Collagen; ultrastructure and its relation to mechanical properties as a function of ageing

1972 ◽  
Vol 180 (1060) ◽  
pp. 293-315 ◽  
Keyword(s):  
Deformation Behaviour ◽  
Life Time ◽  
Periodic Pattern ◽  
Albino Rats ◽  
Structure And Properties ◽  
Stress Strain ◽  
Good Correspondence ◽  
Bearing Unit ◽  
Strain Data ◽  
Good Agreement

Tail tendons from Fischer and Sprague-Dawly albino rats of ages from 2 weeks to 3 years were investigated under the polarizing microscope as regards structure and deformation behaviour. Periodically extinguishing bands were observed along the otherwise featureless tendons. By analysing the behaviour of this extinction pattern under appropriate rotations of the tendon, it could be deduced that the orientation of the basic birefringent units varies periodically along the tendon and that this periodic pattern corresponds to a planar arrangement of the anisotropic entities. All the relevant parameters of this periodic structure could be determined in a representative manner from polarizing optics alone. Subdivision of the tendons revealed regularly undulating or rather crimped subunits in good correspondence to what has been deduced from the extinction bands in the intact tendons. The crimp angle was found to decrease while the periodicity increased - in approximate proportion to the length of the tail - with the age of the rat implying constancy of crimp number during the life time of the animal. On elongation the periodicity was gradually removed. The calculated fibre elongation necessary to eliminate the crimp was in good agreement with observation for mature rats but was larger for young rats implying the simultaneous stretching of the fibre itself. Stress-strain properties of tendons were measured and models for crimp straightening were tested. It was found that a model containing inflexible hinges, corresponding to the ‘elastica’ problem in mechanics gave reasonable fit with experiment. Analysis of stress-strain data on this basis leads to a basic load bearing unit, the diameter of which increases from 100 to 500 nm with the age of the animal. Implications of these findings for the structure and properties of the tendons, also in relation to ageing are pointed out.

A New Look at Measurements of Network Density

1986 ◽  
Vol 59 (1) ◽  
pp. 138-141 ◽  
Author(s):  
Robert A. Hayes
Keyword(s):  
Hysteresis Loop ◽  
Interaction Parameters ◽  
Network Density ◽  
Stress Strain ◽  
Solvent Interaction ◽  
Solvent Method ◽  
Strain Data ◽  
Good Agreement ◽  
Polymer Solvent ◽  
New Look

Abstract A two-solvent method for determining the polymer-solvent interaction parameters independently of stress-strain data is described. The values obtained are much lower than those reported previously. Network densities calculated from swelling data and these interaction parameters are in good agreement with those calculated from the return portion of a hysteresis loop at high elongations.

Micromechanical Modeling of Two-Phase Steels

2000 ◽  
Vol 653 ◽  
Author(s):  
Mikael Nygårds ◽  
Dilip Chandrasekaran ◽  
Peter Gudmundson
Keyword(s):  
Micromechanical Model ◽  
Tensile Tests ◽  
Micromechanical Modeling ◽  
Uniaxial Tensile ◽  
The Finite Element Method ◽  
Stress Strain ◽  
Two Phase ◽  
Representative Cell ◽  
Strain Data ◽  
Good Agreement

AbstractA two-dimensional micromechanical model based on the finite element method is presented to model two-phase ferritic/pearlitic steels, by aid of generalised plane strain elements. A periodic representative cell containing 100 ferrite grains, and the desired fraction pearlite is used. By applying periodic boundary conditions, loading by an average stress or strain state is possible.Uniaxial tensile tests were performed on specimens containing the ferrite and pearlite microstructures, and on two-phase materials containing 25% and 58% pearlite respectively. The stress-strain data of the pearlite material is used to fit a laminar dependent Taylor relation to represent the pearlite workhardening. Thereafter, laminar spacings in the two-phase materials are measured, and the total stress-strain response of the materials is modelled. Comparisons between generated data and experiments show good agreement up to a strain of 2%.

Experimental Characterization of Mechanical Behavior of Cord-Rubber Composites

1982 ◽  
Vol 10 (1) ◽  
pp. 37-54 ◽  
Author(s):  
M. Kumar ◽  
C. W. Bert
Keyword(s):  
Response Characteristic ◽  
Cord Compression ◽  
Complete Characterization ◽  
Strain Response ◽  
Strain Gages ◽  
Experimental Characterization ◽  
Rubber Composites ◽  
Stress Strain ◽  
Strain Data

Abstract Unidirectional cord-rubber specimens in the form of tensile coupons and sandwich beams were used. Using specimens with the cords oriented at 0°, 45°, and 90° to the loading direction and appropriate data reduction, we were able to obtain complete characterization for the in-plane stress-strain response of single-ply, unidirectional cord-rubber composites. All strains were measured by means of liquid mercury strain gages, for which the nonlinear strain response characteristic was obtained by calibration. Stress-strain data were obtained for the cases of both cord tension and cord compression. Materials investigated were aramid-rubber, polyester-rubber, and steel-rubber.

Stresses Around Wellbores in Nonlinear Rock

1968 ◽  
Vol 8 (03) ◽  
pp. 304-312 ◽  
Author(s):  
M.A. Mahtab ◽  
R.E. Goodman
Keyword(s):  
Finite Element Analysis ◽  
Principal Stress ◽  
Intermediate Principal Stress ◽  
The State ◽  
Initial Stresses ◽  
Stress Strain ◽  
Element Analysis ◽  
Deviator Stress ◽  
State Of Stress ◽  
Strain Data

ABSTRACT The state of stress around a vertical wellbore in rock following nonlinear stress-strain laws is examined by means of finite element analysis. The wellbore is considered an axisymmetric body with axisymmetric loading. The initial vertical and horizontal stresses are "locked" in the rock elements around the wellbore and a new state of stress is generated by the displacements which occur around the borehole. A point-wise variation of the elastic moduli is made on the basis of the new stress state and the triaxial data. The initial stresses are now reintroduced along with the changed moduli and original boundary constraints. This procedure is repeated until convergent stresses are reached. The effect of nonlinearity on stresses is examined for a 6,000-ft wellbore in a schistose gneiss and Berea sandstone using results of laboratory triaxial compression tests. The results show that the effect is restricted to one well radius from the bottom periphery of the hole. Beyond a distance of one-quarter radius, the effect of nonlinearity on stresses is almost always less than 5 percent for the cases considered. The consideration of a static pressure inside the well does not magnify the effect of nonlinearity on borehole stresses. INTRODUCTION The terms "wellbore" and "borehole" here designate cylindrical openings in the ground with vertical axis and a circular cross-section. A knowledge of the stress redistribution that occurs on excavating a wellbore is important in understanding the behavior of the lined or unlined hole, hydraulic fracture response, and the effect of stress redistribution on drillability; also it is important in predicting initial stresses in the virgin ground, and in analyzing the response of measuring instruments placed in the borehole. Our knowledge of the state of stress around a wellbore has been restricted to homogeneous, isotropic, elastic material and derives chiefly from the analysis by Miles and Topping1 and the photoelastic work of Galle and Wilhoit2 and Word and Wilhoit.3 In this investigation the state of stress is examined for a nonlinear elastic material by means of finite element analysis. Many rocks possess stress-strain curves that depart notably from straight lines in their initial or final portions. While the literature contains abundant stress-strain data from triaxial tests (axisymmetric loading) on cylindrical rock specimens, there is little information on rock deformability under nonaxisymmetric loading conditions such as occur at each point around the bottom of a wellbore. Although there is some knowledge of the effect of intermediate principal stress on rock strength, there is virtually nothing known about its effect on rock deformability; therefore, we have assumed here that the effect of intermediate principal stress can be ignored. A schistose gneiss4 and Berea sandstone5 were selected as representative rocks for this analysis. The traditional graphs of deviator stress (s1-s3) vs axial strain were reworked to give the tangent modulus as a function of the deviator stress for varying values of the minor principal stress. The result is a nesting family of skewed, bell-shaped curves for the gneiss (Fig. 1A) and the sandstone (Fig. 2A). A similar replotting of the lateral strain data defines the variation of Poisson's ratio (?) with the deviator stress and confining pressure. These curves, shown in Fig. 1B for the gneiss and in Fig. 2B for the sandstone, are not so well ordered as the tangent modulus curves. However, all of these display an increase of ? with deviator stress application, but the rate of increase diminishes with confinement. The ET and ? curves for the two rock types are tabulated in Tables 1A and 1B for use in a digital computer so that material properties corresponding to a given state of stress can be assigned by interpolation.

scholarly journals FABRICATION AND PROPERTIES OF Co DOPED Bi0.5K0.5TiO3 – BiFeO3 SOLID SOLUTION

2018 ◽  
Vol 56 (1A) ◽  
pp. 197
Author(s):  
Nguyen Hoang Tuan
Keyword(s):  
Solid Solution ◽  
Raman Spectroscopy ◽  
Magnetic Properties ◽  
Crystal Structures ◽  
Solid Solutions ◽  
Sol Gel ◽  
Structure And Properties ◽  
Antiferromagnetic Ordering ◽  
Co Doped ◽  
Good Agreement

In this study, we present some results on the structure and properties of the solid solution of Bi0.5K0.5TiO3– BiFeCoO3 (BKT – BFCO) by Sol-gel method. Crystal structures of BKT – BFCO solid solutions were studies by XRD and Raman spectroscopy. The results were in good agreement with the previous reports of Bi0.5K0.5TiO3– BiFeO3 (BKT – BFO) and Bi0.5K0.5TiO3 – BiCoO3 (BKT – BCO) solid solutions. The magnetic properties were investigated via unsaturated M-H loop, which showed the competition of paramagnetic and antiferromagnetic ordering in BKT – BFCO. However, differing from the BKT – BFO and BKT – BCO solid solutions, the unclear values of saturated magnetism in BKT – BFCO raised the unexplained question, which needed further studies.

scholarly journals Identification of orthotropic material parameters for acute, necrotic, fibrotic and remodelling myocardial infarcts in the rat

2019 ◽  
Author(s):  
Mazin S. Sirry ◽  
Laura Dubuis ◽  
Neil H. Davies ◽  
Jun Liao ◽  
Thomas Franz
Keyword(s):  
Constitutive Model ◽  
Orthotropic Material ◽  
Constitutive Models ◽  
Biaxial Stress ◽  
Percentage Error ◽  
Fe Model ◽  
Stress Strain ◽  
Material Parameters ◽  
Strain Data ◽  
Tensile Experiment

AbstractFinite element (FE) models have been effectively utilized in studying biomechanical aspects of myocardial infarction (MI). Although the rat is a widely used animal model for MI, there is a lack of material parameters based on anisotropic constitutive models for rat myocardial infarcts in literature. This study aimed at employing inverse methods to identify the parameters of an orthotropic constitutive model for myocardial infarcts in the acute, necrotic, fibrotic and remodelling phases utilizing the biaxial mechanical data developed in a previous study. FE model was developed mimicking the setup of the biaxial tensile experiment. The orthotropic case of the generalized Fung constitutive model was utilized to model the material properties of the infarct. The parameters of Fung model were optimized so that the FE solution best fitted the biaxial experimental stress-strain data. A genetic algorithm was used to minimize the objective function. Fung orthotropic material parameters for different infarct stages were identified. The FE model predictions best approximated the experimental data of the 28 days infarct stage with 3.0% mean absolute percentage error. The worst approximation was for the 7 days stage with 3.6% error. This study demonstrated that the experimental biaxial stress-strain data of healing rat infarcts could be successfully approximated using inverse FE methods and genetic algorithms. The material parameters identified in this study will provide an essential platform for FE investigations of biomechanical aspects of MI and the development of therapies.

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