Differential Strain Rate Research Articles

Stress state in the upper crust around the source region of the 1891 Nobi earthquake through shear wave polarization anisotropy

We investigate shear wave polarization anisotropy in the upper crust around the source region of the 1891 Nobi earthquake, central Japan. At most stations, the orientation of the faster polarized shear wave is parallel to the axes of the maximum horizontal compressional strain rate and stress, indicating that stress-induced anisotropy is dominant in the analyzed region. Furthermore, near the source faults, the orientation of the faster polarized shear wave is oblique to the strike of the source faults. This suggests that microcracks parallel to the strike of the source fault, which would be produced by the fault movement of the Nobi earthquake, have healed with the healing of the faults. For stress-induced anisotropy, time delays normalized by path length in the anisotropic upper crust as a function of the differential strain rate are coincident with those in the inland high strain rate zone, Japan. These data, together with those of a previous study, show that the variation in the stressing rate, estimated from shear wave splitting, is close to that estimated from geodetic observation. This implies that the variation in the stressing rate in the brittle upper crust is linked to that in the strain rate on the ground surface.

High-Temperature Tensile Flow Behavior of Caliber-Rolled Mg-3Al-1Zn Alloy

Mg-3Al-1Zn (AZ31) alloy was caliber rolled isothermally in the temperature range of 523 K to 723 K (250 °C to 450 °C) to develop fine grains of 3 to 13 µm. Tensile tests by constant initial strain rate as well as differential strain rate test techniques were conducted over the temperature range of 493 K to 723 K (220 °C to 450 °C) and strain rate range of 10−5 to 10−1 s−1. Maximum tensile elongation of 182 pct was obtained at test temperature of 723 K (450 °C) and strain rate of 10−3 s−1 in the sample obtained from caliber rolling at 723 K (450 °C), in spite of its large grain size of 13 µm. The strain rate sensitivity index ‘m’ was found to vary from 0.08 to 0.33 and activation energy for deformation ‘Q’ varied from 30 to 185 kJ mol−1 depending on test condition and caliber-rolling condition. These variations in m and Q values are explained by the difference in prior grain size, texture, and twins developed as a function of caliber-rolling temperature, and further by the concomitant microstructural change occurring during tensile test itself. The presence of twins and orientation of grains influences the parameters of the constitutive relation to varying extent.

Microstructure evolution and flow behavior of hot-rolled aluminum – 5% B4C composite

Differential strain rate compression tests were conducted to study flow behavior of hot rolled Al–5wt% B4C composite as a function of sample orientation (longitudinal and transverse) over the temperature and strain rate ranges of 25–500°C and 10−4 to 1s−1, respectively. The longitudinal samples are found to show lower flow stress than that shown by the transverse samples in the temperature range of 25–200°C. The reverse becomes true at higher temperatures of 300–500°C. The values of stress exponent (n) and activation energy for deformation (Q), based on applied stress, ranged from 10 to 46 and 307–416kJ/mol, respectively. However, by considering effective stress, these values were reduced to n=8 and Q=126–190kJ/mol. This stress exponent ofn=8 is further reduced to n=5 by considering substructural evolution, which suggests the dislocation climb creep mechanism to be favorable for deformation.

Effect of Severe Caliber Rolling on Superplastic Properties of Mg-3Al-1Zn (AZ31) Alloy

Fine grains were developed in Mg-3Al-1Zn (AZ31) alloy by isothermal caliber rolling at five different temperatures in the range of 250-450°C. The samples of different grain sizes were deformed by constant strain rate and differential strain rate test techniques over the temperature range of 220-450 °C and strain rate range of 10-5 to 10-1 s-1. The effects of grain size, test temperature and strain rate on flow stSuperscSuperscript textript textress were analysed to develop the constitutive relationship for supSuperscript texterplastic deformation. The parameters of the constitutive relationship obtained from the constant strain rate tests and differential strain rate tests were used to find out the material constant A of the constitutive relationship.

Hydrolytic weakening of olivine at mantle pressure: Evidence of [1 0 0](0 1 0) slip system softening from single-crystal deformation experiments

To date, most of the experiments performed to quantify the hydrolytic weakening of olivine single crystals have been performed at low confining pressure (and low water fugacities). In order to determine if the degree of hydrolytic weakening changes at higher water fugacities (higher water contents), we have performed a series of high pressure (P) and high temperature (T) deformation experiments in hydrous condition on San Carlos olivine (Fo92) and forsterite (Fo100) single crystals, in a Deformation-DIA apparatus (D-DIA). Deformation was carried out in axial compression along the [110]c crystallographic reference frame direction in order to activate [100](010) dislocation slip system alone, at P ranging from 4 to 7GPa and T=1200°C. Water was supplied during the experiments through dehydration of a talc sleeve (talc→enstatite+coesite+H2O) around the sample, while the differential stress and strain rate of the specimen were calculated from in situ X-ray diffraction and time-resolved imaging, respectively. Run products were investigated using Fourier transform infrared (FTIR) spectroscopy, and optical/electron microscopy (SEM and TEM). Structurally bound hydroxyl content (COH) derived from absorbance in FTIR spectra, based on the Paterson (1982) relation, were typically between 290 and 720ppm H/Si in the run products and the majority of these hydroxyls were observed as distinct peaks in the range of wavenumber from 3620 to 3500cm−1. TEM reveals that the [100](010) slip system was effectively activated and responsible for crystal deformation, and that dislocation glide was significantly assisted by recovering processes such as dislocation climb and dipole annihilation. Combining the experimental data from this study and Mackwell et al. (1985), we estimate the activation volume V∗[110]c for San Carlos olivine in order to produce a reasonable water-fugacity exponent r in the flow law, and obtain V∗[110]c=12.1cm3/mol for r=0 and V∗[110]c=17.3cm3/mol for r=1.2. Comparisons of the strengths of the wet single crystals to the strengths of dry single crystals calculated from the rheological laws (Bai et al., 1991, Darot and Gueguen, 1981, Raterron et al., 2009) indicate that the wet single crystal cylinders were between 1.3 and 1.6 times weaker than their dry counterpart at same conditions, which is consistent with previous studies of [100](010) olivine rheology performed at low confining pressure (300MPa).

Estimates of stress and strain rate in mylonites based on the boundary between the fields of grain‐size sensitive and insensitive creep

Microstructural analyses of mylonites next to the Median Tectonic Line (MTL), SW Japan, reveal a transition in the dominant deformation mechanism of quartz from grain‐size‐insensitive dislocation creep to grain‐size‐sensitive grain‐boundary sliding (GBS). The transition occurred under greenschist‐facies conditions (∼300–400°C) during grain‐size reduction by dynamic recrystallization. The stereologically corrected grain size for the transition is approximately 4.3 μm. At the boundary between the fields of dislocation creep and GBS, as calculated from creep constitutive relations, the differential stress and strain rate for this corrected grain size are estimated to be ∼280 MPa and 1.2 × 10−11 s−1 for 300°C, and ∼110 MPa and 1.0 × 10−10 s−1 for 400°C. The strain rates estimated for the mylonites next to the MTL are much higher than those estimated for the surrounding metamorphic rocks (∼10−14 s−1), and the displacement rates calculated based on the thickness of high‐strain mylonites and their strain rates are comparable with the average slip rates of the most active intraplate faults in Japan. These inferences suggest that the high‐strain mylonite zones next to the MTL are the exhumed downward extension of a seismogenic fault in the ductile region. The zones were highly localized (<10 m) and experienced very high strain rates (10−11 to 10−10 s−1).

Análise de volumes de sal em restauração estrutural: um exemplo na bacia de Santos

Halokinesis complexity in the central portion of Santos Basin involves significant structures and deformed depocenters, differentiated along the tectonic transport direction. Five geological cross-sections with an entire stratigraphic record in the study area have been restored to investigate different deformation styles, including the evolution of Cabo Frio Fault, coherently inserted into the tectonosedimentary evolution of Santos Basin. The procedure combines 2D restoration with 3D treatment and analysis through the following steps: layering removal, decompaction and flexural isostatic compensation; decoupled restoration of salt tectonics; material conservation (including salt); retrieval of the layering when differential strain rates affect uncoupled domains; bathymetric calibration of the restored set, and treatment and spatial analysis of results. Detailing of 14 restoration steps has properly discretized the deformation, minimized procedure deviations, and provided geometric and stratigraphic coherence in the space-time domains. The controlled salt redistribution has confirmed the effects of sedimentary aggradation and pre-existing structures on the strain. The results highlight the reciprocity importance of the effects of the halokinetic lateral displacement on isostasy, eustasy, bathymetry, and decompaction, which was not considered in the existing restoration programs.

Spatial variation in shear wave splitting of the upper crust in the zone of inland high strain rate, central Japan

We investigate a detailed spatial variation in shear wave splitting in the zone of inland high strain rate, called the Niigata-Kobe Tectonic Zone (NKTZ), central Japan. Most observations show stress induced anisotropy, that is, the orientation of the faster polarized shear wave is parallel to the axis of the maximum horizontal compressional strain rate estimated from GPS data. Others show structure induced anisotropy, that is, the orientation is parallel to the strike of active faults. For the stress induced anisotropy, time delays normalized by the path length in the anisotropic upper crust is proportional to the differential strain rate. We estimate a spatial variation in stressing rate of the upper crust beneath the high strain rate zone based on a response of the normalized time delay to a step-wise stress change caused by a moderate-sized earthquake. The variation in the stressing rate of 3 kPa/year estimated from shear wave splitting is coincident with that from GPS data. We conclude, together with other seismological features in the NKTZ reported previously, that the high strain rate in the NKTZ is attributed to the high deformation rate below the brittle-ductile transition zone in the crust.

The effect of prior annealing on high temperature flow properties of and microstructural evolution in SPF grade IN718 superalloy

High temperature flow properties of superplastic forming grade IN718 superalloy, annealed at 1198–1273 K for 15 min–5 h, were investigated. Tensile specimens of grain sizes ( d o) 2.9–16.9 μm were deformed at constant strain rate of 5 × 10 −5 s −1 and by differential strain rate test technique over the strain rate range of ∼2.5 × 10 −6 to 3 × 10 −2 s −1 at 1198 K. The stress–strain curves exhibited flow hardening followed by flow softening. While tensile ductility was found to increase the peak stress generally decreased with the decrease in grain size. Flow hardening was attributed to concomitant grain growth in the fine-grained ( d o = 2.9–4.3 μm) samples and to deformation-induced precipitation in the coarse grained ( d o = 16.9 μm) sample. The occurrence of flow softening, in these two cases, was due to cavitation and precipitate coarsening. log(stress)–log(strain rate) curves delineated superplastic behavior with strain rate sensitivity index ( m) ∼0.7 and the maximum ductility was found to be 579%. However, the higher strain rates and coarser grains led to a loss of superplasticity, with m ≈ 0.2.

Foliation development and progressive strain-rate partitioning in the crystallizing carapace of a tonalite pluton: microstructural evidence and numerical modeling

The San José pluton in Baja California, México, comprises at least two well-defined, texturally distinct units. The northern unit was intruded by the central unit after the former had extensively crystallized at its margins. During intrusion of the central unit, the margin of the northern unit underwent brittle and crystal–plastic deformation, at least part of which occurred in the presence of residual melt. We infer that biotite grains in this rock readily deformed by slip and frictional sliding along (001) planes, which caused strain-rate and differential-stress gradients across their grain boundaries into the surrounding plagioclase framework causing it to fracture. These microfractures grew and coalesced, and became sites of localized ductile flow. Continued development of these microshear zones led to coalescence of biotite grains, mainly by mechanical entrainment, and ultimately to a pervasive mylonitic foliation. Thus, in a single deformation, these rocks passed through a brittle–ductile transition. The development of an anastomosing network of ductile microshear zones allowed the progressive partitioning of strain rates, probably over several orders of magnitude, between the microshear zones and intervening polymineralic aggregates. Numerical experiments were conducted to evaluate the process of biotite-assisted fracturing of the stress-supporting framework, and the progressive evolution of differential stress and strain rate. The results are consistent with experimental evidence that biotite is extremely weak in shear, and that phyllosilicate-bearing rocks may accommodate strain rates several orders of magnitude higher than the bulk strain rate. This study also supports previous suggestions that strain rates associated with the growth of crustal magma chambers may be several, to many, orders of magnitude greater than those normally associated with regional tectonic deformation.

Stress measurements of deforming olivine at high pressure

Rheological properties of mantle minerals are critical for understanding the dynamics of the Earth’s deep interior. Due to limitations in experimental technique, previous quantitative studies of the rheological properties of mantle minerals are limited to either low pressure or low temperature. The present understanding of mantle flow is mostly inferred from the extrapolation of relatively low-pressure data to mantle high-pressure conditions. However, the effect of pressure (represented by activation volume) on the rheological properties of olivine is still controversial. Therefore, deformation experiments, carried out at mantle pressures, are necessary to understand and model mantle flow. Here we report an experimental study of plastic deformation of San Carlos olivine (Mg, Fe) 2SiO 4 under upper mantle conditions. Macroscopic differential stress and strain rates have been measured in situ in a large-volume high-pressure apparatus using newly developed techniques. The differential stress at high temperature and high pressure that we measured is significantly lower than that estimated by many currently accepted olivine flow laws. We document the first in situ experimental differential stress results in a multi-anvil press. Our results give direct evidence for a relatively small activation volume (less than 10 −5 m 3 mol −1). This shows that the effect of pressure on dislocation creep is small.

Superplastic behaviour of annealed AA 8090 Al-Li alloy

High temperature flow behaviour and microstructural evolution were investigated in an annealed AA 8090 Al - Li alloy over the temperature range 623 - 803 K and strain rate range ~ 6 × 106 - 3 × 102 s-1. Stress - strain rate data, obtained using a differential strain rate test technique and plotted in log - log scale, exhibited three regions I, II, and III, with increasing strain rate. In these regions, the values of strain rate sensitivity index m and the activation energy for deformation were determined to be 0.17, 0.43, and 0.17; and 758.8, 93.3, and 184.3 kJ mol-1, respectively. The stress - strain curves obtained from constant strain rate tests exhibited flow hardening at lower strain rates and higher temperatures whereas flow softening occurred at higher strain rates and lower temperatures. The microstructural evolution revealed the dominance of grain growth under the former conditions and dynamic recrystallisation under the latter conditions. Ductility and m were found to increase with temperature, with the maximum values of 402% and 0.55, respectively, at a temperature 803 K and strain rate 2 × 10-4 s-1.

Evaluation of activation parameters by Reed-Hill model

Differential strain rate tests have been carried out at different temperatures and at various stages along the stress-strain curve at a given temperature for a series of Ni—Co alloys of varying stacking fault energy (SFE). The thermal stress component has been estimated and apparent activation enthalpies have been determined. The likely reasons for poor applicability of the Reed-Hill approach to modelling flow stress and activation parameters for a low SFE alloy, and its better applicability to the temperature range where thermal obstacles conform to a linear force-displacement relationship, are discussed. A mixed analysis including both the Reed-Hill approach and a conventional method is suggested for the determination of activation parameters using limited experimentation.

The rheological properties of rocks in a compressional ductile shear zone, pyllite-quartzite series, Péloponnèse

The magnitudes of differential stress, strain rate and viscosity during the formation of an extruding crustalscale shear zone (Phyllite-Quartzite Series, PQS) were estimated providing new insights on the mechanical behavior of the middle continental crust of the External Hellenides during compression. The differential flow stress during ductile deformation of PQS, in the Taygetos and Chelmos tectonic windows, has been analyzed using grain-size piezometer. Quartz tectonites from the Taygetos and Chelmos areas have mean grain sizes of 42 μπι and 51 μπι, respectively. Extrapolation of quartzite flow-laws indicates that tectonic extrusion of the PQS occurred at strain rates slightly faster than 10"13s '. These estimates suggest that the extruding zone had a relatively low-viscosity of the order of 1019 to 1020 Pas. Finally, the combination of the obtained strain rate values with published quantitative analyses for the deformation path in the PQS implies that during the initial stage of the tectonic extrusion process the displacement rates parallel to the Taygetos-Parnon and Chelmos Thrusts, were ~6mm/year and 3mm/year, respectively.

The Influence of Strain Rate and Temperature on the Deformation Behaviour of 63Sn/37Pb and 60Sn/40Pb Solder Alloys

The influence of strain rate and temperature on plastic deformation behaviour of 63Sn/37Pb and 60Sn/40Pb solder alloys is investigated by means of a computer controlled servo-hydraulic machine over a temperature range of -40 to 80°C at constant strain rates of 10 -3 , 10 -2 and 10 -1 s -1 The fracture characteristics of deformed specimens are analyzed using scanning electron microscopy and correlated with macroscopic behaviour. The results indicate that the flow stress of both alloys is largely dependent on strain rate and temperature. The 63Sn/37Pb alloy, however, is stronger than 60Sn/40Pb over the range of 25 to 300°C. The change in flow behaviour is related to differential strain rates and temperature sensitivities. Over the strain rate and temperature range studied, 60Sn/40Pb exhibits higher strain rate and temperature sensitivities than 63Sn/37Pb. 60Sn/40Pb rupture resistance is found superior to 63Sn/37Pb in light of fracture observations revealing an absence of damage as well as an absence of flow instability. 63Sn/37Pb fracture is catastrophic at a strain rate of 10 -3 s -1 and is characterized by shear. With decreasing test temperature, more edge cracks appear due to enhanced brittleness. The use of a deformation constitutive equation in combination with the parameter values obtained through these tests allows for an accurate description of the deformation behaviour of both tin-lead alloys over the range of conditions used in this study.

Deformation, high‐pressure metamorphism and exhumation of ultramafic rocks in a deep subduction/collision setting (Cabo Ortegal, NW Spain)

New petrological and microstructural data from various metaperidotite ‘boudins’ within large ductile shear zones in the Cabo Ortegal allochthonous complex in NW Spain have important implications for the tectonic models of the area. The peridotites (mylonitic garnet harzburgite, Ti‐clinohumite and magnesite–olivine orthopyroxenite) contain mineral assemblages that equilibrated at high‐ to ultra‐high‐pressure metamorphic conditions as well as microstructures of tectonic origin formed at temperatures well above 800 °C. Olivine and orthopyroxene fabrics resulted from flow at high temperature (>1000 °C) and solid‐state non‐coaxial plastic flow at intermediate temperature (800–900 °C). Flow caused dynamic recrystallization and formation of moderate to strong lattice preferred orientations under low to moderate differential stresses and strain rates characteristic of upper mantle and deep crustal deformation. The microstructures and textural relationships suggest that the mylonitic garnet harzburgite represents mantle fragments with lithospheric and asthenospheric imprints, whereas the olivine orthopyroxenite resulted from serpentinite burial to depths where it acquired a characteristic high/ultra‐high‐pressure metamorphic signature. Both types of ultramafites converged to a common site in a subduction zone that was later incorporated during continental collision to the NW Iberian Massif as exotic, allochthonous complexes that record structural and metamorphic evidence of the earliest phases of the Hercynian orogeny.

Effect of strain rate in the distribution of monogenetic and polygenetic volcanism in the Transmexican volcanic belt

Research Article| July 01, 1998 Effect of strain rate in the distribution of monogenetic and polygenetic volcanism in the Transmexican volcanic belt Susana A. Alaniz-Alvarez; Susana A. Alaniz-Alvarez 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Search for other works by this author on: GSW Google Scholar Ángel Francisco Nieto-Samaniego; Ángel Francisco Nieto-Samaniego 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Search for other works by this author on: GSW Google Scholar Luca Ferrari Luca Ferrari 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Search for other works by this author on: GSW Google Scholar Author and Article Information Susana A. Alaniz-Alvarez 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Ángel Francisco Nieto-Samaniego 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Luca Ferrari 1Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México, Campus Juriquilla Apartado Postal 1-742, Querétaro, Querétaro 76001, México Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (7): 591–594. https://doi.org/10.1130/0091-7613(1998)026<0591:EOSRIT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Susana A. Alaniz-Alvarez, Ángel Francisco Nieto-Samaniego, Luca Ferrari; Effect of strain rate in the distribution of monogenetic and polygenetic volcanism in the Transmexican volcanic belt. Geology 1998;; 26 (7): 591–594. doi: https://doi.org/10.1130/0091-7613(1998)026<0591:EOSRIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In the Transmexican volcanic belt, polygenetic and monogenetic volcanism has taken place concurrently with extensional deformation since the late Miocene. At a regional scale, the deformation is manifested by two groups of faults. The dominant group consists of normal faults nearly parallel to the arc. In the other group are north-northwest–trending normal faults that cross the arc and, in places, form the boundaries of crustal blocks. The larger stratovolcanoes of the Transmexican volcanic belt are aligned in north-south volcanic chains along some of these faults, whereas monogenetic volcanoes are usually located along arc-parallel normal fault systems. Because the arc-parallel faults are 15° oblique to the subduction plate boundary, and assuming stretching perpendicular to the trench, the extensional deformation field facilitates activation of both arc-parallel and arc-transverse structures, the former having a higher displacement rate than the latter. We observe that in the Transmexican volcanic belt polygenetic volcanoes develop along faults having small strain rate and monogenetic volcanoes are emplaced along faults having higher strain rate. The agreement with the theoretical model in which monogenetic or polygenetic volcanism depends on the magmatic input rate and the regional stress is true only assuming a linear relation between regional differential stress and local strain rate, as in a continuous and homogeneous medium. We propose that the local strain rate rather than the regional stress field controls the coexistence of both types of volcanism in the Transmexican volcanic belt. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Experimental stress remagnetization of magnetite

Pseudo-single-domain (PSD) and multidomain (MD) magnetite grains remagnetize in weak magnetic field (30 μT) during experimental triaxial deformation. The magnetite is supported in a calcite-cement matrix. Minor remagnetization occurs with hydrostatic stress of 100 MPa. Significant remagnetization requires hydrostatic pressure of 150 MPa with differential stress of ≥5 MPa superposed on the sample. Intergranular differential stresses must be much higher due to amplification at grain asperities. Stress remagnetization does not need chemical or thermal energy. New components of magnetic remanence are added parallel to the remagnetizing field. However, this only happens in grains or parts of grains with coercivities of remanence < 15 and > 60 mT. Grains with coercivities of 20–55 mT remember the primary magnetization and are not stress magnetized. These coercivity limits do not depend on the differential stress or strain rate of the experiment. The spatial distribution of vector components of remanence was isolated by AF demagnetization. After deforming a magnetized sample, the components of remanence spread along a partial great circle between the initial remanence and the direction of the remagnetizing field. The directions of the original magnetization and the remagnetizing field are the only factors controlling the course of the remagnetization path. Triaxial deformation shortened these samples by < 17%. Thus, grain rotation fails to explain the changes in directions of magnetism. The remagnetization is attributed to the low field during stress deflection of domain walls that were possibly locked in place by deformation features. If the experimental results are transferable to nature, it is possible that a pulse of excess crustal stress > 25 MPa could partially remagnetize low-dislocation-density magnetite. The experiments show that the directions of the remagnetizing field and the primary magnetization are the only variables that affect the demagnetization vector path. We do not need to know the strain history (coaxial or noncoaxial), finite strains or principal strain directions to detect the paleofield directions, unlike paleomagnetic vectors affected by large strains. Permanent changes in magnetic structure occur as a result of experimental deformation. Regardless of the differential stress, the proportion of grains with remanence coercivities < 25 mT decreases, and the proportion above 25 mT increases. Even hydrostatic stress can cause this. Thus, grain sizes should only be inferred from hysteresis parameters if their stress histories are similar. This is of some importance in environmental magnetism.

Deformation behavior of an Al-3.37 Wt Pct Li alloy

Al-3.37 wt pct Li alloy was deformed by differential strain rate and constant initial strain rate test techniques to investigate deformation and failure behavior over the strain rate range of 10-5 to 10-2 s-1 and the temperature range of 22 °C to 580 °C. Flow stress first increases then decreases with an increase in test temperature, whereas ductility shows a sigmoidal relationship with the test temperature. The maximum ductility of about 80 pct is obtained at intermediate strain rate and 550 °C. Failure is noted to occur by cavity interlinkage and crack formation. Strain rate sensitivity (m) and activation energy (Q) for deformation are determined to be 0.04 to 0.13 and 96.2 to 157.4 kJ/mol, respectively. Toward lower test temperatures, both them andQ are found to have lower values. Deformation at high temperature is suggested to be controlled by dislocation climb. However, under non-steady-state conditions due to cavitation,m andQ both vary with strain.

Characterization of a commercial superplastic stainless steel, SuperDux64

The superplastic properties of SuperDux64 have been characterized at temperatures ranging from 1173 to 1323 K and strain rate ranging from 10 −4 to 10 −1 s −1. The strain rate sensitivity value for SuperDux64 is about 0.5, suggesting that grain boundary sliding is the dominant deformation mechanism. The apparent activation energy in the superplastic region is approximately 450 kJ mol −1. Strain accommodation at grain triple junctions is accomplished by the preferential dynamic recrystallization in the soft phase (i.e., ferrite). The cavitation behavior of SuperDux64 was also studied. Cavitation was found to occur in distinct bands that corresponded to regions containing high concentrations of γ phase in the δ matrix. The roles of heterophase and homophase boundaries, and their effects on boundary sliding are discussed. Strain incompatibility at grain triple junctions (resulting from the differential strain rates between a hetero-boundary and homo-boundary) is also addressed.