Simulated Temperature Evolution Research Articles

Laser directed energy deposition of Ti-1Al-8V-5Fe alloy: From zero to significant tensile plasticity

Titanium alloy Ti-1Al-8V-5Fe (Ti-185) has essentially remained an experimental alloy since its invention because of the formation of iron-stabilized beta-flecks in conventional manufacturing. Laser directed energy deposition (L-DED) has the potential to avoid this issue while realizing in-situ ageing. This work investigates the L-DED fabrication of Ti-185 alloy. We show that the precipitate phases along the build height of the Ti-185 plate sample have a decisive influence on its tensile properties. Due to the formation of the embrittling isothermal omega-phase (ωiso), the top region of the Ti-185 plate sample exhibited zero plasticity, while the middle region, which is free of the omega-phase (ω), demonstrated significant tensile ductility (20 ± 2 %) and strength (1042 ± 13 MPa). The formation of each phase is elucidated using simulated temperature evolution profiles in the plate sample. Furthermore, we show that converting the isothermal omega-phase into the athermal omega-phase (ωath) through beta-annealing and water quenching restores tensile ductility.

Experimental and numerical study of the liquid nitrogen accumulator based on two-phase thermal stratification

Accurate control and rapid regulation of the liquid nitrogen supplying pressure are the basis for the total temperature operation of the cryogenic wind tunnel. The pressure evolution during the discharging process and external pressurization in an accumulator are measured experimentally. The thermal boundary conditions of the tank during the test are mathematically obtained with the consideration of frosting and convective heat transfer. A numerical framework of two-phase flow based on the volume of fluid (VOF) and the heat and mass transfer model is carried out. The computed results with the accommodation coefficient of β = 10−6 in the Lee model are closer to the measured values than using the original value of 0.1, and the laminar model is more suitable for the numerical study of the gas-liquid transfer in the tank than the turbulent model. The growing dynamic process of gas-liquid interface and temperature distribution during the entire test is achieved. Thermal stratification is formed though the coming liquid nitrogen is highly subcooled. The liquid level has not been stable immediately but grows slowly when the pressure reaches the set value. The simulated temperature evolution, distribution, and the final volume fraction of gaseous nitrogen are satisfactorily consistent with the experiments. The results show that the numerical model can simulate the complex heat and mass transfer characteristics inside the cryogenic accumulator and provide theoretical guidance for injection pressure control.

Early-age heat flow and hydration in cementitious composites: numerical modelling based on temperature measurements

The heat generated during early age cement hydration causes a semi-adiabatic temperature rise of hardening concrete, while starting to develop its physical and mechanical properties. As a matter of principle, the heat generated by the hardening mixture depends on the cement properties and its hardening conditions like for instance the type of binders, quality of aggregates, water-to-cement ratio and type of formwork. A simple 1D numerical model can be formulated for simulating the evolution in time of this reaction, in order to identify the so called degree of hydration. The present paper proposes a detailed description of a theoretical approach which allow to assess the temperature development occurring in concrete elements at the early-age when the produced mixture is cured in semi-adiabatic boundary conditions. In this numerical procedure, the differential heat equation takes into account the heat that liberates to the environment through the formwork or concrete’s surface. This is done by considering the Arrhenius Principle and assuming a pre-defined shape of the adiabatic hydration curve of the concrete mixture. Hence, an indirect identification procedure of the aforementioned adiabatic curve is ideally carried out, as the simulated temperature evolution in semi-adiabatic conditions is brought to match the temperature measurements on a hardening concrete sample. This modelling procedure, enabling various boundary conditions, ranging from semi-adiabatic to isothermal, can be used to calculate the degree of hydration of a real in-situ cast concrete. Specifically, considering the variation of concrete strength class and element size some possible applications are proposed: this represents a simplified approach for the prediction of the temperature time-evolution in the concrete elements at early-age which may be also used as a practical tool for mitigating the risk of premature cracking.

Thermo-chemo-mechanical characterization, modeling, and analysis of hydration of calcium-sulfoaluminate cement paste

The reaction kinetic of a commercial calcium sulfoaluminate (CSA) cement was characterized by heat flow calorimetry. Distinct behavior is observed whether tartaric acid is added as retarding agent or not. Employing the so-obtained calorimetric data, heat of hydration and chemical affinity of the investigated binder mixture was determined. Furthermore, continuous ultrasonic propagation velocity measurement gave access to the stiffness gain of paste samples. However, the ultrasonic test setup is characterized by a non-constant temperature history (temperature rise and fall). Modeling the temperature history and the history of the degree of hydration with a thermo-chemical analysis scheme, the intrinsic material function of the stiffness evolution of the investigated hydrating CSA paste was obtained. Furthermore, the robustness of the thermo-chemical analysis scheme was demonstrated by the comparison of the measured with the simulated temperature evolution. The versatility of the approach may contribute to a systematic assessment and optimization of the heat/mechanical evolution of CSA binder systems under various geometric, temporal, and thermal boundary condition.

Fused Filament Deposition of PLA: The Role of Interlayer Adhesion in the Mechanical Performances.

A set of criteria to enhance mechanical performances of standard specimens (Type V, ANSI D368) made of polylactic acid (PLA) were proposed. Fused PLA deposition was conducted with nozzle temperature ranging from 180 to 230 °C and deposition plate temperature ranging from 70 to 110 °C. Optical microscopy, elastic modulus analysis and density measurement allowed emphasizing the effect of temperature field, also measured during the process, on the morphology and the mechanical characteristics of the specimen. Atomic force microscopy revealed a morphology typical of amorphous samples with globular structures. Poor interlayer adhesion was detected in the part of the specimen located at larger distance from the deposition plate, showing an elastic modulus lower than those measured in the central part (220 MPa vs. 500 MPa). The specimen crystallinity degree was below 3%. The molecular weight between entanglements was adopted as a measure of the interlayer molecular diffusion. A successful diffusion and re-entanglement of the polymer melt at the interface was the key to improving mechanical performance. A mathematical model describing the transient heat transfer during the fused PLA deposition and accounting for solidification and the nonisothermal crystallization kinetics was introduced. Simulated temperature evolutions were consistent with the experimental ones. They were related to the mechanical performances, the morphology, and the molecular weight between entanglements of the parts.

A general IHTC model for hot/warm aluminium stamping

Different hot and warm stamping technologies with particular processing parameters were applied to deform aluminium alloy sheets to satisfy desired requirements, of which the post-form strength of formed components is one of the most important criteria. In order to save experimental efforts, the present research described an efficient method to determine the critical processing parameters, i.e. the integration of the finite element (FE) simulated temperature evolutions with the continuous cooling precipitation (CCP) diagrams of the aluminium alloys. Through the optimisation of the processing parameters, the temperature evolutions and CCP diagrams do not intersect, indicating that the post-form strength of the aluminium alloys could be fully retained after proper artificial ageing processes. Therefore, a precise FE simulation of the temperature evolution is of great importance to this method, which requires the implementation of an accurate interfacial heat transfer coefficient (IHTC) as a decisive boundary condition. A general aluminium alloy-independent model with one set of fixed model constants was therefore developed to predict the IHTC evolutions as a function of contact pressure, surface roughness, initial blank temperature, initial blank thickness, tool material, coating material and lubricant material. Subsequently, the predicted IHTCs for AA6082 and AA7075 aluminium alloys were used to simulate their temperature evolutions, which were then integrated with their CCP diagrams to identify the critical processing parameters in hot/warm stamping processes and thus meet the desired post-form strength of the AA6082 and AA7075. The developed IHTC model and determined critical processing parameters were then experimentally verified by the Fast light Alloy Stamping Technology (FAST) of the dissimilar aluminium alloy blanks joined by Friction Stir Welding (FSW).

The effect of thermo-elastic stress re-distribution on geothermal production from a vertical fracture zone

Injection of cold water into fracture zones in Enhanced Geothermal Systems (EGS) induces contractive thermo-elastic strains in the host rock, locally altering the stress state of the reservoir. Building on previous studies with horizontal fractures we examined how such thermo-elastic effects act during injection and production from a doublet intersecting a vertically extensive fracture zone embedded in impermeable host rock with a vertical geothermal gradient and with vertical aperture variations in response to stress increase with depth. As in horizontal fracture zones, contractive strains propagate outward from point of injection of cold water and are surrounded, due to stress re-distribution, by a ring zone with increased effective normal stress and, therefore, reduced aperture. The reduced aperture ring affects production temperature evolution to different degrees: for fracture zones with initially homogeneous transmissivity the effect on temperature decline is most pronounced for injection in the deeper well while it is small to negligible for injection in the shallower well. Fractures zones with initially heterogeneous transmissivity distribution experience highly channelized flow and the enhanced normal stresses develop preferentially at the sides of the channels, having little effect on flow along the channel and temperature decline. The effects show systematic variation with the rock's Young's modulus as does the tendency to induce shear failure by thermo-elastic effects. The simulated temperature evolutions deviate significantly from previous models that assessed the economics of EGS with sub-horizontal wells intersecting vertically extensive fractures in which the geothermal gradient and thermo-mechanical were not included.

Modeling of the Injection Molding Process Coupled with the Fast Mold Temperature Evolution

The modulation of mold temperature during injection molding is a strategic issue since it allows modulating/calibrating interesting properties of the moldings. In this work, thin heating devices were layered on the cavity surface allowing its fast temperature evolution between injection and cooling channels temperatures. The heating devices were made by a conductive layer between two insulating layers with thicknesses selected in order to realize a heating/cooling cycle as fast as possible. Several tests were performed, injecting polypropylene (iPP), using different heating powers and heating times to analyze the effect of the fast cavity surface temperature evolution on the molding morphology and properties. The heat transfer through the mold was modeled, accounting for the Joule effect in the conductive layer of the heating devices. To validate the proposed modeling of the heat exchange during the process, the simulated temperature evolutions at the polymer–cavity and the heating device–mold interfaces were satisfactorily compared with the experimental ones recorded during the tests conducted adopting different mold temperature evolutions. Furthermore, pressure evolutions during the process recorded in different position along the flow path were satisfactorily compared with the simulated ones to validate the predictions of the thermo–mechanical histories experienced by the polymer.

Temperature Covariance in Tree Ring Reconstructions and Model Simulations Over the Past Millennium

AbstractSpatial covariance in the simulated temperature evolution over the past millennium has been reported to exceed that of multiproxy‐based reconstructions. Here we use tree ring‐based temperature reconstructions and state‐of‐the‐art climate model simulations to assess temporal changes in Northern Hemisphere intercontinental temperature covariance during the last 1000 years. Tree ring‐only approaches reveal stronger agreement with model simulations compared to multiproxy networks. Although simulated temperatures exhibit a substantial spread among individual models, intercontinental temperature coherency is mainly driven by the cooling of large volcanic eruptions in 1257, 1452, 1600, and 1815 Common Era. The coherence of these synchronizing events appears to be elevated in several climate simulations relative to their own unforced covariance baselines and in comparison to the proxy reconstructions. This suggests that some models likely overestimate the amplitude of abrupt summer cooling in response to volcanic eruptions, particularly at larger spatial scales.

Determination of the interfacial heat transfer coefficient for a hot aluminium stamping process

The interfacial heat transfer coefficient (IHTC) is an important thermophysical parameter in hot stamping processes and must be identified not only to retain the full mechanical strength of formed components, but also to optimise the production rate. In this work, a novel experimental facility was developed and applied to measure the temperature evolutions of the specimens and tools in stamping processes. Simulated temperature evolutions obtained using the FE software PAM-STAMP were then fit to this data. The IHTC values between AA7075 and three different tool materials were characterized at different contact pressures under both dry and lubricated conditions. In addition, a mechanism based IHTC model was developed and validated as a function of contact pressure, tool material and lubricant thickness to predict the IHTC values under different conditions.

Linear viscoelastic properties of extruded amorphous potato starch as a function of temperature and moisture content

The effects of temperature and moisture content on the linear viscoelastic behavior of extruded amorphous potato starch were studied using dynamic mechanical analysis (DMA) from the glassy to the rubbery state. Sinusoidal tensile tests were carried out in multifrequency mode in the range of 0.1–40 Hz, with a temperature ramp of 20 to 135 °C. The water loss during DMA thermal scanning was evaluated by gravimetric analysis of batch sampling in parallel experiments that simulated temperature evolution. Loss and storage moduli were then corrected on real moisture content. Using the time–temperature superposition principle, master curves were obtained for loss and storage moduli over 18 decades in frequency. The generalized Maxwell model, in the form of a Prony series obtained from master curve fitting, was used to predict the relaxation modulus. Results showed that the relaxation modulus varied over a wide range, from 2650 MPa (t = 10−2 s, 20 °C, 8 % w.b.) to 0.16 MPa (t = 105 s, 95 °C, 16 % w.b.). The obtained constitutive equation was effective to predict the linear viscoelasticity behavior of potato starch in a wide range of thermomechanical conditions, as shown by the results of simulations of tensile experiments using finite elements.

Modelling of thermal processes during extrusion based densification of agricultural biomass residues

Biomass residues are increasing their share as a feedstock for renewable heat and power systems. Agricultural biomass is available in large quantities but to be utilised in energy systems the bulk density of the material should be increased. A large number of process parameters influence biomass compression and thus affect machinery efficiency and particular energy consumption. Increased concerns related to energy efficiency and environmental impacts of agricultural machinery have led to an increased interest in simulation models which can be used for process optimisation. In this study the influence of temperature on the biomass compression process performance has been analysed. For this purpose, mathematical models describing the thermal processes in the biomass material and the surrounding compression chamber have been elaborated. The heat transfer in the biological material has been described with time dependent Navier–Stokes equations for non-isothermal flow, while time dependent Navier–Stokes equations for heat transfer in solids have been utilised to describe heat transfer in metal structures of the chamber. The prediction performance of the model has been verified by comparing the simulated temperature evolution in the biomass and chamber walls to the corresponding values measured from a biomass compression machine through dedicated tests. The model was found to be able to predict the measured values with an average R2 of 0.82. The influence of friction heat in the compression chamber has been simulated and heat losses during the process have been estimated. The developed simulation model has been used to make suggestions for process improvement.

Numerical analysis of temperature distribution during ultrasonic welding process for dissimilar automotive alloys

Ultrasonic welding is attracting increasing attentions in lithium battery joining in the field of battery electric vehicle manufacturing. A three-dimensional finite element model was constructed to study the temperature distribution and heat generation in ultrasonic welding process. Numerical analysis showed that heat generation from plastic deformation accounts for nearly a quarter of the whole heat generation (material plastic deformation and interface friction). The fraction changes little with different sequence of specimens. The highest temperature locates at the contact interface of specimens and it is much lower than the melting point of the joining materials. Temperature distribution of the structure is not symmetric, and there are abnormal points under the effect of serrated ridges of sonotrode tip. Welding process can be divided in to three periods based on temperature evolution on the contact interface of lower specimen. The proposed model is validated by comparing simulated temperature evolution with experimental result.

Thermal–hydraulic analysis of the cool-down for the ITER magnets

A 3D time-dependent cool-down simulation for the ITER magnet system has been performed. The total cold mass of the magnet system is about 10,130ton, namely 18 Toroidal Field Winding Packs and their mechanical Cases, 6 Poloidal Field coils, Central Solenoid and a set of Correction Coils. All ITER coils are made from cable-in-conduit conductor superconductors. This paper presents the simplified flow scheme of the magnet system and the simulation models. The simulated temperature evolutions of entire processes of cool-down are showed. The functions of the inlet temperature for cool-down are summarized. The simulation results indicate that it is possible to cool down the entire ITER magnet system to 6K within 750h.

Unsteady nanoscale thermal transport across a solid-fluid interface

We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar–Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solidlike interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance Rk,av decreases as the imposed wall temperature Tw is increased, as Rk,av∝Tw−4.8. The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity.

3D simulations of heat transfer and liquid flow during sterilisation of large particles in a cylindrical vertical can

Transient temperature and fluid flow during natural convection heating of a cylindrical can containing large food particles is simulated. The three dimensional equations of mass, momentum and energy conservation are solved using the finite volume method. A can (11 cm high and 10 cm in diameter) containing nine spherical particles (45 mm in diameter) is considered. Two meshes are tested. The first uses 1,650,000 tetrahedral cells. The second uses only 95,000 cells but with smaller prismatic cells near the can walls in order to better take into account the boundary layer phenomena. The simulated temperature evolutions in the liquid and at the centre of the particles obtained with the second grid are in good agreement with the experimental results. The liquid flows upwards in a thin boundary layer (about 2 mm thick) and flows downwards in the interstice between the particles. Due to thermal stratification, the slowest heating is for the particles at the bottom of the can.

Absolute dose calibration in PIII

Accurate absolute dose measurements are still a challenge in plasma immersion ion implantation (PIII). Here, a contact-free method using a pyrometer and the sample as a thermal probe is presented. Good agreement between simulated temperature evolutions and measurements were obtained, allowing a direct determination of the incident ion flux. However, using the whole sample holder as the probe introduces errors due to lateral dose inhomogeneities and a finite thermal conductivity. Nevertheless, the accuracy is sufficient for tribological high dose applications. More demanding standards for semiconductor industry could be met using a small, thermally isolated patch in the center of the sample.

Absolute dose calibration in PIII

Accurate absolute dose measurements are still a challenge in plasma immersion ion implantation (PIII). Here, a contact-free method using a pyrometer and the sample as a thermal probe is presented. Good agreement between simulated temperature evolutions and measurements were obtained, allowing a direct determination of the incident ion flux. However, using the whole sample holder as the probe introduces errors due to lateral dose inhomogeneities and a finite thermal conductivity. Nevertheless, the accuracy is sufficient for tribological high dose applications. More demanding standards for semiconductor industry could be met using a small, thermally isolated patch in the center of the sample.