The Effect of Creep on Human Lumbar Intervertebral Disk Impact Mechanics

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
David Jamison ◽  
Michele S. Marcolongo
Keyword(s):  
Mechanical Response ◽  
Compressive Load ◽  
Fluid Phase ◽  
Constant Load ◽  
Time Of Day ◽  
Intervertebral Disk ◽  
Fluid Loss ◽  
Loading Conditions ◽  
Impact Mechanics ◽  
Continuous Displacement

The intervertebral disk (IVD) is a highly hydrated tissue, with interstitial fluid making up 80% of the wet weight of the nucleus pulposus (NP), and 70% of the annulus fibrosus (AF). It has often been modeled as a biphasic material, consisting of both a solid and fluid phase. The inherent porosity and osmotic potential of the disk causes an efflux of fluid while under constant load, which leads to a continuous displacement phenomenon known as creep. IVD compressive stiffness increases and NP pressure decreases as a result of creep displacement. Though the effects of creep on disk mechanics have been studied extensively, it has been limited to nonimpact loading conditions. The goal of this study is to better understand the influence of creep and fluid loss on IVD impact mechanics. Twenty-four human lumbar disk samples were divided into six groups according to the length of time they underwent creep (tcreep = 0, 3, 6, 9, 12, 15 h) under a constant compressive load of 400 N. At the end of tcreep, each disk was subjected to a sequence of impact loads of varying durations (timp = 80, 160, 320, 400, 600, 800, 1000 ms). Energy dissipation (ΔE), stiffness in the toe (ktoe) and linear (klin) regions, and neutral zone (NZ) were measured. Analyzing correlations with tcreep, there was a positive correlation with ΔE and NZ, along with a negative correlation with ktoe. There was no strong correlation between tcreep and klin. The data suggest that the IVD mechanical response to impact loading conditions is altered by fluid content and may result in a disk that exhibits less clinical stability and transfers more load to the AF. This could have implications for risk of diskogenic pain as a function of time of day or tissue hydration.

The Effect of Creep on Human Lumbar Intervertebral Disc Impact Mechanics

2013 ◽  
Author(s):  
David Jamison ◽  
Michele Marcolongo
Keyword(s):  
Intervertebral Disc ◽  
Impact Loading ◽  
Interstitial Fluid ◽  
Mechanical Response ◽  
Phase 1 ◽  
Compressive Load ◽  
Fluid Phase ◽  
Impact Loads ◽  
Lumbar Intervertebral Disc ◽  
Impact Mechanics

The intervertebral disc (IVD) is often modeled as a biphasic tissue, with both a solid and a fluid phase [1]. While under a constant compressive load, the IVD responds with continuous creep displacement, resulting in the loss of interstitial fluid from the tissue and increased strain on the annular fibers. The mechanical response of the IVD under impact loading conditions has been previously reported by the authors and others. It is unknown, however, how the loss of interstitial fluid affects disc biomechanics under impact loads. In this study, we investigate the effects of creep on IVD impact mechanics.

Creating Physiologically Realistic Vertebral Fractures in a Cervine Model

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Nicole C. Corbiere ◽  
Kathleen A. Lewicki ◽  
Kathleen A. Issen ◽  
Laurel Kuxhaus
Keyword(s):  
Cancellous Bone ◽  
Mechanical Response ◽  
Bone Structure ◽  
Peak Load ◽  
Compressive Load ◽  
Compression Fracture ◽  
Loading Conditions ◽  
Cross Sectional ◽  
Motion Segment ◽  
Cadaver Specimen

Approximately 50% of women and 25% of men will have an osteoporosis-related fracture after the age of 50, yet the micromechanical origin of these fractures remains unclear. Preventing these fractures requires an understanding of compression fracture formation in vertebral cancellous bone. The immediate research goal was to create clinically relevant (midvertebral body and endplate) fractures in three-vertebrae motion segments subject to physiologically realistic compressional loading conditions. Six three-vertebrae motion segments (five cervine, one cadaver) were potted to ensure physiologic alignment with the compressive load. A 3D microcomputed tomography (microCT) image of each motion segment was generated. The motion segments were then preconditioned and monotonically compressed until failure, as identified by a notable load drop (48–66% of peak load in this study). A second microCT image was then generated. These three-dimensional images of the cancellous bone structure were inspected after loading to qualitatively identify fracture location and type. The microCT images show that the trabeculae in the cervine specimens are oriented similarly to those in the cadaver specimen. In the cervine specimens, the peak load prior to failure is highest for the L4–L6 motion segment, and decreases for each cranially adjacent motion segment. Three motion segments formed endplate fractures and three formed midvertebral body fractures; these two fracture types correspond to clinically observed fracture modes. Examination of normalized-load versus normalized-displacement curves suggests that the size (e.g., cross-sectional area) of a vertebra is not the only factor in the mechanical response in healthy vertebral specimens. Furthermore, these normalized-load versus normalized-displacement data appear to be grouped by the fracture type. Taken together, these results show that (1) the loading protocol creates fractures that appear physiologically realistic in vertebrae, (2) cervine vertebrae fracture similarly to the cadaver specimen under these loading conditions, and (3) that the prefracture load response may predict the impending fracture mode under the loading conditions used in this study.

scholarly journals Discrete element analysis of the punching behaviour of a secured drapery system: from laboratory characterization to idealized in situ conditions

2021 ◽  
Author(s):  
Antonio Pol ◽  
Fabio Gabrieli ◽  
Lorenzo Brezzi
Keyword(s):  
Mechanical Response ◽  
Steel Wire ◽  
Discrete Element ◽  
Wire Mesh ◽  
Steel Plates ◽  
Loading Conditions ◽  
Element Analysis ◽  
In Situ Conditions ◽  
Wire Meshes

AbstractIn this work, the mechanical response of a steel wire mesh panel against a punching load is studied starting from laboratory test conditions and extending the results to field applications. Wire meshes anchored with bolts and steel plates are extensively used in rockfall protection and slope stabilization. Their performances are evaluated through laboratory tests, but the mechanical constraints, the geometry and the loading conditions may strongly differ from the in situ conditions leading to incorrect estimations of the strength of the mesh. In this work, the discrete element method is used to simulate a wire mesh. After validation of the numerical mesh model against experimental data, the punching behaviour of an anchored mesh panel is investigated in order to obtain a more realistic characterization of the mesh mechanical response in field conditions. The dimension of the punching element, its position, the anchor plate size and the anchor spacing are varied, providing analytical relationships able to predict the panel response in different loading conditions. Furthermore, the mesh panel aspect ratio is analysed showing the existence of an optimal value. The results of this study can provide useful information to practitioners for designing secured drapery systems, as well as for the assessment of their safety conditions.

scholarly journals Influence of Comprehensive Joint Loads on Tibial Implant Micromotion in Total Ankle Arthroplasty

2020 ◽  
Vol 5 (4) ◽  
pp. 2473011420S0008
Author(s):  
Brett D. Steineman ◽  
Constantine A. Demetracopoulos ◽  
Jonathan T. Deland ◽  
Brett D. Steineman ◽  
Fernando Quevedo Gonzalez ◽  
...  
Keyword(s):  
Finite Element ◽  
Ankle Joint ◽  
Compressive Load ◽  
Compressive Force ◽  
Axial Loading ◽  
Loading Conditions ◽  
Bone Implant ◽  
Level Walking ◽  
Joint Loads

Category: Ankle Introduction/Purpose: Biologic fixation of total joint replacements by bone ingrowth requires minimal bone-implant micromotion [1]. Computational finite element (FE) models used to evaluate the interaction between implant and bone typically only consider simplified loading conditions based on the peak compressive force which occurs near toe-off [2,3]. However, a previous study focused on cementless knee replacements demonstrated that peak micromotion during activity cycles occurred with sub-maximal forces and moments [4]. Our objective was to calculate multi-axial loading at the ankle joint throughout level walking and evaluate tibial fixation of ankle replacements under these loading conditions. We hypothesized that peak micromotion would occur with sub-maximal loads and moments instead of at the instant of peak compressive load. Methods: Our validated six-degree-of-freedom robotic simulator utilizes in vivo data from human subjects to replicate the individual bone kinematics in cadaveric specimen throughout activity [5]. We rigidly fixed retro-reflective markers using bone pins to the tibia, talus, and calcaneus bones of three cadaveric specimens to record individual bone kinematics using motion capture cameras. We recorded the ground reaction and muscle-tendon forces during the simulated stance phase of level walking. Musculoskeletal models were then developed in OpenSim using the specimen-specific morphology and implant position from CT- scans and from the simulator outputs to determine the loading profile at the ankle joint during stance. The calculated loads were then applied to specimen-specific finite element models to evaluate the bone-implant interaction. Peak micromotion at each time point of loading was measured and compared to the loading profile to determine if it corresponded with the peak compressive load. Results: For all specimens, the peak compressive load at the ankle joint was accompanied by multi-axial moments and relatively small shear forces (Figure 1). The peak compressive load for each specimens was between 750 N and 850 N and occurred during 75-80% of gait. The largest moment experienced by all specimens was an internal moment late in stance. The peak micromotion for each specimen did not correspond to the instance of peak compressive load, as indicated in Figure 1. Instead, peak micromotion occurred at 54%, 88%, and 96% of gait. For each specimen, these instances corresponded to the combination of a sub-maximal compressive load with high eversion and internal moments. Conclusion: We have developed a workflow to calculate ankle joint loads corresponding to cadaveric simulations that reproduce a daily activity based on in vivo data. The specimen-specific, multi-axial loading profile at the ankle for our initial results suggests that peak micromotion at the bone-implant interface of the tibial implant does not coincide with the peak compressive force. The instant of peak compressive load may not capture the worst-case scenario for the interaction between the implant and the bone. Instead, the multi-axial forces and moments at the ankle joint throughout activity should be considered when evaluating implant fixation.

Comparing Predictive Accuracy and Computational Costs for Viscoelastic Modeling of Spinal Cord Tissues

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Nicole L. Ramo ◽  
Kevin L. Troyer ◽  
Christian M. Puttlitz
Keyword(s):  
Experimental Data ◽  
Spinal Cord ◽  
Mechanical Response ◽  
Predictive Accuracy ◽  
Material Model ◽  
Loading Conditions ◽  
Nonlinear Viscoelastic ◽  
Arbitrary Loading ◽  
Linear Viscoelastic ◽  
Viscoelastic Modeling

Abstract The constitutive equation used to characterize and model spinal tissues can significantly influence the conclusions from experimental and computational studies. Therefore, researchers must make critical judgments regarding the balance of computational efficiency and predictive accuracy necessary for their purposes. The objective of this study is to quantitatively compare the fitting and prediction accuracy of linear viscoelastic (LV), quasi-linear viscoelastic (QLV), and (fully) nonlinear viscoelastic (NLV) modeling of spinal-cord-pia-arachnoid-construct (SCPC), isolated cord parenchyma, and isolated pia-arachnoid-complex (PAC) mechanics in order to better inform these judgements. Experimental data collected during dynamic cyclic testing of each tissue condition were used to fit each viscoelastic formulation. These fitted models were then used to predict independent experimental data from stress-relaxation testing. Relative fitting accuracy was found not to directly reflect relative predictive accuracy, emphasizing the need for material model validation through predictions of independent data. For the SCPC and isolated cord, the NLV formulation best predicted the mechanical response to arbitrary loading conditions, but required significantly greater computational run time. The mechanical response of the PAC under arbitrary loading conditions was best predicted by the QLV formulation.

Investigation of partially bonded fiber-reinforced elastomeric isolators (PB-FREIs) with nominal vertical tensile loads

2019 ◽  
Vol 46 (8) ◽  
pp. 669-676 ◽  
Author(s):  
Niel C. Van Engelen ◽  
Michael J. Tait ◽  
Dimitrios Konstantinidis
Keyword(s):  
Seismic Isolation ◽  
Low Cost ◽  
Compressive Load ◽  
Polymer Fibers ◽  
Experimental Investigations ◽  
Loading Conditions ◽  
Fiber Reinforced ◽  
Conventional Steel ◽  
Tensile Forces ◽  
The Cost

Unbonded fiber-reinforced elastomeric isolators (FREIs) were initially proposed as a potential low-cost alternative to conventional steel-reinforced elastomeric isolators (SREIs). FREIs are similar to SREIs but comparatively lightweight as the steel components from SREIs have been replaced with polymer fibers in FREIs. Subsequent experimental investigations identified that unbonded FREIs have desirable characteristics for seismic isolation due to the unbonded application and fiber reinforcement. The unbonded application removes mechanical fasteners, relying on friction to transfer horizontal loads, further reducing the cost. However, the unbonded application also introduces limitations, being susceptible to slip in certain loading conditions and being incapable of resisting tensile forces. In this paper, the concept of partially bonded FREIs (PB-FREIs), a proposed solution to these limitations, is further investigated experimentally with nominal vertical tensile loads. It is shown that PB-FREIs can achieve similar properties to an unbonded FREI with a vertical compressive load.

scholarly journals A new methodology to simulate subglacial deformation of water saturated granular material

2015 ◽  
Vol 9 (4) ◽  
pp. 3617-3660 ◽  
Author(s):  
A. Damsgaard ◽  
D. L. Egholm ◽  
J. A. Piotrowski ◽  
S. Tulaczyk ◽  
N. K. Larsen ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Fluid Pressure ◽  
Fluid Phase ◽  
Large Degree ◽  
Numerical Approach ◽  
Unconsolidated Sediments ◽  
Close Monitoring ◽  
Stick Slip ◽  
Rate Dependent ◽  
Water Saturated

Abstract. The dynamics of glaciers are to a large degree governed by processes operating at the ice–bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response of subglacial sediment to the shear stress of an overriding glacier. In this study, we present a new methodology designed to simulate subglacial deformation using a coupled numerical model for computational experiments on grain-fluid mixtures. The granular phase is simulated on a per-grain basis by the discrete element method. The pore water is modeled as a compressible Newtonian fluid without inertia. The numerical approach allows close monitoring of the internal behavior under a range of conditions. The rheology of a water-saturated granular bed may include both plastic and rate-dependent dilatant hardening or weakening components, depending on the rate of deformation, the material state, clay mineral content, and the hydrological properties of the material. The influence of the fluid phase is negligible when relatively permeable sediment is deformed. However, by reducing the local permeability, fast deformation can cause variations in the pore-fluid pressure. The pressure variations weaken or strengthen the granular phase, and in turn influence the distribution of shear strain with depth. In permeable sediments the strain distribution is governed by the grain-size distribution and effective normal stress and is typically on the order of tens of centimeters. Significant dilatant strengthening in impermeable sediments causes deformation to focus at the hydrologically more stable ice–bed interface, and results in a very shallow cm-to-mm deformational depth. The amount of strengthening felt by the glacier depends on the hydraulic conductivity at the ice–bed interface. Grain-fluid feedbacks can cause complex material properties that vary over time, and which may be of importance for glacier stick-slip behavior.

scholarly journals On Microstructure Evolution in Fiber-Reinforced Elastomers and Implications for Their Mechanical Response and Stability

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Oscar Lopez-Pamies ◽  
Martín I. Idiart ◽  
Zhiyun Li
Keyword(s):  
Mechanical Response ◽  
Finite Deformations ◽  
Homogenization Theory ◽  
Loading Conditions ◽  
Fiber Reinforced ◽  
Closed Form Solutions ◽  
Long Wavelength ◽  
Stress Strain Relation ◽  
Material Systems ◽  
3D Loading

Lopez-Pamies and Idiart (2010, “Fiber-Reinforced Hyperelastic Solids: A Realizable Homogenization Constitutive Theory,” J. Eng. Math., 68(1), pp. 57–83) have recently put forward a homogenization theory with the capability to generate exact results not only for the macroscopic response and stability but also for the evolution of the microstructure in fiber-reinforced hyperelastic solids subjected to finite deformations. In this paper, we make use of this new theory to construct exact, closed-form solutions for the change in size, shape, and orientation undergone by the underlying fibers in a model class of fiber-reinforced hyperelastic solids along arbitrary 3D loading conditions. Making use of these results, we then establish connections between the evolution of the microstructure and the overall stress-strain relation and macroscopic stability in fiber-reinforced elastomers. In particular, we show that the rotation of the fibers may lead to the softening of the overall stiffness of fiber-reinforced elastomers under certain loading conditions. Furthermore, we show that this geometric mechanism is intimately related to the development of long-wavelength instabilities. These findings are discussed in light of comparisons with recent results for related material systems.

Finite Element Investigation on the Tensile Armor Wire Response of Flexible Pipe for Axisymmetric Loading Conditions Using an Implicit Solver

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Alireza Ebrahimi ◽  
Shawn Kenny ◽  
Amgad Hussein
Keyword(s):  
Finite Element ◽  
Oil And Gas ◽  
Mechanical Response ◽  
Numerical Models ◽  
Oil And Gas Industry ◽  
Parameter Study ◽  
Loading Conditions ◽  
Flexible Pipe ◽  
Axisymmetric Loading ◽  
Implicit Solver

Composite flexible pipe is used in the offshore oil and gas industry for the transport of hydrocarbons, jumpers connecting subsea infrastructure, and risers with surface platforms and facilities. Although the material fabrication costs are high, there are technical advantages with respect to installation and performance envelope (e.g., fatigue). Flexible pipe has a complex, composite section with each layer addressing a specific function (e.g., pressure containment, and axial load). Continuum finite element modeling (FEM) procedures are developed to examine the mechanical response of an unbonded flexible pipe subject to axisymmetric loading conditions. A parameter study examined the effects of: (1) pure torsion, (2) interlayer friction factor, (3) axial tension, and (4) external and internal pressure on the pipe mechanical response. The results demonstrated a coupled global-local mechanism with a bifurcation path for positive angles of twist relative to the tensile armor wire pitch angle. These results indicated that idealized analytical- and structural-based numerical models may be incomplete or may provide an accurate prediction of the pipe mechanical response. The importance of using an implicit solver to predict the bifurcation response and simulate contact mechanics between layers was highlighted.

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