Showing papers on "Creep published in 1992"
TL;DR: In this paper, the authors studied the effect of dislocation-free nickel base superalloy single crystals with high volume fractions of the γ′ phase on their deformation and found that the dislocation free precipitates are resistant to shearing by dislocations.
Abstract: Creep deformation in 〈001〉 oriented nickel base superalloy single crystals has been studied in an effort to assess the factors which contribute to the overall creep resistance of superalloys with high volume fractions of γ′ phase. Detailed observations of three dimensional dislocation arrangements produced by creep have been made with the use of stereo electron microscopy. In the temperature range of 800–900°C at stresses of 552 MPa or lower, the dislocation-free γ′ precipitates are resistant to shearing by dislocations. As a result, creep deformation occurs by forced bowing of dislocations through the narrow γ matrix channels on {111} planes. At moderate levels of temperature and stress there are incubation periods in virgin crystals prior to the onset of primary creep. The incubations arise because of the difficult process of filling the initially dislocation starved material with creep dislocations from widely spaced sources. When the newly generated dislocations percolate through the cross section, incubation comes to an end and primary creep begins. In primary creep neither work hardening nor any type of recovery plays an important role. The creep rate decelerates because the favorable initial thermal misfit stresses between γ and γ′ phases are relieved by creep flow. Continued creep leads to a build-up of a three-dimensional nodal network of dislocations. This three-dimensional network fills the γ matrix channels during steady state creep and achieves a quasi-stationary structure in time. In situ annealing experiments show that static recovery is ineffective at causing rearrangements in the three-dimensional network at temperatures of 850°C or lower. The kinematical dislocation replacement processes which maintain the quasi-stationary dislocation network structures during apparent steady state creep are not understood and require further study. Because of the impenetrability of the γ′ precipitates, dislocations move through the γ matrix by forced Orowan bowing, and this accounts for a major component of the creep resistance. In addition, the frictional constraint of the coherent or semi-coherent precipitates leads to the build-up of pressure gradients in the microstructure, and this provides load carrying capacity. There is also a smaller component of solid solution strengthening. Work hardening is comparatively unimportant. Finite element analysis shows that the non-deforming precipitates are increasingly stressed as creep deformation accumulates in the matrix. In the later stages of steady state creep and during tertiary creep the stresses in the precipitates rise to high enough levels to cause shearing of the γ′ particles by dislocations entering from the γ matrix. The recovery resistance of the material is in part due to a very low effective diffusion constant and in another part due to the fact that the three-dimensional dislocation networks formed in the γ matrix serve to neutralize the misfit between the γ and γ′ phases.
782 citations
TL;DR: In this article, the porosity within fault zones varies over earthquake cycles so that fluid pressure is in long-term equilibrium with hydrostatic fluid pressure in the country rock, which may explain why major faults such as the San Andreas system are weak.
Abstract: Field and laboratory observations suggest that the porosity within fault zones varies over earthquake cycles so that fluid pressure is in long-term equilibrium with hydrostatic fluid pressure in the country rock. Between earthquakes, ductile creep compacts the fault zone, increasing fluid pressure, and finally allowing frictional failure at relatively low shear stress. Earthquake faulting restores porosity and decreases fluid pressure to below hydrostatic. This mechanism may explain why major faults, such as the San Andreas system, are weak.
413 citations
TL;DR: In this paper, experimental results on 58Bi-42Sn solder joints, optical and SEM microstructures of their matrix and of their interface with copper, solidification behavior studied by differential scanning calorimetry, wettability to copper, creep, and low cycle fatigue.
Abstract: This report presents experimental results on 58Bi-42Sn solder joints, optical and SEM microstructures of their matrix and of their interface with copper, solidification behavior studied by differential scanning calorimetry, wettability to copper, creep, and low cycle fatigue. These results are discussed in comparison with 60Sn-40Pb solder, and with three low temperature solders, 52In-48Sn, 43Sn-43Pb-14Bi, and 40In-40Sn-20Pb. The 58Bi-42Sn solder paste with RMA flux wets Cu matrix with a wetting angle of 35° and had a 15° C undercooling during solidification. The constitutive equation of the steady state shear strain rate, and the Coffin-Manson relation constants for the low cycle shear fatigue life at 65° C have been determined. The test results show that this solder has the best creep resistance but the poorest fatigue strength compared with the other four solders.
275 citations
TL;DR: In this paper, the authors explored the possibility of using a unified theory of creep-fatigue, similar to the Halford-Manson strain-range partitioning method, for examining the effect of cyclic temperature range on fatigue life, over a wide range of temperatures.
Abstract: This study explores the possibility of using a unified theory of creep-fatigue, similar to the Halford-Manson strain-range partitioning method, for examining the effect of cyclic temperature range on fatigue life, over a wide range of temperatures. Other investigators have attempted similar techniques before for solder fatigue analysis. The present study is different since it proposes an energy-partitioning technique rather than strain-partitioning to examine the dependence of solder fatigue behavior on temperature dependent changes in the relative amounts of plastic and creep strains. The solder microstructure also dictates creep behavior but is assumed to be a given invariant parameter in this study. In other words, this study is targeted at as-cast microstructures and does not address post-recrystallization behavior. A sample solder joint of axisymmetric configuration, commonly found in leaded through-hole mounting technology, is analyzed with the help of nonlinear finite element methods. The strain history is determined for constant-amplitude temperature cycling with linear loading and unloading, and with constant dwells at upper and lower ends of the cycle. Large-deformation continuum formulations are utilized in conjunction with a viscoplastic constitutive model for the solder creep-plasticity behavior. Relevant material properties are obtained from experimental data in the literature. The results show significant amounts of rachetting and shakedown in the solder joint. Detailed stress-strain histories are presented, illustrating the strain amplitude, mean strain and residual stresses and strains. For illustrative purposes, the hysteresis cycles are partitioned into elastic, plastic and creep components. Such partitioned histories are essential in order to implement either the Halford-Manson strain-range partitioning technique or the energy-based approach suggested here, for analyzing the creep-fatigue damage accumulation in solder material. This study also illustrates the role and utility of the finite element method in generating the detailed stress-strain histories necessary for implementing the energy partitioning approach for creep-fatigue damage evaluation. Solder life prediction is presented as a function of cyclic temperature range at a given mean temperature.
218 citations
20 Feb 1992-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: A review of creep data of discontinuous SiCAl composites (whisker and particulate) shows that the creep behavior of these composites exhibits two main characteristics: (a) the stress dependence of the steady state (or minimum) creep rate, as described by the value of the stress exponent, is high and variable; and (b) the temperature dependence, measured by the creep activation energy, is much larger than that for self-diffusion in aluminum.
Abstract: A review of creep data of discontinuous SiCAl composites (whisker and particulate) shows that the creep behavior of these composites exhibits two main characteristics: (a) the stress dependence of the steady state (or minimum) creep rate, as described by the value of the stress exponent, is high and variable and (b) the temperature dependence of the steady state (or minimum) creep rate, which is measured by the creep activation energy, is much larger than that for self-diffusion in aluminum. These two characteristics are examined in the light of theoretical treatments describing the origin of high temperature strengthening in discontinuous metal matrix composites and dislocation models proposed for dispersion-strengthened alloys.
203 citations
TL;DR: In this paper, the role of volume fraction and size of reinfrecement on the steady state creep behavior of pure aluminium matrix-silicon carbide particulate composites have been studied in the temperature range 623-723 K.
Abstract: The roles of volume fraction and size of reinfrecement on the steady state creep behaviour of pure aluminium matrix-silicon carbide particulate composites have been studied in the temperature range 623–723 K. The observed apparent stress exponents are higher than 15 and apparent activation energy is 249 kJ mol−1. By considering the existence of a threshold stress, the data for 1.7 μm particulate reinforced composites with different volume fraction can be rationalized according to the substructure invariant model. The effective stress-strain rate behaviour of composites with 10 vol.% of coarser particulates (14.5 and 45.9 μm), however, agree with the stress dependent substructure model. The present analysis is validated by constructing a new type of “dislocation creep mechanism map”. The observed threshold stress varies with the volume fraction of reinforcement and is independent of particulate sizes and test temperatures. It is suggested that a model based on applied stress independent load transfer is required to explain the origin of such a threshold stress.
193 citations
TL;DR: In this article, the macroscopic creep of powder due to diffusional mass transport on the interparticle contacts is modelled, where diffusion is very rapid on the free surface of the powder particles.
Abstract: The creep of powder due to diffusional mass transport on the interparticle contacts is modelled. It is assumed that diffusion is very rapid on the free surface of the powder particles so that the critical phenomenon is mass transport on the interparticle boundary. An interparticle shear viscosity is allowed for also. To characterize the creep law, the macroscopic strain rate in the powder aggregate is specified and the energy dissipated in mass transport and interparticle shear is computed. This work rate is used in a potential to determine the macroscopic creep parameters. The effective macroscopic shear and bulk viscosities resulting from this model depend on the relative density of the powder and disappear at random close packed density. The viscosities depend also on parameters controlling mass transport, the size of the powder particles and, in the case of shear viscosity, on the interparticle shear drag. A term driving sintering arises naturally in the model.
189 citations
Book•
01 Jan 1992
TL;DR: The materials of engineering: non-ferrous metals and alloys iron and steel thermoplastics elastomers thermosetting materials ceramics and glasses composite materials as discussed by the authors.
Abstract: Part 1 The materials of engineering. Part 2 Materials science: atomic structure and bonding influence of bond type on structure and properties the formation of polymers crystalline structures glasses and partial crystallinity elastic behaviour dislocations and plasticity in metals viscoelasticity toughness and fracture of materials phase diagrams and alloy formation phase transformations and diffusion electrical and magnetic properties optical, thermal and other properties. Part 3 The materials of engineering: non-ferrous metals and alloys iron and steel thermoplastics elastomers thermosetting materials ceramics and glasses composite materials. Part 4 Forming and fabrication of materials: forming processes for metals forming processes for polymer materials forming processes for ceramics and glasses material removal processes joining processes. Part 5 Behaviour in service: failure, fatigue and creep oxidation, corrosion and other effects. Part 6 Evaluation of materials: property testing non-destructive testing macro- and micro-examination materials selection.
164 citations
TL;DR: It is suggested that grain-size reduction after a subducting slab passes through the 670-kilometer discontinuity or after a phase transformation from orthorhombic to tetragonal in perovskite will result in rheological softening in the top portions of the lower mantle.
Abstract: High-temperature creep experiments on polycrystalline perovskite (CaTiO(3)), an analog of (Mg,Fe)SiO(3) perovskite of the lower mantle, suggest that (grain size-sensitive) diffusion creep is important in the lower mantle and show that creep rate is enhanced by the transformation from the orthorhombic to the tetragonal structure. These observations suggest that grain-size reduction after a subducting slab passes through the 670-kilometer discontinuity or after a phase transformation from orthorhombic to tetragonal in perovskite will result in rheological softening in the top portions of the lower mantle.
159 citations
TL;DR: In this paper, simple unified constitutive equations to model the mechanical behavior of plain carbon steel in the austenite temperature region for use in finite element stress analysis of processes such as continuous casting were developed and investigated.
Abstract: This work develops and investigates simple unified constitutive equations to model the mechanical behavior of plain carbon steel in the austenite temperature region for use in finite element stress analysis of processes such as continuous casting. Four different forms of constitutive relations are considered: constant structure, time-hardening, strain-hardening, and simultaneous time- and strain-hardening models. Each relation is judged on its ability to reproduce experimental data from both tensile and creep tests and its ability to exhibit reasonable behavior under complex loading conditions. Three of the equations appear suitable for small strain monotonic loading conditions for a wide range of low strain rates (10−3 to 10−6 s−1), high temperatures (950 °C to 1400 °C), and varying carbon contents (0.005 to 1.54 wt pct C).
155 citations
TL;DR: Flux creep in Bi 2 Sr 2 CaCu 2 O 8 crystals exhibits two different regimes as a function of time, as well as of temperature and magnetic field.
Abstract: Flux creep in Bi 2 Sr 2 CaCu 2 O 8 crystals exhibits two different regimes as a function of time, as well as of temperature and magnetic field. The short-time, low-temperature regime has a peak in current density versus field, which is enhanced by irradiation defects. The long-time, high-temperature regime has a monotonic and sharp falloff (step) in current density versus magnetic field, which is suppressed by irradiation defects. The former is identified with bulk pinning, and the latter with a surface barrier
TL;DR: In this paper, the Eshelby-Mori-Tanaka method is extended into the Laplace domain to examine the linearly viscoelastic behavior in two types of composite materials: a transversely isotropic one with aligned spheroidal inclusions and an isotropical one with randomly oriented inclusions.
Abstract: The Eshelby-Mori-Tanaka method is extended into the Laplace domain to examine the linearly viscoelastic behavior in two types of composite materials: a transversely isotropic one with aligned spheroidal inclusions and an isotropic one with randomly oriented inclusions. Though approximate in nature, the method offers both simplicity and versatility, with explicit results for the sphere, disk, and fiber reinforcements in the transformed domain. The results coincide with some exact solutions for the composite sphere and cylinder assemblage models and, with spherical voids or rigid inclusions, the effective shear property also lies between Christensen’s bounds. Consistent with the known elastic behavior, the inverted creep compliances in the time domain indicate that, along the axial direction, aligned needles or fibers provide the most effective improvement for the creep resistance of the aligned composite, but that in the transverse plane the disk reinforcement is far superior. For the isotropic composite disks are always the most effective shape, whereas spheres are the poorest. Comparison with the experimental data for the axial creep strains of a glass/ED-6 resin composite containing 54 percent of aligned fibers indicates that the theory is remarkably accurate in this case.
TL;DR: In this paper, the authors report the major results to date of an ongoing study of the mechanical behavior of nanocrystalline metals produced by the inert-gas condensation method; some results have been reported elsewhere.
TL;DR: In this article, the flexural strength and creep behavior of RE2Si2O7-Si3N4 materials were examined and the retention in room-temperature strengths displayed by these ceramics at 1300°C was 80-91%, with no evidence of inelastic deformation preceding failure.
Abstract: The flexural strength and creep behavior of RE2Si2O7–Si3N4 materials were examined. The retention in room-temperature strengths displayed by these ceramics at 1300°C was 80–91%, with no evidence of inelastic deformation preceding failure. The steady-state creep rates, at 1400°C in flexural mode, displayed by the most refractory materials are among the lowest reported for sintered Si3N4. The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior of these materials. All of the rare-earth oxide sintered materials, with the exception of Sm2Si2O7–Si3N4, had lower creep strains than the Y2Si2O7–Si3N4 material.
15 May 1992-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Physical and mechanical properties of high melting point Ti5Si3 and TiSi2 intermetallics with hexagonal D88 and orthorhombic C54 structure have been investigated as mentioned in this paper.
Abstract: Physical and mechanical properties of high melting point Ti5Si3 and TiSi2 intermetallics with hexagonal D88 and orthorhombic C54 structure have been investigated. Young's moduli of about 160 GPa (Ti5Si3) and 250 GPa (TiSi2) were recorded at room temperature. At 1000°C the elastic moduli are 143 and 215 GPa respectively. Flow stresses of about 1050 MPa for Ti5Si3 and 230 MPa for TiSi2 at 1000°C were measured. With increasing temperature an exponential decrease of the flow stresses occurs. The low density of 4.3 g cm−3 and the pronounced creep resistance are important for high temperature applications of this material.
TL;DR: In this paper, the microstructures of HP-type heat-resistant cast steels, having niobium additions up to 2 wt., were examined in the as-cast condition and after artificial aging at 700, 900, and 1100°C.
TL;DR: In this article, the high-temperature deformation behavior of a fine-grained polycrystalline yttrium aluminum garnet (YAG) was studied in the temperature range of 1400° to 1610°C using constant strain rate compression tests under strain rates ranging from 10−5/s to 10−3/s.
Abstract: The high-temperature deformation behavior of a fine-grained polycrystalline yttrium aluminum garnet (YAG) was studied in the temperature range of 1400° to 1610°C using constant strain rate compression tests under strain rates ranging from 10−5/s to 10−3/s. The stress exponent of the creep rate, the activation energy in comparison with that for single-crystal YAG, and the grain size dependence suggest that Nabarro–Herring creep rate limited by the bulk diffusion of one of the cations (Y or Al) is the operative mechanism.
TL;DR: In this paper, a depth-sensing indentation instrument with indentation depths in the submicron range was used for constant load creep experiments on polycrystalline Sn and sputtered Al films on Si substrates.
Abstract: Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.
TL;DR: In this article, the one-dimensional consolidation behaviour of Bothkennar clay has been examined by testing high quality intact and reconstituted specimens recovered using the Laval sampler.
Abstract: The one-dimensional consolidation behaviour of Bothkennar clay has been examined by testing high quality intact and reconstituted specimens recovered using the Laval sampler. The collaborative test programme consisted of incremental load, constant rate of strain, and restricted flow tests. During the test programme the variation of yield stress with depth, the effect of strain rate on the observed yield stress, the creep behaviour and the variability in soil compressibility were investigated. It was noted that the yield stress is influenced by the strain rate, with faster rates resulting in higher values of yield stress. When this was taken into account, it was found that specimens taken from a single depth showed reasonably consistent behaviour independent of the type of test. Creep occurred in the incremental load tests, with the maximum rate just after yield, indicating a clear linkage between creep and the structural breakdown at yield. The vertical permeability of the specimens was determined by flow...
TL;DR: In this paper, finite element calculations have been carried out for spherical unit cells containing a concentric spherical hole to characterize the power law creep of a material containing voids, and the results of the unit cell calculations are approximated well by a creep potential for the macroscopic behavior of a porous material.
Abstract: Finite element calculations have been carried out for spherical unit cells containing a concentric spherical hole to characterize the power law creep of a material containing voids. Axisymmetric states of macroscopic stress were applied to the unit cells ranging from purely hydrostatic loading to purely deviatoric stressing. The results of the unit cell calculations are approximated well by a creep potential for the macroscopic behavior of a porous material. This potential agrees with the unit cell results for purely hydrostatic stress and purely deviatoric stress and involves a simple elliptical interpolation in between. The model predicts quite well the ratio of transverse to axial strain rate in uniaxial compression tests.
TL;DR: In this article, the phase boundary motion and cusp formation occurred during deformation in quartz-feldspar phase boundaries, which is consistent with the accommodation of some intracrystalline plastic strains by dislocation creep.
TL;DR: In this paper, the strength and fatigue of a commericially available hot isostatically pressed silicon nitride was measured as a function of temperature and the fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure.
Abstract: The strength of a commericially available hot isostatically pressed silicon nitride was measured as a function of temperature. To evaluate long-term mechanical reliability of this material, the tensile creep and fatigue behavior was measured at 1150°, 1260°, and 1370°C. The stress and temperature sensitivities of the secondary (or minimum) creep strain rate were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure. The applicability of the four-point load geometry to the study of strength and creep behavior was also determined by conducting a limited number of flexural creep tests. The tensile fatigue data revealed two distinct failure mechanisms. At 1150°C, failure was controlled by a slow crack growth mechanism. At 1260° and 1370°C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the fatigue behavior. In this temperature regime, the fatigue life was controlled by the secondary (or minimum) creep strain rate in accordance with the Monkman–Grant relation.
TL;DR: In this article, the effects of operational variables on joint strength are discussed, including principal bonding parameters such as temperature, time and pressure, and the influence of atmosphere, mismatch in coefficient of thermal expansion between the joint members, interlayers and surface structure.
Abstract: Diffusion bonding of ceramics to ceramics and to metals is reviewed, with primary emphasis on the effects of operational variables on joint strength. These include principal bonding parameters such as temperature, time and pressure. In addition, the influence of atmosphere, mismatch in coefficient of thermal expansion between the joint members, interlayers and surface structure are discussed. The mechanisms involved, i.e. plastic deformation, various forms of diffusion and power law creep, imply that temperature is the most important process parameter. Finally, a survey of variables employed in bonding of different ceramic-metal and ceramic-ceramic joints is included as a guideline for selection of materials and parameters.
TL;DR: In this paper, the microstructural instability during creep and its effect on creep behavior were investigated for a martensitic 9Cr-2W steel, which was developed as a low radioactive steel suitable for fusion reactor structure.
Abstract: The microstructural instability during creep and its effect on creep behavior were investigated for a martensitic 9Cr-2W steel. The steel was developed as a low radioactive steel suitable for fusion reactor structure. Creep testing was carried out at 873 K for up to 15,100 ks (4200 hours). The creep curve consisted of transition creep, where creep rate decreased with time, and acceleration creep, where creep rate increased with time. During creep, microstructural instability, such as the recovery of dislocations, the agglomeration of carbides, and the growth of martensite lath subgrains, was observed to occur, which resulted in softening but no hardening. The transition creep was a consequence of the movement and annihilation of excess dislocations, resulting in the decrease in dislocation density and the increase in martensite lath size with time. The acceleration creep was a consequence of a gradual loss of creep strength due to the microstructural instability which occurred from the initial stage of creep.
TL;DR: In this paper, the authors used optical, scanning electron, and transmission electron microscopy data to show that the intergranular creep failure in Fe3Al is related to weak high-angle grain boundaries and to formation of subgrain boundary arrays, which reduce the ability of dislocations to glide or multiply to produce matrix plasticity.
Abstract: Recent alloy development efforts have shown that Fe3Al-based alloys can have room temperature tensile ductilities of 10–20% and yield strengths of 500 MPa at temperatures to 600 °C. These property improvements are important for enabling the use of iron-aluminides for structural applications that require their excellent corrosion resistance. New data are presented here from creep-rupture studies on Fe3Al and on Fe3Al-based alloys containing molybdenum or niobium plus zirconium. Binary Fe3Al alloys have low creep resistance, but the addition of 2 at. % Mo or 1% Nb plus 0.1% Zr increases the creep life and reduces the minimum creep rate, with the niobium-containing alloy being the strongest. The improvement in creep life is the result of a combination of factors which include grain boundary strengthening, resistance to dynamic recrystallization during stressing, precipitation strengthening, and changes in the formation and mobility of the dislocation network. Correlation of optical, scanning electron, and transmission electron microscopy data suggests that the intergranular creep failure found in Fe3Al after creep testing at 550–650 °C is related to weak high-angle grain boundaries and to formation of subgrain boundary arrays, which reduce the ability of dislocations to glide or multiply to produce matrix plasticity. The addition of niobium/zirconium results in solid solution strengthening effects, as well as the formation of fine MC precipitates (a small amount of carbon is present as a contaminant from the casting process) which strengthen both the matrix and grain boundaries. The result relative to the binary alloy is increased creep-rupture strength and life coupled with a change to a ductile-dimple transgranular failure mode. This suggests that the mechanisms that cause failure during creep can be controlled by macro- and microalloying effects.
TL;DR: In this paper, the dependence of the amount of checking on shrinkage induced stress level during timber drying is investigated by comparing theoretically calculated maximal stress with observed amounts of checking in a set of drying tests.
Abstract: The dependence of the amount of checking on shrinkage induced stress level during timber drying is considered. This relationship is investigated by comparing theoretically calculated maximal stress with observed amount of checking in a set of drying tests. Different ways of modelling wood creep behaviour are included. It is found that a correlation exists in all the cases studied, except when creep is described with the traditional equation for mechano-sorptive creep. It is shown that this exception is due to a special mathematical property of the equation. A new mechano-sorptive creep model is thus proposed and briefly investigated. Using this model, a method for predicting the amount of checking in timber drying is developed.
TL;DR: In this paper, the authors introduce an approximate strain rate potential for the porous body of a hot isostatic pressing (HIP) cycle, which can be used to model the coupling between the hydrostatic and deviatoric stresses.
Abstract: Hot isostatic pressing (HIP) is potentially a cost-effective and efficient process for the manufacture of high quality metal components from powders. The densification of the powder during HIP proceeds in stages marked by changes in the geometry of the pores and by the dominance of different densification mechanisms. When the density is high and the pores are isolated and roughly spherical, the densification rate under a compressive load due to creep can be approximated by the densification rate of a sphere of creeping material containing a single, centered void. The densification rates predicted by such a model are significantly increased by small deviations of the load from purely hydrostatic compression. Thus, a careful account of the coupling between the hydrostatic and deviatoric stresses is important in the accurate modelling of the process and the design of an efficient HIP cycle; this can be achieved through the introduction of an approximate strain rate potential for the porous body.
TL;DR: In this article, the mechanical properties of dispersion-strengthened aluminum alloys, with various dispersoid types, volume fractions, and grain structures, were investigated in conjunction with systematic microstructural examinations.
Abstract: The mechanical properties of dispersion-strengthened aluminum alloys, with various dispersoid types, volume fractions, and grain structures, were investigated in conjunction with systematic microstructural examinations. New theoretical concepts, based on thermally activated dislocation detachment from dispersoid particles, were used to analyze the creep behavior. A particularly strong dispersoid-dislocation interaction was identified as reason for the excellent creep properties of carbide dispersion-strengthened aluminum. Oxide particles (Al2O3,MgO) seem to exert a weaker interaction force and are therefore less efficient strengtheners. Although fine crystalline in the as-extruded condition, all alloys are remarkably resistant against diffusional creep. It is demonstrated that this behavior can be consistently understood by extending the concept developed for the interaction between bulk dislocations and dispersoids to grain boundary dislocations.
TL;DR: In this paper, the fatigue behavior of two adhesives intended for use in automotive bodyshell construction has been assessed using simple lap shear test-pieces, and it is recommended that, for loadbearing applications, the T g of the adhesive should be above the maximum temperature expected in service.