This study investigates the hygrothermal aging effect on the tensile and impact behavior of flax/PLA biocomposites. Specimens underwent up to four weeks of conditioning at 40°C in a climate chamber with water. Analysis covered porosity, moisture diffusibility, and transversal microstructure, enabling assessment of tensile strength, tensile modulus, and impact performance in relation to moisture uptake and fiber orientation. The study of tensile properties revealed that at approximately 12% moisture content, stiffness and yield stress decrease, while strength remains constant. Moisture diffusivity is higher in warp and weft yarn directions than the out‐of‐plane direction. Tensile testing at environmental equilibrium moisture reveals greater stiffness in the weft direction, correlated with lower crimp percentage and yarn angle. The main contribution of the paper is the study of the influence of moisture on the impact behavior, the results show that energy absorption capability of flax/PLA biocomposite increases with moisture content. Highlights Fully biodegradable composite material by heat‐compression molding subjected to hygrothermal aging conditions for up to four weeks. The moisture diffusivity in both the warp and weft yarn directions registered higher values in comparison to the out‐of‐plane direction. Tensile testing at environmental equilibrium moisture revealed that the stiffness in the weft direction presented higher values. At 12% of moisture uptake, the stiffness and yield stress reached their lowest values, while strength remained constant. However, the low‐velocity impact properties of the composites exhibited improvement with moisture.
The goal of an engineer’s career is solving real problems for social and ecological betterment. At the University of Engineering and Technology (UTEC) in Lima, Peru, this vision is promoted from the earliest stages of a student’s engineering career to enable them to embrace their creativity while developing meaningful solutions for ecosystems in need. In this article, an educational methodology is presented that uses a project-based collaborative learning approach with the aim of evaluating, selecting and developing community-oriented engineering solutions in the Base of the Pyramid (BoP). Communication strategies and evaluation of projects based on co-design methods implemented among engineering students and isolated rural communities in the highlands of Peru are discussed. In conclusion, the process to select a community is analyzed and the most important criteria are determined. In addition, we highlight the importance of defining elements to understand the context (community and place) and to establish future objectives (group and projects) during the exploration period that will help facilitate the decision to select a community.
Interface failure plays an important role in determining the mechanical properties of composites [1]. We studied the effect of matrix-fiber interfacial bonding on the transverse bending properties of glass fiber reinforced polybutylene terephthalate (G/PBT) unidirectional (UD) composites. Six types of specimens were manufactured using three different processing methods, namely reaction-based resin, prepreg and commingled yarn systems. Transverse bending properties of the UD composites were measured. Further tension failure zone after the transverse bending test was examined using scanning electron microscopy (SEM) fractography analysis. Additionally, the composites quality was evaluated using complementary microscopic techniques (optical microscopy, OM and SEM).
On any industry where the natural fibers are used, chemical composition of the fibers is an important parameter to determine, since it allows to predict the product quality. On the other hand, TAPPI standard developed a well described methodology to determine the chemical composition; however, their methodology is time and resource consuming, and furthermore it requires well trained specialist. An alternative to determine the chemical composition is to use the true density, since the density of the fiber constituents are different. In this study, we present a clear relation between the true density and the three major constituents (cellulose, lignin and extractives) with the fitting parameter R > 90%, for the Stipa obtusa base fibers.
Cement production consumes enormous amounts of fossil fuels, generating significant CO2 emissions, seriously impacting the environment, and tons of rice hu
In the recent years, natural fibers are gaining an outstanding position as a reinforcement material, due to diverse advantages like high specific properties, low cost and low environmental impact. On the other hand, according to the market studies, in the next years the offer of the natural fibers will be in deficit; therefore, exploration of new natural fibers from new resources can be an alternative to fill this gap. Along the Andean region there are diverse natural resources from which cellulosic fibers can be extracted, like the Stipa obtusa grass, also commonly known as Ichu. The main purpose of this research was to determine the mechanical properties of unidirectional composite laminates made from Ichu fibers mixed with polyester resin; tensile, compressive and shear properties were evaluated. Results show that the stiffness in the principal direction (E 1 ∼ 16 GPa) and the transverse direction (E 2 ∼ 4.7 GPa) are over the average values compared to the composites made from the commercial fibers; similar behavior was observed in its shear and compression characteristics. Strength shows values around σ 1 ∼ 118 MPa, σ 2 ∼ 13 MPa, τ 12 ∼ 46 MPa and τ 21 ∼ 18 MPa, which is similar to the values reported in the literature for the commercial natural fiber composites. Based on these results, the Ichu fiber has a great potential as a reinforcement in composites materials.
Among the different test methods to characterize the fibre/matrix interfacial shear strength, the fragmentation test is one of the most simple in terms of experimental setup and the amount of data that can be extracted from one single test. In this work, the fragmentation test method was implemented to assess the interface shear strength obtained for a single steel filament embedded in an unsaturated polyester resin.. The fragment lengths were discriminated and processed using the Kolmogorov-Smirnov and Chi-square fitting test methods showing that the fragment lengths correspond to the extreme statistical distributions. In addition, a very high shear strength (67MPa) of the steel/polyester interface was estimated using the Kelly and Tyson criteria considering the critical fragment length.
In the Andean regions, low temperatures (5 to −25°C) combined with the wind effect give the sensation of extreme cold. Besides, in the rural areas, dwelling structures are very rudimentary, being based on adobe walls and galvanized steel corrugated roofs. The combination of weather issues and construction without thermal insulation considerations put people in extreme living conditions. Using local and cheap natural fibers as thermal insulation is a great alternative especially to upgrade/refurbish rudimentary constructions. In areas above 3000m over sea level, natural fibers are vast and cheap (∼0.15USD/kg), especially fibers named “Ichu”. In this study thermal properties of natural fibers were characterized according to the ASTM C177. Results show that the thermal conductivity varies from 0.047 to 0.113W/mK, for mats with unidirectional oriented fibers, being fine Ichu which have the lowest values. For the fine Ichu fiber to be competitive in terms of cost per unit thermal resistance, fiber mat density were reduced, arranging the fibers randomly; results show a significant reduction in density, without increasing significantly the thermal conductivity. According to these results Ichu fibers have exceptional thermal insulation properties. Moreover, this is the first conducted study on the thermal performance of this natural Andeans fiber.
Hydrogen permeation of AF1410 steel membranes due to cathodic polarization using the Devanathan and Starchurski double cell (DSDC) with 0.1M H2SO4 
Fatigue crack initiation and growth process of model AA7075-T6 subjected to simulated marine environment and varying stress ratio is studied using acoustic emission technique.The results indicate a significant reduction in crack initiation and overall lifetime when specimens were tested in the presence of marine environment, while an increase in fatigue life was observed as a function of increasing stress ratio.SEM fracture surface analysis exhibited intergranular, transgranular and cleavage as modes of failure.In general terms, Cleavage fracture produce lower AE signal amplitude, whereas, transgranular tearing produces an increment of signals amplitude.However, the correlation between those modes of failure with the AE results can be cumbersome since the AE signals are highly dependent upon the loading and environmental testing conditions.
Results of hydrogen-assisted fatigue lifetime testing indicated a substantial but gradual increment in crack growth rate as a function of increasing hydrogen content. Hydrogen was introduced into both sides of the specimen simultaneously via galvanostatic charging. Extensive scanning electron microscope fractographic analyses revealed a clear shift in the modes of failure and changes in fracture surface morphology as a function of increasing hydrogen content. A methodology is outlined that can be used to predict fracture surface features as a function of applied stress intensity factor. A convenient deterministic model is proposed that seems to reasonably accurately capture the crack growth rate behavior under strain controlled testing conditions. In addition, successful application of acoustic emission technique to classify various cracking stages in full spectrum testing was performed on hydrogen charged samples.
Article COMPARATIVE STUDY OF HYDROGEN TRANSPORT BEHAVIORS IN ARMCO-FE AND AF1410 STEELS was published on August 1, 2007 in the journal Corrosion Reviews (volume 25, issue 3-4).
En este articulo se estudiaron los fenomenos que se producen en el sistema liquido-particula conformado por una mezcla de agua y granos de quinua, estando estos dentro de un tambor horizontal giratorio. Para tal fin se utilizo la metodologia de velocimetria por imagenes de particulas (Particle Image Velocimetry, PIV); para determinar el comportamiento de los granos durante el regimen estable de movimiento, obteniendo el campo vectorial de desplazamiento y velocidades de los granos. La velocidad angular (rpm) y la longitud de las paletas internas del tambor fueron consideradas en la evaluacion del flujo. Las pruebas experimentales mostraron una alta relacion entre la velocidad de giro del tambor y las velocidades promedio de los granos, forjando remolinos conocidos como vortices de campos cerrados (Re≤6000). Tambien se observo que el incremento de la longitud en las paletas logra aumentar la formacion de vortices elipticos, los cuales son dirigidos hacia el centro del tambor y colisionan entre si, formando los vortices hiperbolicos, lo que ocasiona que aumente la interaccion de los granos. Por otro lado, el aumento excesivo de la velocidad de rotacion inhibe la formacion de los vortices; debido al aumento de la aceleracion normal combinada con la inercia, lo cual sobrepasa el efecto la accion de la gravedad sobre los granos.
The study of hydrogen permeation behavior in Armco-Fe showed that 0.1 M H2SO4 was a more effective medium for cathodic polarization compa
