Global-local Technique Research Articles

A global–local approach for progressive damage analysis of fiber-reinforced composite laminates

The present work applies the global–local technique to the progressive damage analysis of fiber-reinforced composite laminates. A one-way, loosely-coupled global–local approach is developed as a combination of a low-fidelity linear global analysis and a high-fidelity local nonlinear analysis of specific regions within the structure, where damage is expected to occur. The local model is based on higher-order structural theories derived using the Carrera Unified Formulation (CUF), and specifically, Lagrange polynomials are used to model each ply through its thickness, leading to a layer-wise model. Composite damage is described using the CODAM2 material model, which is based on continuum damage mechanics. Initial assessments compare the relative performance of 3D finite elements (FE), 1D-CUF, and the proposed global–local approach via the free-edge stress analysis of a stiffened composite plate. The proposed technique is then used to predict the tensile strength of an open-hole specimen. The last assessment simulates damage progression within an over-height compact tension specimen using the global–local approach. Verification and validation of results are carried out via refined models and experiments from literature. The results demonstrate the accurate evaluation of 3D stress fields and composite laminates’ mechanical response in the progressive damage regime. A multi-fold improvement in the computational cost is shown when compared to full-scale CUF analyses and indicates this technique’s strong potential towards the computationally-efficient high-fidelity analysis of complex and large-scale composite structures.

Efficient prediction of cracking at solid-lattice support interface during laser powder bed fusion via global-local J-integral analysis based on modified inherent strain method and lattice support homogenization

Residual stress induced cracking at the solid-lattice support interface is often observed in laser powder bed fusion (LPBF) additive manufactured metals. Therefore, it is crucial to predict possible cracking before printing a part especially when it is large and complex. Previously, a method has been proposed to predict interfacial cracking during LPBF processing based on performing inherent strain simulations and evaluating J-integral at the critical point in a single model. However, that method is limited to application to small parts due to the high computational cost of explicit modeling of the lattice structure. In the present work, a more robust method based on the global-local technique is proposed to perform homogenized inherent strain analysis for the entire part (global) first, followed by J-integral analysis at several suspected critical locations (local). The proposed local-global analysis technique is validated both numerically and experimentally that it is both efficient and accurate in predicting interfacial cracking in as-built LPBF processed parts.

An Indoor Global Localization Technique for Mobile Robots in Long Straight Environments

Scan matching methods have been widely applied in the fields of autonomous localization and mapping. However, in structured environments where feature differences are less significant, such as long straight corridors, conventional positioning algorithms often suffer from characteristic mismatching, resulting in lower accuracy. As such, a new global localization algorithm, based on environmental difference evaluation and correlation scan matching fusion, is proposed in this study. In this process, the surrounding space was evaluated using a priori understanding of the environment based on a linear fit. Corresponding evaluation and positioning results from correlation scan matching were then modified using dynamic selection and a posture updating strategy. The performance of the proposed technique was compared with other conventional methods using open datasets exhibiting long straight features and a series of tests conducted in a physical corridor. Results showed that the proposed algorithm could effectively improve localization accuracy in narrow environments. The translation and rotation absolute pose errors were reduced by an average of 27.29% and 25.82%, respectively, compared with a correlation matching approach that does not consider the surrounding geometry. These results suggest the proposed technique offers higher adaptability and positioning accuracy in narrow environments.

A global-local approach for the elastoplastic analysis of compact and thin-walled structures via refined models

A computationally efficient framework has been developed for the elastoplastic analysis of compact and thin-walled structures using a combination of global-local techniques and refined beam models. The theory of the Carrera Unified Formulation (CUF) and its application to physically nonlinear problems are discussed. Higher-order models derived using Taylor and Lagrange expansions have been used to model the structure, and the elastoplastic behavior is described by a von Mises constitutive model with isotropic work hardening. Comparisons are made between classical and higher-order models regarding the deformations in the nonlinear regime, which highlight the capabilities of the latter in accurately predicting the elastoplastic behavior. The concept of global-local analysis is introduced, and two versions are presented - the first where physical nonlinearity is considered for both the global and local analyses, and the second where nonlinearity is considered only for the local analysis. The second version results in reasonably accurate results compared to a full 3D finite element analysis, with a twofold reduction in the number of degrees of freedom.

Stress Analysis and Design Optimization for Low-<inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> Chip With Cu Pillar Interconnection

Cu pillar technology can cater for high I/O, fine pitch, and miniaturization requirements compared with wire bonding and conventional solder flip-chip technologies. However, chip-package interaction of Cu pillar and low-k chip is a critical challenge during assembly process due to stiffer Cu pillar structure compared with conventional solder bump. Thermo-compression bonding (TCB) process was adopted and used for fine pitch Cu pillar assembly on Cu/low-k chip to reduce the package warpage and low-k stress. In this paper, a novel TCB process modeling methodology using a 2-D axisymmetric finite-element model with global-local technique was demonstrated by considering step-by-step process conditions. The TCB modeling method was validated by the experimental data. The simulation results show that TCB process results in much lower package warpage and low-k stress compared with conventional reflow (RF) process. Based on the proposed TCB modeling method, the comprehensive parametric studies were conducted to optimize TCB process and Cu pillar design for package reliability improvement, including bonding process conditions, Cu pillar structure design, package geometry, and packaging material selection. RF process-induced package warpage and low-k stress were also simulated for comparison. The final package and assembly solution was successfully achieved based on the suggestions and recommendations provided by the simulation results.

Modelling the simulation of impact induced damage onset and evolution in composites

This paper presents two modelling strategies for the simulation of low velocity impact induced damage onset and evolution in composite plates. Both the strategies use a global–local technique to refine the mesh in the impact zone in order to increase the accuracy in predicting the impact phenomena without affecting the computational cost. Cohesive elements are used to simulate the inter-lamina damage behaviour (delaminations) and Hashin’s failure criteria are adopted to predict the intra-lamina failure mechanisms. The two modelling strategies differ in terms of input parameters for the inter-lamina and intra-lamina damage evolution laws and in terms of modelling solutions in the impacted area. Comparisons between numerical and experimental results on composite plates subjected to different impact energies, according to the ASTM D7136 requirements, have been used to assess the peculiarities and the fields of application for the two proposed modelling strategies. Both the strategies have been tested by adopting the finite element code ABAQUS®. The different approaches to set the parameters of cohesive elements’ constitutive laws and Hashin’s criteria and the different choices made in quantifying the dependence of failure criteria on the finite elements’ average size have been taken into account.

Three-Dimensional Analyses of Spur Gear Bending Stresses by Global-Local Finite Element Technique

Three-dimensional elastic stresses developed in the root fillet of spur gear tooth due to uniform or non-uniform load distribution are analyzed in detail using global-local technique. Results indicate that root stresses distribute always non-uniformly along tooth width, and the maximum critical root stress (CRS) and its position depend on the face width and load distribution form. The maximum CRS is always higher than the corresponding value obtained under plane assumption and the value on the free surface. So, it is dangerous to use the CRSs calculated in practical gear designs. This research provides knowledge of root stresses for engineer to guard against gear failure and to design for increased loading.

Global Localization for a Mobile Robot Using Laser Reflectance and Particle Filter

Global localization is a fundamental requirement for a mobile robot. Map-based global local- ization is a popular technique and gives a precise position by comparing a provided geometric map and current sensory data. However, it is quite time-consuming if 3D range data is processed for 6D global lo- calization. On the other hand, appearance-based global localization using a captured image and recorded images is simple and suitable for real-time processing. However, this technique does not work in the dark or in an environment in which the lighting conditions change remarkably. To cope with these problems, we have proposed a two-step strategy which combines map-based global localization and appearance-based global localization. Firstly, several candidate positions are selected according to an appearance-based technique, and then the optimum position is determined by a map-based technique. Instead of camera images, we use reflectance images, which are captured by a laser range finder as a by-product of range sensing. In this paper, a new technique based on this global localization technique is proposed by combin- ing the two step algorithm and a sampling-based approach. To cope with the odometry data, a particle filter is adopted for tracking robot positions. The effectiveness of the proposed technique is demonstrated through experiments in real environments.

Study of void closure in hot radial forging process using 3D nonlinear finite element analysis

Hot radial forging is used to reduce porosity and increase strength for large-diameter billets. The goal of this research is to study void closure behavior in the hot radial forging process. A nonlinear coupled finite element model is developed to investigate the deformation mechanism of internal void defects during the hot radial forging process. The model is formulated in a three-dimensional frame and a viscoplastic material model has been used to describe the material behavior subjected to large deformation and high temperature. A global–local technique is employed to obtain accurate solutions around the void region. The effects of void location, mandrel, die shape, and the reduction of the tube thickness on the final void reduction are systematically investigated. The predicted reductions for central longitudinal voids in hot upsetting and hot rolling processes are in good agreement with experimental findings. The simulation results provide a valuable procedure for the design of porosity reduction during the hot radial forging process.

An accurate double-superposition global–local theory for vibration and bending analyses of cylindrical composite and sandwich shells subjected to thermo-mechanical loads

Based on the idea of double superposition, an accurate high-order global–local theoryis proposed for bending and vibration analysis of cylindrical shells subjected to thermo-mechanical loads, for the first time. The theory has many novelties, among them: (1) less computational time due to the use of the global–local technique and matrix formulations; (2) satisfaction of the complete kinematic and transverse stress continuity conditions at the layer interfaces under thermo-mechanical loads; (3) consideration of the transverse flexibility; (4) release of Love–Timoshenko assumption; and (5) capability of investigating the local phenomena. Various comparative examples are included to validate the theory and to examine its accuracy and efficiency.

A general nonlinear global-local theory for bending and buckling analyses of imperfect cylindrical laminated and sandwich shells under thermomechanical loads

The accurate shell theories proposed so far have been calibrated based on linear kinematic relations. Many of them have ignored either the interlaminar stress continuity conditions at the interfaces or the transverse flexibility of the layers. Therefore, the available shell theories may encounter accuracy problems when analyzing the nonlinear behaviors, especially for sandwich shells with soft cores. Moreover, almost all of the available shell theories have been proposed employing the Love-Timoshenko assumption. Ideas of the previous global-local plate theory of the author are extended to develop the present nonlinear high-order global-local shell theory. The present theory has the advantages of: (1) suitability for non-linear analyses, (2) higher accuracy due to satisfying the complete interlaminar kinematic and transverse stress continuity conditions at the layer interfaces under thermo-mechanical loads, employing the exact Green’s strain tensor of the curvilinear coordinates, considering the transverse flexibility, and releasing the Love-Timoshenko assumption, (3) less required computational time due to using the global-local technique and matrix formulations, and (4) capability of investigating the local phenomena. To enhance the accuracy of the results, compatible Hermitian elements are employed. Various comparative examples are included in the present paper to validate the theory and to examine its accuracy and efficiency.

Fatigue life prediction for radial truck tires using a global-local finite element method

A global-local finite element modeling technique is employed in this paper to predict the fatigue life of radial truck tires. This paper assumes that a flaw exists inside the tire, in the local model. The local model uses an FEM fracture analysis in conjunction with a global-local technique in ABAQUS. A 3D finite element local model calculates the energy release rate at the belt edge. Using the analysis of the local model, a study of the energy release rate is performed in the crack region and used to determine the crack growth rate analysis. The result considers how different driving conditions contribute to the detrimental effects of belt separation in truck tire failure. The calculation of the total mileage on four sizes of radial truck tires has performed on the belt edge separation. The effect of the change of belt width design on the fatigue lifetime of tire belt separation is discussed.

Global Localization and Position Tracking of an Automated Guided Vehicle

AbstractA swarm of Automated Guided Vehicles (AGVs) can be used in warehouses, distribution centers and manufacturing plants in order to automate the internal material flow. This swarm can overcome the disadvantages of roll conveyors and belts. The main problems of AGVs are global localization, position tracking, path planning and communication (especially within the swarm). Another technique which provides potential for logistic applications are Wireless Sensor Networks (WSNs). They can be used in warehouses to realize a decentralized stock database, monitoring a cold chain as well as for localization of an AGV and communication within the swarm. The paper presents a technique for global localization and position tracking of an omnidirectional AGV equipped with Mecanum wheels, which was designed to transport Euro-bins in a distribution center or warehouse. Global localization is realized through a technique based on range measurements obtained from an IEEE 802.15.4a WSN. The WSN is also used for communication within the swarm as well as for communication with the central warehouse computer. A developed sensor fusion of two safety laser range finders with the range measurements of a WSN solve the position tracking task. Laser range finders are used to detect pairs of landmarks to provide accurate positioning for docking maneuvers. The paper also presents a sensor model for IEEE 802.15.4a range measurements and experimental results. The latter show that the global localization technique guarantees accurate positioning and that the sensor fusion can be used for docking applications.

Non-linear dynamic thermo-mechanical buckling analysis of the imperfect laminated and sandwich cylindrical shells based on a global-local theory inherently suitable for non-linear analyses

The available accurate shell theories satisfy the interlaminar transverse stress continuity conditions based on linear strain–displacement relations. Furthermore, in majority of these theories, either influence of the transverse normal stress and strain or the transverse flexibility of the shell has been ignored. These effects remarkably influence the non-linear behavior of the shells especially in the postbuckling region. Furthermore, majority of the buckling analyses performed so far for the laminated composite and sandwich shells have been restricted to linear, static analysis of the perfect shells. Moreover, almost all the available shell theories have employed the Love–Timoshenko assumption, which may lead to remarkable errors for thick and relatively thick shells. In the present paper, a novel three-dimensional high-order global-local theory that satisfies all the kinematic and the interlaminar stress continuity conditions at the layer interfaces is developed for imperfect cylindrical shells subjected to thermo-mechanical loads.In comparison with the layerwise, mixed, and available global-local theories, the present theory has the advantages of: (1) suitability for non-linear analyses, (2) higher accuracy due to satisfying the complete interlaminar kinematic and transverse stress continuity conditions, considering the transverse flexibility, and releasing the Love–Timoshenko assumption, (3) less required computational time due to using the global-local technique and matrix formulations, and (4) capability of investigating the local phenomena. To enhance the accuracy of the results, compatible Hermitian quadrilateral elements are employed. The buckling loads are determined based on a criterion previously published by the author.

Non-linear dynamic thermo-mechanical buckling analysis of the imperfect sandwich plates based on a generalized three-dimensional high-order global–local plate theory

Abstract The available plate theories either have not considered the interlaminar stress continuity condition or have been calibrated based on linear strain–displacement relations. Moreover, almost all buckling analyses performed so far employing the global–local plate theories, were restricted to linear, static buckling analyses of the perfect plates, neglecting the transverse normal strain and stress. Researches available in literature for dynamic buckling analyses of the sandwich plates are very rare. In the present paper, a generalized high-order global–local theory that satisfies all the kinematic and transverse stress continuity conditions at the interfaces of the layers, is proposed to investigate dynamic buckling of imperfect sandwich plates subjected to thermo-mechanical loads. In comparison to the layerwise, mixed, and available global–local theories, the present theory has the advantages of: (1) less required computational time due to using the global–local technique and matrix formulations, (2) higher accuracy due to satisfying the complete interlaminar kinematic and transverse stress continuity conditions and considering the transverse flexibility, (3) suitability for non-linear analyses, (4) capability of investigating the local phenomena, such as the wrinkling. To enhance the accuracy of the results, compatible Hermitian quadrilateral elements are employed. The buckling loads are determined based on a criterion previously published by the author.

Analysis of Cu/Low- k structure under back end of line process

As the progress of the semiconductor process develops to achieve miniaturization and attain better performances for the electronic device, next-generation IC chips with deep sub-micron Cu/low-k stacked structures adopting the fabrication of (dual) damascene are developed to meet the urgent requirements of reducing high RC delay; the purpose of this is to obtain high-speed signal communication. However, due to poor adhesion and intrinsically lower fracture toughness of low-k materials as well as process loading that introduces flaws and delaminations, the phenomenon of crack growth is observed. To investigate the large scale difference problem, such as the back end of line (BEoL) structure to the silicon chip, a special multi-scale finite element simulation technology, global–local finite element method, is used to deal with this issue. The interfacial crack in the BEoL structure is modeled using the global–local technique. The chemical vapor deposition (CVD) process that induced loading to a micro crack in the interface between etch stop layer and metal track layer (ESL/Mx interface) will also be discussed through a statistical factorial design method in order to understand the crack growth phenomena that might occur during the BEoL process.

Fatigue Life Prediction for Cord-Rubber Composite Tires Using a Global-Local Finite Element Method

Abstract A failure analysis, based on fracture mechanics, may be useful for predicting the lifetime of a cord-reinforced rubber composite pneumatic tire. This paper presents a new three-dimensional Finite Element (FE) local model to calculate the energy release rate at the belt edge region. The new local model uses a three-dimensional (3D) Finite Element Modeling (FEM) fracture analysis based on a steady-state rolling assumption, in conjunction with a global-local technique in ABAQUS. Within the local model, a J-integral variation study is performed in the crack region. This consists of a prediction of the crack propagation direction and a mesh density analysis of the crack model. Furthermore, the study is used to determine the crack growth rate analysis. This study assumes that a flaw exists inside the tire, in the local model, due to a mechanical inhomogeneity introduced in the manufacturing of the tire. This paper also considers how different driving conditions, such as free-rolling, braking and traction, contribute to the detrimental effects of belt separation in tire failure.

Application Of GAP And ROD Non-linear Finite Elements ToDetermination Of Wave Induced Loads Acting On Open Sea Fish Farms

The present paper includes structural analysis and assessment of a set composed of 6 cages. The set floating on a wavy sea surface is subject to pressure and inertial forces. The preliminary analysis neglects, however, the dynamic effects assuming that the set of 6 cages is self-balanced. Such assumption is possible due to the fact that the natural period of cage heave and pitch is several times less than sea wave period. The analysis has been made for the cage set on calm water and for steep sinusoidal wave coming from various directions. Finite element method version applied in computer program MSC Nastran 70.7 was used for the analysis. For computation of 6-cage set special rod-type elements have been used in order to account for nonlinear relationship of local buoyancy versus tube immersion, fully emerged (or submerged) cross-section area, and for effect of structure deformability to the buoyancy forces. Global-local technique has been used for computation of local strength. Beam model of 6-cage set has been assumed as the global model, whereas cage corner andor single cage are represented by local shell model.

Some Nonoverlapping Domain Decomposition Methods

The purpose of this paper is to give a unified investigation of a class of nonoverlapping domain decomposition methods for solving second-order elliptic problems in two and three dimensions. The methods under scrutiny fall into two major categories: the substructuring--type methods and the Neumann--Neumann-type methods. The basic framework used for analysis is the parallel subspace correction method or additive Schwarz method, and other technical tools include local-global and global-local techniques. The analyses for both two- and three-dimensional cases are carried out simultaneously. Some internal relationships between various algorithms are observed and several new variants of the algorithms are also derived.

Global-local analysis of large-scale composite structures using finite element methods

Large domain design problems using finite element methods (FEM) require special techniques to achieve solutions within reasonable computational time. Global-local FEM refers to a set of numerical techniques designed to reduce the total solution time (and therefore the computational effort) for a given level of solution accuracy. In this paper we address the solution to large-scale periodic structures made up of multi-material composite systems, using two different global-local techniques. An error analysis is performed where the spatial distribution of errors due to material discontinuities and numerical solution procedures are evaluated for both of the methods. A simple illustrative example is used in which the error is quantified in relation to the savings in computational time. The two methods are then applied to the design of a high-field hybrid magnet, an axi-symmetric composite structure made up of a periodic array of “unit cells”.