An Examination of the Influence of Strain Rate on Subfailure Mechanical Properties of the Annulus Fibrosus

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Diane E. Gregory ◽  
Jack P. Callaghan
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Nucleus Pulposus ◽  
Annulus Fibrosus ◽  
Maximum Stress ◽  
Axial Direction ◽  
Applied Strain ◽  
Circumferential Direction ◽  
Disk Herniation ◽  
Mechanical Responses

Disk herniation is often considered a cumulative injury in that repetitive stress on the posterior annulus can result in the nucleus pulposus penetrating the annulus fibrosus and eventually extruding posteriorly. Further, it has been documented that the nucleus pulposus works its way through the annulus through clefts, which form as a result of repetitive tensile strain. The annulus fibrosus is viscoelastic in nature and therefore could express different mechanical responses to applied strain at varying rates. Other viscoelastic tissues, including tendons and ligaments, have shown altered mechanical responses to different rates of applied strain, but the response of the annulus to varying rates of strain is largely unknown. The present study examined the mechanical properties of 20 two-layered samples of porcine annulus fibrosus tissue at three distinct rates of applied 20% biaxial strain (20% strain over 20 s (slow), over 10 s (medium), and over 5 s (fast)); these three rates are considered applicable to nontraumatic loading. No differences in the stiffness or maximum stress in each of the two directions of applied strain were observed between the three strain rates. Specifically, the average (standard deviation) moduli calculated at the fast, medium, and slow rates, respectively, in the axial direction were 7.42 MPa (6.06), 7.77 MPa (6.61), and 7.63 MPa (6.67) and 8.22 MPa (8.4), 8.63 MPa (9.00), and 8.49 MPa (8.69) in the circumferential direction. The maximum stress values reached during the fast, medium, and slow rates, respectively, in the axial direction were 0.40 (0.36) MPa, 0.40 (0.36) MPa, and 0.39 (0.35) MPa and 0.45 (0.47) MPa, 0.44 (0.46) MPa, and 0.43 (0.46) MPa in the circumferential direction. At submaximal strain magnitudes over a range of nontraumatic rates likely to result in clefts in the annulus and potentially leading to disk herniation, any strain rate dependence is not significant.

A Comparison of Uniaxial and Biaxial Mechanical Properties of the Annulus Fibrosus: A Porcine Model

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Diane E. Gregory ◽  
Jack P. Callaghan
Keyword(s):  
Mechanical Properties ◽  
Annulus Fibrosus ◽  
Axial Direction ◽  
Stretch Ratio ◽  
Intervertebral Disk ◽  
Circumferential Direction ◽  
Biaxial Tests ◽  
Maximal Stress ◽  
Biaxial Mechanical Properties

The annulus fibrosus of the intervertebral disk experiences multidirectional tension in vivo, yet the majority of mechanical property testing has been uniaxial. Therefore, our understanding of how this complex multilayered tissue responds to loading may be deficient. This study aimed to determine the mechanical properties of porcine annular samples under uniaxial and biaxial tensile loading. Two-layer annulus samples were isolated from porcine disks from four locations: anterior superficial, anterior deep, posterior superficial, and posterior deep. These tissues were then subjected to three deformation conditions each to a maximal stretch ratio of 1.23: uniaxial, constrained uniaxial, and biaxial. Uniaxial deformation was applied in the circumferential direction, while biaxial deformation was applied simultaneously in the circumferential and compressive directions. Constrained uniaxial consisted of a stretch ratio of 1.23 in the circumferential direction while holding the tissue stationary in the axial direction. The maximal stress and stress-stretch ratio (S-S) moduli determined from the biaxial tests were significantly higher than those observed during both the uniaxial tests (maximal stress, 97.1% higher during biaxial; p=0.002; S-S moduli, 117.9% higher during biaxial; p=0.0004) and the constrained uniaxial tests (maximal stress, 46.8% higher during biaxial; S-S moduli, 82.9% higher during biaxial). These findings suggest that the annulus is subjected to higher stresses in vivo when under multidirectional tension.

Effect of Cold Storage on Mechanical Properties of Aorta

2015 ◽  
Author(s):  
Shijia Zhao ◽  
John Lof ◽  
Shelby Kutty ◽  
Linxia Gu
Keyword(s):  
Mechanical Properties ◽  
Uniaxial Tension ◽  
Cold Storage ◽  
Elastic Moduli ◽  
Heart Diseases ◽  
Axial Direction ◽  
Circumferential Direction ◽  
Control Group ◽  
Aortic Tissue ◽  
Tension Tests

Aortic allografts have been widely used in treatments of congenital heart diseases with satisfactory clinical outcomes. They were usually cryopreserved and stored for surgical use. The objective of this work was to investigate the effect of cold storage on mechanical properties of aorta, since the compliance mismatch was one important factor associated with the complication after graft surgery. The segments of porcine descending aorta were divided into two groups: the fresh samples which were tested within 24 hours after harvesting served as control group, and frozen samples which were stored in −20°C for 7 days and then thawed. The uniaxial tension tests along circumferential direction and indentation tests were conducted. The average incremental elastic moduli within each stretch range were obtained from the experimental data obtained during tension tests, and the elastic moduli were also calculated by fitting the force-indentation depth data to Hertz model when the tissue was stretched at 1.0, 1.2, 1.4 and 1.6. In addition, the average incremental elastic moduli of both fresh and frozen aortic tissue along axial direction were also obtained by using uniaxial tension tests. The comparison showed that cold storage definitely increased the average incremental elastic modulus of the aortic tissue along circumferential direction; however, the difference is not significant for the elastic moduli along axial direction.

Influence of Experimental Protocols on the Mechanical Properties of the Intervertebral Disc in Unconfined Compression

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Maximilien Recuerda ◽  
Simon-Pierre Coté ◽  
Isabelle Villemure ◽  
Delphine Périé
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Nucleus Pulposus ◽  
Annulus Fibrosus ◽  
Young's Modulus ◽  
Viscoelastic Model ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Experimental Conditions ◽  
Experimental Protocols

The lack of standardization in experimental protocols for unconfined compression tests of intervertebral discs (IVD) tissues is a major issue in the quantification of their mechanical properties. Our hypothesis is that the experimental protocols influence the mechanical properties of both annulus fibrosus and nucleus pulposus. IVD extracted from bovine tails were tested in unconfined compression stress-relaxation experiments according to six different protocols, where for each protocol, the initial swelling of the samples and the applied preload were different. The Young’s modulus was calculated from a viscoelastic model, and the permeability from a linear biphasic poroviscoelastic model. Important differences were observed in the prediction of the mechanical properties of the IVD according to the initial experimental conditions, in agreement with our hypothesis. The protocol including an initial swelling, a 5% strain preload, and a 5% strain ramp is the most relevant protocol to test the annulus fibrosus in unconfined compression, and provides a permeability of 5.0 ± 4.2e−14m4/N·s and a Young’s modulus of 7.6 ± 4.7 kPa. The protocol with semi confined swelling and a 5% strain ramp is the most relevant protocol for the nucleus pulposus and provides a permeability of 10.7 ± 3.1 e−14m4/N·s and a Young’s modulus of 6.0 ± 2.5 kPa.

scholarly journals Study on the Generation Mechanism and Development Law of the Zonal Disintegration in Deep Burial Tunnels

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Xiaohui Ma ◽  
Jihong Wei ◽  
Jin Liu ◽  
Zezhuo Song ◽  
Yuxia Bai
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Maximum Stress ◽  
Axial Stress ◽  
Axial Direction ◽  
Tensile Failure ◽  
Zonal Disintegration ◽  
Nonlinear Characteristics ◽  
Deep Rock ◽  
New Phenomena

In the development of underground spaces, we found that the mechanical properties of rock mass often demonstrate strong nonlinear characteristics. Some new phenomena emerge in deep rock mass engineering. This includes zonal disintegration and rock burst. Zonal disintegration is very important in deep tunnels. In this paper, we start with the mechanical properties of deep rocks to understand the preconditions for zonal disintegration. Using the Failure Approach Index (FAI), the process of zonal disintegration can be modeled by FLAC (FISH language). Our results indicate that tensile failure in the Supporting Pressure Zone (SPZ) is a precondition for zonal disintegration. Various factors that affect the generation of zonal disintegration are studied. When the maximum stress is in the axial direction, zonal disintegration will be present in deep tunnels. The high axial stress is necessary for zonal disintegration. We will present a zonal disintegration simulation in one coal mine for comparison with the borehole teleview data. We suggest some measures to prevent the development of zonal disintegration.

Spatial Variation in Material Properties in Fascicle-Bone Units from Human Patellar Tendon

2006 ◽  
Vol 326-328 ◽  
pp. 797-802 ◽  
Author(s):  
Keyoung Jin Chun ◽  
D.L. Butler
Keyword(s):  
Strain Rate ◽  
Patellar Tendon ◽  
Material Properties ◽  
Maximum Stress ◽  
Cruciate Ligament ◽  
Mechanical Responses ◽  
Ligament Replacement ◽  
Lateral Portion ◽  
Strength And Stiffness ◽  
Maximum Stresses

An understanding of the mechanical responses of the patellar tendon (PT) subunits should aid in determining which portion of the tissue might best be used as a cruciate ligament replacement. Human cadaveric knees were obtained from young donors. Fascicle groups with patellar and tibial bone blocks (subunits) were cut to provide six equally-spaced test specimens for each PT. After potting each bone end in PMMA, specimens were mounted in a saline-filled chamber, preloaded to 0.26 N and then subjected to 40 cycles of preconditioning to 2.5 % of the initial length at a strain rate of 1.25 %/sec, and then preloaded to 0.26 N again and failed at a strain rate of 100 %/sec using an Instron. The moduli and maximum stresses were generally greater in the lateral and mid subunits than in the medial subunits. The strains to maximum stress were similar between the lateral and medial subunits, but mid subunits had larger strains. Most strain values were distributed between 10 % to 20 %. Mechanical responses of human PT do vary from location to location. In general, the mid and lateral subunits were stiffer and carried greater stresses than the medial subunits. The results of this research should eventually be important, e.g. in selecting which portion of the PT would be the most suitable for cruciate ligament replacements to use as an autograft. On the basis of strength and stiffness, the more lateral portion of the PT would seem to be more advantageous.

Experimental Study of In-plane Mechanical Properties of Carbon Fibre Woven Composite at Different Strain Rates

2017 ◽  
Vol 25 (4) ◽  
pp. 289-298 ◽  
Author(s):  
Jiahai Lu ◽  
Ping Zhu ◽  
Qinghui Ji ◽  
Zhang Cheng
Keyword(s):  
Mechanical Properties ◽  
Carbon Fibre ◽  
Strain Rate ◽  
Complex Loading ◽  
Axial Direction ◽  
Strain Rate Range ◽  
Strain Rates ◽  
Woven Composite ◽  
Rate Range ◽  
Failure Patterns

Carbon fibre woven composite has been increasingly employed in engineering applications undergoing complex loading conditions. For effective use of composite material in dynamic applications, it is essential to fully understand the mechanical behaviour of composite at different strain rates. In the present study, both in-plane tensile and compressive experiments loaded at 0 degree axial direction and 45 degree off-axial direction of a TC33 carbon fibre woven composite were investigated over the strain rate range from 0.001 to 1000 s−1. High strain rate tests were carried out using Split Hopkinson Pressure and Tensile Bar apparatus respectively. The results indicated that the in-plane mechanical properties and failure patterns were strain rate sensitive under both tensile and compressive loadings. The mechanical properties, failure patterns and strain rate effect also showed highly direction dependent and tension/compression asymmetric characteristic within the considered strain rate range. For higher strain rate sensitivity under compression than that under tension, the asymmetry of mechanical properties was less obvious with the increase of strain rate. Finally, two phenomenal models were proposed to quantitatively fit the relationship between strength property and strain rate.

scholarly journals Study on Dynamic Mechanical Properties of Limestone under Uniaxial Impact Compressive Loads

2016 ◽  
Vol 2016 ◽  
pp. 1-11
Author(s):  
Fei Zou ◽  
Zheng-feng Fang ◽  
Ming-yao Xia
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Failure Modes ◽  
Constant Strain Rate ◽  
Reference Value ◽  
Axial Direction ◽  
Dynamic Mechanical Properties ◽  
Impact Pressure ◽  
Pulse Shaper ◽  
Dynamic Mechanical

The dynamic mechanical properties of limestone are studied with 5 types of impact pressure acting on limestone samples in axial direction in this paper. The rubber shaper with a diameter of 5 mm and thickness of 2 mm is adopted. Besides the conical punch of split pressure bar of Hopkinson with a diameter of 50 mm is also used. The half-sinusoid pulse is obtained by using the pulse shaper method and special punch method; the constant strain rate deformation of the sample is realized. Dynamic compressive properties and failure modes of limestone under different impact pressure are investigated. In addition, energy dissipation is studied in the process of experiment. The results show that the dynamic compressive strength of limestone has an exponent relation to strain rate. The failure strain, degree of fragmentation, incident energy, and absorption energy increase, while the energy absorbency decreases with the increasing of strain rate. However, the initial elastic modulus is not sensitive to the strain rate. The research method and conclusions have reference value for the dynamic mechanical properties of other brittle materials.

scholarly journals Theoretical and Uniaxial Experimental Evaluation of Human Annulus Fibrosus Degeneration

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Grace D. O’Connell ◽  
Heather L. Guerin ◽  
Dawn M. Elliott
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Annulus Fibrosus ◽  
Bulk Material ◽  
Axial Direction ◽  
Uniaxial Tensile ◽  
Linear Region ◽  
The Matrix ◽  
Fiber Matrix ◽  
Strain Energy Functions

The highly organized structure and composition of the annulus fibrosus provides the tissue with mechanical behaviors that include anisotropy and nonlinearity. Mathematical models are necessary to interpret and elucidate the meaning of directly measured mechanical properties and to understand the structure-function relationships of the tissue components, namely, the fibers and extrafibrillar matrix. This study models the annulus fibrosus as a combination of strain energy functions describing the fibers, matrix, and their interactions. The objective was to quantify the behavior of both nondegenerate and degenerate annulus fibrosus tissue using uniaxial tensile experimental data. Mechanical testing was performed with samples oriented along the circumferential, axial, and radial directions. For samples oriented along the radial direction, the toe-region modulus was 2× stiffer with degeneration. However, no other differences in measured mechanical properties were observed with degeneration. The constitutive model fit well to samples oriented along the radial and circumferential directions (R2≥0.97). The fibers supported the highest proportion of stress for circumferential loading at 60%. There was a 70% decrease in the matrix contribution to stress from the toe-region to the linear-region of both the nondegenerate and degenerate tissue. The shear fiber-matrix interaction (FMI) contribution increased by 80% with degeneration in the linear-region. Samples oriented along the radial and axial direction behaved similarly under uniaxial tension (modulus=0.32 MPa versus 0.37 MPa), suggesting that uniaxial testing in the axial direction is not appropriate for quantifying the mechanics of a fiber reinforcement in the annulus. In conclusion, the structurally motivated nonlinear anisotropic hyperelastic constitutive model helps to further understand the effect of microstructural changes with degeneration, suggesting that remodeling in the subcomponents (i.e., the collagen fiber, matrix and FMI) may minimize the overall effects on mechanical function of the bulk material with degeneration.

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