Thermomechanical Analysis Research Articles

Development and Thermo-Mechanical Analysis of Bio-based Epoxy Resin/Cardanol Blends as Matrices for Green Composites Manufacturing

Development and Thermo-Mechanical Analysis of Bio-based Epoxy Resin/Cardanol Blends as Matrices for Green Composites Manufacturing

Time-dependent interaction coefficients to quantify the settlement of energy pile groups

The use of energy piles is facing an exponential growth due to the increasing need of exploiting sustainable energy sources. Their design implies the estimation of the displacement induced by the combined thermo-mechanical interaction between piles belonging to the same group. In this regard, the work at hand derives sets of interaction coefficients for piles subjected to thermal load in not stationary conditions, using finite difference numerical analyses. These involved pile pairs embedded in different soil types at multiple spacing, namely 2, 4, 6, 8, 10 times the pile diameter. A new dimensionless parameter is also introduced to describe the evolution with time of the interaction coefficients accounting for pile-to-pile spacing, soil thermal diffusivity, pile-soil stiffness ratio and time. The numerical results demonstrate a strict time-dependence of the interaction coefficients that is worthy to be considered in the design practice. To this aim a practice-oriented approach is proposed allowing to evaluate the interaction effects and thereby derive the settlement of each pile in a straightforward manner. This requires as only ingredient the settlement of the isolated energy pile at the considered time instant. The simplified approach is successfully validated against full 3D thermo-mechanical numerical analyses on pile groups including conventional and energy piles with different layouts.

Static/quasi-static thermomechanical analysis of 3D thin-walled beam structures based on CUF considering radiation dissipation condition

Thin-walled structures are widely applied in spacecraft as structural components due to their lightweight property. Extreme thermal environment in space may cause highly unfavorable thermal responses in thin-walled structures. Therefore, accurately predicting the thermal-coupling responses of thin-walled structures is of great engineering significance. In order to avoid the disadvantages of 3D finite element model caused by an abundance of computational degrees of freedom, the present paper proposes a thermo-mechanical coupling model based on Carrera Unified Formulation (CUF) for the static and quasi-static thermal response of space thin-walled structures. The longitudinal direction of the structures is discretized by one-dimensional linear and cubic finite elements (B2 and B4), whereas Lagrange expansion functions are used for the description of temperature fields and displacement fields within the cross-section. The governing differential equations of thermal-coupling problems are derived in a unified form according to the principle of virtual displacement and the weighted residual method. In order to demonstrate the accuracy of the numerical results, a convergence analysis is conducted on both beam elements and expansion forms. The results reveal that piece-wise quadratic beam theories approximated with B4 elements are accurate enough for the prediction of thermally-induced displacements, while the high-order cubic cross-sectional expansion is required for the description of stresses. Finally, influences of factors like angle of solar radiation, local shadows, emissivity and thermal conductivity on static and quasi-static displacement distributions are discussed. This research may pave a high-efficiency computational method for solving static/quasi-static thermally induced response of space thin-walled structures.

Thermal properties of Al2W3O12/epoxy composites at low filler volume loadings

AbstractThe open‐framework Al2W3O12 ceramic has been perceived as a candidate for controlling the coefficient of thermal expansion (CTE) of polymer matrices due to its low positive CTE and simple low‐cost soft‐chemistry synthesis. Hence, this work aims to study the effect of Al2W3O12 submicronic fillers at low loadings (0.46–1.43 vol%, i.e. 2.0–6.0 wt%) on thermal properties of epoxy‐based composites. The composites were prepared by ultrasonic filler dispersion followed by casting, and characterized through thermomechanical and thermogravimetric analyses. The maximum decrease (11.5%) on the composite CTE in the glassy region was attained with 0.94 vol% Al2W3O12 (4.0 wt%), the highest reported for these open‐framework fillers reinforcing epoxy at low volume fractions. Experimental CTE values contrasted with predictions from micromechanical models, revealed that elastic constants of both phases and filler agglomeration state, cannot be disregarded in predicting the composite CTE. The filler did not affect the onset and the maximum degradation rate temperatures of epoxy, while glass transition temperature was increased (2%–11%) for filler loadings <1.43 vol% (<6 wt%). A higher residue char in the composites suggested that Al2W3O12 can partially prevent the volatiles release from matrix to the atmosphere.Highlights Al2W3O12 is an excellent inexpensive filler for CTE controlling due to its low CTE. Incorporation of Al2W3O12 in an epoxy matrix reduces the CTE in the glassy state. The maximum CTE reduction (11.5%) was achieved for a filler content of 0.94 vol.%. The glass transition temperature of composites increased in the range of 2–11 %. Al2W3O12 can act as a barrier to prevent the transfer of volatiles from the matrix.

Closed-Form Approximate Solution for Thermo-Mechanical Performance Analysis of Thermoelectric Generators with Temperature-Dependent Material Properties by Differential Transform Method

Closed-Form Approximate Solution for Thermo-Mechanical Performance Analysis of Thermoelectric Generators with Temperature-Dependent Material Properties by Differential Transform Method

Effects of Printing Orientation on the Tensile, Thermophysical, Smoke Density, and Toxicity Properties of Ultem® 9085.

Despite the impressive properties of additively manufactured products, their inherent anisotropy is a crucial challenge for polymeric parts made via fused filament fabrication (FFF). This study compared the tensile, thermophysical, smoke density, and toxicity characteristics of Ultem 9085 (a blend of polyetherimide and polycarbonate) for samples printed in various orientations (X, Y, and Z). The results revealed that mechanical properties, such as elastic modulus and tensile strength, significantly differed from the Z printing orientation, particularly in the X and Y printing layer orientations. Thermomechanical analysis revealed that Ultem 9085 had high anisotropic effects in the coefficient of thermal expansion, indicating superior thermal properties along the printing orientation. The smoke density and toxicity test results proved that Ultem 9085 complies with aviation safety standards. Smoke density tests showed that all samples, regardless of print orientation or thickness, stayed well below the regulatory limit, making them suitable for aircraft interiors.

Strength Analysis and Reinforcement of 120 m3 Liquid Helium Storage Tank for Transportation Case

To ensure the safe transportation of a 120 m3 liquid hel ium storage tank, based on the analysis of its structure, material, and load characteristics, a finite element model for stress and strength analysis is established and solved by using the coupled thermo-mechanical analysis method for the accelerating and cornering cases experienced by the tank during transportation. The stress and deformation distributions in different transportation cases are analyzed in comparison to the finite element model, and the strength check is carried out for the tank. The study shows that under various working cases, the extreme value of stress of some parts is 267.5 MPa; this does not satisfy the strength requirement, and therefore requires structural reinforcement. The analysis of the reinforcing effect of the reinforcement structure shows that the stress extremes of the dangerous parts of the tanks after reinforcement decreased by 63.7% and 34.7%; the structural strength meets the standard requirements, and the new reinforcement structure only leads to an increase of 6% in the liquid nitrogen consumption of the cold screen, which is a better reinforcing effect.

Finite element analysis and experimental study on the sealing performance of low-phenyl silicone rubber sealing rings

PurposeThe brake pipe system was an essential braking component of the railway freight trains, but the existing E-type sealing rings had problems such as insufficient low-temperature resistance, poor heat stability and short service life. To address these issues, low-phenyl silicone rubber was prepared and tested, and the finite element analysis and experimental studies on the sealing performance of its sealing rings were carried out.Design/methodology/approachThe low-temperature resistance and thermal stability of the prepared low-phenyl silicone rubber were studied using low-temperature tensile testing, differential scanning calorimetry, dynamic thermomechanical analysis and thermogravimetric analysis. The sealing performance of the low-phenyl silicone rubber sealing ring was studied by using finite element analysis software abaqus and experiments.FindingsThe prepared low-phenyl silicone rubber sealing ring possessed excellent low-temperature resistance and thermal stability. According to the finite element analysis results, the finish of the flange sealing surface and groove outer edge should be ensured, and extrusion damage should be avoided. The sealing rings were more susceptible to damage in high compression ratio and/or low-temperature environments. When the sealing effect was ensured, a small compression ratio should be selected, and rubbers with hardness and elasticity less affected by temperature should be selected. The prepared low-phenyl silicone rubber sealing ring had zero leakage at both room temperature (RT) and −50 °C.Originality/valueThe innovation of this study is that it provides valuable data and experience for the future development of the sealing rings used in the brake pipe flange joints of the railway freight cars in China.

Dimensional Analysis and Validity of Uniaxial Residual Stress Distribution for Welded Box Sections

This paper investigates the residual stresses induced by metal inert/active gas (MIG/MAG) welding in normal strength steel box sections, focusing on the validity of uniaxial residual stress assumption. Advanced manufacturing simulations are conducted using deterministic uncoupled transient thermomechanical analysis with a double-ellipsoidal heat source model, employing 8-node solid elements and material models calibrated for extreme temperatures per EN 1993-1-2. A comprehensive parametric analysis investigates the effects of primary welding variables, such as heat source power and welding speed, alongside geometric parameters of the heat source model using random Latin hypercube sampling technique in the analyzed parameter set. The relationship between the size and shape of the characteristic isotherms, i.e., the aspect ratio and the Rosenthal number, underscores that the analyzed welding heat sources are in the fast regime with the validity of uniaxial residual stresses based on the analytical assumption (minimal values are AR = 9.94 and Ro = 30.47). The validity and limitations of uniaxial residual stress assumptions for 59 welded and 51 heated box sections are critically evaluated by using the finite element model-based stress triaxiality parameter. Results confirm that longitudinal residual stresses dominate typical MIG/MAG welding applications, supporting the application of uniaxial residual stress models in advanced structural design by neglecting in-plane and through-thickness residual stresses. Conversely, three-dimensional residual stress state dominates under conditions such as preheating or thermal straightening.

Thermo-Mechanical Coupled Analysis of Electric Vehicle Drive Shafts

With the growing concerns over global warming and abnormal weather patterns, the development of eco-friendly technologies has emerged as a critical research area in the transportation industry. In particular, the global automotive market, one of the most widely used sectors, has witnessed a surge in research on electric vehicles (EVs) in line with these trends. Compared to traditional internal combustion engine vehicles, EVs require components with high strength and durability to achieve optimal performance. This study focuses on the development of a constant velocity (CV) joint, a critical component for reliably transmitting the maximum output of an electric vehicle motor. Unlike conventional numerical methods, the proposed thermo-mechanical coupled analysis simultaneously accounts for thermal and mechanical interactions, providing more realistic operational performance predictions. This analysis, conducted using the thermal modules of Ls-Dyna and ANSYS Mechanical, effectively simulated field operation scenarios. Prototype testing under simulated conditions showed a 6% discrepancy compared to numerical predictions, validating the high accuracy and reliability of the proposed method. This robust thermo-mechanical coupled analysis is expected to improve the durability and reliability of CV joint designs, advancing electric vehicle component development.

Numerical nonlinear structural analysis of a timber truss roof under fire condition

As greenhouse gases continue to rise and environmental impact reduction gains global attention, timber buildings have emerged as a vital asset in the pursuit of a sustainable future. Throughout history, timber has been linked to fire as a flammable material, and there have been numerous reports of out-of-control fires that highlight the importance of fire safety. Hence, the primary goal of this study is to assess the fire resistance of a timber truss roof. As the temperature rises, changes occur in the physical and mechanical characteristics of the timber members, causing the loss of the strength capacity and rigidity of part or the entire truss. Therefore, this research aims to explore the SAFIR computer program to carry out the following analyses: thermal analysis of the timber cross-section; and the structure’s thermo-mechanical analysis. By conducting the first analysis, it becomes possible to calculate the temperature field of timber members’ cross-section in a transient regime, while also obtaining information about the degradation of material properties. The second analysis provides the displacements, internal forces, critical time, and/or critical temperature of the timber truss during collapse. The numerical results obtained here were compared and validated with those from the literature (experimental results). The truss collapse time predicted by SAFIR’s model was quite similar to the one observed in the laboratory. The developed numerical methodology allows for more realistic studies of timber elements or systems, enabling designs based on safety, economy, and sustainability.

Insights Into the Thermal Stability and Proton Transport Mechanism of PTFE‐Nafion Composite Membranes

ABSTRACTThe controllable design of proton exchange membranes (PEMs) with outstanding temperature resistance and efficient proton conduction is essential for high‐temperature PEM fuel cells. In this study, a polytetrafluoroethylene (PTFE)‐Nafion composite PEM was prepared using immersion and high‐temperature heat treatment methods. To understand the thermal stability, the glass transition temperatures of the PTFE‐Nafion and Nafion membranes were tested using static thermomechanical analysis. The PTFE‐Nafion membrane had a higher glass transition temperature than the Nafion membrane. In terms of the microstructure, the PTFE‐Nafion composite membrane exhibited a slightly larger ion domain structure than the Nafion membrane, and the first scattering peak of the PTFE‐Nafion composite membrane appeared at q ≈ 0.018 nm−1, while the pure Nafion membrane peak was located at q ≈ 0.022 nm−1. The PTFE‐Nafion composite membrane also exhibited higher proton conductivity than the Nafion membrane, and the activation energy of the Nafion membrane was approximately 3.5 times higher than that of the PTFE‐Nafion composite membrane. These results demonstrated the difference in proton transport mechanism for the PTFE‐Nafion composite and pure membranes, which may help guide the rational design of PEMs for fuel cells operating in high‐temperature and low‐humidity environments.

Enhancing soundproofing performance of polypropylene nanocomposites for implantable electrodes inside the body through graphene and nanoclay; thermomechanical analysis

This study explores the creation and evaluation of nanocomposites formed by integrating polypropylene (PP) with montmorillonite nanoclay and graphene nanosheets (GNs). The nanocomposites were produced via melt blending, utilizing different proportions of clay to GN, ultimately achieving a total loading of 4 wt. %. The objective is to utilize these materials in brain pacemakers to minimize noise and improve the signal-to-noise ratio for brain electrodes. While past studies have mainly focused on enhancing electrode materials within the brain, little attention has been given to the pacemaker material, particularly at the outlet gate. This study bridges this gap by investigating the noise-reducing properties of PP nanocomposites. The primary aim was to determine the optimal clay to GN ratio in the PP matrix. The results indicate that the perforated architecture of the nanocomposite, featuring scattered microspheres within the polypropylene matrix that form an extended channel, facilitates the dissipation of sound waves, rendering it ideal for acoustic insulation in brain pacemakers. In addition, the nanocomposite composed of 2.75% clay and 1.25% graphene nanosheets in the polypropylene matrix demonstrated a markedly improved signal-to-noise ratio in comparison to other examined nanocomposites. Moreover, this study examined the impact of adding PP-g-MA on the sound properties of the nanocomposite, revealing that it was not effective for sound absorption due to its more coherent structure. Various tests were conducted on the nanocomposites to evaluate properties such as tensile strength, elongation percentage, and impact toughness. Dynamic mechanical analysis and thermogravimetric analysis were also carried out to assess dynamic storage modulus and thermal stability. Overall, the study aimed to explore the thermal and mechanical attributes of the nanocomposites for potential use in brain pacemakers, highlighting the significance of choosing nanocomposites based on ductility characteristics for pacemaker applications.

Microstructure evolution modeling of Ti6Al4V alloy during cutting using the Particle Finite Element Method and homogeneous field distributions

This paper aims to explore the evolution of microstructural parameters induced during the cutting of Ti6Al4V alloy (TC4). The microstructure characteristics of the workpiece material is directly tied to its mechanical response during machining. During TC4 cutting, microstructure evolution is observed as a result of severe plastic deformations. The characterization of this phenomenon has significant interest from both academia and industry. In this work we present a developed modeling technique which combines the Particle Finite Element Method (PFEM) with incremental homogeneous field distributions. First, the PFEM is extended to perform a thermo-mechanical analysis capable of capturing the material responses of TC4 during orthogonal cutting. To generate serrated chips, an appropriate strain softening-based constitutive plasticity model i.e., TANH (Hyperbolic TANgent) is utilized. The PFEM’s validity is checked through comparison with available experimental results in terms of chip shapes and cutting forces. Second, the evolution of microstructural parameters such as dislocation density, vacancy concentration, dynamic recrystallization (DRx) grain size, and hardness is incrementally developed and incorporated into the PFEM using internal state variables as homogeneous field distributions. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model and Hall-Petch equation are applied for predicting grain size and hardness, respectively. The parameters of the corresponding models are modified for TC4 to accurately capture their alterations. Lastly, the predicted results of the microstructure evolution in serrated chips and machined surfaces, including average grain size and hardness, are compared with experiments, demonstrating good agreement. This implies that the PFEM combined with microscale schemes can reliably simulate the machining process of the TC4.

Nanocrystalline cerium dioxide reduces recrystallization in cryopreservation solutions

Nanocrystalline cerium dioxide is able to protect living cells from oxidative stress under the influence of various stress factors, in particular under the one of low temperatures. This study investigates the phase-structural transformations in aqueous solutions containing CeO2 nanoparticles (NPs) and their impact on the cryopreservation process. Differential scanning calorimetry and thermomechanical analysis were used to analyse the phase transitions in aqueous suspensions of CeO2 NPs and aqueous solutions of the cryoprotectant dimethyl sulfoxide (Me2SO) with CeO2 NPs. Various concentrations of CeO2 NPs were tested to observe their effects on the crystallization and melting behaviours. The addition of CeO2 NPs significantly altered the temperatures and enthalpies of melting and crystallization in water. Low concentrations of CeO2 NPs promoted crystallization, while higher concentrations inhibited it, reducing supercooling and recrystallization during thawing. In Me2SO solutions, CeO2 NPs raised the glass transition temperature and affected the recrystallization process, with higher concentrations leading to more pronounced vitrification and reduced recrystallization. We also investigated the regularities of the effect of CeO2 NPs on phase transitions in combined cryoprotective media with Ham's F12, fetal bovine serum and Me2SO, which can be used in future to design the cryopreservation protocols. In the complex media, CeO2 NPs decreased the metastability and altered eutectic crystallization patterns, indicating potential cryoprotective effects. In conclusion, CeO2 NPs modulate the thermophysical properties of cryoprotective solutions, enhancing vitrification and reducing recrystallization, which could improve cryopreservation efficiency. Optimizing NP concentrations is crucial for practical applications in cryopreservation.

Synthesis and Investigation of the Properties of a Branched Phthalonitrile Containing Cyclotriphosphazene.

To study the properties of cyclotriphosphazene (CTP)-containing phthalonitriles, a branched phthalonitrile containing CTP (CTP-PN) with self-catalytic behavior was designed and synthesized. The structure of CTP-PN was characterized by FT-IR (Fourier transform infrared spectroscopy), MS (mass spectroscopy), 1H-NMR (proton nuclear magnetic resonance spectroscopy), and 13C-NMR (carbon nuclear magnetic resonance spectroscopy). Then, the curing reaction of CTP-PN was studied using DSC (differential scanning calorimetry) and DRA (dynamic rheological analysis). The results show that the curing reaction of CTP-PN is initiated at 200 °C. Additionally, the change in the viscosity of CTP-PN as a function of the temperature was investigated. After curing at different temperatures, the generated structures were characterized by FT-IR. The fracture morphology and thermomechanical properties of cured CTP-PN were scanned and studied using SEM (scanning electron microscopy) and TMA (thermomechanical analysis), respectively. The results demonstrate that CTP-PN exhibits a smooth fracture surface and possesses a relatively low CTE (coefficient of linear thermal expansion) of approximately 25 ppm/°C at 285 °C. A Td5% (temperature at which 5% weight loss occurs) of as high as 405 °C can be obtained for cured CTP-PN, and its char yield at 800 °C exceeds 70% in N2. FT-IR and XPS (X-ray photoelectron spectroscopy) were used to study the thermal decomposition of cured CTP-PN, indicating that it remains stable below 350 °C. With an increasing temperature, there is decomposition first of CTP and P-NH-Ph and C-O-C bonds (>350 °C) and then nitrogen-containing aromatic heterocycles (>500 °C), ultimately resulting in the formation of P-containing residual char.

Influence of Relative Humidity on the Mechanical Properties of Palm Leaf Manuscripts: Short-Term Effects and Long-Term Aging.

Palm leaf manuscripts are a valuable part of world cultural heritage. Studying the mechanical properties of palm leaf manuscripts and their changes due to environmental influences is of great significance for understanding the material characteristics, aging mechanisms, and preventive conservation of these manuscripts. This study used dynamic vapor sorption (DVS) and a thermomechanical analyzer (TMA) to investigate the changes to the mechanical properties of palm leaf manuscripts in response to different relative humidity conditions and different time periods. The short-term study results show that exposure to varying relative humidities leads to changes in the equilibrium moisture content (EMC) of palm leaf manuscripts, causing the bending strength of the samples to decrease significantly with increasing humidity. The bending modulus initially increases and then decreases as the humidity increases. Moreover, the greater the desorption hysteresis of the samples, the more pronounced the changes to the mechanical properties. Therefore, a stable environment in terms of humidity can prevent changes in the mechanical properties of palm leaf manuscripts, thereby preventing the onset of degradation. The results of the long-term aging studies indicate that prolonged exposure to either very dry or very humid conditions greatly affects the mechanical properties of palm leaf manuscripts, which is detrimental to their preservation. The samples kept at 50% RH did not exhibit significant signs of deterioration, with no notable changes in their mechanical properties or chemical structure. This suggests that 50% RH is a relatively optimal humidity condition for the preservation of palm leaf manuscripts.

Quantification of physical aging using two MDSC methods and its effect on initial properties of epoxy films

In this work, the effect of aging times and temperatures on the generation of physical aging (P.A) is investigated, as well as its impact on the physico-chemical and mechanical properties of a model epoxy resin. The DGEBA/Jeffamine D230 system was tested with different amounts of P.A generated by applying steps of varying aging times and temperatures during the cooling. The quantification of P.A is carried out through modulated differential scanning calorimetry (MDSC) using two methods, based on the heat flow or the non-reversing heat flow. The results show that the P.A values obtained with the first method are lower than those obtained by the second method. The theorical model of Kohlrausch-Williams-Watts, used to describe the kinetic behavior of P.A process, showed that the second method underestimates the relaxation time. If no chemical change was observed between systems with and without P.A, the thermo-mechanical analysis showed that physical aging induces a storage modulus increase together with a free volume fraction decrease.

Thermo-mechanical analysis on reflection characteristics of deformed coupling system of a helix traveling wave tube

This paper proposes a fast ANSYS Multiphysics-based system coupling approach to study the impact of structural deformation on the reflection coefficient (S11) of the helix travelling wave tube (TWT) output coupling system at varying output powers. The system, comprising a coaxial stepped impedance transformer, a coaxial-to-rectangular waveguide with a door-knob transition, and a double-mitered bend waveguide, is analysed under 200 W and 250 W RF power in the X-band. The analysis shows that S11 improves at lower frequencies (−17.43 dB to −17.58 dB) and deteriorates at higher frequencies (−10.62 dB to −10.53 dB) due to structural deformation. Thermal simulation results were validated experimentally using infrared thermographic imaging.

Predicting transverse thermal conductivity of flax-fiber using micromechanical model based inverse framework

The paper presents an inverse approach using a micromechanical model for predicting the transverse thermal conductivity of flax fiber, addressing the lack of standard testing protocols for characterizing natural fibers. The model predicts the transverse thermal conductivity of the fiber from experimentally measured properties of the flax-epoxy lamina. The inverse approach was validated using data corresponding to carbon-epoxy composite reported in the literature, with an error of less than 5 %. The transverse thermal conductivity of the flax fiber was estimated to be 0.87 W/m K, which is comparable to other natural fibers. The flax fiber properties were used to evaluate the thermal conductivity of the flax-epoxy lamina for a range of volume fractions, and a simplified non-linear regression equation was proposed. The methodology is further extended to predict the elastic properties of the woven fabric laminate using a multiscale homogenization approach. The proposed framework offers a reliable method for predicting the thermal properties of flax-epoxy composites, which forms the basis for thermo-mechanical analysis and design of automotive and aerospace components.