Abstract

International Journal of Numerical Methods for Calculation and Design in Engineering (RIMNI) contributes to the spread of theoretical advances and practical applications of numerical methods in engineering and other applied sciences. RIMNI publishes articles written in Spanish, Portuguese and English. The scope of the journal includes mathematical and numerical models of engineering problems, development and application of numerical methods, advances in software, computer design innovations, educational aspects of numerical methods, etc. RIMNI is an essential source of information for scientifics and engineers in numerical methods theory and applications. RIMNI contributes to the interdisciplinar exchange and thus shortens the distance between theoretical developments and practical applications.

Desde 1985 la Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (RIMNI) contribuye a la difusión en castellano, portugués e inglés de los desarrollos teóricos y aplicaciones prácticas de los métodos numéricos, tanto en relación con su utilidad como instrumentos de cálculo y análisis para el ingeniero y el científico, como en aspectos que inciden en las nuevas tecnologías de diseño y proyecto de producción y procesos en ingeniería. La revista abarca áreas diversas, tales como: modelos matemáticos y numéricos de problemas de ingeniería, desarrollo y aplicaciones de los métodos numéricos, nuevos avances en temas de software, innovaciones en el campo del diseño por computador, aspectos didácticos de los métodos numéricos, etc. La revista constituye una fuente de información imprescindible para ingenieros y científicos sobre innumerables temas relacionados con los métodos numéricos y sus aplicaciones, contribuyendo a promover la transferencia de conocimiento interdisciplinar y, por consiguiente, a acortar la distancia que existe entre los desarrollos teóricos y las aplicaciones concretas.

Abstract

A new damage feature index is presented for the structural health monitoring based on Hilbert-Huang transform (HHT). The energy marginal spectrum of the dynamic signal is used to construct damage characteristic parameter, which can reflect the signal energy variation and benefit the structural damage detection. A sinusoidal wave with frequency change and a composite plate vibration experiment with pre-defined damage are designed to verify the effectiveness of characteristic parameter in damage detection. Results obtained from simulation and test show that the extracted non-model-based damage feature index is available and sensitive in damage detection of time-varying system.

Abstract

In this article, the nonlinear constitutive behavior is considered in the geometrically nonlinear formulation for beams proposed by
Simo and Vu-Quoc. The displacement based method is employed in solving the resulting nonlinear problem in the static case. Thermodynamically consistent three-dimensional constitutive laws are used in describing the material behavior, leading to a more precise estimation of the energy dissipated by the structures. The simple mixing rule is also applied in modeling materials which are composed by several simple components. An appropriated cross sectional analysis is implemented under the assumption and limitations of the planarity
of the beam cross sections. Special attention is paid to the development of a method for defining the global damage state of a structure
based on a scalar damage index capable of describing the residual strength and the load carrying capacity. Several numerical examples,
including composite materials and strain localization, are presented and discussed.

Abstract

Structures subjected to cyclic loads show alternative tension–compression stress states; in such a case,  even if certain damage (fracture) is reached during the tension cycle, the computational model of the structure should maintain its capacity to withstand subsequent compression based only on the contact effect in the damaged area (opening, closing and reopening of cracks). In order to control this behavior, a phenomenological constitutive model able to consider the contact as a structural limitation is required. From the constitutive point of view, geomaterials have different damage thresholds for tension and compression and, from the structural point of view, it must be ensured that the material damaged in tension still resist compression. In this case, it is accepted that cracks behave as a contact surface at the structural level. To meet the above mentioned phenomenology, a modification of the damage model
differentiated in tension and compression proposed by Faria et al. [Faria R, Oliver J, Cervera M. A strainbased plastic viscous-damage model for massive concrete structures. Int J Solids Struct 1998; 35:1533–58] is performed in this paper, considering independent strength thresholds in each of these processes, controlled with two independent discontinuity threshold functions. Also, in this work an elasto-plastic constitutive model is used to represent the behaviour of the steel bars.

Abstract

There is general agreement in the fact that fully three-dimensional (3D) numerical techniques provide the most precise tools for simulating the behavior of RC buildings even when their computational costs for real structures became them unpractical. Moreover, one-dimensional formulations (1D) are rather limited for predicting the mechanical behavior of framed structures which present local weakness that can determine their global responses, such as it is the case of poor detailed joints of RC buildings in seismic zones or precast concrete structures. An alternative approach, combining both simplicity and computational efficiency, is given by coupling reduced models for prismatic elements with full 3D models for the zones corresponding to connecting joints. In this work, a two-scale approach is developed for obtaining the nonlinear dynamic response of RC buildings with local non-prismatic parts. At global scale level all the elements are rods; however, if local parts with complex geometry appear, the corresponding elements are analyzed considering fully 3D models which constitute the local scale level. The dimensional-coupling between scales is performed imposing the kinematics hypothesis of the beam model on surface-interfaces of the 3D model. An iterative Newton-Raphson scheme which considers the interaction between scales is developed to obtain the response at global level. The tangential stiffness of the local models are obtained numerically. Computationally, the problem is managed by means of a master-slave approach, where the global scale problem acts as the master and the local models are the slaves; iterative communication between scales considers internal forces and moments as well as tangential tensors. The process stops when global convergence is achieved. From the computational point of view, the developed method is implemented in a parallelized scheme, where the master and slave problems are solved independently by different programs thus minimizing the intervention on existing codes specific for beams and solids. Finally, numerical examples are included.

Abstract

The RAMSSES project aims to show the benefits of advanced materials in maritime applications by implementing 13 market driven demo cases. The entire process chain and a wide range of applications (structural components, equipment, ship integration, repair) are covered. Installation and assessment of demonstrators on shore or on board will reveal the high technology readiness. The test program, based on risk assessment and supervised by rule making bodies, targets on ensuring relevance for commercial approval beyond the project. While demonstrators will support commercialisation of specific products, RAMSSES is also engaged strategically in enabling more rapid and agile material innovation in the European Maritime industry. The first key element is a knowledge repository for test data and best practice procedures, allowing reuse of such information for similar future cases. Secondly, standardised risk scenarios will help easing approval processes in the future, and finally a new materials innovation platform will enhance continuous technology transfer within the maritime sector and beyond.

Abstract

An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with their numerical reproduction using the finite element method in order to obtain an estimation of the error between the results. This error estimation is then used by an evolutionary optimizer to determine, in an iterative process, the value of the material parameters which result in the best numerical fit. The novelty of the method is in the coupling between the simple genetic algorithm and the mixing theory used to numerically reproduce the composite behavior. The methodology proposed has been validated through a simple example which illustrates the exploitability of the method in relation to the modeling of damaged composite structures.

Abstract

The use of multi-scale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a non-linear analysis of real composite structures without the aid of large computers. This work proposes a strategy to conduct non-linear multi-scale analysis in an efficient way. The proposed method considers that in a large structure, in general, material non-linear processes only take place in a localized region (or in a reduced number of finite elements, if a FE method is used). The strategy determines the elements that require a non-linear analysis defining of a non-linear activation function that accounts for the failure of the most critical point in the microstructure. The procedure conserves the dissipated energy through the scales, being mesh independent as the mesh objectivity concept is extended to the microstructure. The validity of the strategy proposed is proved with the analysis of academic examples showing not only the mesh independency but also the reduction of computational cost. Finally, an industrial composite component is solved using a standard computer, showing that the proposed strategy is capable of reducing the computational cost from 32 days and 14 hours (required by a classical multi-scale method) to less than 12 hours.

Abstract

The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned tendons taking into account the reduction of the pre-stressing stress due to the steel relaxation. The post-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) (Rastellini et al, 2008; Martinez et al., 2008, 2014) whereas the stress relaxation of the steel is simulated using a viscoelastic model called Generalized Maxwell. A 3D FE model was used, where the nonlinear material behaviour and geometrical analysis based on incremental–iterative load methods were adopted. Validation by comparison with the analytic solution will be done for the case of a concrete beam with a linear steel tendon and for a parabolic pre-tensioned steel tendon embedded. Some viscoelastic cases are presented in order to perceive the behaviour of the Generalized Maxwell model. Several examples are shown where the capabilities of the method on large scale structures are exhibited.

Abstract

In the marine industry, Fibre-reinforced polymers (FRP) are currently dominating the manufacture of vessels up to 50m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique, of which vacuum-assisted liquid resin infusion is the most widely adopted LRI variant. However, current regulations restrict the use of composite materials in vessels over 50m in length. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRPs in vessels over 50m in length by addressing the regulatory restrictions and the numerous other challenges associated with manufacturing long-length FRP composite ships. The mechanical performance of new commercially available composite material constituents as potential candidates for selection in composite ship construction is central to this work. This paper provides an overview of selected work performed as part of the FIBRESHIP project in terms of evaluating various mechanical properties of selected laminates under dry and wet conditions. The laminates were immersed in seawater at 35°C for durations of one to three months. Three-point bend and interlaminar shear strength tests were undertaken in order to investigate the change in the mechanical properties of composite laminates subject to immersion. Finally, tested specimens were observed using micro-computed tomography (μCT) to evaluate the failure morphology.