•Technological advancements in functionally graded materials.•Comparison of various homogenization schemes.•Review on analysis of functionally graded structures.•Suggested future scope in the ...analysis of functionally graded structures.•Review on various fabrication methods of functionally graded materials along their mechanical and tribological performance.
This paper discourses an overview of the recent advancements in functionally graded materials (FGMs) research. The paper also disseminates on the key researches that are carried out in the scientific community on the development of manufacturing and modelling of functionally graded materials. The rationale of the current work is to emphasize the selection of materials, processing techniques and analytical modelling and applications of FGMs. Alongside, challenges involved in developing these materials towards various aspects of scientific and technological fields will be addressed.
•Thermocouples, IR imaging, displacement sensor and DIC system were jointly used to develop a systematic in situ thermo-mechanical field measurement platform.•A 3D thermo-mechanical coupled model was ...experimentally calibrated to study the thermo-mechanical behavior of LSF parts.•The thermal and mechanical responses of single-wall coupons under different process parameters were recorded and compared with the numerical models.•The effect of different process parameters on the thermo-mechanical fields during LSF process was clarified.
Residual stresses and distortions are two technical obstacles for popularizing the additive manufacturing (AM) technology. The evolution of the stresses in AM components during the thermal cycles of the metal depositing process is not yet clear, and more accurate in situ measurements are necessary to calibrate and validate the numerical tools developed for its simulation. In this work a fully coupled thermo-mechanical analysis to simulate the laser solid forming (LSF) process is carried out. At the same time, an exhaustive experimental campaign is launched to measure the temperature evolution at different locations, as well as the distortions and both the stress and strain fields. The thermal and mechanical responses of single-wall coupons under different process parameters are recorded and compared with the numerical models. Good agreement between the numerical results and the experimental measurements is obtained. Sensitivity analysis demonstrates that the AM process is significantly affected by the laser power and the feeding rate, while poorly influenced by the scanning speed.
Thermo-mechanical coupled systems are typically complex, however, the demand for analyses of this kind of multi-physics system is increasing, for example, accurately predicting the temperature and ...thermal stress of the railway disc brakes. However, many models ignore the phenomenon of thermal expansion and wear on brake pads. Therefore, their influence on the result is unclear. This research aims to investigate the effect of these two phenomena on the temperatures and stresses. These influences represent different heat flux input methods. Based on the finite element method (FEM), a three-dimensional (3D) transient thermo-mechanical model is built up. Three cases with or without thermal expansion and wear are conducted. The model is validated against measurement data. Simulation results show that thermal expansion and wear on the brake pads cause a 10% difference in the average temperatures of the brake discs, while a 257% difference in the maximum temperatures. As for the equivalent stresses (Von Mises stress), the difference can reach 3500%. Overall, this research builds a thermo-mechanical model and quantifies the effects of thermal expansion and wear on the temperatures and stresses of railway brake discs. The model can be transferred to other thermo-mechanical coupled multi-physics systems.
Quantitative analysis of the influence of thermal barrier coating spallation on the thermo-mechanical behaviors and creep lifetime of turbine vanes is crucial for their maintenance and reliability ...improvement. The temperature and stress distribution of vanes with preset coating spallation damage are investigated in this study, using the thermal-fluid-solid coupling method. Additionally, a further computational analysis is conducted to predict the hazardous regions and creep lifetime of the vanes. The results indicate that coating spallation leads to significant changes of the temperature and stress distribution at the spalled regions of vanes. The remaining coating on the unspalled regions continues to provide effective protection. Stress concentration primarily occurs at the upstream and downstream of the leading edge film holes, while high-stress regions are observed between adjacent rows of film holes, forming a serrated shape. The creep lifetime of the vanes decreases significantly at the region with coating spallation. When the same spallation area is considered, the coating spallation at the leading edge has a more serious influence on creep lifetime, which is more likely to cause the vanes failure. This study reveals the influence of coating spallation characteristics on the thermo-mechanical behaviors and creep lifetime of vanes, providing valuable insights for durability assessment of coated high-temperature components.
•The thermo-mechanical characteristics of coated vane were analyzed using thermal-fluid-solid coupling method.•The influence of coating spallation on temperature distribution of vanes was quantitatively analyzed.•The creep lifetime of vanes was predicted based on Larson-Miller model.
Rice bran oil oleogel was prepared with candelilla wax and then blended with solid fat (butter) to reduce the content of saturated fat in yeast-leavened baked goods. The solid fat content of butter ...and oleogel blends became less sensitive to temperature change with increasing levels of oleogel. While higher proportions of oleogel in the blends decreased the thermo-mechanical properties of wheat flour dough, they did not negatively affect the dough stabililty. Dynamic oscillatory and extensional measurements demonstrated that the viscous nature of the dough became more dominant as the level of oleogel in the blends increased. When breads with butter and oleogel blends were baked, no significant differences in the specific volume of the bread were noted from the control prepared with butter until 75% replacement with oleogel. The smaller bread volume generally gave rise to greater bread hardness. The ratio of saturated to unsaturated fatty acids in the baked breads containing oleogel were distinctly reduced to 0.34, compared to the control butter bread (2.44).
•Butter-oleogel blends were used for yeast-leavened baked goods with low saturated fat.•Solid fat content of the blends with more oleogels became less temperature-dependent.•Higher level of oleogel in the blends gave lower dough mixing property/viscous nature.•Volume/texture differences were not observed at blending ratio (75-oleogel:25-butter).•Use of oleogels for butter produced bread low in saturated fat (71 → 25%)
In a severe accident scenario of a nuclear power plant involving core meltdown and relocation to the lower head of the reactor pressure vessel (RPV), the vessel may undergo serious deformation and ...even failure due to extreme thermo-mechanical loads from the relocated core melt. Proper material models and detailed structural analysis are paramount in predicting the timing and mode of possible vessel failure.
This paper presents a strain hardening creep model with optimal parameters to simulate the material behavior of the reactor steel 16MND5 under extreme thermo-mechanical loads. First, validations against two experiments, a tensile-creep test and the EU-REVISA RUPTHER #14 test, show that the proposed model is best overall compared to three previous models. Next, the creep model is implemented for the thermo-mechanical analysis of an ablated RPV under a severe accident scenario with external vessel cooling as a mitigation strategy. The effect of internal pressures from 3 to 50 bars is investigated with the assumption that the corners of the ablated part of the vessel have sharp corners. In this case, we found that the vessel fails above 40 bars. However, if we model the corners with varying smoothness or fillet sizes, we found significant delay in failure time and an increase in failure internal pressure.
•A strain hardening creep model of 16MND5 steel is proposed and validated.•The model is used in FE simulations of an ablated RPV under extreme loads.•Failure pressures are determined considering different ablation geometries.•Importance of modeling the corners with varying smoothness is illustrated.
Shape‐memory polymers (SMPs) are well investigated smart materials. With their ability to memorize their original shape they are interesting candidates for a large range of applications. Certain SMPs ...feature triple shape‐memory behavior. In these cases, it is possible to fix two different temporary shapes. However, the exact quantification of the individual steps regarding their programming and recovery rate is difficult and has not been possible so far. In this work, a novel approach for the analysis and exact quantification of triple SMPs is presented. By applying a customized rheology protocol, it is possible to perform and to analyze torsional and tensional experiments simultaneously. Consequently, different shapes in different directions (vertical and horizontal) can be fixed and the individual steps can be investigated independently at different switching temperatures.
A new method for the quantification of triple‐shape memory behavior of polymers is presented. For this purpose, twisting and elongation are studied separately from each other enabling the investigation of each recovery step without the interference of the other one. Thus, realistic values for the triple‐shape memory behavior are obtained.
To solve the problems of the current optimization methods for solar segmented thermoelectric generator performance based on numerical methods, this paper applied deep neural networks to optimize the ...device geometry for improved thermo-mechanical performance. The motivation for using the deep neural network is to overcome the lengthy computational time and very high computational energy required by the traditional numerical method in optimizing the segmented thermoelectric generator performance. The numerical model is built using ANSYS software and the effects of temperature dependency in the 4 thermoelectric materials are considered to ensure result accuracy. Furthermore, 16 possible geometry parameters which were previously not considered, encompassing the individual and combined segment's heights and cross-sectional areas are optimized to find which set of parameters are the best in maximizing the device performance. The deep neural network is a regressive multilayer perceptron with network hyperparameters comprising 2 hidden layers with 5 neurons per layer. The training process is governed by the Levenberg-Marquardt standard backpropagation algorithm to minimize the mean squared error and maximize the regression correlation between the neural network forecasted outputs and the numerical-generated dataset. The most significant contribution of the proposed deep neural network is that it was able to quickly and accurately forecast the device performance in just 10 s, which was 2880 times faster than the conventional numerical-based optimization approach. Additionally, the optimized device had a maximum efficiency of 18%, which was 78% higher than that of the unoptimized device. Also, the thermal stress of the optimized device was 73% less than that of the unoptimized device design, indicating an extension in the device mechanical reliability and service lifetime. The results reported in this paper will accelerate the ease at which efficient, long-lasting segmented thermoelectric generators are manufactured by harnessing the power of artificial intelligence.
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•AI driven geometry optimization of STEG thermo-mechanical performance using DNN.•3D FEM considers 16 STEG geometry parameters that were previously neglected.•AI fixes shortcomings of conventional FEM method in optimizing STEG performance.•DNN forecasted device performance in just 10s, 2880 times faster than FEM.•Optimized STEG is 78% more efficient than conventional STEG, reduces failure by 73%.
•Thermo-mechanical analysis of porous volumetric solar receiver.•Higher values of porosity, pore size and inlet velocities improve mechanical stability.•Uniform solar heat flux distribution ensures ...mechanical safety.•Near wall region at the inlet is most prone to failure.
The damage caused by high working and non-uniform temperature distributions is one of the major obstacles to the development of receivers exposed to concentrated solar radiation. The thermal and mechanical performance of a typical porous Silicon Carbide volumetric receiver with foam structure is investigated in the present study with a coupled thermo-mechanical model. The developed model includes coupling of fluid flow, thermal and mechanical models to determine flow field, temperature and stress distributions. The main objective is to investigate the effects of various geometric, structural and design parameters on the absorber's thermal and mechanical performance and to identify the failure-prone regions when the absorber works under steady-state conditions. The effects of porosity, pore size, inlet velocity, absorber's geometrical dimensions, and incident solar flux distribution on the receiver's performance are investigated in detail. It is observed that higher porosities, pore sizes and inlet velocities result in lesser thermal stresses in the porous absorber. The uniformity of the incident radiation flux also reduces thermal stresses and improves the absorber's performance. The near-wall region at the inlet is found to be most prone to mechanical failure. The results of the study provide important conclusions to help in the selection of the proper set of parameters that ensure the efficient, safe and reliable working of the receiver.
This paper proposes a strategy to optimize the design of the substrate structures used in Additive Manufacturing (AM) by Directed Energy Deposition (DED) to minimize the residual stresses induced by ...this fabrication process. To this end, several numerical analyses were performed to analyse different substrate designs in order: (i) to reduce the sensitivity to the initial non-steady stage when the first layers of material are deposited, (ii) to optimize the heat flux through the substrate to reduce the Maximum Temperature Gradients (MTG) and, (iii) to modify the substrate stiffness and its mechanical constraining to the thermal deformations during the building process and the cooling phase. To ensure the reliability of the numerical simulations, an in-house software is calibrated to allow for an accurate analysis of DED. Thus, an experimental setting is undergone to feed the numerical model with suitable values of both material and process parameters through temperature and displacement measurements and numerical fitting. Once calibrated, the software is used to evaluate the performance of several substrate designs to mitigate the residual stresses induced by the DED process. A thin-walled rectangular part selected as industrial demonstrator showed a significant reduction (up to 62%) of the maximum tensile stresses.
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•Substrate design optimization to reduce the residual stresses in DED.•Coupled thermomechanical analysis for AM by an in-house calibrated software.•Sensitivity of conformal and non-conformal substrates to the lower built surface.•Sensitivity of substrate stiffness and thermal resistance on residual stresses.
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