A carregar...
Projeto de investigação
Otimização multiescala de estruturas compósitas não convencionais para melhoria do comportamento mecânico
Financiador
Autores
Publicações
Stiffness and strength-based lightweight design of truss structures using multi-material topology optimization
Publication . Almeida, Cláudia J.; Conde, Fábio M.; Coelho, Pedro G.; Pratas, Tiago L.; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial
Stiffness and strength are important structural design criteria. However, most contributions to Topology Optimization (TO) deal with the compliance minimization problem. Controlling stresses in a structure is very important to avoid material failure, but that raises complications in TO, such as: nonlinearity, singularity and high computational cost. The total weight of a structure is also another important criterion in optimal design. The multi-material setting is considered in the present work as it opens the possibility to improve structural performance even further allowing extra weight reduction. Recursive SIMP is used as the material interpolation scheme and design solutions are sought using the ground structure approach. This means that truss-like (lattice) designs are obtained here. The problem is relaxed to the continuum by introducing an artificial density variable and it is solved by a gradientbased algorithm (MMA). A stress-constraint relaxation technique (qp-approach) is applied to overcome the stress singularity phenomenon. A continuation approach is used to guarantee discrete solutions, i.e., only the presence or absence of bars is identified. Therefore, design uniformity in terms of bars cross section areas is ensured. Hence, this work proposes a methodology to perform Multi-Material Topology Optimization (MMTO) of truss structures, with density-based design variables, and subject to stress constraints. To discuss the differences between stiffness and strength-oriented optimal designs, a compliance minimization problem subject to mass constraint is also considered. The example chosen demonstrates the viability of the proposed design methodology and it also reveals differences between the strongest and the stiffest designs.
Multiscale optimization of non-conventional composite structures for improved mechanical response
Publication . Conde, Fábio Rúben Monteiro; Coelho, Pedro; Guedes, José
Nowadays, due to governmental requirements to control climate change, there is a great inter-
est on the part of the automotive and aerospace industry to design structures as light as possible,
without jeopardize their performance, thus increasing their efficiency. Multi-material design is a
way to achieve this goal, as will be shown in this work
In this work, multi-material design is considered with the goal of improving the structure’s
stiffness, strength, and non-linear behaviour when it yields. Firstly, a microstructural topology
optimization is carried out seeking for multi-material microstructures with increased stiffness and
strength compared to equivalent single-material microstructures. Afterwards, this study is further
extended to perform multi-scale topology optimization, where a concurrent optimization of ma-
terial and structure is done. Ultimately, the non-linear behaviour of hybrid fibre reinforced com-
posites is optimized in order to introduce a so-called “pseudo-ductility”.
Two different optimization problems are formulated and solved here. One compliance mini-
mization with mass constraint problem and another stress-based problem where the maximal von
Mises stress is locally minimized in the unit-cell. The multi-material design is investigated here
using two different approaches. On one hand, the two solids coexist being bonded together across
sharp interfaces. On the other hand, a functionally graded material is obtained as an extensive
smooth variation of material properties on account of varying composition’s volume fractions of
both solids throughout the design domain. The compliance-based optimization results show that
multi-material microstructures can be stiffer compared to single-material ones for the same mass
requirement. Regarding the stress-based problem, lower stress peaks are obtained in bi-material
design solutions and, specially, in the case of graded material solutions.
As regards multi-scale topology optimization, the results show that a multi-material structure
can be stiffer than its single-material counterpart, which is in accordance with the microstructural
study performed earlier. Hybrid composites can achieve the so-called “pseudo-ductile” behaviour mimicking the well-
known elastic-plastic behaviour. To understand under what circumstances such behaviour is ob-
tained, optimization problems are formulated and solved here. Two different types of optimiza-
tion problems are considered. Firstly, one finds out the optimal properties of fibres to hybridize
and get the pseudo-ductile behaviour. Once an optimal hybridization is found, another optimiza-
tion problem is solved in order to understand the influence of the fibre dispersion on the composite
response. The optimal results obtained show hybrid composites having a considerable pseudo-
ductile behaviour.
The survival of cultural firms: A study of multiple accounting parameters in Spain
Publication . del Pilar Muñoz Dueñas, Ma; Liste, Antonio Vaamonde; do Rosário Cabrita, Maria; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Molecular Diversity Preservation International (MDPI)
Cultural firms are an important development factor in economic and social terms. Their objectives are often aimed at maintaining and disseminating the traditions and values of societies. The prosperity of these firms in a nation ensures that its tangible and intangible cultural heritage is made known to other nations and generations. Despite their importance, little is known about their survival and the factors associated with it. This paper analyses data from 6951 Spanish firms, of which 2105 are cultural firms. We have studied the survival of non-cultural firms in comparison with cultural firms and also the impact that profitability, solvency and indebtedness may have on their survival. We have used the Kaplan-Meier method in order to assess their survival and the Harrington-Fleming test and the Cox regression model to check the statistical significance of variables. These variables are key factors influencing the survival of cultural enterprises. Particularly, low solvency in firms increases by twenty the risk of disappearance. This paper contributes to literature highlighting some of the key factors for the survival of cultural enterprises. It provides administrations with a roadmap in order to implement measures for the promotion of the cultural industry, favouring the process of enhancement of cultural heritage.
Multi-material and strength-oriented microstructural topology optimization applied to discrete phase and functionally graded materials
Publication . Conde, Fábio M.; Coelho, Pedro G.; Guedes, José M.; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Springer Science Business Media
Structural optimization plays an important role in lightweight construction, and stresses need to be controlled to avoid material failure. The multi-material design setting offers additional design freedom which can lead to structures with improved strength and stiffness properties compared to the single-material case. The present work addresses topology optimization of a periodic composite material unit cell, with properties predicted by homogenization, using strength and stiffness design criteria, under bulk and mixed loading cases. Plane stress and linear behavior are assumed. The compliance minimization with mass constraint problem is revisited here, but the paper focus is on multi-material stress-based topology optimization. Specifically, the maximal von Mises stress is minimized in the unit-cell where two solids are mixed amidst void. Depending on the material interpolation law settings, two design solutions are investigated. On one hand, the two solids coexist being bonded together across sharp interfaces. On the other hand, a functionally graded material is obtained as an extensive smooth variation of material properties on account of varying composition’s volume fractions of both solids throughout the design domain. A parallel MMA version is proposed to efficiently deal with several design constraints. The compliance-based optimization results show that multi-material microstructures can be stiffer compared to single-material ones for the same mass requirement. Regarding the stress-based problem, lower stress peaks are obtained in bi-material design solutions and, specially, in the case of graded material solutions. The latter approximates a fully stressed design which excels in stress mitigation. Therefore, the multi-material setting impacts favorably on structural performance, in both stiffness and strength-oriented designs.
Unidades organizacionais
Descrição
Palavras-chave
Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Número da atribuição
SFRH/BD/136744/2018