Search

The Valley of the Kings (KV) is located within a large funerary landscape called the Theban Necropolis, in Luxor, Egypt. In 2018, our team started to monitor the transient conditions of a 15 m rock column of micritic limestone above the tomb KV42 and a fracture located at the west end of the column (lateral fracture), registering thermo-mechanical displacements with a crack metre, infrared thermographic sensor, and a weather station. The data from April 2018 to May 2021 showed seasonal fluctuations in the rock surface temperature (RST) from 12°C (winter) to 45°C (summer), as well as an average reversible fracture opening (FO) rate of 1 mm/year. The measured average thermo-mechanical ratio of FO to RST was 0.05 mm/°C. Data collected at the site were used to calibrate a finite difference model in FLAC®8.0 for thermo-mechanical simulations. The results showed a correlation (R2) of 0.8 between measured data and elastic isotropic mechanical constitutive model results, with a ratio of FO to RST equal to 0.03 mm/°C and rates of reversible displacements of 0.8 mm/year, whereas the average irreversible displacement for the monitored period of 2018–2021 was 0.2 mm/year. The insights from this study can help provide a preservation approach for this area of the UNESCO World Heritage site and also enhance our understanding of environmentally driven long-term fracture growth mechanisms, such as thermo-mechanical fatigue. In the future, such insights could become more important as the global and local magnitude of daily and annual temperature fluctuations continue to increase. Highlights: Our team conducts fieldwork in the Valley of the Kings (Luxor, Egypt), monitoring a rock column of 15 m which is attached at the bottom to the adjacent cliff. Cyclic behaviour of temperature and fracture opening were registered between April 2018 and May 2021, at a ratio of 0.05 mm/°C. The fracture opening trend increased throughout the monitored period at rates of 0.2 mm/year, showing irreversible deformation of the rock column. Thermo-mechanical numerical model in FLAC (R) software intended to fit the observed data, under elastic conditions with an R2 of 0.8. The thermal inputs showed that thermal regions change in extension, associated to the shading patterns from the cliffs and hills around the rock column. For FLAC simulations, the ratio between fracture opening and rock surface temperature is 0.03 mm/°C. Because of the cyclic nature of the displacement with the rock temperature, thermally assisted deformations are relevant to determine stability of the rock mass. This is impacted by the presence of joints, affecting the stability and the heat transfer process inwards the column. This could explain differences between observed and simulated data. [ABSTRACT FROM AUTHOR]

This review article provides a critical assessment of the progress made in computational modelling of metal-based additive manufacturing (AM) with emphasis on its ability to predict physical phenomena, concepts of microstructural evolution, residual stresses, role of multiple thermal cycles, and formation of multi-dimensional defects along with the achieved degree of experimental validation. The uniqueness of this article stems from the inclusion of comprehensive information on computational progress in the field of fusion-based, sintering-based, and mechanical deformation-based AM. A computational model's role in determining the process framework for the desired outcome of the set properties of the AM components is recognised while presenting the process-microstructure maps, thereby appraising computational ability towards the qualification of products. The inclusion of a detailed discussion on the bi-directional coupling of machine learning and physics-based computational models provides a futuristic roadmap for the digital twin of metal-based AM. [ABSTRACT FROM AUTHOR]

Laser-assisted forming provides a perfect solution that overcomes the formability of low-ductility materials. In this study, laser-assisted robotic roller forming (LRRF) was applied to bend ultrahigh-strength steel sheet (a quenching and partitioning steel with a strength grade of 1180 MPa), and the effects of laser power density on the bending forces, springback, and bending radius of the final parts were investigated. The results show that LRRF is capable of reducing bending forces by 43%, and a compact profile with high precision (i.e., a springback angle smaller than 1° and a radius-to-thickness ratio of ~1.2) was finally achieved at a laser power density of 10 J/mm2. A higher forming temperature, at which a significant decrease in strength is observed, is responsible for the decrease of forming forces with a laser power density of higher than 7.5 J/mm2; another reason could be the heating-to-austenitization temperature and subsequent forming at a temperature above martensitic-transformation temperature. Forming takes place at a higher temperature with lower stresses, and unloading occurs at a relatively lower temperature with the recovery of Young's modulus; both facilitate the reduction of springback angles. In addition, the sharp bending radius is considered to be attributed to localized deformation and large plastic strains at the heating area. [ABSTRACT FROM AUTHOR]

Heat shock is a feasible means to break rock mass in engineering duo to the large additional thermal stress caused by thermal expansion. This paper established a coupled thermal transfer and rock deformation model based on the energy conservation and the elastic deformation theory of rock. In the model, the failure and damage of rock are judged according to the Drucker-Prager criterion. A finite element method of COMSOL Multiphysics to study the characteristics of temperature, stress distribution and damage zone on a rock surface is proposed. Results show that the failure of rock mass occurs at the cusps of the heater first duo to stress concentration and then grows at both sides of the heater greatly. [ABSTRACT FROM AUTHOR]

Injection molding (IM) is the most widespread and economical way to obtain high-quality plastic components. The process depends, however, to a great extent, on the quality and efficiency of the injection molding tools. Given the nature of the IM process, the temperature control system (TCS), its design, and its efficiency are of utmost importance for achieving the highest possible quality of plastic parts in the shortest possible time. For that reason, the implementation of additive manufacturing (AM) in novel IM temperature control strategies has gained considerable interest in academia and industry over the years. Conformal cooling channels (CCCs) are TCSs that have already demonstrated great potential when compared to conventional gun-drilling systems. Nevertheless, despite the recent advances, the design of these systems is still an open field of study and requires additional research in both aspects deemed as critical: thermo-mechanical models and the application of optimization techniques. This review paper tackles all the relevant, available papers on this topic, highlighting thermo-mechanical models developed by TCS designers and the optimization techniques used. The articles were thoroughly analyzed, and key points on the design of new TCS and new opportunities were identified. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 316L near-net-shape double hollow cylinder with a joint region component was fabricated by Laser Powder Bed Fusion. • Gradients of residual stresses in the printed part were compared to mechanical and thermo-mechanical model simulations. • The evolution of microstructure and residual stress distribution was studied after printing and 2 h/700 °C of heat treatment. In this work, a double hollow cylinder with a joint region, representative of nozzles, pipe systems, valves, or pressure regulators, was chosen to measure and simulate its 3D residual stress (RS) distribution. The part was printed by Laser-Powder Bed Fusion (L-PBF) using commercial 316L steel powders, and a mapping of residual stress along the joint cross-section was measured at three geometrical sample directions. The distribution of RS in the printed part was not homogeneous, showing important gradients of about ±1200 με from the inner to the outer surface of the wall, as well as along the building direction, translated into an equivalent Von Mises stress gradient up to 400 MPa towards the inner surface. After heat treatment only axial strains are significantly affected and relieved 200 με in average, but not necessarily in a homogeneous manner. The comparison of the Von Mises equivalent stress against available simulation tools based on mechanical and thermomechanical models concluded that although these models succeeded in the benchmarking of total macroscopic distortion of components, they do not capture the asymmetric distribution of RS within the bulk in end-use complex geometries and/or joints and those should be implemented from the microstructural level. [ABSTRACT FROM AUTHOR]

Thermo-mechanical finite element (FE) models predict the thermal behavior of machine tools and the associated mechanical deviations. However, one disadvantage is their high computational expense, linked to the evaluation of the large systems of differential equations. Therefore, projection-based model order reduction (MOR) methods are required in order to create efficient surrogate models. This paper presents a parametric MOR method for weakly coupled thermo-mechanical FE models of machine tools and other similar mechatronic systems. This work proposes a reduction method, Krylov Modal Subspace (KMS), and a theoretical bound of the reduction error. The developed method addresses the parametric dependency of the convective boundary conditions using the concept of system bilinearization. The reduced-order model reproduces the thermal response of the original FE model in the frequency range of interest for any value of the parameters describing the convective boundary conditions. Additionally, this paper investigates the coupling between the reduced-order thermal system and the mechanical response. A numerical example shows that the reduced-order model captures the response of the original system in the frequency range of interest. [ABSTRACT FROM AUTHOR]

An industrial continuous casting process of steel billet is analysed using numerical models for the heat transfer and mechanical deformation in the mould and billet. Elastoplastic thermo-mechanical model, including creep and thermal stresses, is developed to determine the temperature and stress fields, and the resultant deformation in the mould. A three-dimensional, turbulent flow model is also developed to simulate fluid flow and solidification of the molten steel as it flows inside the mould. The heat transfer at the mould-billet interface is decoupled using a heat flux profile obtained from inverse heat transfer calculations, developed in an earlier work. Temperature measurements made in the industrial billet mould have been used for this purpose. Important results from the models are discussed to gain understanding of the physical aspects governing the casting process. The distortion profile of the mould and the thermal shrinkage of the billet are used to determine an optimal taper for the mould. Two separate taper profiles are suggested for the corner and off-corner regions around the mould periphery, due to the different nature of the heat transfer in these regions. Finally, these two profiles are compared with the existing single tapered profile for the operational mould in the industry. It is observed that the existing profile has significantly less taper in the meniscus region which can lead to higher air gap and subsequent defects in casting. [ABSTRACT FROM AUTHOR]

Abstract Tribological conditions in forming operations depend on several parameters such as tool-workpiece interface pressure, surface expansion, sliding length, sliding speed, tool and workpiece materials and the roughness of the parts. Among indirect parameters, the most influential one is the tool-workpiece interface temperature, which directly influences the lubricant performance. Prior to testing new tribo-systems to determine their limits of lubrication, it is therefore important to find the interface temperature. However, measurement of the interface temperature in metal forming is difficult. The present work investigates the determination of the interface temperature in an industrial ironing operation, where severe process parameters lead to lubricant film breakdown and galling after several strokes. The methodology combines finite element simulations and experimental measurements. The overall procedure is based on a steady-state thermal analysis to determine the temperature distribution within the tool and a transient thermo-mechanical analysis of the ironing process when steady-state conditions are achieved. Results show that the proposed methodology applied to a single stroke can effectively and accurately predict the interface temperature in the test tool, thus avoiding the otherwise required thermo-mechanical FEM analyses of hundreds of strokes to reach steady-state. Furthermore, the influence of parameters, such as the predicted steady-state tool temperature, the friction coefficient and the heat transfer coefficient on the contact temperature, is analysed. It is concluded that the frictional heating is the primary cause for the peak temperature. By calibration of the friction coefficient and the heat transfer coefficient to ensure matching of the numerical results and the experimental measurements, a maximum tool-workpiece interface temperature of 158 °C was determined during the forward stroke and 150 °C during the backward stroke. [ABSTRACT FROM AUTHOR]

In the present study the results of experimental tests and numerical simulations on single headed stud anchors cast in concrete member and loaded in shear against concrete edge are presented and discussed. The anchors were exposed up to 90 min of fire and loaded in shear under hot and cold conditions up to failure. The temperature distribution, load-displacement curves and failure patterns were recorded. The numerical simulations were conducted using a thermo-mechanical model that was implemented into a three-dimensional finite element (3D FE) code. The constitutive law for concrete was the temperature dependent microplane model. The results of numerical analysis, including the temperature history profile, load-displacement response and the failure load, were verified by the experimental results. Subsequently, a parametric study was carried out. The experimental and numerical results show that the shear capacity of headed stud anchors is strongly affected by the fire exposure. Especially the cooling process leads to severe loss of load capacity. It is shown that the design formula according to Eurocode 2, Part 4 (Annex D) for concrete edge failure at 90 min of fire is rather conservative for the loading in the hot state, however, it overestimates the resistance for the cold state. [ABSTRACT FROM AUTHOR]

Ball screws are robust and economical linear positioning systems widely employed in high-speed and high-precision machines. Due to precision and stability requirements, the preload force is considered one of the main parameters defining the axial stiffness and the maximum axial load of the ball screw feed drives. In high-speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts result in geometrical variations and, consequently, variations in the preload force. This paper presents a numerical modelling strategy to predict the preload variation due to temperature increase using a thermo-mechanical 3D finite element method (FEM)-based model for double nut-ball screw drives. Two different thermo-mechanical coupling strategies are compared, and the obtained results are validated with experimental measurements for different initial preload and linear speeds. In the mechanical analysis, the nut-screw ball contact interface, the offset-based preloading and the restrictions of the ball bearings are included in the model, while the thermal analysis considers heat generation and heat diffusion. The causes of the thermal preload variation are discussed considering the ball load distribution and the axial and radial thermal displacements of the contacting points. [ABSTRACT FROM AUTHOR]

Ultrasonic welding is becoming an essential technique for joining of thin and dissimilar materials in battery electric vehicle manufacturing because of consumption of less power, unmatched weld quality, high production rate, excellent efficiency, etc. The process control parameters in welding play a vital role in getting a good quality weld. In this study, AA1100 aluminum and UNS C10100 copper are utilized for experimentation by controlling three input parameters such as weld pressure, weld time, and vibration amplitude. The effects of these control parameters on the responses like tensile shear and T-peel failure loads of joints with microstructures are revealed. Furthermore, a three-dimensional thermo-mechanical finite element (FE) model with the relevant welding mechanics is proposed for this dissimilar material combination to predict the temperature distribution in its interface, sonotrode, and anvil. The simulation results are validated by comparing the experimental temperature values, and they are showing good agreement with each other. It provides a significant insight of thermal softening phenomenon in ultrasonic welding process and demonstrates the relationship between physical attributes and the interface temperature. [ABSTRACT FROM AUTHOR]

Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18-1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids remain controversial. In this study, we present the estimates of the mantle potential temperature (Tp) for the WAC, which yields values of about 1500-1600 °C, pressure estimates of initial and final melting yield values of about 3.7-5.2 GPa and 1-1.3 GPa, respectively. Subsequently, 2D thermo-mechanical models have been constructed to explore the width of volcano-sedimentary basin on spatial-temporal evolution of diapirs that emplaced in the lower-middle crust during compression. The models show that the width of the volcano-sediment layer plays an important role in the formation mechanisms of greenstone-granitoid belts. The lower crust beneath sedimentary sequences is deformed into a buckle fold during the first compressional stage, through which relief uplifts slowly. Subsequently, the buckle fold is further deformed into several individual folds. Diapirs made of lower crust rocks ascend and emplace in the middle-upper crust resulting from instability. Benefitting from the mantle temperature, the pressure estimates and the numerical modelling results, a new geodynamic model was constructed. This model indicates that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting that are accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intrude into the upper crust through weakening zones between the diapirs. Our geodynamic model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts. [ABSTRACT FROM AUTHOR]

In this paper, a thermo-mechanical model is proposed to simulate the frost jacking behaviour of screw piles subjected to frost heave, and the results are further validated by laboratory tests. The calculated results show that large multi-helix piles yield the least frost jacking when the freezing depth reaches half the embedment depth of pile. Based on the modified cylindrical shear method and individual bearing method, the optimal geometric parameters of screw piles are determined by a series of numerical calculations. The numerical approach is expected to serve as a reference for designing effective and economical pile types in practice. [ABSTRACT FROM AUTHOR]

Vibration control of structures under near-fault earthquakes by employing a friction pendulum supplemented with thermally modulated shape memory alloy (SMA) springs as damper system is studied. Temperature modulation of the SMA spring during the earthquake effectively alters its hysteretic energy dissipation capacity and thereby the control efficiency of the isolation system. The response of a structure with the isolation system is evaluated through nonlinear dynamic time-history analysis under a set of recorded near-fault ground motions. Through temperature modulation that effectively yields a large SMA hysteretic energy dissipation, the hybrid friction pendulum system with SMA temperature modulation shows enormous control efficiency. A parametric study reveals that under a wide range of conditions, the thermally modulated SMA friction pendulum isolation system shows improved control efficiency over conventional friction pendulum and SMA friction pendulum isolation systems. Further, the temperature-tuned SMA hysteresis loops substantially suppress the high frequency components of earthquake motions, thus reducing the possibility of damage to the structure. [ABSTRACT FROM AUTHOR]

The following work deals with the coupling of a thermo-mechanical model (TMM) of elastomeric membranes of sounding balloons with a flight dynamics model (FDM) of the whole system composed of a sounding balloon and its gondola. This type of balloon, filled with Helium gas, is typically used for its low cost to conduct tests of space technologies in near-space conditions between 20 km and 40 km above sea level where low pressure of the order of millibar can be found. The coupling between the TMM and the FDM is held by the rate of expansion of the balloon. The rate of expansion depends on the mechanical state of the membrane given by the surrounding atmospheric conditions. The model is used to assess the burst altitude, the time of flight during the ascent and the impact velocity of the gondola at the final stage of the descent. A generic model of the atmospheric conditions provides the necessary aerodynamic parameters to describe the balloon ascent to its final altitude. Special attention is given to the balloon membrane as it is subjected to constant changes of pressure during the ascent. The TMM is built to include the details of the temperature-dependent stress–strain relation experienced by the elastomeric membrane as a function of altitude. Knowing its thermo-mechanical state during the flight allows predicting with greater accuracy the burst altitude and the flight duration than provided by a sole FDM. However, in a thorough effort to understand the limitation of the proposed TMM, its results are compared against those computed from classic hyperelastic models showing key differences. Nevertheless, these differences do not translate into any significant impact on the flight dynamics as shown in the comparison between simulation results and experimental data (time of flight, altitude versus time and impact velocity) obtained for three actual flights that occurred over the State of Guanajuato, Mexico, in 2015 (flight F1), 2016 (flight F2) and 2018 (flight F3). It is argued that the present thermo-mechanical flight dynamic model (TMFDM) can be applied to the fair estimation of the flight duration and the burst altitude with sufficient knowledge of the atmospheric conditions. The model can provide key information for the suborbital flight. Amongst these key information, the maximum altitude reached by the balloon is essential to estimate the impact velocity and subsequently to design reliable impact attenuators to ensure the physical integrity of the payload when the gondola touches the ground. The same information can also be used to determine the operating conditions of payloads in high altitudes. Additionally, the time of flight may be used to plan ahead of time the duration of the tests to be performed in a near-space environment. • A detailed thermo-mechanical model coupled to a flight dynamic model to improve the estimation of the burst altitude, the time of flight and the impact velocity during landing. • Comparison of the proposed mechanical model with well-known hyperelastic models showing key differences. These differences do not translate into any significant impact on the results of the TMFDM. • Experimental validation of the TMFDM. • Thorough analyses accounting for the initial conditions of the balloon before flight, the temperature and the choice of the mechanical model. • A novel approach providing further accuracy than existing flight dynamic models reported in the literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive model of the tunnel segmental ring in fire is established. • The model incorporates thermo-mechanical properties of tunnel structure in fire. • Validation of numerical results against experimental data shows good agreement. • Parametric studies are conducted to investigate the diverse fire effects. Investigating fire effects is a continuing endeavour in the research and practice communities concerned with the design and safety of shield tunnels. This paper aims to provide a comprehensive model for the assessment of structural safety of a shield tunnel segmental ring exposed to fire. A thermo-mechanical model for assembled shield tunnel structure in fire is developed to provide a basis for a holistic analysis by incorporating tunnel lining segments and longitudinal joints, as well as improved predictions for the temperature, stress and deformation distributions in the tunnel structure. Validation of the numerical results against experimental data shows satisfactory agreement. Parametric studies are subsequently conducted to investigate the effects of spalling, buried depth and cooling-off phases on the fire behaviour of the shield tunnel. The results show that the damage and failure of a tunnel lining structure under high temperature are mainly due to the combined action of internal thermal expansion force and thermal stress. Spalling leads to the loss of a key "insulation" layer of a tunnel lining structure. On the other hand, the constraint of strata on the tunnel structure under high temperature not only restrains the deformation of key parts of the structure, but also helps offset the adverse effect of load on the structure through elastic resistance. [ABSTRACT FROM AUTHOR]

An internal cracking indicator is designed to quantify the risk of hot tearing in the continuous casting of round billets. For this purpose, the tensional state of the bar is acquired by implementing a thermo-mechanical model that uses a steel material law calibrated with hot tension tests. The cracking indicator is then applied to the phenomenon of diametral pinch-roll compression. Critical combinations of casting speed and steel carbon content are defined to estimate the cracking risk. At last, macro-etching is applied on industrial bars in order to reveal internal cracking, which is then compared to model results to assess its predictability. Influence of pinch-roll pressure and roll shape on the cracking risk is also analyzed. [ABSTRACT FROM AUTHOR]

Although wear mechanism of gun barrel and projectile-barrel interaction have been comprehensively studied in the past three decades, attention has seldom been paid to the interaction between worn barrel and projectile. In the present work, a new parametric geometric modeling method for gun barrel and a new finite element meshing strategy for the worn barrel are proposed which involve the joint use of Python code and ABAQUS software. A transient coupled thermo-mechanical finite element (FE) model is developed to compute the plastic deformation of rotating band and the performance of interior ballistics. Additionally, material thermal properties of the rotating band are considered and user subroutine VUAMP and VFRICTION are implemented within the FE model in order to take account of the propelling force caused by propellant gas and the effect of changing friction stress, respectively. The FE results obtained in simulation verify the ability of the proposed meshing strategy to improve analysis accuracy with respect to the interaction between the worn barrel and the projectile. [ABSTRACT FROM AUTHOR]

This paper proposes a novel mission-profile-based reliability analysis approach for stress on bond wires in Silicon Carbide (SiC) MOSFET power modules using statistics and thermo-mechanical FEM analysis. In the proposed approach, both the operational and environmental thermal stresses are taken into account. The approach uses a two-dimension statistical analysis of the operating conditions in a real one-year mission profile sampled at time frames 5 min long. For every statistical bin corresponding to a given operating condition, the junction temperature evolution is estimated by a thermal network and the mechanical stress on bond wires is consequently extracted by finite-element simulations. In the final step, the considered mission profile is translated in a stress sequence to be used for Rainflow counting calculation and lifetime estimation. [ABSTRACT FROM AUTHOR]

High heat input during layer-wise deposition in the Gas Metal Arc-based Wire-Arc Additive Manufacturing (GMA-WAAM) process leads to significant defects such as high residual stress and distortion. However, the choice of layer-wise heat input is constrained due to the requirement of an optimal set of weld parameters. It is essential to study the effect of heat input on the evolution and control of residual stress in the long-scale WAAM fabricated components. Therefore, this study investigates a novel multi-tier heat input strategy represented by four levels for a GMA-WAAM fabricated long-scale thin-walled component. Accordingly, a layer-wise single-, two-, three-, and four-tier heat input strategy in a twelve-layered long-scale thin-walled component is investigated for transient thermal and residual stress distributions through Finite Element Modelling (FEM). Further, a set of validation experiments was performed, which agreed with the predicted results. It is concluded that a reduced heat input during successive layer deposition greatly influences the cumulative heat input into the system. The two-tier heat-input (case 2) system is found suitable among proposed case studies as an appropriate thermal management system with a variation of 6.98% in peak (melt pool) temperature and 198.4 °C increase of minimum temperature during complete deposition. Also, the four-tier heat input (case 4) produced the component's lowest longitudinal and transverse stresses by 13.07% and 25.83%, respectively. [ABSTRACT FROM AUTHOR]

Magma flow paths in sill-fed dikes of the Ferrar large igneous province (LIP), contrast with those predicted by classic models of dike transport in LIPs and magmatic rift settings. We examine anisotropy of magnetic susceptibility (AMS) flow paths in dike networks at Terra Cotta Mountain and Mt. Gran, which intruded at paleodepths of ~ 2.5 and ~ 1.5 km. These intrusions (up to 30 m thick) exhibit irregular, interconnected dike-sill geometries and adjoin larger sills (~ 200–300 m thick) at different stratigraphic levels. Both shallowly dipping and sub-vertical magma flow components are interpreted from AMS measurements across individual intrusions, and often match macroscopic flow indicators and variations in dike attitudes. Flow paths suggest that intrusive patterns and magma flow directions depended on varying stress concentrations and rotations during dike and sill propagation, whereas a regional extensional tectonic control was negligible or absent. Unlike giant dike swarms in LIPs elsewhere (e.g., 1270 Ma MacKenzie LIP), dikes of the Ferrar LIP show no regionally consistent vertical or lateral flow patterns, suggesting these intrusion were not responsible for long-distance transport in the province. In the absence of regionally significant, colinear dike swarms, or observed intrusions at crustal depths ≥ 4 km, we suggest that long distance magma transport occurred in sills within Beacon Supergroup sedimentary rocks. This interpretation is consistent with existing geochemical data and thermal constraints, which support lateral magma flow for ~ 3,500 km across the Gondwana supercontinent before freezing. [ABSTRACT FROM AUTHOR]

The superheating induced overpressure is one of the key obstacles for long-endurance station-keeping of stratospheric aerostats. A novel stratospheric aerostat by utilizing the natural energy is presented and discussed in this paper. A thermo-mechanical dynamic model is established to analyze the altitude control performance of this novel aerostat. The simulation results show that the novel stratospheric aerostat can ascend to a high altitude about 25.8 km due to the combined heating effects of the solar radiation, the Earth albedo and the infrared radiation from the Earth’s surface and keeps at an altitude about 22 km by the infrared radiation from the Earth’s surface. In addition, the aerostat can be controlled within the desired altitude range by the simple open/close valve control strategy. [ABSTRACT FROM AUTHOR]

This research analyzed the effects of fire duration, groove length, groove (beam) width, groove depth, screw diameter, and screw penetration length on the shear behavior of grooved connectors for glulam-concrete composite beams under fire. Three-dimensional non-linear finite element (FE) models were used to evaluate the thermo-mechanical behavior of grooved connectors under ISO fire. The model was confirmed by comparing load-slip curves with experimental results. Experimental and numerical results showed that when the failure mechanism shifted from the shear plane failure of the concrete groove to compression failure of the wood in front of the groove, the influence of groove length on shear capacity of connectors was no longer significant. Parametric analysis indicated that with the rise of groove depth, the shear capacity and slip modulus of connectors rose progressively. However, when the failure mode shifted from compression failure of wood in front of the groove to the shear plane failure of the concrete groove, the groove depth had no significant influence on the shear capacity of connectors. The groove (beam) width had a substantial influence on the shear capacity and slip modulus of grooved connectors under fire, whereas it was not the case for screw diameter and screw penetration length. [ABSTRACT FROM AUTHOR]

The demand for high-speed/high-precision machine tools is rapidly increasing in response to the development of production technology that requires high-precision parts and high productivity. The thermal deformation of the machine tool structure plays a critical role on the accuracy of machining. Heat generation in the bearings, chucking cylinder, and motor coil are the major sources of thermal deformation. This paper addresses the issues of the thermal displacements in the headstock assembly of a slant bed two-axis CNC lathe. Experimental and numerical investigations were carried out to gain insights into the extent of contribution made by the elements of the headstock assembly on the transient temperature rise and the resulting thermal deformation characteristics. The outcome of the work could be effectively used to improve the machine performance either by making suitable design changes or developing a robust error model for resorting to error compensation. [ABSTRACT FROM AUTHOR]

Abstract: Since the late 1970s, most earth scientists have discounted the plausibility of melting by shear–strain heating because temperature-dependent creep rheology leads to negative feedback and self-regulation. This paper presents a new model of distributed shear-strain heating that can account for the genesis of large volumes of magmas in both the crust and the mantle of the lithosphere. The kinematic (geometry and rates) frustration associated with incompatible fault junctions (e.g. triple-junction) prevents localisation of all strain on the major faults. Instead, deformation distributes off the main faults forming a large process zone that deforms still at high rates under both brittle and ductile conditions. The increased size of the shear-heated region minimises conductive heat loss, compared with that commonly associated with narrow shear zones, thus promoting strong heating and melting under reasonable rheological assumptions. Given the large volume of the heated zone, large volumes of melt can be generated even at small melt fractions. There are clear examples of volcanism correlated with fault complexities that remain enigmatic and that could be related to that mechanism of “process zone heating”. We propose here a simple dislocation model to define the process zones, determine off-fault strain rates and quantify how much plastic work can be dissipated as heat. To provide an example, we examine the case of the junction between the East and North Anatolian shear zones in eastern Turkey. This is chosen because the composition and age of emplacement of the quite extensive volcanics are well known, as are the rates of motion on the associated strike-slip faults. The geometry of the system also allows the dislocation method to be easily adopted. We conclude that melting of the crust and the lithospheric mantle could start only a few Myrs after the onset of deformation. Conservative assumptions for rheological parameters and melting points can explain both the timing and the bimodal nature of the volcanism. Predictions of melt volume are within the rheological uncertainties. While the current paper is focused on strike-slip faults, the approach can be applied to kinematic complexities associated with thrust faults as well, and, maybe more generally, to regions in the lithosphere where oblique boundary conditions force deformation to occur partly in a distributed manner, while still at high rates. [Copyright &y& Elsevier]

Highlights: [•] Discussing the exhumation processes of high-pressure rocks in the West African Craton (2.2–2.0Ga). [•] Thickening of the crust by buckling leading to burial of sedimentary rocks. [•] Partial melting of the mid to lower crust and development of gravitational instabilities. [•] Exhumation controlled by large-scale folding and re-melting of felsic material. [ABSTRACT FROM AUTHOR]

Abstract: A constitutive model is proposed to describe the quasi-static and high rate large deformation response of semi-crystalline polymers. This model is developed based on an elastic–viscoelastic–viscoplastic framework, to predict the temperature and rate-dependent response of an incompressible semi-crystalline polymer, Nylon 6. Material samples are subjected to high rate compressive and tensile loading using Split Hopkinson Bar devices, and they exhibit a temperature increase, which induces a phase change at the glass-transition temperature. The material parameters in the constitutive model, such as the yield stress, stiffness and viscosity coefficients, are proposed as functions of temperature and strain rate. This study aims to formulate a thermodynamics-based model with minimum parameters, for implementation in FEM software (ABAQUS) by the writing of a user-defined material subroutine (VUMAT). The model is validated via comparison with compressive and tensile experimental test results for material response at different temperatures and deformation rates. It shows good potential in describing the thermo-mechanical response of Nylon 6, and in predicting the dynamic behavior of polymeric material. [Copyright &y& Elsevier]

Highlights: [•] Thermo-mechanical model validation shows a satisfying agreement. [•] Increasing forces during thermal cyclic operation compared to the initial values by the factor five. [•] High risks of insulation and particle failures for large-scale packed beds due to the punctiform contacts. [ABSTRACT FROM AUTHOR]

A realistic application of advanced structural and multi-objective optimization for the design of a fully assembled aircraft powerplant installation is presented. As opposed to the classical design process of powerplant installation that does not consider the influence of pylon sizing over engine efficiency, we develop in the present a fully integrated approach where both pylon and compressor intercase are designed at once. The main objective is to consider the impact of weight over tip clearance performance criterion and see how these two objectives are antagonistic. In this work, we perform in the same design session tasks traditionally devoted to the airframe manufacturer and aero-engine manufacturer. The overall weight of the assembly is minimized with respect to Specific Fuel Consumption (SFC) criterion. One interesting aspect of the process is that SFC criterion is based on highly proprietary models and its simulation and call within an optimization process is made available through the development of a webservice. One major phenomenon to consider in both pylon and engine design is Fan Blade Off (FBO) event, i.e. the sudden release of a blade. This event causes high impact loads and must be considered carefully in the design. Such a simulation is not an easy task and several nonlinear phenomena must be addressed (e.g. rotordynamics), not to mention the integration of this nonlinear dynamic response in a static structural optimization process. This article describes how the design of the full assembly is performed taking into account both objectives. Such a problem lies in multi-objective optimization field and then we describe the method we use to solve such a problem. The simulation of an FBO post-impact rotor dynamics is also described and we end up with the final results that show the influence of pylon-engine weight sizing over SFC. [ABSTRACT FROM AUTHOR]

Abstract: A numerical model is developed to analyse the thermo-mechanical fire behaviour of timber-to-timber dowelled and bolted connections in tension parallel to wood grain. The experimental results of two series of tests are used to validate the model based on three-dimensional (3D) finite element modelling. The thermo-mechanical performances of the connections are determined using two different meshing and calculation procedures. The thermal model meshing is continuous to take the thermal continuity between the connection components into account. Regarding mechanical and thermo-mechanical calculations, the meshing is discontinuous to consider the gap and the contact changes between the connection components. The thermal model takes into account the evolution of physical properties of materials as a function of the temperature and is calibrated according to the experimental measurements. The thermo-mechanical model considers the mechanical properties – temperature evolutions of the materials provided by the corresponding Eurocodes. The thermal model can predict the temperature fields inside the connection components. Its validation is conducted through comparison with the experimental temperatures measured in different places inside the connections. The mechanical model is validated using the experimental load–slip curves of the connections in standard conditions. Finally, the thermo-mechanical model is validated by considering the global time–slip curves and by determining the fire resistance rating of the connections. A good agreement is obtained between simulated fire resistance times and experimental ones. [Copyright &y& Elsevier]

Abstract: This study focuses on the load distributions among fasteners in steel-to-timber connections loaded in tension parallel-to-grain under fire exposure. The experimental results of some types of connections with various geometrical configurations are available. The influence of the type of fasteners (bolt, dowel) on the thermo-mechanical behavior of the connections is studied. A three-dimensional finite element model validated on the basis of experimental results is used. Good agreements were observed between the simulated and the experimental values of temperatures and failure times. The type of metal fasteners is crucial to the thermo-mechanical behavior of connections. In the studied connections, one bolt is used in each row of fasteners to prevent the separation between the assembled members. The presence of the bolts greatly influences the behavior of the connections mainly under fire. Various geometrical configurations of connections with only dowels or changing the positions of the bolts are studied. An analytical approach is proposed, from a specific type of connections, by varying some influent geometrical characteristics. A numerical experimental design is realized from the calculated time to failure of the connections. [Copyright &y& Elsevier]

A coupled thermo-mechanical model was developed to study the temperature fields, the plunge force and the plastic deformations of Al alloy 2024-T351 under different rotating speed: 350, 400, and 450 rpm, during the friction stir welding process. 3-D FE model has been developed in ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law, and the Coulomb's Law of friction. Numerical results indicate that the maximum temperature in the friction stir welding process is lower than the melting point of the welding material. The temperature filed is approximately symmetrical along the welding line. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface. With increasing rotation speed, the low plastic strain region is reduced. When the rotational speed is increased, the plunge force can be reduced. Regions with high equivalent plastic strains are observed which correspond to the nugget and the flow arm. [ABSTRACT FROM AUTHOR]

Abstract: A three-dimensional finite element model is developed to predict the thermo-mechanical behavior of steel-to-timber doweled joints in tension parallel to grain exposed to fire. To manage the plastic yielding of the materials, the mechanical model is based on the von Mises criterion for steel and the Hill criterion for timber. In fire, the material characteristics depend on the temperature. Two different meshes are used for the thermal and the thermo-mechanical models. The thermal model is continuous, to take account of the thermal continuity between the joint components. The thermo-mechanical model is discontinuous, to consider the contact evolution between the joint components. The thermal model is used to predict the evolution of the temperature field inside the joint which depend on the gas temperature. It is validated on the basis of measured temperatures during fire tests. The complex transformations in wood during fire are represented by apparent values of thermo-physical characteristics proposed in the bibliography and calibrated on the basis of the experimental measurements. The mechanical model is validated by comparison with the experimental results of joints in normal conditions. The thermo-mechanical model is validated by considering the experimental failure times of some joints. The numerical models showed a good capacity to simulate the behavior of the timber joints in cold and in fire situations. These developed and tested models can be used as a general tool to analyze the behavior of a large variety of joint configurations to constitute a data base that can be used in safe and economic practice of fire engineering of wood joints. [Copyright &y& Elsevier]

Shear band (SB) velocity is a key parameter in assessing the dynamic behavior and also deformation mechanisms of metallic glasses. Using a coupled thermo-mechanical model, we calculated the speed of SB propagation in Vitreloy 1 (Zr41.25Ti13.75Ni10Cu12.5Be22.5) under compression at a strain rate of 10 s−1. The propagation of the SB exhibits a non-uniform speed: a rather slow stage followed by a rapid propagation when the SB is close to the sample surface or at failure. The average speed is estimated to be about 100 m/s, while the maximum speed could reach 1400 m/s. The impact of the varying SB velocity on measurement relying on surface detection such as thermographic images, strain gauge, and surface offsets is discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this work, thermo-mechanical behavior and microstructural evolution in similar and dissimilar friction stir welding of AA6061-T6 and AA5086-O have been investigated. Firstly, the thermo-mechanical behaviors of materials during similar and dissimilar FSW operations have been predicted using three-dimensional finite element software, ABAQUS, then, the mechanical properties and the developed microstructures within the welded samples have been studied with the aid of experimental observations and model predictions. It is found that different strengthening mechanisms in AA5086 and AA6061 result in complex behaviors in hardness of the welded cross section where the hardness variation in similar AA5086-O joints mainly depends on recrystallization and generation of fine grains in weld nugget, however, the hardness variations in the weld zone of AA6061/AA6061 and AA6061/AA5086 joints are affected by subsequent aging phenomenon. Also, both experimental and predicted data illustrate that the peak temperature in FSW of AA6061/AA6061 is the highest compared to the other joints employing the same welding parameters. [Copyright &y& Elsevier]

Abstract: As timber is a combustible material, fire safety is a significant obstacle for the development of timber usage in buildings. Among the various structural components, the connections are often the weakest elements in a timber construction. In fire as well as in normal conditions, they govern the load-bearing capacity of the structure. However, a lack of knowledge is pointed out for the design of connections in normal conditions and even more in fire conditions. In this paper, a three-dimensional finite element approach is developed to investigate the performance of dowelled timber connections in fire. The 3D mechanical model and the thermo-physical model for each connection component are described. For the mechanical model, the plastic behaviour of the materials is considered using the Von Mises criterion for steel and the Hill criterion for timber. Then a thermal and mechanical validation of the proposed model is achieved by comparison with the experimental results in normal and fire situations. The analysis is then focused on the behaviour of dowelled timber connections in a fire situation. Thus, timber-to-timber and steel-to-timber connections with fasteners of 12 to 20 mm in diameter are studied considering a load in direct tension parallel to the grain. A parametric analysis, based on the numerical model, is done to evaluate the influence of the timber thickness on the reduction of the load-bearing capacity of the connections. This influence is evaluated considering the time of fire resistance to deduct simple design methods. [Copyright &y& Elsevier]

Abstract: In this paper, the thermo-mechanical behavior of buckled multi-layered micro-bridge is theoretically analyzed, simulated using ANSYS and experimentally confirmed on a fabricated micro-bridge. The analytical model characterizes its thermo-mechanical behavior by taking into account torsional stiffness, axial stiffness and residual moment at supporting ends of the bridge. The snapping temperatures are obtained from the model and compared with the corresponding ANSYS simulation results. These comparisons were conducted on five composite structures. Four of these are bimorphs consisting of 0.5μm or 1μm thick aluminum layer and 3μm thick PECVD oxide with either 70MPa or 110MPa or 220MPa compressive residual stresses. The fifth structure consists of a tri-morph micro-bridge, which is made of 1μm thick aluminum, 3μm thick compressively stressed PECVD oxide and 1.5μm thick low stress oxide, with various supporting end conditions. Excellent agreement, with an average error of less than 7%, has been obtained between the analytical model and ANSYS simulation. Results show the importance of reducing torsional stiffness of the supporting ends of the bridge if the micro-bridge is to be used for thermal actuation. A micro-bridge device consisting of a tri-layer made of 2.2μm of phosphorus doped silicon, 1μm thick compressively stressed oxide and 2.3μm thick low stress oxide is fabricated, packaged, actuated in situ in a SEM chamber and the mid-point deflection as a function of actuating current is obtained. The measured results are in good agreement with model predictions. [Copyright &y& Elsevier]

Abstract: The connection between the thermal field and the mechanical properties in the northern sector of the Tyrrhenian–Apennines system is analysed. The thermal setting is the result of three main extensional events, which have taken place within relatively small space and time intervals. The oldest tectono-thermal event took place in eastern Corsica 14 Myr ago and the second between Capraia and Elba islands 7 Myr ago. The third and youngest rift episode, with an average age of 3 Myr, affected a wider area extending east of Elba Island and including most of the peri-Tyrrhenian zone. By assuming lithosphere extension, the expected Moho temperature increases eastward from 550 to 750 °C. Uniform stretching cannot account for the high heat flux in the zone affected by the youngest tectono-thermal event. For this zone, we propose a thermo-mechanical model, which incorporates the removal of 15 km of mantle lithosphere, as a result of eastward asthenosphere flow induced by the Apennines subduction. This yields a predicted heat flux in agreement with that observed. Lithosphere mechanical strength analysis indicates that the thickness of the uppermost crustal–brittle layer decreases eastward from 15 to 10 km, while the temperature discriminating the rheological behaviour is rather uniform, being on average, 320 °C. [Copyright &y& Elsevier]

Abstract: We employ finite-element thermo-mechanical modelling to study the dynamics of a continental transform boundary between the Arabian and African plates marked by the Dead Sea Transform (DST), that accommodated ca 105 km of relative transform displacement during the last 20 Myr. We show that in the initially cold lithosphere expected at the DST, shear deformation localizes in a 20–40 km wide zone where temperature-controlled mantle strength is minimal. The resulting mechanically weak decoupling zone extends sub-vertically through the entire lithosphere. One or two major faults at the top of this zone take up most of the transform displacement. These and other modelling results are consistent with geological observations and lithospheric structures imaged along the DESERT seismic line, suggesting that the Arava Valley segment of the DST is an almost pure strike-slip plate boundary with less than 3 km of transform-perpendicular extension. Modelling suggests that the location of the Arava Valley segment of the DST has been controlled by the minimum in lithospheric strength possibly associated with margin of the Arabian Shield lithosphere and/or by regionally increased crustal thickness. Models also show that heating of the Arabian Shield mantle adjacent to the DST, inferred independently by petrological and seismological studies, is required to explain asymmetric Late Cenozoic uplift in the area. [Copyright &y& Elsevier]

Abstract: The Jiufengershan rock-and-soil avalanche is one of the largest landslides triggered by the Chi-Chi Taiwan earthquake (September 21, 1999). In order to study landslide triggering and propagation by seismic shaking, we propose a method that combines features of the classic Newmark approach with mechanical relations involving Mohr-Coulomb failure criteria, pore-water pressure and shear heating during the sliding process. The effective shear strength is affected by shear heating and by pore-pressure variations during the sliding process. The shaking process was simulated using strong-motion accelerograms of the three nearest free-field stations, which surrounded the landslide. The initiation and propagation of earthquake-induced landslides are mainly controlled by the peak and residual shear strengths, respectively. The increase in temperature in the shear zone increases the pore-water pressure and weakens the shear strength. Rock avalanches are generated when mechanical parameters achieve critical threshold values, such that the residual shear strength is less than the tangential projection of body forces. [Copyright &y& Elsevier]

• Transient thermal strain is considered in the model of ultra-high strength concrete encased steel columns (UHSCESC). • Steel section has a lower temperature than its critical value after 150 min's heating in standard fire. • The fire behavior of UHSCESC is governed evenly by steel section and core concrete. • The slenderness ratio, section size and load ratio are three key influencing factors. • EC4 is not applicable to UHSCESC leading to unconservative fire resistances up to 66 min. Ultra-high strength concrete has been applied in concrete encased steel column to enhance strength and reduce usage of concrete. However, there are limited specifications in current design codes on ultra-high strength concrete encased steel columns (UHSCESC), particularly for fire effects. This paper presents numerical simulation of fire behaviour of UHSCESC exposed to standard fires. A thermo-mechanical model of UHSCESC is established by considering the effect of transient thermal strain and validated against experimental results. The effect of slenderness ratio, section size, load ratio, concrete strength, steel strength, reinforcement ratio and steel ratio on the fire behaviour of UHSCESC is investigated through parametric studies. The predicted fire resistance of UHSCESC is finally compared to EC4 results. It is found that the temperature of the steel section is lower than its critical value, and the load bearing capacity of UHSCESC is almost evenly provided by the core concrete and steel section. The slenderness, section size and load ratio have significant effects on fire resistance of UHSCESC, leading to a wide range more than 300 min. The EC4 method is not applicable to UHSCESC which may provide unconservative fire resistances up to one hour and over-conservative results of nearly four hours. [ABSTRACT FROM AUTHOR]

• A numerical methodology to assess the main factors that contribute to frost damage of cement paste. • The presented model is physics-based and takes into account the complex microstructure of the heterogeneous cement paste. • Results highlight the effect of supercooling on frost damage. • The initial w/c ratio and the amount of salt ions are the most harmful factors contributing to damage. Degradation of concrete due to freeze–thaw cycles is a subject that is still debated. For many years, some predictive models have been developed by taking into account the physics, but the choice of parameters which drive the frost kinetics and the couplings are often arbitrarily chosen to fit experimental measurements. Moreover, recalibration becomes necessary each time the mix design or the environmental conditions vary. This article presents a quantitative assessment of the effect of the mechanisms induced by the freeze–thaw action on the internal damage of cementitious materials, using a descriptive numerical methodology at the microscale. The proposed thermo-mechanical model is based on thermodynamic considerations and physical processes related to freeze–thaw applied to virtual microstructures of cement pastes. A statistical study on the main parameters, which govern the frost action, has been performed to highlight their significance on the thermal strain. The numerical results show that the presence of supercooling and delayed nucleation of ice is by far the most harmful cause of degradation. Both the water-to-cement ratio and the minimum freezing temperature reached during freeze–thaw cycles contribute considerably to the deterioration of the material and a decrease in the Young's modulus. It is shown that the effect of de-icing salt ions present in the pore solution depends on the degree of saturation, and that the critical degree of saturation depends on the minimum temperature. The study also demonstrates the beneficial role of using entrained air to reduce damage caused to cement paste. [ABSTRACT FROM AUTHOR]

In the present study, the influence of thermally induced damage of reinforced concrete (RC) frames on their static and dynamic response is experimentally and numerically investigated. In the experimental test, the RC frame is first pre-damaged through fire exposure and then loaded from the side with the impact of a steel pendulum. To verify the recently developed coupled thermo-mechanical model for concrete, transient 3D FE simulation is carried out. The rate and temperature-dependent microplane model is used as a constitutive law for concrete. It is first shown that the simulation is able to realistically replicate the experimental test. Subsequently, the numerical parametric study is performed where the dynamic and static response of RC frame is simulated for both hot and cold states. It is shown that the pre-damage of RC frame through fire exposure significantly reduces the resistance and changes the response. Finally, it is demonstrated that for the impact load the rate sensitive constitutive law of concrete significantly contributes to the response of RC frame. [ABSTRACT FROM AUTHOR]

Element-free Galerkin (EFG) method is applied for the first time to numerical modeling of additive manufacturing (AM) process, in which the superiorities of the EFG method in implementing adaptive computation and in constructing high order approximation are exploited. Second-order moving-least squares (MLS) approximation is constructed for both temperature and displacement. A non-linear coupled thermo-mechanical model considering moving heat sources, radiation boundaries, elastoplastic materials and temperature-dependent parameters is adopted. Adaptive coarsening based on the background integration mesh is developed to efficiently model the layered deposition process. In addition, an efficient integration scheme using background hexahedral elements is proposed to evaluate the domain integrals of the weak forms. Numerical results show that the developed method is able to effectively model the AM process with substantially reduced number of approximation nodes. The effects of laser power, scan speed and scan path on temperature and distortion are investigated. The improved accuracies due to the proposed integration scheme and the adopted second-order approximation are also demonstrated. [ABSTRACT FROM AUTHOR]

Inconel 601 is one material of choice for intermediate- to high-temperature protective coatings for spark plugs' ground electrodes. Production of ground electrodes of spark plugs implies the following operations: the tamping of the copper core in an Inconel 601 cup, cold-forming of the assembly, annealing, welding, and bending of the final spark plug. On the production line, the use of Inconel 601 as a protective coating for ground electrodes leads to possible cracking in the welded area after bending. In the present paper, possible causes of cracking are analyzed. It is clearly shown that a combination of Copper –Inconel interface oxidation, Inconel yielding during the heat treatment, and micro-movements during bending lead to cracks in the welded area of the ground electrode. First, the detrimental effect of gaps, between Copper and Inconel 601, is shown experimentally. Second, a thermo-mechanical analysis combined with SEM (Scanning Electron Microscopy) observations identified the annealing treatment and interface oxidation as the main cause of gaps. Third, bending simulations show the relation between these gaps and cracking. Finally, a new ground electrode design, preventing cracks, is suggested. [ABSTRACT FROM AUTHOR]

Shrinkage and warping of additive manufacturing (AM) parts are two critical issues that adversely influence the dimensional accuracy especially in powder bed fusion processes such as selective laser sintering (SLS). Powder fusion, material solidification, and recrystallization are the key stages causing volumetric changes of polymeric materials during the abrupt heating–cooling process. In this work, the mechanisms of shrinkage and warping of semi-crystalline polyamide (PA) 12 in SLS are well investigated. Heat-transfer and thermo-mechanical models are established to predict the process-dependent shrinkage and warping. The influence of raw material- and laser-related parameters are considered in the heat-transfer and thermo-mechanical models. Such models are established considering the natural thermal gradient and dynamic recrystallization, which induce internal strain and volumetric change. Moreover, an experimental design via orthogonal approach is introduced to validate the feasibility and accuracy of the proposed models. Finally, the quantitative relationships of process parameters with product shrinkage and warping are established; the dimensional accuracy in part-scale can be well predicted and validated with printed parts in a real experiment. [ABSTRACT FROM AUTHOR]