ABSTRACT The use of natural lignocellulosic fiber (NLF) biocomposites for the construction industry has been growing over the years, due to technical and environmental advantages. However, fiber-matrix incompatibility remains a major challenge. Various surface treatments have been investigated to improve fiber-matrix bonding, including sodium lignosulfonate (SLS), a potentially effective and environmentally friendly chemical. In this study, SLS treatment protocols were applied to piassava fibers to evaluate their influence on the fibers. Thermogravimetric Analysis (TG/DTG), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM/EDS), Fourier-transform Infrared Spectroscopy (FTIR), moisture absorption measurements and tensile tests were performed to characterize the modifications. Results demonstrated, for the first time, the efficiency of SLS to remove extractives from the piassava surface. In general, partial degradation of the cellulosic structure was observed, noticeable by the slight drop in crystallinity index (from 42.80 to 39.82%), and an increase in the TG residual mass (from 21.35 to 31.90%), along with changes in DTG curves. However, a particular SLS treatment using ultrasonic bath was able to fully clean the surface preserving the cellulosic structure, and increasing the strength of fibers (from 386 ± 140 MPa to 524 ± 126 MPa).

Shape memory alloys (SMA) are attracting considerable attention owing to possible applications from biomedical to aerospace. In particular, CuAlNi alloys present significant advantages associated with low cost, easy processing and superior thermo-electric conductivity over other SMAs such as the NiTi alloys. Characterization of some properties and structural changes caused by martensitic transformation are still open to investigation. The present work evaluated these characteristics in an as-cast plasma processed shape memory Cu-14wt.%Al4wt.%Ni, which was compression tested until fracture. Experimental results showed that an as-cast ingot presents not only chemical and phase homogeneity, but also microstructures composed of grains with martensitic morphology. Martensites β'1 and γ'1, as well as intermediary martensitic R and high temperature β1 were identified by X-ray diffraction tests. It was found that the compressive deformation does not interfere in the phase composition and martensite morphology. However, compression changes the volumetric fractions and crystallographic orientation of the martensites. The mechanical behavior is characterized by an apparent elastic response until the fracture. The fractured surface exhibits brittle aspect like "river patterns" and evidence of intergranular rupture.

Due to increasing improvement of weaponry and ammunition, attention is being given to the development of new materials that could more effectively resist to ballistic impact. In order to stop high energy bullets, with speed above 800 m/s, a high strength material is necessary. However, if just one material is used, then a relatively thick piece is required, which might affect negatively the wearer mobility. The objective of this work is to investigate the effect of thickness on the ballistic behavior of aramid fabric laminates, Kevlar®, hit by high energy bullet. The purpose is to find the minimum thickness to avoid perforation. Ballistic tests using conventional 7.62 mm ammunition were performed according to standard procedures. The macro and microscopic aspects of the target specimens were evaluated. The results showed a change in the ballistic behavior of the laminates as their thickness increased. It was found that until the laminate was able to capture the bullet, 96 layers (~50 mm) were required. This is significantly higher than the necessary thickness for a multilayered armor to stop the same 7.62 mm bullet.

Stainless steels are well known by their corrosion resistance. The austenitic types, in particular, are also applied as structural components in engineering systems operating at high temperatures such as nuclear reactors, petrochemical furnaces and turbines. For these applications operational temperatures may go up to 800ºC. Under constant load applications the main mechanism of failure, which would limit the material's life, is creep. In the present work creep parameters were evaluated in the high temperature interval of 600 to 800ºC for an AISI 316 austenitic stainless steel. Dislocation substructures were observed by transmission electron microscopy in creep ruptured specimens. Two distinct mechanisms of dynamic strain aging and dynamic recovery associated with different values for the power law exponent n and the Arrhenius activation energy Q for creep were verified below and above 700ºC, respectively.

The interval of existence of dynamic strain aging (DSA) in AISI type 304 austenitic stainless steel subjected to quasi-static tension tests, under strain rates from 3.5 x 10-2 to 3.5 x 10-4 s-1, in the temperature range from 25 to 800ºC was investigated. It was found that DSA occurs in the range extending from around 200 to 700ºC. Plastic instabilities associated with serrations, Portevin-Chatelier effect, allowed activation energies to be calculated and a possible mechanism of dislocation interaction with interstitial carbon atoms to be proposed. Significant increase in the ultimate strength, uniform elongation and work hardening demonstrate that DSA is a relevant phenomenon, which improves the high temperature mechanical properties of 304 steel.

The urban violence and the different types of global armed conflicts demand efficient protective systems against high energy ammunition. Multilayered Armor Systems (MAS) provide efficient protection by making use of lighter and more efficient materials. A typical MAS may be composed of three layers: a front ceramic followed by a composite, backed by a ductile metal. Polymer composites reinforced with natural fibers have proven to be effective second layers, being also lighter, low-cost and environmentally friendly as compared to conventional composites like KevlarTM. The present work evaluates MAS using as second layer polyester composites reinforced with 10, 20, and 30 vol. % of sisal fibers. Ballistic tests were performed using class III 7.62x51 mm ammunition, based on the NIJ 0101.06 backface signature methodology. Both the 30 vol.% sisal fiber composite and the conventional aramid laminates were equally efficient in terms of MAS second layer. The explanation might be the similar capacity of the different composites to retain the fragments generated by the interaction of the projectile with the front ceramic, independently of the percentage of sisal fibers.