Comprehensive Finite Element Model Research Articles

Evaluation of strain and stress states in the single point incremental forming process

Single point incremental forming (SPIF) is a promising manufacturing process suitable for small batch production. Furthermore, the material formability is enhanced in comparison with the conventional sheet metal forming processes, resulting from the small plastic zone and the incremental nature. Nevertheless, the further development of the SPIF process requires the full understanding of the material deformation mechanism, which is of great importance for the effective process optimization. In this study, a comprehensive finite element model has been developed to analyse the state of strain and stress in the vicinity of the contact area, where the plastic deformation increases by means of the forming tool action. The numerical model is firstly validated with experimental results from a simple truncated cone of AA7075-O aluminium alloy, namely, the forming force evolution, the final thickness and the plastic strain distributions. In order to evaluate accurately the through-thickness gradients, the blank is modelled with solid finite elements. The small contact area between the forming tool and the sheet produces a negative mean stress under the tool, postponing the ductile fracture occurrence. On the other hand, the residual stresses in both circumferential and meridional directions are positive in the inner skin of the cone and negative in the outer skin. They arise predominantly along the circumferential direction due to the geometrical restrictions in this direction.

Biomechanics of high-grade spondylolisthesis with and without reduction.

The clinical advantages of reducing spondylolisthesis over fusion in situ have several intuitive reasons such as restore the spinal column into a more anatomic relationship and alignment. However, there is only little evidence in the literature supporting the theoretical advantages of reduction, and its effect on spinopelvic alignment remains poorly defined. In this study, a comprehensive finite element model was developed to analyze the biomechanics of the spine after spinal fusion at L5-S1 in both types of high-grade spondylolisthesis (balanced and unbalanced pelvis). The relevant clinical indices (i.e. spondylolisthesis gradeand Dubousset lumbosacral angle), the displacement of L4-L5, pressure within the annulus and nucleus, and stress at L4-L5 were evaluated and compared. The model can well predict the changes of the important clinical indices during the surgery. For a balanced pelvis, the reduction has a minimal effect on the biomechanical conditions at the adjacent level during postsurgical activities. In the unbalanced case, reduction induced larger deformation in the lumbosacral region and a higher stress concentration at adjacent level. Whether such a stress concentration can lead to long-term disc degeneration is not known. The results provide additional information for the clinician considering reduction of high-grade spondylolisthesis.

Modeling and characterization of fused deposition modeling tooling for vacuum assisted resin transfer molding process

The material extrusion additive manufacturing process, i.e., fused deposition modeling (FDM), as opposed to traditional subtractive manufacturing, offers a superior way of manufacturing tooling components in terms of great design flexibility, rapid tooling development, material requirement reduction and significant cost savings. However, it is always challenging to design a tool structure with minimized material and labor cost while maintaining satisfactory tooling performance. In the current study, a comprehensive finite element model was developed for ULTEM 9085 FDM tools subjected to applied pressure and elevated temperature for vacuum assisted resin transfer molding (VARTM) process. Both solid-build and sparse-build tools were studied. Material properties of the tools were obtained from solid coupon testing at elevated temperatures. The thermo-mechanical behavior of tools during the VARTM process was investigated using the finite element model. The ULTEM tools were manufactured using Stratasys Fortus 400mc FDM machine. Thermal cycling of the tools was performed at elevated temperatures (180°F and 250°F). Dimensional analysis and surface roughness of the tools were evaluated after thermal cycling. This study on the performance of FDM tooling for VARTM composite manufacturing process can be extended to other composite manufacturing processes.

Design Guidance for Blast-Resistant Glazing

AbstractThis paper reviews current design standards and test methods for blast-resistant glazing design and compares a typical design outcome with that from comprehensive finite-element (FE) analysis. Design standards are conservative and are limited to the design of relatively small glazed panels. Standard test methods are expensive, create environmental pollution, and can classify the hazard ratings of only smaller glazed panels. Here the design of a laminated glass (LG) panel is carried out according to an existing design standard, and then its performance is examined using comprehensive FE modeling and analysis. Finite-element results indicate that both glass panes crack, the interlayer yields with little damage, and the sealant joints do not fail for the designed blast load. This failure pattern satisfies some of the requirements for minimal hazard rating in the design standard. It is evident that interlayer thickness and material properties are important during the post-crack stage of an LG panel, b...

Deformation mechanics and efficient force prediction in single point incremental forming

Incremental sheet forming (ISF) is a promising forming process which is able to deform a flat sheet into a complex 3D shape by using a generic moving tool. The flexibility, increased formability and the reduced forming force make the ISF process ideal for rapid prototype and small batch production. However, the effective production design and optimization in ISF require the efficient prediction of forming force, especially the tangential force which is the actual force component that does plastic work during the forming process. In this paper, in order to investigate the deformation mechanism in the ISF process, a comprehensive finite element (FE) model for the cone-forming process with fine solid elements is established which allows the quantitative study of the deformation behavior of stretching, bending and shearing during the process. Based on such analysis, an efficient model for tangential force prediction is deduced analytically in which all these three deformation modes are considered. In particular, the contribution from each deformation mode is related to the variation of forming parameters. Additionally, the proposed efficient model is comprehensively validated with both truncated cone and pyramid shapes by varying four forming parameters (i.e. step down, wall angle, tool radius and sheet thickness). In both cases, the predicted forces show good agreements with the experimental results. Furthermore, the proposed model is generalized to deal with more complex shapes (e.g. ellipsoidal cup). It is found that the trend of tangential force could be properly represented by the change of the curvature of the formed part. Considering the proposed model can be solved within only several minutes, it will guide the forming process and shorten the lead time.

Investigation of the initiation and propagation of cracks in the coated surface of spur gear: An application of irreversible cohesive zone model

Spur gears are the most common type of gears for industry, due to its simple structures and low costs of manufacture. Under the action of rolling contact fatigue, the main mode of the coated teeth failure is surface or subsurface originated micro-pitting, leading to the debonding of coating from substrate, fracture in the coating and even subsurface failure. Failure may originate from initiation of cracks, and its growth and propagation, however, basic failure mechanism is still not clear. In this paper, a comprehensive finite element modeling procedure including submodelling techniques and irreversible cohesive zone modelling techniques (CZM) is developed to investigate the failure mechanisms under the rolling contact fatigue loading. The details of the localized stresses distribution will be simulated using the submodelling technique. Irreversible CZM will be used to simulate the initiation and propagation of the cracks in the coated surface of the spur gears under the cyclic contact loading.

On optimization of a composite bone plate using the selective stress shielding approach

Bone fracture plates are used to stabilize fractures while allowing for adequate compressive force on the fracture ends. Yet the high stiffness of conventional bone plates significantly reduces compression at the fracture site, and can lead to subsequent bone loss upon healing. Fibre-reinforced composite bone plates have been introduced to address this drawback. However, no studies have optimized their configurations to fulfill the requirements of proper healing. In the present study, classical laminate theory and the finite element method were employed for optimization of a composite bone plate. A hybrid composite made of carbon fibre/epoxy with a flax/epoxy core, which was introduced previously, was optimized by varying the laminate stacking sequence and the contribution of each material, in order to minimize the axial stiffness and maximize the torsional stiffness for a given range of bending stiffness. The initial 14×414 possible configurations were reduced to 13 after applying various design criteria. A comprehensive finite element model, validated against a previous experimental study, was used to evaluate the mechanical performance of each composite configuration in terms of its fracture stability, load sharing, and strength in transverse and oblique Vancouver B1 fracture configurations at immediately post-operative, post-operative, and healed bone stages. It was found that a carbon fibre/epoxy plate with an axial stiffness of 4.6MN, and bending and torsional stiffness of 13 and 14N·m2, respectively, showed an overall superiority compared with other laminate configurations. It increased the compressive force at the fracture site up to 14% when compared to a conventional metallic plate, and maintained fracture stability by ensuring the fracture fragments’ relative motions were comparable to those found during metallic plate fixation. The healed stage results revealed that implantation of the titanium plate caused a 40.3% reduction in bone stiffness, while the composite plate lowered the stiffness by 32.9% as compared to the intact femur. This study proposed a number of guidelines for the design of composite bone plates. The findings suggest that a composite bone plate could be customized to allow for moderate compressive force on the fracture ends, while remaining relatively rigid in bending and torsion and strong enough to withstand external loads when a fracture gap is present. The results indicate that the proposed composite bone plate could be a potential candidate for bone fracture plate applications.

Numerical modelling on dynamic behaviour of deepwater S-lay pipeline

The dynamic behaviour of offshore pipeline in the process of deepwater S-lay operations, which is of prime importance in the installation design of the pipeline, has drawn extensive research attention. In this paper, a comprehensive finite element model for S-lay systems within the framework of the commercial computer code OrcaFlex is developed to investigate the dynamic lay effects, including surface waves, ocean currents, pipelay vessel motions, and the clashing contact between the pipeline and stinger rollers. Meanwhile, a non-linear hysteretic soil model is applied to identify the vertical pipe-seabed interaction mechanism. The numerical model is then used to conduct a practical engineering analysis of a 6-inch offshore pipeline being laid to a water depth of 1500m in LW3-1 gas field in the South China Sea using the HYSY 201 pipelay vessel. The dynamic behaviour of offshore pipeline on aspects of deflection, axial tension, bend moment, stress and strain is estimated in detail. Significant differences between static and dynamic results are observed, which offer very intuitive evidences of dynamic effects concerning deepwater S-lay pipeline.

Structural safety evaluation of Karun III Dam and calibration of its finite element model using instrumentation and site observation

In the present paper, a comprehensive finite element model of Karun III double curvature arch dam is calibrated based on the micro geodesies measurements and instrumentation. Thermal properties of concrete are obtained by transient thermal analysis and the results are compared with those obtained from thermometers. Thermal analysis features include air temperature, water layers temperatures, and the solar radiation on the exposed faces. Structural calibration features include thermal distribution within the dam body, dam self-weight, hydrostatic pressure, and silt load applied on the model of dam–reservoir–foundation system. Finite element model calibration provides updated information related to the current dam status and can be used for further safety evaluations.

Numerical investigation on the performance of concrete-filled double-skin steel tubular members under tension

This paper presents a numerical investigation on the tensile behaviour of concrete-filled double-skin steel tubular (CFDST) member. A comprehensive finite element (FE) model is established and calibrated against the test results for the CFDST members under concentric and eccentric tension. The comparison shows that the proposed FE model is capable to capture the structural behaviour of the tensile specimens. Parametric studies are then conducted to investigate the influence of some key parameters, such as the material strength, the nominal steel ratio and the hollow ratio on the tensile behaviour of composite members. The steel–concrete composite action, the effect of loading paths and the tension–bending interaction diaphragm are also discussed. It is found that the tensile strength of the member depends on the composite action between steel tubes and sandwich concrete, and the tension–bending interaction diaphragm can be represented by a simple linear relationship. Finally, the design equation to predict the tensile strength of CFDST member is proposed, and the comparison results show that the proposed equation has a good accuracy.

Performance Evaluation of Out-of-Autoclave Sandwich Structures with K-COR and Nomex Core

Composite sandwich structures are being increasingly employed in the aerospace, marine as well as other applications which require high strength, high in-plane and flexural stiffness coupled with a reduction in weight. In the aerospace industry sandwich composites are usually manufactured using the autoclave process which is expensive and time consuming. A viable alternative is the Out-of-Autoclave (OOA) process whose main advantage is the low cost of manufacturing. One of the most dominant failure modes in sandwich composites is the debonding that occurs at the facesheet-to-core interphase. A well-formed adhesive bond at the skin to core interphase and improved adhesion strength are significant factors in preventing bond failure. In this paper honeycomb and K-COR sandwich composites are manufactured using the Out-of-autoclave process. The adhesive bonding strength in each of the manufactured panels is quantified by evaluating the flatwise tensile strength in accordance with ASTM standards. Core-facesheet debonding was observed in K-COR sandwich while core failure was observed in the Nomex sandwich structures. Finite element modeling and simulation of Nomex and K-COR sandwich structures subjected to flatwise tension is conducted using comprehensive three-dimensional finite element models. Cohesive damage modeling approach is used to simulate delamination failure in both Nomex and K-COR sandwich structures. Finite element results are compared with the experimental results for model validation. The ultimate flatwise tensile strength predicted by simulation was found to be in good agreement with the experimental results.

Field Study of Load Path in Rail and Concrete Crosstie System

The design and performance of concrete ties and elastic fastening systems must be improved to meet demands placed on North America’s railway infrastructure through ever-increasing freight tonnages and development of its high speed rail program. In July 2012, a field experimentation program was performed at the Transportation Technology Center (TTC) in Pueblo, CO by researchers from the University of Illinois at Urbana-Champaign (UIUC). This paper focuses on the transfer of vertical and lateral loads through the system, demonstrating the demands of the fastening components (e.g. insulators, fastening clips) and concrete crossties. Measurements of loads, strains and displacements were used to quantify the physical response of the system under various parameters (track curvature, train speed, and car weight). The experimental data provide validation for a comprehensive finite element model developed by UIUC. Improvements to instrumentation strategies and areas of uncertainty will also be discussed. These experimental results will be used to guide future research in further quantifying the field loading demands, ultimately leading to a mechanistic design approach for the concrete crosstie and components within the fastening system.

Numerical study on human cornea and modified multiparametric correction equation for Goldmann applanation tonometer

Glaucoma, a chronic eye disease, is quoted to be a second leading cause of blindness with 66.8 million people suspected to be victimised by the same in year 2000 (Morrison, 2003), and is caused due to an elevated intraocular pressure (IOP). Goldmann Applanation tonometer (GAT), a gold standard (Organization, 2001), suffers from inefficacies to measure intra-ocular pressure (IOP) independent of the biomechanical properties of an eye. Thus, the purpose of this paper is to study the importance of wide range of corneal parameters and to propose a multiparametric correction equation for GAT based on a numerically simulated comprehensive finite element model (Dohadwala et al., 1998; Morrison, 2003; Organization, 2001). Towards this end, with the help of numerical model, the parameters considered in correction equation proposed elsewhere (Elsheikh et al., 2011) were extended to include combined influence of central corneal thickness (CCT), central anterior curvature (R), peripheral corneal thickness (PCT), corneal asphericity (Pa), age, measured IOP itself and, was separately studied for role played by corneal support orientation (θ°) in this aspect. Findings indicate that for a wide range of parameters considered, while increased age is related with gain in corneal stiffness, the maximum (average) individual effects of variations in PCT, Pa, CCT, age and θ° on IOPG were estimated at 0.25mmHg/100µ of PCT, 0.073mmHg/0.1 of Pa, 1.9mmHg/100µ of CCT, 24.3%/decade relative of IOPT and 0.95mmHg/5° increase in θ°. The multiparametric correction equation has been modified accordingly. The GAT correction equation can consider the combined effect of PCT, Pa, CCT, and age on IOPG. Separately the non-linear effect of θ° on IOPG cannot be ignored for reasons of precision.

An effective finite element model for the prediction of hydrogen induced cracking in steel pipelines

Abstract This paper presents a comprehensive finite element model for the numerical simulation of Hydrogen Induced Cracking (HIC) in steel pipelines exposed to sulphurous compounds, such as hydrogen sulphide (H2S). The model is able to mimic the pressure build-up mechanism related to the recombination of atomic hydrogen into hydrogen gas within the crack cavity. In addition, the strong couplings between non-Fickian hydrogen diffusion, pressure build-up and crack extension are accounted for. In order to enhance the predictive capabilities of the proposed model, problem boundary conditions are based on actual in-field operating parameters, such as pH and partial pressure of H2S. The computational results reported herein show that, during the extension phase, the propagating crack behaves like a trap attracting more hydrogen, and that the hydrostatic stress field at the crack tip speed-up HIC related crack initiation and growth. In addition, HIC is reduced when the pH increases and the partial pressure of H2S decreases. Furthermore, the relation between the crack growth rate and (i) the initial crack radius and position, (ii) the pipe wall thickness and (iii) the fracture toughness, is also evaluated. Numerical results agree well with experimental data retrieved from the literature.

Analysis of the novel flexure parallel micromanipulators based on multi-level displacement amplifier with/without symmetrical design

Conventional flexure-based parallel micromanipulators (FPM) usually suffer from a small stroke. The performance of a FPM is highly related to the stroke of each actuated limb and the associated constraints, including non-actuated joints. To conquer the drawbacks of the small workspace of conventional FPMs, a device for displacement amplification could improve motion ranges when incorporated into the design of the actuated limbs. This research is focused on the development of a group of unique FPMs with/without symmetrical design based on a multi-level displacement amplifier. Firstly, structural modeling based on a compact and modular design is introduced. Then a macro/micro analysis of the displacement amplifier is conducted. Subsequently, a comprehensive finite-element modeling including the strain and total deformation, modal and frequency response is undertaken to examine the mechanical behavior of the proposed mechanism. The developed method and technology provide a promising solution to enhance the performance of generic FPMs.

INVESTIGATION OF HEAD-DISK INTERFACE AND UNLOADING PROCESS IN HDD WITH AN EFFICIENT SCHEME

An efficient scheme was developed to analyze head-disk interfaces (HDIs) in hard disk drives. HDIs were studied by decoupling the nanometer scale variations of the air bearings and the micrometer scale changes of the suspensions. The nonlinear variations of the air bearing forces and moments were described with analytical expressions obtained from a surface fitting scheme. Combined with a 3 degree of freedom (DOF) suspension model whose parameters were estimated from a comprehensive finite element model, the historical behaviors of a subambient slider during an unloading process can be obtained in a very short computation period, thus providing a way of exploring a large number of parameter values of the suspension stiffness matrix.

A simple FE approach to study microstructural influences in power-law creep

Creep of metallic materials is a complex phenomenon, which is depending on temperature, time, the applied load and the specific properties of the material exposed to creep conditions. Especially the influence of the microstructure on creep phenomena is complex, thus a comprehensive finite element model is used to study the heterogeneous deformation on a microstructural level. The different microstructural components are incorporated by using distinct, individual sets of physical parameters for each constituent. The materials response is calculated in terms of creep strains and stresses using a simple approach to simulate power-law creep and the influence of grain boundaries, triple junctions and precipitates on creep strains and stresses is studied.The results indicate that the different microstructure configurations, such as the presence of triple points, second phase particles and the relative orientation of grain boundaries to the loading direction influence the stress distribution and therefore lead to a highly heterogeneous creep strain distribution.

A comprehensive finite element model for tapered composite wing structures

A comprehensive finite element model incorporating the features of comprehensive wing model and finite element method is developed in this paper. This new model extends the applicability of comprehensive wing model from uniform composite wings to tapered composite wings. It preserves the simplicity of one-dimensional finite element but performs like three-dimensional finite element for wing structural analysis. To verify its accuracy and show its efficiency, this model which is applicable to the general dynamic analysis is reduced to two simple cases: static analysis and free vibration analysis. Based upon the reduction results for static and free vibration cases, several numerical examples of composite wing structures are presented such as tapered wings subjected to end load or uniform pressure, and free vibration of tapered wings. The numerical results show that the proposed model is much more efficient than the conventional finite element, and their differences are within 12% in all cases of composite wing structures.

Dynamic Analysis on Underlay Microstructure for Cu/Low-k Wafer during Wire Bonding

Two major analyses were conducted in this paper. In the first, experimental procedures are accomplished to measure the tensile mechanical properties of ultra thin gold wire (=1mil) before/after electric flame-off (EFO). Characteristics of free air ball (FAB), heat affected zone (HAZ) and as-drawn wire have been carefully investigated by nanoindentation, microhardness and self-design pull test fixture. Secondary, with the obtained experimental material data, a comprehensive finite element model using software ANSYS/LS-DYNA is successfully developed to simulate the wirebonding. Dynamic analysis is performed to evaluate the overall stress distributions on the underlay microstructure of Cu/low-k wafer. Special emphasizes are focused on the Copper via and the intermetal dielectric (IMD)/undoped silica glass (USG) dielectric microstructure.

Field investigation and performance of bridge approach slabs

Bridge approach slabs are designed to function as a transitional roadway to the bridge deck, spanning the distance between the abutment and the road pavement. However, the number of rough riding approaches with heavy maintenance requirements is sufficient to convince highway agencies that a serious problem exists. The complaints usually describe a ‘bump’ that motorists feel when they approach or leave bridges. This bump results in reduction of steering response, distraction to the driver, amplified truck impact and dynamic response in bridge decks, and expense to maintenance operations. Approach slabs can lose their contact supports due to various reasons, including the settlement of soil and the bulging of embankments. The objective of this paper is to present results from a study to evaluate the analytical behaviour and the field performance of new design alternatives that could reduce or eliminate this problem. The new designs were analysed using comprehensive finite element (FE) models and were also built and instrumented at the Doremus Avenue Bridge in Newark, New Jersey, for testing and long-term monitoring. Various truck load tests were performed prior to opening the bridge to traffic. The results show that the FE models are accurate and that the new design alternatives have higher load carrying capacities than those of the existing design. In addition, results also show that long-term field monitoring using various sensors can lead to quantitative measurements of various factors that can lead to the cracking of the approach slabs.