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Background: It was aimed to compare conventional surgery and three-dimensional (3D) model-assisted surgery used in the treatment of calcaneal fractures. Materials & Methods: A total of 37 patients with unilateral calcaneal fractures were randomly divided into two groups as a conventional surgery group (n: 19) and a 3D model-assisted surgery group (n: 18). The preoperative, postoperative and last follow up angles of the Bohler and Gissane, calcaneal width and facet height were measured. The duration of the operation, blood loss volume, fluoroscopy usage, instrumentation time for both groups were recorded. Finally, the follow-up AOFAS scores were evaluated. A questionnaire was used to determine the perceptions of the resident doctors about the 3D model. Results: The duration of the operation, blood loss volume, fluoroscopy usage, instrumentation time for 3D model-assisted surgery group were 83.3 +/- 4.6 minutes, 83.6 +/- 4.6 ml, 6.8 +/- 1.4 times and 13.0 +/- 0.8 weeks, and as for conventional group they were 130.0 +/- 5.8 minutes, 105.1 +/- 5.6 minutes, 11.7 +/- 1.5 ml, 22.2 +/- 2.4 times and 13.3 +/- 0.8 weeks, respectively (p < 0.0001). The both groups significantly restored Bohler angle, Gissane angle, calcaneal width and calcaneal facet height after operation (p < 0.0 001). The 3D model-assisted group was significantly more succesful in restoration and protection of achieved correction of calcanel facet height (p < 0.0001). The difference was determined among the groups at the final follow-up examination with respect to the amount of change according the values achieved postop. were significant in Bohler angle (p < 0.001), calcaneal facet height (p < 0.0001) and calcaneal widht (p = 0.017). There was no significant difference between AOFAS scores of the two groups at last follow-up. Resident doctors exhibited high scores of overall satisfaction with the use of a 3D printing model. Conclusions: Compared to the conventional group, the 3D model-assisted group provide successful intervention and reduce operation, instrumentation time and the fluoroscopy usage with less blood loss. Performing 3D-assisted surgery helps the quality of reduction during the surgery and stability of internal fixation to protect achieved reduction at follow-up more succesfully. (C) 2020 Elsevier Ltd. All rights reserved., European Society of Tissue Regeneration in Orthopaedics and Traumatology (ESTROT), This paper is part of a Supplement supported by the European Society of Tissue Regeneration in Orthopaedics and Traumatology (ESTROT).

In this work, we study the transversal vibration of thin periodic elastic plates through asymptotic homogenization. In particular, we consider soft inclusions and rigid inclusions with soft coatings embedded in a stiff matrix. The method provides a general expression for the dynamic surface density of the plate, which we compute analytically for circular inclusions or numerically for two-way ribbed plates. Through asymptotic homogenization, we find that band gaps related to in-plane propagating transversal waves occur for frequency intervals in which the effective surface density is negative. The same result is obtained via an asymptotic analysis of the Bloch-Floquet problem on a unit cell, showing the equivalence of the two approaches. Finally, we validate the method by comparing in several examples the predicted band gaps with those obtained from numerical Bloch-Floquet analyses on the real unit cell.

В условиях ОАО «КУМЗ» из сплава 7475 системы Al–Zn–Mg–Cu в состоянии поставки Т7351 изготавливают плиты толщиной от 6,35 до 101,6 мм, применяемые в авиакосмической технике. Одной из проблем производства данных листов и плит является разность значений прочностных характеристик начала и конца исходной плиты. Разница получаемых результатов испытаний образцов составляет до 34,5 МПа (5 ksi). Проведена корректировка режимов термообработки для стабилизации свойств по концам плит. В эксперименте исследовали 48 исходных плит толщиной от 31,75 до 44,75 мм. Подробно рассмотрен процесс закалочного охлаждения исследуемых плит в горизонтально-закалочном агрегате фирмы EBNER. Выявлено, что снижение скорости движения рольганга при закалке на 10 % приводит к требуемой плоскостности плит и уменьшению длины их переднего участка с пониженной прочностью, при этом разность значений прочностных характеристик начала и конца исходных плит понижается до 15,2 МПа (2,2 ksi), т.е. на 56 %., 6.35 to 101.6 mm thick plates used in the aerospace industry are made under the conditions of JSC KUMZ from the Al–Zn–Mg–Cu alloy 7475 (delivery state T7351). One of the problems in the production of these sheets and plates is the difference in strength characteristics of the leading end and the rear end of the initial plate. The difference in test results is up to 34.5 MPa (5 ksi). The heat treatment conditions were corrected to stabilize the properties at the both ends of the plates. 48 initial plates of 31.75 to 44.75 mm in thickness were studied in this experimental work. The process of quench cooling of the plates under studies in the horizontal quenching unit EBNER was considered in detail. It was found out that a 10 % decrease in the roller conveyor speed during quenching ensures the required flatness of the plates and a shortening in the length of their leading end, where the strength is reduced. At the same time, the difference in the strength characteristics of the leading end and the rear end of the initial plates decreases down to 15.2 MPa (2.2 ksi), i.e. by 56 %.

In this study, viscoelastic damped dynamic behaviors of laminated composite shells (LCS) under different dynamic loads were investigated. In order to obtain better numerical stability, the truncated series method was used in the formation of equations governing the system. While deriving the equations governing the system, the z/R terms are usually neglected, whereas only 3 and higher order terms are truncated here. The method of truncated equations has been used for the first time as suggested here to obtain viscoelastic damped behavior of dynamically loaded LCS. The governing equation of composite shells was obtained with the help of Hamilton's principle. Afterwards, time dependent partial differential equations were obtained by applying Navier solution method to these valid equations. These equations were transformed into Laplace space in order to solve time dependent partial differential equations. The transformation of the resulting calculations from Laplace domain into the time domain was conducted with the help of Modified Durbin algorithm. In addition, one of the goals of this research is to highlight the importance of including the (1+z/R) part in the equations to account for the curvature effect of the shells. The addition of these effects and truncated series method to the equations and the investigation of their effects are the originalities of the present study. The present work obtained values were compared with the results obtained with Newmark's approach and ANSYS finite element methods. The numerical results showed that the proposed approach is a highly effective and efficient solution that can be easily applied to laminated viscoelastic shell problems.

Designing bending elements made of fiber composites requires knowledge of the residual strengths. Residual strengths determined according to PN-EN 14651, regardless of the type of matrix and the fibers used, are characterized by a very-high coefficient of variation, about 30%. The variability of this feature is so large that the normal distribution adopted in statistical analyses, which is consistent for compressive strength or tensile strength, may, in the case of residual strengths, result in a significant overdesign of the elements. Therefore, the article proposes a novel method of determining the residual strength with the use of centrally bent square plates simply supported at the perimeter. The coefficient of variation of this characteristic in the case of plate testing is about 8%.

A significant challenge in the experimental or computational characterisation of porous bodies and wind turbines is the correction of the obtained flow quantities for wall interference effects. Conventional corrective models are based on the Rankine–Froude theory, which is valid when the body solidity, or turbine induction factor, is sufficiently low. To resolve this issue, this work presents a new corrective model that builds on an extension of the Rankine–Froude theory, valid at arbitrary solidities, coupled with the method of mirror images to account for the existence of channel walls. The predictions of the new model are validated using laboratory and numerical experiments of porous plates and wind turbines. The results show that the new model performs equally as well as conventional ones when the solidity is low, but becomes increasingly more accurate as the latter grows.

Plates are being widely used for many structural applications such as aerospace, civil, electronic devices and marine industries etc. For these applications, it is important to know the plate behaviour under static loading condition. The present study focuses on filling the existing gap in the literature in order to know the plate behaviour of different geometrical shapes before and after adding the stiffener. A total of eight geometries namely circular, square, rectangular (with aspect ratio of 1.25, 1.50 and 1.75) and skew square (with 70o, 76.67o and 83.33o skew angles) were considered. Static analysis of considered geometries was carried out by using FEAST (a Finite Element software). To enable comparison of plates, three parameters namely the area of plates, starting point of the stiffener and curvature of the stiffener were kept constant. From the static analysis results, the effect of the curvilinear stiffener on different geometrical shapes, effect of aspect ratio on rectangular plates and effect of skew angle on skew square plates were given. The displacement of plates reduced significantly after adding the curvilinear stiffener to the bare plates and the stiffener was most effective in the case of circular plate. In the present study, the effect of aspect ratio and skew angle on static behaviour of bare and stiffened plates was also studied and discussed.

Made available in DSpace on 2022-04-29T08:40:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-03-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The damage detection process in structures has been an important challenge for the engineering community. The design of structural health monitoring (SHM) systems usually involves selection of actuators and sensors, their positions on the structure and post-processing of output signals. This article presents an approach to determine the optimal frequencies for damage detection in plates considering the perpendicular incidence of longitudinal waves into the damage. At these optimal frequencies are observed the maximum reflected and the minimum transmitted longitudinal wave amplitudes, which are recommended to achieve the damage detection due to their higher differences in wave amplitudes when comparing healthy and damaged conditions. Higher values of two damage detection indexes are obtained at the optimal frequencies. Experimental tests are carried out considering a rectangular aluminum plate with circular piezoelectric transducers. The experimental results demonstrate the proposed approach, and highlight the importance of defining optimal frequencies to detect damage in plates. Department of Mechanical Engineering School of Engineering of Ilha Solteira São Paulo State University (UNESP), SP Department of Mathematics School of Engineering of Ilha Solteira São Paulo State University (UNESP), SP Department of Mechanical Engineering School of Engineering of Ilha Solteira São Paulo State University (UNESP), SP Department of Mathematics School of Engineering of Ilha Solteira São Paulo State University (UNESP), SP CNPq: 133397/2019-0 FAPESP: 2019/21149-9

This paper presents the development of a nonlinear finite element analysis program for reinforced concrete structures, subject to monotonic loading, using thin flat shell finite elements. The element thickness is discretized in concrete and steel layers. It is adopted the Newton-Raphson method, considering a secant stiffness approach for the Material Nonlinear Analysis, based on the Modified Compression Field Model (MCFT), unlike the usual tangent stiffness approach. The original formulation was expanded to also consider the Geometric Nonlinear Analysis, through a Total Lagrangian Formulation. The program was validated through comparison with experimental results, for different structures. It was observed good agreement, besides adequate computational cost. resumo: O presente artigo apresenta o desenvolvimento de uma ferramenta para a análise não-linear de estruturas de concreto armado, sujeitas a carregamentos monotônicos, utilizando o elemento finito de cascas finas e planas, o qual, é discretizado, ao longo da sua espessura, em lamelas de concreto e camadas de aço. É utilizado o método de Newton-Raphson, adotando, na consideração da não-linearidade física, a rigidez secante do material, baseada no modelo do campo de compressão modificado, no lugar da abordagem via rigidez tangente. A formulação original do elemento foi expandida para considerar também a não-linearidade geométrica, através de uma formulação Lagrangiana total. A validação da ferramenta é via comparação com resultados experimentais da literatura, para diversas estruturas, onde pode ser observada boa aderência além de adequado custo computacional.

In this work, a coupled 3D thermo-elastic shell model is presented. The primary variables are the scalar sovra-temperature and the displacement vector. This model allows for the thermal stress analysis of one-layered and sandwich plates and shells embedding Functionally Graded Material (FGM) layers. The 3D equilibrium equations and the 3D Fourier heat conduction equation for spherical shells are put together into a set of four coupled equations. They automatically degenerate in those for simpler geometries thanks to proper considerations about the radii of curvature and the use of orthogonal mixed curvilinear coordinates α, β, and z. The obtained partial differential governing the equations along the thickness direction are solved using the exponential matrix method. The closed form solution is possible assuming simply supported boundary conditions and proper harmonic forms for all the unknowns. The sovra-temperature amplitudes are directly imposed at the outer surfaces for each geometry in steady-state conditions. The effects of the thermal environment are related to the sovra-temperature profiles through the thickness. The static responses are evaluated in terms of displacements and stresses. After a proper and global preliminary validation, new cases are presented for different thickness ratios, geometries, and temperature values at the external surfaces. The considered FGM is metallic at the bottom and ceramic at the top. This FGM layer can be embedded in a sandwich configuration or in a one-layered configuration. This new fully coupled thermo-elastic model provides results that are coincident with the results proposed by the uncoupled thermo-elastic model that separately solves the 3D Fourier heat conduction equation. The differences are always less than 0.5% for each investigated displacement, temperature, and stress component. The differences between the present 3D full coupled model and the the advantages of this new model are clearly shown. Both the thickness layer and material layer effects are directly included in all the conducted coupled thermal stress analyses.

This paper presents a method for determining Green's function for calculating the KIII factor for a crack initiated at the vertex of a sharp corner and coming out at different angles when the crack length is small compared to other element dimensions. A new approach to find a Green's function by means of FEM for symmetric problems and adapting it for non-symmetric problems has been applied, using the hypothesis of free released energy in combination with a special technique of building non-symmetric shapes from symmetric elements. This approach obtained approximate solutions, so special emphasis was placed on estimating the error of the obtained solutions. It was found that the high precision of the obtained Green's function is sufficient for practical use in calculating the durability and strength of structural elements under an anti-plane strain state.

One of the main concerns about the use of fibre reinforced polymer (FRP) materials in civil engineering structural applications is the potential reduction of their stiffness- and strength-related properties when exposed to elevated temperature. The first part of this paper presents an assessment of existing design guidelines for FRP structures, regarding the recommendations they provide about the reduction of FRP mechanical properties at elevated temperature. The second part of this paper presents a survey of test data available in the literature concerning mechanical tests at elevated temperature in FRP materials produced with different fibres, resins, shapes and manufacturing methods. The results of the survey show that the provisions available in existing design guidelines are not always accurate; moreover, in some cases, they are even non-conservative. Based on this assessment, the third part of the paper presents a method to define a temperature conversion factor for design purposes, consistent with the partial factor method of the Eurocodes, which was calibrated with the results included in the database. The method proposed takes into account not only the maximum service temperature experienced by the FRP material, but also its glass transition temperature; the method considers also the type of mechanical property, namely if it is either fibre- or matrix-dominated. The conversion factors obtained applying the method proposed presented a good agreement with the test data available in the literature.

Background The physical properties of tableware could influence selection and consumption of food and alcohol. There is considerable uncertainty, however, around the potential effects of different sizes and shapes of tableware on how much food and alcohol people self-serve. These studies aimed to estimate the impact of: 1. Plate size and shape on amount of food self-served; 2.Wine glass and bottle size on amount of wine self-poured. Methods 140 adults participated in two laboratory studies—each using randomised within-subjects factorial designs—where they self-served food (Study 1) and wine (Study 2): Study 1: 3 plate sizes (small; medium; large) × 2 plate shapes (circular; square). Study 2: 3 wine glass sizes (small; medium; large) × 2 wine bottle sizes (75 cl; 50 cl). Results Study 1: There was a main effect of plate size: less was self-served on small (76 g less, p p p = 0.46) or a size and shape interaction (p = 0.47). Study 2: There was a main effect of glass size: less was self-served in small (34 ml less, p p p = 0.20) or a glass and bottle size interaction (p = 0.18). Conclusions Smaller tableware (i.e. plates and wine glasses) decreases the amount of food and wine self-served in an initial serving. Future studies are required to generate estimates on selection and consumption in real world settings when numerous servings are possible. Protocol registration information: OSF (https://osf.io/dj3c6/) and ISRCTN (10.1186/ISRCTN66774780).

For both linear and nonlinear analysis, finite element method (FEM) software packages, whether commercial or in-house, have contributed significantly to ease the analysis of simple and complex structures with various working conditions. However, the literature offers other discretization techniques equally accurate, which show a higher meshing flexibility, such as meshless methods. Thus, in this work, the radial point interpolation meshless method (RPIM) is used to obtain the required variable fields for a nonlinear elastostatic analysis. This work focuses its attention on the nonlinear analysis of two benchmark plate-bending problems. The plate is analysed as a 3D solid and, in order to obtain the nonlinear solution, modified versions of the Newton–Raphson method are revisited and applied. The material elastoplastic behaviour is predicted assuming the von Mises yield surface and isotropic hardening. The nonlinear algorithm is discussed in detail. The analysis of the two benchmark plate examples allows us to understand that the RPIM version explored is accurate and allows to achieve smooth variable fields, being a solid alternative to FEM., The authors acknowledge the funding provided by Ministério da Ciência, Tecnologia e Ensino Superior—Fundação para a Ciência e a Tecnologia (Portugal) and LAETA, under internal project UIDB/50022/2020.

Introduction/background Metacarpal fractures comprise approximately 35.5% of cases in daily emergencies, mostly due to road traffic accidents (RTA), fall, and assault. The classification is based on the site and pattern of fracture. High-level evidence is lacking for the management of metacarpal fractures. The primary goals of treatment are to achieve acceptable alignment, stable reduction, strong bony union, and unrestricted motion. It can be managed by non-operative methods like close reduction and splintage. Operative management will be required if there is shortening, rotation, and angulation in different planes including close reduction and fixation with percutaneous intramedullary pining/k-wires and open reduction and fixation with screws, plates (compression/locking), and external fixators. This study was done to compare the efficacy of k-wire, screws, and plates in the management of metacarpal fractures and their outcomes based on their union, postoperative pain, range of movement, and grip strength in a tertiary care center, i.e., Liaquat National Hospital and Medical College. Methods It was a retrospective study conducted at the Department of Plastics and Reconstruction Surgery, of a tertiary care hospital. A total of 113 patients who were operated upon for metacarpal fracture were included in the study (open/close) without soft tissue loss or tendon injury, were divided into three groups according to the technique of fracture fixation, i.e., group 1 (k-wire), group 2 (screw), and group 3 (plates). The data like post-operative pain (visual analog scale, VAS) and radiological evidence of union were extracted from the registry. All the patients were called for follow-up in the outpatient department. Out of 113, 97 patients showed up for follow-up and were examined by a hand surgeon, and range of movement (goniometer) and grip strength (sphygmomanometer method) were assessed. Results A total of 97 patients were included in the study (male 66%, female 34%). Group 1 (K-wire) includes n = 61 (62.9%), group 2 (screw) n = 15 (15.5%), and group 3 (plate) n = 21 (21.6%). The mean follow-up time was 12 + 2 weeks after the surgery for post-operative pain and radiological evidence of union while 24 + 6 months for a range of movement and grip strength. Less post-operative pain was noted in group 1 patients while no significant difference was noted in the evidence of radiological union in all groups. Range of movement was better in group 1 patients (89.74 + 0.750) than in group 2 (80 + 0.37°) or group 3 (80.2 + 0.62°). The grip strength (compared to the normal contralateral hand) was normal in the majority of the patients in group 1, i.e., 94% while it was 80% in group 2 and 82% in group 3. Conclusion The significance of these reported findings suggests that open reduction and internal fixation with screw or plate might be a less preferable surgical technique in comparison to k-wire fixation in the treatment of a metacarpal fracture.

Background There is a lack of reliable methods to obtain valid measurements of the tensile response of high performance materials such as fibre composites, ceramics and textile products at high rates of strain. Objective We propose and assess two new test techniques aimed at measuring valid tensile stress versus strain curves at high and ultra-high strain rates. Methods We conduct detailed, non-linear explicit Finite Element (FE) simulations of the transient response of the test apparatus and specimen during the tests and we develop simple analytical models to interpret the test measurements. We consider two test techniques: one based on the split Hopkinson bar apparatus, and suitable for strain rates of up to 1000 /s, and a second technique relying on projectile impact and aimed at measurements at strain rates higher than 1000 /s. Results The simulations are successfully validated using test data at strain rates of order 200 /s and then used to predict the test performance at strain rates up to approximately 5500 /s. We find that both techniques can give valid stress versus strain curves across a wide range of strain rates. Conclusions We identify the limits of both techniques and recommend optimal measurement strategies for dynamic testing of materials with different ductility.

Orientador: Paulo Sollero Tese (doutorado) - Universidade Estaudal de Campinas. Faculdade de Engenharia Mecanica Resumo: Esta tese apresenta o desenvolvimento, a implementação e aplicações de uma formulação de elementos de contorno para análise de problemas estáticos e dinâmicos em placas anisotrópicas submetidas a carregamentos de flexão. O trabalho se baseia na teoria de placas finas de Kirchhoff Uma vez que a formulação dinâmica de elementos de contorno não foi encontrada na literatura consultada, as análises são realizadas utilizando-se uma formulação desenvolvida a partir das soluções fundamentais para elastostática. As integrais de domínio, provenientes dos carregamentos distribuídos ou dos termos de inércia, são transformadas em integrais de contorno usando-se o método da reciprocidade dual. Esta formulação é aplicada no cálculo da deflexão de placas isotrópicas e anisotrópicas, na análise dinâmica de estruturas ortotrópicas, anisotrópicas e estruturas de materiais compósitos laminados, submetidas a cargas harmônicas. É analisada a influência dos nós internos e da malha na precisão dos resultados. Os resultados numéricos são apresentados para problemas quaseisotrópicos, ortotrópicos e totalmente anisotrópicos. Os resultados obtidos são comparados com resultados presentes na literatura e mostram boa concordância Abstract: Here, static and dynamic analysis of a number of anisotropic problems using the boundary element method are presented. The formulation used is developed fram the elastostatic fundamental solutions and the domain integraIs due to inertial terms are transformed into boundary integraIs by using the dual recipracity method. Application is made to the calculation of deflections in anisotrapic plates, to the dynamic analysis of orthotrapic plates and to the analysis of anisotropic and composite laminar plates under harmonic loads. Numerical results are presented for quasi-isotropic, orthotropic and anisotrapic problems. The influence of number of internal nodes and number of boundary elements on the accuracy of the results is analyzed. The results are compared with other results fram the literature showing good agreement Doutorado Mecânica dos Sólidos e Projeto Mecânico Doutor em Engenharia Mecânica

Ultrasound examination of material properties is a precision method for determining their elastic and strength properties in connection with the small wavelength formed in the material after impact of a laser beam. In this paper, the wave processes arising during these measurements are considered in detail. It is shown that full-wave numerical modeling allows us to study in detail the types of waves, topological characteristics of their profile, speed of arrival of waves at various points, identification the types of waves whose measurements are most optimal for examining a sample made of a specific material of a particular shape, and to develop measurement procedures. To carry out full-wave modeling, a grid-characteristic method on structured grids was used in this work and a hyperbolic system of equations that describes the propagation of elastic waves in the material of the thin plate under consideration on a specific example of a ratio of thickness to width of 1:10 was solved. To simulate an elastic front that arose in the plate due to a laser beam, a model of the corresponding initial conditions was proposed. A comparison of the wave effects that arise during its use in the case of a point source and with the data of physical experiments on the propagation of laser ultrasound in metal plates was made. A study was made on the basis of which the characteristic topological features of the wave processes under consideration were identified and revealed. The main types of elastic waves arising due to a laser beam are investigated, the possibility of their use for studying the properties of materials is analyzed. A method based on the analysis of multiple waves is proposed. The proposed method for studying the properties of a plate with the help of multiple waves on synthetic data was tested, and it showed good results. It should be noted that most of the studies of multiple waves are aimed at developing methods for their suppression. Multiple waves are not used to process the results of ultrasound studies due to the complexity of their detection in the recorded data of a physical experiment. Due to the use of full wave modeling and analysis of spatial dynamic wave processes, multiple waves are considered in detail in this work and it is proposed to divide materials into three classes, which allows using multiple waves to obtain information about the material of the plate. The main results of the work are the developed problem statements for the numerical simulation of the study of plates of a finite thickness by laser ultrasound; the revealed features of the wave phenomena arising in plates of a finite thickness; the developed method for studying the properties of the plate on the basis of multiple waves; the developed classification of materials. The results of the studies presented in this paper may be of interest not only for developments in the field of ultrasonic non-destructive testing, but also in the field of seismic exploration of the earth's interior, since the proposed approach can be extended to more complex cases of heterogeneous media and applied in geophysics.

The use of modified couple stress theory to simulate the size-dependent phenomenon of composite laminate microplate is commonly limited to simple boundary conditions and mechanical bending load. The small-scale effects on bending and buckling on composite laminate microplate under complex boundary conditions in thermal environment have not been understood fully in the literature. Hence, this research develops, for the first time, a model to overcome the above limitation through the combination of a new modified couple stress theory and isogeometric analysis (IGA). By solving the governing equation using IGA, the thermal displacement, stress and thermal buckling load for various material length scale parameters are obtained. To satisfy the continuous shear stress condition at the layer interfaces, the equilibrium equations as integrated in-plane stress derivatives over the thickness are imposed. In addition, the non-uniform rational B-splines (NURBS) satisfy the higher-order derivative of shape function using the equilibrium equation. Furthermore, to show the effectiveness of presented model for capturing the size effect on thermal bending and thermal buckling of multi-ply laminate microplate, the influences of fiber orientation, thickness ratio, boundary condition and the variation in material length scale parameter are investigated.

The effect of forming pin arrangement on formed shape accuracy with sparse multi-point flexible (SMPF) tool has been experimentally and numerically investigated for creep age forming (CAF) process. An analytical method has been introduced to predict shape, stress and strain distributions of blanks loaded by SMPF tool with different pin configurations. Experiments and FE simulations of loading and CAF processes by SMPF tool with various pin number/interval conditions have been performed and the formed shapes after loading and CAF have been quantitatively analysed. The results show that increasing pin numbers in SMPF tool decreases shape errors and stress variations in the loaded blank, leading to lower deflections of the formed blank after CAF. With increasing pin numbers, the formed shape approaches the shape formed with corresponding surface tool. The shape error percentage in loaded blanks is significantly enlarged after CAF with SMPF tool, from 3% to more than 20% for singly-curved tool shapes with aluminium alloy 6082, and detailed value varies with tool shapes. Stresses in loaded blanks directly affect CAFed shapes and it has been found for the first time that there is a same stress discrepancy level between loaded blanks with SMPF tool and corresponding surface tool to achieve a particular shape accuracy after CAF with different tool shapes. It is proposed that the stress discrepancy parameter in loaded blanks can be used as a new and more efficient design criterion for pin arrangement in SMPF tool for CAF process. In addition, an asymmetric pin pattern, which reduces half of pins in SMPF tool and increases efficiency, has been proposed and its effectiveness for CAF process has been tested and discussed.

The theoretical and numerical determination of a space-dependent load distribution in a simply supported non-homogeneous Euler–Bernoulli beam and Kirchhoff–Love plate is investigated. The uniqueness of a solution to this inverse source problem is proved, whilst counterexamples are constructed to discuss the conditions under which uniqueness holds. A convergent and stable iterative algorithm is proposed for the recovery of the unknown load source and a stopping criterion is also given. Several one-dimensional numerical experiments are considered to investigate the properties of the proposed iterative procedure.

A recently proposed tuning method for resistive-inductive (RL) shunts is implemented in a commercial finite element (FE) code (ANSYS®). A main result of the paper is therefore the consistent formulation of the tuning method in terms of variables directly available as solutions in any commercial FE code: The two natural frequencies associated with short- and open-circuit (SC and OC) electrodes and a modal charge obtained as the electrical SC reaction force. An alternative method is based on quasi-static solutions with SC and OC electrodes, convenient for both numerical analysis and experiments. The proposed shunt tuning method is suitable for implementation in any commercial FE software supporting electromechanical analysis and ANSYS® has been used to assess its accuracy for a piezoelectric smart plate benchmark problem. The method is finally extended to multiple piezoceramic patches, placed symmetrically on the structure and shunted to a single RL network, whereby more vibration modes can be effectively controlled for the specific plate problem.

This work is a part of a larger research effort to better understand the combined effect of the blast wave and fragment impacts following the detonation of a shrapnel bomb. It is known that the time interval Δt, which represents the difference in arrival time between the blast wave front and the fragment at the position of a given target object, has a significant influence on its response mode. This paper presents insights into the establishment of a laboratory scale technique to generate a combined blast loading and single or multiple projectile impacts on a target. The objective of the setup is to control the time interval Δt to a certain extent so that the different response modes of the tested structures can be investigated. In order to reduce the complexity associated with the random nature of the shrapnel, steel ball bearings are used to simulate the projected fragments. They are embedded in a solid explosive charge, which is detonated at the entrance of an explosive driven shock tube. The experimental work demonstrates that it is possible to orient the path of a single projectile inside the tube when aiming at a target positioned at its exit. The setup guarantees the generation of a well-controlled planar blast wave characterized by its peak pressure, impulse and blast wave arrival time at the exit of the tube. The influence of the mass of the charge and the diameter of the projectile on its velocity study shows that for the same charge mass, the time interval increases with increasing projectile diameter. The experiments are numerically simulated based on an Eulerian approach using the LS-DYNA finite element software. The computational model allows to reveal details about the projectile flight characteristics inside the tube. Both the experimental and numerical data show the influence of the charge and projectile parameters on the time interval.

Introduction The purpose of this study was to evaluate the long-term outcome of an extended range of hand fractures treated with titanium, low profile plates, and screws. Materials and methods This retrospective study included adult patients with at least one phalangeal and/or metacarpal fracture, treated with mini titanium plates and screws, between 2004-2016, in a single trauma center, that were followed-up for at least 24 months and with complete, intact medical records. Results 90 patients (79 men and 11 women) with 114 hand (46 phalangeal, 68 metacarpal) fractures fulfilled the inclusion criteria. Thirty-two fractures were open (28.07%), 27 were intra-articular (23.68%), and 12 were both open and intra-articular fractures. The mean age of the patients was 36.02 years (range 17-75). Mean follow-up was 95.3 months (range 24 to 138). Open fractures had a reduced mean grip strength and total active motion. No difference was observed between intra-articular and extra-articular fractures (for grip strength and total active motion). Predictors of the final outcome included the severity of the initial injury (open vs closed) and not the anatomic location (intra- or extra-articular, metacarpal, or phalangeal) of the fracture. Conclusions Low-profile plates and screws can successfully be used to establish union and restore the alignment of the fractured bone while achieving a satisfactory clinical outcome, even in cases of open or intra-articular fractures.

В работе дается анализ основных эксплуатационных характеристик клапанов на основе изучения различных режимов работы поршневых компрессоров в системе газлифтной эксплуатации скважин. Исследования показывают, что экономичность, безопасность, безотказность и герметичность работы клапанов резко снижается вследствие динамических процессов. Причиной является частое изменение давления и физико-химического свойства газа в общей системе. При этих условиях высокочастотные составляющие изменения давления, а также вызванные за счет этого вибрационные механические колебания пластины, сопровождающиеся нарушением герметичности или поломкой пластины, является основной причиной возникновения отказов клапанов., The paper provides an analysis of the main operational characteristics of the valves based on the study of various operating modes of reciprocating compressors in the system of gas-lift wells operation. Studies show that the efficiency, safety, reliability and tightness of valves are dramatically reduced due to dynamic processes. The reason is the frequent change in pressure and physical and chemical properties of the gas in the general system. Under these conditions, the high-frequency components of the pressure change, as well as the resulting vibrational mechanical vibrations of the plate, accompanied by a breach of tightness or breakage of the plate, is the main cause of valve failures

The classical problem of reflection of Lamb waves from a free edge perpendicular to the centre line of an elastodynamic plate is studied. It is known that Lamb wave expansions for the displacement and stress fields poorly represent the irregular behaviour near corners, leading to the slow convergence of a series of such waves. The form of the irregularity for an elastodynamic corner is derived asymptotically, and a new solution method, which incorporates this corner behaviour analytically, is then implemented. Results are presented showing that this new approach represents the near-field and far-field behaviour very accurately, requiring very modest numbers of Lamb wave and corner modes. Further, it is revealed that the method can recover the trapped-mode phenomenon encountered in this configuration at the Lamé frequency and a specific Poisson’s ratio that we find to be approximately 0.224798.

Notwithstanding advances in medical and surgical management of flail chest, its morbidity and mortality rates are still high. Aim of this study is to compare three approaches for parietal thoracic stabilization by analyzing both early and long-term patient outcomes.A retrospective study from January 2006 to January 2018 involving sixty-five surgical flail chest (25 plates,11 struts and 29 wires fixations) was conducted. A mean Abbreviated Injury Scale (AIS) was 2.38±0.82 and a mean Injury Severity Score (ISS) was 32.02±8.21.Struts and plates stabilizations compared with wires fixation showed an immediate restoring of the partial pressure of oxygen (90.56 mmHg vs 91.90 mmHg vs 89.23 mmHg, p = 0.021), the carbon-dioxide levels (36.00 mmHg vs 35.03 mmHg vs 38.98 mmHg, p = 0.000) and the oxygen-blood saturation (97.71% vs 98.21% vs 92.12%, p = 0.000) in the early postoperative period. Furthermore, struts and plates ensured a better recovery of daily activities up to the 3rdmonth (QoL=1.0: p0.001 in lateral flail chest and p0.02 in anterior and antero-lateral flail chest). At the 12thmonth no difference in QoL was found between the different approaches.Plate and strut fixation revealed a lower rate of postoperative morbidity and mortality. Wires stabilization was characterized for a reduction of operative time.

Changes in trabecular micro-architecture are key to our understanding of osteoporosis. Previous work focusing on structure model index (SMI) measurements have concluded that disease progression entails a shift from plates to rods in trabecular bone, but SMI is heavily biased by bone volume fraction. As an alternative to SMI, we proposed the ellipsoid factor (EF) as a continuous measure of local trabecular shape between plate-like and rod-like extremes. We investigated the relationship between EF distributions, SMI and bone volume fraction of the trabecular geometry in a murine model of disuse osteoporosis as well as from human vertebrae of differing bone volume fraction. We observed a moderate shift in EF median (at later disease stages in mouse tibia) and EF mode (in the vertebral samples with low bone volume fraction) towards a more rod-like geometry, but not in EF maximum and minimum. These results support the notion that the plate to rod transition does not coincide with the onset of bone loss and is considerably more moderate, when it does occur, than SMI suggests. A variety of local shapes not straightforward to categorize as rod or plate exist in all our trabecular bone samples.

Plasticity models provide suitable tools to describe the so-called yield line pattern that occurs with the failure of plates. However, in a Lagrangian description a huge number of finite elements are needed for accurate solutions. Accuracy can be combined with low computer costs by means of the arbitrary Lagrangian–Eulerian (ALE) method. With the ALE method, the finite element mesh is automatically refined in the yield lines. A new remesh indicator is proposed that captures newly appearing yield lines as well as already formed yield lines. Numerical examples show the effectiveness of this approach.

During the evaluation of Young’s modulus by vibroacoustic methods, it is usually assumed that the Poisson's ratio is known. This assumption is based on a reasonable tolerance of the vibroacoustic methods to an inadequate estimate of Poisson's ratio. However, most studies do not consider the influence of the Poisson's ratio error in the estimation of the Young's modulus error. Moreover, the evaluation of the total error typically does not include any parametric analysis at all. Therefore, a new vibroacoustic method is proposed that provides a simple and reciprocal determination of the Young's modulus and Poisson's ratio. The method is based on measurements of the natural vibration modes of elongated plates using a scanning microphone in the very near field. The results of the sound pressure scanning are interpolated with a quadratic harmonic function to improve the spatial resolution in locating the vibration nodes. The advantage of this method is that the Poisson's ratio can be calculated directly by measuring the wavelength of the bending wave. Poisson's ratio is otherwise much more difficult to measure than Young's modulus. Therefore, this method can be used to determine the Poisson's ratio of various polymers, wood, and composites. The parametric analysis of the proposed method is compared with the parametric analysis of the standardised ASTM 1875 method “Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's Ratio by Sonic Resonance”. The results show that the accuracy of the Poisson's ratio determination is mainly influenced by the accuracy of the material density and the accuracy of the measured sample thickness. The accuracy of these two parameters also has a dominant influence on the accuracy of the determination of the Young's modulus. The proposed method and its accuracy are demonstrated on three different plates: aluminium, steel and soft plexiglass. The results of the proposed method for aluminium were compared with those obtained by the standardised ASTM method. The proposed method provides smaller error for given experimental conditions.

A large number of advanced finite element shell formulations have been developed, but their adoption is hindered by complexities of transforming mathematical formulations into computer code. Furthermore, it is often not straightforward to adapt existing implementations to emerging frontier problems in thin structural mechanics including nonlinear material behaviour, complex microstructures, multi-physical couplings, or active materials. We show that by using a high-level mathematical modelling strategy and automatic code generation tools, a wide range of advanced plate and shell finite element models can be generated easily and efficiently, including: the linear and non-linear geometrically exact Naghdi shell models, the Marguerre-von Karman shallow shell model, and the Reissner-Mindlin plate model. To solve shear and membrane-locking issues, we use: a novel re-interpretation of the Mixed Interpolation of Tensorial Component (MITC) procedure as a mixed-hybridisable finite element method, and a high polynomial order Partial Selective Reduced Integration (PSRI) method. The effectiveness of these approaches and the ease of writing solvers is illustrated through a large set of verification tests and demo codes, collected in an open-source library, FEniCS-Shells, that extends the FEniCS Project finite element problem solving environment.

Introduction. Guided growth (temporary hemiepiphyseodesis) methods for the correction of axial deformities at the knee joint level in children are used mainly in patients with idiopathic deformities. In patients with systemic skeletal dysplasias the use of these techniques does not take into account the peculiarities of the pathological process. Purpose of study: to evaluate with radiographs the incidence of incomplete plate-bone contact at temporary hemiepiphyseodesis; to assess tensely deforming condition of metal implants using numerical simulation of strain in patients with systemic skeletal dysplasias for the prognosis of their potential failure.Patients and methods. Postoperative radiographs were analyzed for 58 children with systemic skeletal dysplasias after temporary hemiepiphyseodesis (107 extremities, 188 plates; main group) and 50 patients with the deformities of other etiology (control group). Plate-metaphysis contact was considered to be incomplete if it exceeded 2 mm. To determine the plate strains and displacement during the process of bone growth the numerical simulation using COSMOL Multiphusics Software was performed.Results. Incomplete plate-bone contact was observed in 41 (22%) out of 188 constructions. Mean contact deficit made up 4.1±1.3 mm. In control group incomplete plate- bone contact (over 2 mm) was observed only in 3 (4.5%) cases (pConclusion. In temporary hemiepiphyseodesis the potentiality of incomplete plate-bone contact resulting from the anatomical peculiarities of epimetaphyseal zone is up to 22%. To improve the efficacy of the guided growth method in children with systemic skeletal dysplasias the elaboration of the constructions should take into account of epimetaphyseal zone configuration.

Buckling of thin-walled and load-bearing elements of a structure can have devastating consequences. Hence, buckling checks are an integral part of strength analysis of structures. The buckling problem of thin rectangular plates subjected to in-plane compressive and/or shear loading is of great importance in building, bridge, aerospace, marine, and shipbuilding industries. When buckling occurs, thin plates undergo large out-of-plane deflections, which in turn results in the development of large bending stresses and eventually complete failure of the structure. This paper deals with the buckling stability assessment of uniaxially-compressed plates with different support conditions within the framework of classical plate theory. The main objective of this research is to explore some uncovered aspects of buckling stability of plates by considering the effects of support conditions, aspect ratio, and slenderness ratio, which will consequently result in efficient design of such thin-walled structures. To this end, in addition to validation of the numerical simulation, some case studies have been performed in order to gain a better understanding of different aspects of buckling stability of such thin-walled structures.

Resumo Em uma aciaria, os recipientes que comportam o aço líquido, tais como o forno e a panela de aciaria, são revestidos com materiais refratários especiais para alta temperatura e elevada resistência ao desgaste. O custo desses materiais é alto e, portanto, almeja-se aumentar sua vida útil sem afetar seu desempenho. Este trabalho teve o objetivo de investigar as transformações que ocorrem no material refratário aluminoso de placas de válvula gaveta de panela de aciaria. Para tanto, a região das placas post mortem que entraram em contato com o material líquido a alta temperatura foi caracterizada por meio de análise visual e análises de composição e estrutura através das técnicas de fluorescência de raios X, difração de raios X e análise de microestrutura por microscopia eletrônica de varredura com espectroscopia por dispersão em energia. Como resultado, têm-se contribuições sobre o processo de corrosão química proporcionada pelo contato de escórias residuais com o canal das placas da válvula gaveta. Constatou-se a presença de materiais com alto teor de Ca e compostos por fases como mervinita e guelenita, características de escória, aderidos às placas. Ao mesmo tempo, foi possível estabelecer que a espessura de interação entre o material aderido e a superfície da placa variou entre 0,4 e 1,2 mm. Assim, quando associada à erosão pelo fluxo de aço, a corrosão química decorrente do contato com a escória tem o potencial de intensificar o desgaste da placa refratária.

Collision of particles either between themselves or with the wall, are typically characterized by normal and tangential coefficients of restitution, which depend on material and surface properties of the colliding objects. An accurate estimate of coefficients of restitution is of importance as it is one of input parameters in the discrete element simulations of a large system of particles. Often anomalies in the experimentally obtained values of the coefficients are reported in the literature. In the present work, both normal and tangential coefficients of restitution along with the surface and the local material properties are determined and compared with the predictions of the existing models. In certain cases, the experimentally obtained values agree fairly well with the values determined using the models while in some other cases anomalies in the experimental results are observed. (C) 2017 Published by Elsevier B.V.

The paper describes a general analytical sensitivity analysis method for the composite laminated plates and shells, which is applied to both classical and first-order shear deformation theories and based on the finite element methods. The first derivatives of engineering constants of lamina with respect to fibre volume fractions are computed based on the micromechanics theory. The first derivatives of extensional, bending and bending-extensional coupling stiffnesses of laminate with respect to fibre volume fractions and fibre orientations are derived using classical and first order theories of laminate. Computational methods for the first derivatives of total stiffness and mass matrices are proposed based on finite element method. The analytical sensitivity analysis methods for static responses, eigenvalues and eigenvectors are described using the total stiffness and mass matrices, and their first derivatives. Sensitivity analyses of composite laminated plate and shell are demonstrated. The merits and disadvantages are also discussed.

Elastostatics of laminated and functionally graded (FG) sandwich open cylindrical shells is studied using a refined higher order shear and normal deformation theory. Displacement based approach with twelve middle surface displacement parameters representing bending and membrane response of cylindrical shell is considered. An extended thickness criterion, (h/R)2 ≪ 1, is used to make the present theory more reliable over large range of thickness ratios of shell. Basic equations are obtained using minimum potential energy principle and solved subsequently with Navier solution method for cylindrical shells with all edges diaphragm supported. Two kinds of FG sandwich panels are considered having FG layer with Voigt’s rule of mixture following power law gradation of volume fraction. Results show an excellent accuracy with the three dimensional results available in literature for laminated shells. Also, superiority of present formulation over other higher order theories is shown by carrying out a number of comparative studies.

Background The fracture of ribs is a common injury presenting to trauma centers and hospitals. Along the years, a lot of methods have been introduced to stabilize the rib and sternal fractures, as most of studies reported that the treatment of these cases is warranted. In spite of the large number of methods for fixation introduced; no definitive method has been presented yet. Methods From July 2015 to November 2016, the data of 30 patients with rib or sternal fractures or both who fulfilled the inclusion criteria were collected prospectively. Those patients were assigned into two groups; (group A) the fractures were fixed by plates and (group B) were fixed by stainless steel wires. The choice of method of fixation depended on surgeon's experience. The variables evaluated included stability of chest wall, intensive care unit stay, hospital stay and ventilator days. Results The chest wall stability in (group A) was achieved in 100% of the patients, while in (group B) it was achieved in 60% of patients. Intensive care unit stay for group A was 9 ± 4.37 days and for group B 13.8 ± 7.61 (p = 0.031). Hospital stay for group A was 11.6 ± 5.27 days and for group B 17.1 ± 6.77 (p = 0.021). Ventilator days for (group A) were 6.38 ± 3.83 days, while in (group B) 10.3 ± 8.82days, however this difference was statistically insignificant (p = 0.129). Conclusions Plating of rib and sternal fractures had better outcome than wiring, regarding better chest wall stability and restoration of chest contour; also it had shorter intensive care unit, hospital and ventilator days.

An innovative procedure for the development of 3D patient-specific implants with drilling guides for acetabular fracture surgery is presented. By using CT data and 3D surgical planning software, a virtual model of the fractured pelvis was created. During this process the fracture was virtually reduced. Based on the reduced fracture model, patient-specific titanium plates including polyamide drilling guides were designed, 3D printed and milled for intra-operative use. One of the advantages of this procedure is that the personalised plates could be tailored to both the shape of the pelvis and the type of fracture. The optimal screw directions and sizes were predetermined in the 3D model. The virtual plan was translated towards the surgical procedure by using the surgical guides and patient-specific osteosynthesis. Besides the description of the newly developed multi-disciplinary workflow, a clinical case example is presented to demonstrate that this technique is feasible and promising for the operative treatment of complex acetabular fractures.

Free vibration analysis of functionally graded (FG) open cylindrical shells is presented here using various refined higher order theories. Present study undertakes the displacement based approach including higher order shear and normal deformation theory (HOSNT) along with first order shear deformation theory (FOST) and higher order shear deformation theory (HSDT) models. Difficulty of obtaining three dimensional (3D) solutions and errors associated with classical shell theory (CST) necessitates the requirement of higher order models. Present study takes into account moderately thick shells unlike CST, by considering square of ratio of thickness to radius of shell less than unity, instead of the classical assumption of considering ratio of thickness to radius less than unity. Here Navier method of solution with double trigonometric functions for displacement terms is used to analytically reduce the given set of partial differential equations (PDEs) to an eigenvalue problem. Results are computed using MATLAB and comparison between various higher order models is discussed based on the consideration of middle surface displacement parameters. Present results should establish benchmark solutions for free vibration analysis of isotropic/orthotropic FG cylindrical panels. Functionally graded material properties are graded according to power law variation in thickness direction. Various shell solutions, based on other theories and 3D solutions available in the literature are compiled along with present solutions.

This paper presents Best Theory Diagrams (BTDs) for plates considering all the displacement and stress components as objectives. The BTD is a diagram in which the minimum number of terms that have to be used to achieve the desired accuracy can be read. Maclaurin, zig-zag, trigonometric and exponential expansions are employed for the static analysis of cross-ply composite plates. The Equivalent Single Layer (ESL) approach is considered, and the Unified Formulation developed by Carrera is used. The governing equations are derived from the Principle of Virtual Displacements (PVD), and Navier-type closed-form solutions are adopted. BTDs are obtained using the Axiomatic/Asymptotic Method (AAM) and genetic algorithms (GA). The results show that the BTD can be used as a tool to assess the accuracy and computational efficiency of any structural models and to draw guidelines to develop structural models. The inclusion of the multiobjective capability extends the BTD validity to the recognition of the role played by each output parameter in the refinement of a structural model.

An analytical framework which incorporates damage propagation/growth into the general structural stability analysis is presented. Therefore, the conventional total potential energy approach is extended by introducing an extended total potential energy-like functional capable of describing inelastic processes in which equilibrium holds between available and the required force for producing a change in structure. The work deals with systems which are described by I generalized coordinates and K damage parameters. The damage parameters are found to be functions of I generalized coordinates and M load parameters. The underlying variational principle for inelastic solids may be solved using discrete formulations or approximate methods such as a Rayleigh–Ritz formulation. This leads to a set of non-linear algebraic equations, comprising post-critical equilibrium paths and damage propagation. In order to verify the framework, it is applied to the well-known problem in which a delaminated composite strut/plate is subjected to an in-plane compressive load.

Object and purpose of research: Experimental study on the efficiency of resonating plated vibration absorber tuned in one of the natural bending frequencies of the damped plate (model of the structural element). The paper discusses different variants of the absorber installation in the node and antinode areas for corresponding resonant vibration shape of the plate. Materials and methods: Experimental efficiency determination of resonant plated vibration absorber based on the difference of vibration excitabilities of the damped plate at the points located at its center and other antinodes of vibrations, as measured with and without the absorber. Main results: The effect of the suggested resonant plated vibration absorber (a metal strap fastened by a polymeric tape) was 19 dB. Installation of the improved layered resonant vibration absorber allows ~37 dB reduction of the plate vibration at the lowest resonant frequency. At the rest of the resonant bending frequencies of the plate, the absorber efficiency was 17-29 dB. Conclusion: It has been shown that a tuned multy resonant plated vibration absorber with point fastening to the plate has a high efficiency, as compared to the case when the contact area is the entire surface of the resonating strap. Practical importance of this work is the possibility to apply frequency-adjusted layered plated vibration absorbers with point fastening to the damped structural plate, which mitigates resonant peaks of structural vibration to their minimum levels.

Two ultrasonic techniques are well established for pipe inspection and monitoring: highly sensitive ultrasonic spot thickness measurements, which can be presented in C-scan form, or low frequency guided waves that rapidly screen large areas for big defects. Recently there has been a growing interest in pipe inspection and monitoring systems exploring the middle ground between these two techniques by using higher frequency guided waves over shorter distances. In this paper the use of an axial transducer array (more suitable for monitoring applications) or a single axially scanned transducer (more suitable for inspections) that sends and receives dispersive circumferential guided waves around a pipe has been studied. The presence of a defect is detected as a result of a change in the wave travel time around the pipe circumference as a result of the thickness reduction. Both measurement modalities have a pitch between adjacent transducers/measurements. By approximating the pipe to a plate, a finite element model assisted method to evaluate the detection capabilities (probability of detection-POD) of this short range guided wave technique as a function of scan or transducer pitch is presented. The performance of three guided wave modes (A0, S0, and SH1) are compared in a 10mm thick plate. The results help to optimize the pitch and defect sensitivity of the setup. For the parameters investigated in this study, it was found that the S0 mode, at 2MHz.mm, is the most suitable for detecting wide shallow defects. For the same detection capabilities a much wider pitch can be used for S0 mode transducers as compared to SH1 mode transducers. Whereas the SH1 mode, at 3MHz.mm, is better suited to detecting narrow and deep defects using a relatively small pitch. The S0 mode is much less sensitive to these defects. The A0 mode was excluded from the POD analysis because it had a much higher variability in average thickness measurements, at comparable SNRs, compared to the other two modes.

The buckling and postbuckling behavior of composite struts under uniaxial compression is investigated. A geometrically nonlinear model comprising only four generalized coordinates is applied to multi-layered struts built up of transversally isotropic unidirectional layers. Laminates with a cross-ply layup are investigated. By minimizing the total potential energy of the system, equilibrium paths and critical buckling loads for varying lengths and depths of delamination are determined. Thus, the response of the system in the postbuckling range is analyzed and areas of stable and unstable behavior are determined. The outcome of the work provides detailed information about the influence of delaminations on the buckling behavior of composite struts.

Background Crescent fracture-dislocation of sacroiliac joint is a type of lateral compression pelvic injury associated with instability. These fractures comprise 12% of lateral compression fractures. Objective The objective of this study is to share the experience and to assess the functional outcome of fixation in crescent fracture-dislocation. Methods We analyzed a descriptive case series with clinical data of 15 patients at the Department of Orthopedics Surgery at the Dr. Ruth K.M. Pfau Civil Hospital at Dow University of Health Sciences in Karachi, Pakistan, from January 2016 to August 2018. The patients were treated by closed and open fracture reduction and fixed with percutaneous screws and reconstruction plates. Results A total of 15 patients were included in this study with age ranging from 20 to 60 years (11 men [73%]; four women [27%]). According to the mechanism of injury, five (33%) had motorcycle accidents; four (27%) had collision while sitting in a car; three (20%) were pedestrians hit by a vehicle; four (27%) were injured while sitting in van; two (13%) had bus-related injury, and one (6.5%) presented with a history of wall collapse. Five (33%) patients had type I fractures, seven (47%) had type II fractures, and three (20%) had type III fractures Associated injuries were midshaft femur fracture in two patients, contralateral superior and inferior rami fracture in three patients, and open tibia fracture in one patient. All fractures were fixed with reconstruction plates and screws. Patients were kept as non-weight-bearing on the injured joint for three weeks, mobilized non-weight-bearing on the contralateral leg after three weeks, and partial weight-bearing was started at eight weeks; full weight-bearing was started after three months. Nine patients (60%) had excellent outcomes, three (20%) had a good outcome, and three (20%) had a poor outcome. Conclusion Crescent fracture-dislocations are unstable injuries. These fractures should have proper reduction and fixation that will reduce pain, malunion, and shortening.

Several nuclear research reactors use or are planned with cores containing flat-plate- type fuel elements. The nuclear fuel is contained in parallel plates that are separated by narrow channels through which the fluid flows to remove the heat generated by fission reactions. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the channels can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. As a consequence, the safe operation of the reactor may be affected. In this work, a numerical fluid-structure interaction study was conducted for evaluating the mechanical stability of nuclear fuel plates under axial flow conditions. Five different cases were analyzed. In all cases, the system consisted of two fuel plates bounded by fluid channels but, in case 5, a support comb at the leading edge of the plates was inserted. The pressure loadings caused by the fluid flow were calculated using a Computational Fluid Dynamics model created with ANSYS CFX. The structural response was determined by means of a Finite Element Analysis model generated with ANSYS Mechanical. Both models were coupled using the two-way fluid-structure interaction approach. The results from Case 1 allowed proposing a methodology to predict the critical velocity of the assembly without an inlet support comb. The maximum deflection of the plates was detected at their leading edges. It was detected that, for flow rates in the channels less than a certain value, the maximum deflection increased linearly with the square of the coolant velocity. In contrast, for greater flow rates, a nonlinear behavior was observed. Therefore, that fluid velocity was identified as the critical velocity of the system. Besides, above the critical velocity, an extra deflection peak was observed near the trailing edge of the plates. In cases 2, 3 and 4, the influence of manufacturing deviations and the change of materials properties due to the increment of temperature on the critical velocity was investigated. With these conditions, the critical velocity of the system was found at lower values. Lastly, in Case 5, the effectiveness of using a support comb at the leading edge of the plates was investigated. The results showed that the static divergence at the inlet end is effectively eliminated with the installation of the comb. In addition, the flow-induced deflections along the length of the plates were significantly diminished with the comb. Muitos reatores nucleares de pesquisa usam ou são planejados com elementos combustíveis tipo placas planas. O combustível nuclear está contido em placas paralelas que são separadas por canais estreitos através dos quais o fluido refrigerante passa para remover o calor gerado pelas reações de fissão. Um dos problemas deste tipo de elemento combustível é a estabilidade mecânica das placas de combustível. O líquido refrigerante a alta velocidade pode causar deflexões excessivas dessas placas, bloqueando o canal de escoamento e levar ao superaquecimento nas placas, falha estrutural ou colapso da placa. Como consequência, a operação segura do reator pode ser afetada. Neste trabalho, foi realizado um estudo numérico de interação fluido-estrutura para avaliar a estabilidade mecânica de placas de combustível nuclear sob condições de fluxo axial. Cinco diferentes casos foram analisados. Em todos os casos, o sistema consistiu em duas placas de combustível delimitadas por canais de fluido, mas, no caso 5, um pente de suporte na borda de ataque das placas foi inserido. As cargas de pressão causadas pela vazão foram calculadas usando um modelo de Dinâmica dos Fluidos Computacional, criado com ANSYS CFX. A resposta estrutural foi determinada por meio de um modelo de elementos finitos, gerado com ANSYS Mechanical. Os modelos foram acoplados usando a abordagem de interação fluido-estrutura bidirecional. Os resultados do Caso 1 permitiram propor uma metodologia para prever a velocidade crítica do sistema sem o pente de suporte. A deflexão máxima das placas foi observada em suas bordas de ataque. Foi detectado que, para velocidades nos canais inferiores a um determinado valor, a deflexão máxima aumentava linearmente com o quadrado da velocidade do líquido refrigerante. Em contraste, para maiores vazões, um comportamento não linear foi observado. Portanto, essa velocidade do fluido foi identificada como a velocidade crítica. Além disso, acima da velocidade crítica, um pico extra de deflexão foi observado próximo à borda de saída das placas. Nos casos 2, 3 e 4, a influência dos desvios de fabricação e da alteração das propriedades dos materiais devido ao incremento de temperatura na velocidade crítica foi investigada. Sob essas condições, a velocidade crítica foi encontrada a valores mais baixos. Por fim, no Caso 5, a eficácia do uso do pente de suporte na borda de entrada das placas foi estudada. Os resultados mostraram que a divergência estática na extremidade de entrada foi efetivamente eliminada com a instalação do pente. Além disso, as deflexões induzidas pelo fluido ao longo do comprimento das placas foram significativamente diminuídas com o pente.

It is a major scientific challenge to develop the light-weight materials with high performance simultaneously in diverse applications ranging from civil engineering to defence. Numerical results for composite plates of 5.4-mm, 7.5-mm and 9.6-mm thick bioinspired composite plates were compared with corresponding bulk plates under the impact of a rigid hemi-spherical projectile at same impact velocities. The most significant improvement was recorded for the 5.4-mm thick nacre-like aluminium alloy composite plate, which was attributed to the larger area of plastic deformation due to the tablet arrangement. Experiments data were collected to validate the numerical simulation. It has been found that the nacre-like composites of different thickness had better ballistic behaviour than the bulk ones. The aim of this thesis is to give general background and research progress about natural nacre and the corresponding nacre-inspired artificial composites, to provide the basis for preparing the detailed experimental and numerical study on the ballistic performance of nacre-like aluminium alloy composites. My following ballistic experiments are to validate the numerical simulation results that the nacre-like composite plate has better ballistic performance at high velocity due to the tablets arrangement and plastic deformation. From previous simulation results, 5.4-mm nacre-like plate has shown a significant performance improvement compared with same thickness bulk plate owing to the hierarchical structure induced high energy absorptions. Hence, plate thickness and projectile velocity play a significant role on the performance improvement of the proposed nacre-like AA7075-T651 composites. Further experimental works are needed to assess other crucial parameters for modifying the mechanical behaviours of such bioinspired materials.