Purpose: Each year, many cars (in Poland approximately three hundred) are adopted for disabled driver, to enable them to drive the car independently. The purpose of the paper is to assess the key factors which significantly influence the disabled driver behavior during a frontal crash and have the biggest impact on the safety factors. Methods: To achieve the purpose of the paper, the finite element method was used. The authors built the numerical model which includes operation of all safety systems operating in the real car (sensors, seat belts, airbag). Using this method, the authors simulated few different cases of the frontal crash of the car driven by a person with disabilities. Results: The obtained results were: displacements, velocities and accelerations of the head, pelvis and shoulders. Additional results were also loads in the neck. Based on the achieved results, several biomechanical parameters and criterions (HIC, N ij) were computed. Conclusions: Therefore, during car adaptation for disabled drivers using a four-point seat belts system, this parameter can be optimized to reduce forces acting on the driver chest. Higher values of the force limit reduce N ij and increase HIC and contact forces between the dummy and seatbelts. Therefore, during designing of the pyrotechnic four-point seat belts system, the pretensioner characteristics should be analyzed taking all the driver's biomechanical parameters into account.
The use of bioresorbable polymers such as poly(lactic-co-glycolic acid) (PLGA) in coronary stents can hypothetically reduce the risk of complications (e.g., restenosis, thrombosis) after percutaneous coronary intervention. However, there is a need for a constitutive modeling strategy that combines the simplicity of implementation with strain rate dependency. Here, a constitutive modeling methodology for PLGA comprising numerical simulation using a finite element method is presented. First, the methodology and results of PLGA experimental tests are presented, with a focus on tension tests of tubular-type specimens with different strain rates. Subsequently, the constitutive modeling methodology is proposed and described. Material model constants are determined based on the results of the experimental tests. Finally, the developed methodology is validated by experimental and numerical comparisons of stent free compression tests with various compression speeds. The validation results show acceptable correlation in terms of both quality and quantity. The proposed and validated constitutive modeling approach for the bioresorbable polymer provides a useful tool for the design and evaluation of bioresorbable stents.
The authors present an algorithm for determining the stiffness of the bone tissue for individual ranges of bone density. The paper begins with the preparation and appropriate mechanical processing of samples from the bovine femur and their imaging using computed tomography and then processing DICOM files in the MIMICS system. During the processing of DICOM files, particular emphasis was placed on defining basic planes along the sides of the samples, which improved the representation of sample geometry in the models. The MIMICS system transformed DICOM images into voxel models from which the whole bone FE model was built in the next step. A single voxel represents the averaged density of the real sample in a very small finite volume. In the numerical model, it is represented by the HEX8 element, which is a cube. All voxels were divided into groups that were assigned average equivalent densities. Then, the previously prepared samples were loaded to failure in a three-point bending test. The force waveforms as a function of the deflection of samples were obtained, based on which the global stiffness of the entire sample was determined. To determine the stiffness of each averaged voxel density value, the authors used advanced optimization analyses, during which numerical analyses were carried out simultaneously, independently mapping six experimental tests. Ultimately, the use of genetic algorithms made it possible to select a set of stiffness parameters for which the error of mapping the global stiffness for all samples was the smallest. The discrepancies obtained were less than 5%, which the authors considered satisfactory by the authors for such a heterogeneous medium and for samples collected from different parts of the bone. Finally, the determined data were validated for the sample that was not involved in the correlation of material parameters. The stiffness was 7% lower than in the experimental test.
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