Search Results (112)

Residual stresses and internal strains in 3D printing can lead to issues such as cracking, warping, and delamination—challenges that are amplified when using functional composite materials like magnetic PLA filaments. This study investigates the thermo-mechanical strain evolution during fused filament fabrication (FFF) of magnetite-filled PLA using an integrated methodology combining strain gauge sensors, high-resolution infrared thermal imaging, and synchrotron X-ray microtomography. Printing parameters, including nozzle temperature (190–220 °C), build platform temperature (30–100 °C), printing speed (30–60 mm/s), and cooling strategy (fan on/off) were systematically varied to evaluate their influence. Results reveal steep thermal gradients along the build direction (up to −1 °C/µm), residual strain magnitudes reaching 0.1 µε, and enhanced viscoelastic creep at elevated platform temperatures. The addition of magnetic particles modifies heat distribution and strain evolution, leading to strong sensitivity to process conditions. These findings provide valuable insight into the complex thermo-mechanical interactions governing the structural integrity of magnetically functionalized PLA composites in additive manufacturing. Full article

Friction-spinning is an incremental thermomechanical forming process that has huge potential due to its simple yet effective mechanism of utilising friction between a rotating workpiece and a forming tool to increase the workpiece’s temperature, which reduces the required forces and increases formability during the forming process. Despite the simplicity of the process’s setup, the thermomechanical loads and high relative velocities involved, especially in the contact zone, make the application of classical methods for characterising friction inaccurate. It is therefore essential to find a way to describe the frictional behaviour under real process conditions to be able to gain a holistic understanding of the process and the effect of the adjustable parameters on the outcome, especially the temperature. To achieve this goal, an experimental setup that considers the actual process boundary conditions in forming tubes made of EN AW-6060 was used to measure in situ normal and frictional forces, in addition to process temperatures, under varying rotational speed and feed rate values. Full article

This study investigated the thermomechanical behaviour of the nozzle of a GTM 400MOD miniature turbojet engine during combustion of aviation kerosene and co-combustion of kerosene with hydrogen. Numerical analysis was based on experiments conducted on a dedicated test rig at engine speeds ranging from 31,630 rpm to 65,830 rpm, providing data on the temperature and dynamic pressure at the nozzle outlet. These data served as input to numerical analyses using the ANSYS Fluent, Steady-State Thermal, and Static Structural modules to evaluate exhaust gas flow, temperature distribution, and stress and strain states. The paper performed a basic analysis with additional simplifications, and an extended analysis that took into account, among other things, thermal radiation in the flow. The results of the basic analysis show that, at comparable thrust levels, co-firing and pure kerosene combustion yield similar nozzle temperature distributions, with maximum wall temperatures ranging from 978 K to 1090 K, which remain below the allowable limit of 1193 K (920 °C). Maximum stresses reached approximately 261 MPa, close to but not exceeding the yield strength of 316 stainless steel. Maximum nozzle deformation did not exceed 0.8 mm. Small dynamic pressure fluctuations were observed; For example, at 31,630 rpm, co-firing increased the maximum dynamic pressure from 1.56 × 104 Pa to 1.63 × 104 Pa, while at 47,110 rpm, it decreased from 4.05 × 104 Pa to 3.89 × 104 Pa. The extended analysis yielded similar values for the nozzle temperature and pressure distributions. Stress and strain increased by more than 76% and 78%, respectively, compared to the baseline analysis. The results confirm that hydrogen co-firing does not significantly alter the nozzle thermomechanical loads, suggesting that this emission-free fuel can be used without negatively impacting the nozzle’s structural integrity under the tested conditions. The methodology, combining targeted experimental measurements with coupled CFD and FEM simulations, provides a reliable framework for assessing material safety margins in alternative fuel applications in small turbojet engines. Full article

This study investigates the hot deformation behaviour and microstructural evolution of two AISI 430 ferritic stainless steel variants: 0A (basic) and 1C (modified). These variants primarily differ in chemical composition, with 0A containing higher austenite-stabilizing elements (C, N) compared to 1C, which features lower interstitial content and slightly higher Si and Cr. This research aimed to optimize hot rolling conditions for enhanced forming properties. Uniaxial hot compression tests were conducted using a Gleeble thermo-mechanical system between 850 and 990 °C at a strain rate of 3.3 s⁻¹, simulating industrial finishing mill conditions. Analysis of flow curves, coupled with detailed microstructural characterization using electron backscatter diffraction, revealed distinct dynamic restoration mechanisms influencing each material’s response. Thermodynamic simulations confirmed significant austenite formation in both materials within the tested temperature range, notably affecting their deformation behaviour despite their initial ferritic state. Material 0A consistently exhibited a strong tendency towards dynamic recrystallization (DRX) across a wider temperature range, particularly at 850 °C. DRX led to a microstructure with a high concentration of low-angle grain boundaries and sharp deformation textures, actively reorienting grains towards energetically favourable configurations. However, under this condition, DRX did not fully complete the recrystallization process. In contrast, material 1C showed greater activity of both dynamic recovery and DRX, leading to a much more advanced state of grain refinement and recrystallization compared to 0A. This indicates that the composition of 1C helps mitigate the strong influence of the deformation temperature on the crystallographic texture, leading to a weaker texture overall than 0A. Full article

This study investigates the hot deformation behaviour and flow stress prediction of metastable β-Ti-15Mo alloy, a promising material for biomedical applications requiring strength–modulus optimisation and thermomechanical tunability. Isothermal compression tests were performed within the temperature range of 923–1173 K and at strain rates of 0.17, 1.72, and 17.2 ${\mathrm{s}}^{-1}$ to assess the material’s response under industrially relevant hot working conditions. The alloy showed significant sensitivity to temperature and strain rate, with dynamic recovery (DRV) and dynamic recrystallisation (DRX) dominating the softening behaviour depending on the conditions. A strain-compensated Arrhenius-type constitutive model was developed and validated, resulting in an apparent activation energy of approximately 234 kJ/mol. Zener–Hollomon parameter analysis confirmed a transition in deformation mechanisms. Although microstructural and diffraction data suggest possible contributions from nanoscale phase transformations, including ω-phase dissolution at high temperatures, these aspects remain to be fully elucidated. The model offers reliable predictions of flow behaviour and supports optimisation of thermomechanical processing routes for biomedical β-Ti alloys. Full article

In this work, a finite element modelling methodology is presented for the prediction of the bending behaviour of a glass fibre-reinforced elastomer composite with embedded shape memory alloy (SMA) wire actuators. Three configurations of a multi-layered composite with differences in structural stiffness and thickness are experimentally and numerically analysed. The bending experiments are realised by Joule heating of the SMA, resulting in deflection angles of up to 58 deg. It is shown that a local degradation in the structural stiffness in the form of a hinge significantly increases the amount of deflection. Modelling is fully elaborated in the finite element software ANSYS, based on material characterisation experiments of the composite and SMA materials. The thermomechanical material behaviour of the SMA is modelled via the Souza–Auricchio model, based on differential scanning calorimetry (DSC) and isothermal tensile experiments. The methodology allows for the consideration of an initial pre-stretch for straight-line positioned SMA wires and an evaluation of their phase transformation state during activation. The results show a good agreement of the bending angle for all configurations at the activation temperature of 120 °C reached in the experiments. The presented methodology enables an efficient design and evaluation process for soft robot structures with embedded SMA actuator wires. Full article

This study presents a phenomenological model for predicting the thermomechanical behaviour of spring-type actuators made of shape memory alloys (SMAs). The model incorporates the kinetics of martensite–austenite phase transitions as a function of temperature and applied stress. The primary innovation is the inclusion of a scalar internal variable that represents the evolution of the phase transformation within a phenomenological macroscopic model. This approach enables the deformation–force–temperature behaviour of SMA-based spring elements under cyclic loading to be accurately described. A set of constitutive equations was derived to describe reversible and residual strains, along with transformation start and finish conditions. Model parameters were calibrated using experimental data from VSP-1 and TN-1K SMA springs that were subjected to thermal cycling. The validation results show a high correlation between the theoretical predictions and the experimental data, with deviation margins of less than 6.5%. The model was then applied to designing and analysing thermosensitive actuator mechanisms for temperature control systems. This yielded accurate deformation–force characteristics, demonstrating low inertia and high repeatability. This approach enables the efficient prediction and improvement of the performance of SMA-based spring elements in actuators, making it relevant for adaptive systems in marine and aerospace applications. Full article

This study investigates the novel role of yarn-level fibre hybridisation in tailoring thermomechanical properties and thermal residual stress (TRS) fields in the resin at both micro- and meso-scales of 3D orthogonal-woven flax/E-glass hybrid composites. Unlike previous studies, which primarily focus on macro-scale composite behaviour, this work integrates a two-scale homogenisation scheme. It combines microscale representative volume element (RVE) models and mesoscale repeating unit cell (RUC) models to capture the effects of hybridisation from the fibre to lamina scale. The analysis specifically examines the cooling phase from a curing temperature of 100 °C down to 20 °C, where TRS develops due to thermal expansion mismatches. Microstructures are generated employing a random sequential expansion algorithm for RVE models, while weave architecture is generated using the open-source software TexGen 3.13.1 for RUC models. Results demonstrate that yarn-level hybridisation provides a powerful strategy to balance mechanical performance, thermal stability, and residual stress control, revealing its potential for optimising composite design. Stress analysis indicates that under in-plane tensile loading, stress levels in matrix-rich regions remain below 1 MPa, while binder yarns exhibit significant stress concentration, reaching up to 8.71 MPa under shear loading. The study quantifies how varying fibre hybridisation ratios influence stiffness, thermal expansion, and stress concentrations—bridging the gap between microstructural design and macroscopic composite performance. These findings highlight the potential of yarn-level fibre hybridisation in tailoring thermomechanical properties of yarns and laminae. The study also demonstrates its effectiveness in reducing TRS in composite laminae post-manufacturing. Additionally, hybridisation allows for adjusting density requirements, making it suitable for applications where weight and thermal properties are critical. Full article

This study presents a mathematical model of a three-dimensional thermoelastic half-space with variable thermal conductivity under the definition of fractional order heat conduction based on the Moor–Gibson–Thompson theorem. The non-dimensional governing equations using Laplace and double Fourier transform methods have been applied to a three-dimensional thermoelastic, isotropic, and homogeneous half-space exposed to a rectangular thermal loading pulse with a traction-free surface. The double Fourier transforms and Laplace transform inversions have been computed numerically. The numerical distributions of temperature increment, invariant stress, and invariant strain have been shown and analysed. The fractional order parameter and the variability of thermal conductivity significantly influence all examined functions and the behaviours of the thermomechanical waves. Classifying thermal conductivity as weak, normal, and strong is crucial and closely corresponds to the actual behaviour of the thermal conductivity of thermoelastic materials. Full article

This work concerns a study of the thermomechanical behaviour of a commercial thruster for aerospace use. The thruster, operated using a bipropellant liquid mixture, is used for the motion and in-orbit altitude control of small telecommunications satellites. The mixture used in the combustion process is composed of propylene and nitrous oxide, while the wall of the thruster is made of PH15-5 stainless steel. A computational fluid dynamics analysis of conjugate heat transfer determines the spatial–temporal distribution of temperature within the thruster wall. This information is passed to a finite element mechanical model that simulates the stress and the equivalent plastic strain distribution within the thruster wall. Full article

Powder Bed Fusion–Laser Beam (PBF-LB) is a leading technique in metal additive manufacturing, yet it continues to face challenges related to residual stresses and distortions. The inherent strain method has emerged as a valuable predictive tool, offering early assessments of part behaviour due to its simplicity and manageable computational demands. However, accurately defining the inherent strain tensor, which is critical for these models, remains a challenge. This study provides a comprehensive analysis of the local meso-scale model definition and inherent strain calculation procedure in the PBF-LB process using a multi-scale modelling approach. The primary objective is to guide the definition of local high-fidelity thermo-mechanical models. This research investigates the contributions of thermal, plastic, and activation strains (strains due to Finite Element (FE) activation) to the inherent strain tensor, demonstrating the significant impact of activation strains. A sensitivity analysis identified an optimal control volume size to ensure minimal boundary effects. An optimised local high-fidelity model is proposed to efficiently calculate inherent strain tensor, significantly reducing computational costs without compromising accuracy. The method was validated by applying it to a complex SBA actuator geometry, which showed good agreement between predicted and experimental distortions. The consistency of the proposed method with empirically derived tensors further reinforces its potential to improve predictive capabilities in the PBF-LB process, ultimately enhancing part quality. Full article

During braking, high-power wind turbine disc brake friction pairs experience thermo-mechanical interactions at the interface, which lead to both physical and chemical changes. The friction interface features asperities and embedded hard particles within the substrate. Wear debris from these asperities or dislodged hard particles accumulates at the interface, continuing to participate in the friction process—a phenomenon known as the “endogenous third body”. Throughout braking, the microscopic morphology and contact conditions of the interface evolve dynamically. The stress–strain distribution and vibration behaviour of the friction system, influenced by the endogenous third body, also vary with braking parameters. This study employs the W-M fractal theory to develop a finite element model of a rough friction interface containing hard-particle endogenous third bodies. The model is validated through experimental testing. Based on the performance test parameters of high-power wind turbine disc brakes, a simulation is conducted to analyse the contact friction process involving the endogenous third body at the rough interface between the brake disc and brake pad. The simulation reproduces the formation process of the endogenous third body and reveals its evolutionary stages, including “ploughing”, “gap-filling”, and “aggregation”. Additionally, the study examines changes in the internal stress–strain and vibration states of the friction system under varying braking speeds (5 m/s to 35 m/s) and braking loads (3 MPa to 6 MPa). The findings demonstrate how different braking parameters influence the friction system containing the endogenous third body. The results showed that when the braking speeds were 5 m/s, 15 m/s, 25 m/s, and 35 m/s, and the braking load was 6 MPa, the average amplitude of the brake pads was the smallest, at 0.017 mm, 0.021 mm, 0.025 mm, and 0.020 mm, respectively. This research provides valuable insights into the three-body contact friction mechanism at the micro-braking interface, the formation of composite material third bodies, and the role of wear-stage third bodies in affecting the friction interface. Full article

This study used the Gleeble 3800 thermomechanical simulator to examine the hot deformation characteristics of AISI 8822H steel. The main goal was to understand the alloy’s behaviour under various thermomechanical settings, emphasising temperature ranges between 1173 K and 1323 K and strain rates from 0.01 s⁻¹ to 10 s⁻¹. This study aimed to enhance the alloy’s manufacturing process by offering a thorough understanding of the material’s response to these conditions. Four various constitutive models—Arrhenius-type, Johnson–Cook, modified Johnson–Cook, and Trimble—were used in a comprehensive technique to forecast flow stress values in order to meet the study’s goals. The accuracy of each model in forecasting the behaviour of the material under the given circumstances was assessed. A thorough comparison investigation revealed that the Trimble model was the most accurate model allowing prediction of material behaviour, with the maximum correlation factor (R = 0.99) and at least average absolute relative error (1.7%). On the other hand, the Johnson–Cook model had the least correlation factor (R = 0.92) and the maximum average absolute relative error (32.2%), indicating that it was the least accurate because it could not account for all softening effects. Full article

Compacted graphite iron (CGI) attracts significant attention in the automotive industry thanks to its suitable thermomechanical properties and cost-effectiveness. A primary fracture mechanism at the microscale for CGI involves interfacial damage and debonding between graphite inclusions and its metallic matrix, which can occur under high-temperature service conditions due to a mismatch in the coefficients of thermal expansion between these two phases. Such microscopic interfacial damage can initiate macroscopic fractures in cast-iron components subjected to thermal loading. While this phenomenon was studied in various composites, there remains a lack of detailed information for CGI, especially related to the complex morphology of its graphite inclusions. This study investigates the influence of graphite morphology and type of matrix on the thermomechanical performance of CGI at high temperatures. A set of three-dimensional finite-element models were developed in the form of unit cells with a single graphite inclusion embedded within a cubic domain of the metallic matrix. Elastoplastic behaviour was assumed for both phases in the numerical simulations. The study is focused on the response of the constituents in CGI to pure thermal loading in order to explore the relationship between graphite morphology and fracture mechanisms. The findings aim to enhance understanding of how graphite morphology affects the behaviours of CGI under high-temperature conditions. Full article

In the last few decades, a large number of natural additives have been analysed in connection with the improvement of the properties of poly(lactic acid) (PLA) bioplastic materials. This article comprehensively analyses the applicability of a highly stable and progressive multifunctional additive produced from renewable resources—biochar. The effect of biochar on the structural development and various thermo-mechanical properties was evaluated as a function of the biochar size and volume, addition of an impact modifier and in-mould annealing during injection moulding. In addition, the effect of accelerated ageing on the change in properties was also analysed. The evaluated results showed a significant influence of the particle size and biochar content on the properties of PLA biocomposites. However, the crucial aspect was the production process with a higher mould temperature and longer production time. Consequently, the effect of additives with adjusted processing worked synergistically on the performance of the resulting biocomposites. The accelerated ageing process did not induce any significant changes in the mechanical, impact and heat resistance behaviour of neat PLA. On the other hand, significant effects on the behaviour of the modified PLA biocomposites were observed. Impact-modified PLA achieved a toughness of 28 kJ/m², an increase of 61% compared to neat PLA. Similar observations were made when submicron biochar was incorporated into the PLA matrix (a 22% increase with PLA/5B1). These increases were even more pronounced when injected into a 100 °C mould. Due to the synergistic effect, excellent impact toughness results of 95 kJ/m² (a 428% increase) were achieved with PLA/IM/5B1. Moreover, these results persisted even after accelerated ageing. Full article