Nonlinear Failure Analysis Research Articles

Research on damage characteristics and contact interface evolution behavior of double-block ballastless track considering tunnel floor heave

Excessive railway tunnel floor heave (TFH) will reduce the durability of the track structure and jeopardize train operation safety. The TFH characteristics were fitted into cosine and bilinear curves according to the monitoring data. A nonlinear failure analysis model of double-block ballastless track under TFH was established. The deformation transfer law, structural damage mechanism and the interlayer bonding interface failure evolution of the track structure under different TFH characteristics were explored. The results show that the deformation of TFH can be well mapped to the track. The amplitude transfer ratio is less than 100 %. The maximum wavelength transfer ratio under the cosine and bilinear TFH is 129.3 % and 127.5 %, respectively. To avoid the damage of track structure, when the wavelength is 10 m, the amplitude of cosine and bilinear TFH should be controlled at 2.5 mm and 0.5 mm respectively. When the wavelength is greater than 10 m, the amplitude can be appropriately increased. To avoid interlayer bonding cracking, the cosine and bilinear amplitudes with a wavelength of 10 m should be controlled at 5 mm and 1.5 mm, respectively. The track-tunnel interlayer debonding failure under the cosine curve occurs at the edge of the TFH, while the bilinear curve occurs at the center and edge of the TFH. The gaps under the cosine and bilinear TFH exhibit double-peak and multi-peak shapes, respectively. This study can provide theoretical guidance for controlling the performance degradation of track structure caused by TFH.

Nonlinear failure analysis of bridge pier subjected to vessel impact combined with blast loads

The vulnerability of a reinforced concrete (RC) girder bridge pier is numerically assessed using high- and moderate-resolution finite element (FE) simulations in LS-DYNA under the combination of vessel collisions and blast loadings. The damage levels of the pier under combined loads are quantitatively assessed by proposing three different damage indices based on the residual axial load, shear, and flexural moment capacities of the pier column obtained through a series of multi-step loading procedures on the simplified FE-based model of the pier. In addition, the proposed simplified model of the pier is employed for sensitivity assessments of the damage indices of the pier to several loading-related parameters including the vessel type, the location of applied loads, the impact velocity, and the time lag between the initiations of loadings. From the FE simulations, it is found that the pier undergoes more severe localized failure when both impact and blast loads are applied at the same elevation on the pier column which is more likely to occur during barge collisions. Moreover, it is found that the pier experiences greater internal forces when the sequent blast loading is applied at the occurrence time of the peak impact force.

New procedure of automatic modeling of pipelines with realistic shaped corrosion defects

Corrosion is still one of the most important causes of structural failure of and incidents in pipelines. Up until now, most finite element studies have considered modelling corrosion defects as a single or multiple idealized defects and their interactions. This paper presents an original methodology that has been developed for the automatic modeling of the complex geometry needed to represent real corrosion defects, using data obtained by field inspection, and also for building an appropriate finite element mesh for these defects. This new methodology enables a more in-depth finite element analysis and uses information already available from data obtained in inspections, which are currently only used to create clusters of idealized defects. The methodology enables the structural assessment of corroded pipelines to be further improved, giving more headroom to explore pipelines affected by corrosion. The methodology was validated by non-linear failure analysis, which were compared against semi-empirical methods and experimental results. The results are very promising and the computation efficiency is attractive.

Fracture and load-carrying capacity of 3D-printed cracked components

Regrading to the numerous potentials of additive manufacturing in producing components, three-dimensional (3D)-printed parts are becoming more prevalent in various industries and research associations. In this paper, fracture of U-notched 3D-printed parts under mode I and mixed mode I/II are experimentally investigated. To this aim, specimens are 3D-printed by polycarbonate (PC) and Nylon filaments using fused deposition modeling (FDM) 3D printing. In the fabrication, U-notched rectangular specimens are produced. A series of experimental practices are performed to determine load-carrying capacity of U-notched 3D-printed parts. In the current study, a combination of J-integral failure criterion and the equivalent material concept (EMC) was implemented to investigate failure of the specimens. Since the tested material has shown elastic–plastic behavior, EMC was utilized to avoid computationally inefficient non-linear failure analyses. By the obtained results, it is concluded that combination of EMC and J-integral criterion is able to predict the experimental results for the different 3D-printed materials. Parallel to the experimental investigations, numerical simulations are conducted and a very good agreement between simulation finding and reported experimental results is shown.

J-integral expression for mixed mode I/II ductile failure prediction of U-notched Al 6061-T6 plates under large-scale yielding regime

The main purpose of the present research is to check if the Equivalent Material Concept (EMC) is capable of being combined with the J-integral failure criterion to form a new ductile failure model, called EMC-J criterion, to predict the load-carrying capacity (LCC) of U-notched aluminum plates under mixed mode I/II loading. To achieve this purpose, first, a set of experimental results on LCC of some tested U-notched Al 6061-T6 rectangular specimens, failed by large-scale yielding (LSY) regime, are taken from the recent literature. Due to the elastic–plastic behavior of the tested Al 6061-T6, EMC is utilized to avoid complex and time-consuming non-linear failure analyses for LCC predictions. Then, a new combined ductile failure model is proposed in which J-integral criterion, as a well-established brittle fracture criterion, is combined with EMC to predict theoretically the experimental results of the tested U-notched aluminum plates. Finally, it is shown that EMC-J criterion can predict the experimental results well.

Non-linear failure analysis of HCPB blanket for DEMO taking into account high dose irradiation

For the European helium cooled pebble bed (HCPB) blanket of DEMO the reduced activation ferritic martensitic steel EUROFER has been selected as structural material. During operation the HCPB blanket will be subjected to complex thermo-mechanical loadings and high irradiation doses. Taking into account the material and structural behaviour under these conditions is a precondition for a reliable blanket design.For considering high dose irradiation in structural analysis of the DEMO blanket, the coupled deformation damage model, extended recently taking into account the influence of high dose irradiation on the material behaviour of EUROFER and implemented in the finite element code ABAQUS, has been used. Non-linear finite element (FE) simulations of the DEMO HCPB blanket have been performed considering the design of the HCPB Test Blanket Module (TBM) as reference and the thermal and mechanical boundary conditions of previous analyses. The irradiation dose rate required at each position in the structure as an additional loading parameter is estimated by extrapolating the results available for the TBM in ITER scaling the value calculated in neutronics and activation analysis for ITER boundary conditions to the DEMO boundary conditions. The results of the FE simulations are evaluated considering damage at most critical highly loaded areas of the structure and discussed with regard to the impact of high dose irradiation on it.

Non-Destructive Tests for the Structural Assessment of a Historical Bridge over the Tua River

Paradela Bridge is a metallic bridge located along the bank of the Tua River in northern Portugal. While the bridge is not currently in service, its structure is representative of many metallic truss structures built across the continent between the XIX and the XX century. Tua Line belongs to the Douro area that UNESCO recently declared as world heritage. This study acquires its importance since it might serve as an insight for the study of many other similar structures all over the country. This paper comprises a historic investigation of archived documents, an on-site survey to evaluate its present conditions, a dynamic testing and the construction and calibration of numerical models in finite element analysis (FEA) software, structural assessment and capacity rating estimation. The purpose of constructing numerical models was to evaluate the suitability of the bridge under the original loading and in accordance to modern design standards. The historical research revealed that the truss bridge was designed as a simply supported element and that a series of hand calculations were carried out on individual structural elements (e.g. main trusses, stringers and floor beams). Furthermore, a dynamic test was conducted in order to identify the global dynamic properties of the structure and to calibrate numerical models that ensure reliability and representativeness. FE models served through the structural assessment of the bridge in accordance with modern design codes and to estimate the safety of the bridge. Likewise, a nonlinear failure analysis was also conducted in order to estimate the capacity rate of the bridge and the likely failure modes.

Nonlinear failure analysis of carbon nanotubes by using molecular-mechanics based models

Equivalent nonlinear fracture models for pristine and reconstructed one- and two-atom vacancy defected single wall carbon nanotubes are developed by using the molecular mechanics based models where the initial reconstructed nanotube models are obtained by using molecular dynamic simulations and nonlinear characteristic of the covalent bonds are obtained by using the modified Morse potential. As a result of analyses, it is concluded that fractures of all types of nanotubes are brittle, armchair nanotubes are stiffer than zigzag nanotubes and vacancy defects significantly affect the mechanical behavior of nanotubes. In brief, fracture stress and strain values of pristine armchair nanotubes are respectively 30% and 32% larger than those of pristine zigzag nanotubes, and predicted failure stress and strain values of vacancy defected nanotubes are respectively 27% and 52% smaller than those of pristine ones. It is shown that large deformation and nonlinear geometric effects are important on fracture behavior of nanotubes. Comparisons are made with the failure stress and strain results reported in literature that show good agreement with our results.

Non-linear failure analysis of HCPB Test Blanket Module

For the European Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) the reduced activation ferritic martensitic (RAFM) steel EUROFER 97 is selected as a structural material. During operation the TBM will be subjected to complex thermo-mechanical loadings which yield at certain positions of the structure to stresses beyond the design limits of the structural material. Preliminary structural analyses of the TBM have shown critical behavior in several key points of the structure. An improved design has been proposed and in order to identify and assess the problematic positions in the improved version of the TBM a non-linear failure analysis is performed, for which a coupled deformation damage model developed at KIT for RAFM steels and recently implemented in the finite element code ABAQUS is used. The thermal loads in the form of non-homogeneous temperature fields distributions are obtained from a thermal analysis performed using the finite element code ANSYS on the same structure. Importing the temperature fields into the finite element code ABAQUS and applying the remaining loads – coolant internal pressure and structural boundary conditions – non-linear simulations are conducted taking into account the ITER-typical cyclic nature of the loading. The simulation results are evaluated and discussed considering ratcheting and damage at most critical highly loaded areas of the structure.

Stochastic nonlinear failure analysis of laminated composite plates under compressive transverse loading

This paper present the second ordered statistics of first-ply failure response of laminated composite plate with random material properties under random loading. The basic formulation is based on higher order shear deformation plate theory (HSDT) with the geometrically nonlinearity in the von-Karman. The direct iterative based C 0 nonlinear finite element method combined with mean centered first order perturbation technique developed by the authors are extended and successfully applied nonlinearity for failure problem with a reasonable accuracy to predict the second order statistics (standard deviation) of first-ply failure response using Tsai–Wu and Hoffman failure criterion with macroscopic analysis. Typical numerical results for various combinations of boundary conditions, plate thickness ratios, aspect ratios, laminates scheme and layers, elastic modulus ratios have been presented to illustrate the application of developed procedure. Some new results are presented and examined which clearly demonstrated the importance of the randomness in the system parameters in the failure response of the structures subjected to transverse loadings.

Nonlinear analysis of reinforced concrete beam with/without tension stiffening effect

The aim of this paper is to do materially nonlinear failure analysis of RC beam by using finite element method. In the finite element modeling, two different approaches and different tension stress–strain models with/without tension stiffening effect are used by considering two different mesh sizes. In the first approach, the material matrices of concrete and reinforcement are constructed separately, and then superimposed to obtain the element stiffness matrix. In the second approach, the reinforcement is assumed to be uniformly distributed throughout the beam. So, the beam is modeled as a single composite element with increasing the modulus of elasticity of concrete by considering the reinforcement ratio. For these two approaches, elastic-perfectly plastic stress–strain relationship is used for concrete in compression. For the concrete in tension, a stress–strain relationship with/without tension stiffening is used. It is concluded that the approaches and the models considered in this study can be effectively used in the materially nonlinear analysis of RC beams.

Path-dependent failure analysis of RC shell structures using volume control technique

To overcome the drawbacks of conventional load control method and displacement control method, the so-called volume control method was developed by utilizing a pressure node added into a finite shell element. The pressure node has an increment of pressure as an additional degree of freedom of the shell element. In this study, the so-called path-dependent volume control method which improves the volume control method for the analysis of path-dependent behaviors of RC shell structures subjected to cyclic loading is proposed. The path-dependent volume control method is a technique which calculates control-volume change of the RC structure subjected to the cyclic loading conditions like loading, unloading, reloading for nonlinear failure analysis of RC structures and overcomes the limitation of controlling path-dependent volume change of the RC structure according to the deformational history. For the finite element failure analysis of RC shell structures using the technique, each structure is discretized with multi-layered shell elements and in-plane two-dimensional constitutive equations for concrete and reinforcements are implemented for each layer of the shell elements. The results of failure analysis for RC slab, RC tank, RC box culvert, and RC hollow columns subjected to cyclic loading as well as reversed cyclic loading using the path-dependent volume control method are verified with experimental results.

A simplified method for nonlinear failure analysis of stiffened plates

This paper shows that the application of pre-determined failure equations, derived from nonlinear finite element analyses, is effective in determining failure of structural components in a simpler linear finite element analysis. An analysis method is presented which is called simplified failure analysis. The first step of this method is the nonlinear determination of a component's failure limit. Next, a linear coarse-meshed finite element model of the component is analyzed under the failure load determined in the previous step. The resulting linear stress distribution is a ‘representative failure stress’ for the component because it is in equilibrium with the applied failure load. This ‘failure stress’ is then used in simpler linear analysis to provide a representative failure limit. This method is verified by an analysis of a structural grillage.

Failure analysis of Monastery of Jerónimos, Lisbon: How to learn from sophisticated numerical models

Conservation and restoration of historical structures are still a challenge to modem practitioners even if significant research advances have occurred in the last decades. Significant advances have been made in non-destructive testing, mechanical characterization, tools for advanced numerical analysis, knowledge on traditional materials and techniques, and innovative materials and techniques. In the paper, Monastery of Jerónimos in Lisbon, Portugal is adopted as a case study for structural safety assessment. A first discussion is held on the difficulties related to the need of adopting simplified geometries of the model. After a set of sophisticated non-linear failure analyses, a second discussion is held with respect to the consequences associated with the results obtained. Finally, additional in situ testing and monitoring are carried out in a truly iterative process of knowledge accumulation before defining any remedial measures.

Non-Linear Failure Analysis of FRP Laminates Composed of UD Laminae – a Comparison of the Author's Predictions with Test Results from the Worldwide Failure Exercise in the UK –

Non-Linear Failure Analysis of FRP Laminates Composed of UD Laminae – a Comparison of the Author's Predictions with Test Results from the Worldwide Failure Exercise in the UK –

Failure Analysis of Reinforced Concrete Shell Structures using Layered Shell Element with Pressure Node

In this paper, a finite element analysis technique is presented for the path-dependent nonlinear failure analysis of reinforced concrete shell structures. A so-called pressure node is added into a layered shell element utilizing in-plane constitutive models of reinforced concrete and layered formulation in the failure analysis. By controlling the volume of the shell structures using the pressure node, postpeak softening behavior after the ultimate load of the shell structures is obtained. Since the constitutive models cover loading, unloading, and reloading paths, the element is capable of predicting the behaviors of reinforced concrete shells under cyclic loading. For verification of the techniques in this paper, failure analyses of reinforced concrete slabs subjected to in-plane and out-of-plane loads and cyclic transverse loads are performed and numerical results are compared with experimental data. In addition, reinforced concrete dome structures designed with different reinforcement ratios are also analyzed to check the applicability of the technique in this paper. Results show that the techniques can be applied effectively to the failure analysis of various types of reinforced concrete shell structures.

Linear and non-linear failure analysis of composite laminates with transverse shear

A finite element computational procedure has been developed to find linear and non-linear (von Kármán) first-ply failure loads of composite laminates subjected to in-plane and transverse loads. The finite element model is based on first-order shear deformation theory and several phenomenological failure criteria. Linear and non-linear first-ply failure loads are computed for a uniformly distributed transverse load, a concentrated transverse load acting at the centre of the plate, and a uniformly distributed in-plane edge load for simply supported and clamped boundary conditions. It is found that the failure loads predicted by various failure criteria differ from one another by a maximum of 35% in the case of linearloads and 50% in the case on non-linear loads; the failure locations differ from each other in a random way. Furthermore, it is demonstrated that the difference between the linear and non-linear failure loads is large in the case of transversely loaded simply supported laminates and thin plates. The difference is found to be quite small in the case of in-plane (tensile) loading and thick laminates.