Papers by Keyword: FEA Simulation

Abstract: Functionally graded structures from natural rubber foams were constructed and evaluated in this study. The structures were assembled based on density gradient achieved by stacking layers of natural rubber foams with different densities. Both physical and computational structures were constructed and assembled through experimental work and computer-aided design (CAD) modelling, respectively. Finite Element Analysis (FEA) simulation were conducted on two different assembled structures under compressive deformation mode using Ogden foam hyper-elastic model available in the simulation software package. Experimental result found that the middle section foam with 4/16/4 stacking sequence was deformed significantly compared to that of foam with 16/4/16 stacking sequence. The FEA simulation results indicated that Ogden foam hyper-elastic model is useful in representing deformation at low strain region as the results were in good agreement with those of obtained from the experimental foam compression tests especially for foam with 16/4/16 stacking. The study was able to show that FEA analysis is a good approach to supplement limitation that are encountered by experimental approach in understanding deformation behaviour of functionally graded natural rubber foams.

Abstract: Dental wear has accompanied human evolution, being strictly related to its way of life. Dental wear is a lesion of dental hard tissue commonly found in dental practice. Starting from the virtual skull model, the virtual models of the two upper premolars on the left hemisphere were generated, then the finite element method evaluated the stresses, displacements and strains generated by the resistance forces from the dental tissues of the two premolars during mandibular movements with occlusal contact. It is found that the value of these results increases as dental wear increases. This phenomenon is more visible in the teeth where the value almost doubles. Two explanations could be given for this situation: mechanically, these stresses are inversely proportional to the volume of the dental structures and, as they reduce, through dental wear, increase the stress, also, the sharp edges resulting from dental wear are mechanical stress concentrators.

Abstract: The human skull and the maxillary bones have a very complicated architecture, determined by the outer walls, by the internal bone structures and their joining. In this paper CAD parametric software has been used to define complex virtual models. First, the mandible and jaw were defined using CT images. These images were imported into a CAD software using specific techniques and methods. These models have been finalized in SolidWorks where the virtual model of the studied system has been generated. Then, the virtual models were exported to a software for FEA simulation and prepared for every dentistry simulations. The structure of the maxillary bones contains spongy bone tissue, cortical bone tissue along with dental tissues. Each of these tissues have certain properties (elasticity, plasticity, density) assessed by flexibility. The analysis of the mechanical tension of the dental structures has been a subject of interest in recent years in order to determine the state of tension in the dental structures and to improve the mechanical strength of these structures. Such numerical techniques can give a better understanding of reactions and interactions of individual tissues. This involves a series of computational procedures to calculate stress in each element. Field variables can be interpolated by using form functions for scientific verification and validation of clinical assumptions. Various loadings have been applied to a personalized skull obtained from CT images using CAD techniques and procedures. On this system, FEM simulations were made and maps of stress, displacements and deformations were obtained that show the mechanical behavior of the maxillary dental system. Finally, important conclusions were highlighted.

Abstract: Treatment of hip pathology has evolved over the last two centuries, ranging from rudimentary surgical procedures to modern hip arthroplasty, with an explosion marked in the last 30 years, considered to be one of the most successful surgeries to date. Hip arthroplasty is a permanent challenge due to the desire to discover the "supreme prosthesis", for which competition is still open. Hip disorders requiring prosthesis show a change in articular morphology. Among the most common medical conditions that have as final therapeutic solution hip arthroplasty are: coxarthrosis, both primary and secondary, followed by traumatic conditions: femoral neck collapse and femoral neck pseudarthrosis, aseptic head necrosis femoral stage III, as well as rheumatic coxitis from rheumatoid arthritis, ankylosing spondylitis or juvenile art. Endoprosthetic arthroplasty can be defined as an intervention of reconstructive surgery with bone sacrifice and prosthetic replacement of the articular components. It is, in the end, an operation aimed at restoring joint mobility and normal functioning of the muscles, ligaments and other periarticular structures that control joint movement. The materials initially used (glass, metal, plastic) did not have the desired bone strength and integration capacity. It followed the development of cemented implants, obtaining different types of cement with better and better quality. Problems arising from cemented arthroplasty (decimation, involving prosthetic revision) have led to a parallel development of the design and materials used for uncured prostheses with the possibility of very good integration of prosthetic material into the bone, raising them to the top of preferences in recent years. Treatment of hip pathology has evolved over the last two centuries, ranging from rudimentary surgical procedures to modern hip arthroplasty, with an explosion marked in the last 30 years, considered to be one of the most successful surgeries to date. The purpose of this study was to obtain the three-dimensional models of the hip joint and the prosthesis for the use of these models for various analyzes and virtual experiments. At the end of the paper important conclusions were drawn based on the results obtained in the simulations using the finite element method.

Abstract: Prosthetic alignment is one of the most important factors, both in terms of the correct functioning of neoarticulation and the survival duration of knee arthroplasty. Significant changes in the alignment of prosthetic components affect the distribution of stress in the knee joint. These changes may also affect the distribution of stresses on the contact surface, soft knee joints, and the subjacent bone remodeling under these forces. The malposition of the components and, in particular, the tibial component in the varus, which in practice is the most common situation alongside the malrotation of the femoral component, leads to the excessive intimal tension of the internal tibial plate by the summing of the additional stresses at this level with its physiological loading from during the unipodal support phase during the walk. Although valuable, all of these studies have no capacity to assess these changes in the kinetics of in vivo knee arthroplasty. Two methods are used for this: telemetry and mathematical models. Traditionally, telemetry has been used to determine the forces acting on the hip, and more recently, on the knee. It values ​​very precisely the value of the axial rotation forces as well as the moments of bending; however, this method is little used, because the necessary equipment is very expensive. Taking this into account, the most used method is the finite element method. The objective of this study was to investigate the effect of malpositioning in the valgus and varus of the tibial component on tension developed in polyethylene as well as in the subjacent bone. Obviously, other situations have also been analyzed. In this direction a series of original numerical models of the anatomical elements (tibia, fibula, femur) of the knee were constructed to simulate the biomechanical phenomena occurring in the normal and prosthetic joint during physical activities, in order to evaluate the factors that influence the duration operation of total knee prostheses.

Abstract: The basic concepts of Kuntscher's centromedular osteosynthesis remain largely valid today: centromedular osteosynthesis must be conducted under fluoroscopic control and without fracture outbreak exposure to avoid contamination, the rod must be strong enough to withstand stress caused by muscle contraction, joint movement and body weight load, this to avoid twisting and tearing the rod, the rod must exhibit sufficient elasticity to compress during insertion into the canal and then re-expand for firmly fix the fracture fragments and prevent their rotation. On the other hand, osteosynthesis with flexible centromedullary rods is mainly used in pediatric surgery where elastic rods in secant arch are used applying the principles of stable elastic osteosynthesis. Starting from the research done worldwide, we examined the orthopedic implants used in the long bones as a whole and some inconsistencies were found between the osteosynthesis material and the bone tissue. The necessary materials used in the study are orthopedic implants, different in structure, elasticity, dimensions, which were tested on bone virtual models, according to the CT scan sections. With the help of normal bone virtual models, both bone strength, various orthopedic implants, and the resistance of the osteosynthesis material used were taken into account. On these complete virtual models various simulations were made using FEM. The potential for FEM use in orthopedics and biomechanics has often been overestimated. In many situations, inappropriate use of the method on complicated biological structures can become costly, inefficient or prone to errors. Also, nonlinear soft tissue material has created new difficulties. But these disadvantages and limitations have been diminished successively through new results of biomechanical researches, but also by improving the method by using new types of finite elements. From this results database obtained through various virtual experiments, account will be taken of the most common accidents and incidents occurring in the implanted bone, and solutions will be sought to improve post-implant bone quality.

Abstract: In order, to understand the problems, which occur during the dentistry simulations, it was highly important to be acquainted with the anatomy of the human skull skeleton, the way these bone components are working together to achieve a normal functionality. In this respect CAD parametric software has been used as it allows to define models with a high degree of difficulty. First, the main bone components were defined by using CT images. These images were then transferred to a CAD software using different methods and techniques. These models were completed in SolidWorks where, step by step, the virtual model of the studied bone system has been defined. Using the direct measurement method on some skull components the virtual bone base elements were generated. Then, the virtual models were exported to a software for FEA simulation and prepared for every dentistry simulations. These models were tested and was generated the finite elements structure. In the end of the paper, were extracted interesting conclusions.

Abstract: Automotive exhaust gas temperature sensors are fitted to monitor the performance of a vehicle emission control system. The aggressive working environment is a big challenge in sensor design. This paper introduces an FEA simulation model developed to support the mechanical reliability of new sensor designs. The simulation model was validated by laboratory tests. Suggestions for optimising sensor reliability are given based on the simulation results.

Abstract: In times of increasing international business competition forging companies try to increase their competitiveness by optimization of different factors such as efficient use of resources in the forging process, optimization of processes or managing costs. In common forging processes for geometrically complicated parts such as crankshafts, an excess on material (flash) is technically needed to produce a good part, which results often in a material utilization between 60 % and 80 %. But the material costs in forging represent up to 50 % of the total production costs. By decreasing the flash ratio, the material usage and production costs in forging operations can be reduced significantly, helping to increase the competitiveness of companies. Innovative approaches are required, to achieve a significant reduction of the amount of flash in the forging of complicated parts like crankshafts. For a crankshaft, the development of a new forging sequence was necessary, to achieve the reduction of flash. This development was performed for an industrial two-cylinder crankshaft, based on finite element analysis (FEA) simulations. The new forging sequence consists of three flashless preforming operations, an induction reheating followed by a multidirectional forging and the final forging. By use of this forging sequence the flash ratio was reduced from about 54 % to less than 10 %. The whole forging sequence was set up in an industrial environment and the feasibility of this process chain was proven. Due to the huge reduction of the flash ratio, material as well as energy can be saved from now on, thus increasing the competitiveness of the company.

Abstract: A failure investigation for a diesel engine crankshaft has been conducted which was used for truck in this paper, which is made from 42CrMo steel. The fracture occurred on the crank web between the 4th crankpin and the 4th journal, the fracture section indicates that fatigue is the dominant mechanism. The dimensions, chemical compositions of material and surface hardness were evaluated in order to find the failure causes. Chemical compositions, the depth of hardness layer and surface hardness are qualified; however, there are transition zone of hardness layer on the journal boss fillet, the dimensions of journal boss is not qualified, it less than specified dimension, and many non-metallic inclusions aggregate zones and heavy segregation were found from metallographic photo, these would reduce the tensile strength. FEA analysis is also used to analysis the strength of this crankshaft, and the results suggest that the dimension of journal boss fillet is the key dimension, which has an important effect on the strength of the crankshaft. So the disqualified machining dimensions, material property are the main reasons for the fraction of this crankshaft.