Methods for Quasi-Linear Viscoelastic Modeling of Soft Tissue: Application to Incremental Stress-Relaxation Experiments

2003 ◽  
Vol 125 (5) ◽  
pp. 754-758 ◽  
Author(s):  
Joseph J. Sarver ◽  
Paul S. Robinson ◽  
Dawn M. Elliott
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Normalization Method ◽  
Time Constants ◽  
Future Studies ◽  
Linear Viscoelastic ◽  
Relaxation Experiments ◽  
Different Strains ◽  
Viscoelastic Modeling ◽  
Strain Dependent

The quasi-linear viscoelastic (QLV) model was applied to incremental stress-relaxation tests and an expression for the stress was derived for each step. This expression was used to compare two methods for normalizing stress data prior to estimating QLV parameters. The first and commonly used normalization method was shown to be strain-dependent. Thus, a second normalization method was proposed and shown to be strain-independent and more sensitive to QLV time constants. These analytical results agreed with representative tendon data. Therefore, this method for normalizing stress data was proposed for future studies of incremental stress-relaxation, or whenever comparing stress-relaxation at different strains.

A Quasi-Linear, Viscoelastic, Structural Model of the Plantar Soft Tissue With Frequency-Sensitive Damping Properties

2004 ◽  
Vol 126 (6) ◽  
pp. 831-837 ◽  
Author(s):  
William R. Ledoux ◽  
David F. Meaney ◽  
Howard J. Hillstrom
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Structural Properties ◽  
Structural Model ◽  
Elastic Behavior ◽  
Damping Properties ◽  
Significant Difference ◽  
Linear Viscoelastic ◽  
Relaxation Experiments ◽  
Plantar Soft Tissue

Little is known about the structural properties of plantar soft-tissue areas other than the heel; nor is it known whether the structural properties vary depending on location. Furthermore, although the quasi-linear viscoelastic (QLV) theory has been used to model many soft-tissue types, it has not been employed to model the plantar soft tissue. The structural properties of the plantar soft tissue were quantified via stress relaxation experiments at seven regions (subcalcaneal, five submetatarsal, and subhallucal) across eight cadaveric feet. The cadaveric feet were 36.9±17.4 (mean±S.D.) years of age, all free from vascular diseases and orthopedics disorders. All tests were performed at a constant environmental temperature of 35°C. Stress relaxation experiments were performed; different loads were employed for different areas based on normative gait data. A modification of the relaxation spectrum employed within the QLV theory allowed for the inclusion of frequency-sensitive relaxation properties in addition to nonlinear elastic behavior. The tissue demonstrated frequency-dependent damping properties that made the QLV theory ill suited to model the relaxation. There was a significant difference between the elastic structural properties (A) of the subcalcaneal tissue and all other areas p=0.004, and a trend p=0.067 for the fifth submetatarsal to have less viscous damping c1 than the subhallucal, or first, second, or third submetatarsal areas. Thus, the data demonstrate that the structural properties of the foot can vary across regions, but careful consideration must be given to the applied loads and the manner in which the loads were applied.

A comparison study of athletic kinesio tapes and structural cloth tapes applied to address biomechanical injuries and muscle stabilization

2020 ◽  
pp. 175433712093011
Author(s):  
Declan Shannon ◽  
Brian J Love
Keyword(s):  
Stress Relaxation ◽  
Maximum Stress ◽  
Compressive Force ◽  
Element Model ◽  
Comparison Study ◽  
Zener Model ◽  
Static Tensile ◽  
Relaxation Experiments ◽  
Viscoelastic Modeling

Quasi-static tensile and stress relaxation experiments were performed on several cloth-based and segmented elastomeric tapes, and the results were analyzed using viscoelastic models. The cloth tape modulus of elasticity was ∼340 MPa, while those of the kinesio tapes ranged from ∼15 to 20 MPa. The cloth tapes was also stronger and more brittle. Viscoelastic modeling of the stress relaxation behavior was done using a Zener model for the cloth tapes and a 5-element model for the kinesio tapes. The cloth tape relaxed by ∼20%, while the kinesio tapes relaxed by ∼40% of the applied maximum stress in approximately 300-s as demonstrated by viscoelastic modeling and constant strain experiments. The overall amount of long-term compressive force delivered by kinesio tapes might be inadequate for some applications, but they are more forgiving in how they are deployed.

Quasi-Linear Viscoelastic Theory is Insufficient to Comprehensively Describe the Time-Dependent Behavior of Human Cervical Spine Ligaments

2010 ◽  
Author(s):  
Kevin L. Troyer ◽  
Christian M. Puttlitz
Keyword(s):  
Cervical Spine ◽  
Stress Relaxation ◽  
Strain Range ◽  
Relaxation Curve ◽  
Physiological Strain ◽  
Dependent Behavior ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Relaxation Experiments ◽  
Linear Viscoelastic Theory

Stress relaxation experiments were conducted on cervical spine ligaments at multiple strain magnitudes to determine the validity and applicability of the quasi-linear viscoelastic (QLV) theory to model their dynamic behavior. The results indicate that the shape of the stress relaxation curve is dependent upon the magnitude of the applied strain. Thus, a more general, nonlinear formulation is required to model these ligaments within the physiological strain range.

scholarly journals A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials

2015 ◽  
Vol 12 (113) ◽  
pp. 20150707 ◽  
Author(s):  
Behzad Babaei ◽  
Steven D. Abramowitch ◽  
Elliot L. Elson ◽  
Stavros Thomopoulos ◽  
Guy M. Genin
Keyword(s):  
Stress Relaxation ◽  
Relaxation Spectrum ◽  
Model Identification ◽  
Biological Materials ◽  
Relaxation Data ◽  
Collateral Ligament ◽  
Time Constants ◽  
Discrete Approach ◽  
Standard Tool ◽  
Linear Viscoelastic

The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material's temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model's ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material's relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material's temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model's typical box spectrum provides an accurate representation of a particular material's temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit.

The Effect of Overshooting the Target Strain on Estimating Viscoelastic Properties From Stress Relaxation Experiments

2004 ◽  
Vol 126 (6) ◽  
pp. 844-848 ◽  
Author(s):  
Jonathan A. Gimbel ◽  
Joseph J. Sarver ◽  
Louis J. Soslowsky
Keyword(s):  
Stress Relaxation ◽  
Single Step ◽  
Strain History ◽  
Estimation Of Parameters ◽  
Ramp Rate ◽  
Relaxation Experiment ◽  
Curve Fit ◽  
Target Strain ◽  
Linear Viscoelastic ◽  
Relaxation Experiments

Background: Tendon’s mechanical behaviors have frequently been quantified using the quasi-linear viscoelastic (QLV) model. The QLV parameters are typically estimated by fitting the model to a single-step stress relaxation experiment. Unfortunately, overshoot of the target strain occurs to some degree in most experiments. This has never been formally investigated even though failing to measure, minimize, or compensate for overshoot may cause large errors in the estimation of parameters. Therefore, the objective of this study was to investigate the effect of overshoot on the estimation of QLV parameters. Method of approach: A simulated experiment was first performed to quantify the effect of different amounts of overshoot on the estimated QLV parameters. Experimental data from tendon was then used to determine if the errors associated with overshoot could be reduced when a direct fit is used (i.e., the actual strain history was used in the curve fit). Results: We found that both the elastic and viscous QLV parameters were incorrectly estimated if overshoot was not properly accounted for in the fit. Furthermore, the errors associated with overshoot were partially reduced when overshoot was accounted for using a direct fit. Conclusions: A slow ramp rate is recommended to limit the amount of overshoot and a direct fit is recommended to limit the errors associated with overshoot, although other approaches such as adjusting the control system to limit overshoot could also be utilized.

scholarly journals The Effect of Target Strain Error on Plantar Tissue Stress

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Shruti Pai ◽  
William R. Ledoux
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Soft Tissues ◽  
Peak Stress ◽  
Materials Testing ◽  
Small Target ◽  
Tissue Properties ◽  
Target Strain ◽  
Relaxation Experiments ◽  
Tissue Specimens

Accurate quantification of soft tissue properties, specifically the stress relaxation behavior of viscoelastic tissues such as plantar tissue, requires precise testing under physiologically relevant loading. However, limitations of testing equipment often result in target strain errors that can contribute to large stress errors and confound comparative results to an unknown extent. Previous investigations have modeled this artifact, but they have been unable to obtain empirical data to validate their models. Moreover, there are no studies that address this issue for plantar tissue. The purpose of this research was to directly measure the difference in peak force for a series of small target strain errors within the range of our typical stress relaxation experiments for the subcutaneous plantar soft tissue. Five plantar tissue specimens were tested to seven incremental target strain error levels of −0.9%, −0.6%, −0.3%, 0.0%, 0.3%, 0.6%, and 0.9%, so as to undershoot and overshoot the target displacement in 0.3% increments. The imposed strain errors were accurately attained using a special compensation feature of our materials testing software that can drive the actuator to within 0% (1−2 μm) of the target level for cyclic tests. Since stress relaxation tests are not cyclic, we emulated the ramp portion of our stress relaxation tests with 5 Hz triangle waves. The average total stress variation for all specimens was 25±5%, with the highest and lowest stresses corresponding to the largest and smallest strain errors of 0.9% and −0.9%, respectively. A strain overshoot of 0.3%, the target strain error observed in our typical stress relaxation experiments, corresponded to an average stress overshoot of 3±1%. Plantar tissue in compression is sensitive to small target strain errors that can result in stress errors that are several fold larger. The extent to which the overshoot may affect the peak stress will likely differ in magnitude for other soft tissues and loading modes.

scholarly journals Strain-dependent wicking behavior of cotton/lycra elastic woven fabric for sportswear

e-Polymers ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 263-271
Author(s):  
Yong Wang ◽  
Qifan Qiao ◽  
Zuowei Ding ◽  
Fengxin Sun
Keyword(s):  
Tensile Strain ◽  
Water Drop ◽  
Woven Fabric ◽  
Strengthening Effect ◽  
Wetting Time ◽  
Horizontal Wicking ◽  
Different Strains ◽  
Strain Dependent ◽  
Different Levels ◽  
Strain Strengthening

Abstract The strain-dependent vertical and horizontal wicking of as-prepared cotton/lycra elastic woven fabric was systematically studied. The experimental results revealed that the fabric exhibited a strain strengthening effect. A higher tensile strain results in a higher equilibrium wicking height, and vice versa. Moreover, the results indicated that the proposed Laughlin–Davies model is capable of tracking well the experimental data and replicating the wicking characteristics of fabric under different levels of stretch. In addition, the wetting time and wicking area of fabric under different strains and height regimes were examined during horizontal wicking. It was found that the wetting time decreased with an increase of strain and/or water drop height. The strain-enhanced and height-weakened effects of wicking area were revealed. The spreading mechanism of water drop in elastic fabric was also proposed. Such fundamental work provides a basic support for the in-depth investigation of wicking behavior of complex stretchable textile structures.

scholarly journals Selective cannabis strain allergy in a patient presenting with a local allergic reaction

2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Peter Stepaniuk ◽  
Amin Kanani
Keyword(s):  
Direct Contact ◽  
Cannabis Sativa ◽  
Skin Prick Testing ◽  
Case Presentation ◽  
Published Report ◽  
Cannabis Indica ◽  
Different Strains ◽  
Allergen Identification ◽  
Strain Dependent ◽  
Fresh Skin

Abstract Background Cannabis use is growing domestically due to recent legalization in many jurisdictions. There are two main species of cannabis, Cannabis sativa and Cannabis indica, and thousands of different commercially available cannabis strains. Although there are multiple reports of cannabis allergy in the literature, to our knowledge, there is no prior published report of selective cannabis strain allergy. Case presentation A 31-year-old male was referred for allergy assessment due to several episodes of localized pruritus and erythema after direct contact with various strains of cannabis. He had noted that the severity of his reaction appeared to be strain dependent. He developed a severe local reaction involving bilateral periorbital edema shortly after coming into direct contact with one particular strain of cannabis. He denied any adverse symptoms after inhalation of cannabis. Fresh skin prick testing was performed to various strains of cannabis and had positive testing to the three of the five tested strains. Conclusions We believe this is the first reported case of selective cannabis strain allergy based on patient history and skin prick testing. This case report outlines the variability in different strains of cannabis and stresses the importance of further research into cannabis allergen identification. Multiple cannabis allergens should be included and incorporated into commercial extracts when they become routinely available.

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