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This work presents a viscoelastic in-plane damage model for fibrous composites. The material behavior is modeled as linear viscoelastic, with brittle failure in the fiber-dominated direction, and progressive degradation of the matrix-dominated properties, when the composite is loaded perpendicularly to the fibers or in in-plane shear. An evaluation procedure has been performed by comparing computational stress-strain curves against tensile tests curves under three different displacement rates. In addition, a calibration of the viscoelastic properties, by means of the response surface methodology, is also presented. The proposed material model has shown reasonable performance up to the material reaching an experimentally-verified modulus transition zone. Besides, the viscoelastic calibration procedure has produced a good agreement with the experimental results, concerning maximum stresses. It was observed that the computational stress-strain curve has deviated from the experimental one for higher stress values, indicating that it is necessary to improve the assessment of the nonlinear phenomena, which occur within the material.

Resumo Fundamento Nos últimos anos, o recente aumento no número de procedimentos intervencionistas tem resultado em crescente preocupação em relação à exposição radiológica por pacientes e equipe médica. A avaliação da exposição dos níveis de radiação em crianças é difícil devido à grande variabilidade no peso corporal. Portanto, os valores de referência de radiação não estão bem definidos para essa população. Objetivos Avaliar e validar a razão do produto dose-área (DAP) em relação ao peso corporal como uma medida de referência de radiação em cateterismos cardíacos em crianças. Métodos Estudo multicêntrico observacional com dados do Registro Brasileiro de Cateterismo Cardíaco em Cardiopatias Congênitas (CHAIN) de março de 2013 a junho de 2014. Os critérios de inclusão foram: pacientes

The usage of composite materials on new design structures is still very conservative, mainly due to its very complex failure behavior. Thus, the prediction of these mechanisms requires the development of more accurate damage models. Therefore, a damage model based on CDM concepts is applied in order to predict intra-ply failure mechanisms in impacted carbon-epoxy laminate structures. The damage model was implemented as VUMAT (User Material Subroutine for explicit integration analyses) and linked to ABAQUS™. Several numerical analyses were performed, and the results were compared to experimental tests in order to evaluate the potentialities and limitations of the damage model application.

The EC HYPOS (HYdro-POwer-Suite) project (https://hypos-project.eu/) has the main goal of assessing the environmental impact of existing and future hydropower systems. The project will provide a suite of data analysis applications which integrates Earth Observation (EO) technologies and hydrological modelling. These include an online Decision Support Tool (DST) for investment planning and monitoring, as well as a subscription portal combining satellite data over time, current measurements and detailed estimates for present and near future assessments. A dedicated analysis on the “blue footprint” (i.e. the amount of water used to produce a service) of reservoirs is included for addressing sustainable monitoring solutions. Such analysis comprises the evaluation of the climate change effects on reservoirs management and hydropower production. For instance, extreme weather events like short-term heavy precipitations are connected with flooding and transport of large amounts of sediments in dammed reservoirs, with critical consequences for their management. Similarly, global warming can heat the surface of water bodies and induce higher evaporation rates, thus decreasing the amount of water available for energy production. In this study we present the first products from HYPOS project. These products are representative of what can be generated within the DST using elaboration techniques of EO data. Gridded products of water quality parameters (e.g. water turbidity, Chlorophyll-a concentration, suspended sediments concentration) are generated for the test sites of the project, which are small dammed reservoirs located in Switzerland, France, Albania and Georgia. These products are obtained using the Modular Inversion and Processing System (MIP), a sensor independent image processing chain based on radiative transfer models, which works in a multi-layer system, solving the light transfer in the atmosphere, at the water surface and inside the waterbody.For the assessment of the “blue footprint” of a reservoir, the water loss due to evaporation is computed by applying a consolidated mass transfer evaporation method to EO data. The resulting evaporation rates are first compared with the outputs of semi-automatic evapotranspiration EO-based models (e.g. SEBAL), and then with the estimates ​​obtained from two different numerical models: a hydrological model (E-Hype) and a 3D hydrodynamic model (Delft3D). The key parameters influencing water evaporation rates, their behavior and the issues related to each approach are analyzed. The first comparison results are made for lake Garda, where a complete set of data is available for the production of evaporation maps.

A novel eco-friendly composite material made of polyurethane derived from castor oil reinforced with long cotton fibers was developed. A set of comparative analyses comprising static and dynamic tests was established using specimens made of castor oil-based polyurethane reinforced by glass fibers, and epoxy reinforced by glass and cotton fibers. The manufacturing method and estimation of fiber volume fraction of the specimens were described in detail. Tensile and flexural tests were performed to evaluate the mechanical performance of the novel laminate. Fractographic post-mortem examinations assessed the quality of the fiber–matrix interaction and allowed direct observation of the failure modes. Surface treatment of natural fibers appears necessary to improve the adhesion of the natural fibers to the matrix. Dynamic responses are discussed, considering natural frequencies and modal damping coefficients. In this context, the potentialities and the limitations of using the novel eco-friendly composite material as structural parts are discussed.

Unified formulations (UF) have been increasingly used to analyze laminated plates and shells. A huge number of works was carried out via in-house software, but only few contributions were presented using UF linked to a FE commercial software. In addition, the implementation of a UF within a FE commercial software remains a black box. This work aims at unlocking the difficulties on implementing a UF within the FE software Abaqus. Therefore, an eight-node plate element is developed via a UF and implemented as a User Element subroutine (UEL). In order to evaluate potentialities and limitations of the implemented UEL subroutine, benchmarking cases are evaluated investigating laminated plates under concentrated and distributed load. The displacement fields and, mainly, stress profiles are predicated by three different approaches: i) in-house Matlab framework; ii) standard shell and solid finite elements from Abaqus; and iii) from self-developed finite elements using CUF (via UEL).

Climate change may be considered relevant for hydropower production schemes all over the world. Despite this, the assessment of the impact of climate change on hydropower is uncertain and must be interpreted with that in mind. The paper focuses on the Namakhvani HPP (400 MW), a new project under development in the Rioni River, in Georgia. Using it as an example, the paper emphasizes the critical role that is played by uncertainty in climate impact risk assessments and explores the interpretation of simulation results, providing ways in which they can be transformed in actionable information for decision-making.

Identification of the boundary between failure by buckling, collapse and material failure in cylindrical tubes under axial compression is still challenging. The focus of this research is to investigate the response of carbon/epoxy filament wound cylindrical tubes under axial compression. Three approaches have been studied: (i) linear buckling; (ii) nonlinear buckling; and (iii) progressive damage modeling (PDM). For that, analytical, numerical and experimental approaches have been followed. Key results show that thinner tubes fail by buckling followed by a post-buckling field, whereas material failure due to transverse compression and in-plane shear stresses occur for thicker tubes. Both analytical and linear numerical models predicted very well the critical buckling load for all [±α] tubes, and nonlinear buckling model satisfactorily predicted axial displacement over the loading history. For multilayered tubes, the developed damage model provided better predictions compared to the nonlinear buckling model. Furthermore, for thicker tubes, a hoop layer at the outermost, instead of middle or innermost, improves buckling/compressive resistance.

The focus of this study is the development of a computational model with damage to predict failure of carbon fiber/epoxy filament wound composite tubes under radial compressive loading. Numerical analysis is performed via Finite Element Method (FEM) with a damage model written as a UMAT (User Material Subroutine) and linked to commercial software. The experimental analysis carried out followed ASTM D2412 -11, where the specimen is parallel-loaded by two steel-based plates. Three stacking sequences have been evaluated. Both numerical and experimental results show that the presence of hoop layers at inner and outer layers plus ±75° non-geodesic layers gives maximum compressive load to the composite tube, since the reinforcement is wound closer to the loading direction. Moreover, failure modes are predominantly delaminations, which are confirmed via numerical analyses through high in-plane shear stresses levels, and via experimental analyses through stereoscopic micrographs.

Currently, there is a growing concern for the environment. Several studies of new materials to reduce environmental impact have been carried out by different research groups, and many companies have replaced parts made of fossil sources by renewable materials. The use of polyurethane (PU) derived from castor oil as a matrix for composite materials and adhesives is one example. Hence, the present work aims to compare the numerical and experimental analyses of castor oil PU and epoxy resin not only as a matrix of composite materials, but also as an adhesive of bonded joints. The joint coupons were manufactured by using castor oil PU-glass fibre and epoxy-glass fibre as adherents, which were bonded by epoxy or castor oil PU. Thus, four combinations of adherents and adhesives were investigated. Specimens with identical geometry were used in all tests, which were based on guidelines for single lap bonded joints. Computational simulations via Finite Element Method were performed for predictions of the a...

In this work, damage and failure in carbon fiber reinforced epoxy filament wound composite tubes were thoroughly evaluated through a proposed damage model, which is able to identify different failure modes. Moreover, a non-linear finite element model based on the arc length method was developed. The tubes were manufactured via dry-filament winding using T700 towpregs, and subjected to external pressure tests to evaluate computational analyses. Numerical results indicated that the tubes with a diameter-to-thickness ratio (d/t) lower than 20:1 fail by buckling, whereas the tube [90 ± 5512/90], which has a higher d/t ratio presented failure primarily driven by in-plane shear, with delaminations. These results were compared with experimental tests, and relative differences in external pressure strengths were lower than 8.4%. The developed model presented a low computational cost and a very good agreement with experimental results, being very attractive to both academic and industrial sectors. Keywords: Failure analyses, Buckling, Damage model, Finite element analysis, Filament winding

The present study consists on experimental analyses of composite cylinders made by filament winding process, which are under transverse impact loading. The results are shown and discussed considering the influence of the stacking sequence as well as the total thickness of the cylinders. Thus, the results are normalized regarding the stiffness of each cylinder, and there are discussions based on identified damages, different graphics (force, displacement and strain vs. time), energy balance between impactor and coupons, as well as elastic and dissipated energy ratios and response delays for different strain gauges positions on the cylinders. Finally, guidelines for designing composite cylinders are presented considering the aspects addressed by the experimental analyses.

This work consists on evaluating potentialities and limitations of finite element formulations developed via CUF to predict free vibration response of laminated composite plates by using real experiments. Therefore, finite elements were developed via Carrera’s Unified Formulation (CUF) for laminated plates, which were implemented as a FORTRAN subroutine (UEL – User Element subroutine) linked to commercial finite element software ABAQUS™, to simulate free vibration of composite laminates. In addition, laminated plates made of composite material, resin epoxy and carbon fibre, with two different layups, were submitted to experimental vibration tests. The experimental tests were carried out by using an impact hammer, which excited the structure with impulse signal, and accelerometers, which measured the output data. Dynamic characteristics, such as natural frequencies, mode shapes and Frequency Response Functions were presented for the specimens. Then numerical results were compared to real experiments, discussing different aspects of the formulated finite elements. In addition, there is a demonstration how to connect native finite elements from ABAQUS™ to elements formulated via CUF (using UEL subroutines) and how to solve this problem using numerical time integration algorithms implemented in ABAQUS™, including discussion about the influence of time integration parameters on the dynamic response.

The employment of composite materials in the aerospace industry has been gradually considered due to the fundamental lightweight and strength characteristics that this type of materials has. The science material and technological progress reached matched perfectly with the requirements for high-performance materials in aircraft and aerospace structures; thus, the development of primary structure elements applying composite materials became something very convenient. It is extremely important to pay attention to the failure modes that influence composite materials performances, since these failures lead to a loss of stiffness and strength of the laminate. Delamination is a failure mode present in most of the damaged structures and can be ruinous, considering that the evolution of interlaminar defects can carry the structure to a total failure followed by its collapse. The present work aims at the development of a delamination propagation model to estimate a progressive interlaminar delamination failure in laminated composite materials and to allow the prediction of material’s degradation due to delamination phenomenon. Experimental data, available at literature, was considered to determine some model parameters, like the strain energy release rate, using GFRPs laminated composites. This new delamination propagation model was implemented as subroutines in FORTRAN language (UMAT-User Material Subroutine) with formulations based on the Fracture Mechanics and Continuum Damage Mechanics. Finally, the UMAT subroutine was complemented with an intralaminar model and compiled beside the commercial Finite Element (FE) software ABAQUS™.

Due to the large number of design variables for laminate composite structures, the use of an optimum stacking sequence is a key step in the design of a structure with the most suitable mechanical properties. This work presents a genetic algorithm (GA) for the optimization of the stacking sequence to improve strength of a cylindrical shell under internal pressure. The GA is associated to a meso-scale damage model, which was written in Fortran and later linked to a Finite Element (FE) package to simulate composite damage and failure. Two scenarios were considered: i) without restriction, where an ideal situation is simulated; and ii) with manufacturing restrictions, accounting for limitations on feasible winding angles. The results show that progressive failure analysis generates asymmetric and unbalanced laminates in both cases. Furthermore, the simulations with manufacturing restrictions present internal pressure strengths lower than the idealized case, providing more realistic results.

Introduction: Cost–effectiveness (CE) studies of percutaneous (PC) versus surgical (SC) atrial septal defect closure are lacking. Methods: A systematic literature review in children and a CE analysis based on a model of long-term outcomes were performed. Direct costs of PC and SC were US$8700 (defined arbitrarily) and US$5700 (actually paid), respectively. Three-times the Brazilian GDI (US$28,700) per year of life saved (with a discount rate of 5%) was used as a limit for willingness-to-pay. Discussion: PC had a high (US$104,500) incremental CE ratio despite lower complication rates, shorter hospital stay and better (nonsignificant) adjusted life expectancy. PC would be cost–effective if it cost US$6400 or SC had an 8% loss of utility or its indirect costs were US$2250. Costs of PC should be reduced to be cost–effective in the Brazilian public health system. Indirect costs and impact on quality of life should be further assessed.

Percutaneous coronary interventions (PCI) in chronic total occlusions (CTO) have been increasingly performed worldwide, but there is a paucity of data on procedures performed in Latin America An international multicenter registry was developed to collect data on CTO-PCI performed in experienced

The prediction of dynamic behavior for composite laminates is very complex, because of many concurrent phenomena can take place during impact load. Fiber breakage, delaminations, matrix cracking, plastic deformations due to contact and large displacements are some effects. Thus, in this work, some mechanisms are simulated by using a new failure model, which considers five failure modes: two for fiber-failure (FF) and three for inter-fiber-failure (IFF). For FF modes, the ply fails under longitudinal tension or compression. For IFF modes, the ply fails under shear stress combined to transverse tension (Mode A) or transverse compression stress (Mode B or C). Each failure mode has a failure criteria and an associated degradation function, which decreases the engineering material properties, requiring an iterative procedure for the process of failure analysis. The material model is implemented as sub-routines written in Fortran (UMAT and VUMAT), which are linked to AbaqusTM. First, the material model parameters were identified based on experimental tests. Second, two parameters were calibrated by using three-point bending tests and implicit numerical simulations with UMAT sub-routine. A computational program in Matlab was developed in order to control the calibration process and the post-processing of the results. After calibration procedure, the material model proposal was applied to predict the response of thin composite disks under impact loads. The finite element analyses via VUMAT were carried out considering the influence not only of the torque value on the screws of the composite disk fixation device, but also the friction coefficient between the composite disk and the fixation device. Finally, the finite element results were compared to experimental data and it was discussed the advantages and limitation of the material model proposal.

Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have made composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite failure phenomenon is very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern filament winding techniques have been used to produce a wide variety of structural shapes not only cylindrical parts, but also “flat” laminates. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates made using a filament winding process. The damage model was implemented as a UMAT (User Material Subroutine), in ABAQUSTM Finite Element (FE) framework. Progressive failure analyses were carried out using FE simulation in order to simulate the failure of flat filament wound composite structures under different loading conditions. In addition, experimental tests were performed in order to identify parameters related to the material model, as well as to evaluate both the potential and the limitations of the model. The difference between numerical and the average experimental results in a four point bending set-up is only 1.6 % at maximum load amplitude. Another important issue is that the model parameters are not so complicated to be identified. This characteristic makes this model very attractive to be applied in an industrial environment.

Piano Key Weirs (PKWs) are an alternative to linear overflow structures, increasing the unit discharge for similar heads and spillway widths. Thus, they allow to operate reservoirs with elevated supply levels, thereby providing additional storage volume. As they are relatively novel structures, few design criteria are available. Hence, physical model tests of prototypes are required. This study describes comprehensive model tests on a sectional set-up of several A-type PKWs, in which the relevant parameters were systematically varied. Considering data of former studies, a general design equation relating to the head–discharge ratio is derived and discussed. The latter is mainly a function of the approach flow head, the developed crest length, the inlet key height, and the transverse width. To extend its application range, case study model tests were analysed to provide a design approach if reservoir approach flow instead of channel flow is considered.

Aircraft composite structures must have high stiffness and strength with low weight, which can guarantee the increase of the pay-load for airplanes without losing airworthiness. However, the mechanical behavior of composite laminates is very complex due the inherent anisotropy and heterogeneity. Many researchers have developed different failure progressive analyses and damage models in order to predict the complex failure mechanisms. This work presents a damage model and progressive failure analysis that requires simple experimental tests and that achieves good accuracy. Firstly, the paper explains damage initiation and propagation criteria and a procedure to identify the material parameters. In the second stage, the model was implemented as a UMAT (User Material Subroutine), which is linked to finite element software, ABAQUS™, in order to predict the composite structures behavior. Afterwards, some case studies, mainly off-axis coupons under tensile or compression loads, with different types of stacking sequence were analyzed using the proposed material model. Finally, the computational results were compared to the experimental results, verifying the capability of the damage model in order to predict the composite structure behavior. ispartof: Composite Structures vol:94 issue:2 pages:635-642 status: published