The fique is a plant typical of the Colombian Andes, from which relatively common items are fabricated. One of these is woven fabric extensively applied in sackcloths. The mechanical strength of fique fabric have motivated recent investigations on possible reinforcement of polymer matrix composites. For this purpose its thermo-mechanical behavior was unveiled. In particular, dynamic mechanical analysis (DMA) of fique fabric reinforced polyester matrix composites disclosed improved viscoelastic behavior in association with change in the glass transition temperature. The present work extends this investigation to epoxy matrix, which is one of the most employed thermoset polymer for composite matrix. Fique fabric volumetric fractions of up to 50% are for the first time incorporated into epoxy composites. It was found that these incorporations significantly increased the viscoelastic stiffness of the composite, given by the storage modulus (E’), in the temperature interval from -50 to 170°C. An accentuated softening in viscoelastic stiffness was revealed for all composites above 75°C. Peaks in both the loss modulus (E”) and tangent delta (tan δ), respectively associated with the lower and upper limits of the glass transition temperature, were shifted towards higher temperatures with increasing amount of fique fabric.

Firearms threat has always been a matter of personal concern, especially to soldiers in armed conflicts as well as police officers and civilians involved with public security. A multilayered armor system (MAS) is intended to personal protection against high kinetic energy ammunition, such as that used in rifles. MAS layers are normally composed of a front ceramic followed by a layer that must show both high impact resistance and low weight. Usually, synthetic fiber fabrics, such as aramid in Kevlar® and ultra-high molecular weight polyethylene (UHMWP) in Dyneema® are commonly used as the second layer. Currently, composites reinforced with natural fibers are also being considered as second MAS layer due to their good performance associated with the advantages of being cheaper and environmentally friendly. The fique is a relatively unknown natural fiber extracted from leaves of a plant native of South American Andes. In the present work, fique fibers and fique fabrics incorporated in polyester composite plates with volume fraction of 10, 20 and 30% were ballistic tested. The calculated projectile loss of energy indicated a relatively large energy dissipation by the composite. The tested specimens were statistically treated by the Weibull analysis and were examined by scanning electron microscopy.

Ramie (Boehmeria nivea) fiber is one of several lignocellulosic fibers with superior strength, but the least investigated, particularly as reinforcement in strong, tough polymeric composites. This paper presents mechanical properties for polyester reinforced with aligned ramie fibers up to 30% by volume. It was found that adding 30 vol% of ramie fibers increases the flexural strength of polyester about three times (212 ± 12 MPa vs. 63 ± 7 MPa) and tensile strength by a factor of two (89 ± 9 MPa vs. 53 ± 3 MPa). Polyester-ramie fiber composites also displayed a significant improvement in toughness. The impact energy values, as measured by Charpy and Izod impact tests, increased nearly two orders of magnitude for 30 vol% ramie fiber composite as compared to neat polyester. Additionally, fractographic studies revealed reasonable wetting of fibers by the polyester resin, and FTIR analysis confirmed a hydrophilic nature of ramie fibers. In spite of weak adhesion between hydrophilic fibers and hydrophobic matrix, composites of improved strength and toughness were demonstrated in this study. Limited fiber-matrix adhesion was reflected in preferential longitudinal propagation of cracks along the fiber/polyester interfaces, indicating also that most of the fracture area is associated with the fiber surface.

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.

Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.