scholarly journals Dynamics of necking and fracture in ductile porous materials

2020 ◽  
Author(s):  
Jose Rodriguez-Martinez ◽  
Komi Espoir N'souglo ◽  
Ankit Srivastava ◽  
Xinzhu Zheng
Keyword(s):  
Finite Element ◽  
Initial Porosity ◽  
Expansion Velocity ◽  
Inertia Effects ◽  
Ductile Materials ◽  
Loading Rates ◽  
Unit Cell Size ◽  
Wide Range ◽  
Unit Cells ◽  
Dynamic Loading Conditions

The onset of necking in dynamically expanding ductile rings is delayed due to the stabilizing effect of inertia, and with increasing expansion velocity, both the number of necks incepted and the number of fragments increase. In general, neck retardation is expected to delay fragmentation as necking is often the precursor to fracture. However, in porous ductile materials, it is possible that fracture can occur without significant necking. Thus, the objective of this work is to unravel the complex interaction of initial porosity and inertia on the onset of necking and fracture. To this end, we have carried out a series of finite element calculations of unit cells with sinusoidal geometric perturbations and varying levels of initial porosity under a wide range of dynamic loading conditions. In the calculations, the material is modeled using a constitutive framework that includes many of the hardening and softening mechanisms that are characteristics of ductile metallic materials, such as strain hardening, strain rate hardening, thermal softening, and damage-induced softening. The contribution of the inertia effect on the loading process is evaluated through a dimensionless parameter that combines the effects of loading rate, material properties, and unit cell size. Our results show that low initial porosity levels favor necking before fracture, and high initial porosity levels favor fracture before necking, especially at high loading rates where inertia effects delay the onset of necking. The finite element results are also compared with the predictions of linear stability analysis of necking instabilities in porous ductile materials.

scholarly journals Dynamics of Necking and Fracture in Ductile Porous Materials

2020 ◽  
Vol 87 (4) ◽  
Author(s):  
Xinzhu Zheng ◽  
Komi E. N’souglo ◽  
Jose A. Rodríguez-Martínez ◽  
Ankit Srivastava
Keyword(s):  
Finite Element ◽  
Initial Porosity ◽  
Expansion Velocity ◽  
Inertia Effects ◽  
Ductile Materials ◽  
Loading Rates ◽  
Unit Cell Size ◽  
Wide Range ◽  
Unit Cells ◽  
Dynamic Loading Conditions

Abstract The onset of necking in dynamically expanding ductile rings is delayed due to the stabilizing effect of inertia, and with increasing expansion velocity, both the number of necks incepted and the number of fragments increase. In general, neck retardation is expected to delay fragmentation as necking is often the precursor to fracture. However, in porous ductile materials, it is possible that fracture can occur without significant necking. Thus, the objective of this work is to unravel the complex interaction of initial porosity and inertia on the onset of necking and fracture. To this end, we have carried out a series of finite element calculations of unit cells with sinusoidal geometric perturbations and varying levels of initial porosity under a wide range of dynamic loading conditions. In the calculations, the material is modeled using a constitutive framework that includes many of the hardening and softening mechanisms that are characteristics of ductile metallic materials, such as strain hardening, strain rate hardening, thermal softening, and damage-induced softening. The contribution of the inertia effect on the loading process is evaluated through a dimensionless parameter that combines the effects of loading rate, material properties, and unit cell size. Our results show that low initial porosity levels favor necking before fracture, and high initial porosity levels favor fracture before necking, especially at high loading rates where inertia effects delay the onset of necking. The finite element results are also compared with the predictions of linear stability analysis of necking instabilities in porous ductile materials.

scholarly journals Boundary and interface conditions in the relaxed micromorphic model: Exploring finite-size metastructures for elastic wave control

2021 ◽  
pp. 108128652110489
Author(s):  
Gianluca Rizzi ◽  
Marco Valerio d’Agostino ◽  
Patrizio Neff ◽  
Angela Madeo
Keyword(s):  
Finite Element ◽  
Finite Size ◽  
Interface Conditions ◽  
Short Term ◽  
Element Simulation ◽  
Wide Range ◽  
Unit Cells ◽  
Energy Focusing ◽  
Scattering Response ◽  
Well Posed

In this paper, we establish well-posed boundary and interface conditions for the relaxed micromorphic model that are able to unveil the scattering response of fully finite-size metamaterial samples. The resulting relaxed micromorphic boundary value problem is implemented in finite-element simulations describing the scattering of a square metamaterial sample whose side counts nine unit cells. The results are validated against a direct finite-element simulation encoding all the details of the underlying metamaterial’s microstructure. The relaxed micromorphic model can recover the scattering metamaterial’s behavior for a wide range of frequencies and for all possible angles of incidence, thus showing that it is suitable to describe dynamic anisotropy. Finally, thanks to the model’s computational performances, we can design a metastructure combining metamaterials and classical materials in such a way that it acts as a protection device while providing energy focusing in specific collection points. These results open important perspectives for the short-term design of sustainable structures that can control elastic waves and recover energy.

scholarly journals A machine learning platform for the discovery of materials

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Carl E. Belle ◽  
Vural Aksakalli ◽  
Salvy P. Russo
Keyword(s):  
Machine Learning ◽  
Density Functional ◽  
Gw Approximation ◽  
Dft Methods ◽  
Functional Theory ◽  
Unit Cell Size ◽  
Learning Platform ◽  
Photovoltaic Materials ◽  
Wide Range ◽  
Quantum Espresso

AbstractFor photovoltaic materials, properties such as band gap $$E_{g}$$ E g are critical indicators of the material’s suitability to perform a desired function. Calculating $$E_{g}$$ E g is often performed using Density Functional Theory (DFT) methods, although more accurate calculation are performed using methods such as the GW approximation. DFT software often used to compute electronic properties includes applications such as VASP, CRYSTAL, CASTEP or Quantum Espresso. Depending on the unit cell size and symmetry of the material, these calculations can be computationally expensive. In this study, we present a new machine learning platform for the accurate prediction of properties such as $$E_{g}$$ E g of a wide range of materials.

scholarly journals Fabrication and Compressive Behavior of a Micro-Lattice Composite by High Resolution DLP Stereolithography

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 785
Author(s):  
Chow Shing Shin ◽  
Yu Chia Chang
Keyword(s):  
High Resolution ◽  
Lattice Structure ◽  
Low Cost ◽  
Hierarchical Structures ◽  
Dip Coating ◽  
Unit Cell ◽  
Digital Light Processing ◽  
Unit Cell Size ◽  
Wide Range ◽  
And Performance

Lattice structures are superior to stochastic foams in mechanical properties and are finding increasing applications. Their properties can be tailored in a wide range through adjusting the design and dimensions of the unit cell, changing the constituent materials as well as forming into hierarchical structures. In order to achieve more levels of hierarchy, the dimensions of the fundamental lattice have to be small enough. Although lattice size of several microns can be fabricated using the two-photon polymerization technique, sophisticated and costly equipment is required. To balance cost and performance, a low-cost high resolution micro-stereolithographic system has been developed in this work based on a commercial digital light processing (DLP) projector. Unit cell lengths as small as 100 μm have been successfully fabricated. Decreasing the unit cell size from 150 to 100 μm increased the compressive stiffness by 26%. Different pretreatments to facilitate the electroless plating of nickel on the lattice structure have been attempted. A pretreatment of dip coating in a graphene suspension is the most successful and increased the strength and stiffness by 5.3 and 3.6 times, respectively. Even a very light and incomplete nickel plating in the interior has increase the structural stiffness and strength by more than twofold.

Nonlinear dynamic behaviour of guy cables in turbulent winds

2001 ◽  
Vol 28 (1) ◽  
pp. 98-110 ◽  
Author(s):  
Bruce F Sparling ◽  
Alan G Davenport
Keyword(s):  
Finite Element ◽  
Dynamic Behaviour ◽  
Aerodynamic Drag ◽  
Numerical Study ◽  
Horizontal Displacement ◽  
Wind Loading ◽  
Second Phase ◽  
Nonlinear Coupling ◽  
Wide Range ◽  
Cable Vibrations

Large amplitude cable vibrations are difficult to predict using linear theory due to the presence of sag in the suspended profile. A numerical study was therefore undertaken to investigate the dynamic behaviour of inclined cables excited by imposed displacements. To model the nonlinear nature of cable response, a time domain finite element approach was adopted using nonlinear catenary cable elements. Two types of horizontal displacement patterns were enforced at the upper end of the guy. In the first phase of the study, harmonic displacement histories with a wide range of forcing frequencies were considered. In the second phase, random enforced displacements were used to simulate the motion of a guyed mast in gusty winds. The influence of aerodynamic drag and damping forces was investigated by performing analyses under still air, steady wind, and turbulent wind conditions. It was found that nonlinear coupling of related harmonic response components was significant at certain critical frequencies, particular when the excitation was harmonic and acted in the plane of the guy. Positive aerodynamic damping was shown to effectively suppress resonant and nonlinear coupling response.Key words: cables, structural dynamics, wind loading, finite element method, nonlinear analysis, guyed towers.

scholarly journals Out-of-Plane Vibration of Curved Uniform and Tapered Beams with Additional Mass

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Hamdi Alper Özyiğit ◽  
Mehmet Yetmez ◽  
Utku Uzun
Keyword(s):  
Finite Element ◽  
Free Vibration ◽  
Boundary Conditions ◽  
Natural Frequencies ◽  
Variable Cross ◽  
Additional Mass ◽  
Inertia Effects ◽  
Tapered Beam ◽  
Out Of Plane ◽  
Good Agreement

As there is a gap in literature about out-of-plane vibrations of curved and variable cross-sectioned beams, the aim of this study is to analyze the free out-of-plane vibrations of curved beams which are symmetrically and nonsymmetrically tapered. Out-of-plane free vibration of curved uniform and tapered beams with additional mass is also investigated. Finite element method is used for all analyses. Curvature type is assumed to be circular. For the different boundary conditions, natural frequencies of both symmetrical and unsymmetrical tapered beams are given together with that of uniform tapered beam. Bending, torsional, and rotary inertia effects are considered with respect to no-shear effect. Variations of natural frequencies with additional mass and the mass location are examined. Results are given in tabular form. It is concluded that (i) for the uniform tapered beam there is a good agreement between the results of this study and that of literature and (ii) for the symmetrical curved tapered beam there is also a good agreement between the results of this study and that of a finite element model by using MSC.Marc. Results of out-of-plane free vibration of symmetrically tapered beams for specified boundary conditions are addressed.

scholarly journals Eccentricity based topological indices of face centered cubic lattice FCC(n)

2020 ◽  
Vol 44 (1) ◽  
pp. 32-38
Author(s):  
Hani Shaker ◽  
Muhammad Imran ◽  
Wasim Sajjad
Keyword(s):  
Wiener Index ◽  
Face Centered Cubic ◽  
Eccentric Connectivity Index ◽  
Zagreb Index ◽  
Cubic Lattice ◽  
Chemical Graph ◽  
Chemical Graph Theory ◽  
Wide Range ◽  
Unit Cells ◽  
Face Centered

Abstract Chemical graph theory has become a prime gadget for mathematical chemistry due to its wide range of graph theoretical applications for solving molecular problems. A numerical quantity is named as topological index which explains the topological characteristics of a chemical graph. Recently face centered cubic lattice FCC(n) attracted large attention due to its prominent and distinguished properties. Mujahed and Nagy (2016, 2018) calculated the precise expression for Wiener index and hyper-Wiener index on rows of unit cells of FCC(n). In this paper, we present the ECI (eccentric-connectivity index), TCI (total-eccentricity index), CEI (connective eccentric index), and first eccentric Zagreb index of face centered cubic lattice.

Local Hydrostatic Pressure Test for Cylindrical Vessels

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
H. Al-Gahtani ◽  
A. Khathlan ◽  
M. Sunar ◽  
M. Naffa'a
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hydrostatic Pressure ◽  
Cylindrical Vessel ◽  
Geometrical Parameters ◽  
The Finite Element Method ◽  
Wide Range ◽  
Pressure Test ◽  
Local Test ◽  
Alternative Test

The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pressure vessel industry. Upon fabrication, it is required that the whole structure is subjected to pressure testing. The test can be expensive as it necessitates pressurizing the whole structure typically having a large volume. Hence, it is proposed to make a “local test,” which is considerably simpler as it involves capping the small nozzle and testing only a relatively small portion of the structure. This paper investigates the accuracy and reliability of such an alternative test, using the finite-element method. Two different finite-element types are used in the study, specifically a shell-based element and a solid-based element. The verification of the finite-element results for two different cases shows that the models used in the study are valid. It also proves that the two element types yield very similar stress results. In addition, the study includes a numerical investigation of more than 40 different nozzle-to-vessel junctures with a wide range of parameters for the nozzle and vessel. The results indicate that the use of cylindrical caps that are slightly larger than the nozzle is not recommended as it produces stresses that are significantly different from those for the original required pressure test. As such, the study provides an estimate of the smallest size of the cap that may be used in the local test to generate stresses that agree with the full test. For most practical geometries, it is shown that the size of the cap needs to be at least 2–30 times larger than that of the nozzle, depending on the geometrical parameters of the juncture.

scholarly journals Buckling of regular, chiral and hierarchical honeycombs under a general macroscopic stress state

2014 ◽  
Vol 470 (2167) ◽  
pp. 20130856 ◽  
Author(s):  
Babak Haghpanah ◽  
Jim Papadopoulos ◽  
Davood Mousanezhad ◽  
Hamid Nayeb-Hashemi ◽  
Ashkan Vaziri
Keyword(s):  
Finite Element ◽  
Stress State ◽  
Closed Form ◽  
Plane Stress ◽  
Plane Stress State ◽  
Cellular Structures ◽  
Two Dimensional ◽  
Buckling Strength ◽  
Macroscopic Stress ◽  
Unit Cells

An approach to obtain analytical closed-form expressions for the macroscopic ‘buckling strength’ of various two-dimensional cellular structures is presented. The method is based on classical beam-column end-moment behaviour expressed in a matrix form. It is applied to sample honeycombs with square, triangular and hexagonal unit cells to determine their buckling strength under a general macroscopic in-plane stress state. The results were verified using finite-element Eigenvalue analysis.

NOVEL COUPLING CONSTRAINT TECHNIQUE FOR EXPLICIT FINITE ELEMENT ANALYSIS

2004 ◽  
Vol 01 (02) ◽  
pp. 309-328
Author(s):  
R. J. HO ◽  
S. A. MEGUID ◽  
R. G. SAUVÉ
Keyword(s):  
Finite Element ◽  
Current Method ◽  
Explicit Integration ◽  
Rotation Tensor ◽  
Element Analysis ◽  
Explicit Finite Element ◽  
Explicit Finite Element Analysis ◽  
Wide Range ◽  
Large Rotations ◽  
Generalized Constraint

This paper presents a unified novel technique for enforcing nonlinear beam-to-shell, beam-to-solid, and shell-to-solid constraints in explicit finite element formulations. The limitations of classical multi-point constraint approaches are examined at length, particularly in the context of explicit solution schemes. Novel formulation of a generalized constraint method that ensures proper element coupling is then presented, and its computer implementation in explicit integration algorithms is discussed. Crucial in this regard is the accurate and efficient representation of finite rotations, accomplished using an incremental rotation tensor. The results of some illustrative test cases show the accuracy and robustness of the newly developed algorithm for a wide range of deformation, including that in which large rotations are encountered. When compared to existing works, the salient features of the current method are in evidence.

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