Thermomechanical Numerical Model Research Articles

Various lithospheric deformation patterns derived from rheological contrasts between continental terranes: insights from 2-D numerical simulations

Abstract. Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The crème brûlée (CB) model and the jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength–depth variations. Depending on the strength of the continental lower crust, the CB and JS models can be further subdivided into two subclasses in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II), respectively, have a strong or weak lower crust. During the continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermomechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation and studied the effects of different rheological assumptions on terrane deformation. We found four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis.

Fault Tectonites of the Yenisei Shear Zone (Yenisei Ridge): Evidence and Thermomechanical Numerical Model of Generation of Tectonic Overpressure

Based on the proposed numerical model of the stress-strain state of polymineral rocks, which describes the formation of blastomylonites in the Yenisei Regional Shear Zone (PRSZ) in the Yenisei Ridge, the possibility of local tectonic overpressure exceeding the lithostatic pressure in rocks subjected to shear deformations is shown. For tectonites of the southern (Angara-Kan block) and northern (Isakovka terrane and Garevka complex) segments of the PRSZ, estimates of the maximum overpressure were obtained from 2–3 to 4–5 kbar, which range from 25 to 50% of the lithostatic pressure. It is shown that excess pressures can be preserved in a local volume on a geological time scale sufficient for their fixation in metamorphic minerals. Model values of overlithostatic pressure in garnet-amphibole tectonites and geobarometric estimates of peak values during stress metamorphism allow us to offer new evidence of pressure inhomogeneity in natural mineral associations. Using the results of numerical modeling for the evolution of fault metabasite blastomylonites, it was established that the overpressure at the stage of syn-deformation metamorphism in the shear zone are possible at temperatures up to 600–650°C and not reaching 800°C; the presence of fluid or partial melt prevents the occurrence of overpressure. The amount of excess pressure due to shear stresses depends on the mineral composition and structure of the rock.

Intermediate-depth seismicity and intraslab stress changes due to outer-rise faulting

Intermediate-depth seismicity is common in subducting slabs and the seismicity rate shows some statistically significant yet enigmatic global positive correlation with the maximal throw of outer-rise normal faults. Here, we have simulated the formation and subduction of outer-rise faults, using 2D thermomechanical numerical models of intra-oceanic subduction with coupled brittle-ductile damage of bending plates. We observed that outer-rise faults are formed episodically during slab segmentation and their maximal throw grows with time. When been subducted to intermediate depth, these faults are locally reactivated either by i) slab unbending/bending, simultaneous to the formation of new outer-rise faults or ii) episodic interplate coupling related to the rugged morphology of the faulted downgoing plate. Faults reactivation is concurrent with a local, transient deviatoric stress increase in intraslab domains among these structures. We suggest that slab domains affected by stress increase could be the appropriate location where potential brittle deformation can occur, generating intermediate-depth intraslab earthquakes, that are predominantly localized in heterogeneous regions of dense faulting formed within slab-segments boundaries. The temporal coincidence of stress growth at intermediate depths and throw-growth of, newly-formed, outer-rise faults at the surface may possibly explain the observed global positive correlation of intermediate-depth seismicity rate with maximal fault throw.

Two-Stage Model of Devonian Basic Magmatism in the Vilyui Paleorift (Siberian Platform)

Abstract —We report study results of basic intrusive bodies in the middle Paleozoic Vilyui paleorift (eastern Siberian Platform). Geochemical data for basic sills penetrated by boreholes in the rift’s dike swarms are presented, as well as our data on the time of formation of sills and dikes. We also studied mineral-hosted melt inclusions from a dolerite dike of the Vilyui–Markha dike swarm on the northwestern flank of the Vilyui paleorift. Data on the compositions of homogenous glasses of mineral-hosted melt inclusions yielded the P–T parameters of mantle sources of basic melts responsible for the formation of the Vilyui paleorift gabbro-dolerites. Two depth levels of basic melt generation have been established: 95–65 km at 1480–1400 °C and 55–45 km at 1360–1320 °C. Crystallization of the melts occurred at a shallow depth of 12–4 km with a decrease in temperature from 1185 to 1125 ºС. This occurrence of basic melt sources at two different depths, as well as the heterogeneity of the chemical composition of melt inclusions and their host minerals explains the presence of two pulses of Devonian basic magmatism. Our new numerical thermomechanical model of magma rise during melting of the lithospheric mantle above a mantle plume supports the existence of two chambers at the spinel–garnet peridotite boundary and under the base of the crust, as well as the two-stage nature of Devonian magmatism.

Improvement of the Technology of Precision Forging of Connecting Rod-Type Forgings in a Multiple System, in the Aspect of the Possibilities of Process Robotization by Means of Numerical Modeling.

The study refers to the application of numerical modeling for the improvement of the currently realized precision forging technology performed on a hammer to produce connecting rod forgings in a triple system through the development of an additional rolling pass to be used before the roughing operation as well as preparation of the charge to be held by the robot's grippers in order to implement future process robotization. The studies included an analysis of the present forging technology together with the dimension-shape requirements for the forgings, which constituted the basis for the construction and development of a thermo-mechanical numerical model as well as the design of the tool construction with the consideration of the additional rolling pass with the use of the calculation package Forge 3.0 NxT. The following stage of research was the realization of multi-variant numerical simulations of the newly developed forging process with the consideration of robotization, as a result of which the following were obtained: proper filling of the tool impressions (including the roller's impression) by the deformed material, the temperature distributions for the forging and the tools as well as plastic deformations (considering the thermally activated phenomena), changes in the grain size as well as the forging force and energy courses. The obtained results were verified under industrial conditions and correlated with respect to the forgings obtained in the technology applied so far. The achieved results of technological tests confirmed that the changes introduced into the tool construction and the preform geometry reduced the diameter, and thus also the volume, of the charge as well as provided a possibility of implementing robotization and automatization of the forging process in the future. The obtained results showed that the introduction of an additional rolling blank resulted in a reduction in forging forces and energy by 30% while reducing the hammer blow by one. Attempts to implement robotization into the process were successful and did not adversely affect the geometry or quality of forgings, increasing production efficiency.

Tectonites of the Yenisei Shear Zone (Yenisei Ridge): Evidence and Thermomechanical Numerical Model of Generation of Tectonic Overpressure

Tectonites of the Yenisei Shear Zone (Yenisei Ridge): Evidence and Thermomechanical Numerical Model of Generation of Tectonic Overpressure

Early age cracking relevant to mass concrete dam structures during the construction schedule

Managing the early-age thermal behavior of mass concrete structures like dams, dykes, bridge piers, thick raft foundations, etc., is the major concern during their construction. The heat of hydration (HOH) of the fresh concrete pour does not get easily dissipated to ambiance since concrete is predominantly a poor conductor of heat. Eventually, in the presence of external boundary conditions (thermal or mechanical), the slower rate of heat dissipation may at times induce a substantial thermal gradient within the mass concrete which further may induce thermal stresses leading to the formation of cracks. The article attempts to develop a thermo-mechanical numerical model based on the finite element (FE) methodology to mimic the early age behavior of mass concrete that accounts for time and temperature-dependent heat generation during the hydration process with the evolution of thermal and mechanical properties over time. A two-stage sequential thermo-mechanical model is developed consisting of a thermal model to assess the thermal history of a particular concrete mix which is experimentally validated by performing thermal monitoring of a fresh concrete pour for 10 days, and a mechanical model to assess the stress and the cracking states, the model utilizes the concrete damage plasticity (CDP) model based on the principle of continuum damage mechanics which is characterized by experimental results. Later on, the methodology so developed is employed over a practical scenario of the dam construction process considering the relevant boundary conditions to arrive at a suitable optimum lift height and pouring frequencies.

Product, process, property, and performance (PPPP) relationship of 3D-Printed polymers and polymer composites: Numerical and experimental analysis

Understanding the external and internal factors during an additive manufacturing (AM) process is crucial, as they can significantly affect the final product's performance. Efforts have been made to unwind the product, process, property, and performance (PPPP) relationships. The conventional experimental approaches can lead to boundless runs, resulting in exorbitant costs for research and development. Hence, developing, adapting, and validating numerical models is essential to achieving the desired performance of 3D-printed products with lesser resource utilization. In this study, numerical and experimental techniques were used to perform the PPPP relationship assessment on material extrusion 3D-printed parts. Three infill designs (rectangular, triangular, and hexagonal), with layer heights (0.1 mm, 0.125 mm, and 0.2 mm), and three different materials (carbon fiber-reinforced polyamide-6 (PA6-CF), polyamide-6 (PA6), and acrylonitrile butadiene styrene (ABS)), were selected for the investigation. Taguchi's design of experiments (DOE) method was used to limit the number of numerical simulations and experimental runs. A thermomechanical numerical model was utilized to perform the material extrusion process simulations and mechanical performance prediction of the specimens. Subsequently, the samples were 3D-printed and tested mechanically to validate the numerical simulation results. The dimensional, distortion, and mechanical analysis performed on numerical simulation results agreed well with the experimental observations.

Numerical modeling of induced subduction initiation: Insights from the oceanic plateau accretion

Subduction initiation is a crucial process for plate tectonics. Two scenarios of induced subduction initiation–subduction polarity reversal and subduction transference–are primarily attributed to the accretion of oceanic plateaus. However, the factors governing these two distinct types of subduction initiation remain elusive. Here, we employ 2D thermomechanical numerical models to investigate the dynamics of induced subduction initiation during oceanic plateau accretion. Specifically, we explore the impact of the thickness, density, and rheological strength of the oceanic plateau on subduction initiation. Our results reveal three geodynamic regimes: continuous subduction, subduction transference, and subduction polarity reversal. Thin oceanic plateaus tend to subduct along with slabs into the deep mantle, while thick oceanic plateaus often accrete to the margin, triggering subduction initiation. The rheological strength and density of an oceanic plateau play a significant role in determining whether subduction transference or polarity reversal occurs. Increasing the viscosity and decreasing the density of the oceanic plateau promotes strain concentration in front of the oceanic plateau, resulting in subduction polarity reversal. Our model results provide insights into the dynamics of subduction transference in the Caroline Sea and polarity reversal in Solomon in the western Pacific Ocean.

A thermo-mechanical simulation for the stability analysis of a horizontal wellbore in underground coal gasification

The stability analysis of horizontal wells is essential for a successful underground coal gasification (UCG) operation. In this paper, a new 3D coupled thermo-mechanical numerical modeling is proposed for analyzing the stability of UCG horizontal wells. In this model, the effect of front abutment stresses, syngas pressure, syngas temperature and thermal stresses is considered to predict the mud weight window and drilling mud pressure during UCG process. The results show that the roof caving in UCG panel has a greatest impact on the stability of horizontal well. Moreover, when the time of coal gasification is increased, the well convergence increases and for more stability it is necessary to increase the drilling mud pressure. This research was carried out on the M2 coal seam in Mazino coal deposit (Iran). The results showed that the mud weight window for horizontal well drilling is between 0 and 33 MPa. The appropriate stress for the maximum stability of the horizontal well, taking all the thermal and mechanical parameters into account, is 28 MPa. The suggested numerical method is a comprehensive and consistent way for analyzing the stability of horizontal wells in UCG sites.

Numerical thermomechanical modelling of lava dome growth during the 2007–2009 dome-building eruption at Volcán de Colima

SUMMARY Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007–2009. The mathematical model treats the lava dome extrusion dynamics as a thermomechanical problem. The equations of motion, continuity and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e. the distributions of the temperature, crystal content, viscosity and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome–air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermomechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyse effusive eruptions, dome morphology and carapace evolution including its failure potentially leading to pyroclastic flow hazards.

Multi-scale modelling for optimization of process parameters of laser powder bed fusion processed Inconel 718 surrogate part

This work uses an analytical and multi-scale thermo-mechanical numerical model to optimise the process parameter to prevent porosity while reducing the distortion in the surrogate part. Taguchi’s experimental design technique was used to identify the effect of process parameters on melt pool evolution. A dimensionless relative melt pool depth ratio (d*) ensures the extent of densification in the simulated part for various processing parameters. The Taguchi analysis outcome revealed an increase in d*, solid ratio, residual stress and distortion with increased laser power while a contrary effect with increased hatch spacing and scan speed. A strong interaction is observed for melt pool metrics and residual stress evolution. However, the interactions for residual stress and distortion evolution are more prominent, showing the influence of process parameters on energy density and thermal gradient evolution. The ANOVA analysis also shows a strong influence of process parameters on melt pool development and residual stress evolution. However, for solid ratio development, scan speed shows an insignificant effect. These observations from meso-scale analysis aids in process parameter selection for defect free part fabrication. A reduction in the VED reduced the magnitude of accumulated residual stresses in the surrogate component, thereby reducing the maximum distortion in the part. A decrease of 8.33 % in maximum distortion is observed for a ∼ 20 % reduction in the VED.

Analysis of the Temperature Evolution at Necking during Tensile Deformation of H240LA Steel Sheets

The study of localized necking based on strain analysis using Digital Image Correlation (DIC) is the most widely used technique in sheet metal forming to study the FLD (Forming Limit Diagram). However, due to the heat generated by plastic deformation during the forming operations, another way is to analyze the temperature field of the specimen during the test by using Digital Infrared Thermography (DIT). A series of Nakazima tensile tests of high-strength low-alloy steel were tested using DIC and DIT synchronized systems. In this study, a thermomechanical numerical model was developed in ABAQUS/Standard in order to study the energy balance between the different effects of heat generation by plastic deformation, and transient conductive and convective heat transfers through the sample and to the environment. Analysis of the predicted energy balance during the tests allowed to understand the temperature evolution observed both at the beginning and at the development of the unstable necking until fracture. The numerical results are consistent with the analysis obtained from experimental temperature field, making feasible the use of DIT systems to study new necking detection criteria.

Garnet microstructures suggest ultra-fast decompression of ultrahigh-pressure rocks

Plate tectonics is a key driver of many natural phenomena occurring on Earth, such as mountain building, climate evolution and natural disasters. How plate tectonics has evolved through time is still one of the fundamental questions in Earth sciences. Natural microstructures observed in exhumed ultrahigh-pressure rocks formed during continental collision provide crucial insights into tectonic processes in the Earth’s interior. Here, we show that radial cracks around SiO2 inclusions in ultrahigh-pressure garnets are caused by ultrafast decompression. Decompression rates of at least 8 GPa/Myr are inferred independently of current petrochronological estimates by using thermo-mechanical numerical modeling. Our results question the traditional interpretation of fast and significant vertical displacement of ultrahigh-pressure tectonic units during exhumation. Instead, we propose that such substantial decompression rates are related to abrupt changes in the stress state of the lithosphere independently of the spatial displacement.

Early Paleozoic Tectonothermal Evolution of the Khan-Khukhay Metamorphic Complex (Northern Mongolia)

A reconstruction of metamorphic stages of Moren and Erzin metamorphic Complexes in the Khan-Khuhay block of Nothern Mongolia presented in the paper. Based on it a general geodynamic history of Sangilen terrain of Tuva-Mongolia Massif discussed. Reconstructed “clock-wise” P-T trend demonstrated two stage of metamorphism, the first of which is due to collision metamorphism with P-T parameters of 9 kbar, 740°C, the second one is due to regional magmatic episode with P-T parameters of 6-7 kbar, 860–880°C. Geochemical and petrological peculiarities of rocks in the Khan-Khuhay block demonstrates resemblance with metamorphic block of Western Sangilen in South-East Tuva. In the first time quartz monzodiorite intrusive bodies founded within Khan-Khuhay block. Their geochemical peculiarities are similar to Ordovician gabbro-monzodiorite intrusives of Western Sangilen. Quartz monzodiorite intrusives of Khan-Khuhay are likely a small apophysis of a deep-crust intermediate magma chamber and can present probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. Numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explain heating in the thickening crust during collision due to higher radiogenic heat source of 1.52 μW/m3. Using computer modeling was show that the P-T parameters of second metamorphic stage can realize only by means of magmatic heat from monzodiorite intrusion. Reconstruction of P-T parameters using mineral thermobarometry, similarity of geochemical characteristics, as well as the results of thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution.

Progressive weakening within the overriding plate during dual inward dipping subduction

The evolution of dual inward dipping subduction (DIDS) is crucial to understand multiple slab interaction. Yet, how DIDS influences the thermo-mechanical behaviour of the overriding plate remains unclear, as previous DIDS investigations all applied a compositional or Newtonian rheology that excludes temperature dependency. Here we apply a composite rheology, including temperature dependent creep deformation mechanisms, in 2-D thermo-mechanical numerical modelling to investigate how DIDS modifies the rheological structure of the overriding plate. Three variables on plate sizes are investigated to understand what may control the maximum degree of plate weakening. We find that reducing the initial length or initial thickness of the overriding plate and increasing the initial thickness of the subducting plate can enhance the viscosity reduction within the overriding plate. The progressive weakening can result in a variety of stretching states ranging from 1) little or no lithosphere thinning and extension (<5% accumulation of strain), to 2) limited thermal lithosphere thinning (<30% accumulation of strain), and 3) localised rifting followed by spreading extension. Compared with single sided subduction, DIDS further reduces the magnitude of viscosity in the overriding plate. It does this by creating a dynamic fixed boundary condition for the overriding plate and forming a stronger upwelling mantle flow, both of which promote the progressive weakening in the overriding plate. The result implies that these generic DIDS effects are important aspects to consider to understand extension developed in natural DIDS cases. We also demonstrate that both temperature dependent creep rheologies and yielding deformation mechanism contribute significantly to the continuous viscosity reduction. The finding may also have a broader implication for more general processes that involve plate scale weakening, strain localisation and the formation of new plate boundaries.

Mechanism of Structure Variations at Rifted Margins in the Central Segment of South Atlantic: Insights from Numerical Modeling

AbstractRifted margins in the central South Atlantic portray spatial variability in terms of preserved width and thickness, which relates to complex rift‐related fault activities. However, there is still a lack of systematic and quantitative explanations for the causes of the variations that are observed along the paired rifts. To elucidate this issue, 2D viscous‐plastic thermomechanical numerical models are applied to capture the behavior of deformation, in which we investigate the effects of extensional rate, crustal strength and thickness on crust‐mantle coupling, and timing of transition from rifting to breakup. Our numerical experiments demonstrate that crust‐mantle decoupling accounts for crustal hyperextension, and that incorporating moderate‐intensity rheology into lower crust may yield insights into the hyper‐extended crust and asymmetric architecture observed in the central South Atlantic. The results also suggest that undulations in lithospheric basement cause asymmetric mantle upwelling. The lower crust of fold belts takes priority to be thermally weakened over craton and induces rift migration simultaneously. A new mechanism for the formation of failed rift is described, where the mechanical decoupling derived from thermally weakened lower crust gives access to dual rift migration. These results reinforce the interpretation on how crustal rheology shapes margins architectures and highlight the first‐order effects of crust‐mantle coupling.

Did the Western and the Eastern Vardar ophiolites originate through a single intra-oceanic subduction? Insight from numerical modelling

The ophiolites of the Balkan Peninsula are distinguished into the Western and the Eastern Vardar ophiolites and it is generally accepted that both of them resulted from the latest Jurassic/earliest Cretaceous closure of the Vardar branch of the Tethys Ocean (Vardar Tethys). This study is aimed at testing the possibility that the origin and emplacement of these two ophiolite belts can be explained in terms of a single NE-dipping intra-oceanic subduction, which commences in mid Jurassic and lasts until the lowermost Cretaceous, and then transitions into collision between the African and the European plate. The subduction is accompanied by creation of a new oceanic lithosphere in the back-arc. In order to test this hypothesis, we use 2D numerical thermomechanical modeling for investigating the nucleation of the East Vardar Ocean in the back-arc and intra-arc region. Our numerical results suggest that a single intra-oceanic subduction can indeed be simultaneously responsible for both the westward obduction of the Western Vardar ophiolites and for complex active margin processes along the western rim of the European plate. The simulations show that the single intra-oceanic subduction zone is able to produce a pronounced extension and oceanic spreading along the European margin, which can be associated with the formation of the Eastern Vardar ophiolites in this subduction related setting (SSZ and BAB). The comparison of the numerical modeling results with available natural data suggests that our models are capable to approximate the regional geodynamic evolution during and immediately after the closure of Vardar Tethys.

Experimental and numerical investigations on the energy and structural performance of a full-scale energy utility tunnel

The present study evaluates the performance of a novel tunnel-type ground heat exchanger, an ‘energy utility tunnel (EUT)’. A field test and 3-D time-dependent thermo-mechanical numerical models were utilized to analyze the energy and structural performance of a full-scale EUT during geothermal extraction processes in both continuous and intermittent modes. By utilizing the experimental data to calibrate the numerical model, the impacts of the intermittent operation on the energy and structural performance of the EUT were examined. The results showed that the extracted thermal powers of the EUT were comparable to that of energy traffic tunnels. During geothermal extraction, the EUT experiences additional strains and stresses, which are mainly influenced by the degree of restraint and temperature change. In particular, the axial component of the thermally induced stresses in the EUT is found to be the largest and should be given due attention during the design phase. Furthermore, sensitivity analysis has revealed that as the intermittent ratio (IR) increases, an exponential augmentation (q/qIR=0 = 16.46 × eIR/0.57 + 85.4) is observed in the extracted thermal power of the EUT. Simultaneously, there is an exponential decay in the temperature change and thermally induced strain and stress of the EUT. Therefore, the operating hours of the system should be dynamically adjusted in real-time to the daily heat demand of the energy consumption side, thus achieving maximum efficiency and reduced operating costs while simultaneously minimizing the impact of EUT operation on its thermal–mechanical response.

Do microcontinents nucleate subduction initiation?

Abstract Subduction initiation is a pivotal process in plate tectonics. Models of subduction initiation include the collapse of passive margins, oceanic transform faults, inversion of oceanic core complexes, and ridge failure but have ignored the potential effects of continental crust relicts within the oceanic crust. In this paper, we explore the role of microcontinents on subduction initiation through two-dimensional thermo-mechanical numerical modeling. We consider three scenarios with variable ages of oceanic crust surrounding the microcontinent and parametrically examine the microcontinent characteristics (size, crustal thickness, thermal gradient, and rheology), oceanic plate age, and convergence rates. Results suggest that moderate-size (≥300 km) microcontinents can nucleate subduction initiation at the junction between continental and oceanic plates. A large part of the microcontinent would be dragged into the subduction zone, and the subsequent asthenosphere upwellings would incorporate part of the microcontinent. Our numerical models add a new hypothetical scenario for subduction initiation, especially for those places where a young and buoyant plate subducts beneath an older and denser oceanic plate. Moreover, they can explain the origin of exotic crust materials and ultrahigh-pressure minerals in supra–subduction zone ophiolites.