Failure Analysis Of Structures Research Articles

Collective effect of damage prevention in taenioglossan radular teeth is related to the ecological niche in Paludomidae (Gastropoda: Cerithioidea)

The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for food processing and gathering. For proper functioning, radular failures must be either avoided or reduced when interacting with the preferred food, as this might be of high significance for the individual fitness. Thus, the analysis of structural failure in radular teeth could be included in studies on trophic specializations. Here, we tested the failure of non-mineralized, chitinous radular teeth from taxa, belonging to an African paludomid species flock from Lake Tanganyika and surrounding river systems. These species are of high interest for evolutionary biologists since they represent a potential result of an adaptive radiation including trophic specialisations to distinct substrates, the food is attached to. In a biomechanical experiment a shear load was applied to tooth cusps with a force transducer connected to a motorized stage until structural failure occurred. Subsequently broken areas were measured and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist, could be documented. Wet teeth were able to resist higher forces, because of their increased flexibility and the flexibility of the embedding membrane, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure without the mineralisation with wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. Since the documented mechanical behaviour of radular teeth and the maximal forces, teeth resist, can directly be related to the gastropod ecological niche, both are here identified as an adaptation to preferred feeding substrates. Statement of significanceThe radula, a chitinous membrane with teeth, is the molluscan feeding structure. Here we add onto existing knowledge about the relationship between tooth's mechanical properties and species’ ecology by determining the tooth failure resistance. Six paludomid species (Gastropoda) of a prominent species flock from Lake Tanganyika, foraging on distinct feeding substrates, were tested. With a force transducer wet and dry teeth were broken, revealing the high influence of water content on mechanical behaviour and force resistance of teeth. Higher forces were needed to break wet radulae due to an increased flexibility of teeth and membrane, which resulted in an interlocking or twisting of teeth. Mechanical behaviour and force resistance were both identified as trophic adaptations to feeding substrate.

Finite element implementation and application of a sand model in micropolar theory

In traditional finite element failure analyses of geotechnical structures, the micro grain rotations cannot be modelled and numerical solutions are mesh dependent. In this study, a user element including rotational degree of freedom has been developed based on micropolar theory (Cosserat theory), then an enhanced non-associated sand model is calibrated with laboratory data and used to model the plane strain tests. The simulated results demonstrate the polarized model is able to model reasonably the sand behavior as well as the grain rotations in the localized region. What’s more, with this enhanced model, the mesh independent numerical solutions in terms of mechanical responses, shear bands thickness and orientations have been obtained.Article highlightsIn failure analysis of geostructures, significant rotations of soil grains have been observed to occur in the strain localized regions, but the current commercial Finite Element tools cannot model the micro rotations. Therefore, a user defined element must be developed to include the rotational degree of freedom. The micropolar approach is proven to be effective to model the grain rations in present paper. More suitable than other classical soil or sand constitutive models, the selected non-associated sand model in present paper is capable of describing well the contraction and shear dilatancy behaviors of sand. Then the model has been enhanced by means of micropolar technique, in this way, the reasonable strain localization phenomena in laboratory tests could be predicted well.There are always the mesh dependent problems for traditional simulations of the strain localization phenomena in finite element analysis. It can be found in present paper that the mesh independent numerical solutions are obtained by means of micropolar technique. Furthermore, the micropolar approach can obviously improve convergence difficulties in finite element analyses.

Stability and failure analysis of compressed thin-walled composite structures with central cut-out, using three advanced independent damage models

In this paper, the phenomenon of stability and failure of axially compressed thin-walled structures with central cut-out, made of composite materials, were investigated. The tested structures were made of carbon-epoxy composite material, using autoclave technique. Within the framework of the studies, experimental tests on actual constructions were carried out, as well as advanced numerical simulations using the finite element method in the ABAQUS® software. The process of axial compression of thin-walled composite structures was carried out in the full range of load, up to total failure. During the experimental tests, post-critical equilibrium paths were recorded, using the universal testing machine - Instron 4485. Additionally, acoustic emission signals were recorded using the AMSY-5 device, and the level of deformation was tested, using the non-contact three-dimensional measurement technique offered by the ARAMIS system. Simultaneously to the experimental tests, numerical calculations were carried out using progressive failure analysis (PFA), based on the damage initiation Hashin's criterion of as well as damage evolution based on the energy criterion. In the numerical analyses, the cohesive zone model (CZM) and the model allowing for the simulation of damage due to material cracking (xFEM) were also used. A significant effect of conducted numerical calculations was the simulation of the failure phenomenon of thin-walled composite structures, in terms of loss of load-carrying capacity, using three independent damage models (model PFA, CZM and xFEM). The above constitutes a novelty, with respect to current papers from the subject literature. The use of the above-mentioned techniques of experimental research and numerical simulations made it possible to conduct a comprehensive analysis of the damage state of the composite material. The obtained results of the numerical tests demonstrated very high agreement with the results of the experimental studies.

Structural performance and failure analysis of bubbledeck concrete slabs in construction

In this research paper, as the concrete material is eliminated from the locations situated around the middle of the cross-sections of bubbledecks (BDs), the BD type slabs are lighter than the traditional slabs. In the recent researches, the performance analysis (PA) is generally determined for the reinforced concrete (RC) structures with the moment-resisting frame (MRF) and dual systems. The dual system comprises mainly the MRF with shear wall of building under construction, as well as the flat slab having chiefly the BD system. In this paper, the evaluation of values of the performance and failure analysis of RC structures using BD system are submitted. We recorded a maximum load of 6.48, maximum stress of 75.00, macimum strain of 7.80, with minimum force of 0.83, while minimum slab length of 9.62 and lastly the maximum slab span of 27 for our bubbledeck concrete slab experiment in comparison with reinforced concrete slab to get the best results. The obtained results indicate that the lateral strengths of buildings increase by increasing the span length to story height ratio. Besides, the variations of the span length and the number of the story have more effects than the variation of the usage category buildings on the performance of structures. Furthermore, the span length has more effect than the number of stories in determining performance in an MRF. We observed that the bubbledeck concrete slabs are more lightweight and resistant in comparison with reinforced concrete.

Structural performance and failure analysis of bubbledeck concrete slabs in construction

In this research paper, as the concrete material is eliminated from the locations situated around the middle of the cross-sections of bubbledecks (BDs), the BD type slabs are lighter than the traditional slabs. In the recent researches, the performance analysis (PA) is generally determined for the reinforced concrete (RC) structures with the moment-resisting frame (MRF) and dual systems. The dual system comprises mainly the MRF with shear wall of building under construction, as well as the flat slab having chiefly the BD system. In this paper, the evaluation of values of the performance and failure analysis of RC structures using BD system are submitted. We recorded a maximum load of 6.48, maximum stress of 75.00, macimum strain of 7.80, with minimum force of 0.83, while minimum slab length of 9.62 and lastly the maximum slab span of 27 for our bubbledeck concrete slab experiment in comparison with reinforced concrete slab to get the best results. The obtained results indicate that the lateral strengths of buildings increase by increasing the span length to story height ratio. Besides, the variations of the span length and the number of the story have more effects than the variation of the usage category buildings on the performance of structures. Furthermore, the span length has more effect than the number of stories in determining performance in an MRF. We observed that the bubbledeck concrete slabs are more lightweight and resistant in comparison with reinforced concrete.

A preliminary analysis of late structural failures of the Navion stent graft in the treatment of descending thoracic aortic aneurysms

ObjectivePatients in the Valiant Evo U.S. and international clinical trials had positive short-term outcomes; however, late structural failures, including type IIIb endoleaks have been recently discovered. Type IIIb endoleaks are serious adverse events because the repressurization of the aneurysm sac increases the risk of rupture. The purpose of the present study was to detail the imaging patterns associated with the structural failures with the aim of increasing awareness of failing graft presentation, early recognition, and prompt treatment. MethodsThe Valiant Evo clinical trial was a prospective, single-arm investigation of a thoracic stent graft system. With the recent late structural failures, sites were requested to submit all available imaging studies to date to allow the core laboratory to assess for structural failures such as type IIIb endoleaks, stent ring fractures, and stent ring enlargement. Of the 100 patients originally enrolled in the trial from 2016 to 2018, the core laboratory assessed the imaging studies performed at ≥1 year for 83 patients. ResultsNo structural failures of the graft were reported through 1 year of follow-up. At 1 to 4 years, graft structural failures were detected in 11 patients with descending thoracic aortic aneurysms. Of the 11 patients, 5 had a type IIIb endoleak. Four of the five had imaging findings showing stent fractures consistent with the location of the graft seam and one had a type IIIb endoleak attributed to calcium erosion with no stent fracture or ring enlargement. Of the four patients with stent fracture in line with the graft seam, three underwent a relining procedure that successfully excluded the type IIIb endoleak. One of these three patients died 4 days later of suspected thoracic aortic rupture because the distal thoracic endovascular aortic repair extension had been landed in a previously dissected and fragile section of the aorta. The remaining six patients had had stent ring enlargement. One of the six patients had had persistent aneurysm expansion from the time of implantation onward and had died of unknown causes. The remaining five patients have continued to be monitored. ConclusionsIn the present preliminary analysis, the imaging patterns associated with type IIIb endoleaks, stent fractures, and stent ring enlargement appear to be related to the loss of seam integrity or detachment of the stent rings from the surface of the graft material. The imaging patterns we have detailed should be closely monitored using computed tomography angiography surveillance to allow structural failures to be promptly identified and treated.

Failure analysis of thin-walled composite structures using independent advanced damage models

The aim of the study is to present a complex phenomenon of damage in thin-walled composite structures with an top-hat cross-section subjected to axial compression. Actual structures were prepared using the auto-clave technique (CFRP composite). Research was conducted in a full range of load – until construction damage. In the case of experimental testing both post-critical equilibrium paths and acoustic emission signals were recorded. Numerical simulations were realised using progressive fracture analysis (PFA) and cohesive zone model (CZM). Such approach allowed one to assess the loss of load capacity along with demonstrating the delamination phenomenon. A measurable effect of the experimental-numerical research was presenting the influence of axial compression on post-critical behaviour of the structure and damage phases.

Failure analysis and prevention of metallic structures and components from NPP: case study

Scopul studiului a fost analiza unei tije filetate din suspensia elastică a conductelor de apă brută de la CNE Cernavodă pentru a stabili cauzele care au dus la ruperea acesteia. Pentru analiza defecțiunilor, suprafața de rupere a tijei filetate a fost investigată folosind urmatoarele tehnici de laborator: microscopie optică, microscopie electronică de scanare / dispersie […]

INTEGRATED COMPUTATIONAL MATERIAL SCIENCE ENGINEERING LIFING MODEL OF CMC COUPONS USING NANO-MICROMECHANICS BASED MULTISCALE PROGRESSIVE FAILURE ANALYSIS

The overall objective of this effort was to provide theoretical prediction for damage development for a set of laminated composites using AlphaSTAR Technology Solutions' (ATS's) commercial code GENOA (GENeral Optimization Analyzer) for the Air Force Research Laboratory (AFRL) program entitled "Assessment of Damage Progression Models for SiC/SiC Ceramic Matrix Composites (CMC Lifing Program)." Damage progression and prediction for advance ceramic matrix composite (CMC) benchmarks were done under static, fatigue, and creep service loading using test data from AFRL. Emerging and innovative multiscale (MS) modeling using computational structural mechanics (CSM) and progressive failure analysis (PFA) were proven to address the Air Force's vision to perform predictive evaluation of CMC materials using a building block validation strategy and certification process. Two different material systems and multiple layups were tested for both unnotched and notched configurations and at elevated temperatures. Calibration of the fiber and matrix properties was performed using in plane test data. The static, fatigue, and creep recalibration simulations of strength showed an average error of less than 10% between the simulation and test data. For stiffness the percent difference was found to be within 10% on average as well. All simulations used the same set of inputs (constituents, voids, fiber/matrix interphase, microcrack density, etc.) except for the noted analysis setting differences between blind and recalibration simulations. The method is consistent and follows a building block simulation approach that has an advanced yet simplistic theoretical multiscale progressive failure analysis (MS-PFA) approach.

The plastic dynamics and failure analysis of ship broadside protection structures subjected to contacted UNDEX: energy dissipation model and simulation

ABSTRACT The plastic dynamic response and failure modes of ship broadside protection structures (SBPSs) subjected to contacted underwater explosion (UNDEX) are investigated. A novel engineering analytical model is proposed to evaluate the failure mechanisms and energy absorption characteristics. A numerical model considering the fluid-structure interaction (FSI) is built to analyze the plastic dynamic responses. The results show that the main energy dissipation parts of the SBPS are outside panel, separate bulkhead and inner expandable bulkhead. The maximum error between the analytical model and numerical results is 28%. Parametric studies show that charge position has a significant effect on the damage severity. The difference in the crevasse size can reach up to 40%. The selection of the thickness for shock wave venting bulkhead outside plate and bulkhead stiffener is most important, which coincides with the theoretical solution. The above method could provide worthy guidance to the design of the energy-absorbing structure of underwater weapons defense cabin of naval ships.

A Self-Test Method of Structural Failures of Uncooled Infrared Focal Plane Array

Defective pixels always exist in an uncooled infrared focal plane array (IR FPA), and have a significant impact on image quality. To fundamentally reduce defective pixels and improve IR FPA's reliability, failure analysis (FA) is critically needed. In this work, a self-test (ST) method is proposed to detect the structural failures of uncooled IR FPA. Based on the lumped thermal parameters of a pixel, a structural failures model is presented, and an electrical circuit is designed. The insufficient released, normal released, over released and contaminated IR FPAs are measured. The measured results show that their lumped thermal parameters have a clear differentiation, which not only experimentally verifies the validity of this method, but also shows that it is an effective method for nondestructive analysis of structural failures.

A novel mode-dependent and probabilistic semi-discrete damage model for progressive failure analysis of composite laminates - Part I: Meshing strategy and mixed-mode law

A novel semi-discrete damage model (SD2M) is proposed for the progressive failure analysis (PFA) of composite structures. The presented method utilizes a separation of fiber and matrix failure modes and introduces a material strength distribution to thin strips of matrix-splitting elements in order to capture the progression of transverse crack density. With the proposed meshing strategy, the discreteness is greatly enhanced, while the model remains efficient and simple by using solely continuum elements. The SD2M approach aims to unify desirable features of both smeared and discrete methods and utilizes a practical and simple mesh generation procedure. In addition, a novel mixed-mode law is proposed to capture the damage evolution of matrix cracks. The proposed mixed-mode formulation ensures smooth and simultaneous vanishing of traction components and is suitable for generic softening laws. Applications of SD2M to several examples are presented in part II [1] of this two-part paper.

A New Approach for the Evaluation of Structural Failure by Credibility Distribution

Aim: To devise an effective structural failure analysis approach under uncertainty. Background: In reliability evaluation, plenty of factors are uncertain, or sometimes, spontaneously represented via linguistic expressions, and as a consequence, the traditionalist appraisal methods cannot capably handle the ambiguity and vagueness that occurs in reliability assessment components. Subsequently, this leads to the problem of tremendous computationally multifaceted and scanty correctness. Objective: To overcome the limitations and to develop efficiency as well as accuracy in structural failure evaluation techniques, an attempt has been made to devise a novel structural reliability assessment method via credibility distribution. Methods: To get rid of the problems of massive computationally difficult and inadequate precision, an algorithm has been devised using credibility sampling. To exhibit the novelty, validity, and applicability of the present approach, some structural failure assessment problems are solved along with a comparison with the existing approach. Results: The proposed method was verified by four examples and applied in structural analysis. It was observed that the present approach is technically sound and efficient; it can overcome all the drawbacks of the existing approach. Moreover, the approach can be executed in any uncertain situation. Conclusion: After evaluation of failure assessment, it is experienced that the increase in the number of simulations leads to better precision. Furthermore, it is encountered that when hybridization problems i.e., representation of imprecise components in the problem of structural failure, are both fuzzy and probabilistic nature, then the failure assessment is attained to be maximum.

Effect of build thickness and geometry on quasi-static and fatigue behavior of Ti-6Al-4V produced by Electron Beam Melting

The geometry and material properties of additively manufactured (AM) parts are closely related in a way that any alteration in geometry of the part will change the underlying manufacturing strategy. This in turn, affects the microstructure and consequently, the mechanical behavior of material. This paper aims to evaluate the effect of the AM part’s thickness and geometry on microstructure, surface roughness, and mechanical properties under quasi-static and fatigue loading conditions by performing experimental tests. A series of Ti-6Al-4V specimens with three different thicknesses and two different geometries were fabricated using electron beam melting (EBM). The results of microstructural analyses revealed that specimens with lower build thickness experience finer grain size, higher microhardness, and lower elongation at failure. Although the microstructure of the produced parts was strongly affected by the build thickness, different surface to volume ratios eliminated the effect of microstructural differences and governed the fatigue properties of the parts. The size effect on the microstructural features, geometrical appearance, mechanical properties of the AM parts should be considered for the design and failure analysis of complex structures.

Local Finite Element Refinement for Accurate Dynamic Stress via Modal Information Only

Accurate stress responses are the basics for failure analysis of aerospace structures, but they still can be challenging in numerical simulations for dynamic systems. This work exploits the stress mode shapes (SMSs) in local finite element (FE) refinement for the purpose of accurate dynamic stress estimation. Toward structural FE modeling, identification of critical locations via predominant SMSs is theoretically demonstrated. To pursue more accurate dynamic stress, a strategy for local FE refinement is proposed by using the information from stress modal analysis. The strategy involves a two-step procedure. First, modal participation factors (MPFs) are used to extract the predominant modes. Second, retained SMSs are evaluated for the local remeshing. Numerical simulations of a representative thin plate with geometric details were conducted. The SMSs were investigated in detail. Together with MPFs, SMSs can help to localize the dangerous stresses and then refine the local meshes to accurately calculate stress responses. By taking full advantage of numerically obtained SMSs, local structural FE modeling can be applied in a straightforward way with high efficiency. Results indicate that SMSs can reveal the underlying mechanism that governs the overall dynamic stress response.

Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 1) – without passive fire protection

ABSTRACT The aim of this paper is to present a fire test database on the collapse of a full-scale steel stiffened plate structure without passive fire protection under lateral patch loading. Steel plate panels of an as-built 1900 TEU containership in compliance with test facility in a maximum size and capacity were considered as a reference structure, with principal dimensions of 7 m long and 4.8 m wide fitted with two transverse frames and seven longitudinal stiffeners. Lateral patch loading was applied using two loading actuators at the centre of each transverse frame. A fire test was conducted in a furnace fuelled by liquefied petroleum gas, where the maximum gas cloud temperature inside the furnace was increased up to 800°C during testing. Time history of the lateral deformations of the test structure was measured with the focus on a critical period of time until the structure reached the ultimate limit state (or collapse) after the fires started. Details of the test database are documented, which will be useful for validating computational models for structural failure analysis in fires.

A combined theoretical-experimental approach for modelling ductile fracture of cold-reduced G450 steel sheet

A thermodynamics-based coupled damage-plasticity model for high strength cold-reduced steel is developed on the basis of a generic form, allowing the use of any yield criterion and damage evolution rule. The model possesses essential features of ductile failure, including large plastic deformation prior to fracture and the effects of both triaxiality and Lode angle on the failure. In conjunction with theoretical development, experimental work for both furthering the understanding of ductile fracture in high strength cold-reduced steel and validation of the proposed model under different loading conditions is also performed. In particular, advanced non-contact measurement techniques based on Digital Image Correlation (DIC) are used not only for characterising the material failure/data in both pre- and post-peak phases but also for calibration of parameters and validation of the proposed model. While the pre-peak hardening responses with homogeneous deformation can be described by a nonlinear hardening rule, in the post-peak regime, localisation of deformation before complete fracture requires the use of energy in both characterisation of the material failure and calibration of the model. In this sense, the essential work of fracture obtained from the experiments is linked with parameters controlling the fracture of the material and also used for a simple regularisation technique based on the concept of smeared deformation. The model responses are validated against experimental data in terms of both macro responses and evolving failure patterns, demonstrating good potential for applications in failure analysis of structures made of high strength cold-reduced steel.

Structural Failure Analysis of Building E ITERA Due to The Pounding Effect with Non-Linear Time History

[EN] Lampung, a province where Institut Teknologi Sumatera (ITERA) is located, is an area that has a high level of seismicity. This research takes a case study of the Building E ITERA which has a dilatation building concept. Due to dilatation, inter-buildings have the risk of collisions because of earthquake loads. The purpose of this study is to determine the value of joint displacement in adjacent buildings when given a dynamic load of Time History and determine whether the adjacent buildings experience a pounding effect. A Time History earthquake load data that has been matched with the Lampung region response spectrum by software is applied to the model of Building E. Building E is modeled according to the as built drawing data and the results of field checking. Structure is analyzed using software. The results of the study showed that the structure of the Building E which was loaded by Loma Prieta earthquake that has been matched would experience inter-building collisions. Further research using earthquake record data taken in areas within certain radius from ITERA is need to be conducted to obtain more accurate results.

Discrete and continuous approaches for the failure analysis of masonry structures subjected to settlements

Discrete and continuous approaches for the failure analysis of masonry structures subjected to settlements

Progressive Failure Analysis of Thin-Walled Composite Structures Verified Experimentally.

The subject of the presented research was a thin-walled composite column made of CFRP (carbon-epoxy laminate). The test sample had a top-hat cross-section with a symmetrical arrangement of laminate layers [90/−45/45/0]s. The composite structure was subjected to the process of axial compression. Experimental and numerical tests for the loss of stability and load-carrying capacity of the composite construction were carried out. The numerical buckling analysis was carried out based on the minimum potential energy criterion (based on the solution of an eigenvalue problem). The study of loss of load-carrying capacity was performed on the basis of a progressive failure analysis, solving the problem of non-linear stability based on Newton-Raphson’s incremental iterative method. Numerical results of critical and post-critical state were confronted with experimental research in order to estimate the vulnerable areas of the structure, showing areas prone to damage of the material.