Nonlinear Finite Element Simulations Research Articles

Deep learning for automatic assessment of breathing-debonds in stiffened composite panels using non-linear guided wave signals

This paper presents a new structural health monitoring strategy based on a deep learning architecture that uses nonlinear ultrasonic signals for the automatic assessment of breathing-like debonds in lightweight stiffened composite panels (SCPs). Towards this, nonlinear finite element simulations of ultrasonic guided wave (GW) response of SCPs and laboratory-based experiments have been undertaken on multiple composite panels with and without baseplate-stiffener debonds using fixed a network of piezoelectric transducers (actuators/sensors).GW signals in the time domain are collected from the network of sensors onboard the SCPs and these signals in the frequency domain represent nonlinear signatures as the existence of higher harmonics. These higher harmonic signals are separated from the GWs (raw)and converted to images of time–frequency scalograms using continuous wavelet transforms. Adeep learning architecture is designed that uses the convolutional neural network to automatically extract the discrete image features for the characterization of SCP under healthy and variable breathing-debond conditions. The proposed deep learning-aided health monitoring strategy demonstrates a promising autonomous inspection potential with high accuracy for such complex structures subjected to multi-level breathing-debond regions.

Carbon Footprint between Steel-Reinforced Concrete and UHPC Beams

Due to its superior mechanical and durability performance, ultrahigh performance concrete (UHPC) has gained increasing applications worldwide. While studies have suggested different strategies to design reinforced UHPC beams, their resulting structural behavior is not yet well understood, and their carbon footprint has not been given considerable attention. Based on nonlinear finite element simulations and cradle-to-gate life-cycle analyses, this study compares the performance of two steel-reinforced concrete beams to steel-reinforced UHPC (R/UHPC) beams with the same flexural load capacity but different design strategies. Results show that an R/UHPC beam of the same cross-section but lower reinforcing ratio of a conventional concrete beam could show 166% higher carbon emission and 64% less deformation capacity than a control steel-reinforced concrete beam. On the other hand, a well-designed R/UHPC beam can (1) maintain the carbon footprint; (2) reduce the section size and steel bar usage by 50% and 30%–53%, respectively; and (3) show equivalent or higher service-level stiffness and ultimate deformation capacity.

Study of Applicability of Triangular Impulse Response Function for Ultimate Strength of LNG Cargo Containment Systems under Sloshing Impact Loads

The LNG cargo containment system used in membrane-type LNG cargo tanks must have sufficient dynamic strength to withstand the impact of sloshing loads. However, performing direct dynamic nonlinear transient finite element assessments against design sloshing impact loads with different design specifications can be complicated and time-consuming. To address this, it is effective to use linear superposition methods, such as the triangular impulse response function (TIRF) method, to conduct dynamic transient FE assessments of LNG cargo containment systems. However, as LNG cargo containment systems have a high level of nonlinearities in terms of geometry, material, and boundary effects, it is necessary to evaluate the applicability of the TIRF method in advance. This study investigates the dynamic responses of an LNG cargo containment system using the TIRF method and compares the ultimate value of the structural responses and impulses with that obtained using direct dynamic nonlinear transient assessments. Based on a comparison of a series of FE analyses, the study proposes a design for the partial safety factors for calculating the ultimate bending and shear capacities of an LNG cargo containment system, taking into consideration the dynamic impact of sloshing loads using the TIRF method. Finally, the ultimate shear and bending capacities are calculated using the proposed method and compared with those obtained through direct dynamic nonlinear transient assessments. The results show that the proposed method provides conservative estimates against direct nonlinear finite element simulations, with a difference of around 10% for the mean minus two standard deviations. This approach can be practically applied for early basic design purposes in the shipbuilding industry.

Nonlinear Vibration Behavior of FG Sandwich Beams with Auxetic Porous Copper Core in Thermal Environments

Modeling, analysis, and design are conducted to reveal the nonlinear forced and free vibration behaviors of the functionally graded (FG) sandwich beams with auxetic porous copper core and metal-ceramic facesheets. The copper foams with negative Poisson’s ratio (NPR) are designed to be functionally distributed along the structural thickness direction and possess greater relative density in the adjacent sublayers to the facesheets. Meanwhile, the functionally graded material (FGM) facesheets are designed to be metal-rich in the inner surfaces. Through micromechanical modeling and following the Mori–Tanaka model, material properties of FGM facesheets are determined and further taken to be temperature-dependent with the consideration of thermal environments. Nonlinear finite element (FE) simulations are then conducted. From the results of numerical analysis, one can conclude that when compared with the counterpart having a non-auxetic core, the sandwich beam with an auxetic core has lower nonlinear-to-linear frequency ratios of free vibrations and smaller dynamic deflections under a sudden load.

Numerical investigation of the collapse pressure of concentric tubes with frictionless and tied interface

The understanding and study of the mechanical behavior of submarine pipes have significant relevance in ocean exploration, allowing the application of these structures in adverse conditions. In this sense, protecting the tube's internal surface is vital for the transportation of corrosive materials, threatening structural integrity. Usually, the external surface is at constant hydrostatic pressure, leading to possible structural failure if the project does not consider all failure modes. Within the framework of Metallurgically Cladded Pipes (MCP) and Mechanically Lined Pipes (MLP), Corrosion-Resistant Alloys (CRAs) are inserted in the internal surface of pipelines. However, they are not typically deemed in the structural analysis as an integrant part of the mechanical resistance for the external load. This work presents an initial analytical proposal to calculate the collapse pressure of concentric tubes incorporating the rigidity provided by the CRA. Tied or frictionless numerical models are assumed to describe the interaction between the two bodies at the interface region. These two scenarios establish the upper and lower boundaries for cases where friction is part of the problem. The methodology applies a least-square minimization function based on nonlinear finite element simulations to extract analytical expressions that estimate the collapse pressure. An effort is made to reduce the number of sensitive parameters involved in the analytical proposals and minimize the complexity of the formulation. This process allows the analyst to visualize which parameters are more relevant in various scenarios. Nevertheless, the main goal is to evaluate how the variables are coupled and develop a methodology that can be adapted to reproduce the analyst's necessities.

Influence of aboveground structure on connected underground structure seismic response within an integrated system

Increasing numbers of integrated underground-aboveground structure systems (IUASS) are being constructed in densely populated urban areas. The complex dynamic interaction between the underground structure, its connected aboveground structure, and surrounding soil, brings challenges to the seismic design of such structure systems. This study aims to analyze the influence of an aboveground structure on a connected underground structure seismic response within an integrated system using nonlinear dynamic finite element simulations. The seismic response of an IUASS is compared with that of a single underground structure in both time and frequency domains, under the excitation of 9 seismic records and 0–10 Hz simple harmonic waves. The results reveal the sensitivity of the underground structure’s seismic response to the aboveground structure. Generally, the presence of aboveground structure can significantly increase the racking deformation and internal force of underground structure, particularly for the first underground story and for the underground spans directly below the aboveground structure. In such cases, the aboveground structure aggravates the tensile damage of first and second underground stories and overall compressive damage while alleviates the tensile damage of bottom story. However, when the input motion is dominated by high frequency content, the aboveground structure can act to reduce the underground structure seismic response.

A novel steel bulkhead based on the method of prefabrication and assembly and its first application to the Yuliangzhou immersed tunnel

Temporary bulkheads installed at the end of each tunnel element are indispensable for immersed tunnel elements to be watertight and float. Currently, welded steel bulkheads and cast-in-place concrete bulkheads have been applied in the installation of most immersed tunnels; however, these bulkheads have many inherent drawbacks. For example, existing cast-in-place concrete bulkheads are bulky and cannot be recycled after demolition. In addition, existing welded steel bulkheads, which cannot be fully reused, are installed and dismantled with a large number of on-site welding operations. Relying on the Yuliangzhou Immersed Tunnel in China, a novel steel bulkhead based on the method of prefabrication and assembly, namely, a piece-assembled steel bulkhead, was developed to address the abovementioned problems. The structural components of the new steel bulkhead applied to realize full recycling mainly include steel bulkhead panels, ethylene-propylene-diene-monomer (EPDM) sealing gaskets, steel bearings, and steel connecting bolts. The water tightness function of the new bulkhead was achieved through the compression deformation of the designed EPDM sealing gaskets inside the assembly seams, which were designed as multihole structures to save manufacturing material. Nonlinear finite element simulations were conducted to investigate the gasketed seam mechanical and sealant behavior. It was concluded that the control threshold value of gasketed seam compression displacement needed to satisfy the design requirement for a 250 kPa waterproof capacity could be taken as 15 mm, while that for seam offset displacement was set to 40 mm. To achieve the fast and efficient construction of the new steel bulkhead, a strategy of symmetrically installing and removing steel bulkhead panels piece by piece at one carriageway bore was proposed, and an automatic installation trolley that adjusts the bulkhead panel position in three directions was designed and developed. Finally, the on-site monitoring of the assembly seam displacements and the stress and deformation of the H-shaped steel beam verified that the new steel bulkhead was in a safe state and displayed good watertightness. This bulkhead was successfully applied in the Yuliangzhou Immersed Tunnel project, and this test application supports the use of these technologies in immersed tunnel construction.

Analytical modelling of ship bottom grounding considering combined surge and heave motions

This paper provides a new contribution to the analytical treatment of ship grounding accidents. New formulations are proposed to assess the resisting force of outer/inner bottom plating and transverse floors when the vessel undergoes combined surge and heave motions during the grounding event. Considering shallow and sharp rocks described by parabolic functions, analytical solutions are derived from plastic limit analysis and validated by comparison to non-linear finite element simulations. A failure criterion is also proposed to trigger the rupture of the bottom plating and all the derived closed-form expressions are implemented into an in-house solver. The solver is then coupled to a 6-DOFs external dynamics program, which allows to account for the action of the surrounding water. Resulting tool is first validated on a full scale cruise ship by comparison to finite element results. It appears than although some discrepancies arise, especially in the response of transverse floors after rupture, the bottom damage distribution seems to be well predicted. Finally, the developed tool is used to quickly predict the grounding response of different types of ships and the influence of their mass and hydrodynamic properties on the damage extent is investigated.

Ultimate capacity of large-span soil-steel structures

The ultimate limit states provided by current design codes and standards were based on full-scale field and laboratory tests performed on soil-steel structures (SSS) of spans less than 10.0 m. Recently, the spans of SSS have increased up to 32.4 m with the tendency to exceed this record. The ultimate capacity of SSS utilizing the deepest corrugation profile, i.e., 237 mm depth and 500 mm pitch, has not been yet investigated under earth and truck loading. The current study evaluates the ultimate capacity of the world’s largest-span SSS with 32.4 m span and 9.57 m rise, using three-dimensional (3D) nonlinear finite element simulation. The investigation covered both the maximum backfill height and ultimate truck loading conditions. The 3D finite element modelling technique under ultimate loading was validated by full-scale test measurements of 10.0 m span soil-steel structure subjected to tandem axle loading. The critical straining actions obtained from the steel structure at ultimate condition was used to evaluate the ultimate limit states provided by the Canadian Highway Bridge Design Code (CHBDC, 2019) and AASHTO (AASHTO LRFD, 2019). The results revealed that the ultimate capacity of the SSS was reached without conforming to all ultimate bounds provided by the current design codes. Finally, a limit state function was proposed to account for the structure instability that may occur to the steel structure under ultimate loading condition. The proposed function successfully predicted failure in the steel structure under all cases considered in the current analysis before failure occurred in the numerical results.

Free-Form Shape Optimization of Advanced High-Strength Steel Members

The high yielding strength of advanced high-strength steel (AHSS) provides great opportunities for cold-formed steel (CFS) members with much higher load-carrying capability. However, if manufactured into the traditional cross-section shapes, such as C and Z, the material advantage cannot be fully exploited due to the cross-section instabilities. The purpose of this study was to establish a shape optimization method for cold-formed sections with AHSS and explore the potentially material efficiency that AHSS could provide to these sections in terms of their axial strength. In this study, the insights provided from the elastic buckling analysis and nonlinear finite element (FE) simulations of a set of traditional CFS sections were employed to determine the appropriate section size and length for optimization. Then, the optimization method was established using the particle swarm optimization (PSO) algorithm with the integration of computational analysis through CUFSM and the design approach (i.e., the direct strength method, DSM). The objective function is the maximum axial strength of the CFS sections manufactured with AHSS using the same amount of material (i.e., the same cross-section area). Finally, the optimal sections were simulated and verified by FE analysis, and the characteristics of the optimal cross-sections were analyzed. Overall, the optimization method in this paper achieved good optimization results with greatly improved axial strength capacity from the optimal sections.

Seismic Modelling of Corroded Reinforced Concrete Columns

Deterioration of seismic resistance of columns due to existing corrosion damage is investigated using advanced non-linear finite element simulation and analysis of a large database of tests with the objective to develop performance criteria for seismic evaluation and assessment. Current guidelines for structural seismic evaluation do not address how to account for the condition of the reinforcement. Incorporating the degree of bar corrosion in the evaluation procedures would complicate significantly the problem of seismic assessment. However, bar section loss, embrittlement, loss of material strength and interfacial bond, all affect the member’s residual mechanical properties, the hierarchy of failure modes and the consequences on seismic performance of complete structural components. In this work, simple modifications of existing nonlinear assessment procedures are proposed, in order to account for the effects of corrosion on seismic performance. Reduction factors of reinforcement stress–strain properties and column stiffness, strength and deformation capacity were calibrated to an assembled database of experimentally tested corroded columns, and were verified through advanced nonlinear finite element analysis, after modeling the effect of mass loss on material properties.

Numerical Simulation and Experimental Investigation on Two Strengthening Schemes of Cantilever Brackets

Cantilever brackets have been widely used in buildings to provide support for all kinds of pipes. In order to improve the bearing capacity of cantilever brackets, two types of reinforcement schemes are proposed, one is to sleeve a pipe, and the other is to add a haunch. Their mechanical properties are studied by numerical simulation and experimental investigation. First, the non-linear finite element (FE) simulation analysis was carried out, and the structural bearing capacity, stress distribution, and failure modes were discussed. Then, the full-scale model tests were completed to provide validation of the FE analysis. On this basis, a comparison of the FE results and test results of three kinds of cantilever brackets was discussed in detail. The results show that two reinforcement schemes can enhance the bearing capacity of the cantilever bracket significantly by 38.3% and 25.9%, respectively, and they are applicable for the reinforcement of existing cantilever brackets.

Influence of combined imperfections on lateral-torsional buckling behaviour of pultruded FRP beams

By way of computational analyses using Finite Element (FE) software this paper presents, by way of sensitivity studies, lateral-torsional buckling resistances of I-beams made of pultruded fibre reinforced polymer. Parameters changed in the studies are the geometric imperfections, the vertical load position and the load eccentricity. Measured geometrical and material imperfections are incorporated into the geometrical nonlinear FE simulations. Constants in the FE work are three-point bending loading and the imperfection condition from having different elastic constants in the four flange outstands. Numerical results from the sensitivity studies are verified by comparing them with equivalent buckling load results from a series of physical tests conducted previously. It is found that the influence of combined geometrical and material imperfections on LTB failure can be significant, such that an imperfect beam can be put into a near ‘perfect imperfection’ condition, in which it possesses a higher buckling resistance. The opposite can happen for a ‘more severe imperfection’ with poorer beam response under loading. The load eccentricity on I-beams confirms a complex structural response. To be able to have a recognised design procedure for pultruded I-beam members the influence of combined imperfections on lateral-torsional buckling resistance needs to be reliably quantified.

Axial compressive behaviour of rectangular DCFSST stub columns

In this paper, a new type of rectangular double-opening concrete filled sandwich steel tube (DCFSST) is developed. This new type of composite section can keep the inner steel tubes away from the cross-sectional centroid axis through the reasonable configuration. In order to assess the structural behaviour of rectangular DCFSST members, a pilot research on stub columns under axial compression was conducted. A total of 10 specimens, including 5 with double steel square hollow sections (SHSs) and 5 with double steel circular hollow sections (CHSs), were tested with the various offset rate of inner tube (e0) and opening ratio (ϕ). The experimental observations indicate that, generally, e0 and ϕ have moderate effect on the failure process and failure modes of the specimens, and the failure modes of the specimens include outward local buckling of outer tube, crushing of the sandwiched concrete and inward local buckling of inner tubes. In addition, ϕ has significant influence on the load-deformation curves, axial capacity and axial compressive stiffness of the specimens; however, e0 has no obvious effect on the above performance. Moreover, nonlinear finite element (FE) simulation on the behaviour of axially compressed rectangular DCFSST stub columns was carried out using the ABAQUS software, and the typical performance of new composite members was further analyzed by the verified FE model. Finally, the formulae to calculate the axial capacity of rectangular DCFSST stub columns were also developed based on the FE simulation results and test results.

On the Influence of Direction-Dependent Behavior of Rock Mass in Simulations of Deep Tunneling Using a Novel Gradient-Enhanced Transversely Isotropic Damage–Plasticity Model

In engineering practice, numerical simulations of deep tunneling are commonly based on isotropic linear–elastic perfectly plastic rock models. Rock, however, commonly exhibits highly nonlinear and distinct direction-dependent mechanical behavior. The former is characterized by irreversible deformation, associated with strain hardening and strain softening, and the degradation of stiffness; the latter is due to the inherent rock structure. Nevertheless, the majority of the existing rock models focuses on the prediction of either the highly nonlinear material behavior or the inherent anisotropic response of rock. The combined effects of nonlinear and direction-dependent rock behavior, particularly in the context of the numerical simulations of tunnel excavation, have rarely been taken into account so far. Thus, it is the aim of the present contribution to demonstrate the influence of both effects on the evolution of the deformation and stress distribution in the rock mass due to deep tunnel excavation on the example of a well-monitored stretch of the Brenner Base Tunnel (BBT). To this end, the recently proposed gradient-enhanced transversely isotropic rock damage–plasticity (TI-RDP) model, is employed for modeling the surrounding rock mass consisting of Innsbruck quartz-phyllite. The material parameters for the nonlinear transversely isotropic rock model are identified by means of three-dimensional finite element simulations of triaxial tests on specimens of Innsbruck quartz-phyllite, conducted for varying loading angles with respect to the foliation planes and different confining pressures. Subsequently, the results of the nonlinear 2D finite element simulations of tunnel excavation are presented for different anisotropy parameters and different orientations of the principal material directions with respect to the tunnel axis. The capabilities of the TI-RDP model are assessed by comparing the numerically predicted results with those obtained by the isotropic version of the RDP model.

Mechanical model for the analysis of ship collisions against reinforced concrete floaters of offshore wind turbines

This paper presents a simplified mechanical model to study ship collisions against Reinforced Concrete (RC) floaters of Floating Offshore Wind Turbines (FOWTs). The model accounts for the deformability of both striking ships and struck RC structures, including a method to evaluate the elastic–plastic response of RC slabs with normal horizontal restraints, while considering contact area effects and punching shear failure. In the proposed model, the internal mechanics are coupled to the external body dynamics, whilst the hydro-mechanical effects acting on the collided bodies such as hydrostatic restoring, viscous, and wave damping forces are accounted for by the large rotations rigid-body dynamics solver MCOL. A parametric analysis is conducted on the model to study its sensitivity to changes in impact energy, impact location, reinforcement ratios, wall thicknesses, and striker rigidities, whose outcomes are compared with Non-Linear Finite Element (NLFE) simulations. The results show that the proposed model can accurately capture the penetrations in both structures, their body dynamics, and the contact force through the collision at a significantly lower computational cost than their NLFE counterpart.

Shock and impact reliability of electronic assemblies with perimeter vs full array layouts: A numerical comparative study

Abstract This study aims to assess the effect of the solder joint array layouts, including full and peripheral designs, on the mechanical response and reliability of electronic packages subjected to shock and impact loadings. Linear and nonlinear finite element simulations using the global-local modeling technique are employed to perform the analysis. Several peripheral array configurations are considered and compared to the full array systems. The results showed that, for optimum electronic package designs in terms of reliability and cost, it is highly recommended to use peripheral packages having three or four rows of solder interconnects in electronic systems under shock and impact loadings.

SHEAR BEHAVIOUR ANALYSIS OF REINFORCED CONCRETE BEAM USING NON-LINEAR FINITE ELEMENT SIMULATION

This paper investigates shear behaviour of reinforced concrete using multi-surface plasticity model. This analysis uses nonlinear finite element simulation using 3D-NLFEA finite element package. The experimental data adopted from the results of experimental test on eighteen beams where nine beams carried out by Bresler and Scordelis in 1963 and similar nine beams carried out by Vecchio and Shim in 2004. The constitutive model for the concrete material which used in this simulation is based on the plasticity-fracture model and considered the tension stiffening effect for the concrete. The result of the numerical simulation latter compared with the experimental test including load-deflection response, cracking pattern, and failure mode. Based on the analysis result, it was found that the load-deflection response shows slightly higher response compared with the experimental result. However, the cracking pattern and failure mode of the beam shows good result which is in compliance with the experimental test.

Numerical and random forest modelling of the impact response of hierarchical auxetic structures

Major sources of concern when auxetic protective structures are deployed in service of mission-critical applications encompass the triggering of high impact stress and the weakening of the structures’ elastic strength in response to the impact events. The current prevailing approach to assessing the impact resistance of these structures broadly hinges on mechanics-informed nonlinear finite element (FE) analysis. However, this method is computationally expensive and ill-suited for tackling the implementation of automated condition monitoring schemes. To address these issues, first, this paper proposes a hybrid hierarchical auxetic structure named Hybrid-Hierarchical Re-entrant Honeycomb (HHRH) that is endowed with impact stress-reducing capabilities. Next, using explicit FE, the investigation uncovers the interplay between the key geometric features of this HHRH auxetic structure and the impact performance under low, intermediate, and high crushing velocities. The outcome of the nonlinear explicit FE simulations is then unified with random forests (RF) scheme towards the establishment of intelligent auxetic structural systems. The results revealed that the developed HHRH maintained the auxeticity of the regular re-entrant auxetic and exhibited superior performance in some crushing strain regions. Moreover, the HHRH structure manifests up to an 85 % reduction in peak stress and the proposed reinforcement boosts the auxetic property by up to 23 % when compared to the regular re-entrant auxetic structure under high-velocity applications. Regarding the established data-driven RF-enabled machine learning model, its predictive strength with optimally-tuned hyperparameters is demonstrated to excellently capture the nonlinear multi-modal crushing stress response at various crushing strains, velocities, and geometric variations. Data AvailabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Fracture analysis of A6063-T6 materials used as liner of composite overwrapped and type I pressure vessels under internal pressure

Burst pressure is used as a safety design limit for a pressure vessel. This research aimed at finding burst pressure of three models of cylindrical pressure vessels, i.e. a) composite overwrapped pressure vessel (COPV) with an aluminum liner, b) aluminum pressure vessel with the same thickness as the liner of COPV, and c) aluminum pressure vessel with the same thickness as the total thickness of COPV. Non-linear finite element simulations,were used as a numerical tool to find stress, strain, and deformation of the cylinder. It was found that the aluminum material used as an aluminum liner of COPV has a higher burst pressure up to 55 MPa, while burst pressure of the other two aluminum cylinders only reaches 11.6 and 17.6 MPa. These results show good correlations with the theoretical calculation, which is calculated by using Faupel formulae and the Barlow Equation. In order to investigate the effect of using the CFRP layer on the severity of the crack defect in the aluminum liner, fracture analysis was held to find the stress intensity factor (SIF) along the crack front of a semielliptical crack. It was found that using CFRP layers, the stress intensity factor and energy release rate are reduced to 64.84% and 87.09%, respectively.