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"Engineering Thermodynamics"
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Pantographic metamaterials: an example of mathematically driven design and of its technological challenges
In this paper, we account for the research efforts that have been started, for some among us, already since 2003, and aimed to the design of a class of exotic architectured, optimized (meta) materials. At the first stage of these efforts, as it often happens, the research was based on the results of mathematical investigations. The problem to be solved was stated as follows: determine the material (micro)structure governed by those equations that specify a desired behavior. Addressing this problem has led to the synthesis of second gradient materials. In the second stage, it has been necessary to develop numerical integration schemes and the corresponding codes for solving, in physically relevant cases, the chosen equations. Finally, it has been necessary to physically construct the theoretically synthesized microstructures. This has been possible by means of the recent developments in rapid prototyping technologies, which allow for the fabrication of some complex (micro)structures considered, up to now, to be simply some mathematical dreams. We show here a panorama of the results of our efforts (1) in designing pantographic metamaterials, (2) in exploiting the modern technology of rapid prototyping, and (3) in the mechanical testing of many real prototypes. Among the key findings that have been obtained, there are the following ones: pantographic metamaterials (1) undergo very large deformations while remaining in the elastic regime, (2) are very tough in resisting to damage phenomena, (3) exhibit robust macroscopic mechanical behavior with respect to minor changes in their microstructure and micromechanical properties, (4) have superior strength to weight ratio, (5) have predictable damage behavior, and (6) possess physical properties that are critically dictated by their geometry at the microlevel.
Journal Article
Advances in pantographic structures: design, manufacturing, models, experiments and image analyses
In the last decade, the exotic properties of pantographic metamaterials have been investigated and different mathematical models (both discrete or continuous) have been introduced. In a previous publication, a large part of the already existing literature about pantographic metamaterials has been presented. In this paper, we give some details about the next generation of research in this field. We present an organic scheme of the whole process of design, fabrication, experiments, models and image analyses.
Journal Article
Plastic damage prediction of concrete under compression based on deep learning
Diverse loads frequently damage concrete when it is in use. However, it might be challenging to immediately identify the stress and damage of concrete in actual engineering situations. In order to predict the stress and damage of concrete, a deep learning (DL) model based on the convolutional neural network (CNN) is proposed in this paper. To provide the training and validation data, a finite element (FE) model of uniaxial compression of concrete specimens based on the concrete damage-plasticity (CDP) model is constructed. The DL model is trained with the strain contours with a specified range provided by the FE model as the inputs and the stress and damage assessment of concrete as the outputs. The prediction of the stress and damage of concrete materials was effectively realized by the trained DL model, and it was verified in a larger range of working conditions distinct from the training and verification sets. The results show that the DL algorithm has good accuracy and reliability. By efficiently and correctly recreating the FE prediction results, the DL model offers a method for promptly evaluating the stress and damage of concrete structures under complicated stress circumstances in actual engineering.
Journal Article
Application of the simple Bayesian classifier for the N2 (77 K) adsorption/desorption hysteresis loop recognition
The possibility to recognize the type of the adsorption/desorption hysteresis loop on N
2
(77 K) isotherms is considered. The loop width change against both axes, the number of steps on both branches, including the numbers of steps around the cavitation-induced evaporation point, position of Point B, adsorption uptakes that correspond to Point B and to the maximum loading are considered as the simple Bayesian classifier features. The dataset used for training the classifier included 796 unique adsorption isotherms. The quality of the type prediction aspires 99% regarding H1, H3 and H4 types, and is relatively high for other types.
Journal Article
A review of nonlinear FFT-based computational homogenization methods
Since their inception, computational homogenization methods based on the fast Fourier transform (FFT) have grown in popularity, establishing themselves as a powerful tool applicable to complex, digitized microstructures. At the same time, the understanding of the underlying principles has grown, in terms of both discretization schemes and solution methods, leading to improvements of the original approach and extending the applications. This article provides a condensed overview of results scattered throughout the literature and guides the reader to the current state of the art in nonlinear computational homogenization methods using the fast Fourier transform.
Journal Article