Snoek peak of internal friction (IF) is very popular in the investigation of solute C [6-9]. However, result of internal friction cannot suggest the distribution pattern of solute C as well as its influence on BH phenomenon.Three dimensional atom probe (3DAP) can diagnose solute element atoms as well as nano-sized precipitates, and it is the only instrument that currently can identify the identities of individual atoms in a material and measure their spatial coordinates with the resolution close to 0.3 nm [10]. There have been a number of studies about using 3DAP to detect solute elements as well as nanometer sized precipitates [11-19]. For example, Hono et al. [16] used 3DAP to determine the solute elements in an age-hardened Mg-Ca-Zn alloy, and they also obtained the distribution patterns of the observed elements."

Jan 1, 2011

By Clarence Zener

THE internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites,4,5 localized weak regions introduced by cold-working,6,7 grain boundaries and possibly twinning planes.8.9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, 3-s in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff.10 EXPERIMENTAL METHOD The experimental method used has previously been described in Institute papers.5,6.9 The measure of internal friction adopted here, I/Q, is (p) X the logarithmic decrement, a measure used by some writers, and is also (I/2p) X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the fundamental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. EXPERIMENTAL RESULTS The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°°C. As shown in Fig. i, the internal friction increased by only a factor of 2 from room temperature to 300°°C., then by a factor of 100 during the next :too' interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction ~ e-HI/RT [I]

Jan 1, 1942

By Clarence Zener

THE internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites,4,5 localized weak regions introduced by cold-working,6,7 grain boundaries and possibly twinning planes.8,9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation. was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, ½ in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff.10 EXPERIMENTAL METHOD The experimental method used has previously been described in Institute papers.5,6,9 The measure of internal friction adopted here, 1/Q, is (1/p) X the logarithmic decrement, a measure used by some writers, and is also (1/2p) X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the funda¬mental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. EXPERIMENTAL RESULTS The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°C. As shown in Fig. 1, the internal friction increased by only a factor of 2 from room temperature to 300°C., then by a factor of l00 during the next 100° interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction e~H/RT [I]

Jan 1, 1942

By George H. Found

DURING recent years considerable interest has been focused on the energy-absorption characteristics of metal when it is cyclically stressed in vibration. The most familiar manifestation of this phenomenon, which is called the "damping capacity" or "internal friction" of a material, is involved in the dissipation of mechanical energy of vibration, which otherwise would build up to stress levels where the problems of noise and fatigue are involved. In addition to its engineering importance in structures, the damping behavior of metals, particularly at low stress amplitudes, has also been used as a unique metallurgical research tool with which to provide sensitive means for indicating certain structural changes within metals. Important contributions toward understanding the energy-dissipating mechanisms that are responsible for internal friction in metals have been made in the last few years. The information is not yet sufficiently extensive, however, to provide a useful metallurgical concept describing exactly how the structure affects the internal friction, or to encourage more general use of this technique among metallurgists. Three fundamental mechanisms have been proposed, as a result of recent experimental investigations, to account for the internal friction in nonferrous metals in low-stress amplitude tests. These include damping due to internal thermal currents that are created and flow in metal because of differential vibratory stress effects,1 damping due to localized inelastic stress relaxation at inhomogeneities within the metal,2,3 and damping related to plastic flow of a localized type for which an explanation has been sought in terms of the dislocation theory.4 How each of these mechanisms functions as a result of structural changes in the metal is, in general, not well understood because of insufficient experimental data for which the controlling variables have been segregated and because of uncertainties in regard to the nature of the structural changes themselves. In several investigations the effects of cold-working on the internal friction of polycrystalline brass and aluminum have been described. As reported by Köster and Rosenthal,5 and by Förster and Breitfield,6 there is an initial large increase in the damping when the metal is worked. The initial high value is not stable, but declines rapidly, at first, in a hyperbolic manner. About 100 hr, after straining, a stable value is reached of magnitude proportional to the amount of strain.7 In Fig. I is shown the relationship found by Zener and his collaborators between the internal friction due to cold-working of alpha brass and the amount of cold-working.8 Several investigators have made internal-friction measurements on worked poly-

Jan 1, 1945

By Thomas A. Read

THE internal friction of single crystals of metals is affected markedly by a variety of factors, which, according to the literature, are without influence on the internal friction of polycrystalline metals at strain amplitudes less than 10-5. For example, the internal friction of a suitably oriented zinc single crystal is multiplied by a factor of l00 when the vibration amplitude is slightly increased, and the internal friction of a copper crystal is markedly increased by the application of a stress of 30 lb. per sq. in. for one minute. In this paper it will be shown that these, together with the other phenomena associated with the damping of mechanical vibrations in metal single crystals, can be satisfactorily explained, at least qualitatively, in terms of an atomic mechanism that has been proposed for quite another purpose-that of accounting for slip in metals. The extraordinary agreement between the observed behavior of the metal single crystals and the behavior that could be predicted on the basis of this atomic mechanism leads to the belief that the latter is probably essentially correct. If this is so, it follows that valuable information about the slip process in metals may be gained from measurements of internal friction on single crystals. In this paper the results of the only study to date on the damping of mechanical vibrations in single crystals of metals will be presented. EXPERIMENTAL PROCEDURE The internal friction of a material is a measure of the rate at which the energy of mechanical vibrations is converted into heat. The measure of internal friction used in the present paper is the decrement A, which is defined as the fraction of the energy of vibration lost per half cycle. The measurements described here were .made for longitudinal oscillations at a frequency of 33.5 kc. for the copper crystals, and at a frequency of 39 kc. for the zinc crystals. The method used is that of the composite piezoelectric oscillator. The single-crystal specimens are in the form of circular cylinders ¼ in. in diameter and 1 ½ to 2 ½ in. long. The crystal rods are waxed in a V-block and sawed to the proper length with a fine jeweler's saw. The ends of the specimen are ground flat, and one end is cemented with a very thin film of beeswax and rosin to the end of an x-cut quartz rod which is ¼ in. in diameter and 3 in. long. The length of the specimen rod is determined by the condition that its natural frequency for longitudinal vibration be the same as that of the quartz rod, within 0.5 per cent. The lengths of the specimens are thus different for different orientations of the cylinder axis with respect to the crystallographic axes. When the specimen and quartz rods are thus matched in frequency the adhesive is at a node of stress, and it has been shown experimentally that under these circumstances

Jan 1, 1941

By L. E. Beverage, K. L. Johnston

This paper will address methods for minimizing liability and protecting materials from disclosure as result of self- evaluative audits and internal investigations. Specifically, the paper will cover the role of counsel in the investigative process and how best to design and conduct internal investigations to minimize the development of problematic material and disclosure of information. The paper will also address the extent of privileges that may be relied upon to protect materials and information from disclosure. These include the attorney-client privilege, the self-critical analysis privilege, and the attorney work product privilege. These privileges are qualified and understanding the limits of their coverage is essential to minimizing liability.

Jan 1, 2001

By Rajib K. Mohapatra, K. Vizaya Kumar

In any manufacturing organization internal logistics plays a vital role in improving and maintaining the productivity. In Ferro Alloys manufacturing organization where there is huge input of raw material in terms of ore, reductants and variety of fluxes amounting to about four times of the mass of alloy produced need to be handled from yard to furnaces , internal logistics requires utmost attention. Any deviation or mismatch between stock and requirement will affect furnace operation. Though the activities are being outsourced by most of the organization, these require close monitoring. This communication presents an optimization model which can work as a ready reference for the manager to decide upon the material quantity and the furnace to be fed with an objective of minimizing the cost of handling and zero production loss.

Jan 1, 2007

By P. Cavanagh

Summary This paper discusses the fundamental principles which allow the development of a new method for studying the deformation and failure of metals in terms of 'internal microstrains'. Internal microstrains mechanical and magnetic properties are defined and their influence on of metals is outlined. A research programme at present in progress will determine whether magnetic measurements of internal microstrains give sufficiently accurate values for predicting the performance of metals under service conditions. These magnetic test techniques are also being used to detect the beginning of plastic deformation and to trace the development of deformation processes and failure. Results of the experimental work in each field will be published. Introduction Any attempts are being made to develop a complete theory embracing the mechanical behaviour of metals. In spite of the amount of experimental data available, the theoretical approach is rather difficult, since most of the mechanical properties of a metal are determined by deviations from the pure chemical composition or the perfect crystal. Both types of deviation are difficult to reproduce experimentally and to describe theoretically. In general, there are three main avenues of approach to the problem being followed today.

Jan 1, 1950

By A. H. Grobe, F. N. Rhines

AT elevated temperatures the oxide of silver is unstable in the air at atmospheric pressure, consequently no external oxide scale forms upon pure silver under conditions of high-temperature annealing When small quantities of certain alloying elements are present in the silver, the formation of a thin external scale is possible' and in addition there may form a subscale composed of the oxide of the solute element precipitated within the body of the silver Norbury2 and Leroux and Raub3 have reported internal oxidation (subscale formation) in alloys of silver with 2, 7 5, and 30 per cent of copper The presence of the subscale is believed to be responsible, at least in part, for the objectionable "fire mark" in Sterling silver' Several other alloys of silver, after oxidizing heat-treatments, are known to exhibit undesirable polishing characteristics that may be the result of internal oxidation Except for the absence of an external scale of silver oxide, it is to be anticipated that silver alloys will prove to be very similar in their oxidation behavior to the alloys of copper, the oxidation characteristics of which have been studied in some detail 5,6 The present research confirms this anticipation The oxidation of a series of 20 dilute alloys of silver has been studied metallographically, some types of subscale not encountered among the copper alloys have been found Instances of internal oxidation in alloys of most of the metals of the I-b and VIII groups of the periodic system are on record, but evidence of this type of oxidation in alloys of the metals of the intermediate groups is lacking A number of the metals of the intermediate group, among them cadmium, lead, tin, and zinc, appear to provide the conditions essential to subscale formation, i e , they form oxides with a relatively low negative free energy of formation, they dissolve other metals that form more stable oxides, and, presumably, oxygen will diffuse through them In a study of 4o alloys of these white metals only a few cases of internal oxidation have been found The probable reasons for this difference in behavior will be discussed presently EXPERIMENTAL PROCEDURE Silver -The silver alloys employed in the oxidation studies were prepared in heats of 30 grams each from high-purity silver (99 993 per cent Ag)* and the purest avail-

Jan 1, 1942

By A. H. Grobe, F. N. Rhines

AT elevated temperatures the oxide of silver is unstable in the air at atmospheric pressure, consequently no external oxide scale forms upon pure silver under conditions of high-temperature annealing. When small quantities of certain alloying elements are present in the silver, the formation of a thin external scale is possible' and in addition there may form a subscale composed of the oxide of the solute element precipitated within the body of the silver. Norbury2 and Leroux and Raub3 have reported internal oxidation (subscale forma¬tion) in alloys of silver with 2, 7.5, and 30 per cent of copper. The presence of the subscale is believed to be responsible, at least in part, for the objectionable "fire mark" in Sterling silver.4 Several other alloys of silver, after oxidizing heat-treatments, are known to exhibit undesirable polishing characteristics that may be the result of internal oxidation. Except for the absence of an external scale of silver oxide, it is to be anticipated that silver alloys will prove to be very similar in their oxidation behavior to the alloys of copper, the oxidation characteristics of which have been studied in some detail5,6 The present research confirms this anticipation. The oxidation of a series of 20 dilute alloys of silver has been studied metallographically; some types of subscale not encountered among the copper alloys have been found. Instances of internal oxidation in alloys of most of the metals of the I-b and VIII groups of the periodic system are on record, but evidence of this type of oxidation in alloys of the metals of the intermediate groups is lacking. A number of the metals of the intermediate group, among them cadmium, lead, tin, and zinc, appear to provide the conditions essential to subscale formation; i.e., they form oxides with a relatively low negative free energy of formation, they dissolve other metals that form more stable oxides, and, presumably, oxygen will diffuse through them. In a study of 4o alloys of these white metals only a few cases of internal oxidation have been found. The probable reasons for this difference in behavior will be discussed presently. EXPERIMENTAL PROCEDURE Silver.-The silver alloys employed in the oxidation studies were prepared in heats of 30 grams each from high-purity silver (99.993 per cent Ag)* and the purest avail-

Jan 1, 1942

By R. R. Mankowski

The work described here is an extension of current theory applied to obtaining the power dissipated at the wavefront of a transverse disturbance traveling along a mine hoisting cable. A previously derived empirical relation is adapted to the present problem, and is solved by use of a Lagrange-type reference frame moving with the wavefront. As a result of tie limitations inherent in the original relation, only a lower-bound for the domain of predicted power losses is defined. A qualitative assessment of conditions leading to the undesirable effects of internal frictional losses at the wavefronts are discussed in terms of the operating environment found on typical mining installations

Jan 1, 1990

By M. M. Hajdasinski

For decades, the internal rate of return (IRR) project-evaluation criterion has been under increasing criticism. Torries (1998a) defends the beleaguered criterion. He claims that, as a project-evaluation and ranking instrument, the IRR is as suitable as the net present value (NPV). Torries also maintains that using the IRR to rank projects does not require the incremental approach and introduces his own alternative ranking approach. This paper disputes Torries' pro-IRR arguments and demonstrates that the IRR is a theoretically flawed and operationally dysfunctional criterion whose true meaning has persistently been misinterpreted. In a forthcoming paper by the author it will be shown that Torries' IRR-based project-ranking approach is flawed as well.

Jan 1, 2000

By M. M. Hajdasinski

In his recent paper, Torries (1998a) came to the defense of the much-criticized internal rate of return (IRR) as a project evaluation and ranking criterion. Torries also offered his own approach to the IRR-based project ranking, which he believes to be a more practical alternative to the conventional incremental-ranking approach, which Torries considers to be misleading. In an earlier paper (Hajdasinski, 2000), the author demonstrated that Torries' arguments vindicating the IRR concept are invalid. This paper provides logical and numerical evidence that the same is also true with regard to Torries' IRR based project-ranking approach.

Jan 1, 2000

By J. D. Miller

Flotation chemists have long sought to unravel the mechanisms of carboxylate collector adsorption by semi-soluble salt minerals. In particular, the adsorption density of adsorbed carboxylates, adsorption kinetics, speciation (chemisorbed, physisorbed), orientation, and conformation are of interest. Given the importance of these phenomena in establishing the hydrophobic state at a mineral surface, in-situ surface spectroscopy studies certainly are justified. Such measurements traditionally have been difficult to perform. However, beginning in the late 1980s, a Fourier transform infrared (FTIR) spectroscopic technique was developed that has allowed for the acquisition of a wealth of detailed information concerning carboxyiate adsorption in semi-soluble salt flotation systems. The technique, internal rejection spectroscopy using single-crystal internal reflection elements, is reviewed, as it applies to semi-soluble salt flotation systems.

Jan 1, 1999

By D. K. Crampton

INTERNAL stress and season cracking in brass have been studied for many years and the technical literature contains many data on various phases of the subject. A résumé of the literature shows certain fairly well established points upon which various authors are mostly agreed: 1. Season cracking is primarily caused by the presence of relatively high internal stresses, or possibly in some cases by external stresses, or both. 2. A specific corrosion is also essential to season cracking: Certain agents, particularly mercurous salts, mercuric salts and ammonia salts; have such a specific corrosive effect. 3. The tendency to season crack under given conditions increases with increasing zinc content, brass containing less than 20 per cent zinc being relatively immune. 4. In alpha brass the season cracks are intercrystalline; in alphabeta brass they lie between the two constituents; and in beta brass they are transcrystalline. 5. The ordinary impurities or added elements in special brasses have little or no effect on the tendency to season crack. 6. Internal stresses can be eliminated, or at least reduced to a safe 'limit by annealing treatments at temperatures that do not produce visible microstructural changes or appreciable softening of the worked brasses. There are, however, some points in connection with the phenomenon of season cracking which have not been thoroughly investigated, or wherein different authors and investigators are not entirely in agreement. The investigations described in this paper were undertaken to determine: 1. The correlation between mercurous nitrate tests and actual season cracking on long-time atmospheric exposure. 2. The quantitative effect of type and degree of drawing operations on the intensity of internal stress and on the tendency to season crack in brass tubes. 3. The possibility of drawing high-brass tubes in such a manner as to prevent the occurrence of harmful stresses rather than to find a remedy for such stresses once having obtained them.

Jan 1, 1930

By P. Schloth, H. van Swygenhoven, N. Chobaut, J-M. Drezet

"In the current trend toward thicker aluminium plates, a major concern is the stress build-up during quenching which causes distortions during machining. Indeed, cooling rates are not high enough, especially at the core of such thick plates, to prevent any precipitation and quench induced precipitates lower the hardening potential. Multi-scale modelling is required when predicting macro-scale stresses after quenching for thick heat treatable aluminium components. The reason is the instantaneous strong coupling between phase precipitation at the nano-scale and material hardening due to precipitation or softening owing to solute depletion at the microscale. For thick parts, quenching intensities decrease when going from the skin to the core of the component, thus introducing a gradient of nanostructure and consequently a gradient of mechanical properties. In addition, large thermally induced deformations lead to high macroscale residual stresses although part of them is relaxed by plastic deformation. These stresses have been measured in water quenched thick plates of 7040 and 7449 aluminium alloys using neutron diffraction and layer removal techniques and the results when compared with a thermomechanical finite element model of quenching highlight the influence of precipitation.IntroductionIn the processing route of heat-treatable aluminium alloys (AA), a critical step is quenching from the solutionizing temperature. High cooling rates are desired, as they avoid formation of coarse precipitates, which reduce mechanical properties. Fast quenching, however, cannot be achieved in the centre of thick components, where the quenching rate can be more than one order of magnitude lower than at the surface. The existence of a thermal gradient between core and surface leads to a differential thermal deformation which is accommodated by elastic and plastic deformation to comply with the compatibility of deformation. Whenever the material yields, especially at high temperature when the yield strength is low, residual stress remains after quenching due to the irreversibility of plastic deformation. After quenching, the plates are in a state of residual stress that causes unacceptable distortions during machining and may reduce service life drastically. Since stress relaxation is negligible during ageing treatments [1 ], agehardened aluminium parts are usually stress relieved prior to ageing. This is typically achieved by applying plastic deformation: stretching from 1.5 to 3 % in the rolling direction (L) can reduce the internal stresses by a factor of approximately 10 [2, 3]. However, complex geometries or thicker components like thick sheets require other approaches. Reducing the quenching rate by using boiling water for instance leads to lower residual stresses [1, 4]."

Jan 1, 2013