scholarly journals How Soft Polymers Cope with Cracks and Notches

2019 ◽  
Vol 9 (6) ◽  
pp. 1086 ◽  
Author(s):  
Andrea Spagnoli ◽  
Michele Terzano ◽  
Roberto Brighenti ◽  
Federico Artoni ◽  
Andrea Carpinteri
Keyword(s):  
Large Deformation ◽  
Soft Matter ◽  
Mechanical Response ◽  
Image Correlation ◽  
Thin Plates ◽  
External Loading ◽  
Full Field ◽  
High Deformation ◽  
Flaw Tolerance ◽  
Damage And Fracture

Soft matter denotes a large category of materials showing unique properties, resulting from a low elastic modulus, a very high deformation capability, time-dependent mechanical behavior, and a peculiar mechanics of damage and fracture. The flaw tolerance, commonly understood as the ability of a given material to withstand external loading in the presence of a defect, is certainly one of the most noticeable attributes. This feature results from a complex and highly entangled microstructure, where the mechanical response to external loading is mainly governed by entropic-related effects. In the present paper, the flaw tolerance of soft elastomeric polymers, subjected to large deformation, is investigated experimentally. In particular, we consider the tensile response of thin plates made of different silicone rubbers, containing defects of various severity at different scales. Full-field strain maps are acquired by means of the Digital Image Correlation (DIC) technique. The experimental results are interpreted by accounting for the blunting of the defects due to large deformation in the material. The effect of blunting is interpreted in terms of reduction of the stress concentration factor generated by the defect, and failure is compared to that of traditional crystalline brittle materials.

Osmo-inelastic response of the intervertebral disc annulus fibrosus tissue

2020 ◽  
Vol 234 (9) ◽  
pp. 1000-1010
Author(s):  
Amil Derrouiche ◽  
Ameni Zaouali ◽  
Fahmi Zaïri ◽  
Jewan Ismail ◽  
Zhengwei Qu ◽  
...  
Keyword(s):  
Intervertebral Disc ◽  
Annulus Fibrosus ◽  
Mechanical Response ◽  
Rate Sensitivity ◽  
Image Correlation ◽  
Inelastic Response ◽  
Full Field ◽  
Osmotic Effect ◽  
Rate Dependent ◽  
Optical Strain

The aim of this article is to provide some insights on the osmo-inelastic response under stretching of annulus fibrosus of the intervertebral disc. Circumferentially oriented specimens of square cross section, extracted from different regions of bovine cervical discs (ventral-lateral and dorsal-lateral), are tested under different strain-rates and saline concentrations within normal range of strains. An accurate optical strain measuring technique, based upon digital image correlation, is used in order to determine the full-field displacements in the lamellae and fibers planes of the layered soft tissue. Annulus stress–stretch relationships are measured along with full-field transversal strains in the two planes. The mechanical response is found hysteretic, rate-dependent and osmolarity-dependent with a Poisson’s ratio higher than 0.5 in the fibers plane and negative (auxeticity) in the lamellae plane. While the stiffness presents a regional-dependency due to variations in collagen fibers content/orientation, the strain-rate sensitivity of the response is found independent on the region. A significant osmotic effect is found on both the auxetic response in the lamellae plane and the stiffness rate-sensitivity. These local experimental observations will result in more accurate chemo-mechanical modeling of the disc annulus and a clearer multi-scale understanding of the disc intervertebral function.

scholarly journals A novel apparatus and methodology for the high frequency mechanical characterisation of ultrasoft materials

2021 ◽  
Vol 250 ◽  
pp. 01033
Author(s):  
Aaron Graham ◽  
Clive R Siviour
Keyword(s):  
Mechanical Response ◽  
Soft Materials ◽  
Biological Tissues ◽  
Image Correlation ◽  
Full Field ◽  
Mechanical Characterisation ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Low Modulus ◽  
Elastic Shear

Characterising the mechanical response of ultra-soft materials is challenging, particularly at high strain rates and frequencies [1]. Time Temperature Superposition (TTS) can sometimes be used to mitigate these limitations [2], however not all materials are suitable for TTS. Biological tissues are particularly difficult to test: in addition to the extreme softness, challenges arise due to specimen inhomogeneity, sensitivity to boundary conditions, natural biological variability, and complex post-mortem changes. In the current study, a novel experimental apparatus and methodology was developed and validated using low modulus silicone elastomers as model materials. The full field visco-elastic shear response was characterised over a wide range of deformation frequencies (100-1000+ Hz) and amplitudes using Digital Image Correlation (DIC) and the Virtual Fields Method (VFM). This methodology allows for the extraction of fullfield material properties that would be difficult or impossible to obtain using traditional engineering techniques.

Condition Monitoring of Textiles Using Optical Techniques

2009 ◽  
Vol 413-414 ◽  
pp. 447-454 ◽  
Author(s):  
C.C. Ye ◽  
Janice M. Dulieu-Barton ◽  
A.R. Chambers ◽  
F.J. Lennard ◽  
D.D. Eastop
Keyword(s):  
Mechanical Response ◽  
Adhesive System ◽  
Epoxy Adhesive ◽  
Image Correlation ◽  
Fibre Bragg Grating ◽  
Transfer Coefficients ◽  
Full Field ◽  
Strain Transfer ◽  
Fbg Sensors ◽  
Static Conditions

In the paper it is proposed to use fibre Bragg grating (FBG) sensors to monitor the deformation and strain in a woven textile. Non-contact digital image correlation (DIC) is used to validate the results. The principal objective of the work in this paper is to identify a suitable adhesive for attaching the FBG sensors to tapestries and textiles. To do this, the interfacial interactions of the optical fibre, the textile material and the necessary adhesive must be considered. The performance of two types of adhesive are studied: a PVA conservation adhesive and a two-part epoxy adhesive Araldite 2015. The effect of the application of the adhesives on the mechanical response of the textile is investigated. Full-field stain maps are obtained from the DIC and are used as the basis to characterise the behaviour of the FBG sensors/adhesive system. The strain transfer coefficients and a reinforcement factor are determined under quasi-static conditions. It is shown that the local reinforcement introduced is more significant in the specimen with the FBG bonded using the Araldite adhesive than those with conservation adhesives. Nevertheless, the Araldite adhesive has a better strain transfer coefficient than the conservation adhesive, although not as high as that expect with conventional engineering materials.

Mechanical Response of Aluminium Alloy AA6061 Butt-Welded Joints Subjected to Two Initial Tempers and Different Heat Treatments

2015 ◽  
Vol 752-753 ◽  
pp. 51-54
Author(s):  
A. Alisibramulisi ◽  
Odd Geir Lademo ◽  
Ole Runar Myhr ◽  
Per Kristian Larsen
Keyword(s):  
Aluminium Alloy ◽  
Strain Measurement ◽  
Mechanical Response ◽  
Experimental Studies ◽  
Heat Treatments ◽  
Post Weld Heat Treatment ◽  
Image Correlation ◽  
Response Curves ◽  
Full Field ◽  
Dic Technique

Experimental studies have been carried out on butt-welded specimens of aluminium alloy AA6061. Two tempers; T4 and T6 prior to welding were investigated and the subsequent effects of natural ageing (NA) and post weld heat treatment (PWHT) were assessed. Digital image correlation (DIC) technique was used to obtain full field strain measurement on the transversely loaded tensile specimens. The tensile properties of these specimens are presented in terms of response curves. In addition, hardness profiles were also obtained. Both initial tempers and heat treatments were shown to give a significant effect on the mechanical response of the welded specimens tested.

Use of three-dimensional digital image correlation to evaluate mechanical response of prosthetic systems

2016 ◽  
Vol 41 (1) ◽  
pp. 101-105
Author(s):  
Michelin Alvarez-Camacho ◽  
Victor Alvarez-Guevara ◽  
Carlos Galvan Duque Gastelum ◽  
Daniel Flores Vazquez ◽  
Gerardo Rodriguez-Reyes ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Technical Note ◽  
Image Correlation ◽  
Patient Specific ◽  
Real Patient ◽  
Full Field ◽  
Measurement Protocol

Background and aim:The need of comfortable and safe prosthetic systems is an important challenge for both prosthetists and engineers. The aim of this technical note is to demonstrate the use of three-dimensional digital image correlation to evaluate mechanical response of two prosthetic systems under real patient dynamic loads.Technique:This note describes the use of three-dimensional digital image correlation method to obtain full-field strain and displacement measurements on the surface of two lower limb prostheses for Chopart amputation. It outlines key points of the measurement protocol and illustrates the analysis of critical regions using data obtained on specific points of interest.Discussion:The results show that the use of three-dimensional digital image correlation can be a tool for the prosthetist to optimize the prosthesis considering features related to the material and design, in order to bear with real patient-specific load conditions.Clinical relevanceThree-dimensional digital image correlation can support decision-making on new designs and materials for prosthetics based on quantitative data. Better understanding of mechanical response could also assist prescription for appropriate prosthetic systems.

Validation of Impact Simulations of a Car Bonnet by Full-Field Optical Measurements

2011 ◽  
Vol 70 ◽  
pp. 57-62
Author(s):  
George Lampeas ◽  
Vasilis Pasialis ◽  
Thorsten Siebert ◽  
Mara Feligiotti ◽  
Andrea Pipino
Keyword(s):  
Displacement Field ◽  
High Speed ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Quantitative Information ◽  
Image Correlation ◽  
Optical Measurements ◽  
Optical Techniques ◽  
Full Field ◽  
Dynamic Events

Innovative designs of transport vehicles need to be validated in order to demonstrate reliability and provide confidence. The most common approaches to such designs involve simulations based on Finite Element (FE) analysis, used to study the mechanical response of the structural elements during critical events. These simulations need reliable validation techniques, especially if anisotropic materials, such as fibre reinforced polymers, or complex designs, such as automotive components are considered. It is normal practice to assess the accuracy of numerical results by comparing the predicted values to corresponding experimental data. In this frame, the use of whole field optical techniques has been proven successful in the validation of deformation, strain, or vibration modes [1]. The strength of full-field optical techniques is that the whole displacement field can be visualized and analyzed. By using High Speed cameras, the Digital Image Correlation (DIC) method can be applied to highly non-linear dynamic events and deliver quantitative information about the three-dimensional displacement field [2].

scholarly journals Wrinkling in engineering fabrics: a comparison between two different comprehensive modelling approaches

2018 ◽  
Vol 474 (2216) ◽  
pp. 20180063 ◽  
Author(s):  
I. Giorgio ◽  
P. Harrison ◽  
F. dell'Isola ◽  
J. Alsayednoor ◽  
E. Turco
Keyword(s):  
Discrete Model ◽  
Continuum Model ◽  
Mechanical Response ◽  
Image Correlation ◽  
Full Field ◽  
Explicit Finite Element ◽  
Fitting Procedure ◽  
Constitutive Parameters ◽  
The Continuum ◽  
Modelling Approaches

We consider two ‘comprehensive’ modelling approaches for engineering fabrics. We distinguish the two approaches using the terms ‘semi-discrete’ and ‘continuum’, reflecting their natures. We demonstrate a fitting procedure, used to identify the constitutive parameters of the continuum model from predictions of the semi-discrete model, the parameters of which are in turn fitted to experimental data. We, then, check the effectiveness of the continuum model by verifying the correspondence between semi-discrete and continuum model predictions using test cases not previously used in the identification process. Predictions of both modelling approaches are compared against full-field experimental kinematic data, obtained using stereoscopic digital image correlation techniques, and also with measured force data. Being a reduced order model and being implemented in an implicit rather than an explicit finite-element code, the continuum model requires significantly less computational power than the semi-discrete model and could therefore be used to more efficiently explore the mechanical response of engineering fabrics.

scholarly journals Stereo-DIC Measurements of a Vibrating Bladed Disk: In-Depth Analysis of Full-Field Deformed Shapes

2021 ◽  
Vol 11 (12) ◽  
pp. 5430
Author(s):  
Paolo Neri ◽  
Alessandro Paoli ◽  
Ciro Santus
Keyword(s):  
Single Point ◽  
Excitation Frequency ◽  
Phase Variation ◽  
Operating Conditions ◽  
Image Correlation ◽  
Response Analysis ◽  
Full Field ◽  
Low Speed ◽  
Bladed Disk ◽  
Depth Analysis

Vibration measurements of turbomachinery components are of utmost importance to characterize the dynamic behavior of rotating machines, thus preventing undesired operating conditions. Local techniques such as strain gauges or laser Doppler vibrometers are usually adopted to collect vibration data. However, these approaches provide single-point and generally 1D measurements. The present work proposes an optical technique, which uses two low-speed cameras, a multimedia projector, and three-dimensional digital image correlation (3D-DIC) to provide full-field measurements of a bladed disk undergoing harmonic response analysis (i.e., pure sinusoidal excitation) in the kHz range. The proposed approach exploits a downsampling strategy to overcome the limitations introduced by low-speed cameras. The developed experimental setup was used to measure the response of a bladed disk subjected to an excitation frequency above 6 kHz, providing a deep insight in the deformed shapes, in terms of amplitude and phase distributions, which could not be feasible with single-point sensors. Results demonstrated the system’s effectiveness in measuring amplitudes of few microns, also evidencing blade mistuning effects. A deeper insight into the deformed shape analysis was provided by considering the phase maps on the entire blisk geometry, and phase variation lines were observed on the blades for high excitation frequency.

scholarly journals Full-Field Operational Modal Analysis of an Aircraft Composite Panel from the Dynamic Response in Multi-Impact Test

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1602
Author(s):  
Ángel Molina-Viedma ◽  
Elías López-Alba ◽  
Luis Felipe-Sesé ◽  
Francisco Díaz
Keyword(s):  
Modal Analysis ◽  
Energy Absorption ◽  
High Speed ◽  
Operational Modal Analysis ◽  
Modal Identification ◽  
Image Correlation ◽  
Composite Panel ◽  
Impact Excitation ◽  
Full Field ◽  
The Impact

Experimental characterization and validation of skin components in aircraft entails multiple evaluations (structural, aerodynamic, acoustic, etc.) and expensive campaigns. They require different rigs and equipment to perform the necessary tests. Two of the main dynamic characterizations include the energy absorption under impact forcing and the identification of modal parameters through the vibration response under any broadband excitation, which also includes impacts. This work exploits the response of a stiffened aircraft composite panel submitted to a multi-impact excitation, which is intended for impact and energy absorption analysis. Based on the high stiffness of composite materials, the study worked under the assumption that the global response to the multi-impact excitation is linear with small strains, neglecting the nonlinear behavior produced by local damage generation. Then, modal identification could be performed. The vibration after the impact was measured by high-speed 3D digital image correlation and employed for full-field operational modal analysis. Multiple modes were characterized in a wide spectrum, exploiting the advantages of the full-field noninvasive techniques. These results described a consistent modal behavior of the panel along with good indicators of mode separation given by the auto modal assurance criterion (Auto-MAC). Hence, it illustrates the possibility of performing these dynamic characterizations in a single test, offering additional information while reducing time and investment during the validation of these structures.

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