MECHANICAL CHARACTERIZATION OF ANIMAL DERIVED GRAFTS FOR SURGICAL IMPLANTATION

2016 ◽  
Vol 16 (03) ◽  
pp. 1650023 ◽  
Author(s):  
PIERO GIOVANNI PAVAN ◽  
PAOLA PACHERA ◽  
SILVIA TODROS ◽  
CESARE TIENGO ◽  
ARTURO NICOLA NATALI
Keyword(s):  
Stress Relaxation ◽  
Constitutive Model ◽  
Relaxation Process ◽  
Mechanical Response ◽  
Numerical Models ◽  
Experimental Testing ◽  
Axial Stress ◽  
Experimental Tests ◽  
Tissue Samples

Bioprostheses obtained from animal models are often adopted in abdominal surgery for repair and reconstruction. The functionality of these prosthetic implants is related also to their mechanical characteristics that are analyzed here. This work illustrates a constitutive model to describe the short-term mechanical response of Permacol[Formula: see text] bioprostheses. Experimental tests were developed on tissue samples to highlight mechanical non-linear characteristics and viscoelastic phenomena. Uni-axial tensile tests were developed to evaluate the strength and strain stiffening. Incremental uni-axial stress relaxation tests were carried out at nominal strain ranging from 10% to 20% and to monitor the stress relaxation process up to 400[Formula: see text]s. The constitutive model effectively describes the mechanical behavior found in experimental testing. The mechanical response appears to be independent on the loading direction, showing that the tissue can be considered as isotropic. The viscoelastic response of the tissue shows a strong decay of the stress in the first seconds of the relaxation process. The investigation performed is aimed at a general characterization of the biomechanical response and addresses the development of numerical models to evaluate the biomechanical performance of the graft with surrounding host tissues.

An Elaborate Data Set for Mechanical Characterization of the Foot

2008 ◽  
Author(s):  
Pavana Sirimamilla ◽  
Ahmet Erdemir ◽  
Antonie J. van den Bogert ◽  
Jason P. Halloran
Keyword(s):  
Mechanical Response ◽  
Experimental Testing ◽  
Experimental Tests ◽  
Shear Loading ◽  
Data Set ◽  
Material Response ◽  
Heel Pad ◽  
Biaxial Tests

Experimental testing of cadaver specimens is a useful means to quantify structural and material response of tissue and passive joint properties against applied loading[1,4]. Very often, specific material response (i.e., stress-strain behavior of a ligament or plantar tissue) has been the goal of experimental testing and is accomplished with uniaxial and/or biaxial tests of prepared tissue specimens with uniform geometries[2,5]. Material properties can then be calculated directly and if testing data involves individual sets of multiple loading modes (e.g. compression only, shear only, volumetric) an accurate representation of the global response of the specimen may be possible. In foot biomechanics, however, it is practically impossible to perform isolated mechanical testing in this manner. The structural response, therefore the stiffness characteristics, of the foot have been quantified, usually using a dominant loading mode: e.g., whole foot compression [6], heel pad indentation [3]. This approach ignores the complexity of most in vivo loading conditions, in which whole foot deformation involves interactions between compression, shear (e.g. heel pad) and tension (e.g. ligaments). Therefore, the purpose of this study was to quantify the mechanical response of a cadaver foot specimen subjected to compression and anterior-posterior (AP) shear loading of isolated heel and forefoot regions as well as whole foot compression. Results from the experimental tests represent a novel methodology to quantify a complete structural biomechanical response. Combined with medical imaging, followed by inverse finite element (FE) analysis, the data may also serve for material characterization of foot tissue.

scholarly journals Evolution of Meniscal Biomechanical Properties with Growth: An Experimental and Numerical Study

2021 ◽  
Vol 8 (5) ◽  
pp. 70
Author(s):  
Marco Ferroni ◽  
Beatrice Belgio ◽  
Giuseppe M. Peretti ◽  
Alessia Di Giancamillo ◽  
Federica Boschetti
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Developmental Stage ◽  
Mechanical Response ◽  
Numerical Study ◽  
Numerical Models ◽  
Mechanical Stimulus ◽  
Specific Response ◽  
Mechanical Parameters ◽  
Biochemical Analyses

The menisci of the knee are complex fibro-cartilaginous tissues that play important roles in load bearing, shock absorption, joint lubrication, and stabilization. The objective of this study was to evaluate the interaction between the different meniscal tissue components (i.e., the solid matrix constituents and the fluid phase) and the mechanical response according to the developmental stage of the tissue. Menisci derived from partially and fully developed pigs were analyzed. We carried out biochemical analyses to quantify glycosaminoglycan (GAG) and DNA content according to the developmental stage. These values were related to tissue mechanical properties that were measured in vitro by performing compression and tension tests on meniscal specimens. Both compression and tension protocols consisted of multi-ramp stress–relaxation tests comprised of increasing strains followed by stress–relaxation to equilibrium. To better understand the mechanical response to different directions of mechanical stimulus and to relate it to the tissue structural composition and development, we performed numerical simulations that implemented different constitutive models (poro-elasticity, viscoelasticity, transversal isotropy, or combinations of the above) using the commercial software COMSOL Multiphysics. The numerical models also allowed us to determine several mechanical parameters that cannot be directly measured by experimental tests. The results of our investigation showed that the meniscus is a non-linear, anisotropic, non-homogeneous material: mechanical parameters increase with strain, depend on the direction of load, and vary among regions (anterior, central, and posterior). Preliminary numerical results showed the predominant role of the different tissue components depending on the mechanical stimulus. The outcomes of biochemical analyses related to mechanical properties confirmed the findings of the numerical models, suggesting a specific response of meniscal cells to the regional mechanical stimuli in the knee joint. During maturation, the increase in compressive moduli could be explained by cell differentiation from fibroblasts to metabolically active chondrocytes, as indicated by the found increase in GAG/DNA ratio. The changes of tensile mechanical response during development could be related to collagen II accumulation during growth. This study provides new information on the changes of tissue structural components during maturation and the relationship between tissue composition and mechanical response.

An Experimental Testing of Fillet Welded Specimens

2015 ◽  
Vol 752-753 ◽  
pp. 412-417 ◽  
Author(s):  
Martin Krejsa ◽  
Jiri Brozovsky ◽  
David Mikolasek ◽  
Premysl Parenica ◽  
Libor Zidek ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Stress Analysis ◽  
Numerical Models ◽  
Experimental Testing ◽  
Fem Analysis ◽  
Experimental Tests ◽  
Strength Characteristics ◽  
Fillet Welds ◽  
Commercial Software

The paper describes the experimental tests of steel bearing elements, which were aimed at obtaining material, geometric and strength characteristics of the fillet welds. Preparation of experiment consisted in defining of numerical models of tested samples using FEM analysis and the commercial software ANSYS. Data obtained from described experimental tests are necessary for further numerical modelling of stress analysis of steel structural supporting elements.

CHARACTERIZATION OF THE EFFECT OF ANISOTROPY ON STRESS CONCENTRATION IN BOVINE PERICARDIAL TISSUE

2005 ◽  
Vol 05 (03) ◽  
pp. 397-413
Author(s):  
ŞEBNEM ÖZÜPEK ◽  
HENGCHU CAO
Keyword(s):  
Stress Concentration ◽  
Constitutive Model ◽  
Stress Analysis ◽  
Constitutive Models ◽  
Isotropic Model ◽  
Tissue Samples ◽  
Strain Behavior ◽  
Loading Direction ◽  
Good Agreement

Characterization of anisotropy is studied in a bovine pericardial tissue undergoing non-homogeneous deformations. The purpose of this study is not to formulate an exact constitutive model for a particular tissue, but to develop a methodology for the measurement and representation of the stress-strain behavior of soft planar tissues, such as pericardium. Tissue samples with a central circular hole are subjected to uniaxial loading. A procedure for measuring local displacements is developed. Various constitutive models differing mainly in their representation of anisotropy are considered to simulate the test. The comparison of displacement and strain predictions with the measured values show that although the isotropic model has a good agreement with the data in the loading direction, the introduction of anisotropy is necessary to capture the essential characteristics of the test. The procedure provides a more realistic evaluation of the constitutive models, hence is more useful for stress analysis purposes.

scholarly journals Experimental Investigation on Loading-Relaxation Behaviors of Shear-Zone Soil

2021 ◽  
Author(s):  
Deshan Cui ◽  
shun wang ◽  
Qiong Cheng ◽  
Wei Wu
Keyword(s):  
Experimental Investigation ◽  
Stress Relaxation ◽  
Relaxation Process ◽  
Shear Zone ◽  
Mechanical Response ◽  
Viscoelastic Behavior ◽  
Relaxation Behavior ◽  
Triaxial Tests ◽  
Soil P ◽  
Loading Patterns

This paper presents an experimental investigation on the loading-relaxation behaviors of reconstituted shear-zone soils through drained triaxial tests. A multistage loading-relaxation approach is adopted to perform this test. The test aims to study two main issues: the influence of relaxation on the mechanical response during reloading; and the influence of strain rates, loading increments, and the relaxation time on the relaxation characteristics. The test results indicate that the stress-relaxation behavior of shear-zone soil is dependent on the stress and strain levels. The loading patterns prior to the stress-relaxation process affect mainly the viscoelastic behavior of the soil and subsequently influence the initial relaxation behavior. Moreover, a reloading after a stress-relaxation process gives rise to a higher deviatoric stress owing to the viscoplastic hardening. It is further shown that the loading-relaxation behaviors can be interpreted by the viscoplastic theory.

scholarly journals SIMPLIFIED MODELLING OF CIRCULAR CFST MEMBERS WITH A CONCENTRATED PLASTICITY APPROACH

2018 ◽  
Author(s):  
Yadong Jiang ◽  
António Silva ◽  
Luís Macedo ◽  
José Miguel Castro ◽  
Ricardo Monteiro ◽  
...  
Keyword(s):  
Numerical Models ◽  
Axial Stress ◽  
Local Buckling ◽  
Experimental Tests ◽  
Elastic Stiffness ◽  
Steel Tube ◽  
Deterioration Model ◽  
Cyclic Behaviour ◽  
Flexural Loading ◽  
High Level

The research reported herein aims to propose an accurate and efficient simplified numerical modelling approach for circular Concrete-Filled Steel Tubes (CFST) under flexural loading. Experimental tests were carried out to characterize the monotonic and cyclic behaviour of CFST members under bending. To assess the seismic performance of a composite structure with CFST members, both Distributed Plasticity (DP) and Concentrated Plasticity (CP) models were considered as potential simplified models for CFST members. The DP model was developed on the basis of a fibre discretization of the composite cross-section and displacement-based beam-column finite element. It was concluded that one could not accurately capture the development of local buckling of the steel tube and the development of multi-axial stress state effects (e.g. concrete confinement). Thus the DP model was found to be unsuitable for modelling of CFST members under cyclic flexural loading. Regarding the CP modelling, the modified Ibarra-Medina-Krawinkler deterioration model (with peak-oriented hysteretic response) was selected to define the behaviour of the plasticity spring associated with the plastic hinging region of the member. In order to accurately simulate the cyclic behaviour of the CFST section within the response of the spring, the deterioration model was calibrated, within a parameter-optimization framework, on the basis of 3D comprehensive numerical models in ABAQUS. The CP model was found to capture well the deterioration in both strength and stiffness of the hysteretic loops of the CFST members, which may be mostly associated with the development of local buckling phenomena. Furthermore, the elastic stiffness, the ultimate strength and the pinching effects of the hysteretic loops were also well simulated. Thus, the proposed CP model, coupled with the advanced calibration framework, was concluded to have a high level of accuracy in terms of simulating the cyclic flexural response of CFST members.

Stress Relaxation of Articular Cartilage in Unconfined Compression

2012 ◽  
Author(s):  
Patrick Smyth ◽  
Itzhak Green ◽  
Robert Jackson ◽  
R. Reid Hanson
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Mechanical Response ◽  
Viscoelastic Behavior ◽  
Osteoarthritic Cartilage ◽  
Healthy Cartilage ◽  
Storage And Loss Moduli ◽  
Relaxation Experiments ◽  
Insight Into

The articular cartilage function is to allow the bones in a joint to move without causing excess friction and damage. When this cartilage becomes damaged, the supportive and lubricating mechanisms break down, leading to injuries which can be permanent or take extended periods of time for recovery. Because of its importance in general health and body mobility, the unique lubricating properties of cartilage have been studied for many decades. Many current theories exist to characterize the biphasic and triphasic nature of cartilage; however, an important reason that cartilage is so effective is its viscoelastic nature, which allows elastic and dissipative mechanisms to exist simultaneously. It is desired to derive the material properties of cartilage in order to better understand its mechanical effectiveness. Utilizing a CETR-UMT-3 Tribometer, stress relaxation experiments will be performed on freshly harvested equine cartilage plugs that remain hydrated in a fluid bath. Viscoelastic models, such as the Prony series and fractional derivative, are applied to the experimental data to determine the storage and loss moduli of the sample explants. The storage and loss information characterizes the mechanical response of cartilage, and provides insight into the effectiveness and longevity of biological joints. A comparison will be made between joints that experience similar loads, but undergo different relative motions, to determine if the mechanical properties of cartilage are tailored to joint function. Osteoarthritic cartilage will also be explored for deviations in viscoelastic behavior compared to healthy cartilage. Ultimately, it is hoped that a viscoelastic characterization of articular cartilage will lead to insight into the precursors of osteoarthritis, more advanced prosthetics, and biomimetric applications such as the integration of flexible surfaces in mechanical systems.

scholarly journals Development of Impact-Echo Multitransducer Device for Automated Concrete Homogeneity Assessment

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2144
Author(s):  
Bartłomiej Sawicki ◽  
Tomasz Piotrowski ◽  
Andrzej Garbacz
Keyword(s):  
Nondestructive Testing ◽  
Numerical Study ◽  
Numerical Models ◽  
Experimental Testing ◽  
Experimental Tests ◽  
Impact Echo ◽  
University Of Technology ◽  
Homogeneity Assessment

A combination of multiple nondestructive testing (NDT) methods speeds up the assessment of concrete and increases the precision. This is why the UIR-Scanner was developed at Warsaw University of Technology. The scanner uses an Impact-Echo (IE) method with a unique arrangement of multiple transducers. This paper presents the development of the IE module using numerical models validated with experimental testing. It was found that rectangular arrangement of four transducers with the impactor in the middle is optimal for quick scanning of area for faults and discontinuities, changing the method from punctual to volumetric. A numerical study of void detectability depending on its position with respect to the IE module is discussed as well. After confirmation of the findings of models using experimental tests, the module was implemented into the scanner.

Numerical Simulation of CFRP Reinforced Steel Pipe Elbows Subjected to Cyclic Loading

2016 ◽  
Author(s):  
Giannoula Chatzopoulou ◽  
Ioannis Skarakis ◽  
Spyros A. Karamanos ◽  
Nicholas G. Tsouvalis ◽  
Aglaia E. Pournara
Keyword(s):  
Cyclic Loading ◽  
Structural Integrity ◽  
Mechanical Response ◽  
Numerical Models ◽  
Experimental Testing ◽  
Strain Curve ◽  
Steel Pipe ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Piping Systems

Strengthening of pipelines and piping systems under extreme loading conditions increases their operation safety level towards safeguarding their structural integrity. Motivated by the structural integrity of pipelines and piping systems, the present study aims at investigating the effect of Carbon Fiber Reinforced Plastic (CFRP) wrapping on the mechanical response of cyclically-loaded steel pipe elbows. Based on experimental testing results, a finite element model is developed, which simulates reinforced and non-reinforced pipe elbows specimens subjected to low-cyclic fatigue. For the description of the material nonlinearities, an efficient cyclic-plasticity material model is also employed, capable of describing both the yield plateau region of the steel stress-strain curve and the Bauschinger effect that appears under reverse plastic loading conditions. The results from the numerical models are compared successfully with the experimental data. Furthermore, a parametric analysis is conducted in order to examine the effect of internal pressure on the structural behavior of unreinforced and reinforced elbows, subjected to cyclic loading.

Residual Stresses in Titanium Spinal Rods: Effects of Two Contouring Methods and Material Plastic Properties

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Francesca Berti ◽  
Luigi La Barbera ◽  
Agnese Piovesan ◽  
Dario Allegretti ◽  
Claudia Ottardi ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Gold Standard ◽  
Mechanical Response ◽  
Experimental Tests ◽  
Elastoplastic Material ◽  
Spinal Fixation ◽  
Plastic Properties ◽  
Numerical Predictions ◽  
Residual Stresses And Strains

Posterior spinal fixation based on long spinal rods is the clinical gold standard for the treatment of severe deformities. Rods need to be contoured prior to implantation to fit the natural curvature of the spine. The contouring processes is known to introduce residual stresses and strains which affect the static and fatigue mechanical response of the implant, as determined through time- and cost-consuming experimental tests. Finite element (FE) models promise to provide an immediate understanding on residual stresses and strains within a contoured spinal rods and a further insight on their complex distribution. This study aims at investigating two rod contouring strategies, French bender (FB) contouring (clinical gold standard), and uniform contouring, through validated FE models. A careful characterization of the elastoplastic material response of commercial implants is led. Compared to uniform contouring, FB induces highly localized plasticizations in compression under the contouring pin with extensive lateral sections undergoing tensile residual stresses. The sensitivity analysis highlighted that the assumed postyielding properties significantly affect the numerical predictions; therefore, an accurate material characterization is recommended.

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