Nonlinear Dynamic Finite Element Analysis Research Articles

Effect of Characteristics of Ground Motion on Seismically Induced Sliding Surface of Slopes

The seismic performance of slopes is typically evaluated with a pseudo-static method using equivalent horizontal load or with Newmark sliding block analysis. In both procedures, the definition of the potential sliding surface is a required input. The sliding surface has been reported to be marginally influenced by the input ground motion and, therefore, is most often assumed from a pseudo-static procedure. In this study, extensive series of two-dimensional dynamic nonlinear finite element analyses are performed to evaluate the sensitivity of the sliding surface on the slope geometry, soil strength parameters, and input ground motion characteristics. It is demonstrated that the sliding surface may vary with the intensity and frequency characteristics of the input motion. Slopes with inclination angle equal or less than 35° are shown to be marginally influenced by motion intensity if the mean period (Tm) < 0.3 s. However, slopes inclined at 45° are revealed to be more sensitive to the motion intensity and Tm. For motions with Tm > 0.3 s, the sliding surface is demonstrated to widen with an increase in the intensity of the input ground motions. The degree of widening increases proportionally with an increase in Tm. It is, therefore, recommended to derive sliding surfaces from a dynamic analysis for steep slopes.

Novel testing method to evaluate the mechanical strength of self-adhesive resin cements with reflection of cement thickness.

This study aimed to propose an evaluation method for testing the mechanical strength of film-formed self-adhesive resin cements (SARCs) while reflecting cement layer thickness. Three commercially available dual-cure type SARCs were used for tensile and shear tests using specimens with varying thicknesses (0.05, 0.2, and 0.4 mm). There were no significant differences in tensile strengths among the various specimen thicknesses. In the shear test, there was a significant decrease in the strength with a reduction in specimen thickness. Stress distribution and fracture patterns were analyzed using in silico nonlinear dynamic finite element analysis. Finite element analysis demonstrated that stress distribution on the specimen surface was homogeneous even with different thicknesses in the tensile test, whereas it was inhomogeneous and induced different fracture patterns on the 0.05-mm-thick specimen in the shear test. These results suggest that the tensile test is useful for testing the mechanical strength of film-formed SARCs.

Comparing loosening between cement retained and screw retained implant supported crowns: a dynamic non-linear finite element analysis

Titanium root form implants are widely accepted because of the advantages of their mechanical properties. This study compared the screw loosening between two types of implant supported crowns (cement retained and screw retained) at the location of left lower first molar, using finite element method in a nonlinear analysis. The Dentis system was used for modeling of the implant, abutment and suprastructure. The amount of preload displacement was almost the same for both types of abutments. Applying force in any direction reduced the amount of downward preload displacement and decreased abutment-implant stability. In the cement retained crown, the amount of inner abutment displacement was always less than the screw head displacement by applying vertical, oblique and vertical-horizontal loads, so the stability of the abutment-implant complex was maintained. In the screw retained crowns under vertical-horizontal load the amount of displacement at the screw head and inner side of abutment was close to each other and this put the screw on the verge of loosening. However, under oblique pressure of 100 N, the inner abutment displacement exceeded the screw head displacement and the screw was loosened. Under vertical loading of 100 and 150 N, the stability of implant abutment was maintained. Screw loosening is less likely to occur under vertical load compared with oblique load. The cemented retained crowns have a higher biomechanical stability than screw retained crowns.

Analytical Investigation of Global Deployed Shape of a Spinning Solar Sail Membrane

In this paper, the deployed shape of spinning square solar sails was investigated through dynamic nonlinear finite element analysis of the full model of the solar power sail of the world’s first solar sail: Interplanetary Kite-craft Accelerated by Radiation of the Sun (IKAROS). The on-orbit photographs of IKAROS revealed that the sail membrane was deformed toward the sun and the membrane maintained its deployed shape during very low-spin-rate operations. To clarify the mechanism of the deformation and high stiffness, the authors of the present study previously performed deployed shape analyses of one-quarter of one square sail by employing Abaqus and reported that the phenomenon was probably caused by curvatures of thin-film devices attached to the membrane. In this study, a finite element model of the entire square sail of IKAROS was created. Furthermore, deployed shape analysis under several combinations of curvatures and spin rates was conducted by employing the dynamic solver “Abaqus/Explicit.” The results indicated that the sail deformations were induced by the curvatures of thin-film devices and that umbrella and saddle shapes appeared owing to the curvatures. The results also indicated that the electric harnesses between the sail and spacecraft supported the sail shape when the spin rate was low.

Novel Nonlinear Dynamic Beam–Foundation Interaction Model

A nonlinear dynamic framework for the analysis of beam–foundation interaction is developed. The extended Hamilton’s principle is used to analyze the response of Euler–Bernoulli beams vibrating on nonlinear continuums (e.g., soils) and subjected to vibrating and moving loads. The continuum beneath the beam is characterized by a nonlinear elastic constitutive relationship that connects the secant shear modulus to the induced strain. The novel feature of the analysis is that the nonlinear compression and shear parameters ks and ts of the continuum (i.e., foundation) do not have to be assumed a priori, as is required in conventional beams on foundation analysis, and are obtained as part of the solution. In fact, it is shown that these parameters are not constant but change with time and depend on the beam–foundation interaction. Another novel feature of the analysis is that the mass of the foundation participating in the vibration is obtained as part of the solution and does not have to be assumed a priori. Thus, the analysis rigorously takes into account the nonlinear beam–foundation (soil–structure) interaction within a dynamic time-integration framework. The developed framework is as accurate as and about 50% faster than conventional nonlinear dynamic finite element analysis. Inputs to the analysis can be given in the form of a text file without any requirement of numerical mesh generation, making the approach rather user friendly. The characteristics of the developed nonlinear dynamic foundation model are illustrated through examples of moving and vibrating loads.

Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal

Robustness of reinforced concrete (RC) structures is an ongoing challenging research topic in the engineering community. During an extreme event, the loss of vertical load-bearing elements can activate large-deformation resisting mechanisms such as membrane and catenary actions in beams and floor slabs of cast-in-situ RC buildings to resist gravity loads. However, few studies have been conducted for precast concrete (PC) buildings, especially focused on the capacity of such structures to withstand column loss scenarios, which mainly relies on connection strength. Additional resistance resource and alternate load paths could be reached via tying systems. In this paper, the progressive collapse resistance of a PC frame building is analyzed by means of nonlinear dynamic finite element analyses focusing on the fundamental roles played by beam-to-column connection strength and tying reinforcement. A simplified modelling approach is illustrated in order to investigate the response of such a structural typology to a number of sudden column-removal scenarios. The relative simplicity of the modelling technique is considered useful for engineering practice, providing new input for further research in this field.

Effect of the Reinforced Concrete Slab on the Blast Shock Wave Properties

Based on advanced numerical simulation technologies, such as the birth and death of element technique, large displacement technique, and fluid-solid coupling mechanism, and combined with the strain rate effect of concrete and steel materials, a complicated finite element model of a TNT–air–slab system is set up using the nonlinear explicit dynamic finite element analysis software LS-DYNA. A series of numerical simulation analyses is conducted on the reinforced concrete slab to evaluate the properties of the blast shock wave at the back of the slab. First, the typical characteristics of the blast shock waves at the front and back of the slab are described concisely. Then, the relation between the incident wave and the reflected wave is built by further studying the influence of the slab on the properties of the reflected wave at the front of the slab. And then, the relation between the reflected wave and the reformed wave is established by analyzing the effect of the slab on the change law of the reformed wave at the back of the slab. Finally, the basic steps for predicting the properties of the reformed wave are given considering the effect of the reinforced concrete slab on it. In addition, the case study demonstrates that the predicted results are true and reliable, and it indicates that the proposed method can accurately and effectively predict the properties of the reformed wave at the back of the reinforced concrete slab.

Design optimization of sandwich panels under impact loads

The purpose of this article is to develop numerical models for topology optimization of sandwich panels subjected to impact loads. Numerical models account for the effects of energy absorption capability and impact load resistant capacity on the development of optimal designs. A topology optimization technique based on the evolutionary structural optimization method and nonlinear dynamic finite element analysis with deflection and periodic constraints is used to generate optimal designs of sandwich panels under impact loads. To demonstrate the efficiency of the proposed method, design optimization of various sandwich panels is evaluated. A parametric study is conducted to investigate the effects of unit cells, core height, stiffener configuration and impact load intensity on the optimal designs. Up to 50% reduction in weight, 30% increase in energy absorption and 30% decrease in boundary reaction forces are achieved. Thus, the proposed approach can provide reliable manufacturing designs for sandwich panels under impact loads.

Fracture origin and crack propagation of CAD/CAM composite crowns by combining of in vitro and in silico approaches

PurposeFractographic analysis has been used to investigate the fracture behavior of Computer-aided design/computer-aided manufacturing (CAD/CAM) composite crowns by subjecting them to compression tests. However, it is difficult to investigate details of the fracture, including its initiation and propagation, using in vitro tests. The aim of this study was to determine the fracture origins and the order of crack initiation of CAD/CAM composite crowns using in silico nonlinear dynamic finite element analysis (FEA). Material and methodsThe following materials were used: Cerasmart (CS), Katana Avencia Block (KA), and Shofu Block HC (HC) as CAD/CAM crowns, Panavia SA Cement Plus (SA) as a luting material, and Clearfil DC Core Plus (DC) as an abutment. The elastic moduli and fracture strain of each material were obtained from the stress–strain curve of in vitro three-point bending tests. The fracture origins and order of crack initiation of the materials were determined by in silico nonlinear dynamic compression analysis. Load-displacement curves were statistically compared with the results of the in vitro compression tests (Pearson's correlation test, α = 0.05). ResultsThe nonlinear dynamic FEA demonstrated that crack initiation was primarily observed near the lingual side of the CAD/CAM crowns and immediately propagated to the central fossa. The models were fractured following the in vitro fracture strains, showing the same order for the products tested (CS/KA/HC, SA, and DC). Load-displacement curves with the use of CS, KA, and HC were significantly correlated to the corresponding in vitro compression tests results (CS: r = 0.985, p < 0.05, KA: r = 0.987, p < 0.05, and HC: r = 0.997, p < 0.05). ConclusionsThe in silico model established in this study clarified the crack initiation of the CAD/CAM composite crowns and the order of crack initiation among the investigated products, suggesting that the present approach is useful for analyzing the fracture behavior of CAD/CAM composite crowns in detail.

Effect of Orthodontic Bracket Type and Mouthguard Presence on the Stress and Strain during a Frontal Impact.

The aim of this study was to analyze the influence of orthodontic bracket type (metallic or ceramic) and mouthguard on biomechanical response during impact. Two-dimensional plane-strain models of a patient with increased positive overjet of the maxillary central incisor was created based on a CT scan, simulating the periodontal ligament, bone support, gingival tissue, orthodontic brackets (metallic or ceramic) and mouthguard. A nonlinear dynamic impact finite element analysis was performed in which a steel object hit the model at 1 m/s. Stress distributions (Von Mises and Modified Von Mises) and strain were evaluated. Stress distributions were affected by the bracket presence and type. Models with metallic and ceramic bracket had higher stresses over a larger buccal enamel impact area. Models with ceramic brackets generated higher stresses than the metallic brackets. Mouthguards reduced the stress and strain values regardless of bracket type. Mouthguard shock absorption were 88.37% and 89.27% for the metallic and ceramic bracket, respectively. Orthodontic bracket presence and type influenced the stress and strain generated during an impact. Ceramic brackets generated higher stresses than metallic brackets. Mouthguards substantially reduced impact stress and strain peaks, regardless of bracket type.

Parameters affecting the behaviour of steel pipes under impact loading

Subsea steel pipes are often used to form extensive networks for transporting oil and gas over large distances. Such pipes can be subjected to actions characterised by high loading rates and intensities stemming from high-mass low-velocity collisions. To ensure that such networks continue to operate, even after being subjected to impact loads, it is essential that the behaviour of the pipes is characterised by a certain level of resilience. Considering that most of the available data obtained from drop-weight tests on steel pipe specimens does not provide a detailed description of the behaviour exhibited throughout the loading process, the work herein aims at investigating numerically, via dynamic nonlinear finite element analysis, the problem at hand. After validating the predictions obtained against the available test data, the numerical investigation focuses on studying the effect of a range of parameters on the exhibited behaviour. The latter parameters are associated with the shape and mass of the impacting object, the geometry and the support conditions of the pipe, the level of axial loading (applied along the axis of the pipe) as well as the level of internal and/or external pressures imposed onto the pipe walls. The numerical predictions reveal that the above parameters, most of which are associated with the in-situ conditions imposed onto subsea pipes throughout their operational life, can influence, potentially detrimentally, the exhibited behaviour. The numerical predictions obtained reveal that this effect is not accurately captured by the existing assessment methods employed in practice for predicting the level of damage suffered by pipes during impact.

Numerical Analysis of Shock Initiation on Highly Energetic Material LX-04

The paper presents investigation of shock initiation effects on highly energetic material LX-04, an HMX based one, by a blunt brass projectile using numerical modelling methods implemented in LS-Dyna software. Multi – Material Arbitrary Lagrangian Eulerian (MM-ALE) formulation has been used to provide the possibility of fulfilment of the elements with multiple materials accordingly to multiple phases of the composition detonated. The work is focused on LS-Dyna’s equation of the state keyword *EOS_IGNITON_AND_GROWTH_IN_HE. Proper comparison with experimental data is presented. The introduction into the subject of highly nonlinear transient dynamic finite element analysis, possibilities, and superiority of this kind of modelling are being discussed. Reasons of sustaining the need of data by numerical solutions rather than experimental handling in military applications are given. Some of typical technical issues, occurring during such a fast-performing phenomenon, and the need of experimental validation of the models are typed together with detonation-state determination’s observation capabilities.

In silico non-linear dynamic analysis reflecting in vitro physical properties of CAD/CAM resin composite blocks

PurposeThe aim of this study was to assess the validity of in silico models of three-point bending tests to reflect in vitro physical properties obtained from three commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite blocks and demonstrate notchless triangular prism analysis with those properties. Material and methodsThree types of commercially available CAD/CAM resin composite blocks were used: Cerasmart 300 (CS300; GC, Tokyo, Japan), Katana Avencia P Block (AP; Kuraray Noritake Dental, Tokyo, Japan), and KZR CAD HR3 Gamma Theta (GT; Yamakin, Osaka, Japan). In vitro/in silico three-point bending tests were conducted to obtain elastic modulus and fracture strain for non-linear dynamic finite element analysis (n = 10/each). Fractured surfaces of specimens after in vitro NTP tests were observed, and the fracture toughness of each CAD/CAM resin composite was obtained by in silico NTP analysis. ResultsBoth in vitro and in silico load–displacement curves obtained from three-point bending tests were significantly correlated (p < 0.05). The elastic moduli of CS300, AP, and GT were 8.0 GPa, 10.0 GPa, and 9.0 GPa, respectively. The fracture toughness values obtained from in silico NTP analysis of CS300, AP, and GT were 5.057 MPa m1/2, 4.193 MPa m1/2, and 4.880 MPa m1/2, respectively. There was no significant difference in the length of the stable region among the three CAD/CAM resin composites (p = 0.09). ConclusionsThe in silico approach established in this study showed acceptable reflection of in vitro physical properties and will be useful for assessing fracture toughness related to the longevity of CAD/CAM resin composites without wastage of materials.

Avoiding failures during building construction using structural fuses as load limiters on temporary shoring structures

The risk of structural failure of buildings can be significant during construction. Temporary adjustable telescopic steel shores or props are commonly used in building construction. The failure of shores is sudden and therefore structural fuses as load limiters (LL) can be introduced to provide ductility in the temporary member for a specified limit failure load. Previous work by the authors showed that the design of shoring systems can be improved using LL for standard cases of imposed loads applied during construction. This paper extends this work to cases of accidental loading where the shoring system-permanent structure interaction is less known. The main principles of LLs are discussed and implemented in advanced numerical simulations of a real case RC building during construction by means of explicit nonlinear dynamic finite element analyses. Different local failure scenarios were investigated corresponding to cases observed in practice. The comparison of the numerical results obtained with and without LLs demonstrated for the first time the benefits of using LLs in terms of: (a) mitigating the risk of failure of the temporary structure; and (b) reducing permanent damage (cracking and short-term deflections in the slab) affecting the durability and functionality of the building.

Behaviour of steel-fibre-reinforced concrete beams under high-rate loading

The present study focuses on examining the structural behaviour of steel-fibre-reinforced concrete (SFRC) beams under high rates of loading largely associated with impact problems. Fibres are added to the concrete mix to enhance ductility and energy absorption, which is important for impact-resistant design. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the present study. Experimental static and impact tests were also carried out on beams spanning 1.3 meter with weights dropped from heights of 1.5 m and 2.5 m, respectively. The numerical model realistically describes the fully-brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the post-cracking response (the latter was allowed for by conveniently adjusting the constitutive relations for plain concrete, mainly in uniaxial tension). Suitable material relations (describing compression, tension and shear) were selected for SFRC and incorporated into ABAQUS software Brittle Cracking concrete model. A more complex model (i.e. the Damaged Plasticity concrete model in ABAQUS) was also considered and it was found that the seemingly simple (but fundamental) Brittle Cracking model yielded reliable results. Published data obtained from drop-weight experimental tests on RC and SFRC beams indicates that there is an increase in the maximum load recorded (compared to the corresponding static one) and a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter and the specimens were often tested to complete destruction and thus yielding post-failure characteristics of little design value and making it difficult to pinpoint the actual load-carrying capacity and identify the associated true ultimate limit state (ULS). To address this, dynamic NLFEA was employed and the impact load applied was reduced gradually and applied in pulses to pinpoint the actual failure point. Different case studies were considered covering impact loading responses at both the material and structural levels as well as comparisons between RC and SFRC specimens. Steel fibres were found to increase the load-carrying capacity and deformability by offering better control over the cracking process concrete undergoes and allowing the impact energy to be absorbed more effectively compared to conventional RC members. This is useful for impact-resistant design of SFRC beams.

Stress-based vs. Strain-based safety evaluations of spent nuclear fuel transport casks in energy-limited events

The stress-based criteria specified in ASME Section III (American Society of Mechanical Engineers, 2010) have long been used to evaluate the structural safety of mechanical structures, systems, and components (SSC) associated with nuclear power plants. These evaluation criteria, however, have inevitable limitations in accounting for the structural behaviors of spent nuclear fuel (SNF) transport casks, which likely undergo significant plastic deformations in extreme accidents. Hence, the stress-based evaluation criteria are considered inappropriate for energy-limited events that involve a high impact load, such as an accidental drop.This study evaluates the effectiveness of strain-based criteria, which were recently added in ASME Section III, Nonmandatory Appendix FF (American Society of Mechanical Engineers, 2015) and provides critical comparative study over traditional stress-based criteria for assessing the structural safety of SNF transport casks. Horizontal and vertical accidental drop events specified in NUREG-1536 (US Nuclear Regulatory Commission, 1997) are simulated using nonlinear dynamic finite-element analysis (FEA). Four SNF cask models with different impact-limiter designs are numerically simulated. The design of the impact limiter varies with wood types (redwood and balsa wood) and grain directions (transverse and longitudinal with respect to the loading direction). The FEA stress and strain results for the basket and canister parts are examined according to both stress-based and strain-based criteria. The strain-based criteria provide less conservative and more sensitive estimation than the stress-based criteria.

Seismic Retrofit of Steel Truss Bridge Using Buckling Restrained Damper

Buckling Restrained Bracings (BRBs) are widely used to improve the seismic behavior of buildings. They are employed for bridges as well, but their application in this respect is limited. BRBs can also be used as a function of the individual damper rather than the structural component or the bracing, in which case the device may be called a Buckling Restrained Damper (BRD). Yet, such application has not been explored much. There are quite a few bridges designed according to the old design codes in Japan. Their seismic resistance may not be satisfactory for the current seismic design codes. Against this background, the behavior of a steel truss bridge under a large seismic load was investigated by nonlinear dynamic finite element analysis. Some members were indeed found to be damaged in the earthquake. Retrofitting is needed. To this end, the application of BRD was tried in the present study: a parametric study on the seismic behavior of the truss bridge with BRD was conducted by changing the length, the cross-sectional area, the location and the inclination of BRD. The effectiveness of BRD was then discussed based on the numerical results thus obtained. In all the analyses, ABAQUS was used.

Influence of impacted canines on the stress distribution during dental trauma with and without a mouthguard.

Maxillary canines have a high incidence of impaction which may be associated with unexpected damage during maxillofacial trauma. The aim of this study was to evaluate how an impacted canine could influence the stress distribution in the dentoalveolar complex during a simulated impact before and after surgical removal plus the protective effect offered by a mouthguard. Cross-sectional finite element models of the central incisor and support structures of a patient with an impacted canine in a transverse position were made using ImageJ and Marc/Mentat software. The following impact conditions were simulated: (a) incisor with impacted canine; (b) incisor with surgical socket after impacted canine extraction; and (c) incisor after bone healing. The impacts were also simulated with a 3mm custom-fitted ethylene vinyl acetate mouthguard. A non-linear dynamic impact finite element analysis was performed in which a rigid object hit the model at 1m/s. Maximum and minimum principal stresses as well as von Mises stresses were analyzed. Higher values of compressive and tensile stresses occurred on the cortical bone in the models after impacted canine extraction. The highest stress concentrations in the enamel and dentin structures were observed after bone healing. The mouthguard reduced the stress in the alveolar bone and dental structures. Use of mouthguards during impact reduced the compressive and tensile stresses in the alveolar bone, mainly in the fragile regions of the impacted canine or surgical socket.

Optimization of catenary risers with hydrodynamic dampers

This study presents an optimization process on the design of an improved steel catenary riser configuration with hydrodynamic dampers that seek to minimize the effects caused by compression waves along the risers. The dimensions and positioning of these dampers are obtained using the Globalized Bounded Nelder–Mead optimization method (GBNM). This method requires no gradient and is proved to be capable of identifying the best feasible riser configurations according to a specific performance criteria. A case study addresses the operational viability of the catenary riser with hydrodynamic dampers (CRHD) in an effort to reduce its material cost and improve its structural behavior. A nonlinear dynamic finite element analysis is necessary to evaluate the mechanical behavior of each candidate configuration, which makes the optimization process computationally expensive. As such, we discuss ways of improving the overall efficiency of the method by reducing the number of analyzed configurations.

Multi-objective optimisation of steel moment frames subjected to blast

In recent decades, terrorist attacks have been increased all over the world. For this reason, the design of blast resistant structures is very crucial. On the other hand, for decades the optimum design of structures has been an interesting subject for structural engineers and researchers as it can provide cost and behavioural efficiencies. In the current research, the optimum design of steel moment frames under blast loading has been studied. Towards that end, first, a damage index is developed based on the maximum plastic strain in the members. Then, according to the damage index, a multi-objective optimisation methodology is proposed to minimise the structural weight and the damage index. The method utilises explicit nonlinear dynamic finite element analysis as the structural analysis method and NSGA-II optimisation algorithm as the optimisation technique. At the final point, based on the proposed method a framework is developed, and two numerical examples are studied. Results of this research show that the developed method is effective in achieving optimal designs with desired cost and damage.