Three elements of cable, truss, and beam-column are implemented in proposed software. ? The proposed software consider both geometric and material nonlinearities. ? It is shown to be an efficient and reliable tool for daily use in design.
132
Analysis and design optimization of deep drawing process: Part II: Optimization Original Research Article
Journal of Materials Processing Technology, Volume 184, Issues 1-3, 12 April 2007, Pages 84-92
H. Sattari, R. Sedaghati, R. Ganesan
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In part I of the present work [H. Sattari, R. Ganesan, R. Sedaghati, Analysis and design optimization of deep drawing process. Part 1: Three dimensional finite element and sensitivity analysis, J. Mater. Process. Technol., submitted for publication], a finite element formulation based on a combined Total and Updated Lagrangian approach (TUL) has been developed to calculate the sensitivities in the large elasto-plastic strains in sheet metal forming parts obtained by deep drawing. The present part II deals with the use of multiplicative decomposition of the TUL to improve the efficiency in the analysis and optimum design of blank contours of complicated parts. The TUL exploits the knowledge of the 3D shape of the final workpiece. An iterative scheme is developed to find the original position of each material point in the initial flat blank after which it is possible to estimate the strains and stresses in the final workpiece. The von Mises plasticity is adopted regarding the constitutive equations. In the present work, several developments have been presented: (1) the bending effects are taken into account using shell elements without increasing the number of degrees of freedom per node. (2) Appropriate improvements of resolution algorithms such as the introduction of a relaxation coefficient, a damping factor and a good initial solution are realized. (3) Shape optimization of blank contours is performed using a numerical procedure based on the coupling of the TUL and the sequential quadratic programming method (SQP). The numerical results obtained using the Lagrangian approaches for the benchmark test are compared with existing experimental and numerical results. The optimization procedure is applied to shape optimization of a square blank which is used to produce a cup in deep drawing process. The objective function is defined to minimize the thickness variations.
Article Outline
1. Introduction
2. Improvements in resolution algorithms
3. Numerical results for forming analysis
4. Design optimization
5. Sequential quadratic programming method
6. Convergence criterion
7. Numerical example of optimization
8. Flow chart of algorithm
9. Conclusions
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133
Finite element analysis of tile-reinforced composite structural armor subjected to bending loads Original Research Arti
cle
Composites Part B: Engineering, Volume 35, Issue 1, January 2004, Pages 57-71
S. Mahdi, J. W. Gillespie
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Composite structural armor (CSA) is a multi-functional structure that provides ballistic protection, stiffness and strength at minimum weight. It consists of a multi-layered architecture of polymer composites, rubber and ceramic tiles, stacked in a precise manner to obtain optimal ballistic performance. In the present work, the finite element method is used to conduct a detailed analysis of the mechanisms of load transfer and deformation of CSA subjected to bending loads. The results from two modeling approaches (three-dimensional and two-dimensional simulations) are compared to assess the accuracy of the computationally efficient two-dimensional model. The calculated deflections and surfaces strains from both models are found to agree very well with experimental results. The stress transfer between the layers is further analyzed using the two-dimensional model and the resulting through-thickness strain and stress distributions are discussed. It is found that the deformation of this multi-layered construction is complex and dependent upon the mechanism of stress transfer between the outer surface layer and the ceramic tiles. The effect on non-linear behavior of the constituent materials is investigated. The gap filled with polymer that separates adjacent ceramic tiles is shown to significantly influence the stiffness and strength of CSA. It is found that the plastic deformation of the resin corresponds to the onset of non-linear structural response.
Article Outline
1. Introduction
2. Experimental
2.1. Materials, fabrication and experimental procedure
2.2. Experimental results
3. Finite element analysis
3.1. Introduction
3.2. Three-dimensional finite element model
3.3. Two-dimensional finite element model
3.4. Modeling data
4. Finite elements results
4.1. Stiffness prediction
4.2. Surface strains predictions
4.3. Stress transfer between the cover layer and the ceramic tiles
4.4. Through-thickness stress and strain distribution
5. Effect of non-linearity (geometric and material) on structural response
6. Design issues
7. Conclusions
Acknowledgements
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134
Rate constitutive equations for computational analyses of textile composite reinforcement mechanical behaviour during forming Original Research Article
Composites Part A: Applied Science and Manufacturing, Volume 40, Issue 8, August 2009, Pages 997-1007
P. Badel, S. Gauthier, E. Vidal-Sallé, P. Boisse
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Textile composite reinforcements are made up of fibres. Consequently, their mechanical behaviour is a result of the possible sli
ding and the interactions between the fibres. When they are formed on double curved shapes, these fabrics are submitted to large strains, in particular large in-plane shear. Among the mechanical behaviour models for these textile reinforcements, continuous models are most commonly used for forming simulations because they can be used with standard finite elements. The objective of the present paper is to propose a continuous approach for textile reinforcement deformation analysis based on a rate constitutive equation specific to materials made of fibres. The objective derivative of this constitutive model is defined by the fibre rotation. This constitutive model is implemented in ABAQUS and can be used in most commercial F.E. software. The approach is extended to materials with two-fibre directions in order to perform simulations of woven fabric forming processes. A set of simulations of large deformations of textile composite reinforcements at the mesoscopic scale (deformation of a woven unit cell) and at the macroscopic scale (deep drawing) is presented to show the efficiency of the proposed approach.
Article Outline
1. Introduction
2. Rate constitutive equations
3. Textile composite reinforcement mechanical behaviour
4. Objective derivative based on the fibre rotation
5. Use of Green–Naghdi’s frame associated to a change of basis
6. Numerical simulations for materials with a single-fibre direction
6.1. Elementary tests
6.1.1. 45° Simple shear with horizontal fibres
6.1.2. Extension followed by a rigid body rotation
6.1.3. Extension followed by a 45° simple shear
6.1.4. 45° Simple shear with vertical fibres
6.2. Mesoscopic simulation of the shear of a 2 × 2 twill unit cell
7. Macroscopic simulations of textile reinforcement forming
7.1. Approach to textile with two-fibre directions
7.2. Fabric forming simulations
8. Conclusions and prospects
Acknowledgements
Appendix A. Numerical integration of the rate constitutive equation
Appendix B. Objectivity of the derivative defined from the fibre rotation
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135
New layerwise theories and finite elements for efficient thermal analysis of hybrid structures Original Research Article
Computers & Structures, Volume 81, Issues 26-27, October 2003, Pages 2525-2538
J. Noack, R. Rolfes, J. Tessmer
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Hybrid structures, for example metallic multiwall thermal protection systems, sandwiches or hot structures, consist of layers with different thermal conductivity. In addition, radiation and convection can occur within these layers. Analysis of these internal heat transfer mechanisms and the design of hybrid structures require three-dimensional models leading to a high modelling effort. With a new layerwise theory for heat conduction of hybrid structures this effort can be drastically reduced. Hybrid stru
ctures are idealized as structures with homogeneous layers characterised by different thermal conductivities. For layers with internal radiation exchange and convection an equivalent thermal conductivity is assumed.
By means of two heat transfer equilibrium conditions the nodal degrees of freedom become independent of the number of layers. Two four-noded finite shell elements QUADLLT and QUADQLT based on the new theory have been developed. These 2D finite elements enable the calculation of three-dimensional temperature distributions within hybrid structures. Comparison with 3D analysis and test results shows good agreement.
Article Outline
1. Introduction
2. New layerwise theories
2.1. Linear layerwise theory
2.2. Quadratic layerwise theory
3. Finite element formulation
4. Coupling of elements with different stacking sequence
5. Numerical examples
6. Conclusion
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136
Automated manufacturing environment to address bulk permeability variations and race tracking in resin transfer molding by redirecting flow with auxiliary gates Original Research Article
Composites Part A: Applied Science and Manufacturing, Volume 36, Issue 8, August 2005, Pages 1128-1141
Jeffrey M. Lawrence, Peter Fried, Suresh G. Advani
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Liquid Composite Molding (LCM) processes inject a resin into a closed mold containing fiber preforms to manufacture a polymeric composite. Many a times, resin does not fully saturate the fiber perform causing one to discard the composite part as scrap. In order to make LCM processes more reliable, a scientific understanding of the resin flow and impregnation into the porous network containing fiber preform can lead to advanced manufacturing techniques which can rely on flow control approaches to improve the yield. The flow is usually controlled by redirecting the resin flow by strategically opening and closing auxiliary injection gates as dictated by the flow monitoring sensor system. There are various approaches to generating such strategies. Once such technique, scenario-based control, has exhibited the potential to compensate for flow disturbances such as race tracking. However, a flexible and reliable manufacturing environment is needed in order to carry out experiments in advanced LCM processing. For this, an automated Resin Transfer Molding apparatus was designed and built, containing all of the necessary components. Flow sensors allow for the monitoring of the fluid advancement. Individually controllable injection gates and vents allow for geometrical flexibility and flow control. The following study demonstrates usefulness of the manufacturing tool to implement, validate and uncover limitations of a scenario-based flow control approach with geometries of increasing complexity.
Article Outline
1. Introduction
1.1. Liquid composite molding pr
ocesses
1.2. Modeling and simulation
1.3. Disturbances/variations in the process
2. RTM workstation
2.1. Mold
2.2. Flow distribution system
2.3. Sensor plate
2.4. Controlling computer
3. Flow control during filling
4. Selected geometries for study
4.1. Fender geometry
4.2. Engine hood geometry
4.3. Windows geometry
5. Limitations
5.1. Mode detection sensitivity
5.2. Separation of mode detection and control
5.3. Need for parameters
6. Conclusions
Acknowledgements
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137
Computational homogenization analysis in finite elasticity: material and structural instabilities on the micro- and macro-scales of periodic composites and their interaction Original Research Article
Computer Methods in Applied Mechanics and Engineering, Volume 191, Issue 44, 11 October 2002, Pages 4971-5005
Christian Miehe, J?rg Schr?der, Martin Becker
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Abstract
The paper investigates instability phenomena in the context of homogenization-based micro-to-macro transitions of heterogeneous materials at finite strains. This covers structural instability effects (buckling) and material instability effects (localization) which can occur on both the macro- as well as the micro-scale and may influence each other. We develop a general framework for the theoretical and computational treatment of these instability problems for elastic composites with given periodic fine-scale micro-structures. The key methodology is an investigation of the properties and the interaction of two coupled minimization principles which govern a micro-heterogeneous material in the context of a classical homogenization procedure: The principle of minimum potential energy of the macro-structure and the principle of minimum average energy of the micro-structure. The first variational problem determines the deformation field of the homogenized continuum. The latter yields the fine-scale fluctuation field on a composite micro-structure that is assumed to be attached to each local point of the macro-continuum. Global stability and the existence of solutions are based on weak convexity properties of these variational functionals. The convergence of non-convex homogenization functionals is based on the Γ-limit of periodic heterogeneous micro-structures. It defines the relevant micro-structure as an a priori unknown critical ensemble of periodic cells that catches a possible minimizing buckling mode. We summarize these basic results and recast them in a consistent notation suitable for numerical implementation. Furthermore, we in detail discuss the discretization of the coupled minimization problems by means of finite element methods and point out numerical concepts for the detection of material and structural instabilities. The treatment provides a comprehensive guide to the classification and computation of instabilities
in micro-heterogeneous solids. Focus is put on the interaction of micro- and macro-instability phenomena such as the loss of macroscopic material stability (localization) induced by a microscopic structural instability (buckling). The performance of the proposed computational methods is demonstrated for representative numerical model problems which treat coupled instability phenomena in micro-heterogeneous elastic composites.
138
The influence of software developers’ creative style on their attitudes to and assimilation of a software process innovation Original Research Article
Information & Management, Volume 40, Issue 5, May 2003, Pages 443-465
Michael J. Gallivan
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This study examines outcomes associated with differences in software developers’ creative style, based on Kirton’s adaption–innovation theory. Propositions were developed and tested to identify the relationship between software developers’ creativity and their attitude to a technological innovation that altered the software development process in their organizations. Based on adaption–innovation theory, we expected that innovators (i.e. more innovative employees) would demonstrate higher levels of job satisfaction and performance than adaptors (i.e. less innovative employees), after approximately 4 months of using the innovation. We conducted a survey of 220 developers in two firms that had recently replaced mainframe-based software development with client/server development. Our results demonstrate a pattern of relationships among employees’ creative style, attitude to the innovation, job satisfaction, and performance which we believe have important implications for managers responsible for implementing other technological innovations.
Article Outline
1. Introduction
2. Literature review
2.1. Overview of Kirton’s adaption–innovation theory
2.2. Research on creativity and information systems
3. Research framework and propositions
4. Research design and measures
4.1. Developing the survey instrument
4.2. Measures
4.3. Data analysis
5. Results
5.1. Summary of Proposition 4 results
6. Discussion
6.1. Summary of findings
6.2. Implications for practitioners (IS managers and change managers)
6.3. Implications for researchers
6.4. Limitations and directions for future research
Acknowledgements
References
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139
A multi-layer triangular membrane finite element for the forming simulation of laminated composites Original Research Article
Composites Part A: Applied Science and Manufacturing, Volume 40, Issues 6-7, July 2009, Pages 739-753
R.H.W. ten Thije, R. Akkerman
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Continuous fibre reinforced thermoplastics off
er a cost reduction compared to thermosets due to promising fast production methods like diaphragm forming and rubber pressing. Forming experiments of pre-consolidated four-layer 8H satin weave PPS laminates on a dome geometry demonstrated that inter-ply friction is a dominant parameter in forming doubly curved components. Therefore, simulations of this process as sequentially draping the individual layers are invalid. A multi-layer triangular membrane finite element has been developed for efficient simulation of laminated composite forming processes with only one element in the thickness direction. Contact logic between the individual plies is avoided. The simulations were validated by comparison to the experiments mentioned and agree well. The multi-layer membrane element has shown to be capable of predicting the material instabilities during forming. They appeared to be unsuited for realistic wrinkling simulations due to their lack of a bending stiffness.
Article Outline
1. Introduction
2. Multi-layer triangular membrane finite element model
2.1. Step 1: Global to local conversion
2.2. Step 2: Layer and interface mechanics
2.3. Step 3: Mesh re-map and convection
2.4. Step 4: Local to global conversion
3. Application 1: Punch simulation
3.1. Material characterisation
3.2. Drape simulation
3.3. Results and discussion
4. Application 2: Layered thermoplastic composite forming simulation
4.1. Material characterisation
4.2. Intra-ply properties
4.2.1. Tool-ply and inter-ply friction
4.3. Drape simulations and validation
4.4. Experimental setup
4.4.1. Finite element simulation setup
4.4.2. Experimental results
4.4.3. Simulation results
4.5. Discussion
5. Conclusions
Acknowledgements
Appendix A. Convection algorithm test
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140
The relation between the rate of erosion wear of a pitched blade impeller and its process characteristics Original Research Article
Chemical Engineering Research and Design, In Press, Corrected Proof, Available online 2 February 2011
Ivan Fo?t, Tomá? Jirout
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This paper presents an analysis of the process of erosion wear of a down-pumping pitched blade impeller in a solid–liquid suspension. The time courses of the blending time of miscible liquids and the critical impeller speed for off-bottom suspension are investigated experimentally in dependence on the degree of wear of the impeller blades. On the basis of a description of the fluid flow of the agitated charge, we determine the relations between these process characteristics of the stirred system and the degree of wear of the impeller blades. It follows from the results of the experiments that all investigated characteristics of the tested pitched blade impeller (α = 45°) depend on its erosion rate, with the exception of its energetic efficiency, which exhibits
a constant value independent of the degree of erosion of the impeller blade.
Article Outline
Nomenclature
1. Introduction
2. Theoretical
2.1. Erosion of the impeller blade
2.2. Pumping capacity of an impeller, and the total volumetric flow rate
2.3. Effect of blade erosion on the process characteristics of the pitched blade impeller
3. Experimental
4. Results and discussion
5. Conclusion
Acknowledgements
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Research highlights
? Flow sensitive operations depend mainly on the bulk flow conditions of the mixed charge. ? The wear rate of pitched blade impellers affects significantly the flow sensitive operations. ? Time course of the erosion process of pitched blade impellers exhibits a constant value of the energetic efficiency.
141
Modeling of morphology evolution in the injection molding process of thermoplastic polymers Review Article
Progress in Polymer Science, Volume 30, Issue 12, December 2005, Pages 1185-1222
R. Pantani, I. Coccorullo, V. Speranza, G. Titomanlio
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A thorough analysis of the effect of operative conditions of injection molding process on the morphology distribution inside the obtained moldings is performed, with particular reference to semi-crystalline polymers. The paper is divided into two parts: in the first part, the state of the art on the subject is outlined and discussed; in the second part, an example of the characterization required for a satisfactorily understanding and description of the phenomena is presented, starting from material characterization, passing through the monitoring of the process cycle and arriving to a deep analysis of morphology distribution inside the moldings. In particular, fully characterized injection molding tests are presented using an isotactic polypropylene, previously carefully characterized as far as most of properties of interest. The effects of both injection flow rate and mold temperature are analyzed. The resulting moldings morphology (in terms of distribution of crystallinity degree, molecular orientation and crystals structure and dimensions) are analyzed by adopting different experimental techniques (optical, electronic and atomic force microscopy, IR and WAXS analysis).
Final morphological characteristics of the samples are compared with the predictions of a simulation code developed at University of Salerno for the simulation of the injection molding process.
Article Outline
Nomenclature
1. Introduction
1.1. Morphology distribution in injection molded iPP parts: state of the art
1.1.1. Modeling of the injection molding process
1.1.2. Modeling of the crystallization kinetics
1.1.3. Modeling of the morphology evolution
1.1.4. Modeling of the effect of crystallinity on rheology
1.1.5. Modeling of the molecular orientation
1.1.5.1. Leonov model
1.1.5.2. Non-linear dumbbe
ll model
1.1.6. Modeling of the flow-induced crystallization
1.1.6.1. Approaches based on Nakamura's model
1.1.6.1.1. Enhancement of kinetics equation by a multiplying factor function of stress
1.1.6.1.2. Enhancement of kinetics equation by a multiplying factor function of shear rate
1.1.6.1.3. Enhancement of kinetics equation by a multiplying factor function of strain
1.1.6.1.4. Enhancement of kinetics equation by a multiplying factor function of orientation
1.1.6.1.5. Increase of melting temperature: melting temperature function of stress
1.1.6.1.6. Melting temperature function of molecular strain
1.1.6.2. Morphology-oriented approaches
1.1.6.2.1. Enhancement of nucleation rate (or of nucleation density)
1.1.6.2.2. Enhancement of crystallization kinetics on the basis of free energy considerations
1.2. Comments on the state of the art
2. Material and characterization
2.1. PVT description
2.2. Quiescent crystallization kinetics
2.3. Viscosity
2.4. Viscoelastic behavior
3. Injection molding tests and analysis of the moldings
3.1. Injection molding tests and sample preparation
3.2. Microscopy
3.2.1. Optical microscopy
3.2.2. SEM and AFM analysis
3.3. Distribution of crystallinity
3.3.1. IR analysis
3.3.2. X-ray analysis
3.4. Distribution of molecular orientation
4. Analysis of experimental results
4.1. Injection molding tests
4.2. Morphology distribution along thickness direction
4.2.1. Optical microscopy
4.2.2. SEM and AFM analysis
4.3. Morphology distribution along flow direction
4.4. Distribution of crystallinity
4.4.1. Distribution of crystallinity along thickness direction
4.4.1.1. IR analysis
4.4.1.2. X-ray analysis
4.4.2. Crystallinity distribution along flow direction
4.4.2.1. IR analysis
4.4.2.2. X-ray analysis
4.5. Distribution of molecular orientation
4.5.1. Orientation along thickness direction
4.5.2. Orientation along flow direction
4.5.3. Direction of orientation
5. Simulation
5.1. Pressure curves
5.2. Morphology distribution
5.3. Molecular orientation
5.3.1. Molecular orientation distribution along thickness direction
5.3.2. Molecular orientation distribution along flow direction
5.3.3. Direction of orientation
5.4. Crystallinity distribution
6. Conclusions
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142
Finite element analysis of cracks in aging aircraft structures with bonded composite-patch repairs Original Research Article
Composites Part B: Engineering, Volume 42, Issue 3, April 2011, Pages 505-510
Linxia Gu, Ananth Ram Mahanth Kasavajhala, Shijia Zhao
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Bonded composite-patch repair has been used to transfer load from cracked structures to the reinforcement such that subsequent crack propagation is reduced. In this study, the mechanical behavior of a single edge v-notch Al7075-T6 plate repaired with 1-ply and 4-ply composite patches
was investigated through the finite element method. Contour integral method was used to define and evaluate the stress intensity factors at the crack tip. The effect of the adhesive epoxy film, patch material, thickness and ply orientations on the evolution of the stress intensity factor (SIF) of the repaired structure was examined. The results indicated that the SIF of the notched plate is reduced by 1/6–1/20 as a result of the bonded composite-patch repair. The crack mouth opening displacement (CMOD) is reduced even further by 80–83%. Shear strength and thickness of the adhesive bond were the largest factors in the effectiveness of patch repair.
Article Outline
1. Introduction
2. Geometry and materials
3. Finite element model
4. Results and discussions
4.1. Effect of single and double sided repair
4.2. Effect of initial crack length
4.3. Effect of patch material, number of plies, and orientation of plies
4.4. Effect of a patch thickness
4.5. Effect of adhesive shear modulus
4.6. Effect of adhesive thickness
5. Conclusions
Acknowledgements
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143
Reliability analysis of laminated composite structures using finite elements and neural networks Original Research Article
Composite Structures, Volume 92, Issue 7, June 2010, Pages 1603-1613
P.A.M. Lopes, H.M. Gomes, A.M. Awruch
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Saving of computer processing time on the reliability analysis of laminated composite structures using artificial neural networks is the main objective of this work. This subject is particularly important when the reliability index is a constraint in the optimization of structural performance, because the task of looking for an optimum structural design demands also a very high processing time. Reliability methods, such as Standard Monte Carlo (SMC), Monte Carlo with Importance Sampling (MC–IS), First Order Reliability Method (FORM) and FORM with Multiple Check Points (FORM–MCPs) are used to compare the solution and the processing time when the Finite Element Method (FEM) is employed and when the finite element analysis (FEA) is substituted by trained artificial neural networks (ANNs). Two ANN are used here: the Multilayer Perceptron Network (MPN) and the Radial Basis Network (RBN). Several examples are presented, including a shell with geometrically non-linear behavior, which shows the advantages using this methodology.
Article Outline
1. Introduction
2. Reliability analysis
2.1. Composite materials failure criteria
2.2. The Standard Monte Carlo (SMC) method for failure probability estimate
2.3. Monte Carlo with Importance Sampling (MC–IS)
2.4. First Order Reliability Method (FORM)
2.5. FORM with Multiple Check Points (FORM–MCPs)
3. Artificial neural networks
3.1. Multilayer Perceptron Network (MPN)
3.2. Radial Basis Network (RBN)
3.3. Generation of sampl
e data for artificial neural network training
4. Numerical results
4.1. Example 1
4.1.1. First case – uniaxial load
4.1.2. Second case – bi-axial load
4.1.3. Third case – in-plane general state of load
4.2. Example 2 – semi-cylindrical composite shell under pressure load
5. Final remarks
Acknowledgements
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144
Static and Dynamic Mechanics Analysis on Artificial Hip Joints with Different Interface Designs by the Finite Element Method Original Research Article
Journal of Bionic Engineering, Volume 4, Issue 2, June 2007, Pages 123-131
Hai-bo Jiang
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Four different structural models of artificial joints were developed and the finite element method (FEM) was employed to investigate their mechanical characteristics under static and dynamic conditions. The materials used in the FEM calculation were ultra-high molecular weight polyethylene (UHMWPE), 316L stainless steel, CoCrMo alloy and Ti6A14V alloy. The stress distribution, strain, and elastic deformation under static and dynamic conditions were obtained. Analysis and comparison of the calculation results of different models were conducted. It is shown that with the same parameters the model of a metallic femur head covered with an artificial cartilage layer is more similar to the structure of the natural human joint and its mechanical characteristics are the best of the four models. Purchase
145
Failure analysis of generator rotor fan blades Original Research Article
Engineering Failure Analysis, Volume 14, Issue 5, July 2007, Pages 851-860
E. Poursaeidi, M. Salavatian
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The failure analysis of a generator rotor fan blade was investigated by mechanical analysis and metallurgical examination of fracture surface. Fracture took place at the airfoil root, surface examination showed that the blade had cracked by a high cycle fatigue mechanism. However, there was no evidence of material defect. A series of analytical, finite element and experimental analysis was utilized to determine the steady-state stresses and dynamic characteristic of the blade. Possibly the failure was due to aerodynamical disturbances that resulted in a state of resonant condition of vibration. The simulation of blade with final crack showed the stress intensity factor (SIF) under these condition exceed the critical SIF and final fracture could be occurred under analyzed stresses.
Article Outline
1. Introduction
2. Experimental procedure and result
2.1. Visual inspection
2.2. Chemical analysis
2.3. Microstructure
2.4. Fractography
2.5. Hardness
2.6. Mechanical examination
2.6.1. Examination of clearances after failure
2.6.2. Test on blade to determine influence of fixing bolt tightness o
n natural frequency
2.6.3. Dust analysis
2.6.4. Dynamic test
3. Mechanical analysis
3.1. FE modeling of the blade
3.2. Steady state stress analysis
3.3. Dynamic stress analysis and modal shapes
4. Discussion
5. Simulation of final crack by FRANC3D/BES
6. Conclusion
Acknowledgements
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146
The impacts of user review on software responsiveness: Moderating requirements uncertainty Original Research Article
Information & Management, Volume 45, Issue 4, June 2008, Pages 203-210
Jack Shih-Chieh Hsu, Chien-Lung Chan, Julie Yu-Chih Liu, Houn-Gee Chen
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Rapidly changing business environments and evolving processes increase the uncertainties in IS development. To produce a high-quality system that responds to user needs is challenging. We attempted to determine whether user reviews during the development process could reduce uncertainties and improve the product. Technology structuration theory indicated that users, as actors participating in reviews during the development of a system, could help reduce uncertainty in the organizational requirements and thus improve the software product. A survey of system developers indicated that user requirements uncertainty had a direct, negative effect on software responsiveness but that user review, serving as a moderator, could reduce this effect.
Article Outline
1. Introduction
2. Background and research hypotheses
2.1. Software quality
2.2. User participation and user review
2.3. Structurational model of technology
3. Research methods
3.1. Sampling
3.2. Constructs
3.3. Reliability and validity
3.4. Control variables
4. Data analysis and results
4.1. Direct effect
4.2. Moderating effect
5. Conclusions
5.1. Summary
5.2. Managerial implications
5.3. Limitations of the study
References
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147
Vibration of higher-order-shearable pretwisted rotating composite blades Original Research Article
International Journal of Mechanical Sciences, Volume 45, Issue 12, December 2003, Pages 2017-2041
Naresh K. Chandiramani, Chandrashekhar D. Shete, Liviu I. Librescu
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The free and forced vibration of a rotating, pretwisted blade modeled as a laminated composite, hollow (single celled), uniform box-beam is studied. The structural model includes transverse shear flexibility, restrained warping, and centrifugal and Coriolis effects. A key element of this model is its ability to satisfy the zero shear–traction requirement on the external bounding surfaces. The governing system possesses complicated and eigenvalue-dependent natural boundary conditions. Hence an extended Galerkin method using admissible functions is employed. Free-vibration resul
ts obtained for the present higher-order shearable model are compared with those of the existing first-order shearable and the non-shearable models. For the data considered, the present theory provides conservative predictions. This suggests that through-the-thickness variations of transverse shear strains are significant and should be considered when pursuing non-resonant designs. The effect of pretwist, while marginal for the lowest eigenfrequency, is substantial for the higher ones especially for lower rotation speeds and larger ply angles. A combination of softening and stiffening effects are also possible for the same eigenfrequency when pretwist is varied. Tailoring studies using the present model show an enhancement of eigenfrequency characteristics and also reveal the potential for passive mitigation of forced response.
Article Outline
Nomenclature
1. Introduction
2. Formulation
2.1. Kinematics
2.2. Equations of motion
2.3. Governing system
2.4. Spatial discretization
3. Results and discussion
4. Conclusions
Acknowledgements
Appendix A. Beam forces and moments
Appendix B. Inertia quantities
Appendix C. Global stiffnesses
Appendix D. Mass and stiffness matrices
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148
Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating Original Research Article
Composites Science and Technology, Volume 68, Issues 7-8, June 2008, Pages 1854-1861
D.A. Papargyris, R.J. Day, A. Nesbitt, D. Bakavos
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Microwave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15 °C shif
t in the position of the β-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.
Article Outline
1. Introduction
2. Experimental
2.1. Materials
2.2. Resin transfer moulding (RTM) processing
2.2.1. Conventional thermal RTM processing
2.2.2. Microwave RTM processing
2.3. Mechanical testing
2.3.1. Flexural modulus and flexural strength
2.3.2. Interlaminar shear strength
2.4. Fibre and void volume fraction
2.5. Rheology
2.6. Differential scanning calorimetry (DSC)
2.7. Dynamic mechanical thermal analysis (DMTA)
2.8. Scanning electron microscopy (SEM)
3. Results and discussion
4. Conclusions
Acknowledgements
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149
Design of a single layer micro-perforated sound absorber by finite element analysis
Applied Acoustics, Volume 71, Issue 1, January 2010, Pages 79-85
Onursal Onen, Mehmet Caliskan
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Micro-perforated sound absorbers with sub-millimeter size holes can provide high absorption coefficients. This paper presents results of work on the development of an effective single layer micro-perforated sound absorber from the commercial composite material Parabeam? with micro diameter holes drilled on one side. Parabeam? is used as a structural material made from a fabric woven out of a E-glass yarn and consists of two decklayers bonded together by vertical piles in a sandwich structure with piles (thick fibers) woven into the decklayers. The paper includes, the analytical model developed for prediction of absorption coefficients, finite element solution using commercial software MSC.ACTRAN and experimental results obtained from impedance tube measurements. A simple optimization is performed based on the developed models to obtain an efficient absorber configuration. It has been anticipated that several different and interesting applications can be deduced by combining structural and sound absorption properties of this new micro-perforated absorber.
Article Outline
Nomenclature
1. Introduction
2. Theory and analytical modeling
2.1. Acoustic impedance of micro-perforated layer
3. Finite element modeling
3.1. Overview of finite element models
3.2. Simulation of micro-perforations by Mechel’s Formula
4. Results
5. Conclusions
Acknowledgements
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150
Design features of a three-dimensional molar crown and related maximum principal stress. A finite element model study Original Research Article
Dental Materials, Volume 26, Issue 2, February 2010, Pages 156-163
Brian T. Rafferty, Malvin N. Janal, Ricardo A. Zavanelli, Nelson R.F.A. Silva, E. Dianne Rekow, Van P. Thompson, Paulo G. Coelho
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stract
Objective
To evaluate the effects of clinically relevant variables on the maximum principal stress (MPS) in the veneer layer of an anatomically correct veneer–core–cement–tooth model.
Methods
The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing the proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. ‘Crown systems’ were composed by varying characteristics of a cement layer, structural core, and veneer solid, all designed to fit the tooth preparation. The main and interacting effects of proximal wall height reduction, core material, core thickness, cement modulus, cement thickness, and load position on the maximum stress distribution were derived from a series of finite element models and analyzed in a factorial analysis of variance.
Results
The average MPS in the veneer layer over the 64 models was 488 MPa (range = 248–840 MPa). MPS increased significantly with the addition of horizontal load components and with increasing cement thickness. In addition, MPS levels varied as a function of interactions between: proximal wall height reduction and load position; load position and cement thickness; core thickness and cement thickness; cement thickness and proximal wall height reduction; and core thickness, cement thickness and proximal wall height reduction.
Conclusion
Rational design of veneered structural ceramics must consider the complex geometry of the crown–tooth system and integrate the influence of both the main effects and interactions among design parameters.
Article Outline
1. Introduction
2. Methods
3. Results
4. Discussion
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151
Finite element analysis of thin-walled composite two-span wood-based loadbearing stressed skin roof panels and experimental validation Original Research Article
Thin-Walled Structures, Volume 46, Issue 3, March 2008, Pages 276-289
J.J. del Coz Díaz, P.J. García Nieto, F.P. álvarez Rabanal, C. Betegón Biempica
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The aim of this work is to study the structural behavior of prefabricated thin-walled wood-based loadbearing stressed skin panels for use in roofs. These stressed skin panels are composed of double thin skins, made of waterproof agglomerate and oriented strandboard, with a rigid insulating core made of extruded polystyrene without a vapor control layer or breather membrane. Current design criteria for these panels are often governed by calculating shear strength rather than bending strength. However, bending is often observed as the controlling factor in real structures and experimental studies. This work describes a design procedure based on predicting whether bending or shear will control their structural behavior. In order to get this purpose, we have studied both experimentally and theor
etically the different elements that constitute this construction system to determine accurately its response in the presence of the external loads. The numerical analysis of the different variables using the finite element method (FEM) was validated by means of real tests on prototypes. The biggest difficulties in the simulation were found in the supports, due to the contacts between the different elements that compose them, and in the orthotropic material properties. Finally, the conclusions and suggested simplified procedures of calculation to be applied in similar structures are given. Comparisons with experimental data and with predictions using the quasi-analytic formulas are provided in order to support the validity of the proposed models.
Article Outline
1. Introduction
2. Geometrical model
3. Mathematical model
3.1. Contact conditions: continuum mechanics equations
3.2. Solution approach for contact problems
4. Finite element model and analysis
4.1. Material properties
4.2. Element types
4.3. Loads and boundary conditions
4.4. Finite element results
5. Experimental tests
6. Analytical calculations
6.1. Serviceability limit states criterion
6.2. Ultimate limit states criterion
7. Analysis of results and concluding remarks
Acknowledgements
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152
Incorporation of statistical length scale into Weibull strength theory for composites Original Research Article
Composite Structures, Volume 92, Issue 9, August 2010, Pages 2027-2034
Miroslav Vo?echovsky
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In this paper an extension of Weibull theory by the introduction of a statistical length scale is presented. The classical Weibull strength theory is self-similar; a feature that can be illustrated by the fact that the strength dependence on structural size is a power law (a straight line on a double logarithmic graph). Therefore, the theory predicts unlimited strength for extremely small structures. In the paper, it is shown that such a behavior is a direct implication of the assumption that structural elements have independent random strengths. By the introduction of statistical dependence in the form of spatial autocorrelation, the size dependent strength becomes bounded at the small size extreme. The local random strength is phenomenologically modeled as a random field with a certain autocorrelation function. In such a model, the autocorrelation length plays the role of a statistical length scale. The focus is on small failure probabilities and the related probabilistic distributions of the strength of composites. The theoretical part is followed by applications in fiber bundle models, chains of fiber bundle models and the stochastic finite element method in the context of quasibrittle failure.
Article Outline
1. Introduction
2. Classical Weibull strength theory
2.1. Statistical length s
cale in Weibull strength theory
3. Strength of fiber bundles
4. Strength of chains of fiber bundles
5. Discussion and relations to the strength of composites and quasibrittle structures in general
Acknowledgements
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153
Least-squares variational principles and the finite element method: theory, formulations, and models for solid and fluid mechanics Original Research Article
Finite Elements in Analysis and Design, Volume 41, Issues 7-8, April 2005, Pages 703-728
J.P. Pontaza
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We consider the application of least-squares variational principles and the finite element method to the numerical solution of boundary value problems arising in the fields of solid and fluid mechanics. For many of these problems least-squares principles offer many theoretical and computational advantages in the implementation of the corresponding finite element model that are not present in the traditional weak form Galerkin finite element model. For instance, the use of least-squares principles leads to a variational unconstrained minimization problem where compatibility conditions between approximation spaces never arise. Furthermore, the resulting linear algebraic problem will have a symmetric positive definite coefficient matrix, allowing the use of robust and fast iterative methods for its solution. We find that the use of high p-levels is beneficial in least-squares based finite element models and present guidelines to follow when a low p-level numerical solution is sought. Numerical examples in the context of incompressible and compressible viscous fluid flows, plate bending, and shear-deformable shells are presented to demonstrate the merits of the formulations.
Article Outline
1. Introduction
2. An abstract least-squares formulation
2.1. Notation
2.2. The abstract problem
2.3. L2 least-squares formulation
2.3.1. Space–time coupled formulation
2.3.2. Space–time decoupled formulation
2.4. The variational problem
2.5. The finite element model
2.6. Norm-equivalence and its implications
2.7. A least-squares collocation formulation
3. Viscous incompressible and compressible fluid flows
3.1. Governing equations
3.2. Kovasznay flow
3.3. Compressible flow past a NACA0012 airfoil
4. Plates and shells
4.1. Governing equations
4.2. Simply supported circular plate
4.3. Barrel vault
5. Summary and concluding remarks
References Purchase
154
Finite element modelling and updating of a lively footbridge: The complete process Original Research Article
Journal of Sound and Vibration, Volume 301, Issues 1-2, 20 March 2007, Pages 126-145
Stana ?ivanovi?, Aleksandar Pavic, Paul Reynolds
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155
Strength prediction of multi-layer plain weave textile composites using the d
irect micromechanics method Original Research Article
Composites Part B: Engineering, Volume 38, Issues 7-8, October-December 2007, Pages 924-932
Ryan L. Karkkainen, Bhavani V. Sankar, Jerome T. Tzeng
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156
Graphically driven interactive finite element stress reanalysis for machine elements in the early design stage Original Research Article
Finite Elements in Analysis and Design, Volume 42, Issue 10, June 2006, Pages 884-899
Sachin S. Terdalkar, Joseph J. Rencis
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157
Multi-criteria thermal optimization in liquid composite molding to reduce processing stresses and cycle time Original Research Article
Composites Part A: Applied Science and Manufacturing, Volume 37, Issue 6, June 2006, Pages 913-924
Edu Ruiz, F. Trochu
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158
DCR-based causal design knowledge evaluation method and system for future CAD applications Original Research Article
Computer-Aided Design, In Press, Corrected Proof, Available online 14 December 2010
Yun Seon Kim, Kyoung-Yun Kim
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Research highlights
? A new causal design knowledge evaluation method and system for future CAD applications is developed. ? This new CKN evaluation method compares multiple design knowledge networks using DCR and supports design decision. ? Causal design knowledge networks and their evaluation results can be used to predict the effects of design change and sensitivity analysis for future potential failures.
159
Unified nano-mechanics based probabilistic theory of quasibrittle and brittle structures: I. Strength, static crack growth, lifetime and scaling Original Research Article
Journal of the Mechanics and Physics of Solids, Volume 59, Issue 7, July 2011, Pages 1291-1321
Jia-Liang Le, Zdeněk P. Ba?ant, Martin Z. Bazant
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160
Simulation and tomography analysis of textile composite reinforcement deformation at the mesoscopic scale Original Research Article
Composites Science and Technology, Volume 68, Issue 12, September 2008, Pages 2433-2440
P. Badel, E. Vidal-Sallé, E. Maire, P. Boisse
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