Mechanical behavior of carbon/epoxy cylinders under axial compressive loads

Para estruturas utilizadas no setor aeroespacial, os requisitos de baixo peso, alta resistência e rigidez, além de estabilidade dimensional, têm propiciado o aumento da utilização de materiais compósitos nas suas manufaturas. Em particular, cascas cilíndricas ou estruturas construídas pela junção de cilindros de paredes finas, confeccionadas em fibra de carbono e resina epóxi, são amplamente utilizadas neste tipo de aplicação. Neste trabalho, um programa experimental foi desenvolvido para determinar as tensões de falha, os módulos de elasticidade e o modo de falha de 47 cilindros com diâmetro interno de 40 mm e espessura nominal de 0,6 mm (com exceção de 2 corpos de prova), fabricados em carbono/epóxi, quando submetidos a cargas compressivas uniaxiais. Os espécimes testados possuíam diferentes razões entre comprimento e diâmetro (variando de 2,50 a 11,25) e seqüências de laminação variadas (orientações de camadas). Os resultados dos ensaios foram comparados aos obtidos em análises realizadas com programas de elementos finitos e os fatores que influenciaram o comportamento mecânico destes cilindros foram analisados.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

MODAL ANALYSIS OF HYBRID ADAPTATIVE BEAMS

Smart or adaptative structures are those capable to perform some special functions when stimulated externally. In the context of this type of structure, hybrid adaptative composite beams, reinforced with active Ni-Ti filaments, were simulated in the present work. Such beams may be adopted for vibration control, exploring the possibility of changing their bending stiffness by means of controlling the temperature of the shape memory alloy filaments. The main objective of this paper is to present, for a free-free boundary condition, the vibration modes and their frequencies obtained analytically and numerically for prismatic beams, which incorporate nineteen layers of epoxy reinforced with chopped E-glass mat (17 plies), and two symmetric active plies (A) embedded with up to four Ni-Ti wires each (2+A+13+A+2). One particular aspect of this investigation is to verify how the natural frequency of the beams changes, when an electric current passes through the Ni-Ti wires and elevates their temperature from 25 ºC to 69 ºC, converting 100% of the Ni-Ti wires into the more rigid austenitic phase. In order to verify the accuracy of the analytical method, it was compared with two numerical models based on the finite element method. The maximum differences between the methodologies, in module, was 4.50%

Analysis of the strength of synthetic marble beams through the statistical distribution of Weibull

No presente trabalho, adotou-se a análise estatística de Weibull para avaliação da resistência mecânica à flexão, e sua repetibilidade, de mármores sintéticos, tanto puros quanto reforçados com fibra vidro-E. O objetivo foi observar o comportamento do módulo de Weibull e da resistência mecânica, à medida que se introduz fibra de vidro picotada na composição do mármore sintético. Para isso foram avaliados quatro diferentes teores, em massa, de fibra de vidro, para estabelecer uma curva padrão do comportamento mecânico, à medida em que se alterou a fração de fibra do compósito. A metodologia de Weibull viabiliza esta análise, uma vez que, além dos corpos de prova possuírem grande semelhança dimensional de espessura com os produtos fabricados em mármore sintético, ela quantifica a ocorrência de imperfeições devido ao processo de fabricação. Os resultados demonstraram que a inserção de fibra de vidro, em uma massa de 3 Kg de mármore sintético, em proporções de 12,5 a 100 gramas provocou, dependendo da quantidade de fibra inserida, uma variação na resistência intrínseca, que inicialmente diminuiu (0 a 25 g) e depois aumentou até o valor máximo com 100 gramas. Outro resultado importante foi o tempo de desmoldagem, que influenciou fortemente a dispersão dos resultados, que quando diminuído de 24h para 2h, provocou uma diminuição do módulo de Weibull (i.e. aumento na variação da tensão de ruptura), de até 60%.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%

Damping behavior of synthetic graphite beams

The main objective of this work was to obtain the damping factor 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 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

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

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

RESUMO No presente trabalho, adotou-se a análise estatística de Weibull para avaliação da resistência mecânica à flexão, e sua repetibilidade, de mármores sintéticos, tanto puros quanto reforçados com fibra vidro-E. O objetivo foi observar o comportamento do módulo de Weibull e da resistência mecânica, à medida que se introduz fibra de vidro picotada na composição do mármore sintético. Para isso foram avaliados quatro diferentes teores, em massa, de fibra de vidro, para estabelecer uma curva padrão do comportamento mecânico, à medida em que se alterou a fração de fibra do compósito. A metodologia de Weibull viabiliza esta análise, uma vez que, além dos corpos de prova possuírem grande semelhança dimensional de espessura com os produtos fabricados em mármore sintético, ela quantifica a ocorrência de imperfeições devido ao processo de fabricação. Os resultados demonstraram que a inserção de fibra de vidro, em uma massa de 3 Kg de mármore sintético, em proporções de 12,5 a 100 gramas provocou, dependendo da quantidade de fibra inserida, uma variação na resistência intrínseca, que inicialmente diminuiu (0 a 25 g) e depois aumentou até o valor máximo com 100 gramas. Outro resultado importante foi o tempo de desmoldagem, que influenciou fortemente a dispersão dos resultados, que quando diminuído de 24h para 2h, provocou uma diminuição do módulo de Weibull (i.e. aumento na variação da tensão de ruptura), de até 60%

Mechanical behavior of silver alloys used as cast post and core in maxillary incisors

This experimental "in vitro" investigation is mainly concerned with the mechanical behavior of twenty plastic analogous simulating endodonticaly treated maxillary central incisor roots, divided in two groups, which were restored with: (i) silver (10 specimens, Ag - 80%); and (ii) silver – palladium (10 specimens, Ag – 58.5% / Pd – 27.4%) cast alloys. All the restored analogous were clamped inside stainless steel cylinders filled with acrylic resin, and were tested to failure in an INSTRON machine. The static compressive loads were applied with an inclination of 45° relatively to the longitudinal direction of the teeth. On average, the specimens restored with Ag– Pd presented higher values of final failure load (i.e. fracture or excessive plastic bending) and stiffness. On the other hand, those restored with Ag presented average proportional limit loads which were, in comparison, about 5% higher