Accurate Finite Element Model Research Articles

Seismic safety assessments of historical timber buildings using updated finite element models: Case study of Yingxian wooden pagoda, China

Historical timber buildings are important for the global architectural heritage. However, establishing accurate models for seismic performance evaluations to assess the safety of historical buildings remains challenging. Therefore, simplified simulation methods—the dougong (DG) and mortise-tenon joints (MTJs) based on shear and bending plastic hinges—were developed. Moreover, a model updating method based on multiple degrees of freedom considering the initial inclination was improved to obtain accurate finite element (FE) models. Using the FE model of the Yingxian wooden pagoda in China as an example, the proposed methods were validated against field monitoring measurements. A time history seismic analysis was also conducted on the updated pagoda FE model. The results revealed that the simplified simulation method could accurately and efficiently simulate the plastic behaviors of the DG and MTJs. Furthermore, the model updating procedure reduced the maximum period difference from 9.77% to 2.98%. The maximum story drift ratio reached 1.590% under an earthquake, with a peak ground acceleration of 310 gal; this indicated that the pagoda model described moderate damage; certain components were in a plastic state with a maximum rotation of 0.0427. Notably, this study provides a useful method and a basis for establishing and evaluating models and assessing the seismic safety of historical timber buildings.

3-D coarse-grained reconfigurable array using multi-pole NEM relays for programmable routing

We propose the use of multi-pole nanoelectromechanical (NEM) relays for routing multi-bit signals within a coarse-grained reconfigurable array (CGRA). We describe a CMOS-compatible multi-pole relay design that can be integrated in 3-D and improves area utilization by 40% over a prior design. We then demonstrate a method for placing multiple contacts on a relay that can reduce contact resistance variation by 40× over a circular placement strategy. Additionally, we develop static and dynamic SPICE models (calibrated to accurate finite element models) for predicting circuit-level performance with these devices. Finally, we establish a methodology for integrating these relays into an industry-standard digital design flow. Using our multi-pole relay design, we perform post-layout simulation of a hybrid CMOS-NEMS CGRA processing element (PE) tile in 40 nm technology. We achieve up to 19% lower area and 10% lower power at iso-delay, compared to a CMOS-only CGRA PE tile. The results show a way to bridge the performance gap between programmable logic devices (such as CGRAs) and application-specific integrated circuits using NEMS technology.

Study on protective performance and gradient optimization of helmet foam liner under bullet impact.

Protective equipment in war plays a vital role in the safety of soldiers, the threat to soldiers from brain damage caused by deformation at the back of the helmet cannot be ignored, so research on reduce blunt post-cranial injury has great significance and value. This study first conducted gunshot experiments, used rifle bullets impact bulletproof plate and different density liner foam to record the incident process and internal response of craniocerebral model. After verifying the accuracy of finite element model through experimental data, optimization model is established based on response surface method to optimize the structure of gradient foam, analyze the cranial strain and energy absorption to select the best density and thickness distribution of each foam layer. Optimization results show that liner foam which designed to have lower density and thicker thickness for impact and brace layers, higher density and thinner thickness for middle layer can significantly improve the energy absorption efficiency. Compared to the 40.65 J of energy absorption before optimization, the optimized gradient foam can absorb 109.3 J of energy, with a 169% increase in the absorption ratio. The skull strain in the craniocerebral model was reduced from 1.260 × 10–2 to 1.034 × 10–2, with a reduction of about 22%. This study provides references for the design and development of protective equipment and plays an important role in ensuring the safety of soldiers in the battlefield environment.

Finite element analysis of shear performance of UHPFRC-encased steel composite beams: Parametric study

The shear response of ultra-high performance fiber reinforced concrete (UHPFRC)-encased H-shaped steel section composite beams is simulated using a three-dimensional (3D) non-linear finite element model (FEM) in the present study. The proposed FEM's accuracy is validated against experimental data from previously tested steel and UHPFRC beams available in the literature. Numerical results agreed well with the experimental findings in terms of load–deflection response and failure mode. Before conducting the parametric analysis, the influence of the model mesh size on the ultimate load capacity, as well as the initiation and propagation of cracks along the entire length of H-shaped steel and UHPFRC beams, is considered. The mesh sensitivity analysis, which was performed using three different mesh sizes of 50, 40, and 30 mm, revealed that all mesh sizes successfully predicted the ultimate load of the analyzed beams, while the lowest one (30 mm) was the best in predicting the distribution of shear and flexural cracks along the entire length of the steel and UHPFRC beams. The parametric study investigated the encasement effect as well as the shear-span-to-depth ratio and effective length of the steel beam on the ultimate load capacity, stiffness, ductility, and failure pattern of composite beams. The gain in ultimate load of the composite beam was 448 % and 278 % with respect to the bare steel and UHPFRC beams, respectively. Furthermore, the ultimate load reduction ratios for specimens with shear span-to-depth ratios of 2.1, 2.6, 3.1, and 3.6 were 20, 32, 38, and 41 %, respectively, with respect to the shear span-to-depth ratio of 1.6.

Enhancement of local concrete compression performance by incorporating ultra-high performance concrete (UHPC) tube

PurposeThe application of ultra-high performance concrete (UHPC) in anchorage zones can significantly improve the local compression performance of structures. However, the high cost and complex preparation of UHPC make UHPC difficult to be widely used in practice. This study proposes a method to strengthen the local compression zone of structures built by normal strength concrete (NSC) by incorporating UHPC cores.Design/methodology/approachIn this study, a Finite Element Model (FEM) of local compression specimens was established by ABAQUS, and the accuracy of FEM was verified by comparing the FEM calculation results with experimental results. The verified FEM was adapted to the research on the influences of affecting factors on local compression performance of structures, including NSC strength, UHPC strength, spiral steel bar strength, and UHPC core diameter.FindingsThe results show that the peak load of the strengthened specimen SC1-U + N increases by 210.2% compared to that of the SC1-NSC. Furthermore, compared to SC1, the strengthened specimen SC1-U + N can save 64.7% amount of UHPC while the peak load decreases by only 34.4%. The peak load of the strengthened specimens increases with the axial compressive strength and the diameter of UHPC cores increasing, crack load increases with increasing the compressive strength of NSC, the spiral steel bar with high strength can prevent the sharp drop of load-deflection curve and the residual bearing capacity increases accordingly. All findings indicate that increasing the diameter of UHPC cores can improve the overall performance of the specimens. Under loading, all specimens fail by following a similar pattern. The effectiveness of this new strengthen method is also verified by FEM analytical calculations.Originality/valueBased on the experimental study, this study extrapolates the influence of different parameters on the local bearing capacity of the strengthened specimens by finite element simulation. This method not only ensures the accuracy of bearing capacity assessment, but also does not require many samples, which ensures the economy of the reinforcement process. The research results provide a reference for the reinforcement design of anchorage zone.

The effect of tightening again on bolt loosening under transverse load: Experimental and finite element analysis

Bolt loosening is one of the most common failure modes in bolted joints. Tightening again is often used to compensate for the loss of clamping force in many critical applications. In this study, the effect of load control modes and lubrication conditions on bolt loosening were studied by experiments. Then, a series of experiments were carried out on the tightening again after bolt loosening under transverse load. Finally, in order to study the cause of fatigue fracture, FEA was carried out by using an accurate three-dimensional finite element model. The results show that the bolt loosening is mainly caused by relative motion between the two clamped plates. With oil lubrication, the bolt clamping force was able to reach the magnitude comparable to the initial preload when the nut is released to a specific angle (30° ∼ 60°) before tightening again. Nevertheless, the times of tightening again should be limited to avoid fatigue fracture of the bolt.

Triaxial Contact Stresses of the Green Bus Tire Including Complex Rubber Materials and Rim

The primary purpose of the research is to explore triaxial contact stresses of the green bus tire including complex rubber materials and rim. An accurate finite element model of the bus tire is constructed using ABAQUS software after verification. The measured and calculated values have good consistency under different tire loads and inflation pressures. The finite element model is applied for quantitative research by changing tire loads, inflation pressures, and rolling conditions. The analysis results show that higher inflation pressure increases vertical contact stress, which requires a reasonable balance between high load and high inflation pressure. When the inflation pressure increases, the position of the maximum longitudinal contact stress shifts forward, and the maximum transverse contact stress shifts inboard in the transverse direction. When the tire load becomes larger at the free rolling condition, the position of the maximum vertical contact stress moves forward, and the position at the full braking condition is more advanced under the same load conditions. Overload not only causes great damage to the tire during the braking condition but also accelerates the appearance of the rutting and shoving of the road.

Assessment of cyclic behavior and performance of hybrid linked-column steel plate shear wall system

An innovative hybrid linked columns steel plate shear wall (HLCS) system provided, and its cyclic behavior and energy absorption are investigated by finite element method in this study. The objective of the designed HLCS system was to reduce or possibly prevent damage to the SPSW at low and medium seismic levels by focusing the seismic damage to interchangeable link beams (the energy dissipation components of the presented HLCS system). In this study, the cyclic behavior and energy dissipation of HLCS systems were investigated using numerical methods. To evaluate the hysteresis behavior and energy absorption of the proposed HLCS system, parametric studies were performed. Also, the accuracy of finite element models was evaluated by comparing test results that showed the good accuracy of finite element models in predicting the specimens' hysteresis behavior and failure modes. Due to the failure mechanisms, the coupling ratio amounts meaningfully affect the onset of the first surrender mechanism between the infill steel plate and link beams. In general, by increasing the number of link beams in the floor, the ultimate shear force to the weight ratio of the structure was increased. Also, the type of beam in terms of flexural and shear behavior did not significantly affect the ratio of base shear force to the structure weight. The proposed HLCS system has increased the ratio of base shear force to the weight by an average of 4%–27%, indicating that this system is economically comparable to the SPSW systems. Moreover, the energy dissipation in the HLCS system exhibited a 14%–91% enhancement compared to the SPSW system.

An Insight on the Estimation of Wave Propagation Constants in an Orthogonal Grid of a Simple Line-Supported Periodic Plate Using a Finite Element Mathematical Model

This article describes the propagation of free waves in a two-dimensional periodic plate using the finite element (FE) method. The advantage of periodic structure analysis is that all the dynamic properties of a finite structure are derived from a single phase-frequency curve or surface. Infinite plates are considered as a combination of periodic plates on an orthogonal array of simple, evenly spaced line supports. A single periodic unit of the system is represented by a more accurate high-precision arbitrary triangular shallow shell FE model to find the plane wave frequency in terms of the propagation constants of the 2D periodic plate. Only the purely propagating waves with no attenuation are considered here. The natural frequency of the infinite plate was obtained for different propagation constants in the two directions of the plate. The results are compared with the literature data. The bounding frequency of the propagation surface is compared to the data published from single square and rectangular plates with different edge boundary conditions. In addition, the natural frequency of the plate supported by finite line support with spans Nx (x-direction) and Ny (y-direction) is compared with the frequency obtained from the propagation curve by the discretization principle. The comparison is seen to be very close. It is found that the current PS-FEM approach can be used to generate dispersion relations with reasonable accuracy.

Effects of yield point and plastic anisotropy on results of elastic–plastic finite element analysis of tension leveling

Tension leveling is an important industrial process to eliminate the flatness defects and residual stresses of metal strips to provide high-quality sheet metals for subsequent sheet metal forming. The finite element (FE) method can be applied to elucidate the effects of process parameters on the quality of sheets after tension leveling for various materials. In our previous investigation, an accurate FE model has been established for the elastic–plastic FE analysis of tension leveling. In this study, we further studied the effects of the yield point and plastic anisotropy on tension leveling using the FE model established in our previous investigation. Aiming at improving the accuracy of simulation, a modified constitutive model was developed to describe the anisotropic hardening of materials under cyclic loading. The modified constitutive model was implemented into Abaqus/Standard as a user-defined material subroutine to simulate the development of the anisotropy in materials during tension leveling. The modified model was also applied to the FE analysis of sheet metal forming processes to demonstrate its simulation capability and accuracy.

Improving the accuracy of finite element modeling of superplastic forming processes

A method of improving the accuracy of finite element modeling of superplastic forming processes is suggested. It is based on improving the accuracy of determining the values of material constants for the standard power law of superplastic flow from the results of technological experiments under constant pressure forming of hemispherical domes. Unlike other known procedures, the method suggested takes into consideration the initial stage of superplastic forming, when the pressure of the inert gas changes from the initial zero level to a pre-given constant value. Since this part of loading is usually neglected in reports known in the literature the main attention in the present study is paid to the analysis of its importance as far as the accuracy of finite element modeling is concerned. Besides, the entry radius in the die used is also a variable in the analysis. The calculations are performed for alloys Ti-6Al-4V, AZ31, AA5083 using the experimental data known in the literature. Finite element modeling is carried out using the ANSYS code. It is concluded that the influence of the initial part of loading should be considered in finite element modeling of the superplastic forming processes since this factor can affect the accuracy of predictions.

Using the finite element method to evaluate the load-bearing capacity of beams with a corrugated web subjected to local loading

Introduction. Steel beams with a corrugated web are increasingly frequently applied in industrial and civil engineering due to their cost effectiveness. There are numerous studies proving the advantages of corrugated beams. However, the issue of calculating such elements is insufficiently covered in the standards and engineering literature, which is one of the main factors restraining their widespread use.
 
 Materials and methods. Along with the use of analytical dependencies, which, as a rule, are focused on a specific type of web corrugation and have limitations in terms of the area of experimental susceptibility, numerical methods are widely used. The finite element (FE) method is applied in the article.
 
 Results. The article presents the principles of constructing a FE model for evaluating the load-bearing capacity and service ability of corrugated beams subjected to local loading (patch loading), verified by using the experimental data. The authors have analysed the influence of parameters of the FE model and input variables on the accuracy and uncertainty of modeling results.
 
 Conclusions. The article shows that the use of FE models allows for a highly accurate evaluation of the load-bearing capacity and the behaviour of a beam with a corrugated web subjected to local loading. The description of the behaviour of steel has one of dominant influences on the accuracy of FE models, while the value of yield strength has a dominant influence; values of ultimate strength and the type of deformation diagram have an auxiliary influence. The variability in the web thickness has a directly proportional effect on the value of the bearing capacity. The size of the finite element should be determined according to the condition of convergence of results against the criteria of critical and ultimate forces. The most optimal size of the finite element is about 3–5 web thicknesses. To reduce the total number of finite elements, it is recommended to use local condensation in areas of stresses. The shape of equivalent geometric imperfections is recommended to be assigned based on the forms of elastic buckling of the web.

Thermal FEM Analysis of Surge Arresters During HVdc Current Interruption Validated by Experiments

This paper deals with the development of an accurate finite-element model of an arrester to investigate the electrothermal and mechanical stress during dc current interruption. The comprehensive analysis performed on a ZnO surge arrester is supported by experiments during high-voltage dc circuit breaker current interruption. The performed experimental analysis comprises three sequential 26 kV/10 kA direct current interruption tests carried out within a period of one hour. The dynamic temperature and current distribution of the surge arrester columns during current interruption are measured. The finite-element simulation results are in good agreement with the test results. The influence of the surge arrester temperature on the current distribution among the surge arrester columns is analyzed. The impact of the surge arrester temperature on ZnO electrical characteristics and mechanical stress inside the surge arrester are also investigated. The surge arrester finite-element model can be used with full success for parameter optimization of the surge arresters to prevent possible failures when dc circuit breakers performed multiple interruptions in short period of time.

A computerized method of contact pressure and load distribution for crossed beveloid gears

Exact contact pressure and load distribution are key evaluation indices for beveloid gear design. A numerical calculation approach of contact pressure and load distribution for crossed beveloid gears is proposed, as opposed to the traditional method based on a finite element modeling software package. To acquire the flexibility properties of beveloid gear tooth surfaces, an accurate finite element (FE) model about a beveloid gear tooth with root fillets is first built. A solution model for crossed beveloid gears is developed using the influence coefficients technique. An enhanced solving approach is presented to improve the robustness of the solving model by addressing the limitation of the influence coefficients method. In addition, a unique contact pressure is presented. The numerical example proposed can be used to test the proposed methodology.

Numerical investigation on central tearing behaviors and propagation mechanisms of coated warp-knitted fabrics

To reveal the central tearing behaviors and propagation mechanisms of the architectural non-crimp fabric (NCF) composites with an initial crack, a microscopic finite element (FE) model was proposed and developed to simulate the tearing propagation process of materials in this paper. Firstly, the experimental program including the central crack tearing test of NCF composites and uniaxial tensile test of yarns was performed for gaining the material parameters. Secondly, a finite element (FE) model was developed and validated from the good agreement between numerical and experimental results. Furthermore, tearing damage mechanisms and failure performances of the NCF composites with an initial central crack were simulated and analyzed. Finally, the effects of initial crack length, yarn orientation, and arch curvature of weft yarn on mechanical properties were investigated in depth. The analysis and comparison results indicate that the NCF composite shows the unneglectable orthotropic characteristics, in which the initial crack length, yarn orientation, and arch curvature of weft yarn have the significant effects on the mechanical properties. This paper thus provides an adequately feasible and accurate FE model for the numerical simulation on the central tearing propagation behaviors of the NCF composites with an initial crack.

Vibration-based Bayesian model updating of an actual steel truss bridge subjected to incremental damage

As the finite element (FE) model has become increasingly important in engineering, the model updating method has also received much attention as a means of improving the structural FE model accuracy. However, the objectives of many earlier studies have been laboratory experiments and numerical simulations. Actual structures have not been adequately investigated. This report describes work on a vibration-based Bayesian model updating for an actual steel truss bridge. The transitional Markov chain Monte Carlo (TMCMC) sampling method was used to estimate the posterior distribution. A field experiment assessing this target bridge was conducted under five damage scenarios. Then a fast Bayesian FFT method was used to identify the modal properties. Based on sensitivity analysis, three model classes were proposed for the model updating process of the target bridge. In all cases, the updated modal properties were found to fit well with the experimental data, whereas the updated model parameters cannot. The case with more prior information identified the structural damage. Results demonstrate that making full use of prior information can improve the model updating accuracy. Feasibility of damage detection was observed for an actual steel truss bridge based on the FE model updating method.

Metamodel-based generative design of wind turbine foundations

Wind turbines play an integral role in energy transition agendas. The optimized design of wind turbine foundations is a complex and intricate task that requires iterative running of computationally-intensive and time-consuming finite element models. However, given the popularity of these structures over the past two decades, there is a wealth of data from the designs of the past projects that can be used for the data-driven modeling of these structures. Given the demonstrated accuracy and success of metamodels as an alternative approach for other computationally-intensive simulation-based problems, this study aims to develop a generative-design framework for the optimization of wind turbine foundations using a metamodel, as a complementary step to more accurate finite element modeling, to reduce the overall design time without compromising the accuracy. To this end, first, the random forest method is used to develop a multi-output metamodel for the wind turbine foundations based on a set of historical data. Then, a metaheuristic method, i.e., NSGA II, is adopted to optimize the design process based on the developed metamodel. In a case study, a wind turbine foundation was designed using the proposed framework and the accuracy of the output was assessed in terms of the ultimate bending moment. The results of the case study indicate that the proposed method provides a significant time gain (i.e., 99.93%) without compromising the accuracy (i.e., 1.75% for the percent error). Besides, the conducted study also offers designers a better understanding of the importance of each design variable and how certain design variables influence the moment-rotation behavior of the wind turbine foundation

Model Updating of a Prestressed Concrete Rigid Frame Bridge Using Multiple Markov Chain Monte Carlo Method and Differential Evolution

Model updating is a widely adopted method to minimize the error between test results from the real structure and outcomes from the finite element (FE) model for obtaining an accurate and reliable FE model of the target structure. However, uncertainties from the environment, excitation and measurement variability can reduce the accuracy of predictions of the updated FE model. The Bayesian model updating method using multiple Markov chains based on differential evolution adaptive metropolis (DREAM) algorithm is explored, which runs multiple chains simultaneously for a global exploration, and it automatically tunes the scale and orientation of the proposal distribution during the evolution of the posterior distribution. The performance of the proposed method is illustrated numerically with a beam model and a three-span rigid frame bridge. Results show that the DREAM algorithm is capable for updating the FE model in civil engineering. It extends the Bayesian model updating method to multiple Markov chains scenario, which provides higher accuracy than single chain algorithm such as the delayed rejection adaptive metropolis-hastings (DRAM) method. Moreover, results from both examples indicate that the proposed method is insensitive to values of initial parameters, which avoid errors resulting from inappropriate prior knowledge of parameters in the FE model updating.

Analytical Pushover Curves for X-Concentric Braced Steel Frames

In this work, analytical pushover curves for concentric braced steel frames with active tension diagonal bracings (X-CBF) are proposed. A pushover “spindle”, characterized by two trilinear analytical capacity curves defined for an X-CBF system subjected to prefixed lateral forces distribution, is defined. The curves are able to grasp the elasto-plastic behavior of the X-CBFs. The reliability of this analytical proposal is verified by a series of numerical comparisons obtained through an accurate finite element model, calibrated on the basis of experimental results. The proposal is extended to whole single- and multi-storey structures, showing a good correspondence with the numerical results of the analyzed case studies.

Prediction of the Interface Deformation of Ultrasonic Spot Welding of Multilayer Metal Foils Considering Energy Gradient

Abstract The ultrasonic spot welding (USW) is widely used in the joining of multilayer Cu or Al tabs in the lithium-ion battery. Due to the high-frequency vibration of the sonotrode and various deformation in each interface, the friction behavior is complex which makes it difficult to simulate the welding process of multilayer specimens. In this paper, an efficient and accurate finite element model (FEM) was proposed via introducing the interface heat flux to equivalent the heat generation by the friction. The total heat flux was determined by the heat transfer analysis and the proportion of each interface was determined based on the analysis of the friction behavior. Then, the FEM was validated by comparing the simulated temperature and deformation with experimental results. Finally, the FEM was applied to simulate the USW process of four, five, and ten layers of copper and aluminum foils in order to characterize the gradient of the ultrasonic energy. It was found that the heat generation concentrated in middle interfaces was 65% of the total in the welding of four-layer copper foils. The heat generation was mainly related to the welding parameters and the proportion was related to the size of tips and the structure of specimens. The plastic strain varied in specimens because of the gradient of the input energy. It was most obvious in the welding of 10-layer aluminum foils that the maximum equivalent plastic strain (PEEQ) in the fifth interface was 92.9% smaller than the top interface.