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- Using 3D anthropometric data for the modelling of customised head immobilisation masksPublication . Loja, Amélia; Sousa, E.; Vieira, Lina Oliveira; Craveiro, D.S.; Parafita, Rui; C. Costa, Durval; Costa, DMSHead immobilization thermoplastic masks for radiotherapy purposes involve a distressful modelling procedure for the patient. To assess the possibility of using different acquisition and reconstruction methods to obtain a 3Dskin surface model of PIXY-phantom-head and to present a proposal of an alternative head immobilisation mask prototype. Phantom head geometry acquisitions using: computed tomography (reconstructed with ImageJ and Osirix); and 3DLaserScanner (reconstructed with SolidWorks). From these reconstructed surface models a set of landmarks was measured and subsequently compared with physical measurements obtained with a Rosscraft-Calliper. For statistical evaluation, relative deviations graphics and Friedman-test for non-parametrical paired samples were used, with a significance level of 5%. For a first assessment of the proposed mask performance, a radiotransparent material was considered, the strength and stiffness evaluation being performed using the finite element method. There are small differences between all the acquisitions and reconstructions methods and the physical measurements, statistically significant differences (X2F(6)) = 6.863, p=0.334) were not found. The proposed mask performed well from the strength and stiffness perspectives, leading to the desired immobilisation aim. The immobilisation mask design proposal may be an effective alternative to the present completely hand-made situation, which presents a high-degree of discomfort and stress to the patients.
- A study on the effect of carbon nanotubes’ distribution and agglomeration in the free vibration of nanocomposite platesPublication . Craveiro, D.S.; Loja, M.A.R.The present work aimed to characterize the free vibrations’ behaviour of nanocomposite plates obtained by incorporating graded distributions of carbon nanotubes (CNTs) in a polymeric matrix, considering the carbon nanotubes’ agglomeration effect. This effect is known to degrade material properties, therefore being important to predict the consequences it may bring to structures’ mechanical performance. To this purpose, the elastic properties’ estimation is performed according to the two-parameter agglomeration model based on the Eshelby–Mori–Tanaka approach for randomly dispersed nano-inclusions. This approach is implemented in association with the finite element method to determine the natural frequencies and corresponding mode shapes. Three main agglomeration cases were considered, namely, agglomeration absence, complete agglomeration, and partial agglomeration. The results show that the agglomeration effect has a negative impact on the natural frequencies of the plates, regardless the CNTs’ distribution considered. For the corresponding vibrations’ mode shapes, the agglomeration effect was shown in most cases not to have a significant impact, except for two of the cases studied: for a square plate and a rectangular plate with symmetrical and unsymmetrical CNTs’ distribution, respectively. Globally, the results confirm that not accounting for the nanotubes’ agglomeration effect may lead to less accurate elastic properties and less structures’ performance predictions.
- An optimization strategy for customized radiotherapy head immobilization masksPublication . Craveiro, D.S.; Loja, Amélia; Vieira, Lina Oliveira; Vinyas, M.An effective head immobilization is an important requirement in radiotherapy treatment sessions, although it may also be thought in the future as a precious aid in brain medical imaging. Thus, the present work is focused on the stiffness optimization of a customized head immobilization mask, modelled upon the head reconstruction surface based on computerized tomography images. This paper proposes a strategy supported by a metaheuristic optimization technique and a metamodeling approach for the whole mask, illustrated at its most unfavorable region occurring in the gnathion region.
- An assessment of thick nanocomposite plates' behavior under the influence of carbon nanotubes agglomerationPublication . Craveiro, D.S.; Loja, AméliaThe influence assessment of carbon nanotubes (CNTs) agglomeration on CNT-reinforced composite (CNTRC) thick plates' behavior is the main aim of the present work. CNTs are known to agglomerate into clusters even for relatively low volume fractions, which imposes the need to characterize the effects this may introduce in structures behavior, also knowing that recent works have concluded that neglecting agglomeration phenomenon may lead to an overestimation of the mechanical properties of nanocomposites. Hence, it matters to understand how the arising of these clusters may affect the static and free vibrational behaviors of low side-to-thickness nanocomposite plates. To this purpose, the nanocomposite plate properties' estimation is performed by using the two-parameter model of agglomeration based on the Eshelby-Mori-Tanaka approach, while for behavioral analyses one considers a Higher-order Shear Deformation Theory (HSDT) based on the displacement field of Kant, implemented through the finite element method. The analyses developed consider a set of parametric studies involving the assessment of the influence of side-to-side ratios, side-to-thickness ratios, boundary conditions, and CNTs' distributions along the thickness. The results obtained allow concluding that the transverse deflections and fundamental frequencies of these structures are significantly influenced by the CNTs' agglomeration.