Prediction Of Failure Modes Research Articles

Experimental and Theoretical Study on High Strength Steel Extended Endplate Connections After Fire

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.

A numerical procedure for failure mode detection of masonry arches reinforced with fiber reinforced polymeric materials

In this paper a mechanical model of masonry arches strengthened with fibre-reinforced composite materials and the relevant numerical procedure for the analysis are proposed. The arch is modelled by using an assemblage of rigid blocks that are connected together and, also to the supporting structures, by mortar joints. The presence of the reinforcement, usually a sheet placed at the intrados or the extrados, prevents the occurrence of cracks that could activate possible collapse mechanisms, due to tensile failure of the mortar joints. Therefore, in a reinforced arch failure generally occurs in a different way from the URM arch. The numerical procedure proposed checks, as a function of an external incremental load, the inner stress state in the arch, in the reinforcement and in the adhesive layer. In so doing, it then provides a prediction of failure modes. Results obtained from experimental tests, carried out on four in-scale models performed in a laboratory, have been compared with those provided by the numerical procedure, implemented in ArchiVAULT, a software developed by the author. In this regard, the numerical procedure is an extension of previous works. Although additional experimental investigations are necessary, these former results confirm that the proposed numerical procedure is promising.

Modelling and simulation methodology for unidirectional composite laminates in a Virtual Test Lab framework

A reliable virtual testing framework for unidirectionally laminated composites is presented that allows the prediction of failure loads and modes of general in-plane coupons with great realism. This is a toolset based on finite element analysis that relies on a cohesive-frictional constitutive formulation coupled with the kinematics of penalty-based contact surfaces, on sophisticated three-dimensional continuum damage models, and overall on a modelling approach based on mesh structuring and crack-band erosion to capture the appropriate crack paths in unidirectional fibre reinforced plies. An extensive and rigorous validation of the overall approach is presented, demonstrating that the virtual testing laboratory is robust and can be reliably used in for composite materials screening, design and certification.

MARSTRUCT benchmark study on nonlinear FE simulation of an experiment of an indenter impact with a ship side-shell structure

This paper presents a benchmark study on collision simulations that was initiated by the MARSTRUCT Virtual Institute. The objective was to compare assumptions, finite element models, modelling techniques and experiences between established researchers within the field. Fifteen research groups world-wide participated in the study. An experiment involving a rigid indenter penetrating a ship-like side structure was used as the case study. A description of how the experiment was performed, the geometry model of it, and material properties were distributed to the participants prior to their simulations. The paper presents the results obtained from the fifteen FE simulations and the experiment. It presents a comparison of, among other factors, the reaction force versus the indenter displacement, internal energy absorbed by the structure versus the indenter displacement, and analyses of the participants' ability to predict failure modes and events that were observed in the experiment. The outcome of the study is a discussion and recommendations regarding mesh size, failure criteria and damage models, interpretation of material data and how they are used in a constitutive material model, and finally, uncertainties in general.

Prediction of Failure mode of thin FRP laminate under Thermal Loading

The present work deals with the prediction of failure mode in thin FRP laminates under uniform temperature. The failure occurs either in static or in buckling mode for a thin FRP laminate. A 2-D finite element method that works on classical lamination theory is employed to analyze the structure which in the form of a thin rectangular plate. The problem is modeled in commercial software ANSYS version 12. Effect of plate in-plane aspect ratio (a/b), Fiber stacking sequence ((i) symmetric cross ply, (ii) Quasi-isotropic, and (iii) symmetric angle ply with 450 angle) on mode of failure is studied for three different composite materials ((i) E-Glass/Epoxy with Vf = 0.55, (ii) Kevlar 49/Epoxy with Vf = 0.60, and (iii) Carbon/Epoxy bidirectional fabric with Vf = 0.62).

Reproducing Failure Mode and Life Prediction of Expansion Joint Using Field Data

In this study, among plant equipment, valve and piping fitting which is vulnerable to waterhammer was selected for diagnosis. Impulsive vibration by waterhammer was measured and applied to HIL simulator as operation data using HILS method for reproducing failure mode and life prediction of them. For effective measuring vibration, accelerometer was adapted for in the poor surroundings. Measurement results shows max. peak-to-peak vibration displacement was 21.40 mm caused by waterhammer on the valve etc., which could affect structure stability of plant equipment. After that, using the acquired data, the vibration durability of the expansion joint was tested. Meanwhile, in the case of vibration durability, internal pressure in the expansion joint was proposed as main stress factor of durability life, life prediction model was induced by curve fitting along with the datum at each pressure and verified. Thus, a further study will develop mixed life prediction model which will contain another stress factor such as temperature.

Time-Domain Modeling of All-Digital PLLs to Single-Event Upset Perturbations

A uniform technology-agnostic time-domain model for both linear and nonlinear all-digital phase-locked loops (ADPLLs) is presented. This time-domain model can be used for single-event upset (SEU)-induced perturbation time prediction and SEU sensitivity characterization of common ADPLL topologies. The model is validated against field-programmable gate array-based fault injection experiments and two photon absorption laser experimental results on three different types of designs. The model is applicable to rad-harden by design activities, failure mode predictions, and general ADPLL design optimizations.

Parametric Study on Mixed Torsional Behavior of U‐Shaped Thin‐Walled RC Girders

Nowadays, U‐shaped thin‐walled concrete girders have been widely applied in the urban construction of rail viaducts in China as well as worldwide. However, the mixed torsional behaviors of these structures are not well understood. In this paper, the mixed torsional behaviors of the U‐shaped thin‐walled RC girders are theoretically analyzed, and a method predicting failure modes and ultimate torques is proposed. Nonlinear FE models based on ABAQUS to simulate the mixed torsional behaviors are built and calibrated with the test results. Parametric studies considering three crucial parameters (boundary condition, span length‐section height ratio, and ratio of longitudinal bars to stirrups) are conducted based on both the above suggested calculating method and the FE modeling. The calculated and the simulated results agree well with each other and with the test results. It is found that the failure modes of the U‐shaped thin‐walled RC girders under torsion are influenced by all the three parameters. Three kinds of failure modes are observed: flexural failures dominated by warping moment, shear failures caused by warping torque and circulatory torque, and flexural‐shear failures in the cases where flexural failure and shear failure appear almost at the same time.

Predicting bond behavior of HB FRP strengthened concrete structures subjected to different confining effects

This paper presents an analytical model to predict the bond behavior of hybrid bonded (HB) fiber reinforced polymer (FRP) strengthened concrete structures considering different confining effects. The bond strength of HB-strengthened concrete structures subjected to uniaxial loading is attributed to the friction-type bond from steel plate and the chemical bond provided by epoxy-based resin. The friction-type bond is assumed to develop before any interfacial slip occurs, and remain constant when the interfacial slip is nonzero; for the chemical bond between FRP and concrete, a tri-linear bond-slip relation is adopted. The loading process of HB-strengthened structures consists of three stages, and the stage-wise solution to slip, bond stress, and axial force of HB FRP are derived based on a governing ordinary differential equation (ODE). In this study, the experimental program includes twelve HB-strengthened concrete specimens, using different confining effects (twisting moments on the steel bolts). Test results indicated that the ultimate pullout strength increases and the failure mode switches from debonding to FRP rupture as the twisting moment increases. Moreover, by comparison to three series of experimental results, the proposed model can precisely predict failure mode, ultimate strength, load-slip relation and bond stress distribution. The twisting moment on bolts is found to have the most significant improvement on the ultimate tensile strength. Finally, the critical twisting moment without yielding FRP rupture is derived.

Design of Experiments Approach to Evaluating the Reliability of System-in-Package Assemblies

Abstract Reliability in microelectronic packaging has been, and will continue to be, a major concern that must be taken into account early in the design of a package. System-in-package (SiP) assemblies, as well as other high density packaging technologies, are being used in many system architectures in order to incorporate a high level of integration, reduce cost and fit on tighter next higher assembly (NHA) grid spacing. While these technologies are being adopted into system architectures, there is limited test data on the reliability of these packages in military applications. A better understanding of the impacts of design variables in a SiP assembly allows the design community to determine the most appropriate packaging solution for use in a given application. The term “system-in-package” covers a wide range of microelectronic packaging technologies. Microelectronic packaging technology is trending towards taking the SiP concept and incorporating a very high level of integration within as small of a footprint as possible. In many cases, a fan out design technique is used in order to utilize die with high density bump patterns and then use an interposer technology to increase the bump pitch to match pitches achievable on NHA board technologies. While increasing the packaging density appears beneficial in theory, its reliability becomes a risk as the complexity of the assembly increases and more interfaces are added. Mechanical and structural considerations must be taken into account when designing this type of assembly in order to limit the stresses observed in the assembly, especially when exposed to environmental conditions. This study will focus on traditional two dimensional (2D) integrated circuit (IC) designs. For the purposes of this study, a 2D IC package will be considered as multiple die attached to a SiP substrate via flip-chip bumps. These SiP assemblies will in turn be attached to a test circuit board via solder bumps, which are at a larger pitch relative to the flip-chip bump patterns. A daisy-chain circuit design was incorporated into the test board and die in order to evaluate the reliability of the assembly interconnects at various points throughout the assembly. Design variables such as underfill material, SiP substrate material and flip-chip bump density were incorporated into a design of experiments in order to evaluate their impact on the reliability of a SiP assembly. The materials selected for use in this testing allow for the evaluation of the impacts of coefficient of thermal expansion (CTE), modulus and other material properties on the reliability of a SiP assembly. Reliability of the assemblies was tested via temperature cycling and biased humidity testing. Successful reliability of each test was dictated by the continuity of the daisy chain circuits throughout testing, as well as a visual examination of the interconnects after test. Samples of each assembly design configuration were used in cross sectional analysis to further examine the effects of the reliability on the assembly. Material characterization techniques such as scanning electron microscopy (SEM) and focus ion beam scanning electron microscopy (FIB-SEM) were used, as necessary, to investigate failure modes. This paper will review a design of experiments study of SiP assemblies and present the results of reliability testing on various SiP assembly designs. Further study is suggested for the use of these results in developing and refining finite element models capable of accurately predicting failure modes in SiP assemblies.

A new discrete macro-element in an analytical platform for seismic assessment of unreinforced masonry buildings

This paper proposes a practice-oriented platform for numerical simulation of Unreinforced Masonry (URM) buildings. It is based on introducing a new two-dimensional discrete model compatible with most existing structural analysis softwares. The proposed platform comprises of two individual two-dimensional macro-elements, a basic macro-element for modeling the piers and spandrels and a rigid-interface macro-element for modeling the nodal regions. A complete set of constitutive equations and behavioral specifications is proportionally characterized and discussed for the basic macro-element based on its phenomenology and the past experimental studies. The proposed approach provides a rather simple and efficient platform for linear or nonlinear static and dynamic analyses by considering the in-plane behavior of the URM panels. The validation of the proposed analytical platform is conducted using the results of the past experimental tests on a considerable number of piers, spandrels and a perforated wall. The comparisons indicate that the predicted failure mode and hysteretic behavior as well as the ultimate strength and displacement capacity of these specimens are in a satisfactory agreement. In particular, derivation and interpretation of the results in the proposed approach are straightforward and simple; hence, engineers can use this approach for seismic design or retrofit studies. The proposed platform can be further developed and effectively used for modeling a large building or numerous buildings.

Predicting failure modes in creep and creep-fatigue crack growth using a random grain/grain boundary idealised microstructure meshing system

An idealised microstructure mesh model combined with a novel creep and creep-fatigue damage accumulation model was employed to simulate crack growth behaviour under creep/fatigue conditions for a modified 9Cr-1Mo steel. The influence of microstructures on the crack growth behaviour was studied using a random grains separated by idealised grain boundaries. For accurately representing the damage accumulation in creep-fatigue regime, a non-linear damage model was employed. In this case, creep damage was determined by multiaxial ductility exhaustion approach and fatigue damage was reliant on maximum stress and plastic range ahead of crack tip per loading cycle. When creep dominated, cracks mainly propagated along grain boundaries in steady crack growth stage. As an exception, the crack growth in the tertiary crack growth stage gradually changed from intergranular to mixed model and finally transgranular fracture. In contrast, in creep-fatigue regime, the crack growth behaviour was greatly reliant on the dwell time. For short duration period, the crack mainly propagated in a transgranular manner. But as the dwell time increased to greater than 600s, the creep intergranular fracture dominated once again. Furthermore, the grain size gradient had little influence on the crack growth model and only affected the fracture life in creep and creep-fatigue regimes.

Simulation of Mechanical Behavior and Damage of a Large Composite Wind Turbine Blade under Critical Loads

Issues such as energy generation/transmission and greenhouse gas emissions are the two energy problems we face today. In this context, renewable energy sources are a necessary part of the solution essentially winds power, which is one of the most profitable sources of competition with new fossil energy facilities. This paper present the simulation of mechanical behavior and damage of a 48 m composite wind turbine blade under critical wind loads. The finite element analysis was performed by using ABAQUS code to predict the most critical damage behavior and to apprehend and obtain knowledge of the complex structural behavior of wind turbine blades. The approach developed based on the nonlinear FE analysis using mean values for the material properties and the failure criteria of Tsai-Hill to predict failure modes in large structures and to identify the sensitive zones.

A simplified approach to assess the size effect on the shear-flexure interaction in RC elements

Following the concept of design capacity, the main purpose of the structural design of RC elements is to avoid brittle failures and to ensure ductile behavior. Under cyclic loading, the shear strength is reduced by increasing the flexural ductility. A good estimation of the failure mode of RC elements exhibiting a shear-flexural interaction relies on a good estimation of the flexural capacity (strength and ductility) and the shear capacity. In the present paper, a simplified model is proposed to describe the flexural behavior. The size effect is taken into account for the assessment of the flexural ductility. On the other hand, based on a comparative study of existing shear capacity models, a shear capacity formula is proposed to evaluate the shear strength and the shear reduction. The failure mode prediction is assessed following the ATC (Applied Technology Council) conceptual model. Comparison with experimental tests shows the ability of the proposed approach to predict the failure mode and the corresponding ductility.

Strut-and-Tie Model for seismic design of confined masonry buildings

The Strut-and-Tie-Model (STM) of a confined masonry wall, with or without opening, consists of an equivalent system, in which the masonry wall is modelled as compression struts and the reinforced concrete (RC) confining elements are modelled as is (i.e., as present in the wall). Tension ties are ignored owing to the negligible tensile strength of masonry. Although the joints of tie-column and tie-beams are not intended for moment resisting, these are yet treated as the moment resisting in numerical model to avoid instability. Consequently, a typical compression strut is connected to the joints at either end with moment released. Purpose of this paper is to outline the guidelines for developing STMs for seismic design of confined masonry wall panels, including single- and multi-storey wall panels with and without openings. Behaviour of two single-storey adjacent panels with or without openings, are also considered. Although the main objective is to develop STMs for walls subjected to lateral seismic loading, the effect of gravity load has been also considered in the analysis. Well distinct STM configurations are noted for the single storey panels. STM for adjacent wall panels and multistorey wall are shown to be arrived at from that of the individual single storey panels. Throughout this paper, the masonry is modelled using equivalent properties and hence, the effect of relative variation of mortar and brick properties are not adequately captured. This may have considerable influence on the resulting STM configurations. Although STM should be evolutive in nature enabling prediction of different failure modes of CM walls, the scope of the analytical model in this paper is limited to the linear-elastic analysis and hence, the strut orientation is likely to be altered as the building ventures into the inelastic regime. Nevertheless, the STM proposed in this paper may be used as the basis of developing such an evolutive model enabling a displacement based design framework of confined masonry buildings.

Reply to Giannakos, K. Comment on: Toughness of Railroad Concrete Crossties with Holes and Web Openings. Infrastructures 2017, 2, 3

This paper responds to the discussion [1] by Dr. K. Giannakos over our technical note [2].[...]

Managing risk in modular construction using dimensional and geometric tolerance strategies

Abstract The accumulating effects of dimensional and geometric variability in modular construction have traditionally been managed using trial and error strategies and use of standardized tolerance values for similar stick-built construction scenarios. This approach often leads to site-fit rework and increase in project risk, since dimensional and geometric variability is more problematic in modular construction than stick-built construction due to module interfacing and erection on site. To address this persistent challenge within modular construction, this article presents a framework for an optimal design of dimensional and geometric variability through the use of comprehensive tolerance strategies by minimizing both fabrication costs and project risks. A methodology for developing tolerance strategies in modular construction is introduced and demonstrated using a case study on an industrial pipe chassis module. The proposed methodology links a structural analysis framework which aims to predict the performance of various assembly configurations to construction costs and various types of project risks. While structural analysis techniques mainly aim to predict failure modes and mechanisms of assemblies, this research aims to further enhance such models by adding risk and cost measures to the structural analysis models. This methodology aims to manage dimensional and geometric variability by the goal of reducing rework and decreasing project costs by providing a set of Pareto-optimal design solutions ranging from strict to lose tolerance control with respect to an amalgamated cost for module production and project risk. This allows the stakeholders, engineers and construction managers to better understand the trade-offs between fabrication costs and alignment, rework, safety, and transportation risks (in terms of cost) of modules, and therefore enhance the planning and design phases of modular construction.

Ring Attractor Dynamics Emerge from a Spiking Model of the Entire Protocerebral Bridge.

Animal navigation is accomplished by a combination of landmark-following and dead reckoning based on estimates of self motion. Both of these approaches require the encoding of heading information, which can be represented as an allocentric or egocentric azimuthal angle. Recently, Ca2+ correlates of landmark position and heading direction, in egocentric coordinates, were observed in the ellipsoid body (EB), a ring-shaped processing unit in the fly central complex (CX; Seelig and Jayaraman, 2015). These correlates displayed key dynamics of so-called ring attractors, namely: (1) responsiveness to the position of external stimuli; (2) persistence in the absence of external stimuli; (3) locking onto a single external stimulus when presented with two competitors; (4) stochastically switching between competitors with low probability; and (5) sliding or jumping between positions when an external stimulus moves. We hypothesized that ring attractor-like activity in the EB arises from reciprocal neuronal connections to a related structure, the protocerebral bridge (PB). Using recent light-microscopy resolution catalogs of neuronal cell types in the PB (Lin et al., 2013; Wolff et al., 2015), we determined a connectivity matrix for the PB-EB circuit. When activity in this network was simulated using a leaky-integrate-and-fire model, we observed patterns of activity that closely resemble the reported Ca2+ phenomena. All qualitative ring attractor behaviors were recapitulated in our model, allowing us to predict failure modes of the putative PB-EB ring attractor and the circuit dynamics phenotypes of thermogenetic or optogenetic manipulations. Ring attractor dynamics emerged under a wide variety of parameter configurations, even including non-spiking leaky-integrator implementations. This suggests that the ring-attractor computation is a robust output of this circuit, apparently arising from its high-level network properties (topological configuration, local excitation and long-range inhibition) rather than fine-scale biological detail.

Constitutive representation and damage degree index for the layered rock mass excavation response in underground openings

In this study, a layered rock mass was regarded as a composite material, composed of interlayered intact rocks and bedding planes. Based on this assumption, we developed a transversely isotropic elastic–plastic model to describe the elastic response and post-peak failure behavior based on the Mohr–Coulomb and maximum tensile-stress criteria. Then, we proposed a damage index to estimate the damage degree of layered rock mass during excavation based on the developed model. The numerical simulation of the conventional uniaxial tests indicated that the failure mode and strength predictions of the model were in well agreement with the physical model test results. The index distribution was also shown to be more effective than the plastic zone distribution in identifying layered rock mass failure. The combined application of the mode and the index to assess the stability of the rock mass around the diversion tunnels at the Wudongde hydropower station in China showed that they could accurately estimate the locations and the depth of the potential collapses. Therefore, they are of significant practical value in the stability evaluation of layered rock mass surrounding underground openings.

Prediction of size-dependent fatigue failure modes by means of a cyclic cohesive zone model

Cyclic cohesive zone models offer the ability for a unique modelling of fatigue. The local damage processes occurring inside the cohesive zone manifest themselves macroscopically between two limiting cases of failure mode: uniform debonding and fatigue crack growth. In this study, we introduce a length ratio between the structural dimensions and the characteristic material length contained in the cohesive law. At the example of a modified double cantilever beam specimen, it is shown that this length ratio explains the size effect and the failure mode at the macroscopic scale. The analytically and numerically obtained results are plotted in failure maps, which show the predicted fatigue behaviour of the considered material in dependence on two loading parameters: nominal stress and J-integral. A cyclic failure assessment diagram (CFAD) is elaborated and the relationship to the well-known Kitagawa-Takahashi-Diagram is demonstrated. This way, cyclic cohesive zone models link classical failure assessment concepts of fracture mechanics and structural durability.