•Original lightweight hybrid lattice structures formulated and fabricated by FDM-based 3D printer to achieve favorable energy absorption characteristic.•Addressing limitations of conventional octet ...topology regarding its severely fluctuating post-yield response following a high yield stress.•Stable post-yield stress plateau without sacrificing stiffness and strength significantly in proposed hybrid structures validated by both compression experiments and finite element simulations.•Incorporating fabrication-angle-dependent strut material properties into simulations identified as essential to correlate with experimental results.
Lightweight cellular materials and structures are widely used in load-bearing and energy absorption applications, because of favorable mechanical properties such as high compressibility and low relative density. Recent progress in additive manufacturing techniques has enabled specific architectural geometries of unit cells in cellular structures to be tailored for particular needs. Numerous metallic and polymeric cellular lattices comprising different unit cell topologies have been manufactured and examined in terms of their energy absorption performance. In this study, two designs of hybrid three-dimensional cubic lattices which combine the advantages of an octet and a bending-dominated structure were established, and fabricated via the Fused Deposition Modeling technique. To validate the energy absorption capability of these new hybrid lattices, quasi-static uniaxial compression tests were conducted on samples made from Polylactic Acid. Numerical simulations were also performed to facilitate analysis of the deformation modes of the specimens tested in experiments. Tensile tests on solid dog-bone samples printed at various angles with respect to the build plate reveal fabrication-angle-dependent anisotropy. Consequently, material properties that depend on cell strut inclination were incorporated into the simulations. Compared with a conventional octet that possesses a high stiffness but a fluctuating post-yield response, the experimental results show that the new designs are capable of producing a relatively stable post-yield stress plateau without sacrificing stiffness and strength significantly. The present study indicates the potential for further enhancement of the energy absorption performance of lattice structures by tuning their topological architectures appropriately.
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Boron carbide (B4C), known for its unique properties, presents challenges in reaching its full density with sintering process due to low diffusion coefficients. This study explores the application of ...Spark Plasma Sintering (SPS) to overcome these challenges and enhance the understanding of its impact on pure B4C ceramics. The study outlines a comprehensive methodology for developing an SPS sintering model. Starting with a summary of conducted studies, powder oxidation analysis, characterization methods, and dilatometry curves processing, the article details the derivation of constitutive parameters based on the Skorohod-Olevsky theory. Isothermal profiles at different temperatures, variation in heating regimes, and a stepwise approach for SPS pressure application form the basis of the derivation methods. A grain growth model is developed for a comprehensive simulation of sintering, incorporating microstructural analysis and parameter derivation. Finally, the article addresses the integration of this mechanical sintering model with thermal and electrical considerations into a finite element method (FEM) software for a holistic SPS modeling. Thermo-electrical considerations, including the Peltier effect, are also computed, providing a well-rounded understanding of the SPS process for B4C ceramics. This study contributes valuable insights to optimizing the SPS parameters to achieve enhanced densification and microstructure control in B4C ceramics.
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•Finite element simulation of the braiding process at the fiber scale.•A penalty stiffness optimization method is proposed to solve the contact penetration problem of the fibers ...during modeling.•The mesoscopic geometry predictions of models with four kinds of pitch lengths are validated by quantitative comparison with micro-CT scans.
This paper presents a fiber-level finite element model (FE) based on the digital element approach (DEA) for simulating the braiding process and predicting the geometry of tubular braided ropes. The braided yarn is modeled as a bundle of virtual fibers, using chains of truss (rod) elements. In the simulation of the braiding process, a penalty stiffness optimization method is proposed to solve the fiber penetration. The optimization studies show that fiber penetration caused by the combination of insufficient standard penalty stiffness and different number of fibers in the discretized yarn are effectively eliminated until the penetration rate dropped close to 1.85 %. The mesoscopic geometry predictions of models with four kinds of pitch lengths (24 mm, 36 mm, 48 mm, and 60 mm) are validated by quantitative comparison with micro-computed tomography (micro-CT) scans of braided polyarylate fiber ropes. It is shown that geometric convergence of the models can be achieved when each yarn contains 30 fibers. The predicted results of pitch lengths, braiding angles, outer diameters, inner diameters and cross-sectional areas correlate well with those obtained from micro-CT scans.
•The first auxetic nails are designed, fabricated, and experimentally investigated.•The auxetic nails do not always exhibit superior mechanical performance to non-auxetic nails.•The surface roughness ...plays a significant role in the applications of auxetic nails.•Several criteria are proposed for the future design of auxetic nails.•Some disadvantages of auxetic materials are discussed.
Under uniaxial compression (tension), auxetic materials would shrink (expand) laterally. It has been speculated that the auxetic property could be used to design superior nails for easier push-in and harder pull-out. In this study, the first auxetic nails are designed, fabricated and experimentally investigated. Pine timber and medium-density fibreboard are selected as testing materials. The push-in and pull-out performance of auxetic and non-auxetic nails is compared by using two key parameters of the maximum compressive force and the maximum tensile force. It is found that the auxetic nails do not always exhibit superior mechanical performance to non-auxetic ones. Also, the small auxetic deformation of one typical designed auxetic nail is revealed by the experimentally validated finite element model. The experimental and numerical results illustrate the limitations of exploiting the auxetic property in the nail application. Some suggestions are provided for more effective designs of future auxetic nails.
This paper presents a comprehensive approach for the linearized frequency-domain analysis of hydrodynamic loading and structural responses on a deformable body. The structural and hydrodynamic ...analyses are integrated by employing the mode superposition method. Commencing with an eigenvalue analysis on the structural model, the shapes of selected modes, mass, and structural stiffness matrices are extracted as input to the subsequent hydrodynamic analysis, where the global response is solved in the modal space. The resulting hydrodynamic and inertial loads are then transferred to the same finite element model for stress assessment. To exemplify the proposed methodology, a bottom-fixed flexible cylindrical monopile and a long box-shaped barge model are investigated. For the barge model, the sectional loads are obtained from the integral of stresses in the cuts along the structure model, which are found to be consistent with those from the hydrodynamic analysis, demonstrating the consistency of the entire workflow. In particular, this paper introduces a straightforward formulation for evaluating the generalized restoring matrices, eliminating the need for spatial derivatives of the mode shape function and thereby significantly reducing numerical uncertainties in using the flexible modes derived from finite element model for hydrodynamic analysis.
•An integrated hydrodynamic-structural analysis workflow is proposed to account for the deformable motions of large volume floating structures.•Mode shapes FE model is taken as input to hydrodynamic analysis, with the resulting loads applied to the same model for stress evaluation.•Straightforward formulations proposed for restoring matrices, eliminating the need to operate with the spatial derivatives.•Mode superposition approach is validated against discrete module method to evaluate sectional loads and stresses for a flexible barge model.
In this study, we used a multi-physics coupling approach integrating the electrochemical and solid mechanics fields to develop a three-dimensional finite element model. This model was specifically ...designed to investigate the effects of mechano-electrochemical (M-E) effects on pipeline corrosion. The boundary conditions for the finite element simulation were established using experimental data, enabling the model to effectively predict the corrosion potential and current density, which aligned well with the experimental findings. Subsequently, the validated model was applied to examine the M-E effects near the pipe corrosion defects, considering various depths of corrosion defects and axial strain. Our results indicate that the stress concentration at the core of the defect increases with increasing axial tensile strain and deepening corrosion. The investigation of the correlation between the corrosion potential and net current density revealed that mechanical forces significantly impact metal corrosion rates, thus influencing pipeline longevity. When the metal structure of the pipeline is deformed within the elastic deformation range, the impact of the M-E effects on corrosion is minimal. However, when a tensile strain is applied or the defect geometry induces plastic deformation at the defect site, a notable increase in the local corrosion activity is observed.
•Developed a multi-physics model integrating electrochemical and solid mechanics for pipeline corrosion.•The refined model accurately predicts corrosion potential and current density under tensile stress.•Elastic deformation gradually increases corrosion rate with stress, while plastic deformation at defects significantly escalates it.•Effective corrosion protection in practical engineering applications requires careful management of potential levels and current densities.
Due to their potential to recover strength and stiffness with a minimum impact on aerodynamic performance of a damaged structure, scarf repairs are boosted as a viable repair option for primary ...aero-structures. So far, most of the experimental and numerical studies have been limited to joint specimens and their equivalent 2 Dimensional models and a few number of studies attempted to examine the results using real scarf repair geometry. Suggestions previously made to justify the difference between scarf joint and scarf repair strength and possible solution to diminish the difference are challenged in current work. Here, it is tried to investigate the strengths and shortcomings of 2D scarf joint modelling and their influence on the associated results by promoting 3 Dimensional Finite Element Modelling of complete geometry of the scarf repair. A method to assign material properties to a planar geometry of composite material has been developed that provides the possibility of plane strain, plane stress, and generalized plane strain modelling options of a scarf repair cross section under uniaxial load. Besides, accuracy of scarf joint specimen as a representative to scarf repair to predict load carrying capacity of a circular scarf repair is investigated. The study mainly focuses on 2D and 3D FEM simulation results discrepancies considering the effect of angle ply, cross ply and various stacking sequences of quasi-isotropic laminate under uniaxial and equi-biaxial loads. Results show that the laminate lay-up angles and stacking sequence substantially affect the 2D and 3D simulations agreement. Also, the observed discrepancies in scarf repair and scarf joint results are not limited to the effects of plastic deformation of the adhesive, but it seems the modelling shortcomings greatly affect the results. In overall, the current work demonstrates that for a particular laminate, joint specimen does not represent reasonably a scarf repair. In fact, the load carrying capacity estimated based on joint specimen data can mislead decision making procedure in a way that results in rejection of an eligible repair. To avoid inaccurate strength estimation, a 3D simulation of a scarf repair especially for a load other than uniaxial tension or compression is strongly recommended.
The gear foundation is commonly assumed to be a rigid body in analyzing the dynamic characteristics of the gear system. This modeling approach may not be appropriate for building the gear model with ...lightweight features. Therefore, this paper proposes a gear dynamic model considering the flexible gear. The shell element with gyroscopic effect is employed to establish the gear finite element model, retaining the gear foundation and teeth structure. The fixed interface modal synthesis method is used to improve computational efficiency. The proposed model is verified by comparing it with the results calculated by Ansys. Based on the proposed model, the effects of gear flexibility on the dynamic characteristics of the spur and helical gear system are investigated. Numerical results show that the developed model can degenerate into the classical gear dynamic model. Due to the assumption of the gear as rigid discs, the predicted resonance speed by the conventional gear dynamic model is larger than the proposed model. Gear flexibility affects the dynamic characteristics of the spur and helical gear system differently. It's worth noting that the dynamic axial meshing force can excite the nodal diameter vibration in the helical gear system. The proposed model provides the theoretical basis and optimization tools for the high-performance design and vibration and noise reduction of high-speed lightweight gear transmission systems.
When the power transformer is connected to the power grid, a surge of inrush current may occur as a result of residual flux. In order to mitigate this effect, measurement of residual flux is ...necessary. In this paper, a method for measuring the residual flux of ferromagnets was proposed, utilizing magnetic sensors and a finite element model. Residual flux originated from residual magnetization, which could be obtained from a matrix of spatial magnetic flux density measured by sensors and the conversion matrix calculated from the finite element model. By combining the residual magnetization with the background magnetic field, the residual flux could be determined. Experimental results confirmed the accuracy of the proposed method, which was particularly suited for measuring non-uniform residual flux, and also enabled determination of residual flux direction. In comparison to existing methods, this approach offered significant advantages.
•The proposed optimization formulation updates stiffness and damping parameters in a non-viscous damping system.•The method uses complex eigenvalues/vectors from measurements of a limited number of ...DOFs and modes.•The method is validated on a full-scale pedestrian bridge (544 DOFs).•Analytical gradient improves computational efficiency over numerical gradient.
This paper proposes a finite element model updating method for non-proportional viscous and exponential non-viscous damping systems using complex eigenvalues and eigenvectors. The exponential non-viscous damping provides complex eigenvalues/vectors for elastic modes and real-valued eigenvalues/vectors for non-viscous modes. This study first highlights the challenges in accurately identifying real-valued eigenvalues/vectors for non-viscous modes with a commonly used system identification method. In contrast, complex eigenvalues/vectors for elastic modes are reliably identified and, therefore, utilized in the proposed model updating approach. Consequently, an optimization formulation is proposed to minimize the difference between the simulated and experimental complex eigenvalues/vectors. The method applies large structures that can contain multiple substructures with different damping properties. For brevity, damping properties are assumed to be uniform over each substructure. In addition, mass-proportional viscous damping and stiffness-proportional non-viscous damping are adopted for each substructure, which results in overall damping being non-proportional. To improve computational efficiency, the analytical gradient of the proposed optimization formulation is derived and implemented. For validation, the model updating of a full-scale steel pedestrian bridge is performed. The method is first validated in simulation and further validated by experimental data considering the statistical properties of system identification results. The proposed method successfully identifies stiffness and damping parameters using only a limited number of measured DOFs and modes.
