Jonas A. Pramudita

Effect of cervical spine alignment on neck injury risk during rear-end impact – numerical study using neck finite element model

ABSTRACT Many neck safety technologies have been developed in recent years; however, the incidence of whiplash-associated disorders (WAD) in rear-end collision accidents remains high. A lack of consideration of individual differences among vehicle occupants is considered a major factor. Individual differences in the neck can be represented by the differences in cervical spine alignment. In this study, images of typical cervical spine alignments, such as lordotic, straight, kyphotic, s-shaped, and inverse s-shaped alignments, were selected from a hospital database. Shape transformations of a head–neck finite element model were then performed to obtain multiple head–neck finite element models with five different cervical spine alignments. Rear-end impact analysis results showed quantitative differences in relative intervertebral rotation and ligament strain. These differences might be the cause of variability in the neck injury risk and severity among occupants in rear-end impact accidents.

Analysis of Intervertebral Strain Response during Rear Impact Using Head-Neck Finite Element Model

Minor neck injuries in rear collision accidents have become a huge problem in many countries. Therefore, it is urgent to develop a suitable criterion for assessing neck injury risk. In this study, a detailed head-neck finite element (FE) model was developed. Skull and vertebrae models were created based on CT images of a typical Japanese male. Models of intervertebral discs, ligaments and muscles were also created according to literatures. Furthermore, material properties were taken from the published data. In order to evaluate intervertebral soft tissue strain due to translational rotational coupled motion of vertebrae, a 2D strain analysis method was also proposed. The method was applied to cervical vertebral motion data obtained from previous rear impact tests using human volunteers and from test reconstruction using the head-neck model. A potential correlation between intervertebral strain and neck injury was clarified from the comparison between the intervertebral strain level and existence of neck discomforts. The model’s response is also in good agreement with the volunteers’ response, indicating that the head-neck model is suitable for minor neck injury analysis and that it is possible to analyze the intervertebral strain with a head-neck model.

Out-of-Plane Deformation Measurement of Soft Solid Using a Stereo Camera System

Soft solid undergoes large deformation under external loading. In order to understand the mechanical characteristics of soft solid, a quantitative evaluation of the deformation behavior is necessary. In the previous study, a strain distribution on the surface of soft solid during an indentation (penetration) test was obtained by evaluating the deformation behavior using isoparametric finite element. However, three-dimensional deformations including out-of-plane deformation was neglected. In this study, the deformation behavior of the soft solid was analyzed using a stereo camera system and binocular disparity method. The out-of-plane deformation of the soft solid was then reconstructed three-dimensionally. Analysis result showed that this study was able to reconstruct the out-of-plane deformation in the area below the indenter. In addition, the displacements of specific points located on the deformed surface could also be estimated. Under the indentation loading condition, the out-of-plane displacements of points in the area below the indenter were estimated to be between 5.9 and 9.9 mm. However, the accuracy of the estimation should be validated by other measurement techniques in the future.

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.

Assessment of Dynamic Responses of Skin Simulant in a Drop Weight Penetration Test

Skin laceration injury caused by a penetration of small curvature edge frequently occurs in a domestic accident. An assessment method for this injury is necessary in order to develop a safer manufactured product. To assess the risk of skin laceration injury in a penetration accident, a skin simulant made from silicone rubber was proposed. However, mechanical responses of this skin simulant under dynamic penetration loading have not yet been investigated. In this study, a drop weight penetration test device was developed in order to simulate penetration accidents under impact velocities of over 1 m/s. The device was then used for investigating the dynamic responses of skin simulant against several blades with different tip curvature radii. Load, penetration depth, impulse and energy at rupture were then determined from the test results. Load and penetration depth at rupture increased with the increase of tip curvature radius of the blades. Furthermore, the drop weight test result showed larger response compared to the quasi-static test result which might be caused by the viscous effect and the polymer characteristics such as cross-linking of the skin simulant.

Development of an occupant multi-body model based on Japanese male characteristics data for rear impact analysis

A human multi-body model was developed to quickly analyse vehicle occupant responses during rear collision. The outer body geometry of the human model was obtained from scan data of a Japanese male. Data were divided into 17 rigid body segments. The centre of gravity, mass and moment of inertia of each segment was determined by regression. Sixteen articulations were modelled with revolute joints. Characteristics of each joint were defined according to data of passive joint resistance and range of motion for Japanese men. The model was then validated against results of reported Japanese volunteer rear impact tests. Simulation and experimental results agreed well in terms of the rotational angle of the head and neck and the horizontal displacement of the first thoracic vertebra (T1). Hence, a reasonable occupant model can be developed by appropriately combining published data of human characteristics.

Numerical Analysis of Vehicle Occupant Responses during Rear Impact Using a Human Body Model

Understanding vehicle occupant responses during real-world rear collision accidents is very important in the development of appropriate safety technologies for neck injury lessening. In this study, numerical analysis of vehicle occupant responses during rear impact were conducted by using a human multi-body model, a seat finite element model and crash accelerations obtained from real-world accidents. The human multi-body model was developed based on the body characteristics of a typical Japanese male, including the outer body geometry, inertial properties of body segments and passive joint characteristics. The seat finite element model was extracted from a detailed car finite element model. A small modification was done to the seat model to deal with the rear impact simulations. The crash accelerations were obtained from the drive recorder database of rear collision accidents occurred in Japan. Several crash accelerations were selected and used as input conditions during the rear impact simulations. Kinematic responses of the occupants during the accidents can be reasonably predicted by the simulations. Furthermore, different level of accelerations leads to different kinematics responses that may cause variation in injury occurrence and injury severity.