Degree Of Strain Localization Research Articles

Modulation of plasticity by crystalline precipitates in CuZr metallic glasses

Amorphous/crystalline composites consist of crystalline phases embedded in an amorphous matrix that offer the possibility for synthesizing materials with tailored properties. Here, molecular dynamics simulations were performed to study the plastic behavior of CuZr metallic glasses (MGs) with CuZr B2 spherical precipitates under tensile tests. Shear transformation zones were observed to nucleate at the MG/B2 interface, a phenomenon that was more remarkable at larger precipitate sizes. Furthermore, large precipitates acted as barriers for shear band (SB) propagation. To overcome such barriers, and owing to the lack of phase transformation and plastic activity in the CuZr B2 structures, SBs displaced the precipitates, leading to increased stress in the sample. In addition, the degree of strain localization was higher when the precipitates were closer to each other. Thus, the plasticity in our MG composites was modulated by the size and distribution of the precipitates.

Strain partitioning in dual-phase eutectic high-entropy alloy: Dependence on phase boundary morphology

Strain partitioning in dual-phase eutectic high-entropy alloy, AlCoCrFeNi2.1, is investigated under uniaxial tension with in situ high-resolution digital image correlation (DIC) in a scanning electron microscope (SEM). Nanoscale speckles are fabricated on the sample surface. Three regions with different phase morphologies at different applied strains are characterized by SEM for DIC analysis. Strain localization tends to form at softer face-centered cubic (FCC) rather than body-centered cubic phase domains, and the degree of strain localization in a lamellar structure is much lower than in a bimodal structure. Transmission electron microscopy is conducted to characterize the phase interaction at the nanoscale. A straight phase boundary in a lamellar structure allows more geometrically necessary dislocations to pile up at the phase boundary and form a wide interface affected zone (IAZ) in the soft FCC domain. The IAZ strengthens the soft FCC and better accommodates the deformation of the two phases, resulting in a relatively uniform strain partitioning.

Insights into thermomechanical fatigue behavior of nitrogen alloyed 316LN stainless steel under various temperature cycling ranges

Thermomechanical fatigue (TMF) failure has become one of the most important life-limiting factors of components exposure to the high temperature in the fourth-generation sodium-cooled fast reactor (SFR) nuclear power plant. Therefore, TMF tests at different temperature cycling ranges are performed to study the cyclic deformation behavior and damage mechanism of a nitrogen alloyed 316LN stainless steel. Moreover, the isothermal fatigue (IF) tests at the maximum temperature of TMF cycling are conducted for comparison. The cyclic hardening and softening response are analyzed, taking into account the phenomenon of dynamic strain aging which occurs at the temperature range of 350 °C–650 °C. Furthermore, the critical strain corresponding to the occurrence of serrated stress flow in engineering stress-strain curves keeps decreasing from 28.94% at 350 °C to 0.09% at 650 °C. The distribution of plastic deformation and the degree of strain localization are evaluated by the characterization results of kernel average misorientation map, high/low angle grain boundary map and dislocation configuration. The dominant damage mechanism and its corresponding cracking behavior in both IF and TMF tests are analyzed based on the observation of fracture surface morphology. In addition, the sequence order of fatigue life is determined as IF < IP-TMF < OP-TMF. Moreover, the maximum difference of fatigue life between IF test and TMF test occurs at the temperature range of 400 °C–600 °C, in which the IP and OP life is about 2.91 and 3.65 times larger than the IF life. The results in this work provide reliable data support and theoretical guidance for the fatigue design of high-temperature components in SFR.

The effect of shear strain and shear localization on fault healing

SUMMARY The seismic cycle of repeated earthquake failure requires that faults regain frictional strength during the interseismic phase, when the fault is locked or undergoing quasi-static creep. Fault healing plays a central role in determining earthquake stress drop, recurrence interval, elastic radiation frequency and other source parameters. In particular, the longer a fault remains quasi-stationary, the stronger it becomes and the larger the potential stress drop can be for the next event. Here, we address the role of shear strain and strain localization on fault healing and healing rate. We performed slide-hold-slide friction experiments on quartz gouge in the double-direct shear configuration for shear strain up to 25 and hold times from 10 to 1000 s. The results show that both healing and healing rate increase nonlinearly with increasing shear strain. Frictional healing scales with volumetric strain within the laboratory fault zone. Using the volumetric strain upon reshear as a proxy for strain localization, we demonstrate that the capacity of a fault to heal is directly proportional to shear bandwidth and degree of strain localization. The more the deformation is localized, the higher are the healing and healing rate, and thus, the fault strength. Our data provide a framework for understanding variations in fault strength over the seismic cycle and the role of brecciation and strain localization on spatiotemporal variations in fault strength.

40Ar/39Ar dates controlled by white mica deformation and strain localization: Insights from comparing in situ laser ablation and single‐grain fusion techniques

AbstractIn situ laser ablation and single‐grain fusion 40Ar/39Ar geochronological techniques were directly compared using white mica from nine metasedimentary rocks from the Vaimok Lens of the Seve Nappe Complex (SNC) in the Scandinavian Caledonides. Seven of the rocks are from the eclogite‐bearing Grapesvare nappe within the lens that is defined by D2 structures (S2 and F2), which were formed during exhumation following late Cambrian/Early Ordovician ultra‐high pressure metamorphism. Two other rocks were obtained from ‘Scandian’ shear zones that delimit the nappes within the lens. The shear zones were active during terminal collision of Baltica and Laurentia in the Silurian to Devonian. The rocks exhibit variable deformation intensities and degrees of strain localization, expressed in particular by white mica. The in situ laser ablation and single‐grain fusion 40Ar/39Ar dates both span from the late Cambrian to Middle Devonian. Results of both techniques generally show decreasing dates with increasing bulk deformation intensity and successive structural generations (i.e., D2 then Scandian structures). Furthermore, several discrepancies are evident when comparing the results of the two techniques for the same rocks, indicating the 40Ar/39Ar dates are not solely governed by bulk deformation intensities and structural generations. Instead, the discrepancies demonstrate the additional influence of white mica strain localization, which is illuminated by the different analytical volumes of the techniques. Thus, the 40Ar/39Ar datasets are altogether deciphered as a function of bulk deformation intensity and degree of strain localization that affected the overall white mica volume. The former controls the gross 40Ar loss from the overall volume and the latter dictates the variability of 40Ar loss within the volume. Exploiting the interplay of these two phenomena for the Vaimok Lens rocks with in situ laser ablation allows for the broad span of 40Ar/39Ar dates to be contextualized into a sequence of tectonic events: (1) cooling at 474 ± 3 Ma, (2) pre‐collision deformation at 447 ± 2 Ma and (3) activation of crustal‐scale shear zones in the SNC related to continental collision at 431 ± 3 Ma and 411 ± 3 Ma.

Extremely Large Off-Fault Deformation during the 2021 Mw 7.4 Maduo, Tibetan Plateau, Earthquake

AbstractThe 21 May 2021 Mw 7.4 Maduo earthquake ruptured a 170 km long immature strike-slip fault within the eastern Tibetan plateau. Based on pixel correlation of pre- and postevent Sentinel-2 optical satellite images (band 8; pixel = 10 m), we determine the coseismic horizontal displacement and deformation-zone width at the surface. These results, compared with the on-fault slip from geological measurements, document that &amp;lt;20% of the fault displacement is localized on the fault plane, whereas as high as &amp;gt;80% of the fault displacement occurred as off-fault deformation (OFD), over a mean deformation-zone width of 835 m (ranging from 60 to 1670 m). The OFD% of the Maduo earthquake is significantly larger than the OFD% (28%–64%) of all other (eight in total) previously documented earthquakes occurring on immature strike-slip faults, amongst which five earthquake faults have a structural maturity (cumulative displacement) even lower than the Maduo earthquake fault. These observations may be explained by that (1) the fault maturity is not the only factor controlling the behavior of OFD or the degree of strain localization during an earthquake, or that (2) the calculated OFD includes some elastic deformation due to fault slip reduction in the shallow depth. Our results have an implication that the seismic hazard assessment of immature strike-slip faults is more challenging than previously thought.

The effect of loading methods on the microstructural evolution and degree of strain localization in Cu50Zr50 metallic glass composite nanowires: A molecular dynamics simulation study

In this work, the Cu50Zr50 metallic glass composite nanowire (MGCNW) is subjected to uniaxial tensile, bending, and cyclic deformation. The effect of loading methods on the microstructural evolution and degree of strain localization is investigated. The simulations are performed using molecular dynamics (MD) code. The embedded atom method (EAM) is used to model the interactions between Cu–Zr atoms. The model for the study is created by embedding spherical copper nanocrystallites (diameter = 50 Å) in the Cu50Zr50 metallic glass matrix. Uniaxial tensile simulations have been carried out at strain rates in the range of 106 s−1 to 109 s−1. Three-point bend tests are carried out at different loading rates (1 m/s to 10 m/s). Finally, a strain-controlled cyclic deformation test is carried out at a strain amplitude of 0.02. All the tests are carried out at a temperature of 300 K. Atomic clusters of high shear strain are observed at the yield that later develops into bands with increasing strain. The degree of strain localization is observed to be higher in the bend tests as compared to the tensile and cyclic deformations. Also, it increases with decreasing strain rate. Voronoi polyhedral analysis reveals the breakdown of (0, 0, 12, 0) icosahedral clusters during plastic deformation, which is prominent during tensile deformation.

Shear banding instability in multicomponent metallic glasses: Interplay of composition and short-range order

The shear-banding instability in quasistatically driven bulk metallic glasses emerges from collective dynamics, mediated by shear transformation zones and associated nonlocal elastic interactions. It is also phenomenologically known that sharp structural features of shear bands are typically correlated to the sharpness of the plastic yielding transition, being predominant in commonly studied alloys composed of multiple different elements, that have very different atomic radii. However, in the opposite limit where elements' radii are relatively similar, plastic yielding of bulk metallic glasses is highly dependent on compositional and ordering features. In particular, a known mechanism at play involves the formation of short-range order dominated by icosahedra-based clusters. Here, we report on atomistic simulations of multicomponent metallic glasses with different chemical compositions showing that the degree of strain localization is largely controlled by the interplay between composition-driven icosahedra-ordering and collectively-driven shear transformation zones. By altering compositions, strain localization ranges from diffuse homogenized patterns to singular crack-like features. We quantify the dynamical yielding transition by measuring the atoms' susceptibility to plastic rearrangements, strongly correlated to the local atomic structure. We find that the abundance of short-range ordering of icosahedra within rearranging zones increases glassy materials' capacity to delocalize strain. This could be understood on the basis of structural heterogeneities that are enhanced by the presence of local order. The kind of plastic yielding can be often qualitatively inferred by the commonly used compositional descriptor that characterizes element associations, the misfit parameter ${\ensuremath{\delta}}_{a}$, and also by uncommon ones, such as shear-band width and shear-band dynamics' correlation parameters.

Links Between Faulting, Topography, and Sediment Production During Continental Rifting: Insights From Coupled Surface Process, Thermomechanical Modeling

AbstractContinental rifts form by extension, and their subsequent evolution depends on the tectonic and climatic boundary conditions. We investigate how faulting, topography, and the evolution of the sediment flux during rifting are affected by these boundary conditions, in particular whether it is possible to correlate tectonic activity, topography, and sediment flux on long timescales (40 Myr). We use a thermomechanical model coupled with a landscape evolution model and present a series of 14 models, testing the sensitivity of the models to crustal strength, extension rate, and fluvial erodibility. The degree of strain localization drives the structural evolution of the modeled rifts: slow extension, high crustal strength, and efficient surface processes promote a high degree of strain localization, resulting in fewer active faults with larger offset. Overall, the magnitude of sediment production correlates with the degree of strain localization. In case of unchanged erosional power and similar amount of extension, systems with slower extension produce more sediment owing to a stronger positive feedback between erosion and fault offset. We observe a characteristic sequence of events, reflecting the morpho‐tectonic evolution of rifts: the highest rock uplift rates are observed before the maximum elevation, and the highest sediment flux postdates the peak in elevation. Our results indicate that for natural systems, the evolution of the sediment flux is a good proxy for the evolution of topography, and that a time lag of 2–5 Myr between the peaks in main tectonic activity and sediment flux can exist.

The evolving energy budget of experimental faults within continental crust: Insights from in situ dynamic X-ray microtomography

We investigate the evolving distribution of strain produced by a sliding fault within intact crystalline rock, and the energetics of deformation that occur both on- and off-fault. We slid precut faults of differing roughness oriented at 45° to σ1 while acquiring in situ X-ray microtomograms. Digital volume correlation of tomograms provide estimates of the 3D displacement and strain fields. This characterization of the strain tensor field reveal that the differing fault roughness produced distinct slip behavior, degree of strain localization and accumulation, and energy budget partitioning. The rougher fault slipped more episodically, hosted a wider and more asymmetric damage zone, and accommodated less normal and shear strain. This fault consumed more energy in off-fault deformation (Wint) per volume and more energy in frictional slip (Wfric) as portions of the total energy input to the system (Wext) than the smoother fault. In both experiments, Wfric consumed the largest portion of the energy budget (50–100%), while Wint consumed smaller percentages (5–20%). Tracking the temporal variability of energy partitioning revealed how evolving fault architecture determined the energetic dominance of particular deformational processes, and so highlighted the importance of tracking energy partitioning through time.

Linking macroscopic failure with micromechanical processes in layered rocks: How layer orientation and roughness control macroscopic behavior

To constrain the impact of preexisting mechanical weaknesses on strain localization culminating in macroscopic shear failure, we simulate triaxial compression of layered sedimentary rock using three-dimensional discrete element method simulations. We develop a novel particle packing technique that builds layered rocks with preexisting weaknesses of varying orientations, roughness, and surface area available for slip. We quantify how the geomechanical behavior, characterized by internal friction coefficient, μ0, and failure strength, σF, vary as a function of layer orientation, θ, interface roughness, and total interface area. Failure of the simulated sedimentary rocks mirrors key observations from laboratory experiments on layered sedimentary rock, including minima σF and μ0 for layers oriented at 30° with respect to the maximum compressive stress, σ1, and maxima σF and μ0 for layers oriented near 0° and 90° to σ1. The largest changes in σF (66%) and μ0 (20%) occur in models with the smoothest interfaces and largest interface area. Within the parameter space tested, layer orientation exerts the most significant impact on σF and μ0. These simulations allow directly linking micromechanical processes observed within the models to macroscopic failure behavior. The spatial distributions of nucleating microfractures, and the rate and degree of strain localization onto preexisting weaknesses, rather than the host rock, are systematically linked to the distribution of failure strengths. Preexisting weakness orientation more strongly controls the degree and rate of strain localization than the imposed confining stress within the explored parameter space. Using the upper and lower limits of μ0 and σF obtained from the models, estimates of the Coulomb shear stress required for failure of intact rock within the upper seismogenic zone (7 km) indicates that a rotation of 30° of σ1 relative to the weakness orientation may reduce the shear stress required for failure by up to 100 MPa.

Strengthening and toughening of layered Ti-Al metal composites by controlling local strain contribution

Layered Ti-Al metal composites (LMCs) with different thickness ratios of the Ti and Al layers were fabricated by hot-rolling and annealing. To study the effect of layer thickness on the mechanical properties of LMCs from the viewpoint of local strain distribution, the strain evolution of LMCs was investigated via in-situ tensile testing. It is found that the mechanical properties of LMCs are correlated with the degree of strain localization. Suppressing strain localization during plastic deformation is crucial to achieve the goal of both strengthening and toughening in LMCs. Additionally, the layered structure can facilitate the redistribution of strain localization, and the transfer of strain localization can be effectively controlled by changing the thickness ratio of the Ti and Al layers.

Numerical Study of the Formation of Shear Bands in Soil under Interface Shearing

When a granular material such as soil interacts with a hard artificial structure, it commonly involves a considerable degree of material heterogeneity. The shear deformation largely localizes into a narrow band: the shear band. The mechanism of the shear band formation at the soil–structural interface is of significant interest to researchers and engineers, for it explains the process of soil failure under interface shearing as well as the physical essence of the soil behaviors associated with such failure – for example, stress peak, stress softening, and dilatancy. In this paper, we employ the discrete element method (DEM) to analyze the formation of the shear band in a series of 2D interface shear tests in which specimens are initialized with different void ratios. During the interface shearing process, we analyze the shear velocity field vx and its gradient field, both of which are extracted on the basis of kinematic quantities given by grains. In the dense specimen, imperfections – indicated by the discontinuities in the field of vx and ▪ – are observed appearing in the stress hardening regime. These imperfections progressively accumulate and converge with each other, threatening to form several potential failure bands. This continues until the stress peak, after which a major failure band appears to be dominant over others. The shear band is then shaped, and the stress softening occurs. In the loose specimen subjected to interface shearing, the domain of the strain localization is so unstable and varied that a steady shear band cannot be steadily formed. In both samples, stress variations are shown to be highly dependent on degree of strain localization.

Evaluation of stress corrosion cracking of irradiated 304L stainless steel in PWR environment using heavy ion irradiation

IASCC has been a major concern regarding the structural and functional integrity of core internals of PWR's, especially baffle-to-former bolts. Despite numerous studies over the past few decades, additional evaluation of the parameters influencing IASCC is still needed for an accurate understanding and modeling of this phenomenon. In this study, Fe irradiation at 450 °C was used to study the cracking susceptibility of 304 L austenitic stainless steel. After 10 MeV Fe irradiation to 5 dpa, irradiation-induced damage in the microstructure was characterized and quantified along with nano-hardness measurements. After 4% plastic strain in a PWR environment, quantitative information on the degree of strain localization, as determined by slip-line spacing, was obtained using SEM. Fe-irradiated material strained to 4% in a PWR environment exhibited crack initiation sites that were similar to those that occur in neutron- and proton-irradiated materials, which suggests that Fe irradiation may be a representative means for studying IASCC susceptibility. Fe-irradiated material subjected to 4% plastic strain in an inert argon environment did not exhibit any cracking, which suggests that localized deformation is not in itself sufficient for initiating cracking for the irradiation conditions used in this study.

Localized and distributed creep along the southern San Andreas Fault

AbstractWe investigate the spatial pattern of surface creep and off‐fault deformation along the southern segment of the San Andreas Fault using a combination of multiple interferometric synthetic aperture radar viewing geometries and survey‐mode GPS occupations of a dense array crossing the fault. Radar observations from Envisat during the period 2003–2010 were used to separate the pattern of horizontal and vertical motion, providing a high‐resolution image of uplift and shallow creep along the fault trace. The data reveal pervasive shallow creep along the southernmost 50 km of the fault. Creep is localized on a well‐defined fault trace only in the Mecca Hills and Durmid Hill areas, while elsewhere creep appears to be distributed over a 1–2 km wide zone surrounding the fault. The degree of strain localization is correlated with variations in the local fault strike. Using a two‐dimensional boundary element model, we show that stresses resulting from slip on a curved fault can promote or inhibit inelastic failure within the fault zone in a pattern matching the observations. The occurrence of shallow, localized interseismic fault creep within mature fault zones may thus be partly controlled by the local fault geometry and normal stress, with implications for models of fault zone evolution, shallow coseismic slip deficit, and geologic estimates of long‐term slip rates.

Initiation, geometry and mechanics of brittle faulting in exhuming metamorphic rocks: insights from the northern Cycladic islands (Aegean, Greece)

AbstractInitiation, geometry and mechanics of brittle faulting in exhuming metamorphic rocks are discussed on the basis of a synthesis of field observations and tectonic studies carried out over the last decade in the northern Cycladic islands. The investigated rocks have been exhumed in metamorphic domes partly thanks to extensional detachments that can be nicely observed in Andros, Tinos and Mykonos. The ductile to brittle transition of the rocks from the footwall of the detachments during Aegean post-orogenic extension was accompanied by the development of asymmetric sets of meso-scale low-angle normal faults (LANFs) depending on the distance to the detachments and the degree of strain localization, then by conjugate sets of high-angle normal faults. This suggests that rocks became progressively stiffer and isotropic and deformation more and more coaxial during exhumation and localization of regional shearing onto the more brittle detachments. Most low-angle normal faults result from the reactivation of precursory ductile or semi-brittle shear zones; like their precursors, they often initiate between or at the tips of boudins of metabasites or marbles embedded within weaker metapelites, emphasizing the role of boudinage as an efficient localizing factor. Some LANFs are however newly formed, which questions the underlying mechanics, and more generally rupture mechanisms in anisotropic rocks. The kinematics and the mechanics of the brittle detachments are also discussed in the light of recent field and modeling studies, with reference to the significance of paleostress reconstructions in anisotropic metamorphic rocks.

The causes of sinuous crustal-scale deformation patterns in hot orogens: Evidence from scaled analogue experiments and the southern Central Andes

The cause of upper-crustal segmentation into rhomb-shaped, shear zone-bound domains associated with contractional sedimentary basins in hot, wide orogens is not well understood. Here we use scaled multilayered analogue experiments to investigate the role of an orogen-parallel crustal-strength gradient on the formation of such structures. We show that the aspect ratio and size of domains, the sinuous character and abundance of transpressional shear zones vary with the integrated mechanical strength of crust. Upper-crustal deformation patterns and the degree of strain localization in the experiments are controlled by the ratio between the brittle and ductile strength in the model crust as well as gradients in tectonic and buoyancy forces. The experimental results match the first-order kinematic and structural characteristics of the southern Central Andes and provide insight on the dynamics of underlying deformation patterns in hot, wide orogens.

Effect of hydrogenation on the mechanical property of amorphous Ni90Al10 membranes

To investigate the mechanism of hydrogen embrittlement in amorphous membranes, changes in the stress–strain curves of an amorphous Ni90Al10 model membrane as a function of hydrogen concentration were examined using Molecular Dynamics (MD) simulations. In addition, the fractional change of short-range ordered (SRO) structures during uniaxial tensile deformation was scrutinized using the Voronoi tessellation method. By correlating these structural evolutions related to volume expansion with changes in the mechanical property, the hydrogen embrittlement phenomenon occurring in the amorphous membrane was discussed with respect to the abrupt increase in the degree of strain localization during deformation. The possibility, not only of hydrogen embrittlement, but also of hydrogen-induced ductility enhancement, was demonstrated by the decrease in the degree of strain localization. Finally, we proposed a fundamental mechanism that can explain these overall phenomena occurring in the amorphous membrane by the introduction of hydrogen.

Compression along the Easy-Glide Orientation of Ultrafine and Fine-Grained Mg-3Al-1Zn Alloy

The deformation behavior of textured ultrafine-grained (UFG) and fine-grained (FG) Mg-3Al-1Zn alloy compressed along the easy-glide orientation was studied. It was found that severe strain localization within very thin shear bands (SBs) caused the loss of ductility in UFG Mg-3Al-1Zn alloy. Increasing grain size increases the width of SBs, which decreases the degree of strain localization. The reason for the occurrence of severe strain localization in textured UFG Mg-3Al-1Zn alloy is proposed.

Heterogeneous shear zone evolution: The role of shear strain hardening/softening

Mathematical models are proposed to describe heterogeneous shear zones characterized by variation thickness with time. These models take into account several combinations of deformation type regime (simultaneous simple shear, pure shear, and volume change) and degree of strain localization. Increasing or decreasing shear zone thickness results, respectively, from strain hardening where deformation progressively diffuses into the host rock, and strain softening where deformation gradually localizes within a narrow zone. Shear zone models are made of a series of layers, each characterized by homogenous strain. A quantitative evaluation of displacement–thickness relationship and finite strain development may be obtained from each model. Temporal evolution depends on the following parameters: (i) rate of shear strain hardening/softening, (ii) initial shear strain increment imposed to the system, and (iii) thickness of homogenously deformed units within a layered shear zone. Based on data coming from natural shear zones, displacement rates may be obtained independently of shear zone thickness.