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To what extent mechanical anisotropy is required to explain the dynamics of the lithosphere is an important yet unresolved question. If anisotropy affects stress and deformation, and hence processes such as fault loading, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with linear anisotropic viscosity can lead to deviatoric stress heterogeneity, strain-rate enhancement, as well as non-coaxial principal stress and strain rate. We develop an open-source finite-element software based on FEniCS for more complicated scenarios in both 2-D and 3-D. Mechanics of shear zones with transversely isotropic and orthorhombic anisotropy subjected to misoriented shortening and simple shearing are explored. A simple regional example for potential non-coaxiality for the Leech River Schist above the Cascadia subduction zone is presented. Our findings and these tools may help to better understand, detect and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation through fault loading. [ABSTRACT FROM AUTHOR]

The advent of digital image and volume correlation has attracted wide use in fracture mechanics. The full‐field nature of digital image and volume correlation allows for the integration of computational fracture mechanics to analyse cracked samples quantitatively. This review provides a comprehensive overview of current methods used to extract fracture properties from full‐field displacement data. The term full‐field fracture mechanics is introduced to highlight the uniqueness of using inherently noisy experiential data to extract fracture properties. The review focuses on post‐processing‐based approaches rather than integrated approaches, as these have less limitations and are more commonly employed. There are four approaches that are discussed in extracting fracture properties from experimentally computed displacement data: field‐fitting, integral, crack‐opening and cohesive zone modelling approaches. This is further developed to discuss problems associated with using digital image and volume correlation to extract properties, including application examples. [ABSTRACT FROM AUTHOR]

The tectonic configuration of the Caribbean plate is defined by inward‐dipping double subduction at its boundaries with the North American and Cocos plates. This geometry resulted from a Paleogene plate reorganization, which involved the abandonment of an older subduction system, the Great Arc of the Caribbean (GAC), and conversion into a transform margin during Lesser Antilles (LA) arc formation. Previous models suggest that a collision between the GAC and the Bahamas platform along the North American passive margin caused this event. However, geological and geophysical constraints from the Greater Antilles do not show a large‐scale compressional episode that should correspond to such a collision. We propose an alternative model for the evolution of the region where lower mantle penetration of the Farallon slab promotes the onset of subduction at the LA. We integrate tectonic constraints with seismic tomography to analyze the timing and dynamics of the reorganization, showing that the onset of LA subduction corresponds to the timing of Farallon/Cocos slab penetration. With numerical subduction models, we explore whether slab penetration constitutes a dynamically feasible set of mechanisms to initiate subduction in the overriding plate. In our models, when the first slab (Farallon/Cocos) enters the lower mantle, compressive stresses increase at the eastern margin of the upper plate, and a second subduction zone (LA) is initiated. The resulting first‐order slab geometries, timings, and kinematics compare well with plate reconstructions. More generally, similar slab dynamics may provide a mechanism not only for the Caribbean reorganization but also for other tectonic episodes throughout the Americas. Plain Language Summary: The Caribbean tectonic plate is bounded by subduction to the east and west. However, it is unclear how this plate configuration was achieved. Previous models suggest that the North American continental margin entered an ancient Caribbean subduction zone between 66 and 34 Mya, converting the margin to strike‐slip and initiating subduction to the east at the Lesser Antilles. However, the deformation expected for this event is absent at the site of the supposed collision. Considering geological and geophysical constraints across the Caribbean, we instead suggest that mantle processes drove the reorganization. Combining tomographic images of the mantle with plate modeling, we reconstruct subduction below the Caribbean. Then, through numerical mantle convection modeling, we simulate the Caribbean subduction setting at the time of the reorganization. Our results show that when a subducting plate enters the lower, higher viscosity part of the mantle, it affects mantle flow, causing compression in the overriding plate and the potential initiation of a second subduction zone. The timing when the first slab enters the lower mantle and subduction initiates aligns well with our reconstructions and geological constraints in the Caribbean. We hypothesize that a similar process may explain other major deformation episodes throughout the Americas. Key Points: Tectonic constraints conflict with previously proposed collision and escape models for Paleogene Caribbean reorganizationSlab reconstructions and geodynamic models suggest Farallon slab anchoring induced tectonic reorganizationIn this model, lower mantle slab penetration triggers mantle flow, lithospheric compression, and subduction initiation [ABSTRACT FROM AUTHOR]

Precise and accurate digital image correlation computed displacement data requires sufficient noise suppression and spatial resolution, which improve and diminish, respectively, with increased subset size. Furthermore, spatially varying speckle pattern quality and displacement field complexity ideally necessitate a location‐specific optimal subset size to obtain a favourable compromise between noise suppression and spatial resolution. Although dynamic subset selection (DSS) methods have been proposed based on speckle pattern quality metrics (SPQMs), they do not ensure such a favourable compromise. This work investigates using an artificial neural network (ANN) for DSS. An ANN is trained to predict the displacement error standard deviation of a subset from multiple SPQMs and the standard deviation of image noise, such that the smallest subset offering sufficient noise suppression, dictated by a displacement error standard deviation threshold, is appointed. Validation, both within and outside the domain of the training images, shows that the smallest subset providing sufficient noise suppression offers a favourable compromise for up to moderate displacement gradients. Additionally, the proposed method is shown to perform with greater consistency and reliability relative to existing SPQM‐based DSS methods. The novel proposition lies in utilising an ANN as an error prediction tool, based on multiple SPQMs, and hence, is an attractive alternative for DSS. [ABSTRACT FROM AUTHOR]

The effect of mantle plumes is secondary to that of subducting slabs for modern plate tectonics when considering plate driving forces. However, the impact of plumes on tectonics and planetary surface evolution may nonetheless have been significant. We use numerical mantle convection models in a 3‐D spherical chunk geometry with damage rheology to study some of the dynamics of plume‐slab interactions. Substantiating our earlier 2‐D results, we observe a range of interaction scenarios, and that the plume‐driven subduction terminations we had identified earlier persist in more realistic convective flow. We analyze the dynamics of plume affected subduction, including in terms of their geometry, frequency, and the overall effect of plumes on surface dynamics as a function of the fraction of internal to bottom heating. Some versions of such plume‐slab interplay may be relevant for geologic events, for example, for the inferred ∼183 Ma Karoo large igneous province formation and associated slab disruption. More recent examples may include the impingement of the Afar plume underneath Africa leading to disruption of the Hellenic slab, and the current complex structure imaged for the subduction of the Nazca plate under South America. Our results imply that plumes may play a significant role not just in kick‐starting plate tectonics, but also in major modifications of slab‐driven plate motions, including for the present‐day mantle. Plain Language Summary: Subduction of cold, strong lithospheric slabs is the main plate driving force within mantle convection. However, hot upwellings, mantle plumes, may have a greater role in modulating plate motions and slab trajectories than previously thought. We use 3‐D numerical convection models that account for the weakening of rocks due to the accumulation of deformation to understand the effect that mantle plumes can have on subduction zones. We show that plumes can terminate subduction in a range of circumstances. We also test the effect of the amount of internal heating compared to heat from the core which is the major convective control on the importance of plumes. We discuss cases where these plume‐slab terminations may have occurred on Earth, in the geological past, and for the present day through plate reconstructions and consideration of seismic tomography. Key Points: Mantle plumes can terminate subduction in 3‐D, damage rheology convectionPlumes can modulate subducting slabs and plate tectonic regimesPlume‐slab interactions are plausible contributions to the Karoo‐Gondwana event [ABSTRACT FROM AUTHOR]

This study used laser powder bed fusion to produce highly dense Ti-4.7Mo-4.5Fe through in-situ alloying. The relative density range of the printed samples was from 96. 3 to 99.5 %. Partially unmelted Mo and lack of fusion pores were observed on some samples produced using a laser power of 80 W with a high scanning speed. Better diffusion of Mo in the Ti matrix and pores were observed at a higher laser power of 164-200 W. The microhardness of the printed samples was higher than that of other β-Ti with Mo as β stabiliser and was comparable to the microhardness of the Ti-4.7Mo-4.5Fe alloy produced using conventional methods. The phase identification of the printed samples indicated that samples of Ti-4.7Mo-4.5Fe containing α+β phases were produced, with β being the dominant phase. Microstructural analyses showed that the lamellar α structure was embedded within the equiaxed columnar β grains.

Predicting and preventing stress induced support failure during laser powder bed fusion (LPBF) processing requires knowledge of the fracture toughness of the material in its as-built condition. When performing laboratory measurement of fracture toughness, large residual stresses that are present in the part due to the LPBF process can significantly affect the measurement and must be taken into consideration. In this article, fracture toughness in the as-built condition was measured to be 26 MPa.m1/2 and the residual stress distribution in the crack plane was determined with simulation. Finally, the effective fracture toughness of the material was calculated, using the principle of superposition, to be ~ 47 MPa.m1/2.

Biomedical implants require stiffnesses matching those of the surrounding bone to avoid stress shielding. Triply-periodic-minimal-surface (TPMS) structures have shown promising characteristics in preventing stress shielding; however, they are limited in allowing for anisotropic stiffness properties that are typically inherent in bone. This paper presents an approach to simplifying a TPMS structure so that common geometries can be used to approximate it. The wall thickness is varied until the desired functional and directional stiffnesses are determined through finite element modelling. Validation of the finite element models is provided through the compression testing of laser powder bed fusion (LPBF) produced specimens. The displacement response to compression testing is presented along with the final structure, which closely matches the stiffness of bone. This approach has the potential to increase implant longevity and improve the lives of implant recipients.

Earth's style of planetary heat transport is characterized by plate tectonics which requires rock strength to be reduced plastically in order to break an otherwise stagnant lithospheric lid, and for rocks to have a memory of past deformation to account for strain localization and the hysteresis implied by geological sutures. Here, we explore ∼107 Rayleigh number, visco‐plastic, 3‐D global mantle convection with damage. We show that oceanic lithosphere‐only models generate strong toroidal‐poloidal power ratios and features such as a mix of long‐wavelength tectonic motions and smaller‐scale, back‐arc tectonics driven by downwellings. Undulating divergent plate boundaries can evolve to form overlapping spreading centers and microplates, promoted and perhaps stabilized by the effects of damage with long memory. The inclusion of continental rafts enhances heat flux variability and toroidal flow, including net rotation of the lithosphere, to a level seen in plate reconstructions for the Cenozoic. Both the super‐continental cycle and local rheological descriptions affect heat transport and tectonic deformation across a range of scales, and we showcase both general tectonic dynamics and regionally applied continental breakup scenarios. Our work points toward avenues for renewed analysis of the typical, mean behavior as well as the evolution of fluctuations in geological and model plate boundary evolution scenarios. Key Points: Results from global, ∼107 Rayleigh number, visco‐plastic mantle convection models with damageStrong toroidal‐poloidal coupling and mix of small and large‐scale plate tectonic features generatedSupercontinental rafts interact with oceanic lithosphere to generate complex spreading center morphologies [ABSTRACT FROM AUTHOR]

Transpressional margins are widespread, and their dynamics are relevant for plate boundary evolution globally. Though transpressional orogen evolution involves a topographic response to deformation, many studies focus only on the structural development of the system ignoring surface processes. Here, we present a new set of analog models constructed to investigate how tectonic and surface processes interact at transpressive plate boundaries and shape topography. Experiments are conducted by deforming a previously benchmarked crustal analog material in a meter‐scale plexiglass box while controlling erosion through misting nozzles mounted along the transpressional wedge. To analyze the experiments, we generate digital elevation models from laser scans and conduct image correlation analysis on photos taken during experiments. We focus on three experiments that cover a range of erosional conditions and shortening stages (two end‐member erosion models and a dry reference). In all experiments, a bivergent wedge forms, and strain partitioning broadly evolves according to previously established models. Regarding drainage networks, we find that the streams in our models develop differently through feedback between fault development and drainage rearrangement processes. Differences between end‐member erosional models can be explained by the varying response of streams to structure modulated by rainfall. Additionally, erosion may influence the structural evolution of transpressional topography, leading to accelerated strike‐slip partitioning. From these results, we create a model for developing structures, streams, and topography where incision and valley formation along main structures localize exhumation. We apply insights from the models to natural transpressional systems, including the Transverse Ranges, CA, and the Venezuelan Andes. Key Points: Feedback between fault and drainage network development regulates the deformation, exhumation, and morphology of transpressional systemsIncreased erosion accelerates the progression from distributed deformation to complete strike‐slip strain partitioningDue to heightened rock uplift and incision, the maximum exhumation in a transpressional wedge is along the master fault and axial valley [ABSTRACT FROM AUTHOR]

Several continuum damage mechanics (CDM) modelling approaches for predicting creep deformation of tempered ferritic steels have been developed in the literature, which have evolved from efforts to extend the operability of power plant components. Few of these models, however, focus on damage assessment of ex-service states of power plant steels through the extraction of damage parameters. Furthermore, few CDM approaches leverage the high density of creep curve data available through full-field strain measurement techniques such as digital image correlation (DIC). This work uses multiple creep curves obtained from DIC computed strain data at several stresses and temperatures from individual specimens of X20CrMoV12-1 (X20) piping steel. These curves serve as input data to a modified Oruganti continuum damage mechanics (CDM) model whereby microstructural-specific damage parameters can be extracted. Good agreement is noted between CDM-extracted parameters and microstructural, creep cavity density and hardness damage indicators. Damage parameters based on subgrain growth are particularly sensitive to the ex-service state of the X20 steel. The proposed CDM approach using DIC computed creep curves is shown to be a material efficient alternative to traditional damage assessment methods of ex-service material. [ABSTRACT FROM AUTHOR]