Ryoji Watanabe

Development of an Equibiaxial Tensile Test Device and Associated Test Method for Parameter Identification of Hyperelastic Ogden Model of Soft Material

Three different tensile tests are required to characterize a soft solid material that exhibits large deformations under external loading. The tensile tests include the uniaxial tensile, planar tensile, and equibiaxial tensile tests. In this study, a novel equibiaxial tensile test device was developed, and a test method combining the test device and a universal testing machine was proposed. Additionally, uniaxial tensile, planar tensile, and equibiaxial tensile tests of a silicone rubber were conducted, and stress-strain curves obtained from the three tests were then utilized to identify the parameter values of the hyperelastic Ogden model. The parameter values were validated by reconstructing the three tests in a finite element analysis software via the identified hyperelastic Ogden model. The findings indicated that the simulation results were in strong agreement with the test results. This validated the test method and the identified hyperelastic Ogden model. Furthermore, parameter values identified only by the uniaxial tensile test were used to perform the reconstruction analysis. The results of the analysis indicated that it was important to incorporate results from several types of tensile tests in the parameter identification process in order to obtain better simulation results.

INVESTIGATION OF SKIN LACERATION THRESHOLD UNDER A SPECIFIC CONDITION: BLADE PENETRATION TEST ON PORCINE SKIN

Skin lacerations are not fatal but constitute one of the most common injuries in daily life. There is a need, therefore, for measures to prevent skin lacerations caused by accidents; however, since only a few engineering studies have been undertaken, the threshold of skin laceration is still unclear. In this study, the thresholds of skin laceration under moderate loading rate are proposed according to the results of penetration tests on porcine skin using a knife or blunt blade. In the tests, a sharp blade (knife) and blunt blade with an edge having a small radius of curvature were applied to the external surfaces of dorsal and ventral porcine skin specimens. Penetration tests using sharp blades showed that the average rupture load was 39.0N for dorsal skin and 36.0N for ventral skin. On the other hand, the results of the penetration tests using the blunt blade were statistically analyzed by ordinal logistic regression, because the rupture load could not be defined precisely based on the load sequence dat...

An integrated study on the optimal shape design of cruciform specimen used in equibiaxial tensile test of a hyperelastic material

To conduct a finite element analysis of a material exhibiting large deformations (hyperelastic material), hyperelastic Ogden model is commonly used. However, hyperelastic Ogden model requires several tensile tests data including equibiaxial tensile test during the parameter identification. In equibiaxial tensile test, although cruciform-shaped specimen is often adopted as the test specimen, high stress concentration at the corner area causes an early rupture in the specimen. Therefore, it is difficult to obtain the mechanical response of the material under large equibiaxial strain condition. In present study, an experimental study using equibiaxial tensile test device developed previously by authors and a numerical study using finite element analysis were conducted to investigate the stress distribution and the stress-strain response of cruciform specimen under an equibiaxial tensile loading. The optimal shape design of the corner area of the cruciform specimen was then discussed according to the results.

Estimation of conditions evoking fracture in finger bones under pinch loading based on finite element analysis.

Abstract A finger finite element (FE) model was created from CT images of a Japanese male in order to obtain a shape-biofidelic model. Material properties and articulation characteristics of the model were taken from the literature. To predict bone fracture and realistically represent the fracture pattern under various loading conditions, the ESI-Wilkins-Kamoulakos rupture model in PAM-CRASH (ESI Group S.A., Paris, France) was utilized in this study with parameter values of the rupture model determined by compression testing and simulation of porcine fibula. A finger pinch simulation was then conducted to validate the finger FE model. The force-displacement curve and fracture load from the pinch simulation was compared to the result of finger pinch test using cadavers. Simulation results are coincident with the test result, indicating that the finger FE model can be used in an analysis of finger bone fracture during pinch accident. With this model, several pinch simulations were conducted with different pinching object’s stiffness and pinching energy. Conditions for evoking finger bone fracture under pinch loading were then estimated based on these results. This study offers a novel method to predict possible hazards of manufactured goods during the design process, thus finger injury due to pinch loading can be avoided.