Explicit Finite Element Method Research Articles

Crashworthiness of innovative hexagonal honeycomb-like structures subjected to out-of-plane compression

Seeking for innovative structures with higher mechanical performance is a continuous target in railway vehicle crashworthiness design. In the present study, three types of hexagonal reinforced honeycomb-like structures were developed and analyzed subjected to out-of-plane compression, namely triangular honeycomb (TH), double honeycomb (DH) and full inside honeycomb (FH). Theoretical formulas of average force and specific energy absorption (SEA) were constructed based on the energy minimization principle. To validate, corresponding numerical simulations were carried out by explicit finite element method. Good agreement has been observed between them. The results show that all these honeycomb-like structures maintain the same collapsed stages as conventional honeycomb; cell reinforcement can significantly promote the performance, both in the average force and SEA; full inside honeycomb performs better than the general, triangular and double schemes in average force; meanwhile, its SEA is close to that of double scheme; toroidal surface can dissipate higher plastic energy, so more toroidal surfaces should be considered in design of thin-walled structure. These achievements pave a way for designing high-performance cellular energy absorption devices.

The Flux Reconstruction Method with Lax–Wendroff Type Temporal Discretization for Hyperbolic Conservation Laws

In this paper, we develop a Lax–Wendroff type time discretization method for high order Flux Reconstruction scheme to solve hyperbolic conservation laws. Through Cauchy–Kowalewski procedure, the resulting Lax–Wendroff Flux Reconstruction (LWFR) scheme is an alternative spatial–temporal coupling method to the popular Runge–Kutta Flux Reconstruction (RKFR) scheme. LWFR is a one-step explicit high order discontinuous finite element method and its discretization procedure is more compact and effective for certain problems than that of RKFR. Furthermore, aiming at accurate simulation of discontinuity, we propose a robust local artificial viscosity formulation of LWFR for the first time. A collection of successful numerical experiments show that LWFR can give essentially non-oscillatory and sharp solutions for discontinuity, and maintain designed order of accuracy for smooth regions, both in one-dimensional and two-dimensional Euler equations. In conclusion, LWFR scheme is cost effective and accuracy-preserving for certain problems and can be an attractive candidate to solve hyperbolic conservation laws.

Impact penetration and perforation performance of square sandwich panels with EPS foam core

This paper addresses the impact penetration and perforation behaviour of sandwich panels having a low density core expanded polystyrene foam (EPS) bonded to two aluminum (6061-T6) face-sheets. The effects of foam and plate thicknesses on the impact energy absorption of sandwich panels were also investigated. The dynamic response of panels was analyzed using the explicit finite element method. The foam core material was modeled as a crushable foam material with ductile damage, and the metal face-sheets as Johnson-Cook (JC) material. The cohesive response of the adhesive interface was considered using cohesive zone model. The analyses showed that the impact energy, face-sheet and foam core thickness affected significantly failure modes, contact force levels and histories. The low-speed impact tests of the sandwich panels with different face-sheet and foam core thicknesses showed similar contact force histories, energy absorption ability and deformation modes to those of finite element analyses.

A predictive approach to investigating effects of ultrasonic-assisted burnishing process on surface performances of shaft targets

The ultrasonic-assisted burnishing process (UABP) is an effective surface finishing technology that obtains compressive residual stress and surface work hardening and decreases surface roughness. A three-dimensional explicit nonlinear finite element model (FEM) of the UABP on a shaft specimen was established and calibrated in this paper. A comparison of finite element (FE) simulation results with experimental data showed good agreement in terms of the predicted residual stress in both tangential and axial directions. The established FEM explores the influence of treatment parameters, such as ball diameters, static forces, spindle speeds, ultrasonic frequencies, vibration amplitudes, and friction coefficients, on the resultant profile of residual stress and equivalent plastic deformation. This dynamic explicit FE method is an effective approach to investigate the UABP, to relate the processing parameters with surface integrity, including the depth of residual stress and work hardening of objective surfaces, and to guide the design of the UABP parameters.

Research on the relationship between the rail corrugation and the vibration response of the wheel-rail system

Rail corrugation is a very common phenomenon in high-speed railways. Rail corrugation can cause increased vibration of trains and tracks, and may even affect the safety of train operation. Therefore, this paper will analyze the vibration of the wheel-rail system caused by the rail corrugation. The actual transient rolling contact model is established by using explicit and implicit finite element methods. Through the calculation of the wheel-rail contact force and the wheel-rail mode, the vibration relationship between the rail corrugation and the wheel-rail system is obtained. It can provide some references for further analysis of the cause of rail corrugation.

ИССЛЕДОВАНИЕ ЖИВУЧЕСТИ ЖЕЛЕЗОБЕТОННОЙ КОНСТРУКТИВНО НЕЛИНЕЙНОЙ РАМНО-СТЕРЖНЕВОЙ СИСТЕМЫ КАРКАСА МНОГОЭТАЖНОГО ЗДАНИЯ В ДИНАМИЧЕСКОЙ ПОСТАНОВКЕ

The article presents the results of numerical simulation of the dynamic response of a reinforced concrete frame of a multi-story building with the sudden removal of load-bearing columns using a detailed 3D model in the LS-DYNA program, whichimplements the explicit finite element method. The model takes into account the nonlinear behavior of the material. The influence of the deformation rate of concrete and steel reinforcement is taken into account using the coefficient of increasing the strength of materials, normalized in SP 385.1325800.2018. The numerical results of the study showed that using the proposed calculatedmodel, it is possible in each moment to track the stress-strain state of load-bearing elements of frame-rod system frame high-rise buildings, to check criteria special limit state designs, and to answer the important practical question of the sustainability of a building to progressive collapse under a given beyond design action and as a result take in the design of necessary protection measures.

Investigation on Wheel-Rail Contact and Damage Behavior in a Flange Bearing Frog with Explicit Finite Element Method

Flange bearing frogs are designed to provide continuous rolling surfaces for trains traveling on the through line, but the interaction between wheel and rail in a diverging line is more complex than that for a common crossing, especially including flange bearing mode and multipoint contact during the transition. The wheel load will be transited from tread to flange and back to tread, which will intensify the wheel-rail interaction. In this paper, a numerical procedure is presented for the analysis of wheel-rail rolling contact behavior and damage prediction for the flange bearing frog. The three-dimensional explicit finite element (FE) model of a wheel passing the flange bearing frog is established to obtain the dynamic wheel-rail interaction in both the facing and the trailing move. The evolution of contact forces, the distribution of adhesion-slip regions, and shear surface stress and microslip at the contact patch are revealed. Then, the competition relationship between RCF (rolling contact fatigue) and wear of a flange bearing frog is analyzed. The results of numerical simulations can contribute to an understanding of the mechanism of the transient rolling contact behavior and provide guidance in design optimization for flange bearing frogs.

Numerical and Experimental Investigation on the Energy Absorption Capability of a Full-Scale Composite Fuselage Section

In the case of catastrophic events, such as an emergency landing, the fuselage structure is demanded to absorb most of the impact energy preserving, at the same time, a survivable space for the passengers. Moreover, the increasing trend of using composites in the aerospace field is pushing the investigation on the passive safety capabilities of such structures in order to get compliance with regulations and crashworthiness requirements. This paper deals with the development of a numerical model, based on the explicit finite element (FE) method, aimed to investigate the energy absorption capability of a full-scale 95% composite made fuselage section of a civil aircraft. A vertical drop test, performed at the Italian Aerospace Research Centre (CIRA), carried out from a height of 14 feet so to achieve a ground contact velocity of 30 feet/s in according to the FAR/CS 25, has been used to assess the prediction capabilities of the developed FE method, allowing verifying the response under dynamic load condition and the energy absorption capabilities of the designed structure. An established finite element model could be used to define the reliable crashworthiness design strategy to improve the survival chance of the passengers in events such as the investigated one.

Numerical investigation on low-velocity impact response of CFRP wraps in presence of concrete substrate

Under the levels of low-velocity impact far below those considered by current design codes, the carbon fiber-reinforced polymer (CFRP) wraps externally bonded for retrofitting reinforced concrete (RC) columns might suffer severe damage. In this study, explicit finite element method was used to fill the knowledge gap, which was verified by experimental tests. Twenty-four transverse impact scenarios related to a CFRP-retrofitted RC column-to-impactor system were investigated, which were designed according to the different combinations of a series of parameters, namely incident kinetic energy of impactor, CFRP thickness, and shape of impactor. The energy distribution among the different parts in the system was presented. The contact force time histories obtained from the scenarios indicated that a damage threshold load associated with a prescribed shape of impactor existed in the case of the CFRP wraps with concrete substrate. Furthermore, the significant differences among the roles of the parameters were revealed, and the reasons behind the differences were analyzed.

Rayleigh damping parameters estimation using hammer impact tests

Structural Health Monitoring (SHM) systems for aerospace applications are becoming more prevalent and its potential cost-benefit relation is rapidly improving as more structures that were traditionally made with metallic materials are gradually being replaced by composites. To support these systems, simulations can play a crucial role; however, in the case of low energy impacts, the structural damping becomes a very significant element in the simulation. This damping is usually not well known, or is based in estimates with very low reliability. Therefore, in order to improve the reliability of these values this paper presents an attempt to estimate the Rayleigh damping parameters with the application of time-frequency analysis methods to transient signals, specifically, the reduced interference distribution. These parameters are estimated based in the results of a large number of structural tests done in a square carbon-fiber reinforced plastic panel, and are then validated by correlation of an explicit Finite Element Method (FEM) simulation. A discussion on how to apply the reduced interference distribution to the signals measured by piezoelectric sensors under an impact scenario and other possible usages of these results is also presented in this document.

Impact response of reinforced concrete slabs in elastic half space

The analysis of the mechanical behaviour of reinforced concrete slabs on elastic foundation under impact loads is of great significance in the construction and protection of concrete pavements in airports. Based on the Elastic Half-space Foundation Model and Concrete Damage Plasticity Model, the displacement and stress fields of reinforced concrete slabs under impact loading are numerically simulated by explicit nonlinear finite element method. The result can be used to design and evaluate the safety of foundations and reinforced concrete slabs under impact loads.

A numerical study on waves induced by wheel-rail contact

Recent finite element (FE) simulations have revealed the generation and propagation of waves in rail surfaces induced by wheel-rail frictional rolling. These waves have rarely been addressed in the literature. This paper presents an in-depth analysis of these waves, aiming to give new insights into the contact mechanics, a research area in which waves have generally been ignored. The study first categorises the simulated contact-induced waves according to their generation mechanisms as impact-induced, creepage-induced and perturbation-induced waves. The link between the generation of perturbation-induced waves and the stick-slip contact mechanism is then explored. Next, by examining the rail surface nodal motion that forms the wave, the creepage-induced wave is demonstrated to be a Rayleigh wave; this result also shows that the explicit FE method can effectively simulate physical contact-induced waves and provide reliable dynamic contact solutions. Finally, FE modelling is presented to investigate the effects of surface cracks on the waves, which may contribute to wave-based crack detection.

A local collocation method to construct Dirichlet-type absorbing boundary conditions for transient scalar wave propagation problems

This paper introduces an effective way to equip the standard finite element method (FEM) for the solution of transient scalar wave propagation problems in unbounded domains. Similar to many other methods, we truncate the unbounded domain at an artificial boundary and convert the problem into a bounded one by prescribing appropriate absorbing boundary conditions (ABCs) at the truncating boundary. In the present method, the ABCs are time-dependent, and they are constructed by a simple collocation approach which is local in space and time. Therefore, the method does not make use of any routine schemes such as Fourier and Laplace transform. We shall show that the method is simple, and it can be easily applied to an explicit time domain FEM approach so that the sparsity of the FEM scheme (as well as its efficiency) can be preserved. The proposed method does not require any auxiliary variables as well as any approximating differential operators. This feature roots from the fact that here the ABCs are Dirichlet-type (or first-type) and thus they can be easily imposed to the corresponding boundaries. Therefore, the method shares some similarities with the conventional 1st and 2nd order ABC methods in terms of the simplicity of implementation. The method employs basis functions that exactly satisfy the governing and dispersion wave equations. The basis function can be easily adjusted to act as outgoing waves transmitting energy from the interior domain (near field) towards exterior domain (far field); i.e, they can cope with satisfaction of radiation boundary conditions. Several numerical examples are presented to evaluate the performance and to demonstrate the effectiveness of the approach. We shall show that the present method is capable of yielding results with a proper level of accuracy, similar to that of the perfectly matched layers method (PMLs), and it performs stably even in the case of long-term computations.

Detection of Dynamic Modulus and Crack Properties of Asphalt Pavement Using a Non-Destructive Ultrasonic Wave Method

Non-destructive ultrasonic testing has attained popularity due to its robustness and cost-effectiveness in monitoring the structural health and performance evaluation of pavements, thus replacing traditional methods. This paper presents the application of an explicit finite element method for the modeling of ultrasonic wave propagation through asphalt concrete. Prior to modeling, non-destructive ultrasonic testing was conducted on four different types of asphalt concrete (AC-13, SMA-13, AC-20, and AM-20). Based on acoustic information (wave velocity) obtained in non-destructive testing (NDT) and density, the dynamic moduli of these asphalt concretes were evaluated and used in numerical modeling of ultrasonic wave propagation using the commercial software package ABAQUS. The ultrasonic wave results obtained by numerical modeling were compared with experimental results. This comparison showed a good fit between the finite element (FE) results and the experimental results and confirmed a good FE approach for ultrasonic wave propagation. In addition, the influence of varying dynamic moduli, density, varying location, and crack size/depth on ultrasonic wave propagation was analyzed.

A New Analytical Prediction for Energy Responses of Hemi-Cylindrical Shells to Explosive Blast Load

This study presents a new analytical model on the dissipation process of the initial total energy of the hemi-cylindrical shell subjected to the explosive blast load. The analytical formulation has been established using the energy method. The analytical predictions have been validated and found to be in excellent agreement with numerical simulations calculated by explicit finite element method (via LS-DYNA). The variational parameters considered are the shell thickness, elastic modulus, densities of the shell, and the positions of the detonation. Considering varieties of the parameters, the analytical and numerical results demonstrate that the pattern of vibrating deformations can be classified into two types according to the detonation positions. If the detonation position was at the midpoint of the width, there was no main frequency, whilst if the detonation position was at the edge of the width, the shell vibrated with a main frequency. It was also found from both analytical and numerical models that the total initial energy is inversely proportional to the thickness of the shell ( T ), namely, the exact formula can be written as β = ρ a c / ρ s T . Surprisingly, this study is the first to highlight that the total energy decreases with time by the exponential function, and the exponential ratio ( β ) is inversely proportional to the thickness of the shell as well.

Experimental and numerical studies of stress/strain characteristics in riveted aircraft lap joints

The fatigue property of riveted lap joint is greatly related to the riveting-induced residual stress, especially the stress distribution on the faying surface. However, an accurate study of the residual stress characteristics in the riveted sheet could be very difficult. In this paper, both numerical and experimental investigations were carried out on the stress/strain characteristics in riveted aircraft lap joints. A special specimen was designed for the test of strain variations on the faying surface of the sheet by microstrain gages. For the numerical simulation, the rivet squeezing process was analyzed using the explicit dynamic finite element (FE) method, whilst a general static FE analysis was employed for the elastic springback after the squeeze force was removed. A comparison of the strain variations between the experimental results and FE simulations shows a general good agreement, although there may be some difference for points measured near the hole surface. The FE analysis reveals that both compressive and tensile residual stresses could be introduced in the riveted sheet. Massive compressive residual stress can be created in the near-surface layer of the hole. However, the stress level is not always increased with increasing the squeeze force, and so is the improvement of fatigue life observed. Further study is still necessary to account for the fatigue life decreasing effect caused by a high squeeze force.

Fracture and fragmentation of blast-loaded laminated glass: An experimental and numerical study

In this study, we use the explicit finite element method in combination with higher order elements and 3D node splitting to simulate fracture and fragmentation of blast-loaded laminated glass. Node splitting is a modelling technique where elements are separated instead of being eroded when a fracture criterion is reached. The resulting FE simulations are thus capable of describing behaviours such as fragmentation without loss of mass or momentum, fine cracking of the glass plates, and delamination and separation between the glass and the polymer interlayer. The simulations are compared to blast experiments conducted in a shock tube. In total, 15 laminated glass specimens (consisting of annealed float glass plates and PVB) were tested at five different pressure levels. The time and position of fracture initiation in the glass plates varied, which in turn resulted in varying post-fracture behaviour within the different pressure levels. The simulations were in good agreement with the blast tests, revealing the potential of the selected numerical method. Additional simulations of monolithic (i.e., non-laminated) glass plates were conducted and compared to experiments that were presented in an earlier study. Again, these simulations displayed a highly comparable response to the experiments, and were able to describe crack branching, formation of large glass splinters and free-flying fragments.

Composite Geological Strength Index Approach with Application to Hydrothermal Vein Networks and Other Intrablock Structures in Complex Rockmasses

Conventional rockmass characterization and analysis methods for geotechnical assessment in mining, civil tunnelling, and other excavations consider only the intact rock properties and the discrete fractures that are present and form blocks within rockmasses. As modern underground excavations go deeper and enter into more high stress environments with complex excavation geometries and associated stress paths, healed structures within initially intact rock blocks such as hydrothermal veins, veinlets and stockwork (termed intrablock structures) are having an increasing influence on rockmass behaviour and should be included in modern geotechnical engineering design. Field observations indicate the conventional Geological Strength Index (GSI) does not accurately estimate rockmass strength and behaviour of complex rockmasses. A modified GSI chart to include intrablock structures and a new Composite Geological Strength Index (CGSI) methodology to combine multiple suites of rockmass structure using a weighted harmonic average are presented as tools to evaluate complex rockmasses that contain multiple suites of structure for application to geomechanical numerical models. CGSI is introduced and numerically validated using implicit and explicit finite element method numerical simulations of an underground excavation and a case study of field observations in an adit at the El Teniente mine in Chile. In both cases, the CGSI approach using the modified GSI chart results in an improved estimate of rockmass behaviour in implicit equivalent continuum numerical models when compared to a conventional GSI approach.

Numerical simulation of dynamic large deformation and fracture damage for solid armature in electromagnetic railgun

Abstract The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electrical, thermal and mechanical process in the interior ballistic cycle. In this paper present, we first introduced a multi-physical field model of railgun, followed by several examples to investigate the launching process. Especially, we used the explicit finite element method, in which material nonlinearity and geometric nonlinearity were accounted, to investigate the deform behaviors of solid armature. The results show that the dynamic mechanical process of armature is dependent on the armature geometry, material and exciting electric current. By the numerical simulation, the understanding of the fracture mechanism of solid armature was deepened.

Material defects localization in concrete plate-like structures – Experimental and numerical study

Summary In this paper, the hybrid algorithm for localization of damage and defects is implemented on the concrete plate-like structures for localizing the clay and gypsum inclusions. The hybrid approach employs fast discrete wavelet decomposition of sensor output signals, as well as energy and time of flight criteria. The applied localization algorithm is verified both experimentally and numerically on the concrete plates with one and two inclusions. The experiment is conducted in controlled laboratory conditions, using a piezoelectric actuator for excitation of the wave propagation in the structure, while the ultrasonic laser is used for measuring vibrations at the sensor locations. Numerical simulation of wave propagation is done using the explicit finite element method on 3D models. The numerically obtained results are in full correspondence with the experimental results. The images of material defects positions obtained by the hybrid approach show a good agreement with the actual positions, which indicates a good potential of the used approach in localization of various types of material defects in plate-like concrete structures.