Antonio F. Ávila

A mechanical analysis on recycled PET/HDPE composites

The large amount of disposable bottles presently produced makes imperative the search for alternative procedures for recycling or reuse of these materials, since they are not biodegradable. As chemical processing is most often costly and sometimes aggressive to the environment, a possible solution is the recycling of such material by thermo-mechanical techniques. This paper takes into consideration the thermo-mechanical recycling of post-consumed plastic bottles, especially the ones made of polyethylene terephtalate (PET), and its use as composite materials for engineering applications. To be able to evaluate the new composite performance from the mechanics point of view, i.e. stiffness and machinability, two sets of tests were carried out. For the first set, compression tests were applied. For the machinability evaluation, the final roughness was measured after the milling procedure at different speeds and leads. Experimental data showed good performance for compression and machinability. Finally, spur gears were cut from cylindrical specimens made of PET/HDPE blend.

Proposing a better forming limit diagram prediction: a comparative study

Abstract In this work, it is shown an algorithm for the prediction of the right-hand side of forming limit diagram (FLD) using the methodology proposed by Marciniak and Kuczynski. Five different yield criteria were used: von Mises’, Hill’s (1948), Hill’s (1979), Logan and Hosford’s, and Hill’s (1993) [Metal Forming—Mechanics and Metallurgy, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1993; Proc. R. Soc. London 193A (1948) 197; Math. Proc. Camb. Philos. Soc. 85 (1979) 179; Int. J. Mech. Sci. 22 (1980) 419; Int. J. Mech. Sci. 35 (1993) 19]. The results were compared against theoretical and experimental data present in literature with good agreement. The materials used in the comparison were the 2036-T4 aluminum and the AK, IF and EEP steels. It was observed that the predicted FLD was strongly influenced by the type of yield criterion used in the analysis. The best agreement between the predicted curves and the experimental data for each material was obtained from different criteria. The best result for the AK steel was achieved from the Logan and Hosford’s criterion. The 2036-T4 aluminum was better represented when the Hill’s criterion [Int. J. Mech. Sci. 35 (1993) 19] was used. The IF and EEP steels were well represented by the results based on either Hill’s [Math. Proc. Camb. Philos. Soc. 85 (1979) 179] or Logan and Hosford’s criterion [Int. J. Mech. Sci. 22 (1980) 419].

An investigation on graphene and nanoclay effects on hybrid nanocomposites post fire dynamic behavior

This paper deals with the post fire behavior of hybrid nanocomposites under dynamic loadings. A series of tests were performed to investigate how nanoparticles (i.e. nanoclay and graphene nanosheets) affect the post-fire overall composite behavior. Carbon fiber/epoxy-nanoclay and carbon fiber/epoxy-graphene nanosheets were manufactured. The nanoparticles employed were Cloisite 30B nanoclay, and surface modified graphene nanosheets. The epoxy system used was RemLam M/HY956. The nanocomposites were made using ultrasonic mixer for nanoparticle dispersion in acetone followed by a shear mixing of acetone/nanoparticle/hardener. The following steps involved degassing, the addition of resin to the mixture and, the hand lay-up with vacuum assisted cure. Thermo gravimetric analysis (TGA) indicates an average decrease on peak mass loss around 41% with the addition of small amount of nanoparticles. The sample plates were exposed to a heat flux of 800 kW.m-2 for a period up to 120 seconds. The post-fire low velocity impact tests indicated the impact resistance degraded as a function of heat exposure. However, the addition of nanoclay leads to an increase on impact peak force of 11.69%. The carbon oxidation could be the main cause of the increase on impact peak load is lower than expected, only 6.72%. The model predictions are overestimated by approximately 8%. Even though, it can be a good tool for composites design.

Nano-modified adhesive by graphene: the single lap-loint case

This paper addresses the performance study on, low viscosity, nano-modified adhesives by graphene. For achieving this goal, single-lap joints following ASTM D 5868-01 were manufactured and tested. X-ray diffraction, scanning electron microscopy and nanoindentation were employed for graphene based nanostructures characterization. The increase on joint strength was around 57% when compared against the control group. Furthermore, all failures for the nano-modified adhesive were cohesive failure for the carbon fibre/epoxy composites indicating that the adhesive was tested. X-ray diffractions signatures indicate formation of nano-structures with 17-19 nm diameters. Moreover, nanoindentation tests revealed a homogeneous dispersion of graphene.

Nano-engineered composites: interlayer carbon nanotubes effect

The concept of carbon nanotube interlayer was successfully introduced to carbon fiber/epoxy composites. This new hybrid laminated composites was characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy and tensile tests. An increase on peak stress close to 85% was witnessed when CNTs interlayer with 206.30 mg was placed to carbon fiber/epoxy laminates. The failure mechanisms are associated to CNTs distribution between and around carbon fibers. These CNTs are also responsible for crack bridging formation and the increase on peak stress. Initial stiffness is strongly affected by the CNT interlayer, however, changes on stiffness is associated to changes on nano/micro-structure due to damage. Three different behaviors can be described, i.e. for interlayers with ≈ 60 mg of CNT the failure mode is based on cracks between and around carbon fibers, while for interlayers with CNT contents between 136 mg and 185 mg cracks were spotted on fibers and inside the CNT/matrix mix. Finally, the third failure mechanism is based on carbon fiber breakage, as a strong interface between CNT/matrix mix and carbon fibers is observed.

Bending investigation on carbon fiber/epoxy composites nano-modified by graphene

An extreme conditions situation, e.g. pre-salt deep sea exploration, requires new materials with even better performance. Nanotechnology is the new paradigm that can lead to the development of these new super materials. The effect of graphene pileups dispersion into carbon fiber/epoxy composites was investigated experimentally. The dispersion process was based on sonication and high shear mixing. XRD and SEM indicate that although the dispersion process can lead to exfoliated nanostructures, there is a saturation limit for the epoxy system, around 0.5 wt. %. The addition of graphene to carbon/epoxy composites seems to have no influence into stiffness, as the slopes of the stress-strain curves were near constant for all specimen tested. The bending strength, however, was heavily influenced by formation of graphene pileups into epoxy matrix and its dispersion around the carbon fibers. The increase on bending strength from 623.01±70.16 MPa (control samples) to 1259.92±61.73 MPa for 0.5 wt. % graphene addition represents an average improvement of 102%. This can be attributed to changes on failure mechanism, moving from intra-laminar failure to a mix failure mode where inter- and intra-laminar failure are combined in a zigzag pattern. A possible explanation for such behavior is the formation of strong bonds at the fiber/matrix surroundings due to nanostructures formation.

MODELING RECYCLED POLYMERIC MATRIX COMPOSITES: A SOCIAL-ENVIRONMENTAL SOLUTION

Municipalities are increasingly concerned about a 25% increase in plastic waste generation per year while the landfill cost is also increasing at a 7.5% annual rate. One possible solution to such a problem is the recycling procedure. The purpose of this paper is drawing the potential use of fully recycled melt-blended matrices in polymeric matrix composites, and its application for the construction of low cost houses in developing countries. To achieve such a goal a two-step homogenization procedure is proposed. The melt-blended matrix is homogenized by applying the concentric spheres model under weak interface condition and the linear functional of transformation. The overall composite effective properties are estimated from the composite cylinder assemblage model under weak interface condition for each lamina. Finite element simulation of beam problem is performed to evaluate the possible application of recycled polymeric matrix composites into the construction of low cost houses; the results are compared against conventional materials.

Food mechanics: a new device for testing fruits and vegetables

The new mechanical device developed is capable of performing compression tests but also bending, torsion and tensile tests. Its measurement system has the following components: a load cell (0 to 9800 N), a strain gauge signal conditioning board, a plug-in general purpose data acquisition board, and a displacement sensor (0 to 29.7 mm). These components are connected to a personal computer that has specially developed software. The load cell consists of four extensometers, which are sensible to compressive load. The signal conditioning board filters and amplifies the signal, which is acquired by the AD converter, making this information available to be processed by the software. The device is powered by a DC motor (12 to 24 Volts). By setting the motor voltage, it is possible to control its rotation. The displacement sensor was made with a sliding potentiometer, which is pushed by the mobile component of the device while the tests are performed. Finally, the software provides the stress-strain diagram for each test. In order to guarantee reliable results, tests are made with cylindrical samples with same dimensions (radius and length). For the first set of tests, potatoes were studied. The test results for compressive showed an average value of 897.64 kPa. This value seems to be compatible to the ones from the literature. The device proves to be reliable. Moreover, its flexibility allowed testing a variety of fruits and vegetables under compression, tension, torsion and combined loads.

The Influence of Intercalated Nanoclay Into Nanocomposites Impact Behavior

A new nanocomposite is prepared by cold direct mixing. To investigate how this new nanocomposite behaves under low velocity impact loads, a set of plates with 16 layers and 65% fiber volume fraction is manufactured by vacuum assisted wet lay-up. The fibers have a plain-weave configuration, while the epoxy system is ARALDITE M/HY956. The nanoclay is an organically modified montmorillonite ceramic and it is dissolved into the epoxy system in a 1%, 2%, 5% and 10% ratio in weight with respect to the matrix. X-ray diffraction tests indicate that rather than exfoliated, these nanocomposites are mostly in intercalated form, with possible presence of immiscible nano systems at 10% concentration. The impact tests are based on the ASTM D5628-01 standard. For the 20 joules impact energy condition, the energy absorption by delamination increases close to 48%, while for larger energies, i.e. 40 and 60 joules, the average improvement into energy absorption is around 15%. Even for larger energies close to total perforation, i.e. 80 joules, the use of nanoclays leads to an average increase in energy absorption of close to 4%.Copyright

Impact Analysis of NanoComposites

A new nanocomposite is prepared by direct mixing without heating procedure, which not only leads to a more homogeneous material but it also avoids epoxy resin deterioration by heat. To investigate how this new nanocomposite behaves under low velocity impact loads, a set of plates with 16 layers and 65% fiber volume fraction is manufactured by vacuum assisted wet lay-up. Fibers have a plain-weave configuration with density of 200 g/m, while the epoxy resin system is made of diglycidyl ether of bisphenol A resin with aliphatic amine as the curing agent. The nanoclay (Nanomer I30E) is an organically modified montmorillonite ceramic and it is dissolved into the epoxy system in a 1%, 2%, 5% and 10% ratio in weight with respect to the matrix. X-ray diffraction tests indicate that rather than exfoliated, these nanocomposites are mostly in intercalated form, with possible presence of immiscible nano systems at 10% concentration. The impact tests are based on the ASTM D5628-01 standard. The results have shown that for the four edges clamped condition not only the delamination and/or fiber damage phenomenon is reduced, but also the energy absorption is increased during the rebounds. Moreover, for the 20 joules impact energy condition the energy absorption by delamination increases close to 48%, while for larger energies, i.e. 40 and 60 joules, the average improvement into energy absorption is around 15%. Even for larger energies close to total perforation, i.e. 80 joules, the use of nanoclays leads to an average increase in energy absorption of close to 4%. Those results are very encouraging, especially when the amount of nanoclay is retraced to the composite total weight, i.e. 3.5 % maximum concentration.