J. L. Alves

Blood-brain barrier and traumatic brain injury.

The blood–brain barrier (BBB) is an anatomical microstructural unit, with several different components playing key roles in normal brain physiological regulation. Formed by tightly connected cerebrovascular endothelial cells, its normal function depends on paracrine interactions between endothelium and closely related glia, with several recent reports stressing the need to consider the entire gliovascular unit in order to explain the underlying cellular and molecular mechanisms. Despite that, with regard to traumatic brain injury (TBI) and significant events in incidence and potential clinical consequences in pediatric and adult ages, little is known about the actual role of BBB disruption in its diverse pathological pathways. This Mini‐Review addresses the current literature on possible factors affecting gliovascular units and contributing to posttraumatic BBB dysfunction, including neuroinflammation and disturbed transport mechanisms along with altered permeability and consequent posttraumatic edema. Key mechanisms and its components are described, and promising lines of basic and clinical research are identified, because further knowledge on BBB pathological interference should play a key role in understanding TBI and provide a basis for possible therapeutic targets in the near future, whether through restoration of normal BBB function after injury or delivering drugs in an increased permeability context, preventing secondary damage and improving functional outcome.

Study on the Influence of the Refinement of a 3‐D Finite Element Mesh in Springback Evaluation of Plane‐Strain Channel Sections

Springback phenomenon associated with the elastic properties of sheet metals makes the design of forming dies a complex task. Thus, to develop consistent algorithms for springback compensation an accurate prediction of the amount of springback is mandatory. The numerical simulation using the finite element method is consensually the only feasible method to predict springback. However, springback prediction is a very complicated task and highly sensitive to various numerical parameters of finite elements (FE), such as: type, order, integration scheme, shape and size, as well the time integration formulae and the unloading strategy. All these numerical parameters make numerical simulation of springback more sensitive to numerical tolerances than the forming operation. In case of an unconstrained cylindrical bending, the in‐plane to thickness FE size ratio is more relevant than the number of FE layers through‐thickness, for the numerical prediction of final stress and strain states, variables of paramount importance for an accurate springback prediction. The aim of the present work is to evaluate the influence of the refinement of a 3‐D FE mesh, namely the in‐plane mesh refinement and the number of through‐thickness FE layers, in springback prediction. The selected example corresponds to the first stage of the “Numisheet’05 Benchmark♯3”, which consists basically in the sheet forming of a channel section in an industrial‐scale channel draw die. The physical drawbeads are accurately taken into account in the numerical model in order to accurately reproduce its influence during the forming process simulation. FEM simulations were carried out with the in‐house code DD3IMP. Solid finite elements were used. They are recommended for accuracy in FE springback simulation when the ratio between the tool radius and blank thickness is lower than 5–6. In the selected example the drawbead radius is 4.0 mm. The influence of the FE mesh refinement in springback prediction is discussed, for this example where the drawbead restraining force results in a non‐symmetrical through‐thickness stress gradient.

Application of the Incremental Volumetric Remapping Method in the Simulation of Multi‐Step Deep Drawing Processes

Since sheet metal forming has a high percentage contribution in the overall design costs of a new car, this engineering area assisted in the last decades to considerable development efforts. The present challenge is to simulate all the production stages, from the initial blank sheet to the final part ready to assembly. On this particular issue of multi‐step deep‐drawing simulation, this work presents a new remapping method called Incremental Volumetric Remapping (IVR) developed to minimize the error that occurs, when performing the variable transfer operation between two different meshes. The IVR method is based in a volumetric approach where the calculus of the remapped state variables is obtained by means of a weighted average of the intersection volume between the meshes. The method performance is tested and compared with a standard extrapolation‐interpolation, by applying a numerical example of the Numisheet’005 Conference, “The Channel Draw/Cylindrical Cup Benchmark”.

Cazacu and Barlat Criterion Identification Using the Cylindrical Cup Deep Drawing Test and the Coupled Artificial Neural Networks – Genetic Algorithm Method

This paper deals with the identification of the anisotropic parameters using an inverse strategy. In the classical inverse methods, the inverse analysis is generally coupled with a finite element code, which leads to a long computational time. In this work an inverse analysis strategy coupled with an artificial neural network (ANN) model is proposed. This method has the advantage of being faster than the classical one. To test and validate the proposed approach an experimental cylindrical cup deep drawing test is used in order to identify the orthotropic material behaviour. The ANN model is trained by finite element simulations of this experimental test. To reduce the gap between the experimental responses and the numerical ones, the proposed method is coupled with an optimization procedure based on the genetic algorithm (GA) to identify the Cazacu and Barlat’2001 material parameters of a standard mild steel DC06.

Local Bifurcation and Instability Theory Applied to Formability Analysis

Sheet metal forming components are typically studied with the aid of finite element method based virtual tryout tools, since they allow to save money, time and effort in the design, production and process set‐up of deep drawn parts. In all these development phases the analysis of defects is performed with the aid of the material forming limit diagram (FLD), since it allows defining a safe region that reduces: (i) necking; (ii) wrinkling and (iii) large deformation occurrence.It is known that the FLD represented in the strain space presents some disadvantages. The local bifurcation criterion proposed by Ito and Goya defines the critical state for a local bifurcation to set in, as a function of the stress level to work‐hardening rate ratio. Thus, the main advantage is that the FLD represented in the stress plane is completely objective [1]. In this work the Ito and Goya model is used to evaluate formability, as well fracture mode and direction along different strain paths: (i) uniaxial tension; (ii) equibia...

Complex sacral fracture

We reported a case of a patient with suspected cauda equina syndrome secondary to sacral fracture, after sustaining a fall. The difficulty in early diagnosis of complex sacral fractures and the lack of clearly defined guidelines for treatment are highlighted. Thorough clinical examination is mandatory, in order to make an adequate initial assessment and follow symptoms progression and response to treatment. The threshold for performing CT imaging (or MRI, if advised), when suspecting sacral fracture and neurological compromise, should be low. A multidisciplinary approach, with contributions from orthopaedic and/or neurosurgical surgery and physiatry, should be the gold standard of treatment. In this particular case, conservative management and close follow-up led to a significant improvement of problems and a good final outcome, showing that surgical decompression is not the only valid option and that further prospective studies are needed, regarding patient selection and timing of intervention.

Hematoma iatrogênico simulando lesão tumoral intradural lombar

Em um quadro clinico de lombociatalgia, o diagnostico diferencial engloba uma variedade de possiveis etiologias. Descreve-se um caso de um doente do sexo feminino, com historia de lombociatalgia incapacitante relacionada com hematoma intradural, consequencia de puncao lombar e drenado apos laminectomia lombar. Sao revistas as varias series descritas na literatura, assim como sao discutidos os diferentes fatores de risco, quadros clinicos e estrategias de prevencao e tratamento.(AU) In the presence of lumbar radicular pain, the differential diagnosis includes several possible etiologies. Here is described a case of a female patient with incapacitating low back pain and lumbar radicular pain caused by an intradural hematoma, consequence of lumbar puncture, surgically drained after laminectomy. The several series in the literature describing these cases are revised, and the different risk factors, clinical pictures, prevention and treatment strategies are discussed.(AU)

Influence of Drawbeads in Deep‐Drawing of Plane‐Strain Channel Sections: Experimental and FE Analysis

The main purpose of the “Numisheet’05 Benchmark♯3: Channel Draw/Cylindrical Cup” was to evaluate the forming characteristics of materials in multi‐stage processes. The concept was to verify the strain fields achieved during the two stage forming process and also to test the ability of numerical models to predict both strain and stress fields. The first stage consisted of forming channel sections in an industrial‐scale channel draw die. The material that flows through the drawbead and over the die radii into the channel sidewalls is prestrained by cyclic bending and unbending. The prestrained channel sidewalls are subsequently cut and subjected to near plane‐strain Marciniak‐style cup test. This study emphasizes the analysis of the first stage process, the Channel Draw, since accurate numerical results for the first stage forming and springback are essential to guarantee proper initial state variables for the subsequent stage simulation. Four different sheet materials were selected: mild steel AKDQ‐HDG, hi...

Influence of Anisotropy Properties in Finite Element Optimization of Blank Shape Using NURBS Surfaces

Sheet metal forming is a complex process controlled by process parameters and material properties of the blank sheet. The initial anisotropy has influence on the determination of optimal blank shape because it governs the material flow. In this paper, the influence of the initial anisotropy, in achieving an optimal blank shape, is analyzed using mild steel (DC06) blank sheet and two different tool geometries: circular and rectangular cup. The numerical method is based on the initial NURBS surface used to produce the mesh that models the blank and the resulting flange geometry of the deformed part. Different rolling direction orientations were considered in the blanks for deep drawing to investigate their effect on the blank shape optimization procedure. From the numerical study it is evident that the described method is sensitive to the initial anisotropy in the material and can produce optimal initial blank shape within few iterations.