Equivalent sandwich panels composed of auxetic and conventional honeycomb cores and metal facets are analysed and compared for their resistance performances against impulsive loadings. The dynamic ...behaviours of these structures are numerically investigated, taking into account the rate-dependent effects. The Johnson-Cook model is employed to describe the dynamic responses of the composite sandwiches subjected to high strain-rate loadings. Analytical models are derived correlating unit cell geometrical parameters and crushing strengths of the representative panels at different impact velocities. Parametric studies are conducted to evaluate the performances of different sandwich panel designs under impulsive loadings. In particular, transmitted reaction forces and maximum stresses on the protected structure are quantified for various design parameters including the geometrical factors and the effective Poisson’s ratios. A quarter of the panel is symmetrically modelled with shell elements and the CONWEP model is used to simulate the blast loading. Auxetic panels demonstrate interesting crushing behaviour, effectively adapting to the dynamic loading by progressively drawing material into the locally loaded zone to thereby enhance the impact resistance. Meanwhile, conventional honeycomb panels deform plastically without localised stiffness enhancement.
Soft magnetic skins have been widely adopted for tactile perception due to their high accuracy and simple wiring advantages. However, the perceptual properties of magnetic skins are limited by ...information mapping relationships with weak interpretation. To overcome existing limitations, dynamic Young's modulus (DYM) is proposed in this paper based on strain energy density function to precisely describe the compression stiffness of magnetic skins. Furthermore, a highly interpretable and broadly applicable method is derived using DYM to analyze a cylindrical magnetic skin's deformation process as the skin deformed under external mechanic load. Extensive experiments in simulated and real situations with different deformations are carried out to verify the proposed method. Experimental results demonstrate that 0.14% and 0.43% relative errors in simulated and real environments, respectively, can be reached. Moreover, the proposed method can achieve minimum errors in almost all situations than data-driven or state-of-the-art analysis approaches. And the generality of the proposed method is validated by experiments conducted on skins with two different shapes. These promising results indicate the potential of the proposed method in establishing practical information mapping relationships for magnetic skins, probably addressing the significant challenges for magnetic skin application in complex scenarios.
During operating time of electronic systems, the used materials in such devices are potentially subjected to ageing effects, which might limit the lifetime. Therefore, knowledge about the used ...materials and the way the materials are affected by ageing effects is of key importance to develop reliable products.
In this study, a simulation approach is discussed that is able to consider ageing effects caused by oxidation at elevated temperature of a printed circuit board material, typically used for high frequency applications. The material was characterized for its thermomechanical properties with state-of-the-art techniques for different ageing durations. Ageing was accelerated by storing the samples in an oven at 175 °C for up to 1000 h.
Within the simulation workflow, the thermomechanical properties of the different aged states are defined by modifying the pristine viscoelastic properties. Four exponential functions are derived modifying the initial modulus, the characteristic time constants, the shift function and the coefficient of thermal expansion, all in dependency of ageing time.
To demonstrate the approach, the soldered interconnection lifetime of a theoretical chip-size-package on a printed circuit board is studied. State-of-the-art lifetime predictions of such interconnections only include thermomechanical ageing effects, for example by creep effects of the solder. By additionally considering the ageing of the printed circuit board, thermal ageing is combined with thermomechanical ageing.
Results in the soldered interconnection are compared between either considering additional ageing effects of the printed circuit board or neglecting this behavior. Thus it is shown that thermal ageing plays a significant role in the development of accumulated creep strain which becomes increasingly important with increasing expected lifetime.
•Viscoelasticity.•Finite element simulation.•Ageing of Polymers.•Lifetime prediction.•Ageing.
Sandwich panels composed of auxetic cellular cores and metal facets are presented for blast resistance applications. The performance of this hybrid composite structure under impulsive loading is ...numerically studied, taking into account the rate-dependent effects. The Johnson–Cook law is used to model the behaviours of composite materials at high strain rates. Parametric analyses are performed to evaluate the performances of different designs of composite panels and compared with equivalent monolithic panels of identical areal masses in terms of deformations and dissipated plastic energy of the metal facets and auxetic crushable cores. Various design parameters are considered, including the auxetic unit cell effective Poisson’s ratio, material properties, thickness of facet, and diameter of the unit cell truss member. To reduce the computational time, a quarter of the panel is modelled with shell elements for the facets and beam elements for the core. In blast events, auxetic composite panels are found to effectively absorb double the amount of impulsive energy via plastic deformation, and reduce up to 70% of the back facet’s maximum velocity when compared with monolithic ones. The maximum back facet displacement is also noticeably reduced by up to 30% due to the densification and plastic deformation of the auxetic cores.
Fittings have extensive use in the aerospace, automotive, and other industries as they serve as sealing and connecting components for tube systems. External Swaging (ES) forming creates a permanent ...joint through plastic deformation of the metal. This technique is not dependent on the tube's wall thickness and offers benefits such as high-pressure resistance and effective sealing. Using the forming process of a 10 mm Ti-3Al-2.5 V tube with an adapted 21-6-9 fitting as an illustration, a three-dimensional finite element model for the entire assembly was developed. The model consists of the tube, fitting, elastic clamp, and crimping tool. The formation mechanism and joint strength of external swaging are analyzed by numerical simulation and experimental testing. The results show that during the extrusion process, the tangential contact between the extrusion tool and the elastic clamps converts external radial loads into circumferential loads, resulting in circumferential strains in the tube. Circumferential strain creates an arched sealing area between the tube and fitting contact surfaces, providing sealing and joint strength. The joint strength of 10.60 kN was determined through finite element simulation. The load required for forming is determined by analysis to be 80.13 kN. and the relationship between squeeze load, crimp volume and joint strength is clarified. The study revealed that the height of the arch area aligns with the connection strength's change rule concerning extrusion load, fitting the two found that when the external extrusion load changes, the two are linear rule of changing. Based on this, a method is suggested for forecasting the strength of a joint by measuring the height of the arch in the tube after forming.
•Explaining how the radial load is converted to circumferential loads to complete the external swaging•Investigation of the relationship between the extrusion load, extrusion volume, and connection strength after forming.•A novel approach for assessing the strength of a connection by measuring the arch's height.
Abstract
In the present paper, finite element analysis of the knee joint is performed for stress and strain estimation of the knee joint for osteoarthritis patients. Osteoarthritis (OA), called the ...wear and tear arthritis is commonly occurring arthritis wherein a gradual loss of cartilage from the joints are observed. This leads to the joint bones rubbing quite close against one another with less amount of shock-absorbing done by the cartilage causing pain, stiffness, swelling, decreased movability and bone spur formation can be observed. It is mostly observed in patients above 45 years old, but weight and gender are also some of the factors forcing a quick onset of the disease. Using modelling software Blender, a solid model is made of the bone component, namely tibia, fibula, femur and patella as well as Ligaments and cartilages. Using finite element simulation software, analysis is done to determine the level of stress under various forces on the joint. The knee joint experiences a maximum stress and strain of 2.352 MPa and 0.02454 respectively which are within safe static condition. The study can be further extended to predict the danger of failure for the patients having osteoarthritis conditions which in turn will help to take a preventive measure for the knee joint.
This investigation explores the fabrication of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolytes, specifically focusing on the evolution of densification and resulting stress within the sintered structure ...of LLZTO electrolytes. Through a combination of experimental methods and numerical simulations based on finite element analysis, this study clarifies the mechanisms underlying the enhanced densification and grain growth of LLZTO with the addition of the sintering aid, liquid metallic gallium, attributing these effects to the reduced activation energies. With elevated sintering temperatures or the addition of gallium, the fired LLZTO exhibits heightened conductive performance, with conductivity increasing from < 10−4 to > 10−4 S cm−1. The numerical simulations further elucidate the correlation between stresses and the agglomeration/distribution of components during sintering. Non-uniform component distribution and agglomeration significantly escalate stress levels by two to four orders, compromising the structural integrity of the sintered electrolytes. The imperative need to address these challenges in the early stages of battery fabrication becomes apparent for the successful developments of ceramic electrolytes and the corresponding solid-state lithium batteries.
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In laser-based metal additive manufacturing (MAM), effective process optimization requires a thorough analysis of variations across the process window. Despite the common practice of utilizing ...small-sized coupons to optimize process parameters in laser-based MAM, this study challenges this convention. Through an analysis of microstructure and defect differences in Fe-Ni material parts produced via laser-powder bed fusion (L-PBF), the study reveals significant discrepancies in microstructure, defect and mechanical property based on part size. As part size increases, lack-of-fusion defects and cracks become more pronounced, resulting in a decrease in density from 8.11 g/cm3 to 8.02 g/cm3, leading to constrained grain growth with a decrease of grain size from 41.88 μm to 23.07 μm in the scanning plane. Each defect and microstructural difference was traced back to variations in thermal history based on part size. Finite element method simulations, highlighting differences in thermal history from scanning a single layer to the entire part, showed that an increase in scan length with a widened scan area enlarged the period of the thermal history cycle, leading to considerable cooling. This study underscores crucial considerations for future researchers engaged in process optimization for novel alloy systems using laser-based MAM processes.
•Part size matters at thermal history in laser-based MAM process.•Microstructure and defects variation due to thermal history difference stems from part size.•FEM simulations reveal thermal history differences due to the part size variation.•Limitation of the conventional process parameter optimization using process window.
The behavior of gas bubbles produced during electrochemical processes is of large interest because of the increase in cell overpotential induced by their production, the electrode surface covering by ...them and, finally, the detachment of these bubbles and their direct impact on the energy consumption during the reaction. In this work, we used coupled experimental and computational approaches to investigate bubble formation under those conditions where there are important convective effects. We have measured both normal and parallel velocity of the solution and built up a computational fluid dynamics (CFD) model. The results were compared to experimental data. Then, having the computational model validated by experimental data, we have simulated different conditions following bubble displacement. An important change of the surface covering is observed during the electrochemical reaction. Considering just the covering change, for example, there is up to 23 % increase comparing to the electrode edge and center.
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•Finite element method is suitable to evaluate the bubble-induced convection.•The bubbles create a vortex in the electrolyte.•The induced convection create a non-homogeneous gas covering over electrode surface.•The bubble size has an important effect in the covering variance.
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