1,721,000 research outputs found
Programmable materials: Current trends, challenges, and perspectives
No full textResearch into programmable materials has attracted extraordinary interest since the nineties, when the term “programmable” was introduced for the first time. In its widest definition, the term is used to denote materials that are designed to be highly dynamic, either in shape and/or physical/functional properties, on-demand and in a precise, sequential predetermined way. Such unique feature allows them to adapt to various needs and offers new opportunities in several application fields, enabling them to overcome the limitations of traditional materials. The present paper aims to introduce readers to the world of programmable materials, enhance their interest, knowledge, and skills in the field, and provide useful insights and new ideas on how to approach their development and implementation. Accordingly, this paper offers an overview and discussion of current state-of-the-art and recent progress up to future perspectives. First, the historical evolution and definition of these materials as well as the types of programmable properties achievable are presented. Then, the different programming strategies that could be used to tune material properties are covered, with an emphasis on the constituent materials, applied stimuli, and geometrical arrangements. Finally, real-world applications, ongoing challenges, and future directions for this exciting class of materials are discussed
4D fabrication of shape-changing systems for tissue engineering: state of the art and perspectives
No full textIn recent years, four-dimensional (4D) fabrication has emerged as a powerful technology capable of revolutionizing the field of tissue engineering. This technology represents a shift in perspective from traditional tissue engineering approaches, which generally rely on static—or passive—structures (e.g., scaffolds, constructs) unable of adapting to changes in biological environments. In contrast, 4D fabrication offers the unprecedented possibility of fabricating complex designs with spatiotemporal control over structure and function in response to environment stimuli, thus mimicking biological processes. In this review, an overview of the state of the art of 4D fabrication technology for the obtainment of cellularized constructs is presented, with a focus on shape-changing soft materials. First, the approaches to obtain cellularized constructs are introduced, also describing conventional and non-conventional fabrication techniques with their relative advantages and limitations. Next, the main families of shape-changing soft materials, namely shape-memory polymers and shape-memory hydrogels are discussed and their use in 4D fabrication in the field of tissue engineering is described. Ultimately, current challenges and proposed solutions are outlined, and valuable insights into future research directions of 4D fabrication for tissue engineering are provided to disclose its full potential
Efficiency and effectiveness of implicit and explicit approaches for the analysis of shape-memory alloy bodies
No full textThe increasing number of applications incorporating shape-memory alloy (SMA) components motivates the development of three-dimensional constitutive models to enhance their analysis and design. These models only reach their full utility if they are then implemented into numerical (e.g. often finite-element-based) frameworks. The present article addresses a topic rarely considered in the myriad of SMA computational analysis works in the literature: the analysis of the time and accuracy of implementation options. In particular, this work proposes to compare the performance of the implicit and explicit integration methods for two common three-dimensional phenomenological constitutive models: (i) the model by Lagoudas et al.; and (ii) the model by Auricchio et al. available in all installations of Abaqus. In doing so, the present work develops and implements an explicit algorithm for the model by Lagoudas et al. for the first time. The investigated models are compared in a chosen benchmark boundary value problem analysis considering both thermally induced actuation and isothermal stress-induced transformation of an SMA beam. The performance of the methods in terms of analysis time and parallelization efficiency are also investigated
A Numerical/Experimental Study of Nitinol Actuator Springs
No full textThis study deals with the numerical modeling, simulation and experimental analysis of shape-memory alloy (SMA) helicoidal springs. An experimental campaign is conducted on both SMA straight wires and helicoidal springs that experienced the same annealing process. Then, we use such experimental results to investigate three phenomenological constitutive models able to represent SMA macroscopic behavior. In particular, after the identification of all the material parameters from experimental results on SMA wires, we inspect the thermo-mechanical behavior of SMA helicoidal springs by comparing numerical predictions to experimental data. Finally, we discuss models capabilities and some aspects characterizing SMA material behavior
A three-dimensional finite-strain phenomenological model for shape-memory polymers: Formulation, numerical simulations, and comparison with experimental data
No full textShape-memory polymers (SMPs) represent a class of smart materials able to store a temporary shape and to recover the original shape upon an external stimulus, such as temperature. The present paper proposes a three-dimensional finite-strain phenomenological model for thermo-responsive SMPs, which distinguishes between two material phases presenting different properties and is based on a rule of mixtures. The proposed model is motivated by the earlier work of Reese et al. (2010) and it considers several significant material features that had not been addressed in previous phenomenological approaches. Specifically, the model reproduces both heating-stretching-cooling and cold drawing shape-fixing procedures and it takes into account the non-ideal behavior of realistic SMPs (i.e. imperfect shape-fixing and incomplete shape-recovery). Several numerical tests are reported to assess model performances, from simple uniaxial and biaxial tests to complex simulations of biomedical devices. Comparisons with experimental data taken from the literature are also provided to validate the model. The proposed improvements increase the model applicability over a wide range of polymer types and operating conditions
Computational Methods for Elastoplasticity: An Overview of Conventional and Less-Conventional Approaches
No full textThe need of accurately reproducing the behaviour of elastoplastic materials in computational environments for the solution of engineering problems motivates the development of efficient and robust numerical schemes. These engineering problems often involve complex designs and/or conditions and are further complicated by the necessity of employing highly nonlinear and nonsmooth elastoplastic constitutive equations and constraints to describe material behaviour. Therefore, the numerical solution of such problems is not trivial and requires careful analyses to guarantee algorithm robustness, accuracy, and convergence in a reasonable amount of time. The aim of the present paper is to provide the reader with both an analysis and discussion, helpful in choosing the suitable numerical scheme when considering the implementation of a plasticity model. After a brief overview of the fundamental concepts for classical plasticity theory, we revise the state-of-the-art of computational methods by discussing conventional and less-conventional algorithms, formulated in a unified setting to allow for a comparison. Several approaches are implemented and discussed in representative numerical simulations
Theoretical and numerical modeling of shape memory alloys accounting for multiple phase transformations and martensite reorientation
No full textThe present paper develops a refined and general three-dimensional phenomenological constitutive
model for shape memory alloys (SMAs), along the lines of what recently proposed by Auricchio
and Bonetti (2013) in a more theoretical context. Such an improved model takes into
account several physical phenomena, as martensite reorientation and different kinetics between
forward/reverse phase transformations, including also smooth thermo-mechanical response, lowstress
phase transformations as well as transformation-dependent elastic properties. The model is
treated numerically through an effective and efficient procedure, consisting in the replacement of
the classical set of Kuhn-Tucker inequality conditions by the so-called Fischer-Burmeister complementarity
function. Numerical predictions are compared with experimental results and the finite
element analysis of a SMA-based real device is described to assess the reliability of the proposed
model as well as the effectiveness of its numerical counterpart
Development and Comparison of Model-Based and Data-Driven Approaches for the Prediction of the Mechanical Properties of Lattice Structures
No full textLattice structures have great potential for several application fields ranging from medical and tissue engineering to aeronautical one. Their development is further speeded up by the continuing advances in additive manufacturing technologies that allow to overcome issues typical of standard processes and to propose tailored designs. However, the design of lattice structures is still challenging since their properties are considerably affected by numerous factors. The present paper aims to propose, discuss, and compare various modeling approaches to describe, understand, and predict the correlations between the mechanical properties and the void volume fraction of different types of lattice structures fabricated by fused deposition modeling 3D printing. Particularly, four approaches are proposed: (i) a simplified analytical model; (ii) a semi-empirical model combining analytical equations with experimental correction factors; (iii) an artificial neural network trained on experimental data; (iv) numerical simulations by finite element analyses. The comparison among the various approaches, and with experimental data, allows to identify the performances, advantages, and disadvantages of each approach, thus giving important guidelines for choosing the right design methodology based on the needs and available data
Computational Analysis of Advanced Shape-Memory Alloy Devices Through a Robust Modeling Framework
No full textShape-memory alloys (SMA) provide significant advantages in various industrial fields, but their manufacturing and commercialization are currently hindered. This is attributed mainly to the poor knowledge of material behavior and the lack of standards in its mechanical characterization. SMA products are usually developed by trial-and-error testing to address specific design requirements, thus increasing costs and time. The development of simulation tools offers a possible solution to assist engineers and designers and allows to better understand SMA transformation phenomena. Accordingly, the purpose of the present paper is to numerically analyze and predict the response of spring-like actuators and septal occluders, which are industrial components exploiting the shape-memory and pseudoelastic properties of SMAs, respectively. The methodology includes two main stages: the implementation of the three-dimensional phenomenological model known as Souza-Auricchio model and the finite element modeling of the device. A discussion about the steps of each stage, as parameter identification and model generalizations, is provided. Validation results are presented through a comparison with the results of a performed experimental campaign. The framework proves good prediction capabilities and allows to reduce the number of experimental tests in the future
Fiber-reinforced materials: finite elements for the treatment of the inextensibility constraint
No full textThe present paper proposes a numerical framework for the analysis of problems involving fiber-reinforced anisotropic materials. Specifically, isotropic linear elastic solids, reinforced by a single family of inextensible fibers, are considered. The kinematic constraint equation of inextensibility in the fiber direction leads to the presence of an undetermined fiber stress in the constitutive equations. To avoid locking-phenomena in the numerical solution due to the presence of the constraint, mixed finite elements based on the Lagrange multiplier, perturbed Lagrangian, and penalty method are proposed. Several boundary-value problems under plane strain conditions are solved and numerical results are compared to analytical solutions, whenever the derivation is possible. The performed simulations allow to assess the performance of the proposed finite elements and to discuss several features of the developed formulations concerning the effective approximation for the displacement and fiber stress fields, mesh convergence, and sensitivity to penalty parameters
- …
