Nonlinear Finite Element Study Research Articles

Análise de falha localizada em uma grande parede de concreto armado

Abstract Reinforced concrete structures must be designed in a manner that assures an acceptable level of safety and performance. However, accidents still occur nowadays causing interdiction, financial losses, or even human casualties. Therefore, succinct studies are required to give answers to such an undesirable situation, helping to prevent repetition and enlightening new design and construction methods. This paper analyzes the failure mechanism in a large reinforced concrete panel composed of one L-shaped cantilevered wall and structural walls in Campinas. The investigation was carried out using in-situ destructive and non-destructive tests and also through numerical simulation. In-situ tests revealed that the region where the fracture happened had no sufficient resisting steel area. The fracture line developed through the end of the wall’s horizontal rebars anchored within the column. It was concluded that the reinforced concrete panel failure happened due to structure misconception and incorrect design, once columns stirrups were responsible for the equilibrium of the cantilevered part of the building, as demonstrated by the nonlinear finite element study and in-situ investigations.

Effect of customized abutment taper configuration on bone remodeling and peri-implant tissue around implant-supported single crown: A 3D nonlinear finite element study.

The optimal configuration of a customized implant abutment plays a crucial role in promoting bone remodeling and maintaining the peri-implant gingival contour. However, the biomechanical effects of abutment configuration on bone remodeling and peri-implant tissue remain unclear. This study aimed to evaluate the influence of abutment taper configurations on bone remodeling and peri-implant tissue. Five models with different abutment taper configurations (10°, 20°, 30°, 40°, and 50°) were analyzed using finite element analysis (FEA) to evaluate the biomechanical responses in peri-implant bone and the hydrostatic pressure in peri-implant tissue. The results demonstrated that the rate of increase in bone density was similar in all models. On the other hand, the hydrostatic pressure in peri-implant gingiva revealed significantly different results. Model 10° showed the highest maximum and volume-averaged hydrostatic pressures (69.31 mmHg and 4.5 mmHg), whereas Model 30° demonstrated the lowest values (57.83 mmHg and 3.88 mmHg) with the lowest excessive pressure area. The area of excessive hydrostatic pressure decreased in all models as the degree of abutment taper increased from 10° to 30°. In contrast, Models 40° and 50° exhibited greater hydrostatic pressure concentration at the cervical region. In conclusion, the abutment taper configuration had a slight effect on bone remodeling but exerted a significant effect on the peri-implant gingiva above the implant platform via hydrostatic pressure. Significant decreases in greatest and average hydrostatic pressures were observed in the peri-implant tissues of Model 30°. However, the results indicate that implant abutment tapering wider than 40° could result in a larger area of excessive hydrostatic pressure in peri-implant tissue, which could induce gingival recession. This article is protected by copyright. All rights reserved.

Investigation on primary stability of dental implants through considering peri-implant bone damage, caused by small and large deformations: A validated non-linear micro finite element study

Primary stability of a dental implant is defined as its ability to resist the applied load without showing excessive damage in peri-implant bone, which is a prerequisite for secondary stability, and consequently for implantation success. The main goal of this study was to develop a validated micro-finite element (μFE) approach to assess the primary stability of dental implants in terms of stiffness, stiffness reduction, and irreversible displacement of the bone-implant system, subjected to an increasing step-wise quasi-static compressive loading-unloading test. The μFE models were generated based on the μCT images of bone, taken from extracted bovine tibia trabecular bone samples after drilling and implantation. A tissue constitutive model was considered for trabecular bone by describing elasto-plasticity with a modified von Mises yield criterion and element deletion technique to account for trabecular bone damage behavior. Then, the obtained force-displacement curves from the simulation were compared with the in-vitro mechanical test curves to evaluate the validity of the model. The results showed that the proposed μFE model could be properly predict the bone-implant system mechanical response in terms of irreversible displacement (R2 = 0.99), stiffness (R2 = 0.77), and stiffness reduction (R2 = 0.72) of the bone-implant construct for all the applied displacements without a significant difference from the unit slope and zero intercept of the QQ-plot (p-value<0.05). Moreover, a qualitative agreement was seen between the peri-implant bone damage predicted by the μFE model and the observed from μCT images. The adopted methodology used in this study can predict the mechanical failure response of the bone-implant system, which can be employed as a representative tool to study the effects of various dental implant design parameters on the primary stability with the ultimate goal of optimizing dental implants design.

Effect of gingival height of a titanium base on the biomechanical behavior of 2-piece custom implant abutments: A 3-dimensional nonlinear finite element study

Statement of problemTitanium base (TiBase) abutments to restore an implant-supported single crown are available in different gingival heights, but information on the biomechanical effects of the gingival heights is lacking. PurposeThe purpose of this nonlinear finite element analysis study was to evaluate the effects of TiBase gingival heights on the biomechanical behavior of custom zirconia (CustomZir) abutments and TiBase, including von Mises stress and maximum and minimum principal stress. Material and methodsTiBases with different gingival heights (0.5 mm, 1 mm, 1.5 mm, and 2 mm) with internal hexagon Morse taper connections were simulated in 3-dimensional models. The simulations (ANSYS Workbench 2020; ANSYS Inc) included the OsseoSpeed EV implant (Ø5.4 mm) (AstraTech; Dentsply Sirona), restoration, and surrounding bone in the mandibular first molar region. An occlusal force of 200 N was applied with a 2-mm horizontal offset toward the buccal side and a 30-degree inclination from the vertical axis. ResultsHigh-stress concentration was observed in the uppermost internal connection area on the buccal side and the antirotational part of the titanium abutment on the lingual side in all models. CustomZir abutments with a shorter gingival height exhibited larger concentrated areas of volume average stress von Mises stress and higher magnitude of maximum and minimum principal stress compared with a taller gingival height. ConclusionsA TiBase abutment with a taller gingival height reduced the fracture risk of a CustomZir abutment without increasing any mechanical risk.

Energy Absorption Capacity of Empty and Foam- Filled Concentric Cylindrical Tubes

Axial folding of metal tubes has been renowned over ages as a superb energy-absorbing method. High-volume industrial items like automobiles, trains, and other sectors where energy must be absorbed in a controlled manner during a crush situation are using components based on this concept. From the perspective of passenger automobile safety design, it is crucial and anticipated to investigate crushing energy absorption.&#x0D; These are thoroughly investigated experimentally and computationally how aluminium foam-filled sections behave when compressed axially. To represent quasi-static test circumstances, nonlinear dynamic finite element studies are conducted. It is discovered that the predicted crushing force and fold formation are rather similar to the experimental facts. The mean crushing force of the foam-filled sections is calculated using straightforward closed-form methods based on the computational models. It is shown that the increase in the mean crushing force of a full column increases linearly with the cross-sectional area and foam compressive resistance. The proposal, for a variety of column designs, materials, and foam strengths, has been within 8% of the experimental data.&#x0D; Ultimately, the results highlight the advantages of using concentric cylindrical tubes to absorb impact energy in circumstances with axial loads. It only understands well how control the absorbed energy by using the geometrical features of such structures. The purpose of this study is to suggest design solutions on how to use concentric cylindrical tubes in energy absorption applications like crash-worthiness.

Moment capacity of apex brackets of cold-formed steel portal frames

The strength and stiffness of cold-formed steel portal frames are heavily related to the performance of their joints; these joints are normally formed through brackets, bolted to the webs of channels. They should have adequate strength to ensure the frame fails within the members, and the design moment capacity of a joint should be equal to or exceed the moment to which the joint is subjected. For apex brackets, based on the results of a non-linear elasto-plastic finite element study, the authors have recently proposed design guidance in the form of equations for predicting the moment capacity. However, this prediction was limited to fully restrained apex joints against lateral torsional buckling, which is an arrangement not commonly used in practice. Furthermore, the joints considered were composed of back-to-back brackets connecting back-to-back channels. The design recommendations were further limited to apex joints under bearing gravity load, equivalent to the opening moment applied to the bracket. This paper extends the previous work by now considering both single and double apex brackets, which are partially restrained, consistent with New Zealand practice, and considering both opening and closing moments on apex joints (or gravity and wind uplift load on portal frames). This study proposes unified design equations from a parametric study comprising 5,040 finite element models.

Flexural and shear behaviours of GFRP-reinforced concrete beams based on nonlinear finite element studies

This paper presents the finite element analysis of glass fiber-reinforced polymer (GFRP)-reinforced concrete beams. The research focuses on refining and validating concrete constitutive modelling within the commercial software ABAQUS. The accuracy of the proposed models is evaluated against a set of experimentally tested GFRP-reinforced concrete beams with, and without, GFRP shear reinforcement. The validated models are then used to conduct a parametric study on the influence of slenderness and shear reinforcement on the behaviour of GFRP-reinforced beams, the results of which are compared to the CSA S806-12 and ACI440.1R-15 design provisions. A discussion is provided on the effectiveness of the current design methods in predicting strength and failure modes of the GFRP-reinforced beams.

Forensic assessments of the influence of reinforcement detailing in reinforced concrete half-joints: A nonlinear finite element study

This paper presents the results of forensic assessments on reinforced concrete half-joint beams tested within the literature through the application of nonlinear finite element analyses. The software package ATENA Science was utilised, in which critical evaluations were conducted into the accuracy of the software in predicting the response of reinforced concrete half-joints with inadequate reinforcement detailing. It was shown that the load capacity of the half-joints could be predicted accurately, with an average experimental-over-predicted ratio of 1.04 and a coefficient of variation of 7.3%. The predicted crack patterns and modes of failure consistently coincided with those obtained experimentally, exhibiting localised failures at the re-entrant corner of the nib, along with failures located within the full depth of section due to an inadequate amount of shear reinforcement. Moreover, the combination of bar reductions to replicate severely corroded reinforcement at critical zones highlighted the influence deterioration mechanisms have on the structural capacity, with reductions of more than 50% observed in comparison to newly constructed half-joints with no deterioration.

Kinematic analysis of L4–L5 spinal segment with spondylolysis and different types of grade 1 spondylolisthesis: a nonlinear finite element study

Purpose: This work aimed to evaluate and characterize the motion of the fourth and fifth lumbar vertebrae functional spinal unit with spondylolysis and different types of grade 1 spondylolisthesis using the finite element method. Methods: Nine nonlinear three-dimensional finite element models were reconstructed from computed tomography scans to five educational fourth and fifth lumbar vertebrae models. The intervertebral disc was simulated in two conditions: four models with healthy discs and five models with degenerated discs. Each model consisted of two vertebrae divided into three bony parts, two endplates, an intervertebral disc and five ligaments. The flexion, extension, lateral bending and rotation loading conditions were simulated, and the ranges of motion were measured and plotted. Results: In flexion, compared to the baseline intact model, the most significant increase in the range of motion was experienced by the isthmic spondylolisthesis model, while in extension, a reduction in the range of motion was measured in both prolonged pars and unilateral pars defect and healthy disc models. In degenerated disc results, the unilateral pars defect and degenerative spondylolisthesis models had the lowest range of motion. No large differences were noticed in lateral bending results. Lastly, in axial rotation, the most significant increase in the range of motion was measured in the isthmic spondylolisthesis model, followed by the spondylolysis model and similarly, in the degenerated disc models. Conclusions: The isthmic spondylolisthesis displayed hypermobility in flexion and rotation. Moreover, the model with unilateral pars defect showed hypermobility in axial rotation only. Finally, hypomobility in all movements was noticed with the degenerative spondylolisthesis model.

Nonlinear finite element study on element size effects in alkali-activated fly ash based reinforced geopolymer concrete beam

The practical application of geopolymer concrete structure is getting attention due to its environmentally friendly characteristics. This paper presents non-linear Finite Element Analysis (FEA) on the element size effect in reinforced geopolymer concrete beam. Element size significantly influences the failure mechanism of structure especially in ductile fracture of reinforced concrete. The critical failure strain, crack patterns and orientations are mesh sensitive in finite element analysis for reinforced concrete structure. The impact of the element size on behavioral aspects of reinforced geopolymer concrete beam such as the crack pattern, ultimate load capacity and load-displacement behavior studies discussed along with a formerly conducted experimental data. Further validation of FEA is carried out using the theoretical flexural strength of the beam according to Euro code 2. Results show that element size has a significant effect in capturing the cracking pattern of reinforced geopolymer concrete beam. FEA result from the positive principal strain contour confirms that the fine mesh size captured the tension, the diagonal shear and compression cracks, even the band of surrounding cracks around the bottom reinforcement, precisely as compared to coarse meshes. It has been observed that the utilization of fine mesh with 10 mm element size predicts the experimental and theoretical ultimate load by 99.46% and 96.11%, respectively. Coarse mesh having 25 mm element size shows slightly higher variation in predicting the experimental and theoretical ultimate load by 93.75% and 90.42%, respectively. In addition, fine mesh confirms the experimental mid-span vertical deflection by 99.44% however the coarse mesh predicts in significant deviation by estimating 48.04% of the experimental mid-span vertical deflection. Furthermore, the ductile failure of the beam was accurately traced by the fine mesh.

Effects of Variable Composite Attachment Shapes in Controlling Upper Molar Distalization with Aligners: A Nonlinear Finite Element Study.

The objective of the present study is to describe the stress and displacement patterns created by clear aligners and composite attachments bonded with the acid-etch technique on the labial surface of the maxillary first upper molar during its distalization. Maxillary molar distalization is a clinical orthodontics procedure used to move the first maxillary molar distally. The procedure is useful in patients with some Class II malocclusion allowing the first molar to move into a Class I relationship and the correction of associated malocclusion features. Three finite element models were designed to simulate the alveolar bone, molar tooth, periodontal ligament, aligner, and composite attachments. The first model had no composite attachment, the second model had a vertical rectangular attachment, and the third model had a newly designed attachment. A loading method was developed that mimicked the aligner's molar distal movement. PDL was set as a viscoelastic material with a nonlinear mechanical response. von Mises and maximum principal stresses and tooth displacement patterns were analyzed using dedicated software. All the configurations showed some form of clockwise rotation in addition to the distal movement. The crown portion of the tooth showed maximum displacement in all three models; however, in the absence of attachment, the root apex moved in the opposite direction which was compatible with uncontrolled tipping movement. Simulations with attachments exhibited the best performance regarding the movement patterns. The third group, with the newly designed attachment, exhibited the best performance concerning stress distribution (principal stress and von Mises stresses) and higher stresses in the periodontal ligament and tooth. Incorporating a vertical rectangular attachment in a clear aligner resulted in the reduction of mesiodistal tipping tendency during molar distalization. The third model was the most efficient considering both displacement pattern and stress distribution. The level of stress generated by the third model needs to be further investigated in future studies.

Nonlinear finite element study on forced vibration of cylindrical micro-panels based on modified strain gradient theory

This research deals with the nonlinear forced vibration analysis of cylindrical micro-panels (CMP) under the modified strain gradient shell theory using the higher-order finite element method. The main objective is to study the impacts of length scale and geometrical parameters on the forced vibration behavior of CMP. The mechanical model based on the modified strain gradient theory (SGT), shear deformation shell theory (SDST), and von Kármán nonlinear kinematic relations is developed using Hamilton’s principle and the hermitian finite elements are employed to solve the problem. Variations of the frequency responses are presented to analyze the nonlinear forced vibration of CMP.

Finite element analysis of 90 degree pipe elbow sustained stress indices

Paper deals in-depth with the topic of sustained stress indices applicable to 90° elbows based on non-linear finite element analysis models. A comprehensive overview of the existing literature sources is given in the first part of the paper, showing that there are little sources which deal specifically with this topic and that the ones that do exist result in important scatter of the results. As a result, more than few of the existing sources are non-conservative in their nature. Dedicated non-linear finite element studies have been performed on shell and solid models which are used in conjunction with the regression analysis in order to obtain explicit equations which can be used to calculate both in- and out-plane sustained stress indices in 90° pipe elbows, which can then be used in the typical pipe stress analysis. Newly proposed equations prove to be a good fit for the numerical data, showing little deviation as shown by the correlation parameters presented in the paper. Final part of the paper presents a dedicated section on the high wall thickness elbows and shows the relationship between elbow wall thickness and maximum stress location. It is shown that beyond certain thickness, the maximum stress location shifts from the typical failure location (i.e., side wall) to the locations which are not typically expected (i.e., intrados or even away from elbow). This shifting may have an important effect on the theoretical models which assume failure location.

Modern numerical modeling of reinforced concrete structures

Nowadays, many computer software products are available for the numerical modeling of reinforced concrete structures; however, the accuracy of the numerical models created by the programs can only be accepted with a properly developed and verified modeling procedure. Within the framework of the present article, we present the numerical modeling possibilities of reinforced concrete structural elements and their connections through numerical models made by a modeling procedure we have built. In our studies, we also dealt with quasi-static unidirectional (horizontal and vertical) and cyclically variable direction and magnitude loads. The numerical models were created using the ATENA 3D three-dimensional nonlinear finite element software developed specifically for the study of concrete and reinforced concrete structures. In many cases, the results obtained by numerical experiments were compared with the results obtained by laboratory experiments, and some of our numerical experiments were compared with the results obtained using two-dimensional finite element software. Within the framework of this article, we would like to give a comprehensive picture of the numerical studies we have performed. We have also briefly summarized the results and experiences obtained from 3D nonlinear finite element studies.

A study on the ultimate strength of ship plate with coupled corrosion and crack damage

Under fatigue loading, crack damage shaped by stress concentration of pitting corrosion in the steel plate adversely affects the strength of ship structure. A nonlinear finite element study is carried out in this paper to investigate how coupled corrosion and crack damage influences the ultimate strength of ship plate. The parameters such as the length, angle and transverse position of cracks, corrosion density and depth and the plate slenderness ratio are taken into account in the present study. It is presumed that the crack is through-thickness and symmetrically distributed inside and on both sides of the corrosion pits, and no contact of crack faces occurs at the ultimate limit state. Reasonable crack gap and a shape of semicircular tip are employed based on numerical results. The crack propagation is not considered in this paper. It is found that the major crack impacts on the ultimate strength depend on the interactions between the length and location as well as the plate slenderness ratio. In addition, the effect of different corrosion factors can be attributed to the corrosion volume. When the crack and corrosion exist together in the plate, their reduction for the ultimate strength is less than their superposition when they exist alone. Moreover, the difference of these two reductions becomes larger as the crack angle increases. Based on numerical results, two mathematical formulas for predicting the residual ultimate strength of steel unstiffened plates with coupled corrosion and crack damage are proposed for longitudinal cracks, transverse and inclined cracks, respectively.

Nonlinear Finite Element Study of Beams with Elasto‐Plastic Damage Behavior in the Post‐Buckling Regime

AbstractLattice structures with low density tend to localize under compressive loading. The localizations start in a single cell band due to buckling of the beams and lead to compaction of the cells. To identify an appropriate discretization and to determine the influence of damage in an elasto‐plastic material behavior two simple load cases are analyzed with the finite element (FE) method. Simulations of an axial loaded beam in the post‐buckling regime with and without damage are carried out. In addition, a triangular cell under compression with different discretizations is analyzed.

Semi-analytical simulation of plastic collapse mechanism of cracked continuous unstiffened plates used in ship structure under in-plane longitudinal compression

The present study is undertaken based on a nonlinear finite element study carried out by the same authors for estimation of ultimate strength of cracked continuous unstiffened plates used in ship structures under in-plane longitudinal compression. Investigations show that in addition to the magnitude of ultimate strength, the deflection shape and plastic collapse mechanism will also change completely. Results show that deflection in the cracked half wave increases more rapidly than other half waves. Consequently generated half waves in a cracked plate will not have identical length and amplitude. This implies that the conventional plastic collapse mechanism cannot be used to predict the behavior of cracked plates in the post ultimate strength region. A new plastic collapse mechanism based on the FEM results is suggested and the principle of virtual work is used to derive the axial stress-deflection relation of the plate. However, due to inequality of the length and amplitude of generated half waves, the axial stress-deflection relation cannot be directly derived from the principle of virtual work. Therefore, in order to solve the virtual work equation, some auxiliary relations between the involved parameters are required. Auxiliary equations are derived using regression analysis based on FEM results. Finally, a semi-analytical formulation is derived to estimate post ultimate strength behavior of cracked plates. It is shown that the proposed semi-analytical formulation can predict both magnitude and slope of the stress-deflection curves with better accuracy compared to the conventional plastic collapse mechanism. The formulation can be used within the defined ranges of simulated crack lengths, slenderness and aspect ratios.

Experimental and analytical studies of base pipe pin connections under direct tension

Base pipe pin connections were developed to simulate a hinge behavior at the base of cast-in-place or precast bridge columns. Base pipe pins are composed of two steel pipes: one pipe is embedded in the column and the other in the adjoining member. Shear force is transferred through contact of the pipes and friction. The uplift force is resisted by a tension member and welded studs on the surface of the column pipe. To investigate the behavior and failure mode of base pipe pins under direct tension and to determine the ultimate tensile capacity of the pins, two scaled pipe pin connections were tested under direct tension. Elaborate nonlinear finite element (FE) studies of the pipe pins were also conducted to explore the effects of different parameters on the response of the pins. There are many possible failure modes that could occur under tension. Test results depicted that rupture of the pin tension member with no damage to the connection was the dominant failure mode in pure tension. The FE models accurately estimated the response of the test models and the observed failure mode. The analytical results showed that decreasing the pipe height alters the failure mode but does not affect the ultimate capacity of the connection significantly. Furthermore, reducing the pipe height or increasing the number of stud layers has a small effect on the ultimate capacity and stiffness of the connections.

Micromotion analysis of different implant configuration, bone density, and crestal cortical bone thickness in immediately loaded mandibular full-arch implant restorations: A nonlinear finite element study.

Excessive micromotion may cause failure of osseointegration between the implant and bone. This study investigated the effects of implant configuration, bone density, and crestal cortical bone thickness on micromotion in immediately loaded mandibular full-arch implant restorations. A finite element model of the edentulous mandible was constructed. Four implants were inserted in two different configurations, which were four parallel implants or tilted distal implants according to the all-on-four concept. Different cancellous bone densities and crestal cortical bone thicknesses were simulated. The framework was made of acrylic resin. A vertical load of 200 N was applied at the cantilever or on the distal implant (noncantilever loading). The maximum extent of micromotion was significantly influenced by the density of cancellous bone and to a lesser extent by implant configuration and the crestal cortical bone thickness. The all-on-four configuration showed less micromotion than the parallel implant configuration in some circumstances. The maximum micromotion detected with noncantilever loading was less than 1/3 of that with cantilever loading. Implant configuration had a limited influence on micromotion. Avoiding cantilever loading during the healing period should effectively reduce the risk of excessive micromotion in patients with low-density cancellous bone and thin crestal cortical bone.

Experimental Investigation on Flexural Response of Hybrid Steel Plate Girder

Flexural tests were conducted on five full scale I-shaped steel beams, three hybrid and two homogeneous, with two aims: 1) validate the inelastic flexural behavior of hybrid girder that is manufactured using lower grade steel 2) simplify finite element (FE) analysis procedure, for further parametric studies, by neglecting residual stresses when symmetrical welding sequence is adopted. Effect of material properties and member slenderness on flexural strength, ductility, and failure mode shapes is discussed. It is also found that failure mode shape and expansion of plastic field are mainly influenced by slenderness of member. Load-deflection and moment rotation response in tests are closely matching with non-linear finite element study. Close match is also observed in failure mode shapes and plastic field expansion. Considerable reduction is observed in residual stresses in symmetrically welded sections as compared to sections welded without proper sequence. This validates non-linear FE analysis procedure by neglecting residual stresses. Test results are compared with prediction equations for flexural strength, rotation capacity available in literature. Test results are also compared with provisions in EN 1993-1-1 and IS 800. Moment gradient (3-P) and uniform moment (4-P) loading have been considered to ensure that results are equally applicable in both cases.