A. A. Fernandes

Mechanical properties of polypropylene mesh used in pelvic floor repair

The aim of this study was the comparison of the stiffness of different meshes under two types of mechanical tests. Five different mesh types were mechanically tested. The methods used consisted on uniaxial tension test (tensile stiffness) and tape ring tests, experimental continuous compression of the mesh loops (flexural stiffness). The most significant difference of tensile stiffness behaviour appears between Aris™ and TVTO™. From the analysis of the experimental data, we divided the flexural stiffness, in two main groups. The first group includes Auto Suture™ and Aris™ meshes. The two meshes seem to have a similar flexural behaviour. The second group includes TVTO™, Uretex™ and Avaulta™. The difference between these two groups is clearly evident comparing TVTO™ and Aris™. This study shows that there are significant differences on the mechanical properties between urogynecology meshes.

The influence of the material properties on the biomechanical behavior of the pelvic floor muscles during vaginal delivery

In this work, a finite element model intends to represent the effects that the passage of a fetal head can induce on the muscles of the pelvic floor, from a mechanical point of view. The finite element method is a valuable tool, that is contributing to the clarification of the mechanisms behind pelvic floor disorders related to vaginal deliveries, although some care is necessary in order to obtain correct results. The present work shows how the variation of the material parameters, used in the constitutive model, can affect the obtained results from a finite element simulation. The constitutive equation adopted in this work for the pelvic floor muscles is a modified form of the incompressible transversely isotropic hyperelastic model proposed earlier by Humphrey and Yin. Results for the pelvic floor strain and stresses obtained during the passage of the fetus head are presented. The results show the importance of the material parameters and the need for a correct constitutive model.

Modelling of concrete beams reinforced with FRP re-bars

Abstract A finite element analysis of reinforced concrete beams with fiber-reinforced plastic re-bars is performed. Corrosion of steel re-bars is a common problem encountered in the civil construction sector, due to the porosity of concrete. The use of fiber-reinforced polymers (FRP) instead of steel re-bars can lead to a better corrosion-resistant reinforced concrete with applications in many construction fields. The need for non-linear geometrical and material models implies the use of numerical methods such as the finite element method. In this paper the use of a first-order shear-deformation theory in the analysis of concrete shells reinforced with internal composite unidirectional re-bars is proposed. The theory is implemented in a shell element that allows for a layered discretization of the laminate materials. A perfect plastic and a strain-hardening plasticity approach are used to model the compressive behavior of the concrete. A dual criterion for yielding and crushing in terms of stresses and strains is considered, which is complemented by a tension cut-off representation. The material law for the unidirectional re-bars is linear elastic/brittle, whereas the concrete allows for elasto-plastic–brittle behavior. A simply-supported concrete beam, reinforced with composite re-bars is analysed. The effects of the reinforcement and the comparison of composite and steel re-bars on concrete are discussed. Comparison between numerical and experimental results is made for a RC beam reinforced with pultrusion rods.

Bending characteristics of resin concretes

In this research work the influence of composition and curing conditions in bending strength of polyester and epoxy concrete is analyzed. Various mixtures of resin and aggregates were considered in view of an optimal combination. The Taguchi methodology was applied in order to reduce the number of tests, and in order to evaluate the influence of various parameters in concrete properties. This methodology is very useful for the planning of experiments. Test results, analyzed by this methodology, shown that the most significant factors affecting bending strength properties of resin concretes are the type of resin, resin content and charge content. An optimal formulation leading to a maximum bending strength was achieved in terms of material parameters.

The influence of an occipito-posterior malposition on the biomechanical behavior of the pelvic floor

OBJECTIVES Contribute to the clarification of the mechanisms behind pelvic floor disorders related to a vaginal delivery. Verify the effect of an occipito-posterior malposition of the fetus during delivery on the stretch values when compared to the normal occipito-anterior position. STUDY DESIGN A numerical simulation based on the Finite Element Method was carried out. The Finite Element Model intends to represent the effects that the passage of a fetal head can induce on the muscles of the pelvic floor, from a mechanical point of view. The model used for the simulation represents the pelvic bones, with the attached pelvic floor muscles and the fetus. In this work the movements of the fetus during birth, in vertex position, with the fetus presenting in an occipito-posterior malposition were simulated. The results obtained were compared with a simulation in which the fetus presents in the normal occipito-anterior position. RESULTS A maximum stretch value of 1.73 was obtained in the numerical simulation conducted on this work, where the occipito-posterior malposition was simulated. CONCLUSION During a vaginal delivery, the levator ani muscle and the pubococcygeus muscle are the muscles that are subjected to the largest values of stretch and strain. These muscles are the ones at greater risk for a stretch related injury. When compared to the normal occipito-anterior position, the occipito-posterior malposition produces substantially higher stretch vales for the pelvic floor muscles, increasing the risk for a stretch related injury.

Computational modeling approach to study the effects of fetal head flexion during vaginal delivery

OBJECTIVE The purpose of this study was to investigate the influence of fetal head flexion during vaginal delivery with a 3-dimensional computational finite element model. STUDY DESIGN A finite element model of the pelvic skeletal structure, pelvic floor, and fetus was developed. The movements of the fetus during birth were simulated in engagement, descent, flexion, internal rotation, and extension of the fetal head. The opposite forces against the fetal descendent and the stress of the pelvic floor muscles were obtained on simulations with different degrees of head flexion. RESULTS The simulated increase in fetal head flexion is associated with lower values of opposite forces against the fetal descent. The descending fetus with abnormal head flexion also meets resistance in later stations. Lower stress on the pelvic floor was demonstrated with simulated increase in fetal head flexion during vaginal delivery. CONCLUSION This analytic evidence suggests that the fetal head flexion during vaginal delivery may facilitate birth and protect the pelvic floor.

Structured Methods of New Product Development and Creativity Management: A Teaching Experience

Using structured methods for managing business innovation can be an effective way to improve the ideation process. Teaching structured methods is a potent way to enhance the innovative capabilities of companies and to develop creative products for the marketplace. In this paper, structured models of innovation and product development are reviewed and an approach to them is presented, based on several MSc student projects. The implications for managers, such as the need to train employees in structured methods, and the implications for those who teach innovation management are discussed in detail.

Low and High Cycle Fatigue and Cyclic Elasto-Plastic Behavior of the P355NL1 Steel

A normalized fine grain carbon low alloy steel, P355NL1 (TStE355), intended for service in welded pressure vessels, where notch toughness is of high importance, has been investigated. Low and high cycle fatigue tests have been conducted on several series of smooth specimens under both strain and stress control. The monotonic and cyclic elasto-plastic behavior of the material is characterized and described using relations available in the literature. The shape of hysteresis loops are conveniently modeled, taking into account the observed non Masing behavior of the steel. Some important cyclic phenomena, observed for the studied steel, such as the cyclic creep and the cyclic stress relaxation, are illustrated. Strain, stress, and energy based relations for fatigue life prediction until crack initiation, are evaluated based on experimental results. The adequacy of several rules for damage accumulation is also investigated. Finally, along the paper, some comparisons are performed between the cyclic elasto-plastic and fatigue behaviors of the steels P355NL1 and ASTM A516 Gr. 70.

Finite Element Modeling of Fatigue Damage Using a Continuum Damage Mechanics Approach

In this paper, a fatigue model formulated in the framework of the continuum damage mechanics (CDM) is presented. The model is based on an explicit definition of fatigue damage and introduces a kinematic damage differential equation formulated directly as a function of the number of cycles and the stress cycle parameters. The model is initially presented for uniaxial problems, which facilitates the identification of its constants. An extension of the fatigue model to multiaxial problems is also proposed. This model was implemented in a nonlinear finite element code in conjunction with a constitutive model for cyclic plasticity. The cyclic plasticity model considered is based on a J2-plasticity theory with nonlinear isotropic and kinematic hardenings. In order to enhance the description of the cyclic elastoplastic behavior, the superposition of several nonlinear kinematic hardening variables is suggested. Both fatigue and plasticity models are identified for the P355NL1 (TStE355) steel. Finally, the numerical model is used to predict the fatigue crack initiation for a welded nozzle-to-plate connection, made of P355NL1 steel, and results are compared with experimental fatigue data.

Biomechanical properties of breast tissue, a state-of-the-art review

This paper reviews the existing literature on the tests used to determine the mechanical properties of women breast tissues (fat, glandular and tumour tissue) as well as the different values of these properties. The knowledge of the mechanical properties of breast tissue is important for cancer detection, study and planning of surgical procedures such as surgical breast reconstruction using pre-surgical methods and improving the interpretation of clinical tests. Based on the data collected from the analysed studies, some important conclusions were achieved: (1) the Young’s modulus of breast tissues is highly dependent on the tissue preload compression level, and (2) the results of these studies clearly indicate a wide variation in moduli not only among different types of tissue but also within each type of tissue. These differences were most evident in normal fat and fibroglandular tissues.