scholarly journals The Influence of the Specimen Shape and Loading Conditions on the Parameter Identification of a Viscoelastic Brain Model

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Costin D. Untaroiu
Keyword(s):  
Parameter Identification ◽  
Strain Distribution ◽  
Nonlinear Behavior ◽  
Relaxation Curve ◽  
Uniform Strain ◽  
High Rate ◽  
Optimization Approach ◽  
Material Models ◽  
Fe Simulations ◽  
Specimen Height

The mechanical properties of brain under various loadings have been reported in the literature over the past 50 years. Step-and-hold tests have often been employed to characterize viscoelastic and nonlinear behavior of brain under high-rate shear deformation; however, the identification of brain material parameters is typically performed by neglecting the initial strain ramp and/or by assuming a uniform strain distribution in the brain samples. Using finite element (FE) simulations of shear tests, this study shows that these simplifications have a significant effect on the identified material properties in the case of cylindrical human brain specimens. Material models optimized using only the stress relaxation curve under predict the shear force during the strain ramp, mainly due to lower values of their instantaneous shear moduli. Similarly, material models optimized using an analytical approach, which assumes a uniform strain distribution, under predict peak shear forces in FE simulations. Reducing the specimen height showed to improve the model prediction, but no improvements were observed for cubic samples with heights similar to cylindrical samples. Models optimized using FE simulations show the closest response to the test data, so a FE-based optimization approach is recommended in future parameter identification studies of brain.

On the parameter identification of visco-hyperelastic material models for adhesive tapes

PAMM ◽  
2014 ◽  
Vol 14 (1) ◽  
pp. 341-342 ◽  
Author(s):  
Nils Hendrik Kröger ◽  
Daniel Juhre
Keyword(s):  
Parameter Identification ◽  
Hyperelastic Material ◽  
Material Models

AFM Indentation and Material Property Identification of Soft Hydrogels

2007 ◽  
Author(s):  
Sakya Tripathy ◽  
Edward Berger ◽  
Kumar Vemaganti
Keyword(s):  
Experimental Data ◽  
Parameter Identification ◽  
Material Property ◽  
Contact Point ◽  
Hyperelastic Material ◽  
Agarose Gel ◽  
Afm Indentation ◽  
Fe Simulations ◽  
Property Identification ◽  
Identification Approach

There is growing evidence of the importance of mechanical deformations on various facets of cell functioning. This asks for a proper understanding of the cell’s characteristics as a mechanical system in different physiological and mechanical loading conditions. Many researchers use atomic force microscopy (AFM) indentation and the Hertz contact model for elastic material property identification under shallow indentation. For larger indentations, many of the Hertz assumptions are not inherently satisfied and the Hertz model is not directly useful for characterizing nonlinear elastic or inelastic material properties. We have used exponential hyperelastic material in FE simulations of the AFM indentation tests. A parameter identification approach is developed for hyperelastic material property determination from the simulated data. We collected AFM indentation data on agarose gel and developed a simple algorithm for contact point detection. The contact point correction improves the prediction of elastic modulus over the case of visual contact point identification. The modulus of 1% agarose gel was found to be about 15 kPa using the proposed correction, with mild but non-trival hardening with deeper indentation. The experimental data is compared with the results from the FE simulations and shows that over the hardening portion of the indentation response, our proposed parameter identification approach successfully captures the experimental data.

scholarly journals Strain Gage Test Results of Band-Type Locking Rings for a Typical Drum Type Radioactive Material Package

2002 ◽  
Author(s):  
Charles A. McKeel ◽  
Allen C. Smith
Keyword(s):  
Uniform Distribution ◽  
Strain Gage ◽  
Strain Distribution ◽  
Drop Test ◽  
Uniform Strain ◽  
Radioactive Material ◽  
Test Results ◽  
Lower Weight ◽  
Band Type

Band type closure rings are commonly used for securing the drum lid on radioactive material packages of lower weight classifications. Lid installation is achieved by placing the band around the perimeter of the lidded drum and tightening the single bolt in stages until a designated torque value is obtained. The band is subjected to heavy rapping with a soft hammer during installation to equilibrate the band strains around the drum perimeter. The study described here investigated the strain distributions in the band throughout the installation process. The results show that a uniform strain distribution is achieved during installation and that the hammering of the band aids in achieving the uniform distribution. The results of the strain levels after the drop test indicate that the locking rings maintain some pre-tension, even after severe targeted drops that crush a portion of the drum top.

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