Local Finite Element Analysis Research Articles

A machine learning assisted multifidelity modelling methodology to predict 3D stresses in the vicinity of design features in composite structures

Multifidelity global–local finite element (FE) analyses are typically used to predict damage initiation hotspots around repetitive design features in large composite structures, such as composite airframes. We propose the use of machine learning (ML) methods to accelerate these analyses. We demonstrate this ML assisted framework for the stress analysis of a hole in plate feature in an aerospace C-spar structure. To enable this framework, we develop the following original features: a computationally efficient sampling scheme; a work-equivalent boundary condition homogenisation scheme; a volume averaged ply-by-ply stress approach; and a sequential long-short term memory neural network reformulated from a time basis to a stacking sequence basis with further bi-directionality customisation. Overall, we show that the developed method results in high-accuracy prediction of 3D stresses, with over two orders of magnitude reduction in modelling and simulation time compared to FE analyses.

Static and Dynamic Stability Analyses of Functionally Graded Beam with Inclined Cracks

The focus of this paper is to examine the static and dynamic instabilities of functionally graded beam that contains multiple inclined cracks under the influence of an axial force comprising both static and time-varying harmonic components. The elasticity modulus and mass density of the functionally graded beam are assumed to vary exponentially along its thickness direction. Local stiffness matrix model-based finite element analysis (FEA) is conducted to determine the bending stiffness and tensile stiffness of the section with a crack, and the coupled effect of tensile and bending loadings. Two-node beam elements with three degrees-of-freedom per node are utilized. By combining the Euler–Bernoulli beam theory with Lagrange method, we derive the governing equations that describe the static and dynamic instabilities of a functionally graded beam with multiple inclined cracks. These equations can be solved as eigenvalue problems to obtain the natural frequency and static critical buckling load of the beam. Furthermore, to investigate the dynamic instability of the system, we use the Bolotin method to determine the boundary between the regions of instability and stability based on the same governing equations. By adopting this approach, the study comprehensively investigates the impacts of crack position, inclination angle, and length, as well as elasticity modulus ratio, static and dynamic load factors on both static and dynamic stabilities of a cracked functionally graded beam to gain valuable insights into the stability and performance of cracked functionally graded structures.

Numerical and Experimental Evaluation of a CFRP Fatigue Strengthening for Stringer-Floor Beam Connections in a 19th Century Riveted Railway Bridge

A local and global finite element analysis of the stringer-floor beam connection of a 19th century riveted railway bridge in Spain made of puddle iron were performed to obtain the maximum principal strains in the riveted connecting angles corresponding to bending moments from train loading on the bridge. Due to the anisotropic nature of puddle iron, the connecting angles were modelled using Hill anisotropic plasticity potential and a parametric study in the local FE model of the connection was performed. A laboratory specimen fabricated with original stringers dismantled from the railway bridge was tested to calibrate the numerical models, so the yield stress ratio that best fitted experimental results was obtained. Based on the method of constant fatigue-life diagram and modified Goodman fatigue failure criterion, it was detected that the connecting angles were prone to fatigue crack initiation, as the combination of mean stress and alternating stress amplitude at the toe of the angle fillet remained outside the infinite fatigue-life region. An innovative strengthening system based on adhesively-bonded carbon-fiber reinforced polymer (CFRP) angles was designed to prevent fatigue crack initiation in the connecting angles of the stringer-floor beam connection. Different CFRP laminate layouts were numerically evaluated and a proper configuration was obtained that reduced both the mean stress and the alternating stress amplitude in the connecting angle to shift from finite fatigue-life region to infinite fatigue-life region in the constant fatigue-life diagram. To validate the effectiveness of the proposed CFRP strengthening method, its application on a second laboratory specimen fabricated with original stringers was evaluated experimentally and compared with numerical results. The research study conducted showed that the use of adhesively-bonded CFRP angles was an effective strengthening system in reducing the stress level in the fillet region of the puddle iron connecting angles (where fatigue cracks are prone to initiate) and consequently could increase fatigue life of the stringer-floor beam connection.

A global-local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible marine risers

In this paper, a global-local fretting design methodology for the pressure armour layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.

Finite Element Analysis of Progressive Failure and Strain Localization of Carbon Fiber/Epoxy Composite Laminates by ABAQUS

Interaction mechanism between the intralaminar damage and interlaminar delamination of composite laminates is always a challenging issue. It is important to consider the progressive failure and strain softening behaviors simultaneously during the damage modeling and numerical simulation of composites using FEA. This paper performs three-dimensional finite element analysis of the progressive failure and strain localization of composites using FEA. An intralaminar progressive failure model based on the strain components is proposed and the nonlinear cohesive model is used to predict the delamination growth. In particular, the nonlocal integral theory which introduces a length scale into the governing equations is used to regularize the strain localization problems of composite structures. Special finite element codes are developed using ABAQUS to predict the intralaminar and interlaminar damage evolution of composites simultaneously. The carbon fiber/epoxy composite laminates with a central hole demonstrates the developed theoretical models and numerical algorithm by discussing the effects of the mesh sizes and layups patterns. It is shown the strain localization problem can be well solved in the progressive failure analysis of composites when the energy dissipation due to the damage of the fiber, matrix and interface occurs at a relatively wide area.

Bending stress analysis of flexible touch panel

Flexible touch panel is required to undertake extensive bending operations during service; thus, bending testing of flexible touch panel for mechanical behaviors and even reliability is crucial for realizing the technology. This study aims at exploring the bending behaviors of a flexible touch panel under a four-point bending test using finite element analysis. The touch panel is a laminated structure composed of seven thin film layers, namely a polyester layer, an adhesive layer, a polyimide layer, two organic layers and two indium tin oxide conductive layers. Because the touch panel structure is symmetry, only a quarter of the flexible touch panel is established in the analysis model. The mechanical properties of the materials are first obtained using both nanoindentation and uniaxial tensile/compressive testing. Furthermore, a modeling technique based on global and local finite element analysis is applied to evaluate the bending stress at a specified radius of curvature. Special emphasis of the calculation is put on the critical region with respect to stress, which is identified as the most susceptible cracking site.

Efficient optimisation of large aircraft fuselage structures

AbstractThis paper presents an innovative optimisation method for aircraft fuselage structural design. Detailed local finite element analyses of panel buckling are further processed such that they can be applied as failure constraints in the global level optimisation. The high computational costs involved with the finite element analyses are limited by advanced use of surrogate modelling methods. This yields high flexibility and efficiency in the local level optimisation procedure and allows for efficient gradient based search methods as well as more costly direct search optimisations like genetic algorithms (GAs). The method is demonstrated on a composite fuselage barrel design case considering common structural sizing variables like thicknesses and stringer dimensions. Optimised barrel designs are obtained where the constraints that are derived from the panel buckling analyses are active. The total computational cost for the complete local and global level optimisation procedures is in the order of days on common-performance hardware.

Global–Local Finite Element Analysis of Adhesive Joints and Crack Propagation

Accurately capturing the stress distribution in an adhesive joint of aircraft structures requires discretizing the adhesive layer with a very fine finite element mesh. Because such a simulation requires high computational processing unit time, researchers are looking for alternative methods to simulate adhesive joints of aircraft structures for saving the computational processing unit time. Another high computational processing unit requiring the study of aircraft structures is the evaluation of delamination growth in adhesive joints and crack propagation in brittle materials using cohesive zone modeling along with the very fine finite element mesh for the bulk material. To reduce these computational times, a possible alternative is to use a global–local finite element method. Therefore, both the crack propagation and the characteristics of adhesive joints were studied using a global–local finite element method. Three cases were studied using the proposed global–local finite element method, including 1) an adhesively bonded double cantilever beam, 2) an adhesive lap joint, and 3) a three-point bending test specimen. Using global–local methods, in a crack propagation problem of an adhesively bonded double cantilever beam, more than 80% data storage space and more than 65% computational processing unit time requirement could be saved. In the adhesive lap joints, around 70% data storage space and 70% computational processing unit time requirement could be saved using the global–local method. For the three-point bending test specimen case, more than 90% for both data storage space and computational processing unit time requirement could be saved using the global–local method.

Fracture Analysis of a Curvilinearly Stiffener Panel Subjected to Multiple Combined Loadings

A global–local finite element analysis was performed to study the damage tolerance of curvilinearly stiffened panels, fabricated using the modern additive-manufacturing process that can create so-called unitized structures. In the first step, a buckling analysis of panels was performed to determine whether the panels satisfied the buckling constraint in an undamaged state. In the second step, stress distributions in the panel were analyzed to determine the location of the critical stress under combined shear and compression loadings. Then, a fracture analysis of the curvilinearly stiffened panel with a crack designed at the earlier-obtained location of the critical stress, which was the common location with the maximum magnitude of the principal stresses and von Mises stress, was performed under combined shear and tensile loadings. A mesh-sensitivity analysis was performed to validate the choice of the mesh density near the crack tip. All analyses were performed using the global–local finite element method using MSC.Marc, and the global finite element methods using MSC.Marc and ABAQUS. A negligible difference in results and 94% savings in the CPU time were achieved using the global–local finite element method over the global finite element method by using a mesh density of 8.4 element/mm ahead of the crack tip. To study the influence of different loads on basic modes of fracture, the shear and normal (tensile) loads were varied differently. It was observed that the case with the fixed shear load but variable normal loads, and the case with the fixed normal load but variable shear loads were mode I. Under the maximum combined-loading condition, the largest effective stress-intensity factor was much smaller than the critical-stress-intensity factor.

Study on Simulation and Design of Fitness Entertainment Machine Based on the Fischertechnik Model and UG, ANSYS

Provide an innovative design of a new fitness entertainment machine which based on fischertechnik model.[1] Using fischertechnik creative combination model (fischertechnik) to make conceptual design quickly dematerialized.With the help of software such as UG and Ansys etc, finishing the model building of fitness entertainment machine, the establishing of virtual prototype and optimization of mechanism parameters,local motion mechanism simulation and finite element analysis, thus realizing the entertainment machine which based on optimal design.

A composite runout specimen subjected to tension–compression loading conditions: Experimental and global–local finite element analysis

Runout regions in aeronautical structures take place when a stiffener is interrupted due to the presence of significant geometrical conflicts between adjacent areas. At these locations, the load path is substantially modified, and therefore they are identified as one of the most critical regions of an aircraft. The structural design of the regions, in terms of damage tolerance, becomes one of the crucial aspects in the mechanical performance of the whole component, the use of virtual testing techniques playing an important role in optimizing the costs associated to this task. The work developed in this paper deals with the experimental and numerical characterization of the structural performance of a composite runout specimen subjected to uniaxial mechanical actions, specifically to traction–compression loading conditions. Several numerical computations by means of global–local modeling strategies included in the commercial FEA package ABAQUS were accomplished. Particularly, the damage initiation and propagation at the skin–stringer joint around the runout region are explicitly taken into consideration through the use of cohesive interface elements at local level of analysis. The numerical results are compared with the experimental evidences in order to evaluate the level of fidelity and reliability of these simulations.

Mechanical characterization of polyamide cellular structures fabricated using selective laser sintering technologies

The significantly growing use of Additive Manufacturing (AM) enables the fabrication of innovative parts, characterized by lightness and good mechanical properties. The biomedical field takes great advantage of these capabilities: in particular, the ability of producing porous or lattice structure-based parts allows to obtain prostheses with human bone like stiffness, with a positive influence in patient’s lifestyle. The knowledge of the mechanical behavior of materials used in AM and producible geometries is an essential requirement to profit and improve this characteristic: in particular, recent studies focus on the correlation between strength parameters and relative porosity of the part. In a previous work a set of tensile tests have been performed on different types of specimens, reproducing a set of corresponding emptying strategies, with different resulting porosity rates, and a linear predictive model has been proposed. Aim of this work is to integrate the already acquired data, providing an interpretation on previous results by numerical simulations: the influence of porosity rate on mechanical properties was investigated by performing both global and local Finite Element Analyses, finding out an explanation on inverse proportionality between material strength properties and porosity rate. The methodology proved to be a profitable way in the optimization of lattice structures for Additive Manufacturing.

3-D global–local finite element analysis of shallow underground caverns in soft sedimentary rock

We present a realistic approach for a 3-D finite element analysis of shallow underground openings excavated in soft and discontinuous rock mass. We address the stability analysis on two different scales, local-discontinuous and global-continuous, and promote the use of computationally effective linear analysis and multiple loading scenarios as a trade-off for elaborate non-linear analysis. The research was performed using the well-documented case of the ancient caverns of the Bet-Guvrin National Park in Israel. Well preserved damage zones indicate that local instabilities are associated with exposure of pre-excavation joints and development of tensile stresses exceeding the tensile strength of the rock. Global stability is compromised when supporting pillars within the caverns are diminished.Results of the local-discontinuous analysis were compared with a well-documented local failure, and were found to be in agreement with the ground truth. Following, we performed a comprehensive global stability analysis using a linear analysis of a large-scale global model (6.3×106 DOF). We modeled different scenarios of supporting pillar integrity, thus gaining comprehensive understanding of possible stress fields otherwise requiring excessive computational resources. We conclude this article with simple guidelines for performing local-discontinuous and global-continuous analysis.

Validation and enhancements for the localised experimental–numerical technique

Over many years the use of composite structures in aerospace and automobile applications has been expanding. Thus, the study of weaknesses associated with composite materials has become paramount. Delamination is a fundamental concern with these structures, and mixed mode strain energy release rates are valuable information for analysing delamination cracks. The localised experimental–numerical technique (LENT), which measures local test displacement data and combines this with local finite element analysis to evaluate the mixed mode strain energy release rates, is examined via extensive experimental testing and analysis to provide validation for the technique. Additionally, a sensitivity analysis is presented to assess the influence of pixel size on the strain energy release rate results determined using LENT. Enhancements to the method are presented focusing on reducing the pixel size and improving post-processing techniques for increased accuracy. Variations in the local area analysed with LENT are also investigated. The results demonstrate that the localised experimental–numerical technique has potential for the evaluation of mixed mode strain energy release rates using localised test data.

Finite Element Analysis of Strain Localization under Static and Dynamic Loading Conditions Based on Cosserat Continuum Model

In the present work, the Cosserat micro-polar continuum theory is introduced into the FEM numerical model, which is used to simulate the strain localization phenomena under static and dynamic loading conditions. The numerical studies on progressive failure phenomena, which occur in a panel, characterized by strain localization due to strain softening and its development, are numerically modelled by two types of Cosserat continuum finite elements, i.e. u8ω8 and u8ω4 elements. It is indicated that both two Cosserat continuum finite elements possess better performance in simulation of strain localization. Because of the presence of an internal length scale in Cosserat continuum model a perfect convergence is found upon mesh refinement. A finite, constant width of the localization zone is computed under static as well as under transient loading conditions.

Finite Element modelling of elastomeric sealing components for cylinder-head cover noise and vibration prediction

Finite Element (FE) modelling has been used extensively in designing automotive engines and subsystems for evaluating their noise and vibration performance. However, the elastomeric components at the interfaces are often omitted in the FE models owing to the lack of 'effective' elements. The present paper presents a methodology to model the elastomeric sealing components using viscoelastic gasket elements. A cylinder-head cover assembly is analysed because it is a known major contributor to radiated engine noise. First, detailed local FE analyses were performed on an elastomeric gasket and grommet to capture their non-linear load-deflection and contact interferences. Secondly, a global FE model of the cover assembly was constructed where the gasket and grommet were re-modelled with viscoelastic gasket elements. The forced response dynamic analysis was performed to calculate the transmissibility of the cover assembly. The overall approach is applicable to the modelling of elastomeric components in similar structures or engines.

Fatigue analysis of riveted railway bridge connections using the theory of critical distances

Recent studies have found that stringer-to-cross-girder connections in riveted railway bridges are susceptible to fatigue cracking, caused by secondary, deformation induced effects. These effects are difficult to interpret in terms of a single applied stress descriptor, which is customarily used in an S–N assessment. In order to address this problem, the results of a global–local finite element analysis of a riveted railway bridge are used in this paper within the context of the theory of critical distances (TCD). Using the TCD in the way proposed by Taylor [Bellett D, Taylor D, Marco S, Mazzeo E, Guillois J, Pircher T. The fatigue behaviour of three-dimensional stress concentrations. Int J Fatigue 2005; 27(3) 207–21], fatigue damage (a) is shown to converge upon mesh refinement and (b) is found to be relatively sensitive to the selection of the characteristic dimension of the critical volume. Furthermore, comparisons of the TCD-based method with its more traditional, detail-specific S–N counterpart, reveal that the latter can underestimate fatigue damage, in some cases by a factor of 3.5.

Finite element analysis of localization and micro–macro structure relation in granular materials. Part I: Formulation

The formation of strain localization influences the stability and stiffness of the soil mass or geosystem. The thickness of shear bands provides insight into overall strength and stiffness inside the granular body, and the shear band angle gives information about the failure surface in a given soil or soil mass. Thus, it is important to be able to predict when a shear band forms and how this zone of intense deformation is located and oriented within the granular medium. A rational finite element analysis for capturing the formation and development of shear bands has been formulated by using a micropolar continuum in finite element analysis. Hardening parameters including nonsymmetric stress and length scale are implemented for a realistic stress–strain analysis. Implementation and simulations of the model will be discussed in the Part II of this research. The micro–macro structure relation for finite element analysis based on this formulation paper will be simulated in the corresponding paper.

Finite element analysis of localization and micro–macro structure relation in granular materials. Part II: Implementation and simulations

The formation of strain localization influences the stability and stiffness of the soil mass or geosystem. The thickness of shear bands provides insight about overall strength and stiffness inside the granular body, and the shear band angle gives information about the failure surface in a given soil or soil mass. Thus, it is important to be able to predict when a shear band forms and how this zone of intense deformation is located and oriented within the granular medium. A rational finite element analysis for capturing the formation and development of shear bands has been performed and implemented by using a Cosserat continuum in finite element simulations. An extension of plane strain Drucker–Prager elastoplasticity to Cosserat continua is implemented in ABAQUS by using its User-defined ELement (UEL) option. The finite element formulation is discussed in the companion paper. The length scale–size effect relation has been investigated to understand the micro–macro structure relation. Several practical engineering problems are simulated in two dimensions by using the finite element code ABAQUS together with analyst-supplied extensions. The effect of Cosserat parameters on the finite element simulations has been simulated.

Hot Spot Stress Analysis of Fatigue for Tsing Ma Bridge Critical Members under Traffic Using Finite Element Method

The suspension bridge has more flexibility and repetitive vehicles produce stress cycles in members. Then fatigue of the member is accumulated with the daily traffic loadings. In order to evaluate the working condition of the Tsing Ma Bridge, the online monitoring health system has been installed in long suspension bridge. The location of the strain sensor is not exactly at the critical member locations. The hot spot stress analysis for critical members is necessary for accurate fatigue evaluation of the bridge. The global finite element analysis of the Tsing Ma Bridge under traffic loading is performed to determine the critical fatigue member locations. A detailed local finite element analysis for the welded connections is performed to determine the hot spot stress of critical fatigue location. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.