Flaminio Levy Neto

Mechanical behavior of GRP pressure pipes with addition of quartz sand filler

In comparison with steel, concrete, and polymeric pipes, glass-reinforced plastic (GRP) pressure pipes use more expensive raw materials. Thus, despite of their attractive structural performance, mainly in terms of mechanical strength combined with low weight, the higher cost can be a limitation in many applications. In this scenario, an alternative to reduce the final price of GRP pipes is the addition of quartz sand filler. In this experimental and numerical study, filament-wound E-glass/polyester pipes with nominal inside diameter of 300 mm and wall thickness of 5.7 mm were produced with the incorporation of quartz sand as filler and tested to failure under internal pressure. The mechanical behavior of the composite pipes was evaluated experimentally, throughout short-time hydraulic failure pressure tests, as well as using finite element analysis (FEA). In the FEA simulations, the shell wall was modeled as an axisymmetric layered orthotropic material. A good agreement, varying from 96% to 98%, was obtai...In comparison with steel, concrete, and polymeric pipes, glass-reinforced plastic (GRP) pressure pipes use more expensive raw materials. Thus, despite of their attractive structural performance, mainly in terms of mechanical strength combined with low weight, the higher cost can be a limitation in many applications. In this scenario, an alternative to reduce the final price of GRP pipes is the addition of quartz sand filler. In this experimental and numerical study, filament-wound E-glass/polyester pipes with nominal inside diameter of 300 mm and wall thickness of 5.7 mm were produced with the incorporation of quartz sand as filler and tested to failure under internal pressure. The mechanical behavior of the composite pipes was evaluated experimentally, throughout short-time hydraulic failure pressure tests, as well as using finite element analysis (FEA). In the FEA simulations, the shell wall was modeled as an axisymmetric layered orthotropic material. A good agreement, varying from 96% to 98%, was obtained between the average hydraulic failure pressure measured and FEA predicted failure pressures, using Tsai—Hill and Hoffman failure criteria, respectively.

Assessement of tensile strength of graphites by the Iosipescu coupon test

Polycrystalline graphites are widely used in the metallurgical, nuclear and aerospace industries. Graphites are particulated composites manufactured with a mixture of coke with pitch, and changes in relative proportions of these materials cause modifications in their mechanical properties. Uniaxial tension tests must be avoided for mechanical characterization in this kind of brittle material, due to difficulties in making the relatively long specimens and premature damages caused during testing set-up. On other types of tests, e.g. bending tests, the specimens are submitted to combined stress states (normal and transverse shear stresses). The Iosipescu shear test, is performed in a beam with two 90° opposite notches machined at the mid-length of the specimens, by applying two forces couples, so that a pure and uniform shear stress state is generated at the cross section between the two notches. When a material is isotropic and brittle, a failure at 45° in relation to the beam long axis can take place, i.e., the tensile normal stress acts parallel to the lateral surface of the notches, controls the failure and the result of the shear test is numerically equivalent to the tensile strength. This work has evaluated a graphite of the type used in rocket nozzles by the Iosipescu test and the resulted stress, ~11 MPa, was found to be equal to the tensile strength. Thus, the tensile strength can be evaluated just by a single and simple experiment, thus avoiding complicated machining of specimen and testing set-up.

Damping behavior of synthetic graphite beams

The main objective of this work was to obtain the damping factor (x ) as well as the elasticity modulus (E) of two kinds of synthetic graphite (HLM and ATJ), using the modal analysis technique. Prismatic beams of square section (~ 11 x 11 mm) and length over thickness ratio (L/t) of about 22.7 were tested in the free - free boundary condition. The first four modes of vibration were taken into account in the non-destructive evaluation of the materials. In addition, numerical simulations were also carried out in this investigation. The agreement between the theoretical and the experimental results was quite good. The average values of E and x for the HLM graphite were 20% and 90% higher, respectively, than those presented by the ATJ graphite, indicating that the HLM graphite has, proportionally, more damping mechanisms than the ATJ graphite.

Estudo fotoelástico do controle vertical com o arco de dupla chave na técnica Straight wire

INTRODUCTION: There are clinical situations in which the extraction of bicuspids becomes necessary and, eventually, the extraction spaces are completely closed after aligning and leveling the teeth. The Double Key Loop (DKL) is a stainless steel arch for retraction, with two loops (keys), one mesial and another distal to the canine. AIM: This study aims to study the area where the force is exerted after the activation of the distal loop, the activation of the loops among themselves and the distal loop, and the activation with Gurin®. METHODS: Nine photoelastic models of the inferior arch were made, without the first bicuspids and the third molars, with In-Ovation brackets and the DKL. With the interposition of polarizing filters, pictures of incisors canines and posterior teeth were taken, after the activation of the arch. RESULTS AND CONCLUSIONS: Based on the analysis of the photoelastic model, we concluded that the activation in the distal loop can produce an anterior retraction movement without an extrusive component, while the activation with Gurin® produces an extrusive component; besides that, the activation of the keys among themselves and the distal loop activation can produce an anterior retraction movement with an intrusive component.

Análise da resistência mecânica de vigas de mármore sintético através da teoria estatística de Weibull

In the present study, the Weibull statistical analysis was adopted for evaluating the flexural strength, as well as its repeatability, of cultured marbles, both pure and reinforced with fiberglass. The objective of this study was to observe the behavior of the Weibull modulus and mechanical strength, as chopped fiberglass was incorporated in the composition of cultured marble. For this purpose, four different compositions with different amounts of glass fiber, by weight, were evaluated, to establish a standard curve of the mechanical behavior of the composite fiber. The Weibull approach enables this analysis since, in addition to the dimensional thickness resemblance of test samples with the products made of synthetic marble, it quantifies the occurrence of imperfections due to the manufacturing process. The results showed that the glass fiber insertion into a mass of 3 kg of synthetic marble, in proportions of 12.5 to 100 grams, caused a variation in the intrinsic resistance, depending on the amount of fiber inserted, which initially fell (0 to25 g) and then increased to a maximum of 100 grams. Another important result was the time of demolding, which strongly influenced the dispersion of the results that, when reduced by 2h to 24h, caused a decrease in Weibull modulus (i.e. increase in the variation of the rupture stress), up to 60%.

Comportamento de cilindros de carbono/epóxi submetidos a cargas compressivas axiais

The requirements of low weight and dimensional stability, combined with high strength and stiffness, for aerospace structures has prompted an increasing use of fiber reinforced materials in manufacturing such structures. In particular, carbon/epoxy cylinders have been widely used in aerospace applications. In this work, an experimental program was developed to determine failure loads, modulus of elasticity and failure modes of 47 carbon/epoxy cylinders shells under compressive loads. The specimens tested had several different length/diameter (from 2.50 to 11.25) ratios and laminate lay-up. These results were compared to the analytical results from finite element code and the most important factors influencing the mechanical behavior of this type of structure were analyzed.

Simulação numérica do comportamento mecânico de tubos poliméricos de parede fina submetidos à pressão interna

This work presents the numerical simulation of thin perfect, machined and repaired PVC pipes subjected to internally hydrostatic pressure, with ratio between the diameter (D) and the thickness (t), above or equal 20, D/t > 20. The numerical simulations were carried out with a finite element program, called Compshell, using PVC tubes, from elastic behavior to the failure. The boundary conditions were: clamped in one end and simple supported in the other, with freedom along the axial direction. The longitudinal and radial displacements, the bending moments and normal stresses resultants for pipes were evaluated. The maximum pressure was estimated using the Tsai-Hill failure criterion. The best result for repaired pipes was obtained with a laminate of epoxy matrix (E) filled with cotton cloth (C), since this composite and PVC Youngs modulus are close to each other. The ideal composite repairing is the one that restores the structural stiffness of the affected region, in the way that it does not strangulate nor bulge out the tube. The purpose of the work is to compare the results obtained with two types of composite repairing for polymeric pipes: (i) epoxy matrix reinforced with E-glass fiber and (ii) epoxy matrix filled with cotton cloth, indicating the geometrical characteristics and mechanical proprieties of composite repairing that presented the best behavior.

Análise das deformações em tubos de aço reparados com compósitos tipo carbono/epóxi

The main objective of this work is to present the values of the circumferential normal deformations obtained from numerical simulations of metallic pipes (AISI Steel 1020, length L = 400 mm, external diameter D = 400 mm and thickness t = 2 mm) in the following conditions: (i) perfect; (ii) machined on 25% of its length along its central region to a thinckness reduction of 50%, in order to simulate a defect; and (iii) repaired with a carbon/epoxy composite (balanced woven fabrics of fibers, AS4 - Hexcel), subjected to different internal pressures, from 2 to 10 MPa, using the non linear finite element program COMPSHELL. And, in addition, to verify if the applied composite repairing are able to restore the original stiffness of the pipes, previous to the machining operation. It was observed that there is a minimum thickness, which is required for the carbon/epoxy repairing to restore the local stiffness lost on the machining operation. The radial displacements and the circumferential strain were used as references to evaluate how effective the repair was. The minimum thickness of the repairing depends on the ratio of the elasticity moduli of the repaired and the original material of the tube. As far as this work is concerned, the required repair thickness is 3.05 mm.