Differential ultrasonic stress–strain measurements

1999 ◽  
Vol 106 (4) ◽  
pp. 2167-2167
Author(s):  
Sissay Hailu ◽  
Gary R. Halford ◽  
Dov Hazony ◽  
Gerhard Welsch
Keyword(s):  
Stress Strain ◽  
Strain Measurements

scholarly journals Comparison of waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness using different cross-linking irradiances: an experimental study with air-puff applanation of ex vivo porcine eyes

2020 ◽  
Vol 258 (10) ◽  
pp. 2173-2184 ◽  
Author(s):  
Robert Herber ◽  
Mathew Francis ◽  
Eberhard Spoerl ◽  
Lutz E. Pillunat ◽  
Frederik Raiskup ◽  
...  
Keyword(s):  
Experimental Study ◽  
Ex Vivo ◽  
Cross Linking ◽  
Displacement Curve ◽  
Stress Strain ◽  
Strain Measurements ◽  
Deflection Amplitude ◽  
Force Displacement ◽  
Stiffening Effect ◽  
Porcine Eyes

Abstract Purpose To assess corneal stiffening of standard (S-CXL) and accelerated (A-CXL) cross-linking protocols by dynamic corneal response parameters and corneal bending stiffness (Kc[mean/linear]) derived from Corvis (CVS) Scheimpflug-based tonometry. These investigations were validated by corneal tensile stiffness (K[ts]), derived from stress-strain extensometry in ex vivo porcine eyes. Methods Seventy-two fresh-enucleated and de-epithelized porcine eyes were soaked in 0.1% riboflavin solution including 10% dextran for 10 min. The eyes were separated into four groups: controls (n = 18), S-CXL (intensity in mW/cm2*time in min; 3*30) (n = 18), A-CXL (9*10) (n = 18), and A-CXL (18*5) (n = 18), respectively. CXL was performed using CCL Vario. CVS measurements were performed on all eyes. Subsequently, corneal strips were extracted by a double-bladed scalpel and used for stress-strain measurements. K[ts] was calculated from a force-displacement curve. Mean corneal stiffness (Kc[mean]) and constant corneal stiffness (Kc[linear]) were calculated from raw CVS data. Results In CVS, biomechanical effects of cross-linking were shown to have a significantly decreased deflection amplitude as well as integrated radius, an increased IOP, and SP A1 (P < 0.05). Kc[mean]/Kc[linear] were significantly increased after CXL (P < 0.05). In the range from 2 to 6% strain, K[ts] was significantly higher in S-CXL (3*30) compared to A-CXL (9*10), A-CXL (18*5), and controls (P < 0.05). At 8% to 10% strain, all protocols induced a higher stiffness than controls (P < 0.05). Conclusion Several CVS parameters and Kc[mean] as well as Kc[linear] verify corneal stiffening effect after CXL on porcine eyes. S-CXL seems to have a higher tendency of stiffening than A-CXL protocols have, which was demonstrated by Scheimpflug-based tonometry and stress-strain extensometry.

scholarly journals Direct Stress-Strain Measurements from Bulged Membranes Using Topography Image Correlation

2014 ◽  
Vol 54 (5) ◽  
pp. 717-727 ◽  
Author(s):  
J. Neggers ◽  
J. P. M. Hoefnagels ◽  
F. Hild ◽  
S. Roux ◽  
M. G. D. Geers
Keyword(s):  
Image Correlation ◽  
Stress Strain ◽  
Strain Measurements

Tensile Stress—Strain Measurements for Characterization of Gum Elastomers and Filled Compounds

1990 ◽  
Vol 63 (4) ◽  
pp. 624-636 ◽  
Author(s):  
N. Nakajima ◽  
M. H. Chu ◽  
R. Babrowicz
Keyword(s):  
Shear Modulus ◽  
Tensile Stress ◽  
Shear Deformation ◽  
Tensile Modulus ◽  
Nonlinear Behavior ◽  
Material Behavior ◽  
Structural Constraints ◽  
Stress Strain ◽  
Strain Measurements ◽  
Diene Rubbers

Abstract For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.

Crosslink Density Evaluation of EPDM Vulcanizates

1971 ◽  
Vol 44 (4) ◽  
pp. 1109-1129 ◽  
Author(s):  
V. Zamboni ◽  
U. Flisi ◽  
G. Giunchi
Keyword(s):  
Crosslink Density ◽  
Amplification Factor ◽  
Large Degree ◽  
Stress Strain ◽  
Solvent Interaction ◽  
Strain Measurements ◽  
Density Evaluation ◽  
Rubber Phase ◽  
The Difference

Abstract Crosslink density of EPDM vulcanizates, both gum and filled, has been evaluated from stress-strain measurements on both dry and swollen samples, by plotting the data according to the Mooney-Rivlin diagram. Values of the C1 constant of swollen specimens were generally found to be much higher than those of the dry ones, and the difference was ascribed to the effect of entanglements, which probably act as stable crosslinks in swollen networks. The Flory-Huggins equation has also been studied and its applicability to EPDM vulcanizates examined ; a large degree of uncertainty was found for the polymer-solvent interaction parameter, μ, that suggests the use of this equation with reservation in the case of EPDM elastomers. Many data of the Mooney-Rivlin C2 constant being available, its dependence on various parameters has been investigated and the hypothesis has been confirmed that it is associated with entanglements and intermolecular structure. The stress-strain curves of samples filled with both mineral and black fillers were analysed using the Mullins and Tobin “strain amplification factor.” This technique, which allows one to describe the behavior of the rubber phase in filled vulcanizates, has given good results that endorse the use of the Mooney-Rivlin plot for the characterization of rubbery networks. The Mooney-Rivlin constants also gave very interesting results for the investigation of the networks obtained from curing elastomer blends.

scholarly journals Imaging Mass Spectrometry by Matrix-Assisted Laser Desorption/Ionization and Stress-Strain Measurements in Iontophoresis Transepithelial Corneal Collagen Cross-Linking

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Paolo Vinciguerra ◽  
Rita Mencucci ◽  
Vito Romano ◽  
Eberhard Spoerl ◽  
Fabrizio I. Camesasca ◽  
...  
Keyword(s):  
Imaging Mass Spectrometry ◽  
Laser Desorption ◽  
Cross Linking ◽  
Laser Desorption Ionization ◽  
Stress Strain ◽  
Strain Measurements ◽  
Maldi Ims ◽  
Corneal Rigidity ◽  
Collagen Cross Linking ◽  
Corneal Collagen

Purpose.To compare biomechanical effect, riboflavin penetration and distribution in transepithelial corneal collagen cross-linking with iontophoresis (I-CXL), with standard cross linking (S-CXL) and current transepithelial protocol (TE-CXL).Materials and Methods.The study was divided into two different sections, considering, respectively, rabbit and human cadaver corneas. In both sections corneas were divided according to imbibition protocols and irradiation power. Imaging mass spectrometry by matrix-assisted laser desorption/ionization (MALDI-IMS) and stress-strain measurements were used. Forty-eight rabbit and twelve human cadaver corneas were evaluated.Results.MALDI-IMS showed a deep riboflavin penetration throughout the corneal layers with I-CXL, with a roughly lower concentration in the deepest layers when compared to S-CXL, whereas with TE-CXL penetration was considerably less. In rabbits, there was a significant increase (by 71.9% andP=0.05) in corneal rigidity after I-CXL, when compared to controls. In humans, corneal rigidity increase was not significantly different among the subgroups.Conclusions.In rabbits, I-CXL induced a significant increase in corneal stiffness as well as better riboflavin penetration when compared to controls and TE-CXL but not to S-CXL. Stress-strain in human corneas did not show significant differences among techniques, possibly because of the small sample size of groups. In conclusion, I-CXL could be a valid alternative to S-CXL for riboflavin delivery in CXL, preserving the epithelium.

Sign in / Sign up

Export Citation Format

Share Document