Thermo-mechanical Performance Research Articles

Influence of Catalyst Content and Epoxy/Carboxylate Ratio on Isothermal Creep of Epoxy Vitrimers.

In the present work, a commercial epoxy based on epoxy anhydride and tertiary amine was modified by a metallic catalyst (Zn2+) to induce vitrimeric behavior by promoting the transesterification reaction. The effect of two different epoxy/acid ratios (1 and 0.6) at two different zinc acetate amounts (Zn(Ac)2) on the thermomechanical and viscoelastic performances of the epoxy vitrimers were investigated. Creep experiments showed an increase in molecular mobility above the critical "Vitrimeric" temperature (Tv) of 170 °C proportionally to the amount of Zn(Ac)2. A procedure based on Burger's model was set up to investigate the effect of catalyst content on the vitrimer ability to flow as the effect of the dynamic exchange reaction. The analysis showed that in the case of a balanced epoxy/acid formulation, the amount of catalyst needed for promoting molecular mobility is 5%. This system showed a value of elastic modulus and dynamic viscosity at 170 °C of 9.50 MPa and 2.23 GPas, respectively. The material was easily thermoformed in compression molding, paving the way for the recyclability and weldability of the thermoset system.

Thermomechanical evaluation and thermodynamic simulation via FactSage of NCCs and ULCCs with different MgO content

Thermomechanical properties are the most important for refractories and these give an idea about the bonding strength between the fine-grained matrix and the aggregates in the refractory body. Mentioned properties characterize the deformation of the refractories at high temperature, mainly due to the formation of the liquid phases of different quantity and viscosity. The objective of this study is to elucidate the role of the Mg-Al spinel content, stoichiometry and synthesis method on structural, microstructural, thermomechanical and other properties NCCs and ULCCs. The results show that the differences in thermomechanical performance of the ULCCs can be related to the CA6, Al2O3 and both pre-formed and in situ Al-excess Mg-Al spinel contents, whereas NCCs exhibit the best performance decreasing with an increasing the Al-rich spinel content. The thermodynamic simulation via FactSage 8.2 showed consistent results managing to indicate the effect of liquid phase on the thermomechanical properties of castables.

Alkali-treated date palm fiber-reinforced unsaturated polyester composites: thermo-mechanical performances and structural applications

Alkali-treated date palm fiber-reinforced unsaturated polyester composites: thermo-mechanical performances and structural applications

New optimum configuration for the FGM rotating disc in gas turbines using combined thermal-mechanical analysis: An analytical approach

The gas turbine is one of the most suitable equipment for various applications. Usually, a gas turbine comprises a set of discs to maintain turbine blades. The rotating disc in gas turbines is one of the critical components affected by various thermal and mechanical loads. The current article considers a new rotating disc with variable thickness (power-law profile). The functionally graded material has been used as the disc material, and the disc’s properties vary with temperature and location. Therefore, the mechanical and thermal behaviours of the disc are a function of temperature and location. The differential energy balance equation has been derived for analysing the new disc. In the performed analysis, the conduction and convection heat transfer coefficients vary with temperature and location; thus, the derived final heat transfer equation has high nonlinearity. One of the efficient expansion methods, the so-called Differential Transformation Method (DTM), is used for the governed equation’s analytical solution, and the numerical solution is used for validation. Then, the stress analysis is performed using analytical expressions according to the temperature profile. The impacts of geometrical and thermophysical characteristics on the temperature and stress distribution are evaluated using the analytical solution in the new disc. The comparison of displacement and stresses in the new FGM disc and old discs shows that the thermo-mechanical performance of the new proposed disc is improved significantly.

A continuum micromechanics model challenged to predict thermo-mechanical properties of 18 different clay bricks and sensitivity analysis revealing effects of compositional and microstructural features

Optimizing fired clay bricks to improve the thermo-mechanical performance requires a fundamental understanding of the links between brick microstructure and macro-properties. This is herein tackled by adopting a recently developed multiscale micromechanics model and challenging it with novel macroscopic test results for 18 fired clay bricks produced from seven different clays using different pore-forming additives. This comparison allows us to quantify the vitrification-induced strength increase of the microscopic binding matrix for clays with high carbonate and low illite contents. Micromechanics-based sensitivity analyses reveal optimization potentials regarding pore geometry and pore size distribution.

On quantifying uncertainty in lightning strike damage of composite laminates: A hybrid stochastic framework of coupled transient thermal-electrical simulations

Lightning strike damage can severely affect the thermo-mechanical performance of composite laminates. It is essential to quantify the effect of lightning strikes considering the inevitable influence of material and geometric uncertainties for ensuring the operational safety of aircraft. This paper presents an efficient support vector machine (SVM)-based surrogate approach coupled with computationally intensive transient thermal-electrical finite element simulations to quantify the uncertainty in lightning strike damage. The uncertainty in epoxy matrix thermal damage and electrical responses of unprotected carbon/epoxy composite laminates is probabilistically quantified considering the stochasticity in temperature-dependent multi-physical material properties and ply orientations. Further, the SVM models are exploited for variance-based global sensitivity analysis to investigate the input parameters' relative influence on the lightning strike-induced damage behavior. Due to the adoption of a coupled SVM-based simulation approach here, it has become possible to carry out a comprehensive uncertainty quantification leading to complete probabilistic descriptions of the electrical and lightning damage parameters despite the requirement of performing a large number of computationally intensive function evaluations. The results reveal that source-uncertainty of the unprotected laminates significantly influences the epoxy matrix decomposition, electrical current density and electric potential, wherein longitudinal electrical conductivity is most sensitive to stochastic variations followed by other electrical, thermal and geometric parameters.

Exploratory Thermo-Mechanical Assessment of the Bottom Cap Region of the EU DEMO Water-Cooled Lead Lithium Central Outboard Blanket Segment

The Water-Cooled Lead Lithium (WCLL) Breeding Blanket (BB) is one of the two BB concept candidates to be selected as the driver blanket for the EU DEMO fusion reactor. In this regard, the development of a sound architecture of the WCLL Central Outboard Blanket (COB) Segment, ensuring the fulfilment of the thermal and structural design requirements, is one of the main goals of the EUROfusion consortium. To this purpose, an exploratory research campaign has been launched to preliminarily investigate the thermo-mechanical performances of the Bottom Cap (BC) region of the WCLL COB segment because of its peculiarities making its design different from the other regions. The assessment has been carried out considering the nominal BB operating conditions, the Normal Operation (NO) scenario, as well as a steady-state scenario derived from the in-box LOCA accident, the Over-Pressurization (OP) scenario. Starting from the reference geometric layout of the WCLL COB BC region, a first set of analyses has been launched in order to evaluate its structural performances under a previously calculated thermal field and to select potential geometric improvements. Then, the analysis of a complete BC region was conducted from both the thermal and structural standpoints, evaluating its structural behaviour in compliance with the RCC-MRx code. Finally, after some iterations and geometric updates, a promising geometric layout of the BC region has been obtained even though some criticalities still persist in the internal Stiffening Plates and First Wall. However, the obtained results clearly showed that the proposed layout is worthy to be further assessed to achieve a robust enough configuration. The work has been performed following a theoretical-numerical approach based on the Finite Element Method (FEM) and adopting the quoted Ansys commercial FEM code.

Thermo-Mechanical Performance of Epoxy Hybrid System Based on Carbon Nanotubes and Graphene Nanoparticles.

This study focuses on epoxy hybrid systems prepared by incorporating multi-wall carbon nanotubes (MWCNTs) and graphene nanosheets (GNs) at two fixed filler amounts: below (0.1 wt%) and above (0.5 wt%), with varying MWCNT:GN mix ratios. The hybrid epoxy systems exhibited remarkable electrical performance, attributed to the π-π bond interactions between the multi-wall carbon nanotubes and the graphene layers dispersed in the epoxy resin matrix. The material's properties were characterized through dynamic mechanical and thermal analyses over a wide range of temperatures. In addition to excellent electrical properties, the formulated hybrid systems demonstrated high mechanical performance and thermal stability. Notably, the glass transition temperature of the samples reached 255 °C, and high storage modulus values at elevated temperatures were observed. The hybrid systems also displayed thermal stability up to 360 °C in air. By comparing the mechanical and electrical performance, the formulation can be optimized in terms of the electrical percolation threshold (EPT), electrical conductivity, thermostability, and mechanical parameters. This research provides valuable insights for designing advanced epoxy-based materials with multifunctional properties.

Guanine and cytosine‐containing acrylic supramolecular networks

AbstractThis manuscript describes the synthesis and characterization of guanine and cytosine‐containing supramolecular copolymers, which are inspired from the guanine and cytosine nucleobase pair in deoxyribonucleic acid. Regioselective Michael‐addition allowed the efficient installation of the nucleobases on acrylate‐containing monomers, which enabled the preparation of a series of nucleobase‐functionalized acrylate and n‐butyl acrylate copolymers using conventional free radical copolymerization. Guanine‐containing copolymers exhibited superior thermal properties, thermomechanical performance, and more defined morphological structure than cytosine‐containing copolymer analogs due to the relatively strong guanine self‐association, thus expanding the potential applications for mechanically reinforced polymeric networks. Blending guanine‐ and cytosine‐containing copolymers formed a supramolecular structure through multiple hydrogen bonding between guanine and cytosine units. The supramolecular blend exhibited intermediate thermomechanical and morphological properties, which suggested that guanine and cytosine units were not fully associated in the random copolymer composition. This work provides valuable fundamental understanding of structure–property‐morphology relationships in acrylic copolymers with the presence of guanine‐cytosine self‐ and complementary interactions, suggesting new understanding in supramolecular design for enhanced mechanical and morphological properties.

Superelastic bionic graphene/nanoceramic metamaterials with tunable thermo-mechanical performances

Limited by the intrinsic strong bonds between the composing atoms, engineering materials are plagued by the inevitable trade-offs among thermo-mechanical strength, toughness, and stability. In this work, a graphene/nanoceramic metamaterials (GNC) metamaterial was created by in-situ intercalation of Zr(WO4)2 nanoparticles within the multilayered microcell wall of a 3D hyperbolic graphene template. The bionic lamellar feature of the reduced graphene oxide (RGO)-Zr(WO4)2 sheet makes it highly ductile and stiff at the microscale, while the hyperbolic mesoscopic structure of GNC significantly enhanced the resistance to shear slip-induced fracture. 3D lightweight GNC metamaterials, therefore, exhibited synergic improvement in elastic compressibility (90%), strength (1.4 MPa), and toughness (1.62 N/m) than those of reported materials with similar architectures from either individual component or sandwiched microcell. Moreover, due to the lattice rotation of Zr(WO4)2 effectively regulated by the RGO sheet, the 3D GNC demonstrated tunable thermal expansion coefficient (TEC) as near-zero (−1.1 × 10−6 K−1), negative (−11.6 × 10−6 K−1), positive (1.2 × 10−6 K−1), and even combinations of three schemes. The resultant low thermal conductivity (∼0.007 W m−1 K−1), prior thermal shock resistance (200 K/s), and fireproof make GNC metamaterial show promise for applications in extreme conditions, such as lightweight protective filler, thermal insulator, robust damper, fire-retardant coating, thermal stress regulator, etc.

Modelling FeCrAl cladding thermo-mechanical performance. Part II: Comparative analysis with Zircaloy under LOCA conditions

The demonstration of the enhanced thermo-mechanical response of iron-chromium-aluminum (FeCrAl) cladding under any circumstances, particularly under postulated accident scenarios, requires the development of analytical capabilities. By extending FRAPTRAN-2.0 to model the instantaneous plasticity and high-temperature creep of FeCrAl, among other properties, its performance under LOCA conditions has been assessed in comparison with that of Zircaloy-4. Based on the conditions set in the IFA-650.10 test of the HALDEN project, FeCrAl has shown an enhanced thermo-mechanical response due mainly to its superior mechanical strength, which led to a significant extension of the time to failure, even with a reduced cladding thickness. This time gain is expected to be even longer given that irradiation-induced hardening (not considered in the present model) might further delay the onset of plastic deformation. This effect is planned to be implemented in the future in-house extension of FRAPTRAN-2.0.

Development of high thermal conductivity of Ag/diamond composite sintering paste and its thermal shock reliability evaluation in SiC power modules

Diamond has the highest thermal conductivity among naturally occurring materials and a relatively low coefficient of thermal expansion (CTE), making it a promising interconnected material for next-generation semiconductor power devices. In this study, Ag/diamond composite sintering paste was developed. The agglomerated diamond particles were uniformly dispersed in the sintered Ag porous structure, and the thermal conductivity was increased from 171.4 W/(m·k) for pure Ag sintering to 288 W/(m·k) for an Ag@2%diamond (2% of the total weight of Ag) specimen. The interfacial microstructure evolution and fracture behavior were investigated in detail for a SiC/Direct Bond Copper (DBC) joint structure during an extreme thermal shock test (TST) in the range of −50 °C–250 °C. Importantly, with a moderate amount of diamond additive, the microstructural degradation and severe deformation of the DBC substrate were effectively suppressed. This is mainly attributed to the diamond addition, which can block the migration pathways of Ag atoms toward long-term thermal shock and adjust the thermo-mechanical performance of the sintered layer. This detailed study about Ag/diamond composite paste can provide new guidance for strengthening sintered Ag interconnections for SiC power modules.

Thermomechanical performances of sandwich panels with multi-layer multi-row lightening holes: Comparative study on corrugated-core and X-core

Thermomechanical performances of sandwich panels with multi-layer multi-row lightening holes: Comparative study on corrugated-core and X-core

Multi-objective optimization design of TRISO-based fully ceramic microencapsulated fuel

Fully Ceramic Microencapsulated (FCM) fuel is a new type of material in nuclear energy field. It has become a promising accident tolerant fuel (ATF) candidate due to its advantages of high radiation stability, high fission product containment capacity and excellent thermo-mechanical performance. During operation, the temperature, stress, deformation and other key parameters will change significantly, which directly affect the safety of nuclear reactor. Therefore, it is necessary to carry out a multi-physics fully-coupled analysis suitable for the multi-scale, multi-component, multi-phase and nonlinear coupling processes in the reactor, so as to sort out the influences of material properties, radiation behavior, thermo-mechanical performance from numerous influencing factors. In this paper, based on the irradiation-thermo-mechanical coupling method, the performance of TRISO-based FCM fuel under irradiation conditions was analyzed, key thermo-mechanical parameters and other influencing factors of the fuel were obtained, failure behavior of the fuel element was evaluated. On this basis, the theoretical and numerical model of multi-objective optimization method were established, the optimum parameters including material properties, fuel geometry and particle arrangement were found by optimization method. The optimization results showed that the multi-objective optimization results could provide multiple Pareto optimal solutions for the FCM fuel. Specifically, when the TRISO particle spacing is 200 µm and 150 µm, the objective function difference between the optimal heat transfer solutions is only about 1.7%, meanwhile the mechanical properties vary significantly (the difference between the objective functions of the optimal solutions is about 12.4% ∼26.5%), indicating the response of stress is more sensitive than temperature. When the TRISO particles are tightly packed (particle spacing less than 100 µm), the difference of objective function between the optimal solutions is less than 5%, illustrating the optimization has limited improvement on the thermo-mechanical performance of the fuel, namely the optimization space is limited.

Thermomechanical performance of energy retaining pile influenced by surrounding utility tunnel via the regression tree model

The thermomechanical performance of energy retaining pile differs from that of axisymmetric energy pile due to utility tunnel excavation. This study presents four field tests of energy retaining pile conducted before and after utility tunnel construction. A regression tree (RT) model for predicting the thermally induced stress of energy retaining pile was established based on the measured water temperature, pile temperature and previous stage thermally induced stress to evaluate the effect of shallow buried utility tunnel on the thermomechanical performance of adjacent energy pile. The established thermally induced stress RT prediction model could acceptably predict the thermally induced stress of the future short-team. Surrounding utility tunnel excavation alters the distribution of the axial thermally induced stress. The axial thermomechanical response of the energy retaining pile after utility tunnel construction is approximately 50% that before utility tunnel construction. The asymmetrical boundary conditions cause a limited bending moment of the energy retaining pile at the top or bottom of the utility tunnel, which is not enough to threaten the pile safety. Moreover, the thermal performance of the energy retaining pile slightly increases due to the heat exchange between the pile and the air in the surrounding utility tunnel.

The atomic structure and mechanisms of formation of some geometrically incompatible interfaces within cubic B2 austenite – monoclinic B19′ martensite shape memory alloy microstructures

Microstructures of aged nickel‑titanium‑hafnium shape memory alloys (SMAs) Ni50.3Ti41.2Hf8.5 and Ni50.3Ti43.7Hf6 (at.%) are examined using high-resolution transmission electron microscopy (HRTEM) techniques. Characterizations of the structures of austenite-martensite, martensite-martensite, and martensite-precipitate interfaces provide new insights into cubic B2 austenite–monoclinic B19′ martensite phase transformation and martensite reorientation mechanisms. Specifically, in the absence of external load, theoretically unfavorable (001) compound martensite twins nucleate at H-phase precipitate interfaces. At the interface of these twins and the austenite matrix, a zig-zag-rise structure follows an extension of superdislocation theory previously developed to explain analogous zig-zag structured interfaces in non-shape-memory martensitic alloys. Additionally, 〈011〉 type II martensite twins that are theoretically favorable to form were also observed within the austenite matrices. However, instead of forming defect-free habit planes accommodated by elastic strains as predicted by theory, misfit dislocations worked in cooperation with elastic strain fields to accommodate atomic misfits between the austenite and martensite phases, and the elastic strain fields were smaller at the interfaces. Finally, the atomic scale thermoelastic mechanism of <011> type II twins reorienting to form (001) compound twins within the martensite is proposed in a manner consistent with direct observations of such interfaces. In total, connections with previous work on other binary and ternary NiTi base alloys show that these new mechanistic understandings generalize to other B2 - B19′ SMAs that should not perform well according to the elasticity-based Phenomenological Theory of Martensite Crystallography, yet still exhibit robust cyclic thermomechanical performances due to transformation-plasticity interactions.

Equivalent mechanical property calculation method of mini-channels in printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is a critical component to transfer heat from the primary loop to the secondary loop in supercritical carbon dioxide (SCO2) Brayton cycle system used for Generation IV nuclear reactors. The PCHE is operated at high temperature and high pressure, and thus the thermo-mechanical analysis is essential to its structural safety. However, it is difficult to directly model the whole PCHE by the finite element method because the PCHE is composed of large amounts of mini-channels. The simplified approach based on equivalent-homogeneous-solid concept was used by many researchers, but accurate method to calculate the equivalent mechanical properties of PCHE mini-channels is lacking. In this paper, an asymptotic homogenization method is proposed to calculate the equivalent mechanical properties of PCHE mini-channels. Firstly, the periodicity of mini-channels is considered as a small parameter, and the statement of equivalent elasticity matrix of mini-channels is derived in the form of stain energy of the unit cells. Secondly, numerical implementation of asymptotic homogenization method for a unit cell in the PCHE mini-channels is conducted. The equivalent Young’s modulus, Poisson’s ratio and shear modulus of mini-channels are fitted as functions of temperature. Finally, the thermo-mechanical performance of the equivalent PCHE core model is compared with the actual model. The results show that the maximum deviations in mechanical and thermal deformations between the equivalent and actual PCHE core models are less than 2.4% and 1% respectively. However, the computation time of the equivalent model is a factor of 45–190 below the value of actual model.

Chitin Nanofibrils from Fungi for Hierarchical Gel Polymer Electrolytes for Transient Zinc-Ion Batteries with Stable Zn Electrodeposition.

Rechargeable batteries play an integral role toward carbon neutrality. Environmentally sustainable batteries should consider the trade-offs between material renewability, processability, thermo-mechanical and electrochemical performance, as well as transiency. To address this dilemma, we follow circular economy principles to fabricate fungal chitin nanofibril (ChNF) gel polymer electrolytes (GPEs) for zinc-ion batteries. These biocolloids are physically entangled into hierarchical hydrogels with specific surface areas of 49.5 m2 ·g-1 . Ionic conductivities of 54.1 mS·cm-1 and a Zn2+ transference number of 0.468 are reached, outperforming conventional non-renewable/non-biodegradable glass microfibre separator-liquid electrolyte pairs. Enabled by its mechanically elastic properties and large water uptake, a stable Zn electrodeposition in symmetric Zn|Zn configuration with a lifespan above 600h at 9.5 mA·cm-2 is obtained. At 100 mA·g-1 , the discharge capacity of Zn/α-MnO2 full cells increases above 500 cycles when replacing glass microfiber separators with ChNF GPEs, while the rate performance remains comparable to glass microfiber separators. To make the battery completely transient, the metallic current collectors are replaced by biodegradable polyester/carbon black composites undergoing degradation in water at 70 °C. This work demonstrates the applicability of bio-based materials to fabricate green and electrochemically competitive batteries with potential applications in sustainable portable electronics, or biomedicine.

Numerical and Experimental Analysis of Mechanical Properties in Hybrid Epoxy-Basalt Composites Partially Reinforced with Cellulosic Fillers.

The current work is focused on numerical and experimental studies of woven fabric composites modified by hybridisation with biological (cellulosic) filler materials. The mechanical performance of the composites is characterized under tensile, bending and impact loads and the effect of hybridisation is observed with respect to pure and nonhybrid composites. Numerical models are developed using computational tools to predict mechanical performance under tensile loading. The computational prediction results are compared and validated with relevant experimental results. This research is aimed at understanding the mechanical performance of basalt-epoxy composites partially reinforced with micro-/nano-sized bio-fillers from cellulose and intended for various application areas. Different weave structures, e.g., plain, twill, matt, etc., were investigated with respect to the mechanical properties of the hybrid composites. The effects of hybridizing with cellulose particles and different weave patterns of the basalt fabric are studied. In general, the use of high-strength fibres such as basalt along with cellulosic fillers representing up to 3% of the total weight improves the mechanical performance of the hybrid structures. The thermomechanical performance of the hybrid composites improved significantly by using basalt fabric as well as by addition of 3% weight of cellulosic fillers. Results reveal the advantages of hybridisation and the inclusion of natural cellulosic fillers in the hybrid composite structures. The material developed is suitable for high-end applications in components for construction that demand advanced mechanical and thermomechanical performance. Furthermore, the inclusion of biodegradable fillers fulfills the objectives of sustainable and ecological construction materials.

Enabling superior thermo-mechanical performance of hydrated salt-based phase change energy storage cementitious composite using graphene oxide reinforced micro-interface

Thermal energy storage cementitious composites (TESCCs) with encapsulated phase change materials (PCMs) were promising candidates for thermal comfort and energy saving in solar passive buildings. However, serious deterioration of mechanical properties and low heat transfer efficiency had hindered their application. In this study, a high-strength encapsulated PCM with a simple production process was developed by encapsulating eutectic hydrated salt PCM within UV-curable polyurethane acrelate resin, and the presented encapsulated PCM (UPE) was used to partially replace sand in cement mortar to prepare TESCC/UPE. Moreover, graphene oxide (GO) modification was conducted to form GO-TESCC/UPE, synergistically enhancing the mechanical strength and heat transfer efficiency. The compressive strength, microstructure and thermal conductivity of TESCCs were studied. Surface heat storage coefficient was presented to further assess the heat transfer and heat storage capacity of TESCCs. Moreover, GO-TESCC/UPE containing 20 vol% encapsulated PCM exhibited 28-day compressive strength of 35.3 MPa, with a 25% improvement over TESCC/UPE. The thermal conductivity and surface heat storage coefficient were also optimized by GO modification. The enhancement of thermal and mechanical properties can be attributed to the fact that GO-TESCC/UPE had a denser interface transition zone (ITZ) and lower harmful porosity due to the excellent compatibility between cement matrix and UPE. In addition, a simplified meso-mechanical model demonstrated that a denser ITZ can mitigate the stress concentration inside the matrix, thus enhancing mechanical properties of TESCCs. This study confirmed the effectiveness of reinforcing ITZ to enhance the thermo-mechanical properties of heat storage cementitious materials.