A study of the early stage of crack formation in unidirectional composites subjected to transverse tension in the presence of micro voids in the matrix is conducted by computational simulation. The ...focus of the study is brittle cavitation leading to fiber/matrix debonding followed by debond crack growth and kink-out into the matrix. These failure events are studied considering a nonuniform fiber distribution and a uniform hexagonal fiber pattern in the cross section of a unidirectional composite with voids in the vicinity of the initiated cracks. A dilatational energy density criterion is used for initiation of debonding while the debond crack growth and kink-out into the matrix are studied by the energy release rate, which is calculated by the virtual crack closure technique (VCCT). Results show that while the debond initiation site is not affected significantly, the debond growth and kink-out are affected by circular voids in the close vicinity and when the diameter of these voids is a significant fraction of the fiber diameter. The effect of fiber distribution nonuniformity is manifested in the inter-fiber distances that governs the critical conditions for the debonding and kink-out processes.
The automated design of synchronous reluctance (SyR) motors based on multiobjective genetic optimization and finite-element analysis is considered in this paper. Three types of barrier shapes are ...considered, all described by an effective limited set of input variables. The three solutions are investigated to establish which of the geometries can give the best torque output and also which one represents the best compromise between output performance and computational time. The analysis presented in this paper shows that SyR motors designed automatically can give a good performance and can be designed in a reasonable time, and it is also shown that not all design degrees of freedom are useful in terms of motor performance. Two prototypes of automatically designed machines have been fabricated and experimentally compared with a third prototype designed according to state-of-the-art design principles.
Effective thermal conductivity is an important property of composites for different thermal management applications. Although physics-based methods, such as effective medium theory and solving ...partial differential equations, are widely applied to extract effective thermal conductivity, recently there is increasing interest to establish the structure-property linkage through machine learning methods. The prediction accuracy of conventional machine learning methods highly depends on the features (descriptors) selected to represent the microstructures. In comparison, 3D convolutional neural networks (CNNs) can directly extract geometric features of composites, which have been demonstrated to establish structure-property linkages with high accuracy. However, to obtain the 3D microstructure in the composite is challenging in reality. In this work, we use 2D cross-section images and 2D CNNs to predict effective thermal conductivity of 3D composites, since 2D pictures can be much easier to obtain in real applications. The results show that by using multiple cross-section images along or perpendicular to the preferred directionality of the fillers, 2D CNNs can provide quite accurate prediction. Such a result is demonstrated with isotropic particle filled composites and anisotropic stochastic complex composites. In addition, we also discuss how to select representative cross-section images. It is found that the average over multiple images and the use of large-size images can reduce the uncertainty and increase the prediction accuracy. Besides, since cross-section images along the heat flow direction can distinguish between serial structures and parallel structures, they are more representative than cross-section images perpendicular to the heat flow direction.
The increased use of hybrid joints such as bonding composites to metals in aerospace, hull, civil and automotive structures in the past decades makes it essential to find methods to improve the ...performance of the joints. This study presents both experimental and numerical investigations into a novel dissimilar single-lap joint (SLJ) with interfacial stiffness improvement. The main objective of this research is to minimise the peak stress concentration by reinforcing the lower stiffness adherend’s interface through embedding discrete AL patches to increase the performance of the dissimilar single-lap joint with epoxy adhesive. Finite element models (FEA) were developed in Abaqus® software to analyse the effects of thickness and length of the patches, and the failure mechanism due to the reinforcement. Dissimilar single lap joints with different configurations were fabricated and tested using single lap shear tests to validate the numerical analysis. Both the experimental and numerical results show that the strength of the reinforced joint is significantly enhanced by using the aluminium patches.
A structural analysis and an optimization method for anisogrid composite lattice shell structures is proposed, considering cylindrical structures simultaneously subjected to different external loads ...and multiple stiffness constraints. A discrete approach is used to exactly estimate the critical buckling load of the anisogrid lattice structure, independently of the buckling failure mode. The method makes use of a full FE parametric modeling technique able to manage all the geometrical parameters of the anisogrid composite lattice structure. Then an optimization procedure based on the genetic algorithm NSGA-II has been performed; it allows to analyze different alternatives in terms of geometrical variables, both continuous and discrete, driving the search towards the optimal solution in term of mass and conformity with all structural and stiffness constraints, aiming at the preliminary design of an actual structure. The practical usefulness and applicability of the proposed procedure to industrial cases was demonstrated through numerical examples where the anisogrid lattice structure was subjected to multiple external loads and stiffness constraints simultaneously applied.
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The present work proposed a multiscale finite element (FE) analytical approach to investigate the mechanical behavior of elasto-plastic aluminum matrix composites reinforced with nano-micro hybrid ...inclusions. To study the effect of microstructural effects, 3D representative volume elements (RVEs) of nano- and micro-scales are established, where the nano-RVE considers the aluminum matrix with carbon nanotubes (CNTs)-reinforcement whose homogenization is treated as the equivalent matrix (EM) phase for micro-RVE with SiC particles. The FE-based ABAQUS simulation is employed to recover the local stress distributions within RVE of either scales, and the corresponding effective stress–strain relationship, damage and failure behavior are calculated and predicted. Results generated from the present simulations are validated against the experimental measurement of CNTs/SiC/Al composites and good agreement is generally obtained. What’s more, several microstructural parameters are tested on the composites’ effective behavior, including the elaso-plastic constitutive relation and damage response of aluminum matrix, the elastic-brittle failure mechanical behavior of the micro-scale SiC particles. We also consider the traction-separation mechanical behavior at the SiC-Al interface. It is demonstrated that the present numerical method is suitable to study the comprehensive behavior of composites with hybrid inclusions.
To fully take the high-frequency advantage of gallium nitride (GaN) devices, this article presents a face-up integrated power module based on the printed circuit board embedding technology to tackle ...the challenges caused by the conventional discrete solutions. The proposed GaN module highly integrates a GaN-bare-dies-based full bridge, driving circuits, and decoupling capacitors, in which the advanced bismaleimide-triazine material is used as the packaging material and the copper-filled laser microvias are used for low-parasitic-inductance and high-thermal-conductivity interconnection. Careful electro-thermal codesign and optimization of power loop is conducted to make the tradeoff between power loop inductance and thermal performance. The proposed full bridge power module achieves the lowest power loop inductance of about 0.305 nH in power modules with the same power level. The maximum thermal resistances from the embedded GaN bare dies to top and bottom surface are 3.39 and 0.42 °C/W, respectively. Benefitting from the ultralow power loop parasitic inductances, the switching speed of GaN devices reaches to 57.5 V/ns, while the voltage overshoot is not higher than 5.35% of the dc bus voltage. The superior performance of the proposed integrated GaN module makes it a promising application prospect in high frequency high power density converters.
Hard turn rolling is a hybrid manufacturing process that affects the surface integrity of hardened components, aiming to enhance the lifespan of components such as rolling bearings. Hard turn rolling ...combines the thermal influence of hard turning with a subsequent deep rolling process to modify the properties of the surface and surface near layer. To better understand the effects of deep rolling on AISI 52100 at elevated temperature that are generated by the hard turning process, finite element simulations were conducted to analyze the surface formation at elevated temperatures. These simulations enable the estimation of the workpiece surface, guiding the optimal positioning of the deep rolling tool in alignment with the hard turning process. However, the results indicate that there is a buildup observed in the simulation, which was not detected in the experiments. The width of the rolling tracks in the simulation at different specimen temperatures of 20°C, 200°C, and 400°C does not exhibit significant differences. Only the rolling pressure has an influence on the width of the rolling tracks. By controlling the parameters of hard turn rolling, further investigations are possible to achieve enhanced surface and subsurface properties and improved performance of the hardened components in the future.
•Effect of hybrid ratios on ballistic penetrations were revealed via FEA and tests.•Ballistic impact damages of hybrid laminates have been shown for optimization.•Hybrid schemes have been recommended ...for high ballistic energy absorptions.
Fiber hybrid is a promising strategy for improving ballistic penetration behaviors of fiber-reinforced laminated composites. Ballistic impact performance of hybrid fiber laminates against projectiles depends on various parameters not only with respect to the material properties, fiber types, yarn properties, fabric structures of the constituent plies but also with the hybrid configuration, material combinations and stacking sequences. It has a substantial growth demand to obtains the optimal hybrid design of the fiber hybrid composites, for maximizing the potential of the constituent materials and improving the overall anti-impact performance of the hybrid composites. However, the effect of the hybridization ratios on ballistic penetration behaviors of the hybrid composites is still infant. Here we report the hybridization ratios on ballistic impact damage of carbon/Kevlar/UHMWPE (ultra-high molecular weight polyethylene) hybrid laminates through ballistic impact experiments and three-point bending tests. The fiber hybrid laminates with different hybrid ratios had been fabricated and studied under the impact of FSP (fragment simulating projectiles). The effect of the hybridization ratios on the flexural behaviors, ballistic curves, energy absorptions and damage modes were investigated. The FEA (finite element analysis) was carried out from meso- to macro- scale model. We found that the flexural behaviors are related to the material properties and mechanical balance among different material components in the hybrid systems. The damage modes for various hybrid ratios have a typical impact damage mode like matrix cracking, fiber breakage and delamination. A rational accuracy in residual velocities and damage modes can be obtained between ballistic experiments and FEA results. The hybrid ratios would affect the stress wave propagation in the composites with a gradual attenuation development and lead to different failure mechanisms. This study is expected to reveal a fundamental failure mechanism for the fiber hybrid composites incorporated with three different fiber combinations in different hybrid ratios under ballistic impact. The results can provide important theoretical basis and experimental reference for designing and developing hard multiphase anti-impact composite structures.
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The popularity of tiny houses is increasing, but the technical details are rarely covered. Therefore, this study examines the structural, stability, weight, and thermal requirements of tiny houses. A ...configurable SolidWorks model was created, and the location and quantity of structural supports were determined by performing structural finite element analyses (FEA). The center of mass, tip angles, overall weight, and tongue weight were computed to ensure stability while stationary or during transit. The heating and cooling needs for the tiny houses were calculated using thermal FEA for twelve cities of varying climates across the United States.The result was a Scilab design tool that takes as input, items such as location, desired size, utility needs, etc. It calculates the materials needed for the structure and the projected cost. This design tool, along with the provided construction drawings, allows the user to build a safer, efficient, and cost-effective tiny house.
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•Tiny houses have become popular for people seeking to live more sustainably.•Considered structural, stability, weight and thermal requirements of tiny houses.•Design tool aids in designing a safe, efficient, and cost-effective tiny house.
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