Finite Element Analysis Predictions Research Articles

Local web buckling of double-coped steel beam connections

This paper presents a comprehensive study on local web buckling behaviour of double-coped steel beam connections, cases which are common when beams of similar heights are joined. The study commenced with a series of full-scale tests on 11 specimens, covering a spectrum of cope lengths and cope depths. Local web buckling was observed as the main failure mode for most specimens. The ultimate load was found to decrease with increasing coped length and cope depth, and in addition, an increase of the rotational stiffness of the beam end connection could benefit the local web buckling capacity. A numerical study was subsequently performed enabling further interpretation of the test results. Good agreements were observed between the test results and finite element analysis predictions, and the stress conditions within the coped web panel at different loading stages were fully revealed. The numerical study also showed that the ultimate loads of some models were not sensitive to initial imperfection amplitudes, especially when the cope length was large (i.e. 450mm or longer). It was believed that the imperfection insensitivity characteristic was due to the presence of post-buckling mechanism. Summarising the available test data, including the current test results and those previously reported by other researchers, design comments were made through comparisons against the existing design method. Conservative test-to-predicted ratios were generally shown, but unsafe predictions were obtained for some cases. A modification to the existing design approach was finally proposed for safer design of such connections.

Mechanics of Interfacial Bonding in Dissimilar Soft Transient Materials and Electronics

ABSTRACTSoft transient electronics of polymeric substrates and silver-ink electronics are studied for correlated mechanical-electrical properties. Experimental and predictive finite element analysis are used to understand, explain and predict delamination, cracking, buckling, and failure of printed conductive components of such systems. An active transient polymer system consisting of poly(vinyl alcohol) and sodium bicarbonate is introduced that results in byproducts (alkaline and bubbles) when undergoing transiency. These byproducts are facilitated to control and expedite transiency of the electronic components based on redispersion of metallic nano/micro materials. Complete mechanical and electrical characterization of such systems is reported.

Magnetic Saturation in Semi-Analytical Harmonic Modeling for Electric Machine Analysis

A semi-analytical method based on the harmonic modeling (HM) technique is presented for the analysis of the magneto-static field distribution in the slotted structure of rotating electric machines. In contrast to the existing literature, the proposed model does not require the assumption of infinite tooth permeability, material property homogenization, or a hybrid modeling approach. In fact, the permeability variation in the slotted machine parts is embedded directly into the magnetostatic field solution. Currently, only linear soft-magnetic materials with finite permeability are considered. However, non-linear materials could be considered iteratively, and therefore the proposed model presents a first step toward including the magnetic saturation effects into HM. To validate the presented method, semi-analytical models are implemented for two benchmark topologies with slotted rotors. Magnetic field calculations are performed for two different values of linear rotor tooth permeability and compared to finite-element analysis predictions. The results show that a very good agreement is obtained.

Design and Fabrication of a Skew-Typed Longitudinal-Torsional Composite Ultrasonic Vibrator for Titanium Wire Drawing

In this paper, a new longitudinal-torsional (L&T) hybrid vibrator driven by two longitudinal ultrasonic transducers is proposed for ultrasonic-assisted wire drawing. The two identical transducers were vertically installed on the two side surfaces of a transformer, however, with an offset distance (Δx) and stagger angle (α) between their axes. Therefore, the transformer could synthesize and amplify the vibration of the two transducers to produce an L&T composite vibration. Harmonic and transient simulations were performed in ANSYS to investigate the dynamic characteristics and frequency-dependent sensitivity of the vibrator. Δx and α between the transducers were subsequently optimized to maximize the output amplitude. Based on the finite element analysis (FEA) results, a prototype was manufactured with an electrical circuit developed for impedance matching. The vibrator generates an L&T composite vibration with a measured longitudinal amplitude of about 20 μm when driven by a voltage of 400 Vp-p, 19.597 kHz. The result is consistent with the FEA prediction, which indicates a new method of combining two different forms of ultrasonic vibration.

On-Line Monitoring of Environment-Assisted Cracking in Nuclear Piping Using Array Probe Direct Current Potential Drop

A direct current potential drop method utilizing array probes with measurement ends maintaining an equalized potential designated as equi-potential switching array probe direct current potential drop (ESAP-DCPD) technique has been developed earlier at Seoul National University. This paper validates ESAP-DCPD technique by showing consistency among experimental measurements, analytical solution and numerical predictions using finite element analysis (FEA) of electric field changes with crack growth in metals. In order to examine its viability as an on-line monitoring of environment assisted crack growth at the inner surface of piping welds, artificial inner surface cracks were introduced in a full-scale weldment mockup pipe and stainless steel metal mockup pipe. The weldment was joined by low alloy steel and stainless steel pipes. The pipes were monitored by using ESAP-DCPD in laboratory environments. Optimization of electrical wiring configuration has produced results with significantly reduced noise for adequately long period of time. Then optimized experimental results were compared with the FEA prediction results for the mockup to show a good agreement. Also a round-robin measurement has been made at three laboratories. It has been found that the developed ESAP-DCPD can detect circumferential cracks with a depth of 40 % of wall thickness in stainless steel with a good detectability for further growth behaviors. For axial cracks, however, the measurements showed poor detectability. Hence the developed ESAP-DCPD system can be used to monitor large circumferential cracks that existing non-destructive examination techniques often fail to detect until leakage takes place.

FINITE ELEMENT MODEL FOR PREDICTING RESIDUAL STRESSES IN SHIELDED MANUAL METAL ARC WELDING OF MILD STEEL PLATES

This paper investigates the prediction of residual stresses developed in shielded manual metal arc welding of mild steel plates through Finite Element Model simulation and experiments. The existence of residual stresses that cause fatigue and distortion in welded structures has been responsible for failure of machine parts in service. These stresses if not properly controlled can lead to loss of lives and property. The highlight is that various trial and error welding runs have to be carried out while hoping for the best performance during operation. This is wasteful of time, material and finance. Thus the need to incorporate Finite Element Analysis prediction of residual stresses by computational methods to first determine satisfactory welding conditions before actual production. The geometry of the butt welded Low Carbon (ASTM A36) steel plates was modeled and the residual stresses simulated using ANSYS Multiphysics V14. Three experimental samples of similar geometry were also produced using the shielded manual metal arc welding process to verify the result. Low carbon steel (ASTM A36) was used as the parent metal, E066 electrodes were used to complete the weld. The generated residual stresses were measured using an X-Ray Diffractometer (XRD 6000). From the Finite Element Model Simulation, the transverse residual stress in the x-direction (σ x ) had a maximum value of 375MPa (tensile) and minimum value of -183MPa (compressive) while in the y-direction (σ y ), the maximum value of 172MPa (tensile) and minimum value of zero. The longitudinal stress in the x-direction (σ x ) indicated a maximum value of 355MPa (tensile) and a minimum value of -10MPa (compressive) while in the y-direction (σ y ), the maximum value was 167MPa and the minimum value of the residual stress was -375MPa. The experimental values as measured by the X-Ray diffractometer were of reasonable correlation as transverse residual stress (σ x ) along the weld line in the transverse x-direction varied from 353MPa (tensile) to -209MPa (compressive) while in the y-direction, stress (σ y ) along the weld line varied from 177MPa (tensile) to zero. The longitudinal stress measured by the X-Ray diffractometer in the x-direction (σ x ) varied from 339MPa (tensile) to zero (compressive) while in the y-direction (σ y ) varied from 171MPa (tensile) to -366MPa (compressive). These results shows that the residual stresses obtained by prediction from the finite element method are in fair agreement with the experimental results. Based on this, it can be concluded that Finite Element Model can be used to replicate and determine the expected residual stresses that would be generated before an actual welding process is carried out. http://dx.doi.org/10.4314/njt.v35i1.14

Out-of-Plane Translational PZT Bimorph Actuator with Archimedes’ Spiral Actuating Tethers

The design, finite element analysis (FEA), and experimental characterization of a MEMS out-of-plane (vertical) translational lead-zirconate-titanate (PZT) bimorph actuator supported on Archimedes’ spiral tethers are presented. Two types of bimorph actuators with different electrode patterns (with spiral tethers half actuated or fully actuated) are designed and fabricated. Both designs are fabricated by commercial processes and are compatible with integration into more complex MEMS systems. Finite element analysis (FEA) was used to analyze and predict the displacements of both types of actuators. The deflections of both fully- actuated and half-actuated devices were measured experimentally to validate the design. At an applied voltage of 110V, the out-of-plane deflections of the actuators with half-actuated and fully-actuated tethers were measured at about 17 μm and 29 μm respectively, in good agreement with FEA predictions of 17.1 μm and 25.8 μm. The corresponding blocking forces are predicted as 10 mN and 17 mN by FEA.

A Cohesive Zone Model to Predict Dynamic Tearing of Rubber

ABSTRACT Tire failures, such as tread separation and sidewall zipper fracture, occur when internal flaws (cracks) nucleate and grow to a critical size as result of fatigue or cyclic loading. Sudden and catastrophic rupture takes place at this critical crack size because the strain energy release rate exceeds the tear energy of the rubber in the tire. The above-mentioned tire failures can lead to loss of vehicle stability and control, and it is important to develop predictive models and computational tools that address this problem. The objective of this article was to develop a cohesive zone model for rubber to numerically predict crack growth in a rubber component under dynamic tearing. The cohesive zone model for rubber was embedded into the material constitutive equation via a user-defined material subroutine (VUMAT) of ABAQUS. It consisted of three parts: (1) hyperviscoelastic behavior before damage, (2) damage initiation based on the critical strain energy density, and (3) hyperviscoelastic behavior after damage initiation. Crack growth in the tensile strip and pure shear specimens was simulated in ABAQUS Explicit, and good agreement was reported between finite element analysis predictions and test results.

EFFECT OF RELATIVE DENSITY AND VELOCITY TOWARDS DYNAMIC RESPONSE OF METAL FOAM

Dynamic response of ALPORAS aluminium foam has been investigated experimentally and numerically. The dynamic response is quantified by the force produced as the foam deforms as a function of time. Quasi-static tests are conducted to determine the quasi-static properties of the foam. In the impact test, the aluminium foams are fired towards a rigid load-cell and the force signals developed are recorded. Experimental dynamic stress is also compared with theoretical prediction using existing theory. Finite element model is constructed using LS-DYNA to simulate the impact test. Results from the experiment, finite element analysis and theoretical prediction are in acceptable agreement. Finally, parametric studies have been conducted using the verified model to investigate the effect of impact velocity and relative density towards the dynamic response of the foam projectile. It is found that the dynamic response of the foam is more sensitive towards impact velocity as compare with the foam relative density.

Investigation of an Improved Hybrid-Excitation Flux-Switching Brushless Machine for HEV/EV Applications

In this paper, based on 2-D finite-element analysis (FEA), the hybrid-excitation principle of a hybrid-excitation flux-switching (HEFS) machine is analyzed, and consequently, an improved topology is proposed to enhance the flux-regulation capability. These two machines are termed as the basic HEFS machine and the improved HEFS machine, respectively. In the basic HEFS machine, each permanent magnet (PM) is located at the middle of the corresponding slot and wound by a field winding coil. When field excitation is applied, it is found that the currents in the two field slots adjoining each PM exhibit reversal excitation functions, thus reversal flux-regulation functions. Hence, to improve the flux-regulation performances, an improved HEFS topology is proposed based on the basic one by reversing current direction in one of the field slots. Therefore, the improved topology shares identical structure with the basic one but has different field current directions in some field slots and thus different field winding accommodations. Comparisons of the FEA predictions indicated that both armature no-load flux-regulation capability and armature load torque capability in the improved HEFS machine are much better than those in the basic one. Finally, the FEA results are validated by experimental measurements on two prototyped HEFS machines.

A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle. The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds. The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.

Experimental and finite element analysis for prediction of kidney injury under blunt impact

Kidneys are third most injured organs in abdominal trauma after liver and spleen; this study therefore is an attempt to understand the behaviour of kidneys under blunt trauma. Dynamic impact tests were performed on 20 fresh porcine kidneys to study the injury propagation in the organ, and the acceleration of the impactor was measured. A kidney model was developed with structural details like capsule and cortex. The kidney cortex was modelled with solid hexahedral elements and the capsule was modelled with quadratic shell elements. The material models for the capsule and cortex were used from the experimental data reported in our previous study. The developed model was calibrated using previous and current experimental results to reproduce the injuries of the organ in terms of acceleration of the impactor, and the injuries sustained by the organ during the experiments. The developed kidney model is observed to be robust and can be integrated with the available human body finite element models to simulate accidents and to predict or simulate injuries.

A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle.The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds. The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.

Results of high heat flux testing of W/CuCrZr multilayer composites with percolating microstructure for plasma-facing components

Reliable joining of tungsten to copper is a major issue in the design of water-cooled divertor components for future fusion reactors. One of the suggested advanced engineering solutions is to use functionally graded composite interlayers. Recently, the authors have developed a novel processing route for fabricating multi-layer graded W/CuCrZr composites. Previous characterization confirmed that the composite materials possess enhanced strength compared to the matrix alloy and shows reasonable ductility up to 300°C indicating large potential to extend the operation temperature limit. Furthermore, a three-layer composite system (W volume fraction: 70/50/30%) was developed as a graded interlayer between the W armour and CuCrZr heat sink.In this study, we investigated the structural performance of the graded joint. Three water-cooled mock-ups of a flat tile type component were fabricated using electron beam welding and thermally loaded at the hydrogen neutral beam test facility GLADIS. Cycling tests at 10MW/m2 and screening tests up to 20MW/m2 were successfully performed and confirmed the expected thermal performance of the compound. The measured temperature values were in good agreement with the prediction of finite element analysis. Microscopic investigation confirmed the structural integrity of the newly developed functionally graded composite after these tests.

Electrode size and boundary condition independent measurement of the effective piezoelectric coefficient of thin films

The determination of the piezoelectric coefficient of thin films using interferometry is hindered by bending contributions. Using finite element analysis (FEA) simulations, we show that the Lefki and Dormans approximations using either single or double-beam measurements cannot be used with finite top electrode sizes. We introduce a novel method for characterising piezoelectric thin films which uses a differential measurement over the discontinuity at the electrode edge as an internal reference, thereby eliminating bending contributions. This step height is shown to be electrode size and boundary condition independent. An analytical expression is derived which gives good agreement with FEA predictions of the step height.

Anisotropic Constitutive Model for Predictive Analysis of Composite Laminates

An anisotropic plastic constitutive model for fiber-reinforced composite material, is developed, which is simple and efficient to be implemented into computer program for a predictive analysis procedure of composite laminates. An anisotropic initial yield criterion, as well as work-hardening model and subsequent yield surface are established that includes the effects of different yield strengths in each material direction, and between tension and compression. The current model is implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS). The accuracy and efficiency of the anisotropic plastic constitutive model and the computer program PACS are verified by solving a number of various fiber-reinforced composite laminates. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model. Keywords: Anisotropic Plasticity, Fiber Composite, Predictive Finite Element Analysis

Quantitative computed tomography-based finite element analysis predictions of femoral strength and stiffness depend on computed tomography settings

The aim of the present study was to compare proximal femur strength and stiffness obtained experimentally with estimations from Finite Element Analysis (FEA) models derived from Quantitative Computed Tomography (QCT) scans acquired at two different scanner settings. QCT/FEA models could potentially aid in diagnosis and treatment of osteoporosis but several drawbacks still limit their predictive ability. One potential reason is that the models are still sensitive to scanner settings which could lead to changes in assigned material properties, thus limiting their results accuracy and clinical effectiveness. To find the mechanical properties we fracture tested 44 proximal femora in a sideways fall-on-the-hip configuration. Before testing, we CT scanned all femora twice, first at high resolution scanner settings, and second at low resolution scanner settings and built 88 QCT/FEA models of femoral strength and stiffness. The femoral set neck bone mineral density, as measured by DXA, uniformly covered the range from osteoporotic to normal. This study showed that the femoral strength and stiffness values predicted from high and low resolution scans were significantly different (p<0.0001). Strength estimated from high resolution QCT scans was larger for osteoporotic, but smaller for normal and osteopenic femora when compared to low resolution scans. In addition, stiffness estimated from high resolution scans was consistently larger than stiffness obtained from low resolution scans over the entire femoral dataset. While QCT/FEA techniques hold promise for use in clinical settings we provided evidence that further improvements are required to increase robustness in their predictive power under different scanner settings and modeling assumptions.

Sheet Metals Forming Die Design Using Finite Element Analysis and the Taguchi Method

Sheet metal deep-draw die is primarily constructed with draw bead, which is then modified based on trial and error to obtain a successful forming without splitting. This work aims at a robust design of forming die using numerical analysis and the Taguchi method. A three dimensional elastoplastic finite element model of a sheet metal forming process of SPCEN steel has been successfully developed using the material flow stress obtained from the modified Erichsen cup test. The model was validated with the actual forming experiment and the results agreed well. The influence of draw bead parameters on splitting and thinning distributions were examined using the Taguchi method. Four parameters, namely the friction coefficient, draw bead height, radius and shoulder radius were investigated. The Taguchi main effect analysis and ANOVA results show that the height and shoulder radius of the draw bead are the most important factor influencing the thinning distribution. Applying the Taguchi method and using the minimum thinning percentage as the design criteria, the optimum die design was identified as height, radius, shoulder radius and the friction coefficient of 4, 8, 8 mm and 0.125 respectively. The verified finite element model using the optimum die design was conducted. The predicted Taguchi response was within 5.9% from finite element analysis prediction. The improvement in the reduction of thinning percentage was 22.35%.

A versatile stereo photogrammetry based technique for measuring fracture mode displacements in structures

The measurement of fracture mode displacements in structures which are susceptible to cracking such as adhesive joints in composite components – is becoming increasingly important. Such measurements are essential for the understanding of the root causes for specific fracture damage types. Furthermore, they can be used to assess the remaining life span of a structure for its safe operation. An improved version of a previously devised small displacement measurement system (SDMS) is used to measure local relative displacements (LRDs) at the trailing edge of a wind turbine blade. A purpose-made automated image processing software (AIPS) allows a rapid and reliable evaluation of a multitude of subsequently taken measurements at a high-precision level. The SDMS is used to measure the LRDs at three different locations close to the trailing edge of a wind turbine rotor blade. In addition, complementary measurements obtained by linear transducers are compared with the associated LRD component obtained by the SDMS. The 3D LRD measurements showed to be in good agreement with the predictions of non-linear finite element analysis. The paper closes with a brief discussion of the proposed measurement approach and the nature of LRDs as they appear in close vicinity to trailing edge joints.

Analysis of strength and failure pattern of human proximal femur using quantitative computed tomography (QCT)-based finite element method

This paper presents a novel method for fast and reliable prediction of the failure strength of human proximal femur, using the quantitative computed tomography (QCT)-based linear finite element analysis (FEA). Ten fresh frozen human femora (age: 34±16) were QCT-scanned and the pertinent 3D voxel-based finite element models were constructed. A specially-designed holding frame was used to define and maintain a unique geometrical reference system for both FEA and in-vitro mechanical testing. The analyses and tests were carried out at 8 different loading orientations. A new scheme was developed for assortment of the element risk factor (defined as the ratio of the strain energy density to the yield strain energy for each element) and implemented for the prediction of the failure strength. The predicted and observed failure patterns were in correspondence, and the FEA predictions of the failure loads were in very good agreement with the experimental results (R2=0.86, slope=0.96, p<0.01). The average computational time was 5min (on a regular desktop personal computer) for an average element number of 197,000. Noting that the run-time for a similar nonlinear model is about 8h, it was concluded that the proposed linear scheme is overwhelmingly efficient in terms of computational costs. Thus, it can efficiently be used to predict the femoral failure strength with the same accuracy of similar nonlinear models.