Parameter identification of a second-gradient model for the description of pantographic structures in dynamic regime

AbstractPantographic structures are examples of metamaterials with such a microstructure that higher-gradient terms’ role is increased in the mechanical response. In this work, we aim for validating parameters of a reduced-order model for a pantographic structure. Experimental tests are carried out by applying forced oscillation to 3D-printed specimens for a range of frequencies. A second-gradient coarse-grained nonlinear model is utilized for obtaining a homogenized 2D description of the pantographic structure. By inverse analysis and through an automatized optimization algorithm, the parameters of the model are identified for the corresponding pantographic structure. By comparing the displacement plots, the performance of the model and the identified parameters are assessed for dynamic regime. Qualitative and quantitative analyses for different frequency ranges are performed. A good agreement is present far away from the eigenfrequencies. The discrepancies near the eigenfrequencies are a possible indication of the significance of higher-order inertia in the model.

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Are higher-gradient models also capable of predicting mechanical behavior in the case of wide-knit pantographic structures?

Mathematics and Mechanics of Solids ◽

10.1177/1081286520937339 ◽

2020 ◽

Vol 26 (1) ◽

pp. 18-29 ◽

Cited By ~ 3

Author(s):

Mario Spagnuolo ◽

M Erden Yildizdag ◽

Ugo Andreaus ◽

Antonio M Cazzani

Keyword(s):

Continuum Model ◽

Central Theme ◽

Fiber Density ◽

Pantographic Structures ◽

Numerical Predictions ◽

Second Gradient ◽

Bias Extension ◽

Second Gradient Continuum ◽

Gradient Models ◽

Good Agreement

The central theme of this study is to investigate a remarkable capability of a second-gradient continuum model developed for pantographic structures. The model is applied to a particular type of this metamaterial, namely the wide-knit pantograph. As this type of structure has low fiber density, the applicability of such a continuum model may be questionable. To address this uncertainty, numerical simulations are conducted to analyze the behavior of a wide-knit pantographic structure, and the predicted results are compared with those measured experimentally under bias extension testing. The results presented in this study show that the numerical predictions and experimental measurements are in good agreement; therefore, in some useful circumstances, this model is applicable for the analysis of wide-knit pantographic structures.

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Triaxial compression behavior of 3D printed and natural sands

Granular Matter ◽

10.1007/s10035-021-01143-0 ◽

2021 ◽

Vol 23 (4) ◽

Author(s):

Sheikh Sharif Ahmed ◽

Alejandro Martinez

Keyword(s):

3D Printing ◽

Critical State ◽

Mechanical Response ◽

Triaxial Compression ◽

Coarse Grained ◽

Compression Tests ◽

Natural Sand ◽

Compression Behavior ◽

3D Printed ◽

Triaxial Compression Tests

AbstractDifferent particle properties, such as shape, size, surface roughness, and constituent material stiffness, affect the mechanical behavior of coarse-grained soils. Systematic investigation of the individual effects of these properties requires careful control over other properties, which is a pervasive challenge in investigations with natural soils. The rapid advance of 3D printing technology provides the ability to produce analog particles with independent control over particle size and shape. This study examines the triaxial compression behavior of specimens of 3D printed sand particles and compares it to that of natural sand specimens. Drained and undrained isotropically-consolidated triaxial compression tests were performed on specimens composed of angular and rounded 3D printed and natural sands. The test results indicate that the 3D printed sands exhibit stress-dilatancy behavior that follows well-established flow rules, the angular 3D printed sand mobilizes greater critical state friction angle than that of rounded 3D printed sand, and analogous drained and undrained stress paths can be followed by 3D printed and natural sands with similar initial void ratios if the cell pressure is scaled. The results suggest that some of the fundamental behaviors of soils can be captured with 3D printed soils, and that the interpretation of their mechanical response can be captured with the critical state soil mechanics framework. However, important differences in response arise from the 3D printing process and the smaller stiffness of the printed polymeric material. Graphic abstract Artificial sand analogs were 3D printed from X-ray CT scans of sub-rounded and sub-angular natural sands. Triaxial compression tests were performed to characterize the strength and dilatancy behavior as well as critical staste parameters of the 3D printed sands and to compare it to that exhibited by the natural sands.

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Experimental Methods for Measuring the Viscous Friction Coefficient in Hydraulic Spool Valves

Sustainability ◽

10.3390/su13137174 ◽

2021 ◽

Vol 13 (13) ◽

pp. 7174

Author(s):

Massimo Rundo ◽

Paolo Casoli ◽

Antonio Lettini

Keyword(s):

Friction Coefficient ◽

Viscous Friction ◽

Experimental Tests ◽

Experimental Methods ◽

Displacement Transducer ◽

A Posteriori ◽

Displacement Control ◽

Spool Valves ◽

The University ◽

Good Agreement

In hydraulic components, nonlinearities are responsible for critical behaviors that make it difficult to realize a reliable mathematical model for numerical simulation. With particular reference to hydraulic spool valves, the viscous friction coefficient between the sliding and the fixed body is an unknown parameter that is normally set a posteriori in order to obtain a good agreement with the experimental data. In this paper, two different methodologies to characterize experimentally the viscous friction coefficient in a hydraulic component with spool are presented. The two approaches are significantly different and are both based on experimental tests; they were developed in two distinct laboratories in different periods of time and applied to the same flow compensator of a pump displacement control. One of the procedures was carried out at the Fluid Power Research Laboratory of the Politecnico di Torino, while the other approach was developed at the University of Parma. Both the proposed methods reached similar outcomes; moreover, neither method requires the installation of a spool displacement transducer that can significantly affect the results.

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Investigating the mechanical response of microscale pantographic structures fabricated by multiphoton lithography

Extreme Mechanics Letters ◽

10.1016/j.eml.2021.101202 ◽

2021 ◽

Vol 43 ◽

pp. 101202

Author(s):

Zacharias Vangelatos ◽

M. Erden Yildizdag ◽

Ivan Giorgio ◽

Francesco dell’Isola ◽

Costas Grigoropoulos

Keyword(s):

Mechanical Response ◽

Pantographic Structures ◽

Multiphoton Lithography

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Additively Manufactured Parts Made of a Polymer Material Used for the Experimental Verification of a Component of a High-Speed Machine with an Optimised Geometry—Preliminary Research

Polymers ◽

10.3390/polym13010137 ◽

2020 ◽

Vol 13 (1) ◽

pp. 137

Author(s):

Artur Andrearczyk ◽

Bartlomiej Konieczny ◽

Jerzy Sokołowski

Keyword(s):

Polymer Material ◽

High Speed ◽

Numerical Models ◽

Flow Analysis ◽

Experimental Tests ◽

Strength Analysis ◽

Compressor Wheel ◽

Operational Characteristics ◽

3D Printed ◽

Novel Method

This paper describes a novel method for the experimental validation of numerically optimised turbomachinery components. In the field of additive manufacturing, numerical models still need to be improved, especially with the experimental data. The paper presents the operational characteristics of a compressor wheel, measured during experimental research. The validation process included conducting a computational flow analysis and experimental tests of two compressor wheels: The aluminium wheel and the 3D printed wheel (made of a polymer material). The chosen manufacturing technology and the results obtained made it possible to determine the speed range in which the operation of the tested machine is stable. In addition, dynamic destructive tests were performed on the polymer disc and their results were compared with the results of the strength analysis. The tests were carried out at high rotational speeds (up to 120,000 rpm). The results of the research described above have proven the utility of this technology in the research and development of high-speed turbomachines operating at speeds up to 90,000 rpm. The research results obtained show that the technology used is suitable for multi-variant optimization of the tested machine part. This work has also contributed to the further development of numerical models.

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Visco-Hyperelastic Characterization of the Equine Immature Zona Pellucida

Materials ◽

10.3390/ma14051223 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1223

Author(s):

Elisa Ficarella ◽

Mohammad Minooei ◽

Lorenzo Santoro ◽

Elisabetta Toma ◽

Bartolomeo Trentadue ◽

...

Keyword(s):

Zona Pellucida ◽

Soft Matter ◽

Mechanical Response ◽

Mechanical Characterization ◽

Nonlinear Material ◽

Prony Series ◽

Critical Comparison ◽

Highly Nonlinear ◽

Good Agreement

This article presents a very detailed study on the mechanical characterization of a highly nonlinear material, the immature equine zona pellucida (ZP) membrane. The ZP is modeled as a visco-hyperelastic soft matter. The Arruda–Boyce constitutive equation and the two-term Prony series are identified as the most suitable models for describing the hyperelastic and viscous components, respectively, of the ZP’s mechanical response. Material properties are identified via inverse analysis based on nonlinear optimization which fits nanoindentation curves recorded at different rates. The suitability of the proposed approach is fully demonstrated by the very good agreement between AFM data and numerically reconstructed force–indentation curves. A critical comparison of mechanical behavior of two immature ZP membranes (i.e., equine and porcine ZPs) is also carried out considering the information on the structure of these materials available from electron microscopy investigations documented in the literature.

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On the Post-Processing of 3D-Printed ABS Parts

Polymers ◽

10.3390/polym13101559 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1559

Author(s):

Mohammad Reza Khosravani ◽

Jonas Schüürmann ◽

Filippo Berto ◽

Tamara Reinicke

Keyword(s):

Surface Treatment ◽

Fused Deposition Modeling ◽

Three Dimensional ◽

Acrylonitrile Butadiene Styrene ◽

Experimental Tests ◽

Fracture Load ◽

Post Processing ◽

Fused Deposition ◽

Dog Bone ◽

3D Printed

Application of Additive Manufacturing (AM) has significantly increased in the past few years. AM also known as three-dimensional (3D) printing has been currently used in fabrication of prototypes and end-use products. Considering the new applications of additively manufactured components, it is necessary to study structural details of these parts. In the current study, influence of a post-processing on the mechanical properties of 3D-printed parts has been investigated. To this aim, Acrylonitrile Butadiene Styrene (ABS) material was used to produce test coupons based on the Fused Deposition Modeling (FDM) process. More in deep, a device was designed and fabricated to fix imperfection and provide smooth surfaces on the 3D-printed ABS specimens. Later, original and treated specimens were subjected to a series of tensile loads, three-point bending tests, and water absorption tests. The experimental tests indicated fracture load in untreated dog-bone shaped specimen was 2026.1 N which was decreased to 1951.7 N after surface treatment. Moreover, the performed surface treatment was lead and decrease in tensile strength from 29.37 MPa to 26.25 MPa. Comparison of the results confirmed effects of the surface modification on the fracture toughness of the examined semi-circular bending components. Moreover, a 3D laser microscope was used for visual investigation of the specimens. The documented results are beneficial for next designs and optimization of finishing processes.

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Ground Flutter Simulation Test Based on Reduced Order Modeling of Aerodynamics by CFD/CSD Coupling Method

International Journal of Applied Mechanics ◽

10.1142/s175882511950008x ◽

2019 ◽

Vol 11 (01) ◽

pp. 1950008

Author(s):

Binwen Wang ◽

Xueling Fan

Keyword(s):

Aerodynamic Force ◽

Test System ◽

Simulation Test ◽

Robust Controller ◽

Test Technique ◽

Reduced Order ◽

Aerodynamic Model ◽

Flutter Boundary ◽

Computational Fluid Dynamics Cfd ◽

Good Agreement

Flutter is an aeroelastic phenomenon that may cause severe damage to aircraft. Traditional flutter evaluation methods have many disadvantages (e.g., complex, costly and time-consuming) which could be overcome by ground flutter test technique. In this study, an unsteady aerodynamic model is obtained using computational fluid dynamics (CFD) code according to the procedure of frequency domain aerodynamic calculation. Then, the genetic algorithm (GA) method is adopted to optimize interpolation points for both excitation and response. Furthermore, the minimum-state method is utilized for rational fitting so as to establish an aerodynamic model in time domain. The aerodynamic force is simulated through exciters and the precision of simulation is guaranteed by multi-input and multi-output robust controller. Finally, ground flutter simulation test system is employed to acquire the flutter boundary through response under a range of air speeds. A good agreement is observed for both velocity and frequency of flutter between the test and modeling results.

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Fluid Added Mass Effect in the Modal Response of a Pump-Turbine Impeller

Volume 1: 22nd Biennial Conference on Mechanical Vibration and Noise, Parts A and B ◽

10.1115/detc2009-86830 ◽

2009 ◽

Cited By ~ 4

Author(s):

Eduard Egusquiza ◽

Carme Valero ◽

Quanwei Liang ◽

Miguel Coussirat ◽

Ulrich Seidel

Keyword(s):

Natural Frequencies ◽

Experimental Tests ◽

Mass Effect ◽

Added Mass ◽

Mode Shapes ◽

Pump Turbine ◽

Modal Response ◽

Surrounding Fluid ◽

Turbine Impeller ◽

Good Agreement

In this paper, the reduction in the natural frequencies of a pump-turbine impeller prototype when submerged in water has been investigated. The impeller, with a diameter of 2.870m belongs to a pump-turbine unit with a power of around 100MW. To analyze the influence of the added mass, both experimental tests and numerical simulations have been carried out. The experiment has been performed in air and in water. From the frequency response functions the modal characteristics such as natural frequencies and mode shapes have been obtained. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a mass of water). The modal behaviour has also been calculated. The numerical results were compared with the available experimental results. The comparison shows a good agreement in the natural frequency values both in air and in water. The reduction in frequency due to the added mass effect of surrounding fluid has been calculated. The physics of this phenomenon due to the fluid structure interaction has been investigated from the analysis of the mode-shapes.

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Numerical Investigation of Ductile Fracture in Pipelines Under Complex Loading Using a Phenomenological Damage Model

10.1115/pvp2021-62017 ◽

2021 ◽

Author(s):

Iago S. Santos ◽

Diego F. B. Sarzosa

Keyword(s):

Ductile Fracture ◽

Mechanical Response ◽

Numerical Study ◽

Damage Model ◽

Stress Triaxiality ◽

Numerical Procedure ◽

Complex Loading ◽

Experimental Tests ◽

Compact Tension ◽

Axial Tensile

Abstract This paper presents a numerical study on pipes ductile fracture mechanical response using a phenomenological computational damage model. The damage is controlled by an initiation criterion dependent on the stress triaxiality and the Lode angle parameter, and a post-initiation damage law to eliminate each finite element from the mesh. Experimental tests were carried out to calibrate the elastoplastic response, damage parameters and validate the FEM models. The tested geometries were round bars having smooth and notched cross-section, flat notched specimens under axial tensile loads, and fracture toughness tests in deeply cracked bending specimens SE(B) and compact tension samples C(T). The calibrated numerical procedure was applied to execute a parametric study in pipes with circumferential surface cracks subjected to tensile and internal pressure loads simultaneously. The effects of the variation of geometric parameters and the load applications on the pipes strain capacity were investigated. The influence of longitudinal misalignment between adjacent pipes was also investigated.

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