Thermal Finite Element Simulation Research Articles

Thermal shock resistance of γ-Y2Si2O7/Y2O3-Al2O3-SiO2 coating for porous Si3N4 ceramics

A double-layer γ-Y2Si2O7/Y2O3-Al2O3-SiO2 glass coating on porous Si3N4 ceramic was fabricated by melt-infiltration/sintering (MIS) method, and its thermal shock behavior was investigated by rapid quenching thermal shock tests and transient finite element simulation method. Coupling effects of coating microstructure and mechanical properties on the thermal shock behavior were discussed. Results show that thickness of the bonding layer and Young's modulus of the surface layer play a decisive role in thermal stress during the thermal shock process. The coating with lower Young's modulus and thicker bonding layer shows better comprehensive performance.

Thermal histories and microstructures in Direct Energy Deposition of a High Speed Steel thick deposit

The results of 2D Finite Element thermal simulations of Direct Energy Deposition of a High Speed Steel thick deposit explain the observed microstructural heterogeneities over the whole height of a 36-layer deposit. The Finite Element model is validated by the recorded substrate temperature and the melt pool depth of the last clad layer experimentally measured. The correlation between the computed thermal fields and the microstructures of three points of interest located at different depths within the deposit is carried out. The effect of both the melt superheating temperature and the thermal cyclic history on the carbides type, shape and size is discussed.

Finite Element Thermal Simulations for the Design of Mold Conformal Heating Channels Manufactured by 3D Printing Sand Casting for Molding of EPDM Rubber

This paper presents an application of Additive Manufacturing (AM) technology that is suitable for manufacturing molding tools with conformal heating channels to increase productivity for EPDM rubber molding. The design and the manufacturing of a molding tool by combining 3D sand printing and casting processes was analyzed. A simplified finite element thermal analysis was used to optimize the EPDM molding cycle time of an automotive hood seal. The simulation results showed that by using a mold with conformal heating channels manufactured by 3D printing sand casting, the cycle time process of EPDM can be reduced by 41.5%.

A combined experimental and numerical examination of welding residual stresses

This study examines residual stresses in bead-on-plate welded specimens in transverse direction over the thickness of the plate, using a combination of experimental and numerical procedures. Dilatometer and tensile tests were used to determine the phase transition temperatures with associated volumetric strains and the stress-strain relationships of the S355G10 + M base material. Temperature profiles have been measured during welding. Residual stresses of the base plate and the welded specimen were determined with the crack compliance method. The thermal (finite element) simulations used the measured material parameters as input and the experimentally obtained temperature profiles were used as calibration data for the welding process. The residual stress predicted by the subsequent mechanical simulations were compared with the measured residual stress and a good agreement was obtained. This study demonstrates the importance of using correct phase transition temperatures and volumetric strains in simulations of residual stresses.

Novel solder-mesh interconnection design for power module applications

Abstract This study introduces a novel concept that uses composite structures of thin metallic meshes and Sn3.0Ag0.5Cu (SAC305) solder alloys to interconnect semiconductor chips to DBC substrates. The feasibility was proven by bonding Cu-to-Cu substrates. The averaged shear strength was measured as 44.1, 44.7 and 51.4 MPa for samples bonded with SAC305 (reference), Ni mesh/SAC305 and Cu mesh/SAC305 composites, respectively. The solder-mesh joints revealed a specific fracture behavior where crack propagation occurred partly within the solder and partly at the solder-mesh interface. Microstructural analyses confirmed that the metallic meshes were bonded by the formation of intermetallic compounds (IMC) while almost no (larger) defects were found. The solder-mesh concept was subsequently applied on Si-to-DBC assemblies. A very good resistance of Cu mesh/SAC305 composite joints against cyclic temperature between 80 and 200 °C was observed when the bonded area only reduced by 4.2 % after 8000 cycles. Thermal finite element (FE) simulations indicated that in particular Cu mesh/SAC305 composites can significantly reduce the thermal resistance of the interconnections which is equivalent to a better heat dissipation through the bonding layer. Thus, solder-mesh composite joints seem to be an attractive solution for high-temperature applications up to 200 °C.

Influence of weld-induced residual stresses on the hysteretic behavior of a girth-welded circular stainless steel tube

The present study attempts to characterize the relevance of welding residual stresses to the hysteretic behaviour of a girth-welded circular stainless steel tube under cyclic mechanical loadings. Finite element (FE) thermal simulation of the girth butt welding process is first performed to identify the weld-induced residual stresses by using the one-way coupled three-dimensional (3-D) thermo-mechanical FE analysis method. 3-D elastic-plastic FE analysis equipped with the cyclic plasticity constitutive model capable of describing the cyclic response is next carried out to scrutinize the effects that the residual stresses have on the hysteretic performance of the girth-welded steel tube exposed to cyclic axial loading, which takes the residual stresses and plastic strains calculated from the preceding thermo-mechanical analysis as the initial condition. The analytical results demonstrate that the residual stresses bring about premature yielding and deterioration of the load carrying capacity in the elastic and the transition load ranges, whilst the residual stress effect is wiped out quickly in the plastic load domain since the residual stresses are nearly wholly relaxed after application of the cyclic plastic loading.

Underwater Robotic Welding of Lap Joints with Sandwiched Reactive Multilayers: Thermal, Mechanical and Material Analysis

ABSTRACTUnderwater welding using reactive materials pre-deposited at the junction surfaces as a self-contained, in-situ ignitable heat source mitigates external power and gas supply requirements. Consequently, lending itself to robotic implementation eliminating the cost along with health and safety hazards of human welder-divers. This project reports on lap joining of aluminum sheets with sandwiched commercial reactive Ni-Al multilayers that are perforated to allow for melt fusion under compression upon ignition, in saline and deionized water as well as air for comparison. Finite-element thermal simulations are employed to study the resulting welding temperature field and melt conditions. Infrared pyrometry and thermocouple measurements during welding were used to validate the computational simulations. The lap joints are subjected to standard shear testing, and comparable compliance, strength and toughness values of the welds are assessed for underwater and dry joints. Scanning electron (SEM) of the weld sections reveal rapidly melting and solidifying microstructures of the parent metal, with minimal melt flow and perfusion of nickel aluminide aggregates from the reacted multilayers, and no signs of cavitation.

The thermal conductivity of cortical and cancellous bone.

Surgical interventions close to vulnerable structures, such as nerves, require precise handling of surgical instruments and tools. These tools not only pose the risk of mechanical damage to soft tissues, but they also generate heat, which can lead to thermal necrosis of bone or soft tissues. Researchers and engineers are trying to improve those tools through experimentation and simulations. To simulate temperature distributions in anatomical structures, reliable material constants are needed. Therefore, this study aimed at investigating the thermal conductivity of cortical and cancellous bone. Accordingly, a custom-made steady-state experimental setup was designed and validated. 6 bovine and 3 human cortical bone samples, as well as 32 bovine cancellous bone samples, with variable bone volume fraction were tested. The cancellous bone samples were scanned by micro-computed tomography (µCT) and micro-finite element (µFE) voxel models were created to calculate iteratively the thermal conductivity of the bone marrow. The experimental results provided 0.64 ± 0.04 W/mK for bovine cortical bone and 0.68 ± 0.01 W/mK for human cortical bone. A linear dependency of thermal conductivity on bone volume fraction was found for cancellous bone [R-square (R2) = 0.8096, standard error of the estimates (SEE) = 0.0355 W/mK]. The thermal conductivity of the bone marrow was estimated to be 0.42 ± 0.05 W/mK. These results will help to improve thermal finite element simulations of the human skeleton and aid the development of new surgical tools or procedures.

Analysis of a Dry-type Reactor Fault Based on COMSOL Thermal Field Simulation and High Frequency Pulse Oscillations

For a single-phase earth fault of 35 kV dry-type reactor, the 5th package area is found with serious turn-to-turn short circuit after it conducts the DC resistance test, turn-to-turn insulation test of high frequency oscillation pulse and rework disassembly. The turn-to-turn short circuit of resistance will lead to wire fusing, which makes the conventional pre-test projects have limitations. With COMSOL finite element thermal field simulation of the fault 35kV dry-type reactor, the temperature distribution result of the reactor indicates that the hottest point is at the 6th package during the reactor operation and the temperature rises 73.75K. In addition, the temperature rises of the 5th, 7th, 14th, 15th package is also higher than other packages, which easily causes device failure due to insulation deterioration. Through the analysis and thermal field simulation of the test for failed reactor, it can provide the reference basis for equipment design, manufacture, daily repair and maintenance.

Hybrid simulation of laser deep penetration welding

AbstractIn laser deep penetration welding, the knowledge on the temperature history of the material is of great interest for the assessment of the quality properties of the weld. For this purpose a hybrid process model that enables the fast calculation of temperature distributions as a function of process parameters is applied. The interaction between laser and material is taken into account by a reduced keyhole model, which exploits a hierarchy in the spatial dimensions occurring at high feed rates. The resulting shape of a stationary keyhole is introduced as a Dirichlet boundary into a thermal finite element simulation in which it is moved through the workpiece according to the process control of the laser beam. The boundary is mathematically described by a level set function and immersed in a fixed computational mesh. The Dirichlet boundary condition is imposed using an embedded boundary method. The calculated temperature distributions are evaluated by means of bead on plate welds conducted in 0.9 mm thick sheets of 1.4301 (AISI 304) stainless steel.

Nanoscale temperature of plasmonic HAMR heads by polymer imprint thermal mapping

ABSTRACT Polymer imprint thermal mapping (PITM) is a high-resolution thermal mapping technique that is especially valuable for nanoscale plasmonic devices. PITM leverages a ∼50 nm polymer film coating that crosslinks irreversibly with temperature, which records the peak temperature rise of the surface in the local, linear reduction of polymer film thickness. Using AFM to measure topography before and after heating, but not during operation, PITM sidesteps plasmonic artifacts seen in other near-field thermometries, where the probe tip disturbs and is heated directly by the near- and far-field radiation around the plasmonic device. This is notably troublesome for characterizing heat-assisted magnetic recording (HAMR) heads for next-generation hard disk drives. HAMR heads use near-field transducers (NFTs) to focus light on a magnetic media, heating a nanoscale region to its Curie temperature to enable magnetic writing. The PITM proof-of-concept was introduced at The Magnetic Recording Conference (TMRC) in 2015: here, we present a mature technique capable of benchmarking finite-element thermal simulations of nanoscale devices.

Significant enhancement of metal heat dissipation from mechanically exfoliated graphene nanosheets through thermal radiation effect

We demonstrate a facile approach to significantly enhance the heat dissipation potential of conventional aluminum (Al) heat sinks by mechanically coating graphene nanosheets. For Al and graphene-coated Al heat sinks, the change in temperature with change in coating coverage, coating thickness and heat flux are studied. It is found that with the increase in coating coverage from 0 to 100%, the steady-state temperature is decreased by 5 °C at a heat flux of 1.8 W cm-1. By increasing the average thickness of graphene coating from 480 nm to 1900 nm, a remarkable temperature reduction up to 7 °C can be observed. Moreover, with the increase in heat flux from 1.2 W cm-1 to 2.4 W cm-1, the temperature difference between uncoated and graphene-coated samples increases from 1 °C to 6 °C. The thermal analysis and finite element simulation reveal that the thermal radiation plays a key role in enhancing the heat dissipation performance. The effect of heat convection remains weak owing to the low air velocity at surface-air boundary. This work provides a technological innovation in improving metal heat dissipation using graphene nanosheets.

Progressive inelastic deformation of a girth-welded stainless steel pipe under internal pressure and cyclic bending

This study aims to characterize numerically the ratcheting behavior of a girth-welded straight stainless steel pipe in combined action of internal pressure and cyclic bending loading. Finite element (FE) thermal simulation of the girth butt welding process is first performed to identify weld-induced residual stresses. Three-dimensional (3-D) elastic-plastic FE analyses incorporated with the cyclic plasticity constitutive model capable of describing the cyclic plastic performance are next conducted to scrutinize the local (circumferential strain) and global (cross-section diameter change) ratcheting responses of the girth-welded stainless steel pipe under internal pressure and cyclic bending, which take the residual stresses and plastic strains obtained from the preceding thermal simulation as the initial condition. The analytical results demonstrate that welding residual stresses in combination with the internal pressure have significant effects on the hoop strain rate and the in-plane and out-of-plane diameter changes, and the degree and shape of the ovalization which occurs during the multiaxial ratcheting are dependent on the applied loads.

The influence of the phosphor layer as heat source and up-stream thermal masses on the thermal characterization by transient thermal analysis of modern wafer level high power LEDs

In the last years Waver Level LED Packages (WLP-LEDs) were developed. They are thin film flip chips where the sapphire substrate remains attached on top of the epitaxial light emitting layer (EPI) which can be assembled directly on a printed circuit board. The thermal resistance and the thermal path of WLP-LED packages are measured by transient thermal analysis and transient finite element simulation. This study investigates the impact of the upstream thermal masses, i.e. the sapphire (SP), phosphor layer (PL) and the side coating (SC) on the transient thermal impedance curve and the cumulative structure function. It is shown that the standard approach to extract thermal properties by features (steps) within the structure function is misleading for thermal networks with upstream thermal load and distributed heat source (EPI and PL) because they influence the shape of the structure function. By transient thermal measurements and finite element (FE) simulation the transient thermal measurements are analysed to extract information about the thermal parameters and the thermal path. Starting from the analysis of the blue flip chip LED (FC-LED, no PL and no SC) the FE-model is set up. Stepwise the FE model is extended and the influence of the PL and the SC on the transient thermal measurement is investigated. A FE model is validated and calibrated which allows simulating the transient thermal curves of these modern LEDs. Using the model the impact of structural changes in the LED package on the transient thermal curves can be identified for reliability analysis.

Wafer level measurements and numerical analysis of self-heating phenomena in nano-scale SOI MOSFETs

We present an experimental technique and a Finite Element thermal simulation for the determination of the temperature elevation in Silicon on Insulator (SOI) MOSFETs due to self-heating. We evaluate the temperature elevation in two steps, as we calibrate the gate resistance over temperature with the transistor at off state at a first stage, and then we deduce the temperature elevation through gate resistance measurements. We simulate the self-heating phenomena in a Finite Elements Method (FEM) environment, both with 2D and 3D models. In order to set up the simulations, we weight the effects of several parameters, such as thermal material properties, the modeling of heat generation and a careful setting of boundary conditions. We present typical temperature fields and local heat fluxes, thus giving concrete indications for solving thermal reliability issues. Simulation results show temperature elevations up to approximately 120K in the hot spot, 70K in the gate and 7K in the Back End of Line (BEoL). The 3D model gives results that are satisfying over the whole set of MOSFETs we consider in this work. Temperature elevation strongly depends on physical dimensions, where transistors endowed with shorter gates suffer from more severe self-heating. We propose a simplified model based on geometrical parameters that predict maximum and gate temperatures, obtaining satisfying results. Since correlation with measurements confirms the correctness of our model, we believe that our simulations could be a useful tool to determine accurate reliability rules and in a context of thermal aware design.

Macroscopic simulation and experimental measurement of melt pool characteristics in selective electron beam melting of Ti-6Al-4V

Selective electron beam melting of Ti-6Al-4V is a promising additive manufacturing process to produce complex parts layer-by-layer additively. The quality and dimensional accuracy of the produced parts depend on various process parameters and their interactions. In the present contribution, the lifetime, width and depth of the pools of molten powder material are analyzed for different beam powers, scan speeds and line energies in experiments and simulations. In the experiments, thin-walled structures are built with an ARCAM AB A2 selective electron beam melting machine and for the simulations a thermal finite element simulation tool is used, which is developed by the authors to simulate the temperature distribution in the selective electron beam melting process. The experimental and numerical results are compared and a good agreement is observed. The lifetime of the melt pool increases linearly with the line energy, whereby the melt pool dimensions show a nonlinear relation with the line energy.

Rapid Degradation of Mid-Power White-Light LEDs in Saturated Moisture Conditions

Serious silicone carbonization has been reported in mid-power white-light LEDs during highly accelerated temperature and humidity stress test, although the junction temperature of the LED chip is much lower than the critical temperature of silicone carbonization (300 °C). This paper presents a comprehensive investigation, through which the effects of Joule heating and phosphor self-heating have been eliminated as main failure mechanisms. As a result, the over-absorption of blue lights by silicone bulk is considered as the root cause for silicone carbonization. This is mainly due to the scattering effect of water particles inside the silicone materials, which can increase the silicone temperature significantly. Furthermore, finite-element thermal simulation has also been performed, confirming the validity of the failure mechanism.

Optimized Thermal Performance Design of Filled Ceramic Masonry Blocks

Clay brick as building material has been used for thousands of years. Nowadays, the energy performance of new products has to meet rigorous requirements, therefore in design of fired clay blocks, building physical calculations and optimization are essential. The aim of this research is to design optimized fired clay building blocks using numerical finite element thermal simulations supported by laboratory tests. The paper analyses 38 cm or 44 cm thick hollow building blocks occurring nowadays in the industry, taking into account of single blocks as well as tongue and groove connections. The study compares blocks having different internal structures: rhomboid, triangular and small or big rectangular gaps. It also deals with the effect of different fillings: air, expanded perlite, mineral wool, polyurethane (PUR) foam and aerogel. During the research, 20 different masonry elements were analysed using the above-listed varying parameters and the equivalent thermal conductivities were compared.

Experimental and numerical study of frictional heating during rapid interactions of a Ti6Al4V tribopair

Frictional work dissipated into a pair of bodies in contact can lead to the generation of high temperatures at the interface. For extreme conditions, knowledge of such temperatures is indispensable for predicting material damage. Friction experiments have been performed for a Ti6Al4V tribopair on a ballistic bench at elevated sliding velocities and at high normal pressure (V0=43–65m/s and p=110MPa). A specific foil-workpiece thermocouple was developed to measure interface temperature; it was determined that such a sensor is particularly well-adapted to severe interaction conditions (very short response times, adhesive wear and high plastic strain). The experimental study shows that under such extreme conditions, sliding velocity effects on maximum temperatures reached are quite negligible. Using experimentally measured friction coefficients, thermal finite element simulations were performed to examine thermal fields along a sliding path. The temperature and thickness of the heat-affected zone are in good agreement with our postmortem SEM observations, indicating that wear phenomena do not modify the temperature field. A complex partition of heat flux is observed due to differences in the temperatures of the bodies in contact, being accentuated by temperature dependent thermal diffusivity of the Ti6Al4V alloy. Based on these partition coefficients, gradients of dissipated energy along the sliding path are determined.

Analysis of solder joint reliability of high power LEDs by transient thermal testing and transient finite element simulations

An innovative sensitive test method is developed to detect solder joint cracking for high power LED packages. The method is based on transient thermal analysis and can fully replace the still dominating light-on test. For experimental application of the model, test groups of LED packages were soldered with two different lead free solders (SnAgCu305 and Innolot FL-640) on Aluminum Insulated Metal Substrate (Al-IMS) and exposed to temperature cycles. Transient thermal measurements were performed directly after assembly and after specific cycle numbers. After data processing the increase of the relative thermal resistance between the initial signal at “0” cycles and “n” cycles is obtained and correlated with cracks in the solder joint by cross sections. Based on the CAD and material data of the LED package a finite element (FE) model is set up. The time-resolved temperature curves are properly reproduced by transient thermal simulation. The measured “0” cycle curves are fitted using the FE model by adjusting a few material parameters within their allowed tolerance range. A parameter sensitivity analysis is performed. The impact of a crack in the solder joint between package and printed circuit board (PCB) on the time resolved temperature curve is simulated. The simulated crack propagates from the corner of the package to its center. The experimental measured curves are reproduced. Based on the simulation a failure criteria is defined, representing a crack length between 20% and 30% of the solder joint area, and Weibull curves are calculated. A higher creep resistance for the test group soldered with Innolot FL-640 compared to the test group soldered with SAC305 is observed.