Nonlinear Viscoelastic Analysis of Uniaxial Stress‐Strain Measurements of Elastomers at Constant Stretching Rates

1986 ◽  
Vol 30 (2) ◽  
pp. 301-312 ◽  
Author(s):  
Boudewijn J. R. Scholtens ◽  
Henk C. Booij ◽  
Paul J. R. Leblans
Keyword(s):  
Uniaxial Stress ◽  
Stress Strain ◽  
Strain Measurements ◽  
Viscoelastic Analysis ◽  
Nonlinear Viscoelastic

Delamination in the scoring and folding of paperboard

TAPPI Journal ◽  
2012 ◽  
Vol 11 (1) ◽  
pp. 61-66 ◽  
Author(s):  
DOEUNG D. CHOI ◽  
SERGIY A. LAVRYKOV ◽  
BANDARU V. RAMARAO
Keyword(s):  
Finite Element ◽  
Plane Deformation ◽  
Strain Analysis ◽  
Local Strain ◽  
Uniaxial Stress ◽  
Material Model ◽  
Element Model ◽  
Plastic Behavior ◽  
Stress Strain ◽  
Strain Fields

Delamination between layers occurs during the creasing and subsequent folding of paperboard. Delamination is necessary to provide some stiffness properties, but excessive or uncontrolled delamination can weaken the fold, and therefore needs to be controlled. An understanding of the mechanics of delamination is predicated upon the availability of reliable and properly calibrated simulation tools to predict experimental observations. This paper describes a finite element simulation of paper mechanics applied to the scoring and folding of multi-ply carton board. Our goal was to provide an understanding of the mechanics of these operations and the proper models of elastic and plastic behavior of the material that enable us to simulate the deformation and delamination behavior. Our material model accounted for plasticity and sheet anisotropy in the in-plane and z-direction (ZD) dimensions. We used different ZD stress-strain curves during loading and unloading. Material parameters for in-plane deformation were obtained by fitting uniaxial stress-strain data to Ramberg-Osgood plasticity models and the ZD deformation was modeled using a modified power law. Two-dimensional strain fields resulting from loading board typical of a scoring operation were calculated. The strain field was symmetric in the initial stages, but increasing deformation led to asymmetry and heterogeneity. These regions were precursors to delamination and failure. Delamination of the layers occurred in regions of significant shear strain and resulted primarily from the development of large plastic strains. The model predictions were confirmed by experimental observation of the local strain fields using visual microscopy and linear image strain analysis. The finite element model predicted sheet delamination matching the patterns and effects that were observed in experiments.

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.

Three Types of Stress-Strain Relationship’s Comparison of Circular Tubed Reinforced Concrete in FEA

2012 ◽  
Vol 204-208 ◽  
pp. 930-933
Author(s):  
Xiao Hu ◽  
Zhen Lin Chen
Keyword(s):  
Finite Element ◽  
Reinforced Concrete ◽  
Uniaxial Stress ◽  
Steel Tube ◽  
Finite Element Analyses ◽  
Stress Strain ◽  
Concrete Filled Steel Tube ◽  
Bearing Analysis

The paper introduces 3 types of uniaxial stress-strain relationships of concrete filled steel tube by Pan Youguang, Susantha and Saenz, and performs finite element analyses of the axial strengths of 18 CTRC columns, studies the characters of three models, and comprises between the axial strengths from FEA and existed experiments. Results show these 3 types of model are all suitable for bearing analysis, but Pan’s model is more accurate.

Sign in / Sign up

Export Citation Format

Share Document