Simulation Results Of Finite Element Model Research Articles

The present-day in-situ stress field and its effect on shale gas development in Zigong area of southern Sichuan Basin

The Zigong area in southern Sichuan Basin is one of the key shale gas production areas in China, and the Longmaxi and Wufeng Formations within it are currently the key exploration and development layers. The present-day in-situ stress field has a significant impact on well trajectory deployment, horizontal well construction, hydraulic fracturing and other aspects. However, it has not been finely quantified in shale gas reservoirs of Zigong area, making it difficult to effectively guide development practice. Therefore, this study constructed a geomechanical model of the target layer in the Zigong area, quantitatively characterized the distribution of present-day in-situ stress, and explored its shale gas development effects. The results show that: (1) Based on the analysis of drilling induced fractures obtained from rock acoustic emission experiments and imaging logging interpretation, the dominant orientation of the maximum horizontal principal stress in the target layer is mainly NW-SE-trending; (2) The horizontal principal stress difference in the Layer S1l1-1−1 and Wufeng Formation is 5–30 MPa (the majority is 6–15 MPa) and 5–35 MPa (the majority is 6–18 MPa), respectively. Low stress difference values are mainly concentrated in the southeastern and northern parts. The overall prediction accuracy is high, with an error rate of less than 8% for the Layer S1l1-1−1 and less than 10% for the Wufeng Formation; (3) Based on rock acoustic emission experiments and finite element model simulation results, the study area is mainly under strike-slip stress faulting mechanism; (4) Due to the influence of the strike-slip faulting stress mechanism, when deploying horizontal wells in the area, priority should be given to selecting areas with low stress mechanism factor (Aφ) and low stress differences, to achieve better fracturing and transformation effects and reduce the risk of casing deformation and wellbore instability.

Variation in the nonlinear stiffness of bolted joints due to tangential hysteresis behavior

Obtaining the stiffness variation characteristics of a bolted joint during service is essential for predicting the response of an entire structure. In this study, we propose a relationship between the macro deviation, microtopography of the bearing surface, and hysteretic characteristics of a bolted joint. We first analyze the stiffness variation caused by the hysteretic characteristics during the tightening and service processes. Next, we investigate the influence of non-parallel bearing surfaces and displacement loads on pressure distribution and stiffness, both at macro and micro scales, using Finite Element Modeling (FEM) and experiments. Finally, we compare data from a hysteresis behavior test of a single-bolt lap beam with the FEM simulation results. The comparison demonstrates that macro deviations in the bearing surface alter the preload after assembly, while the bearing surface experiences dynamic changes in pressure due to microtopography and cyclic displacement loads. Consequently, this leads to irregular dynamic changes in joint stiffness during the service process, significantly affecting the dynamic/static response of the bolted assembly structure.

Electromechanical Impedance Instrumented Wearable Piezoelectric Ring-Type Sensor for Bolted Connection Monitoring

Due to the loss of preload, structural failure caused by bolt loosening is common in engineering structures. Effective monitoring of bolted connections is of great importance in providing early warning to the structural maintenance department. In this study, a novel and reusable electromechanical impedance (EMI) instrumented wearable piezoelectric ring (WPR) was proposed to detect bolted connection loosening. In the experimental investigation, the EMI spectra of three identical WPRs during the bolt-loosening process were acquired and analyzed. It was concluded that bolt looseness changes can be qualitatively and quantitatively characterized by conductance spectra. Specifically, the resonance frequency and amplitude at certain frequencies were reduced correspondingly as bolts loosen. This was further validated by finite element model simulation results. Moreover, two statistical metrics including mean absolute percentage deviation (MAPD) and root mean square deviation (RMSD) were adopted to evaluate different degrees of bolted connections quantitatively. Both metrics showed an increasing tendency during the bolt loosening process in three different frequency bands. It was found that both metrics demonstrated a significant linear correlation with bolt torque variations. Both of them serve as reliable indicators to detect loose bolts in the bolted connection. The present work verifies the feasibility and applicability of using EMI-instrumented WPR to monitor bolted connections.

A Thermal Twin Modeling Method of Press Pack IGBT Based on Power Loss

The thermal modeling of a press pack insulated gate bipolar transistor (PP-IGBT) is crucial for device reliability estimation and operation management. However, the traditional finite element model (FEM) cannot simulate the temperature of a PP-IGBT device in real time, resulting in lifetime evaluation delays and errors. Therefore, this article proposes a thermal twin (TT) modeling method of a PP-IGBT based on power loss. First, common PP-IGBT TT modeling based on the reduced-order model (ROM) technology is introduced, and an optimized PP-IGBT TT modeling method based on power loss is proposed and compared with the common TT modeling method. Second, the electro-thermal coupling PP-IGBT FEM is determined, and the optimized PP-IGBT TT and a digital interface based on FEM simulation results are established and analyzed. Finally, the digital twin (DT) interaction system of the PP-IGBT is established, and the accuracy of the proposed TT model is verified via infrared experiments. The results reveal that the proposed PP-IGBT TT realizes the real-time and comprehensive mapping of the device temperature, and has great applicability potential in temperature monitoring and reliability evaluation.

Surrogate modeling of parametrized finite element simulations with varying mesh topology using recurrent neural networks

A machine learning based strategy is proposed for creating parametric surrogate models from parametrized finite element model simulation results. In the first major step, a unified nodal data structure is created from the topologically inhomogeneous set of finite element simulations. This is achieved by utilizing re-sampling and the coherent point drift method for node registration of the different designs. In the second major step, a parametric surrogate model is trained for predicting the initial coordinates using a fully-connected feed-forward neural network. Two different recurrent neural network modeling approaches are presented and compared for the prediction of various field quantities with different degrees of complexity and non-linearity. For the first proposed modeling approach, a node-by-node prediction is applied, where the time series of each structural node is predicted independently via a compact long-short term memory (LSTM) model. For each node, the initial coordinates of the node are used as additional input features. For the second modeling approach, an all-at-once prediction is applied, where the time series of all structural nodes are predicted at once by training an LSTM model on a reduced output space obtained by principal component analysis (PCA). Output fields exhibiting moderate non-linearity could be well predicted by both approaches, but only the node-by-node approach allowed an accurate generalized representation of a strongly non-linear and narrow field quantity representing the observed crack patterns within the finite element structure. The existence of a new yet unobserved crack pattern could be identified by the node-by-node approach and confirmed by subsequently running the corresponding FE simulation.

A thermo – Mechanical modelling approach on the residual stress prediction of SLM processed HPNGV aeroengine part

In the present study, selective laser melting (SLM) is used to fabricate the Inconel 718 high-pressure nozzle guide vane (HPNGV), an aero-engine part. Inconel 718 is widely used in aero-engine components due to its inherent characteristics at elevated temperature. The aim of the study is to investigate the residual stresses developed on the HPNGV part with and after removal of the base plate in the SLM process. The residual stresses were determined experimentally using X-ray diffraction technique. The maximum residual stress at location 4 was found around 700 MPa and A thermo-mechanical finite element model (FEM) was developed for SLM processed Inconel HPNGV using ANSYS software. SLM processed HPNGV part exhibited a higher magnitude of residual stresses after base plate removal. It is found that there is an increase of residual stress (about 16%) at location 4 and an increase of residual stress (about 27%) at location 2 after removal of base plate from the component. The experimental results of the samples were comparable with FEM simulation results.

Experimental and theoretical investigation on flexure performance of pultruded GFRP composite beams with damage analyses

Fiber reinforced polymer (FRP) composite materials produced by pultrusion technique attract the attention of researchers due to their superior properties. Limited studies are available in the literature where experimental and theoretical investigations on the FRP composites are carried out together. In this study, the flexure performances of pultruded glass FRP (P-GFRP) composite beams were investigated experimentally and theoretically. Theoretical approaches for flexural analysis of P-GFRP composite beams were developed with the help of variational methods. Kinematic relations of composite beams were defined based on high order shear deformation beam theory. Effective material properties of composite beams were obtained by using mixture rule model. The differential field equations were transformed to functional with Gâteaux differential method. The element matrix with a total of 10 degrees of freedom was obtained by using the mixed finite element method (MFEM). Moreover, classical finite element modeling (FEM) was performed with the help of ABAQUS program. Various beam specimens with different fiber orientations were extracted from the P-GFRP box profile. Tensile and burnout tests were performed to determine the mechanical properties of the obtained P-GFRP composite beam specimens. Three-point bending test was utilized to investigate flexure performance. Kinetic, macro and micro mechanical damage analyzes were performed to better understand the behavior of the P-GFRP composite beams. Experimental results, theoretical solution results and FEM simulation results were compared and numerical values ​​were found to be very close to each other.

Investigation of failure during rubber pad forming of metallic bipolar plates

Abstract In this study, the forming of metallic bipolar plates micro-channel was investigated. Rubber pad forming process was employed to fabricate the parallel micro-channels. According to the experimental observation, the onset of failure was the main limiting factor during the deformation of micro-channels. Therefore, the fracture behavior was studied during rubber forming processes. Experimental analysis with the finite element model (FEM) simulation was adopted to investigate the fracture mechanism. Three different fracture criteria were used to predict the fracture. Critical damage values were determined through conducting the uniaxial tension test. The fracture surface was constructed using ductile fracture criteria, and the most accurate fracture prediction was obtained via normalized Cockroft-Latham fracture criterion (9.14% fracture prediction error). The effect of process parameters on stress triaxiality and normalized Lode angle parameter was analyzed by FEM simulation results. According to the results, process parameter variation did not significantly affect the stress state. Thus, the normalized Cockroft-Latham fracture criterion was employed to investigate the onset of fracture in different forming conditions and the effect of process parameters on damage evolution. Based on the findings, draft angle, corner radius, and the ratio of w/h should be set to 15°, 0.2 mm, and 1.6 in order to achieve 100% filling percentage.

Finite element analysis for engine crankshaft torsional stiffness

Accurate crankshaft torsional stiffness is important to build the lumped parameter model (LPM) for crankshaft torsional vibration analysis. For the crankshaft system of a four-cylinder in-line gasoline engine, a procedure to build the finite element model (FEM) is presented. And the applicability of two ways to set the equivalent mass or equivalent moment of inertia for piston-rod in FEM is declared. When building a lumped parameter model, the concept of rigid-rotation of the crank pin central section around the central line of the crankshaft is proposed, and a method to obtain the torsional angle of the central section is declared. What is more, three post-processing methods are presented to obtain the torsional stiffness coefficients. According to three load cases of no-load, half load and full load, the tests are carried out. The simulation results of FEM and LPM, and the test results have good agreement with each other.

Finite element analysis for engine crankshaft torsional stiffness

Accurate crankshaft torsional stiffness is important to build the lumped parameter model (LPM) for crankshaft torsional vibration analysis. For the crankshaft system of a four-cylinder in-line gasoline engine, a procedure to build the finite element model (FEM) is presented. And the applicability of two ways to set the equivalent mass or equivalent moment of inertia for piston-rod in FEM is declared. When building a lumped parameter model, the concept of rigid-rotation of the crank pin central section around the central line of the crankshaft is proposed, and a method to obtain the torsional angle of the central section is declared. What is more, three post-processing methods are presented to obtain the torsional stiffness coefficients. According to three load cases of no-load, half load and full load, the tests are carried out. The simulation results of FEM and LPM, and the test results have good agreement with each other.

Reduction thermal damage to cortical bone using ultrasonically-assisted drilling.

Thermal damage induced by bone drilling is a common problem during surgical procedures. A recent and promising method utilizes high-frequency low-amplitude vibration in the feed direction during drilling and has the potential to reduce drilling temperature, minimizing the risk of thermal damage. The purpose of this study was to investigate the effects of ultrasonically-assisted drilling (UAD) on cortical bone temperature. A series of experiments was conducted to compare the cortical bone temperature during UAD with that during conventional drilling (CD). A thermo-mechanical 3D finite element model (FEM) of UAD was developed, using ABAQUS, to help understand temperature changes during drilling of cortical bone. The numerical simulation results of FEM showed good agreement with the experimental data. Subsequently, a predictive model was developed for bone temperature during drilling, using multiple regression analysis based on the results from numerical simulation. The results showed drill diameter had the greatest influence on drilling temperature, followed by the rotational speed of the drill. Additionally, the variation of vibration frequency had more influence on the drilling temperature than did the amplitude. Ultrasonically-assisted drilling is helpful to lower drilling temperature to reduce the thermal damage of bone tissue.

Interacted buckling failure of thin-walled irregular-shaped aluminum alloy column under axial compression

Interacted buckling behaviors and ultimate strength of thin-walled aluminum alloy columns with irregular-shaped cross section were studied using a verified Finite Element Model (FEM). Six interacted buckling failure modes were studied, which were: (1) the interaction of Local bucking and sectional Yielding (LY); (2) the interaction of Local and Global buckling (LG); (3) the interaction of Distortional buckling and sectional Yielding (DY); (4) the interaction of Distortional and Global buckling (DG); (5) the interaction of Local bucking, Distortional bucking and sectional Yielding (LDY or DLY); and (6) the interaction of Local, Distortional and Global buckling (LDG). The load-axial displacement curve, the deflection-axial displacement curve, the development of the axial stress at different positions in the section at mid-span, the out-of-plane displacement at failure along the column length and the axial stress distribution at failure across the section at mid-span were presented. The local buckling and distortional buckling were detected by the turning points on the load-axial displacement curves. The out-of-plane displacement along the column length at failure was used to illustrate the failure mode of the column. Ultimate strengths and failure modes of 174 columns failed by interacted buckling failure modes were investigated by both FEM and current design approaches. For the ultimate strength of the columns under DY failure mode, the results predicted by North American specification for the design of cold-formed steel structural members of American Iron and Steel Institute (AISI) were higher than FEM simulation results. The ultimate strength predicted by American Aluminum Design Manual (AA), Direct Strength Method (DSM), European Code (EN1999) and Chinese Design Specification for Aluminum Alloy Structures (GB50429) were lower than FEM simulation results, no matter what kind of failure modes the column encountered. Mean values of PAA/PFEA, PEC9/PFEA and PGB/PFEA were 0.81, 0.79 and 0.74. DSM could precisely predict the Global buckling (G), LG and DY failure modes. However, for the columns failed by LY, DG, LDY and LDG, they were LG, G, DY and LG when predicted by DSM, respectively. The applicability of DSM to thin-walled aluminum alloy columns with irregular-shaped cross section should be investigated further.

Studies on wears of ultrafine-grained ceramic tool and common ceramic tool during hard turning using Archard wear model

Hardened steels are difficult to be machined due to their high tensile strength and work-hardening rate, low thermal conductivity, and abrasive behavior. In this paper, finite element modeling (FEM) approaches with lagrangian increment method for 3D metal turning of hardened steel H13 by common ceramic tool and ultrafine-grained tool respectively have been investigated by simulation of DEFORM-3D software and turning test. Conditions of initial and boundary and turning process parameters have been chosen. Material properties of H13 and ceramic have been described in details. Johnson–Cook model of H13 model has been applied to the hard turning modeling. Archard wear model has been built, and the correlation coefficients were decided by reciprocating friction experiments. The simulation results showed that predicted primary turning force and maximum temperature in common ceramic are bigger than which was caused by ultrafine-grained ceramic tool for the ultrafine-grained ceramic tools have better thermal stability and bigger hardness. The wear depths of common ceramic tool are about many times than that of ultrafine-grained ceramic tool according to the simulation and experimental results. And their wear patterns are very different. The FEM simulation results have entirely explicated experimental results. The obtained results would provide the fundamental and practical guidelines of tool material choice for hard turning.

Significant Improvement in Mechanical Performance for Grid-Stiffened Polymer Composites

This work studies the static mechanical properties of grid stiffened polymer composites. This developed composite is expected to have an ultra-higher mechanical performance than traditional composite structures. Static mechanical measurements show that the combination of gridding reinforcement and epoxy polymer (Diglycidyl 4,5-epoxy cyclohexane-1,2-dicarboxylate) helps the advanced composite to possess extremely high mechanical properties, such as resistive properties in axial pressure (more than 160% improvement) and external pressure (more than 102% improvement) for comparison. Subsequently, the effects of wetting angle of reinforcement, quantity of gridding reinforcement, and type of grid on the mechanical properties of the advanced polymer composites have been studied and analyzed. Finally, the finite element model (FEM) method is employed to substantiate these experimental results. The FEM simulation results are in such great agreement with the experimental results that the standard deviations between them are strictly limited to 15%. Furthermore, it demonstrates that the FEM technology is an effective approach for predicting and optimizing structure design, as well as the mechanical behaviors.

Dynamic Analysis and Experiment of Beamlike Space Deployable Lattice Truss

The dynamic equivalent continuum model of beamlike space deployable lattice truss which is repetition of the basic truss bay is established based on the energy equivalence. The finite element model of the lattice truss is also developed. Free vibration frequencies and mode shapes are calculated and simulated based on equivalent continuum model and discrete finite element model. The analytical solutions calculated by equivalent continuum model match well with the finite element model simulation results. A prototype of deployable lattice truss consist of 20 truss bays is manufactured. The dynamic response of lattice truss with different truss bays are tested by dynamic vibration experiment, and natural frequencies of lattice truss with different length are obtained from acceleration response curves. The experiment results are compared with simulation results which verifies that the correctness of finite element model, which also validate the effectiveness of equivalent continuum model indirectly.

Development of Micromechanics Models and Innovative Sensor Technologies to Evaluate Internal Frost Damage of Concrete

Internal frost damage is a major problem affecting the durability of concrete in cold regions. Micromechanics models and innovative sensor technologies were used to study the mechanisms of frost damage in concrete. Crystallization pressure resulting from ice nucleation within capillary pores is the primary cause of internal frost damage of concrete. Crystallization pressure of a cylinder pore was formulated with interface energy balance with thermodynamics analysis. Crystallization pressure on the pore wall was input for fracture simulation with the extended finite element model on a homogeneous beam sample with a vertical cylinder pore; this simulation led to a straight line. An image sample was obtained with imaging process and ellipse fitting techniques to capture microstructure of a tested specimen. Crack simulation of this image sample with the same cylinder pore under crystallization pressure matched fracture patterns of the single-edge-notched bending specimen. Extended finite element model simulation results were verified by open-mode fracture behavior in middle-notched single-edge-notched bending and freezing tests. An innovative time-domain reflectometry sensor was developed to nondestructively monitor the freezing process. Data show that sensor signals from time-domain reflectometry can detect the freezing degree, an important input parameter. Studies indicate that the micromechanics models and time-domain reflectometry sensor techniques can help practitioners evaluate internal frost damage of concrete. Future work will incorporate sensor measurements into micromechanics models to predict, in real time, internal frost damage process in concrete specimens. The goal of this study was to provide practical nondestructive testing and computational tools for designing concrete that is resistant to freezing damage.

Effects of Temperature on Laser Shock Induced Plastic Deformation: The Case of Copper

Laser shock induced plastic deformation has been used widely, such as laser shock peening (LSP), laser dynamic forming (LDF), and laser peen forming. These processes have been extensively studied both numerically and experimentally at room temperature. Recently, it is found that at elevated temperature, laser shock induced plastic deformation can generate better formability in LDF and enhanced mechanical properties in LSP. For example, warm laser shock peening leads to improved residual stress stability and better fatigue performance in aluminum alloys. There is a need to investigate the effects of elevated temperature on deformation behavior of metallic materials during shock induced high strain rate deformation. In this study, LSP of copper are selected to systematically study the effects of elevated temperature in shock induced high strain rate deformation. Finite element modeling (FEM) is used to predict the deformation behavior. The FEM simulation results of surface profile and residual stress distribution after LSP are validated by experimental results. The validated FEM simulation is used to study the effects of temperature on the plastic deformation behaviors during LSP, such as plastic affected zone, stress/strain distribution, and energy absorption.

Design and Development of Fine Pitch Copper/Low-K Wafer Level Package

Copper (Cu)/low-dielectric constant (K) structures are desired choices for advanced integrated circuits (ICs) as the IC technology moving towards fine pitch, high speed, increased integration and high performance. Copper interconnects with low-k dielectric material improve the performance of ICs by reducing interconnect the RC delay, the cross talk between the adjacent metal lines and the power loss. However, the packaging of Cu/low-k IC device is a challenge for the packaging industry to integrate these devices without any failure during assembly and reliability. The current work presents, 1) the finite element model (FEM) based parametric study on Cu/low-K wafer level package (WLP) reliability and stresses on Cu/low-K layers, and 2) experimental validation of WLP reliability by fabricating the test chips. FEM modeling and simulation results have shown that high aspect ratio interconnects, thinner die, and thinner printed circuit board can reduce the stress in low-k layer and enhance the board level interconnect reliability. Test chip of 7 mm ? 7 mm size is designed with 128 input/output (I/O) off-chip interconnects at 300-?m pitch in two depopulated rows using redistribution layers (RDL). Test chips are fabricated on 200-mm-diameter wafer with blanket black diamond (BD) low-K layers structure. Two different Pb free solder interconnects, thick copper column of 100 ?m height with SnAg solder cap and SnAg solder bump of 150 ?m height with 5-?m-thick copper under bump metallurgy (UBM), are fabricated. The Cu/low-K test chips are assembled onto a two layer high glass transition temperature (Tg) FR-4 substrate using two different types of no-flow underfills (NFU) to build the test vehicles and assembled test vehicles are subjected to various JEDEC standard reliability tests, and related failure analysis is carried out. Cu/low-k WLP with copper column interconnects without no-flow underfill passed 1000 h high-temperature storage (HTS) test, and passed the JEDEC drop test with no-flow underfill. Thin die test vehicles of Cu column interconnects with no-flow underfill and extra solder shown better thermal cycling (TC) performance and the board level TC performance can be improved further using thicker RDL.

Topology Optimized Design, Microfabrication and Characterization of Electro-Thermally Driven Microgripper

This article presents a systematic and logical study of the topology optimized design, microfabrication, and static/dynamic performance characterization of an electro-thermo-mechanical microgripper. The microgripper is designed using a topology optimization algorithm based on a spatial filtering technique and considering different penalization coefficients for different material properties during the optimization cycle. The microgripper design has a symmetric monolithic 2D structure which consists of a complex combination of rigid links integrating both the actuating and gripping mechanisms. The numerical simulation is performed by studying the effects of convective heat transfer, thermal boundary conditions at the fixed anchors, and microgripper performance considering temperature-dependent and independent material properties. The microgripper is fabricated from a 25 μm thick nickel foil using laser microfabrication technology and its static/dynamic performance is experimentally evaluated. The static and dynamic electro-mechanical characteristics are analyzed as step response functions with respect to tweezing/actuating displacements, applied current/power, and actual electric resistance. A microgripper prototype having overall dimensions of 1 mm (L) × 2.5mm (W) is able to deliver the maximum tweezing and actuating displacements of 25.5 μm and 33.2 μm along X and Y axes, respectively, under an applied power of 2.32 W. Experimental performance is compared with finite element modeling simulation results.