Mechanical interactions between collagen and proteoglycans: implications for the stability of lung tissue

2005 ◽  
Vol 98 (2) ◽  
pp. 672-679 ◽  
Author(s):  
Francisco S. A. Cavalcante ◽  
Satoru Ito ◽  
Kelly Brewer ◽  
Hiroaki Sakai ◽  
Adriano M. Alencar ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Lung Tissue ◽  
Strain Curve ◽  
Uniaxial Stress ◽  
Lung Parenchyma ◽  
Alveolar Wall ◽  
Stress Strain ◽  
Experimental Conditions ◽  
The Stability ◽  
Repulsive Forces

Collagen and elastin are thought to dominate the elasticity of the connective tissue including lung parenchyma. The glycosaminoglycans on the proteoglycans may also play a role because osmolarity of interstitial fluid can alter the repulsive forces on the negatively charged glycosaminoglycans, allowing them to collapse or inflate, which can affect the stretching and folding pattern of the fibers. Hence, we hypothesized that the elasticity of lung tissue arises primarily from 1) the topology of the collagen-elastin network and 2) the mechanical interaction between proteoglycans and fibers. We measured the quasi-static, uniaxial stress-strain curves of lung tissue sheets in hypotonic, normal, and hypertonic solutions. We found that the stress-strain curve was sensitive to osmolarity, but this sensitivity decreased after proteoglycan digestion. Images of immunofluorescently labeled collagen networks showed that the fibers follow the alveolar walls that form a hexagonal-like structure. Despite the large heterogeneity, the aspect ratio of the hexagons at 30% uniaxial strain increased linearly with osmolarity. We developed a two-dimensional hexagonal network model of the alveolar structure incorporating the mechanical properties of the collagen-elastin fibers and their interaction with proteoglycans. The model accounted for the stress-strain curves observed under all experimental conditions. The model also predicted how aspect ratio changed with osmolarity and strain, which allowed us to estimate the Young's modulus of a single alveolar wall and a collagen fiber. We therefore identify a novel and important role for the proteoglycans: they stabilize the collagen-elastin network of connective tissues and contribute to lung elasticity and alveolar stability at low to medium lung volumes.

Elastomer Behavior IV. Loop Structure of Elastomer Networks

1966 ◽  
Vol 39 (5) ◽  
pp. 1489-1495
Author(s):  
L. C. Case ◽  
R. V. Wargin
Keyword(s):  
Experimental Data ◽  
Crosslink Density ◽  
Strain Curve ◽  
Uniaxial Stress ◽  
Polymer Chains ◽  
Theoretical Treatment ◽  
Loop Structure ◽  
Stress Strain ◽  
Strain Behavior ◽  
Selection Of

Abstract A new theoretical treatment strongly indicates that an elastomer network actually consists of a system of fused, closed, interpenetrating loops of polymer chains. This interpenetrating loop structure restricts the movement of the chains and thereby affects the stress-strain behavior of the elastomer. Methods have been developed to enable the calculation of the number of effective crosslinks caused by loop interpenetrations (virtual crosslinks). The uniaxial stress-strain behavior of an elastomer predicted using our methods can be fitted almost perfectly to published experimental data by proper selection of chain parameters. Previous theoretical treatments gave only a qualitative fit to the experimental data for the stress-strain behavior of elastomers and were not capable of predicting the correct shape of the experimental stress-strain curve. The present treatment gives a nearly perfect fit for both stress as a function of strain at constant crosslink density, and stress as a function of crosslink density at constant strain, and thus represents a vast improvement.

Inverse Calculation of Uniaxial Stress-Strain Curves From Bending Test Data

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
G. S. Schajer ◽  
Y. An
Keyword(s):  
A Priori ◽  
Strain Curve ◽  
Uniaxial Stress ◽  
Inverse Solution ◽  
Surface Strain ◽  
Bending Test ◽  
Stress Strain ◽  
Strain Data ◽  
Tension And Compression ◽  
Priori Information

Uniaxial tension and compression stress-strain curves are simultaneously evaluated from load and surface strain data measured during a bending test. The required calculations for the uniaxial results are expressed as integral equations and solved in that form using inverse methods. This approach is taken to reduce the extreme numerical sensitivity of calculations based on equations expressed in differential form. The inverse solution method presented addresses the numerical sensitivity issue by using Tikhonov regularization. The use of a priori information is explored as a means of further stabilizing the stress-strain curve evaluation. The characteristics of the inverse solution are investigated using experimental data from bending and uniaxial tests.

scholarly journals Comparative study of two elasto-plastic work-hardening spatial models for concrete

2018 ◽  
Vol 196 ◽  
pp. 01019
Author(s):  
Paweł M. Lewiński ◽  
Marta Zygowska
Keyword(s):  
Work Hardening ◽  
Strain Curve ◽  
Side Surface ◽  
Uniaxial Stress ◽  
Failure Criteria ◽  
Plastic Work ◽  
Biaxial Stress ◽  
Flow Rule ◽  
Stress Strain ◽  
Stress Regime

A concept of elasto-plastic, work-hardening constitutive models for the multiaxial behaviour of concrete under short-term loading and the comparison with test results is presented in this paper. Two failure surfaces are utilized: the criterion of Podgórski and the three-parameter surface of Willam and Warnke. Both triaxial failure criteria have been calibrated in terms of different multiaxial strength tests. A non-associated flow rule has been used. The plastic potential function has been assumed in the form of the Drucker-Prager cone with variation of the angle of the cone side surface. In order to cover the plastic hardening behaviour, the equivalent uniaxial stress-strain curve has been adopted. An incremental stress-strain relationship has been formulated. The results of the numerical analysis performed by a direct integration of the constitutive relationships for the biaxial stress regime have been compared with the test data.

Influence of Uniaxial Stress on the Stress-Strain Curve Measured by Nanoindentation

2014 ◽  
Vol 597 ◽  
pp. 17-20
Author(s):  
Ikuo Ihara ◽  
Kohei Ohtsuki ◽  
Iwao Matsuya
Keyword(s):  
Compressive Stress ◽  
Strain Curve ◽  
Uniaxial Stress ◽  
Local Area ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Compressive Stresses ◽  
Multiple Loading ◽  
Tip Radius ◽  
Uniaxial Compressive Stress

A nanoindentation technique with a spherical indenter of tip radius 10 μm is applied to the evaluation of stress-strain curve at a local area of a pure iron under the uniaxial compressive stress exerted through the iron, and the influence of the compressive stress on the estimated stress-strain curve has been examined. A continuous multiple loading method is employed to determine the stress-strain curve. In the method, a set of 21 times of loading/unloading sequences with increasing terminal load are made and load-displacement curves with the different terminal loads from 0.1 mN to 100 mN are then continuously obtained and converted to a stress-strain curve. To examine the stress dependence of the stress-strain curve, the estimation by the nanoindentetion is performed under different uniaxial compressive stresses up to 250 MPa. It has been found that the stress-strain curve determined by the nanoindentation shifts upward as the compressive stress increases and the quantity of the shift is almost equal to the uniaxial stress acting on the iron specimen. It is also noted that the yield stress (0.2 % proof stress) estimated from the stress-strain curve increases almost proportionally to the uniaxial stress and the increase ratio tends to decrease as the stress reaches around 200 MPa.

Tension-compression stress-strain curves from bending tests

1971 ◽  
Vol 6 (4) ◽  
pp. 286-292 ◽  
Author(s):  
P W J Oldroyd
Keyword(s):  
Strain Curve ◽  
Bending Moment ◽  
Uniaxial Stress ◽  
Bending Test ◽  
Compression Stress ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Bending Tests ◽  
Original Length ◽  
Annealed Copper

A formula—Nadai's bending formula—is derived which enables the tension (or compression) stress-strain curve for a material to be obtained from the curve relating bending moment to curvature for a beam of solid rectangular section. The method is extended to give a formula which covers deformations in which reversals of plastic strain occur. The results obtained from a unidirectional bending test made on annealed copper are compared with those obtained from a tensile test made on the same material and the accuracy of the stress-strain values obtained from the bending test is discussed. The results obtained from a reversed bending test are also compared with those obtained from a tension-compression test in which a specimen was first stretched and then compressed to its original length. The limitations imposed by this method of obtaining the stress-strain curve for a material are examined and the advantages its presents in the study of the behaviour of materials under uniaxial stress are outlined.

scholarly journals A 3D finite element model for reinforced concrete structures analysis

2011 ◽  
Vol 4 (4) ◽  
pp. 548-560 ◽  
Author(s):  
G. F. F. Bono ◽  
A. Campos Filho ◽  
A. R. Pacheco
Keyword(s):  
Finite Element ◽  
Reinforced Concrete ◽  
Numerical Model ◽  
Concrete Structures ◽  
Strain Curve ◽  
Uniaxial Stress ◽  
Element Model ◽  
Reinforced Concrete Structures ◽  
Principal Stresses ◽  
Stress Strain

This work presents a numerical model for 3D analyses through the finite element method of reinforced concrete structures subjected to monotonic loads. The proposed model for concrete is orthotropic and uses the equivalent uniaxial strain concept. The equivalent uniaxial stress-strain relation is generalized to take into account the triaxial stress conditions. The parameters used in the equivalent uniaxial stress-strain curve are determined from the failure surface defined in the principal stress space. The implementation in finite elements is based on the consideration of smeared cracks with cracks rotating according to the directions of the principal stresses. Also, an embedded reinforcement model was implemented to represent existent reinforcing bars. Finally, some results are compared with experimental data from the literature to demonstrate the validity of the numerical model developed.

EXPERIMENTAL ANALYSIS ON THE MECHANICAL PROPERTIES OF SOIL-ROCK MIXED FILLERS WITH DIFFERENT ROCK CONTENTS ON A HIGH EMBANKMENT

10.6036/10235 ◽  
2021 ◽  
Vol 96 (5) ◽  
pp. 478-483
Author(s):  
YANQING ZHANG ◽  
HONGJUN JING ◽  
JUNYI DAI
Keyword(s):  
Mechanical Properties ◽  
Large Scale ◽  
Volumetric Strain ◽  
Strain Curve ◽  
Mountainous Area ◽  
Stress Strain ◽  
Study Results ◽  
The Stability ◽  
Chang Model ◽  
Properties Of Soil

The mechanical properties of soil-rock mixed filler are the key factors influencing the high rockfill embankment stability. However, they remain unclear, given the complexity of soil-rock mixed filler structure. To analyze the stability of high rockfill embankment in the construction and operation phases, under the engineering background of a high rockfill embankment with a filling height of 50.6 m in the national highway 316 project within the Qinba mountainous area in China, a series of large-scale triaxial consolidated drained shear tests were performed on two soil-rock mixed fillers with 40% and 70% rock contents. Their stress-strain relation, deformation, and strength characteristics were observed. The applicability of Duncan-Chang model was also determined on the basis of the above tests. Results demonstrate that the stress-strain curve and volumetric strain of the filler with 40% rock content are strain hardening type and shear shrinkage type. The filler with 70% rock content has a weak strain softening, and its volumetric strain is first shear shrinkage and then shear dilation. The filler with 70% rock content has larger peak and critical frictional angles than the filler with 40% rock content. The tangential Poisson's ratios of the E-B and E-? models are obtained. The former can approximately reflect the volumetric strain characteristics of the filler with 40% rock content. The latter can approximately reflect those of the filler with 70% rock content. Yet, both models fail to describe the influence of confining pressure on the volumetric strain. The study results provide a reference for the stability analysis of high rockfill embankment engineering and provide parameters for constructing the constitutive model of soil-rock mixed fillers. Keywords: high embankment; soil-rock mixed filler; large-scale triaxial shear test; deformation characteristics; Duncan-Chang model

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