Finite Element Modeling Approach Research Articles

Computational analysis and experimental calibration of cold isostatic compaction of Mg-SiC nanocomposite powders

The consolidation process and density distribution of Mg-SiC nanocomposite powder were studied using computational finite element modeling (FEM) and experimental approaches. Cold isostatic pressing (CIP) was employed for producing fully dense Mg-SiC nanocomposites with a homogeneous distribution of SiC nanoparticles. The elastoplastic modified Drucker-Prager Cap (DPC) model was applied to predict SiC nanoparticle density distribution effects on the milled powder compressibility after the CIP. The FEM results revealed that increasing SiC nanoparticles from 1% (M1Sn) to 10% (M10Sn) volume leads to harder compressibility, increasing the maximum equivalent pressure stress value 717.2 to 737.1 MPa, and decreasing the relative density value 94.63% to 88.67%. The maximum element volume (EVOL) for pure Mg (MM), M1Sn, and M10Sn powders was estimated as 21.69, 20.13, and 15, respectively. The model is validated by comparing finite element simulations with experimental results of relatve density and reduction of volume under 700 MPa cold isostatic pressure for MM, M1Sn, and M10Sn powders. The finite element modeling results of samples after the CIP process were consistent with the experimental results. These results indicate the effectiveness of the modified DPC model and confirmed compaction behavior and relative density of Mg-SiC nanocomposite powders.

An analytical model of full-field displacement and strain induced by amplitude-modulated focused ultrasound in harmonic motion imaging

The majority of disease processes involves changes in the micro-structure of the affected tissue, which can translate to changes in the mechanical properties of the corresponding tissue. Harmonic motion imaging (HMI) is an elasticity imaging technique that allows the study of the mechanical parameters of tissue by detecting the tissue response by a harmonic motion field, which is generated by oscillatory acoustic radiation force. HMI has been demonstrated in tumor detection and characterization as well as monitoring of ablation procedures. In this study, an analytical HMI model is demonstrated and compared with a finite element model (FEM), allowing rapid and accurate computation of the displacement, strain, and shear wave velocity (SWV) at any location in a homogenous linear elastic material. Average absolute differences between the analytical model and the FEM were respectively 1.2% for the displacements and 0.5% for the strains for 41 940 force voxels at 0.22 s per displacement evaluation. A convergence study showed that the average difference could be further decreased to 1.0% and 0.15% for the displacements and strains, respectively, if force resolution is increased. SWV fields, as calculated with the FEM and the analytical model, have regional differences in velocities up to 0.57 m s−1 with an average absolute difference of 0.11 ± 0.07 m s−1, primarily due to imperfections in the non-reflecting FEM boundary conditions. The apparent SWV differed from the commonly used plane-wave approximation by up to 1.2 m s−1 due to near and intermediate field effects. Maximum displacement amplitudes for a model with an inclusion stabilize within 10% of the homogenous model at an inclusion radius of 10 mm while the maximum strain reacts faster, stabilizing at an inclusion radius of 3 mm. In conclusion, an analytical model for HMI stiffness estimation is presented in this paper. The analytical model has advantages over FEM as the full-field displacements do not need to be calculated to evaluate the model at a single measurement point. This advantage, together with the computational speed, makes the analytical model useful for real-time imaging applications. However, the analytical model was found to have restrictive assumptions on tissue homogeneity and infinite dimensions, while the FEM approaches were shown adaptable to variable geometry and non-homogenous properties.

Finite element modelling of concrete-filled spiral-welded mild-steel and stainless-steel tubes in flexure

This study investigated the capability of widely-used finite element modelling (FEM) methods, to predict the flexural capacity behaviour of concrete-filled spiral-welded mild-steel and stainless-steel tubes (CF-SWMSTs and CF-SWSSTs). For this purpose, twelve CF-SWMST and CF-SWSST flexural tests each were modelled using the ABAQUS software. The main parameters that had been varied in the respective tests were the outside diameter to thickness (D/t) ratio and infill concrete strength. The nominal D/t of the modelled specimens were in the range 51–114.5, while the infill concretes were of nominal grades 20 and 50 MPa. The moment capacities predicted by the FEM were observed to be, on average, conservative for the modelled CF-SWMSTs. The predicted flexural capacities were more closely in agreement with the corresponding experimental capacities for the CF-SWSSTs. The respective average actual to predicted moment capacity ratios were 1.07 and 1.00, respectively. The experimental and predicted deformation modes were also in qualitative agreement, with local buckling also being predicted by the finite element models. Though the experimentally obtained local buckling patterns were not exactly replicated, there was, nonetheless, good qualitative agreement. This study provided evidence of the capacity of commonly used FEM approaches, relating to CFSTs, to act as a predictive tool for CF-SWMSTs and CF-SWSSTs in flexure. Given the distinct difference in capacity prediction conservativeness, the study also indicated that separate material model formulations may be warranted for CF-SWSSTs compared to CF-SWMSTs. The predicted results were also found to be negligibly sensitive to explicitly modelling the spiral weld seam geometry, even though it was the default case adopted for the FEM in this study.

Mechanical properties evaluation for engineering materials utilizing instrumented indentation: Finite element modelling approach

Instrumented indentation technique gives the possibility to determine the mechanical properties for small specimens and material in service. Several researchers have attempted to evaluate this approach experimentally and investigated the factors that affect it by using different indenter’s geometries for different engineering materials. In this work, the instrumented indentation technique was used to evaluate the mechanical properties experimentally and numerically using finite element simulation to understand the contact mechanics between the indenter surface and the substrate for two types of steel alloys namely ASTM516-G70 and AISI1010 steel. Two shapes of indenters, blunt (spherical) and sharp (Vickers) were used. The results were then compared with the experimental results extracted from the instrumented indentation test. The results have demonstrated a good agreement between the experimental and the finite element simulation results with error bound a ±5 % for young’s modulus and ±7.7 % for yield strength. Whereas excellent agreement is observed in the elastic region and the beginning of the plastic region for the true stress-strain curve. Finally, it is to be emphasized that the obtained results are more applicable for the tested materials and further research is recommended to accommodate other materials as well and to confirm the generality of this method.

DBS electrode localization and rotational orientation detection using SQUID-based magnetoencephalography

Objective. The aim of the present study was to investigate the accuracy of localization and rotational orientation detection of a directional deep brain stimulation (DBS) electrode using a state-of-the-art magnetoencephalography (MEG) scanner. Approach. A directional DBS electrode along with its stimulator was integrated into a head phantom and placed inside the MEG sensor array. The electrode was comprised of six directional and two omnidirectional contacts. Measurements were performed while stimulating with different contacts and parameters in the phantom. Finite element modeling and fitting approach were used to compute electrode position and orientation. Main results. The electrode was localized with a mean accuracy of 2.2 mm while orientation was determined with a mean accuracy of 11∘. The limitation in detection accuracy was due to the lower measurement precision of the MEG system. Considering an ideal measurement condition, these values represent the lower bound of accuracy that can be achieved in patients. Significance. However, a future magnetic measuring system with higher precision will potentially detect location and orientation of a DBS electrode with an even greater accuracy.

Validation of a finite element modelling approach for mitigated and unmitigated pile driving noise prognosis.

Piles are the state-of-the-art foundation type for offshore structures like offshore wind turbines. The pile driving process induces high sound pressure levels into the water, which are potentially harmful for the marine environment. To protect the marine life, regulations for these levels apply in many regions of the world. Therefore, detailed pile driving noise models are necessary to allow for both a prognosis of the underwater noise levels and the dimensioning and optimization of possible noise mitigation systems. In this paper, an established model based on a finite element approach is validated by means of three measurement campaigns. These have been conducted at different sites in the North Sea and include piling with and without noise mitigation measures. The noise mitigation systems are modelled as fully absorbing by applying a mixed Dirichlet-Neumann boundary condition at its position. Therefore, the computational results with noise mitigation measures are generally below the measured data and present the highest achievable noise reduction. The measurement campaigns have been conducted with a big bubble curtain and a noise mitigation screen. The occurring differences between the modelled and measured results with and without noise mitigation are shown.

Sliding of spherical ball on solid lubricating coating combined with wear process

In present paper we show results of ball-on-disk wear experiment of MoS2 film deposited on Ti6Al4V substrate. The ball materials is aluminum oxide. The tests are performed for different surrounding temperature conditions: 20 oC, 200 oC and 350 oC. It is shown that depth of the wear groove increases with increasing surrounding temperature. A finite element modeling approach is next developed to mimic the experimental observations of ball-on-disk wear process. It is based on the assumption of steady state condition developed during short time scale at contact region. The steady state results can next be applied to long time scale in which wear process is numerically simulated. Model results are compared with experimentally obtained wear groove and show satisfactory agreement.

A mesoscale finite element modeling approach for understanding brain morphology and material heterogeneity effects in chronic traumatic encephalopathy

Chronic Traumatic Encephalopathy (CTE) affects a significant portion of athletes in contact sports but is difficult to quantify using clinical examinations and modeling approaches. We use an in silico approach to quantify CTE biomechanics using mesoscale Finite Element (FE) analysis that bridges with macroscale whole head FE analysis. The sulci geometry produces complex stress waves that interact with one another to create increased shear stresses at the sulci depth that are significantly larger than in analyses without sulci (from 0.5 to 18.0 kPa). Sulci peak stress concentration regions coincide with experimentally observed CTE sites documented in the literature. Highlights Sulci introduce stress localizations at their depth in the gray matter Sulci stress fields interact to produce stress concentration sites in white matter Differentiating brain tissue properties did not significantly affect peak stresses

Chord-end RHS-to-RHS and CHS-to-CHS X-connections with rigid cap plates: Stress concentration factors

For rectangular hollow section (RHS)-to-RHS and circular hollow section (CHS)-to-CHS connections situated near a truss/girder end, reinforcement using a chord-end cap plate is common; however, for fatigue design, formulae in current design guidelines [for calculation of stress concentration factors (SCFs)] cater to: (i) unreinforced connections, with (ii) sufficient chord continuity beyond the connection on both sides. To develop definitive design guidelines for end connections with rigid cap plates, previous full-scale connection test results have been used to validate a finite element (FE) modelling approach, and a total of 496 FE models with different chord end distance-to-width (or diameter) (e/b0 or e/d0), branch-to-chord width (β), branch-to-chord thickness (τ), and chord slenderness (2γ) ratios have been modelled and analyzed. Existing SCF formulae in CIDECT Design Guide 8 are shown to be inaccurate if applied to cap plate-reinforced end connections. SCF correction factors (ψ), and parametric formulae to estimate ψ based on e/b0 (or e/d0), β, τ and 2γ, are derived.

An In-depth Analysis for Optimal Cable Tray Support Span

Nowadays, it is crucial to reduce the cost of the overall project so that the competitiveness of offshore oil and gas without compromising on quality or safety can be achieved. This study investigates how to define the longest cable tray support span considering constructability in order to reduce the number of supports which is a chief cost of a cable tray system. This study presents not only material and geometry frequently used for cable tray but also the formula to estimate the maximum cable load which can be installed within cable tray. To verify the longest span without increasing the crosssection of cable tray, finite element modelling approach was employed based on ANSYS and comparisons were made between numerical analysis and simplified hand calculation. The constructability for the longer span obtained from finite element analysis has been validated in view of manual handling of the cable tray. It is shown that the optimal span suggested in this paper can lead to a better economic benefit without degrading the constructability. For instance, as the span is longer, the cost of material as well as construction manpower can be saved. It is also expected that this approach will contribute to enhance the competitiveness of offshore oil and gas.

Femoral neck strain prediction during level walking using a combined musculoskeletal and finite element model approach.

Recently, coupled musculoskeletal-finite element modelling approaches have emerged as a way to investigate femoral neck loading during various daily activities. Combining personalised gait data with finite element models will not only allow us to study changes in motion/movement, but also their effects on critical internal structures, such as the femur. However, previous studies have been hampered by the small sample size and the lack of fully personalised data in order to construct the coupled model. Therefore, the aim of this study was to build a pipeline for a fully personalised multiscale (body-organ level) model to investigate the strain levels at the femoral neck during a normal gait cycle. Five postmenopausal women were included in this study. The CT and MRI scans of the lower limb, and gait data were collected for all participants. Muscle forces derived from the body level musculoskeletal models were used as boundary constraints on the finite element femur models. Principal strains were estimated at the femoral neck region during a full gait cycle. Considerable variation was found in the predicted peak strain among individuals with mean peak first principal strain of 0.24% ± 0.11% and mean third principal strain of -0.29% ± 0.24%. For four individuals, two overall peaks of the maximum strains were found to occur when both feet were in contact with the floor, while one individual had one peak at the toe-off phase. Both the joint contact forces and the muscular forces were found to substantially influence the loading at the femoral neck. A higher correlation was found between the predicted peak strains and the gluteus medius (R2 ranged between 0.95 and 0.99) than the hip joint contact forces (R2 ranged between 0.63 and 0.96). Therefore, the current findings suggest that personal variations are substantial, and hence it is important to consider multiple subjects before deriving general conclusions for a target population.

Assessment of Compression Driven Shock Tube Designs in Replicating Free-Field Blast Conditions for Traumatic Brain Injury Studies.

Compression driven shock tubes are indispensable in studies of blast-induced traumatic brain injury (bTBI). The ability of shock tubes in faithfully recreating free-field blast conditions is of enormous interest and has a direct impact on injury outcomes. Toward this end, the evolution of blast wave inside and outside of the compression driven shock tube has been studied using validated, finite element based shock tube models. Several shock tube configurations (uniform cross-section, transition, conical, suddenly expanded, and end plate) have been considered. The finite element modeling approach has been used to simulate the transient, dynamic response of blast wave propagation. The response is studied for longer durations (40-100 msec) compared with the existing literature. We demonstrate that locations inside and outside of the shock tube can generate free-field blast profile in some form, but with numerous caveats. Our results indicate that the locations inside the shock tube are affected by higher underpressure and corresponding kinetic energy yield compared with free-field blast. These effects can be minimized using optimized end plate configuration at the exit of the shock tube, yet this is accompanied by secondary loading that is not representative of the free-field blast. Blast wave profile can be tailored using transition, conical, and suddenly expanded sections. We observe oscillations in the blast wave profile for suddenly expanded configuration. Locations outside the shock tube are affected by jet-wind effects because of the sudden expansion, barring a narrow region at the exit. For the desired overpressure yield inferred in bTBI, obtaining positive phase durations of <1 msec inside the shock tube, which are sought for studies in rodents, is challenging. Overall, these results underscore that replicating free-field blast conditions using a shock tube involves tradeoffs that need to be weighed carefully and their effect on injury outcomes should be evaluated during laboratory bTBI investigations.

Optimization Study on Longitudinal Joints in Quasi-Rectangular Shield Tunnels

There are large bending moments in quasi-rectangular shield tunnels due to their deviation from the circular shape, and as for other types of shield tunnels, the longitudinal joints are the most critical parts in the lining structure. A new type of joint with ductile iron joint panels (DIJPs) was installed in quasi-rectangular tunnels to solve these problems. The distance from the bolts to the segment’s inner surface was improved for better performance under specific bending moment types. Both tests and finite element modeling (FEM) simulations were conducted to investigate the effect of the bolt position improvements. The resistances to crack appearance increased by 33.6% and 18.0% for positive and negative moment cases, respectively. The resistances to crack penetration increased by 13.8% and 18.4% for positive and negative cases. From the FEM approach, it was found that the behavior of the joint under the design bending moment range can be divided into three stages, whereby the bolts are only active from the second stage on. The effects of other optimizing methods, such as enhancement of concrete properties and increase of bolt diameters and numbers, are explored. Through comparison, it is believed that optimizing the joint section to increase the lever arm between bolts and the compression zone can improve the joint behavior most effectively. This optimization direction is recommended when designing a shield tunnel joint with DIJPs.

Nonlinear integrated dynamic analysis of drill strings under stick-slip vibration

Stick-slip torsional vibration raising from bit-formation contact is a catastrophic dynamic phenomenon occurring in deep-water oil and gas drilling systems. The torsional vibrations can result in premature fatigue failure of drilling equipment and reduce drilling efficiency. Thus, studying the dynamics of the system is a vital key to identify the roots of the vibration and establish appropriate mitigation and remediation methods. In this paper, an efficient approach for finite element (FE) modeling of stick-slip vibrations of the full drill strings was proposed. The model was developed based on a rate-dependent formulation of bit-rock interaction, in which the cutting process was integrated through the frictional contact. The nonlinear effects of the large rotations and the geometrically nonlinear axial-torsional coupling were taken into account. The effect of energy dissipation due to the presence of drill mud along the drill pipes and drill collars was incorporated through Rayleigh viscous damping. Modal analysis was conducted to determine the natural frequencies and the mode shapes of the drill string. Furthermore, a five degree-of-freedom lumped parameter model was developed. The performance of the developed models was verified through comparisons with example stick-slip results from a field test. The study showed that the self-excited torsional vibrations may also occur at fundamental frequencies lower than the first natural torsional frequency of the drill string, depending on operational parameters. The conducted research work resulted in a robust and practical integrated FE model to simulate the entire drill string system dynamics under torsional vibrations.

A Study on Fatigue Behaviors of Concrete under Uniaxial Compression: Testing, Analysis, and Simulation

Abstract The fatigue damage of concrete is an important reason for cracking and failure. To comprehensively study fatigue behaviors of concrete under uniaxial compression, cylindrical specimens with two different strength levels were made for cyclic loading tests. The evolution of fatigue process was detected via sensors, strain gages, and an X-ray computed tomography (CT) scanner. Parameters of fatigue life, deformation, internal cracks, and strength under different stress levels are analyzed based on measurements. The stress-cyclic number (S-N) equation is also given. Then, the fatigue damage parameter D is used to evaluate the status of damage. Additionally, a finite element modeling approach is developed based on the CT images to simulate the evolution of fatigue cracks within concrete specimens. With results of both macroscopic and microscopic analysis, the fatigue failure mechanism of concrete is expounded. The analysis results of this paper can provide a basis for the safety assessment for concrete structures.

Investigation of the biaxial flexural fracture of aluminosilicate glass by smeared fixed crack method

Ball-On-Ring (BOR) and Ring-On-Ring (ROR) tests are experimental methods used to characterize biaxial flexural strength of brittle materials. In this study, the quasi-static biaxial fracture behavior of aluminosilicate glass is investigated via BOR and ROR tests aided by a three-dimensional Digital Image Correlation (3D-DIC) technique. The in-plane strain field and out of plane deformation distribution during the loading process can be obtained by this special-designed test system. A finite element modeling approach incorporating smeared crack model is chosen to represent the discontinuous macrocrack brittle behavior of aluminosilicate glass. The simulations are conducted using the commercial software LS-DYNA with the implemented material model MAT280_GLASS. This numerical method is carefully assessed, and the capability of this model is evaluated by comparing the results of the numerical simulations with the corresponding experimental results.

3D finite element model of dynamic material behaviors for multilayer ultrasonic metal welding

Ultrasonic metal welding (UMW) has been widely applied as a high throughput solid-state joining technology for multilayers of sheet metal. During a typical UMW process, multilayer work materials are mechanically compressed by a knurl-patterned horn (also known as a sonotrode) onto an anvil tool, and a simultaneous in-plane sliding is applied to the horn at an ultrasonic frequency (20 kHz or higher) to help form the weld at the material interfaces. There is a great challenge in modeling and simulating the dynamic behavior of the work material and the whole weld formation process is subject to ultrasonic mechanical loadings imposed by the knurl-patterned horn tool. In this work, finite element (FE) models are developed to simulate the multilayer UMW process using knurl-patterned tools by directly applying the ultrasonic vibration as a model input. For a short weld duration of 0.1∼0.5 s, a high-fidelity FE modeling approach is developed using ABAQUS/Explicit to simulate the dynamic material response under the 20 kHz horn vibration. For an extended long welding duration of approximately 1.0 s, a computationally efficient hybrid approach is developed using both ABAQUS/Explicit and DEFORM-3D in order to leverage the strengths of each software package. The developed models are validated using experimental data of dynamic welding force, temperature, and weld geometry from in-situ process measurements of UMW. The 3D FE models developed in this study are the most comprehensive solution to date to simulate the complex material response subject to UMW process conditions and provide engineering guidance for the design of UMW applications.

A High-Precision Diagnosis Method for Damp Status of OIP Bushing

An accurate assessment of the damp status of oil-impregnated paper (OIP) bushings is crucial for the power industry to make informed decisions on the maintenance and replacement schedule of bushings. This article proposes a hybrid of the convolutional neural network (CNN) and the hidden Markov model (HMM) for estimating the damp status (i.e., moisture level and moisture source) of bushings especially when nonuniform moisture distribution exhibits in the bushing. First, simulation models of moisture diffusion and frequency-domain spectroscopy (FDS) of the OIP bushing were constructed using the finite element modeling (FEM) approach. Then, CNN was employed to extract informative features from FDS results of the OIP bushing, which is sensitive to both concentrations and sources of moisture. Finally, HMMs were further utilized as a strong stability tool to recognize the damp status of OIP bushings. The proposed method was implemented to identify the bushing damp status using both simulation data and real-life measurements. Identification results demonstrate that the proposed method has high accuracy in determining the moisture level and moisture source of the OIP bushing insulation.

Experimental and numerical study of mortise-tenon joints reinforced with innovative friction damper

A new friction damper is proposed for improving the cyclic response of mortise-tenon joints at multiple levels of seismic motion. In order to investigate the combined behavior of the proposed damper, quasi-static cyclic tests are conducted on five reinforced joints and one contrast joint made by Pinus sylvestris in strict accordance with the international test standard ISO-16670. Experimental results indicate that the smaller amount of tenon pullout, larger bearing capacity and initial stiffness, lower strength and stiffness degradation, and higher energy dissipation capacity simultaneously are exhibited in the reinforced joints. Increasing the friction coefficients of friction pads and the values of the clamping force helps to effectively improve the seismic performance of the mortise-tenon joints. The friction coefficient of 0.4 of the friction pads and the pre-tension strain of 0.03 in the bolt are considered as the optimal parameters to achieve the better reinforcement effect. High deformation capacities exist in the reinforced joints. A detailed finite element modeling approach is illustrated followed by the validation studies to obtain further insight into the mechanical behaviors of the reinforced connections described herein.

Modelling prediction on the degradation in mode II fracture energy of structural adhesive subjected to hygrothermal ageing

ABSTRACT In this work, the effect of hot-humid environment on the mode II fracture energy (G IIc) of the selected structural adhesive was experimentally evaluated through End-Notched Flexure (ENF) testing as well as corresponding finite element (FE) modelling approach. The ready-cured ENF samples were first immersed in distilled water and 5% NaCl solution under 50°C for different durations, and then removed from the hot-wet environment for mode II loading up to failure. Degradation was observed in the experimentally measured G IIc for adhesives immersed in both aqueous environments, while a further decrease was found in the samples immersed in distilled water, possibly due to the fact that more water was absorbed than saltwater immersion. A two-step FE modelling approach was developed to simulate the water absorption process under-elevated temperature (Step 1) and subsequent mode II loading test after hygrothermal ageing (Step 2) of ENF specimens. User subroutines were developed to accurately simulate the water ingress process in the adhesive layer and properly transfer the moisture distribution data between the two FE models. The feasibility of the established FE modelling was then successfully validated through comparison between the experimental and numerical results.