Identification of Orthotropic Elastic Properties of Wood by a Synthetic Image Approach Based on Digital Image Correlation

No 888153 CENTRO-01-0145-FEDER-029713 POCI-01-0145-FEDER-031243 POCI-01-0145-FEDER-030592 ENTRO-01-0145-FEDER-022083This work aims to determine the orthotropic linear elastic constitutive parameters of Pinus pinaster Ait. wood from a single uniaxial compressive experimental test, under quasi-static loading conditions, based on two different specimen configurations: (a) on-axis rectangular specimens oriented on the radial-tangential plane, (b) off-axis specimens with a grain angle of about 60◦ (radial-tangential plane). Using digital image correlation (DIC), full-field displacement and strain maps are obtained and used to identify the four orthotropic elastic parameters using the finite element model updating (FEMU) technique. Based on the FE data, a synthetic image reconstruction approach is proposed by coupling the inverse identification method with synthetically deformed images, which are then processed by DIC and compared with the experimental results. The proposed methodology is first validated by employing a DIC-levelled FEA reference in the identification procedure. The impact of the DIC setting parameters on the identification results is systematically investigated. This influence appears to be stronger when the parameter is less sensitive to the experimental setup used. When using on-axis specimen configuration, three orthotropic parameters of Pinus pinaster (ER, ET and νRT ) are correctly identified, while the shear modulus (GRT ) is robustly identified when using off-axis specimen configuration.publishersversionpublishe

Analysis of heterogeneous tests for sheet metal mechanical behavior

Strategies combining heterogeneous mechanical tests and full-field strain measurement techniques are providing increasingly more valuable data, ensuring calibrated constitutive models for the accurate representation of the elastoplastic behavior of sheet metals. However, the accuracy of these strategies is still dependent on many factors, such as the shape of the specimen, the choice of an appropriate strain field measurement technique, or the selection of an identification strategy. Recently, many heterogeneous tests with different specimen shapes and boundary conditions have been proposed using optimization techniques or empirical knowledge. Examples of these specimens include shapes based on cubic splines, notches, holes, slits or even Greek letters. However, the qualitative and quantitative comparison of each heterogeneous test is a difficult task, as studies tend to use different materials and representations of the strain and stress tensors. As a result, the selection of a single heterogeneous test is still a dilemma and a subject under research. Thereby a set of indicators to evaluate and qualitatively rank each heterogeneous test is proposed, calculated through the strain and stress fields on the sheet plane of the specimen, within a virtual (numerical) approach, and investigate its application to steel and aluminum, to account for the material dependency.publishe

Identification of Swift Law Parameters Using FEMU by a Synthetic Image DIC-Based Approach

Funding Information: This project has received funding from the Research Fund for Coal and Steel under grant agreement No 888153. The authors also gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under the projects CENTRO-01-0145-FEDER-029713, POCI-01-0145-FEDER-031243 and POCI-01-0145-FEDER-030592 by UE/FEDER through the programs CENTRO 2020 and COMPETE 2020, and UIDB/00481/2020 and UIDP/00481/2020-FCT under CENTRO-01-0145-FEDER-022083. Authors also acknowledge Fundação para a Ciência e a Tecnologia (FCT-MCTES) for its financial support via the projects UIDB/00667/2020 (UNIDEMI). J. Henriques is also grateful to the FCT for the PhD grant 2021.05692.BD. Funding Information: This project has received funding from the Research Fund for Coal and Steel under grant agreement No 888153. The authors also gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under the projects CENTRO-01-0145-FEDER-029713, POCI-01-0145-FEDER-031243 and POCI-01-0145-FEDER-030592 by UE/FEDER through the programs CENTRO 2020 and COMPETE 2020, and UIDB/00481/2020 and UIDP/00481/2020-FCT under CENTRO-01-0145-FEDER-022083. Authors also acknowledge Fundação para a Ciência e a Tec-nologia (FCT - MCTES) for its financial support via the projects UIDB/00667/2020 (UNIDEMI). J. Henriques is also grateful to the FCT for the PhD grant 2021.05692.BD. Publisher Copyright: © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.Computer-aided engineering systems rely on constitutive models and their parameters to describe the material behaviour. The calibration of more elaborated material models with a larger number of parameters becomes very time and cost consuming. The development of image-based technology has enhanced the interest in inverse identification methods, which, when coupled with full-field measurements, have the potential to reduce the number of experimental tests required to accurately identify material properties. This work aims to identify the Swift hardening law parameters of a dual-phase steel using a tensile test on a heterogeneous dogbone specimen under uniaxial and quasi-static loading conditions using the finite element model updating (FEMU) technique. The numerical results were used to generate synthetic images, which were then processed by digital image correlation (DIC) and used as the reference in the identification procedure. Two different approaches were tested: (i) directly comparing the numerical results to the reference; (ii) using DIC-levelled numerical data by iteratively generating synthetic images and using the DIC filter with the same settings as were used on the reference (virtual experiment). The identification results obtained from both approaches are compared and discussed.publishersversionpublishe

Dynamic capabilities and their relations with elements of digital transformation in Portugal

The objective of the article was to identify as relations between IoT, Big Data and Artificial Intelligence with the microfoundations of the dynamic capabilities. It was characterized as an exploratory, descriptive and inferential research, with a quantitative approach. In non-parametric tests (Chi-square / Spearman correlation), in Portuguese companies, totaling 137 respondents with valid questionnaires (only business and IT managers) were applied. It has been shown that as 3 technologies, IoT, Big Data and IA, in different proportions of performance, are large in the 3 microfoundations of our dynamic capabilities. The highlight was for the performance presented by Big Data in the Seising microfoundation. The highest correlations were observed for the Seising microfoundation, with emphasis on the strong correlation between IoT and Big Data and moderate correlations between Big Data and AI.info:eu-repo/semantics/publishedVersio

On the computational performance of advanced optimization methods in mechanical design

Advanced optimization methods are widely applied to mechanical design, mainly for its abilities to solve complex problems that traditional optimization techniques such as gradient-based methods do not present. With its increasing popularity, the number of algorithms found in the literature is vast. In this work three algorithms are implemented, namely Particle Swarm Optimization (PSO), Differential Evolution (DE) and Teaching- Learning-Based Optimization (TLBO). Firstly, the application of these algorithms is analyzed for a composition function benchmark and three mechanical design minimiza- tion problems (the weight of a speed reducer, the volume of a three-bar truss and the area of a square plate with a cut-out hole). Furthermore, as the scope of available algorithms increases, the choice of programming tools to implement them is also vast, and generally made considering subjective criteria or difficulties in using enhancing strategies such as parallel processing. Thereby an analysis of programming tools ap- plied to metaheuristic algorithms is carried out using four programming languages with distinct characteristics: Python, MATLAB, Java and C++. The selected algorithms and applications are coded using each programming language, which are initially compared in a sequential processing implementation. Additionally, in order to analyze potential gains in performance, parallel processing procedures are implemented using features of each programming language. The application of the algorithms to the mechanical design problems demonstrates good results in the achieved solutions. In what concerns to the computational time, sequential and processing results present considerable differ- ences between programming languages while the implementation of parallel processing procedures demonstrates significant benefits for complex problems.publishe

Modelação e análise numérica do comportamento mecânico e térmico de ligas de aluminio

Neste trabalho desenvolve-se e implementa-se um modelo matemático tridimensional conducente à simulação do comportamento térmico e mecânico das ligas de alumínio. O objectivo é a simulação de processos tecnológicos que envolvam deformações termomecânicas nestas ligas. Neste âmbito, introduz-se uma formulação cinemática preparada para processos em grandes deformações e rotações. Considera-se um modelo constitutivo termoelástico-viscoplástico baseado num conjunto de variáveis de estado internas e externas e com o qual é possível modelar os fenómenos de encruamento e restauração estática e dinâmica do material. Este modelo, preparado para gamas de temperatura que vão desde a temperatura de solidificação até à temperatura ambiente, é implementado recorrendo a uma formulação lagrangeana reactualizada e a um método de integração temporal semi-implícito. O comportamento térmico do material é modelado recorrendo a um algoritmo do tipo previsão-correcção. A fase de previsão é baseada num esquema semi- -implícito, com o qual é possível determinar uma primeira estimativa para a configuração final do incremento. A solução semi-implícita é corrigida na fase de correcção, recorrendo a um esquema implícito do tipo Newton-Raphson. A solução de acoplamento termomecânico, que envolve a implementação de um modelo termoplástico, é encontrada recorrendo a uma abordagem staggered. Desenvolve-se um programa específico, baseado em algoritmos evolucionários, para a determinação dos parâmetros materiais associados ao modelo constitutivo. A eficiência do método utilizado, que conduz a resultados excelentes, é comparada com um método baseado no gradiente. Realizam-se testes numéricos com o objectivo de validar os modelos e algoritmos implementados. Descreve-se um ensaio numérico de têmpera de um sólido de geometria complexa e analisam-se e discutem-se os resultados obtidos. As simulações efectuadas confirmam o bom desempenho do programa quer em problemas mecânicos e térmicos quer em problemas com acoplamento termomecânico.A three-dimensional mathematical model is developed and presented leading to the simulation of the thermal and mechanical behaviour of aluminium alloys. The main goal is the simulation of specific technological processes that involve the thermo-mechanical deformation of aluminium alloys. A kinematic formulation suitable for large deformations and rotations is introduced. A thermoelastic-viscoplastic constitutive model is considered based on a set of internal and external state variables and with which it is possible to model strain hardening and static and dynamic restoration effects. This model, prepared for temperature levels that range from the solidification temperature to room temperature, is implemented with an updated lagrangean formulation and a forward gradient time integration procedure. The thermal behaviour of the material is modelled with a prediction-correction algorithm. The prediction stage is based on a semi-implicit scheme and is used to determine a first estimate of the final configuration of the increment. This first solution is then corrected using a Newton-Raphson implicit scheme. A thermoplastic model is implemented and a staggered approach is adopted for the solution of the thermo-mechanical coupling problem. A specific program, based on evolutionary algorithms, is developed in order to determine the large number of material parameters associated to the constitutive model. The efficiency of the method developed for this particular purpose is compared with a gradient based method, leading to excellent results. Numerical tests are performed in order to validate the set of implemented models and algorithms. The numerical simulation of the quenching of a geometrically complex solid is presented and its results are thoroughly analysed and discussed. Results from the numerical simulations confirm the good performance of the program in mechanical, thermal and thermomechanically coupled problems

Design of heterogeneous interior notched specimens for material mechanical characterization

Nowadays, virtual predictions are essential in the design and development of new engineering parts. A critical aspect for virtual predictions is the accuracy of the constitutive model to simulate the material behavior. A state-of-the-art constitutive model generally involves a large number of parameters, and according to classical procedures, this requires many mechanical experiments for its accurate identification. Fortunately, this large number of mechanical experiments can be reduced using heterogeneous mechanical tests, which provide richer mechanical information than classical homogeneous tests. However, the test’s richness is much dependent on the specimen's geometry and can be improved with the development of new specimens. Therefore, this work aims to design a uniaxial tensile load test that presents heterogeneous strain fields using a shape optimization methodology, by controlling the specimen's interior notch shape. The optimization problem is driven by a cost function composed by several indicators of the heterogeneity present in the specimen. Results show that the specimen's heterogeneity is increased with a non-circular interior notch. The achieved virtual mechanical test originates both uniaxial tension and shear strain states in the plastic region, being the uniaxial tension strain state predominant.publishe

On the optimisation efficiency for the inverse identification of constitutive model parameters

The development of full-field measurement techniques paved the way for the design of new mechanical tests. However, because these mechanical tests provide heterogeneous strain fields, no closed-form solution exists between the measured deformation fields and the constitutive parameters. Therefore, inverse identification techniques should be used to calibrate constitutive models, such as the widely known finite element model updating (FEMU) and the virtual fields method (VFM). Although these inverse identification techniques follow distinct approaches to explore full-field measurements, they all require using an optimisation technique to find the optimum set of material parameters. Nonetheless, the choice of a suitable optimisation technique lacks attention and proper research. Most studies tend to use a least-squares gradient-based optimisation technique, such as the Levenberg-Marquardt algorithm. This work analyses optimisation algorithms, gradient-based and -free algorithms, for the inverse identification of constitutive model parameters. To avoid needless implementation and take advantage of highly developed programming languages, the optimisation algorithms available in optimisation libraries are used. A FEMU based approach is considered in the calibration of a thermoelastoviscoplastic model. The material parameters governing strain hardening, temperature and strain rate are identified. Results are discussed in terms of efficiency and the robustness of the optimisation processes.publishe

Genetic algorithms approach for containerships fleet management dependent on cargo and their deadlines

This work proposes a method to improve the flexibility of short sea shipping and to increase its competitiveness with other means of freight transport. A logistic model and a mathematical model are developed to manage a fleet of two or more vessels which transport cargo to and from several ports, bearing in mind the cargo distribution and delivery deadlines. At each port, the model determines which port to visit next, which containers to embark, disembark and to shift, as well as how to stow them on board. In fact, this formulation brings together the fleet management problem, the container stowage problem (CSP) and the vehicle routing problem (VRP). An example scenario is set up, using generated but realistic data. The problem is then solved, in a simplified version, using a Genetic Algorithm. The results show that introducing the possibility of route changes, the overall efficiency (and thus competitiveness) of short sea shipping can be improved