Full Finite Element Model Research Articles

Development of Composite Propeller Blade Model for High Velocity Impacts on Aircraft Fuselage using Finite Element Analysis

An open rotor blade failure and release event can result in a high energy impact on an aircraft fuselage that can reduce the strength of the structure and challenge the safe continuation of the flight and landing. This work highlights the development of a numerical approach and methodology in order to improve the assessment of the damage predictions of a composite propeller blade impact against the fuselage of an aircraft to be able to estimate a minimum thickness of shielding for the full protection of the airframe. A number of dynamic simulations were carried out, from rigid up to deformable and frangible projectiles at different angles of incidence, varying the material and the thicknesses using Abaqus/Explicit. The finite element (FE) models for blade and target were calibrated and validated separately allowing to capture the right behavior and failure modes. Impact tests of partial blade fragments against stiffened composite panels were correlated with simulations and the obtained results show a good agreement regarding deformations and delaminated area. Finally, a full blade FE model was generated and used for the fuselage impact numerical analysis. This was done within the frame of the Open Rotor project funded by Clean Sky European research programme.

Effect of Compressive and Shear Deformation of 2.5D Preform on its Stiffness of Composites

Transverse compaction and in-plane shear deformartion are the dominative deformation mode for woven preform during forming process. A full finite element model of the 2.5D woven composites has been established by the computed tomography (CT) in this paper. Based on the energy method, the effective orthotropic/anisotropic stiffness coefficientsCijare calculated by performing a finite element analysis (FEA) of this full cell model. Using this model, the effects of the compaction and shear deformation of the 2.5D woven preform on the composites stiffness are investigated in detail. Compared the results of the static tensile tests, the rationality of the model and the method is verified.

Full finite element models and reduction strategies for the simulation of friction-induced vibrations of rolling contact systems

The aim of this paper is to develop a full Finite Element (FE) computational method for the dynamics of unstable frictional rolling contact systems in order to calculate reference solutions in many applications, especially curve squeal for railway transportation but also roller bearing or metal cutting. The proposed method is characterized by the use of a fine FE discretization of the contact surface in a Eulerian frame, nonlinear frictional contact laws and model reduction techniques. An application to the frictional rolling contact between two annular cylinders is presented in both quasi-static and dynamic cases with mode coupling instabilities. The validation of the approach in quasi-static conditions is carried out by comparison with CONTACT software. Stability and transient results show that the technique is able to simulate friction-induced vibrations at high frequencies. Reduced models are tested and show a good agreement with the full model.

A textile architecture-based hyperelastic model for rubbers reinforced by knitted fabrics

A new anisotropic hyperelastic model has been developed to model the deformation response of a knitted-fabric-reinforced rubber composite. The composite has a sandwich structure with a fiber net layer embedded in two rubber layers. Due to the architecture of the knitted fabric, the composite demonstrates an anisotropic hyperelastic response, which is modeled through a strain energy density function that incorporates the effects of deformed rubbers and stretched fibers. The rubber is considered as a neo-Hookean material, while the knitted fabrics are modeled as cords with negligible stiffness in bending. The effect of reinforcement comes from the conservation of the total length of the fiber cords. In addition, a slack variable is proposed to account for the effect of processing-induced fabric pre-stretch or fabric slack on the resulting composite response. This novel approach enables the determination of the constitutive behavior of the composite in closed form based on the constituent rubber and fiber properties and fabric architectures. The proposed analytical model is validated through a full 3D finite element (FE) model, in which the rubber and fiber reinforcement are modeled explicitly. Since the proposed model captures the key parameters that dictate the deformation response of knitted-fabric-reinforced composites, it can be employed as an efficient modeling tool to guide the design of rubbers and fabric architectures with targeted composite performance.

Analysis of lateral loading of pile groups using embedded beam elements with interaction surface

SummaryThe numerical simulation of soil‐pile interaction problems, by means of full 3D finite element models, involves a large number of degrees of freedom (DOF) and difficulties during the mesh generation process. In order to reduce the unknowns and simplify and properly analyze such class of geotechnical problems, the so‐called embedded beam elements (EBE) have recently been developed. In a preceding contribution of the authors, an improved EBE formulation, which brings into play the soil‐pile interaction surface, was proposed with the aim to localize material plasticity in the soil surrounding the pile. This embedded beam model couples two different finite elements, each described by distinct kinematics (ie, solid and beam). The coupling is incorporated in the formulation by means of kinematical constrains established over the solid and beam displacement fields on the interaction surface. One of the main advantages of the embedded elements is that the addition of beams structural members immersed within the 3D soil model does not represent a constraint for the solid mesh, which can be adopted independently from the beam mesh. In this paper, the lateral loading of pile groups is studied by means of the proposed EBE approach with elasto‐plastic interfaces. In order to represent a rigid cap, a master node and a special set of kinematical restrictions are incorporated into the formulation. The paper presents results obtained by means of the present formulation compared against other well‐established analysis methods and test results published in the literature, for both elastic and elasto‐plastic cases.

Acoustic characterization of ducts lined with poroelastic materials based on wave finite element method

A wave finite element (FE) approach is presented for investigating acoustic characteristics of an axisymmetric duct lined with poroelastic materials. A short segment of the poroelastic lined duct is modelled using commercial FE software package, and an eigenvalue problem is established by applying periodic conditions, which greatly reduces the complexity associated with the formulation of eigenvalue problem especially when the intricate two-phase interaction within the poroelastic material is of significance. The predicted wavenumbers agree with those by forced response simulation with full FE simulations. The acoustic characteristics of poroelastic lined duct is analyzed based on the numerical model, which is verified by a full FE model, with emphasis on the effect of skeleton elasticity. For the structure-borne modes, a strong coupling between the fluid phase and solid phase is observed; while for the fluid-borne modes, such coupling is found to be negligible. For a poroelastic lined duct silencer, it is found that the structure-borne mode accounts for the spectral peaks in transmission loss spectrum through enhanced absorption and reflection effects. Meanwhile, the boundary condition of poroelastic material has significant effect on the structure-borne mode. In the simulated case, the change of boundary condition from fixed to rolling causes the first structure-borne mode to change from an evanescent higher-order-like mode to a propagating plane-wave-like mode in low frequency range, which affects the acoustic characteristics of the poroelastic lined silencers noticeably.

Numerical and experimental investigation on the deformation mechanism of micro single point incremental forming process

Single-point Incremental Sheet Forming (ISF) is a die-less forming process with advantages of high-flexibility, low-cost and short lead time. Recently, micro components have been employed in many applications, especially in medical industry using as implant components, surgical tool and tooth caring accessories etc. Therefore, the reduction of component size to micro-domain has becoming one of the key elements for the development of ISF technique, which will encounter many challenges, such as reduction of formability, tool wear, inaccuracies in tooling fabrication, etc. This work combined numerical and experimental approaches to study the deformation mechanisms in micro ISF process. Aluminum 1145 soft-temper foils with thickness of 38.1 μm and 50.8 μm were employed. A truncated pyramid with variable half-apex angle was employed here as the standard geometry for measuring the maximum forming angle that could be achieved in micro-ISF process. The result shows that forming angle has direct link with material formability. A full tool path micro-ISF finite element model has been developed using incompatible mode eight-node brick element C3D8I, which is capable to capture the shape and thickness distribution of the formed parts with most accuracy and least computational time. The thickness distribution of the workpiece was compared with the Sine Law to unveil the additional stretch region appearing at the top edge of the formed feature in the micro ISF as compared to macro ISF.

A Reduced Order Model for Nonlinear Dynamics of Mistuned Bladed Disks With Shroud Friction Contacts

A new reduced order modeling technique for nonlinear vibration analysis of mistuned bladed disks with shrouds is presented. The developed reduction technique employs two component mode synthesis methods, namely, the Craig-Bampton (CB) method followed by a modal synthesis based on loaded interface (LI) modeshapes (Benfield and Hruda). In the new formulation, the fundamental sector is divided into blade and disk components. The CB method is applied to the blade, where nodes lying on shroud contact surfaces and blade–disk interfaces are retained as master nodes, while modal reductions are performed on the disk sector with LIs. The use of LI component modes allows removing the blade–disk interface nodes from the set of master nodes retained in the reduced model. The result is a much more reduced order model (ROM) with no need to apply any secondary reduction. In the paper, it is shown that the ROM of the mistuned bladed disk can be obtained with only single-sector calculation, so that the full finite element model of the entire bladed disk is not necessary. Furthermore, with the described approach, it is possible to introduce the blade frequency mistuning directly into the reduced model. The nonlinear forced response is computed using the harmonic balance method and alternating frequency/time domain approach. Numerical simulations revealed the accuracy, efficiency, and reliability of the new developed technique for nonlinear vibration analysis of mistuned bladed disks with shroud friction contacts.

Efficient structural analysis of gas turbine blades

PurposeThe purpose of this study a fast procedure for the structural analysis of gas turbine blades in aircraft engines. In this connection, investigations on the behavior of gas turbine blades concentrate on the analysis and evaluation of starting dynamics and fatigue strength. Besides, the influence of structural mistuning on the vibration characteristics of the single blade is analyzed and discussed.Design/methodology/approachA basic computation cycle is generated from a flight profile to describe the operating history of the gas turbine blade properly. Within an approximation approach for high-frequency vibrations, maximum vibration amplitudes are computed by superposition of stationary frequency responses by means of weighting functions. In addition, a two-way coupling approach determines the influence of structural mistuning on the vibration of a single blade. Fatigue strength of gas turbine blades is analyzed with a semi-analytical approach. The progressive damage analysis is based on MINER’s damage accumulation assuming a quasi-stable behavior of the structure.FindingsThe application to a gas turbine blade shows the computational capabilities of the approach presented. Structural characteristics are obtained by robust and stable computations using a detailed finite element model considering different load conditions. A high quality of results is realized while reducing the numerical costs significantly.Research limitations/implicationsThe method used for analyzing the starting dynamics is based on the assumption of a quasi-static state. For structures with a sufficiently high stiffness, such as the gas turbine blades in the present work, this procedure is justified. The fatigue damage approach relies on the existence of a quasi-stable cyclic stress condition, which in general occurs for isotropic materials, as is the case for gas turbine blades.Practical implicationsOwing to the use of efficient analysis methods, a fast evaluation of the gas turbine blade within a stochastic analysis is feasible.Originality/valueThe fast numerical methods and the use of the full finite element model enable performing a structural analysis of any blade structure with a high quality of results.

Inelastic condensed dynamic models for estimating seismic demands for buildings

Computationally-efficient simulations of structural responses, such as displacements and inter-story drift ratios, are central to performance-based earthquake engineering. Calculating these responses involves potentially time-consuming response history analysis of inelastic structural behavior. To overcome this burden, this paper introduces a new inelastic model condensation (IMC) procedure. The method presented here is non-iterative and uses the modal properties of the full model (in the elastic range) to condense the structural model such that the condensed elastic model preserves the modal properties of the full model at certain modes specified by the analyst. Then, by replacing the inter-story elastic forces with hysteretic forces, the inelastic behavior of the full finite element model is incorporated into the condensed model. The parameters of these hysteretic forces are easily tuned, in order to fit the inelastic behavior of the condensed structure to that of the full model under a variety of simple loading scenarios. The fidelity of structural models condensed in this way is demonstrated via simulation for different ground motion intensities on three different building structures with various heights. The simplicity, accuracy, and efficiency of this approach could significantly alleviate the computational burden of performance-based earthquake engineering.

Numerical analysis of timber-to-timber joints and composite beams with inclined self-tapping screws

In this paper, a Finite-Element (FE) numerical investigation on timber-to-timber joints and composite beams with inclined self-tapping screws (STSs) is presented. Based on past experimental data and numerical literature efforts, full 3D solid FE models of selected geometrical and mechanical configurations of technical interest are implemented in ABAQUS software package and analysed under static loading conditions. The typical push-out samples include GL24h timber members with several types (WT-T-8.2, 190 mm and 220 mm their length), layouts (2 + 2, 4 + 4, 2 + 2 X-shaped) and inclination of screws (up to ±45°). For the full-scale beam samples in bending (8 m their span), composite systems consisting of GL24h timber beam, wooden plank, spruce floorboards and STSs are investigated. There, the STS joints take the form of two-rows or X-shaped connections, respectively (45° or 90° their inclination), including four screw types and different spacing. In both the push-out and full-scale cases, simple modelling approaches are taken from the ABAQUS library and adapted to the timber-to-timber structural system under investigation, so as to explore their structural performance in the elastic and post-damage phases, up to failure. A key role in the typical FE models is assigned to input material properties and mechanical contacts, including damage constitutive laws so as to reproduce possible local failure phenomena in the timber or steel components, as well as cohesive damage interactions for the joints. The presented FE models are calibrated in accordance with past research studies, and validated – for the examined structural typology – against experimental results available in literature. Comparative calculations are hence presented, based on the collected numerical, experimental and analytical estimations for the selected samples. As shown, the examined modelling approach can reasonably capture the expected performance of timber-to-timber joints and composite systems.

A 3D computational model of electrospun networks and its application to inform a reduced modelling approach

In this contribution, a full 3D finite element model of electrospun networks is presented. The model explicitly accounts for the specific microstructure of these networks by generating representative volume elements through a particular fibre deposition method inspired by the process of network formation during electrospinning. The modelled fibre material and structural properties, such as different fibre shapes and distributions in diameter, can vary over a wide range, and mutual fibre contact is considered in addition to permanent cross-links. In addition to the homogenized mechanical response to macroscopic in-plane loads, the model provides access to structural information which can hardly be determined in experiments, such as fibre disposition and interconnectivity. In the present work, this asset is used to inform a recent 2.5D modelling approach (Zündel et al., 2017) and to validate inherent assumptions on network structure. The comparison between the responses of the two approaches reveals that for networks of high porosity, the reduced 2.5D model captures well the mechanical behaviour in plane stress load cases. At lower porosities though, the increasing out-of-plane orientation of fibre segments leads to effects that cannot be captured by planar approaches and necessitate a 3D approach.

FRF Sensitivity-Based Damage Identification Using Linkage Modeling for Limited Sensor Arrays

This paper presents a novel method to localize and quantify damage in a jack arch structure by introducing a linkage modeling technique to overcome issues caused by having limited sensors. The main strategy in the proposed Frequency Response Function (FRF)-based sensitivity model updating approach is to divide the specimen into partitions. The Young’s modulus of each partition is then updated to detect stiffness reduction caused by damage. System Equivalent Reduction Expansion Process (SEREP) is used to reduce the full finite element (FE) model to a linkage model. The number of measured degrees of freedom (DOFs) is then expanded to the linkage model using the mass and stiffness matrices of the linkage model for the synthesis of interpolated FRFs. The FRF sensitivities are then formulated using the linkage model along with the interpolated FRFs to iteratively calculate the values of the updating parameters until convergence is achieved. The methodology and theory behind this procedure are discussed and verified using a numerical and experimental study. The successful implementation of this method has the potential to detect the location and severity of damage where sensor placement is limited.

Modal Expansion Method for Eigensensitivity Calculations of Cyclically Symmetric Bladed Disks

A diverse set of technical fields such as design optimization, structural system identification, and probabilistic modeling require accurate and efficient calculation of modal sensitivities to structural parameters for bladed disks (blisks). However, obtaining sensitivities by traditional finite difference schemes of full blisk finite element models fails to meet the efficiency requirement. An approach is presented here that meets both the accuracy and efficiency requirements for calculating modal sensitivities by formulating a modal expansion method for blisk models. This approach accommodates repeated eigenvalues common to blisks, where traditional approaches result in singular equations when solving for sensitivities. Results illustrate the efficiency and efficacy of the approach for a simple academic model and an industrial model. It is also shown that repeated eigenvalues and eigenvectors also have repeated derivatives.

Model reduction for friction-induced vibration of multi-degree-of-freedom systems and experimental validation

Most frictional systems are composed of components that are in sliding contact. Thus they have natural contact interfaces on which normal contact forces and tangential friction forces are acting. These real systems are complicated and friction brings further complexity, which presents a challenge to their dynamic analysis and control. In this paper, a model reduction strategy for complicated frictional systems is put forward based on the idea of mode synthesis, and its applications and experimental validation are presented. Firstly, the accuracy of the reduction method and the feasibility of the reduced model in stability analysis are verified on a theoretical multi-degree-of-freedom frictional system. Then, a tribometer in the form of a pad-on-disc test rig is designed and built and its corresponding detailed finite element (FE) model is constructed. A specific reduction strategy for this real friction system which involves direct contact at the pad-disc interface, is proposed. It is found that the reduced model with 80 modes of each of the two substructures of the system can already correctly predict the mode-coupling instability of the full FE model (which has over 900,000 degrees of freedom) of the real system, and unstable frequencies that are fairly close to the unstable frequencies of the FE full model computed by Abaqus CEA and the vibration frequencies measured in the test on the tribometer, which demonstrates the efficiency and accuracy of the model reduction strategy for dynamic analysis of real friction systems. Its computational efficiency would be even much greater when applied to nonlinear dynamic analysis of real friction systems. Model reduction for friction-induced vibration validated by experiments has not been reported in the literature.

Wave Interaction with Defects in Pressurised Composite Structures

There exists a great variety of structural failure modes which must be frequently inspected to ensure continuous structural integrity of composite structures. This work presents a finite element (FE) based method for calculating wave interaction with damage within structures of arbitrary layering and geometric complexity. The principal novelty is the investigation of pre-stress effect on wave propagation and scattering in layered structures. A wave finite element (WFE) method, which combines FE analysis with periodic structure theory (PST), is used to predict the wave propagation properties along periodic waveguides of the structural system. This is then coupled to the full FE model of a coupling joint within which structural damage is modelled, in order to quantify wave interaction coefficients through the joint. Pre-stress impact is quantified by comparison of results under pressurised and non-pressurised scenarios. The results show that including these pressurisation effects in calculations is essential. This is of specific relevance to aircraft structures being intensely pressurised while on air. Numerical case studies are exhibited for different forms of damage type. The exhibited results are validated against available analytical and experimental results.

Seismic damage assessment and mechanism analysis of underground powerhouse of the Yingxiuwan Hydropower Station under the Wenchuan earthquake

The Yingxiuwan underground powerhouse is one of the closest large-scale underground structures from the epicenter of the Wenchuan earthquake and suffered significant damage during this earthquake. What makes this case even more interesting is that the seismic damage is mainly distributed in the upper part of the concrete structure in the underground powerhouse. A full three-dimensional dynamic finite element model of the underground structure and rock system is adopted to make a reasonable assessment for the seismic damage observed in the field and to study the damage characteristics and mechanisms of the underground powerhouse. Additionally, to approximate actual field conditions, the oblique incidence of seismic waves and the rock-structure interaction (RSI) are both considered in this study, and their effects on the seismic response are evaluated. The numerical results indicate that the oblique incidence of the seismic wave and the RSI both contribute to a larger seismic response, and the results compare well with the field observations when the two are considered. The damage distribution of the concrete structure is mainly dominated by the structure feature itself. The main cause of the severe damage in the upper structure is due to the lack of sufficient constraints on it, which leads to a large deformation in the upper structure.

Experimental and numerical study on heating performance of the mass and thin concrete radiant floors with ground source systems

The thickness of the slabs is imperative when considering the method of heating system due to the thermal mass and thermal lag properties. Thermal properties of concrete allow thermal energy to be stored in the mass floor after heating cycles. In this study, the experimental heating performance of a 1.22 m-thick mass concrete radiant floor and a 0.18 m-thick concrete floor is investigated. In addition, a full 3D finite element model of the mass concrete radiant floor is performed and validated by the full-scale building measurements. The mass floor simulation contains embedded pipes, vertical steel anchors, and horizontal reinforcing steel grids at the top and bottom. The experimental results show that the initial temperature of the thick concrete slab is increased by a few cycles and the mass heated concrete floor acts as a thermal storage battery for the building. Also, the modeling results are in good agreement with construction site measurement. This model is further expanded to simulate different thermal loadings on the pipes to predict the temperature development inside of the mass floor. Furthermore, importance of the vertical steel anchors in conduction the generated heat to the surface of the floor would be seen in the modeling results.

Prediction of riveting deformation for thin-walled structures using local-global finite element approach

Riveting is a crucial manufacturing process and widely used in the assembly of aeronautical thin-walled structures, such as wing panels and fuselage panels. However, the dimensional errors of final products often violate the allowed tolerance due to riveting-induced deformation, which significantly degrades the dynamic performance of aircraft and decreases the productivity. In this study, a two-step computational approach, which combines a full 3D dynamic explicit finite element model (FEM) and a local-global FEM with consideration of local bulging, is proposed to evaluate the riveting deformation for thin-walled structures. Firstly, a freedom expanding method was developed to eliminate additional stress, emerging in general connection of solid element and shell element. In addition, the plastic zone after riveting was determined by the cold expansion of hole. Secondly, the inherent deformations of nodes in typical riveted joints involved in thin-walled structure were calculated using the 3D dynamic explicit FEMs and their characteristics were also examined. Thirdly, based on the improved connection method and estimated plastic zone, the local-global FEM was built through equivalent model. Finally, three representative thin-walled riveted structures were simulated using the proposed method. By comparing predicted results and measurements, the accuracy and efficiency of the two-step computational approach are verified.

General shell section properties and failure model for cross-laminated timber obtained by numerical homogenization

In this study homogenized mechanical properties are derived for structural finite element analysis of cross-laminated timber (CLT) discretized by means of shell elements. In the first step, based on the results of experimental three-point bending tests on a CLT slab component, a numerical optimization procedure is applied to identify the elastic and plastic properties of the individual spruce wood laminates, considering orthotropic elasticity and Hill’s yield criterion. Taking into account its periodic structure, a repeating unit cell (RUC) of the CLT is defined in the subsequent step. To this RUC specific loading conditions are imposed successively, yielding the entries of the homogenized elastic stiffness matrix of a general shell section. Extending the RUC simulations into the inelastic domain of deformation results in a homogenized failure surface on the structural scale, which is implemented as a postprocessing variable in a commercial finite element program. Throughout all analyses, in sensitivity studies the most decisive material properties are identified. Results of comparative simulations on a homogenized structural model and an elaborate full three-dimensional finite element model of a point-supported CLT slab show the accuracy and efficiency of the proposed approach based on homogenized mechanical properties.