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 Role of smooth muscle activation in the static and dynamic mechanical characterization of human aortas

2022 ◽  
Vol 119 (3) ◽  
pp. e2117232119
Author(s):  
Giulio Franchini ◽  
Ivan D. Breslavsky ◽  
Francesco Giovanniello ◽  
Ali Kassab ◽  
Gerhard A. Holzapfel ◽  
...  
Keyword(s):  
Experimental Data ◽  
Smooth Muscle ◽  
Muscle Activation ◽  
Mechanical Response ◽  
Mechanical Characterization ◽  
Viscoelastic Behavior ◽  
Material Model ◽  
Suitable Material ◽  
Dynamic Mechanical

Experimental data and a suitable material model for human aortas with smooth muscle activation are not available in the literature despite the need for developing advanced grafts; the present study closes this gap. Mechanical characterization of human descending thoracic aortas was performed with and without vascular smooth muscle (VSM) activation. Specimens were taken from 13 heart-beating donors. The aortic segments were cooled in Belzer UW solution during transport and tested within a few hours after explantation. VSM activation was achieved through the use of potassium depolarization and noradrenaline as vasoactive agents. In addition to isometric activation experiments, the quasistatic passive and active stress–strain curves were obtained for circumferential and longitudinal strips of the aortic material. This characterization made it possible to create an original mechanical model of the active aortic material that accurately fits the experimental data. The dynamic mechanical characterization was executed using cyclic strain at different frequencies of physiological interest. An initial prestretch, which corresponded to the physiological conditions, was applied before cyclic loading. Dynamic tests made it possible to identify the differences in the viscoelastic behavior of the passive and active tissue. This work illustrates the importance of VSM activation for the static and dynamic mechanical response of human aortas. Most importantly, this study provides material data and a material model for the development of a future generation of active aortic grafts that mimic natural behavior and help regulate blood pressure.

scholarly journals Conventional Nanoindentation in Self-Assembled Monolayers Deposited on Gold and Silver Substrates

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Leila Costelle ◽  
Liina Lind ◽  
Pasi Jalkanen ◽  
Minna T. Räisänen ◽  
Roman Nowak ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Self Assembled Monolayers ◽  
Energy Calculation ◽  
Complex Behaviour ◽  
Assembled Monolayers ◽  
Efficient Data ◽  
Self Assembled ◽  
Efficient Data Analysis ◽  
Insight Into

Self-assembled monolayers (SAMs) are promising materials for micromechanical applications. However, characterization of mechanical properties of monolayers is challenging for standard nanoindentation, and new efficient analysis techniques are needed. Hereby, a conventional nanoindentation method has been combined in a unique way with efficient data analysis based on consumed energy calculation and load-displacement data. The procedure has been applied on SAMs of 4,4′-biphenyldithiol (BPDT) on Au, 1-tetradecanethiol (TDT), and 1-hexadecanethiol (HDT) on Au and Ag substrates being the first study where SAMs of the same thiols on different substrates are analyzed by nanoindentation providing a new insight into the substrate effects. Unlike TDT and HDT SAMs, which are found to strongly enhance the homogeneity and stiffness of the underlying substrate, the BPDT covered Au substrate appears softer in mechanical response. In the case of TDT and HDT SAMs on Ag the structures are softer showing also faster relaxation than the corresponding structures on Au substrate. The proposed procedure enables a fast and efficient way of assessing the complex behaviour of SAM modified substrates. As a consequence, the results are relevant to practical issues dependent on layer activity and toughness.

Study on Nonlinear Viscoelastic Properties of Asphalt Mixture Based on Stress Relaxation Test

2014 ◽  
Vol 563 ◽  
pp. 48-52
Author(s):  
Lei Chen ◽  
Zhi Xin Yu ◽  
Wei Ping Cui ◽  
Li Juan Qin
Keyword(s):  
Stress Relaxation ◽  
Asphalt Mixture ◽  
Viscoelastic Behavior ◽  
Exponential Model ◽  
Relaxation Test ◽  
Asphalt Binders ◽  
Stress Relaxation Test ◽  
Nonlinear Viscoelastic ◽  
Low Temperature Cracking ◽  
Relaxation Experiments

Development of normal stress in the direction perpendicular to the asphalt mixture is an important feature of the nonlinear viscoelastic behavior of asphalt binders. In this paper, this phenomenon was studied with the help of stress-relaxation experiments in torsion.  Results indicate that stress relaxation test by controlling strain could be used to evaluate the stress relaxation ability of asphalt mixture. With the aging degree of asphalt mixtures increased, the low temperature cracking resistance got worse; the higher the temperature is, the faster the stress relaxed; the smaller the initial strain, the worse the stress relaxation ability also. The viscoelasticity of asphalt mixture could be simulated by exponential model fractional and the experiments well supported the modeling results.

Comparison of a Novel Nonlinear Viscoelastic Finite Ramp Time Correction Method to a Heaviside Step Assumption

2011 ◽  
Author(s):  
Kevin L. Troyer ◽  
Christian M. Puttlitz
Keyword(s):  
Stress Relaxation ◽  
Soft Tissues ◽  
Viscoelastic Behavior ◽  
Relaxation Modulus ◽  
Correction Method ◽  
Nonlinear Viscoelastic ◽  
Instantaneous Strain ◽  
Relaxation Experiments ◽  
Time Correction

Connective soft tissues exhibit time-dependent, or viscoelastic, behavior. In order to characterize this behavior, stress relaxation experiments can be performed to determine the tissue’s relaxation modulus. Theoretically, the relaxation modulus describes the stress relaxation behavior of the tissue in response to an instantaneous (step) application of strain. However, a step increase in strain is experimentally impossible and a pure ramp load is intractable due to the inertial limitations of the testing device. Even small deviations from an instantaneous strain application may cause significant errors in the determination of the tissue’s relaxation modulus.

Nonlinear Dynamic Viscoelastic Model for Osteoarthritic Cartilage Indentation Force

2011 ◽  
Author(s):  
A. Vidal-Lesso ◽  
E. Ledesma-Orozco ◽  
R. Lesso-Arroyo ◽  
L. Daza-Benitez
Keyword(s):  
Mechanical Properties ◽  
Soft Tissues ◽  
Mechanical Response ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Indentation Test ◽  
Maxwell Model ◽  
Relaxation Curve ◽  
Geometrical Parameters ◽  
Osteoarthritic Cartilage

Biomechanical properties and dynamic response of soft tissues as articular cartilage remains issues for attention. Currently, linear isotropic models are still used for cartilage analysis in spite of its viscoelastic nature. Therefore, the aim of this study was to propose a nonlinear viscoelastic model for cartilage indentation that combines the geometrical parameters and velocity of the indentation test with the thickness of the sample as well as the mechanical properties of the tissue changing over time due to its viscoelastic behavior. Parameters of the indentation test and mechanical properties as a function of time were performed in Laplace space where the constitutive equation for viscoelasticity and the convolution theorem was applied in addition with the Maxwell model and Hayes et al. model for instantaneous elastic modulus. Results of the models were compared with experimental data of indentation tests on osteoarthritic cartilage of a unicompartmental osteoarthritis cases. The models showed a strong fit for the axial indentation nonlinear force in the loading curve (R2 = 0.992) and a good fit for unloading (R2 = 0.987), while an acceptable fit was observed in the relaxation curve (R2 = 0.967). These models may be used to study the mechanical response of osteoarthritic cartilage to several dynamical and geometrical test conditions.

Ultrastructural Mechanical and Material Characterization of Fossilized Bone

2006 ◽  
Vol 975 ◽  
Author(s):  
Sara Elizabeth Olesiak ◽  
Michelle Oyen ◽  
Matthew Sponheimer ◽  
Jaelyn J. Eberle ◽  
Virginia L. Ferguson
Keyword(s):  
Material Characterization ◽  
Mineral Content ◽  
Mechanical Response ◽  
Biological Tissues ◽  
Tissue Level ◽  
Organic Content ◽  
Future Studies ◽  
Transverse Modulus ◽  
Insight Into

ABSTRACTBone plays a key role in the paleontological and archeological records and can provide insight into the biology, ecology and the environment of ancient vertebrates. Examination of bone at the tissue level reveals a definitive relationship between nanomechanical properties and the local organic content, mineral content, and microstructural organization. However, it is unclear as to how these properties change following fossilization, or diagenesis, where the organic phase is rapidly removed and the remaining mineral phase is reinforced by the deposition of apatites, calcites, and other minerals. While the process of diagenesis is poorly understood, its outcome clearly results in the potential for dramatic alteration of the mechanical response of biological tissues. In this study, fossilized specimens of mammalian long bones, collected from Colorado and Wyoming, were studied for mechanical variations. Nanoindentation performed in both longitudinal and transverse directions revealed preservation of bone's natural anisotropy as transverse modulus values were consistently smaller than longitudinal values. Additionally modulus values of fossilized bone from 35.0 to 89.1 GPa increased linearly with logarithm of the sample's age. Future studies will aim to clarify what mechanical and material elements of bone are retained during diagenesis as bone becomes part of the geologic milieu.

The Biomechanical Function of Arterial Elastin in Solutes

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Yu Zou ◽  
Yanhang Zhang
Keyword(s):  
Stress Relaxation ◽  
Matrix Protein ◽  
Mechanical Response ◽  
Sodium Dodecyl ◽  
Extracellular Matrix Protein ◽  
Holding Period ◽  
Relaxation Experiments ◽  
Viscoelastic Behaviors ◽  
Phosphate Buffered Saline

Elastin is essential to accommodate physiological deformation and provide elastic support for blood vessels. As a long-lived extracellular matrix protein, elastin can suffer from cumulative effects of exposure to chemical damage, which greatly compromises the mechanical function of elastin. The mechanical properties of elastin are closely related to its microstructure and the external chemical environments. The purpose of this study is to investigate the changes in the macroscopic elastic and viscoelastic properties of isolated porcine aortic elastin under the effects of nonenzymatic mediated in vitro elastin–lipid interactions and glycation. Sodium dodecyl sulfate (SDS) was used for elastin–lipid interaction, while glucose was used for glycation of elastin. Elastin samples were incubated in SDS (20 mM) or glucose (2 M) solutions and were allowed to equilibrate for 48 h at room temperature. Control experiments were performed in 1  ×  Phosphate buffered saline (PBS). Biaxial tensile and stress relaxation experiments were performed to study the mechanical behavior of elastin with solute effects. Experimental results reveal that both the elastic and viscoelastic behaviors of elastin change in different biochemical solvents environments. The tangent stiffness of SDS treated elastin decreases to 63.57 ± 4.7% of the control condition in circumference and to 58.43 ± 2.65% in the longitude. Glucose treated elastin exhibits an increase in stiffness to 145.06 ± 1.48% of the control condition in the longitude but remains similar mechanical response in the circumferential direction. During stress relaxation experiments with a holding period of half an hour, elastin treated with SDS or glucose shows more prominent stress relaxation than the untreated ones.

Viscoelastic Characterization of an Epoxy-Based Molding Compound

1995 ◽  
Vol 390 ◽  
Author(s):  
V. H. Kenner ◽  
M. R. Julian ◽  
C. H. Popelar ◽  
M. K. Chengalva
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Viscoelastic Behavior ◽  
Tensile Tests ◽  
Prony Series ◽  
Master Curves ◽  
Molding Compound ◽  
Relaxation Curves

ABSTRACTThis paper describes the viscoelastic characterization of a highly filled epoxy molding compound commonly used in electronic packaging applications. Both stress relaxation tests and constant strain rate tensile tests were conducted. The material was found to be nonlinear in its viscoelastic behavior and to be amenable to horizontal shifting to form master curves. A representation of the master stress relaxation curves in terms of a Prony series is given, and the use of this representation illustrated in the context of both linear and nonlinear representations of the viscoelastic behavior to predict the results of the constant strain rate experiments.

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.

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.

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