Luis Roseiro

Introduction to Finite Element Method

As discussed in Chap. 1, mechanic problems are governed by a set of partial differential equations that are valid in a certain domain and they needed to be solved for evaluating the stress condition of mechanical components. Although analytic methods can be employed to solve linear problems involving partial differential equations, its use to analyze complex structures may be a difficult or, even, an impossible task. Thus, in this chapter, Hamilton’s principle, which one of the most powerful energy principle, is introduced for the FEM formulation of problems of mechanics of solids and structures. The approach adopted in this chapter is to directly work out the dynamic system equations, after which the static dynamic equations can be easily obtained by simply dropping out the dynamic terms

Engineering Computation of Structures: The Finite Element Method

This book presents theories and the main useful techniques of the Finite Element Method (FEM), with an introduction to FEM and many case studies of its use in engineering practice. It supports engineers and students to solve primarily linear problems in mechanical engineering, with a main focus on static and dynamic structural problems. Readers of this text are encouraged to discover the proper relationship between theory and practice, within the finite element method:Practice without theory is blind, but theory without practice is sterile. Beginning with elasticity basic concepts and the classical theories of stressed materials, the work goes on to apply the relationship between forces, displacements, stresses and strains on the process of modeling, simulating and designing engineered technical systems. Chapters discuss the finite element equations for static, eigenvalue analysis, as well as transient analyses. Students and practitioners using commercial FEM software will find this book very helpful. It uses straightforward examples to demonstrate a complete and detailed finite element procedure, emphasizing the differences between exact and numerical procedures.

External fixator configurations in tibia fractures

The use of external fixation devices in orthopedic surgery is very common in open tibial fractures. A properly applied fixator may improve the healing process while one improperly applied might delay the healing process. The several external fixator systems used in clinical today, can be categorized into uniplanar-unilateral, uniplanar-bilateral, biplanar and multiplanar. The stability on the fracture focus and, therefore, the fracture healing process, is related with the type of external fixator configuration that is selected. The aim of this study is to discuss the principles for the successful application of unilateral-uniplanar external fixation, the assembly of its components, for the case of a transverse fractures using computational models. In this context, the fixation stiffness characteristics are evaluated using a simplified 1D finite element model for the tibia and external fixator. The beams are modeled with realistic cross-sectional geometry and material properties instead of a simplified model. The VABS (the Variational Asymptotic Beam Section analysis) methodology is used to compute the cross-sectional model for the generalized Timoshenko model, which was embedded in the finite element solver FEAP. The use of Timoshenko beam theory allows accounting for several kinds of loads, including torsion moments. Optimal design is performed with respect to the assembly of fixator components using a genetic algorithm. The optimization procedure is based on the evaluation of an objective function, which is dependent on the displacement at the fracture focus. The initial and optimal results are compared by performing a 3D analysis, for which different three-dimensional finite element models are created. The geometrical model of a tibia is created on the basis of data acquired by CAT scan, made for a healthy tibia of a 22 year old male. The 3D comparison of the 1D optimal results show a clear improvement on the objective function for the several load cases and, therefore, it is shown that appropriate selection of the external fixator geometrical features can lead to an improvement on the stability of the external fixator. The results obtained show that the optimal position of the side beam and the first pin should be as close as possible to the bone interface and as close as possible to the fracture focus, respectively. Concerning the second pin, it should be placed away from the first pin in case of flexion loads, to axial and torsion loads the second pin should be placed near the first pin.

Finite Element Method for Beams

A beam is a structural member whose geometry is very similar to the geometry of a bar. It is also geometrically a bar of an arbitrary cross-section, by bar it is meant that one of the dimensions is considerably larger than the other two, whose primary function is to support transverse loading. The main difference between the beam and the truss is the type of load that they support. In fact, beams are the most common type of structural component, especially in civil and mechanical engineering. A beam resists to transverse loads mainly through a bending action and, the bending is responsible for compressive longitudinal stresses in one side of the beam and tensile stress on the other beam side. These two regions are separated by the neutral axis in which the stress is zero. The combination of tensile and compressive stresses produces an internal bending moment. Finite element equations for beam-like structures are developed in this chapter.

Pre and post surgery evaluation of patients with hallux pathology using an insoles measurement system of plantar pressure distribution

In the context of orthopedic, the use of plantar pressure distribution can be important as a complementary method of evaluation and diagnosis, as in the follow-up of patients. The present study has its framework in the context of the distribution of plantar pressure in patients with hallux valgus pathology, with indication for surgical treatment. The work involves gait analysis in nine volunteers with surgery indication. The registered data was obtained in two moments: the day before surgery and ninety days after surgery. The analysis of the results shows that pedobarographic pressure analysis may play an important role in helping clinical decision-making, as well as follow-up in the postoperative phase, allowing the study and evaluation of the surgical proceedings and correlating the clinical evolution with the changes in pedobarography maps.

Bluetooth low energy profile for MPU9150 IMU data transfers

An increasing number of commercial and scientific solutions for unmanned vehicles, aeronautical/aerospace navigation systems, health and sports monitoring solutions, has been prompted by the development of Micro-Electro-Mechanical Systems based inertial sensors. These sensors, with small form factor and low cost, present an advantage for computing three-dimensional space object orientation. Also radio frequency communication (RF) devices are frequently associated with inertial sensors and embedded systems. Radio frequency communication protocols allow immediate data transfer and processing without cumbersome cabling. With special relevance for sports monitoring, gait analysis and general movement assessment inertial sensors have been embedded together to form one device with several sensors. The so called Inertial Measurement Units (IMU), that include an accelerometer, a gyroscope and sometimes may include one magnetometer, are increasingly used, despite their inherent inaccuracy, to determine a body orientation and/or movement profile. These sensors present therefore an advantage for computing three-dimensional space object orientation. The inherent inaccuracy is addressed by using sensor fusion algorithms that increase system reliability. In the work presented in [1], a survey of a number of relevant sensor fusion algorithms was presented. In [2] a Yaskawa Motoman robotic arm is used to implement a set of predefined movements that granted accuracy and repeatability conditions to a framework that is able to test systems that are able to determine a body position. In both [1] and [2], a Bluetooth Low Energy based CC2541 Texas Instruments device has been used to transfer the required data from the IMU sensors to a PC computer running a Windows operating system. This paper presents the BLE proprietary profile that has been implemented to transfer data in wireless mode. Moreover, the paper describes the BLE protocol basics and the relevant options so that implemented systems are low power and fully compatible with the protocol. Also the future use of the developed device is addressed within the context of the Parkinson disease early diagnosis and Canoeing sport monitoring.

Facial Temperature Recovery After Ice Therapy: A Comparative Study Based on Thermography Evaluation

Thermography is a non-radiating and contact-free technology which can be used to monitor skin temperature. The efficiency and safety of thermography technology make it a useful tool for detecting and locating thermal changes in skin surface, characterized by increases or decreases in temperature. This work intends to be a contribution for the use of thermography as a methodology for evaluation of skin temperature in the context of orofacial biomechanics. The study aims to identify the oscillations of skin temperature in hemiface’s region of the masseter muscle and estimate the time required to restore the initial temperature after the application of an ice stimulus. Using an infrared camera, a data acquisition protocol was followed with a group of volunteers in a controlled environment. The thermal stimulus involves the use of an ice volume and the skin surface temperature was recorded in two distinct situations, namely without further stimulus and with the addition of a complementary stimulus obtained by a chewing gum. The results shows that recovery is faster with the addition of the stimulus and may guide clinicians regarding the pre and post-operative times with ice therapy, in the presence or absence of mechanical stimulus that increase muscle functions.

Foot Pressure Distribution of Patients with Hallux Valgus During Walking up and Down Stairs

Hallux Valgus is one of the most common deformities in orthopedic context, with direct influence on gait. For this pathology, the plantar pressure distribution analysis can be important as a complementary method of evaluation and diagnosis, as also in the follow-up of patient’s rehabilitation. This study has its framework in the context of the distribution of plantar pressure in patients with Hallux Valgus, with clinical indication for surgical treatment. The work involves the gait analysis in nine volunteers. The plantar pressure distribution was collected with an insoles measurement system for a defined protocol based on walking down and upstairs. The data have been registered in two moments: the day before surgery and ninety days after surgery. The analysis of the results, focused on the pathologic foot, shows that the foot pressure analysis, following a down and upstairs protocol, can play an important role as a surgical follow-up for the post-surgery phase.

Effect of round curvature of anterior implant-supported zirconia frameworks: finite element analysis and in vitro study using digital image correlation

Abstract Two groups of 4-unit zirconia frameworks were produced by CAD/CAM to simulate the restoration of an anterior edentulous gap supported by 2 implant-abutment assemblies. Group 1 comprised straight configuration frameworks and group 2 consisted of arched frameworks. Specimens were made with the same connector cross-section area and were cemented and submitted to static loads. Displacements were captured with two high-speed photographic cameras and analysed with video correlation system. Frameworks and the implant-abutment assembly were scanned and converted to 3DCAD objects by reverse engineering process. A specimen of each group was veneered and the corresponding 3D geometry was similarly obtained after scanning. Numerical models were created from the CAD objects and the FE analysis was performed on the zirconia frameworks and on the FPDs bi-layered with porcelain (veneered frameworks). Displacements were higher for the curved frameworks group, under any load. The predicted displacements correlated well with the experimental values of the two framework groups, but on the straight framework the experimental vertical displacements were superior to those predicted by the FEA. The results showed that the round curvature of zirconia anterior implant-supported FPDs plays a significant role on the deformation/stress of FPDs that cannot be neglected neither in testing nor in simulation and should be considered in the clinical setting.

Advanced FEM Modelling

This chapter presents a discussion on some modelling techniques for the stress analyses of solids and structures. Mesh symmetry, rigid elements and constraint equations, mesh compatibility, modelling of offsets, supports and connections between elements with different mathematical bases are all covered. Advanced modelling of laminated composite materials are also presented.