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In the forging industry, surface quality and surface treatments of dies are crucial parameters to extend their life. These components are usually machined by milling or by Electrical Discharge Machining (EDM), and the final surface roughness depends on the machining techniques and operational conditions used in its fabrication. After milling, a nitriding treatment is widely applied to extend its service life. Nevertheless, no scientific report that informs about nitriding after EDM has been found. Accordingly, this work focuses on the wear and friction behavior of pins made of brass and medium carbon steel sliding over AISI H13 discs, made by wire EDM in the conditions of finishing and roughing. The discs are plasma nitride, and their effect on the wear during pin-ondisc tests is evaluated. In this sense, the analysis of the surface damage for the different pins will help us to understand the service life and wear evolution of the forging dies. The results show that plasma nitride reduces the friction and prevents the degradation of the pin, independently of the material of the pin, when sliding over finishing and roughing EDM conditions., This work is supported by the National Agency for Research and Development of Chile (ANID)— grant number: 3180006 and the Serra Húnter program (Generalitat de Catalunya)—reference number UPC-LE304 (2018)., Peer Reviewed, Postprint (published version)

El TFG té com a objectiu estudiar la influència que té el pretensat dels teixits de materials tipus Fabric-Reinforcement Cementitious Matrix (FRCM) a diferents nivells de càrrega sobre les propietats mecàniques del material compost, Recerca bibliogràfica sobre la tecnologia a estudiar (FRCM), el disseny, planificació i execució d’una campanya experimental; l’anàlisi crític dels resultats i la redacció d’una memòria

The goal of the present work is to characterise the influence of static prestrain on the elastic and dissipative properties of constrained viscoelastic films. Dynamic mechanical analysis (DMA) technique is considered for measuring the dynamic properties under several static prestrain levels, and a new material constitutive model is presented for characterising the frequency–prestrain dependence of the viscoelastic material. The results indicate that the static prestrain strongly affects the elastic and dissipative properties of the analysed viscoelastic material. The proposed material constitutive model properly describes the frequency–prestrain dependence of the tested viscoelastic material., Peer Reviewed, Postprint (published version)

Se caracterizan por DMTA espumas de policarbonato (PC) y de policarbonato con nanopartículas de grafeno, producidas mediante dos procesos diferentes de disolución de CO2 supercrítico con posterior expansión en una o en dos etapas. Se analizan los efectos derivados de la presencia del grafeno en el PC, así como la influencia de la densidad relativa de la espuma y de sus características morfológicas y microestructurales sobre su respuesta elástica y viscosa. De modo general, el módulo de almacenamiento específico se ve mejorado en las espumas de PC con la incorporación del grafeno. Por lo que respecta a la componente de disipación viscosa, existen sendas relaciones entre la posición e intensidad del pico de tand, asociado a la transición vítrea del polímero, con la densidad relativa. No obstante, estas relaciones se ven modificadas al cristalizar el PC durante la espumación, ya que la presencia combinada de grafeno y CO2 induce la cristalización del polímero., Postprint (published version)

Electrical discharge machining (EDM) provides an effective means of shaping hardmetals. However, it is also known that surface integrity of these materials may be affected by EDM, degrading their tribomechanical characteristics. This work focuses on assessing the use of two different surface modification routes: thermomechanical treatments (shot blasting, polishing and final high temperature annealing) and/or physical vapor deposition of hard coatings, for improving the fracture and fatigue strength of an EDM-shaped fine-grained hardmetal grade. In doing so, an optimal EDM's surface finish variant and a diamond ground and polished one are used. Mechanical behavior is evaluated under four-point bending and fatigue characterization is given in terms of fatigue limit following the staircase method. Experimental results indicate that both approaches markedly decrease the lessening effect of EDM on the mechanical strength of hardmetals, although a complete fracture and fatigue strength retention is only achieved by combining both of them. The improved mechanical behavior is rationalized on the basis of the beneficial changes induced by surface modification on the effective residual stress field at the surface of EDM-shaped hardmetals, as assessed by a linear elastic fracture mechanics analysis combined with fractographic examination., Postprint (published version)

Microcellular injection-molding technology is capable of producing lightweight polymeric products. The foam morphology is determined by the injection-molding parameters, and it has been observed that depending on the parameter variations, the cell structure may exhibit substantial morphological differences through the entire section along the melt flow direction of the injected part. The effects of varying injection-molding parameters on foam morphology and thermal mechanical properties of a multiphase ethylene-propylene block copolymer (EPBC) were tested on 5-mm plaque specimens using a constant temperature profile. It has been found that injection speed does not have a significant effect on the thermal-mechanical properties of the foam, whereas shot volume and mold temperature do have a significant influence. Low shot volume produces uniform density cellular structures and larger cores, whereas lower mold temperatures help maintain small cell sizes. Furthermore, the effect of the copolymer’s crystalline phase on foam morphology has been observed. This study identifies the achievable foam morphologies and the thermal-mechanical performance of cellular molded EPBC parts., Postprint (published version)

The aim of this paper is to analyze the influence of the nature of the orthodontic archwires on the friction coefficient and wear rate against materials used commonly as brackets (Ti–6Al–4V and 316L Stainless Steel). The mate- rials selected as orthodontic archwires were ASI304 stainless steel, NiTi, Ti, TiMo and NiTiCu. The array archwire’s materials selected presented very similar roughness but different hardness. Materials were chosen from lower and higher hardness degrees than that of the brackets. Wear tests were carried out at in artificial saliva at 37 C. Results show a linear relationship between the hardness of the materials and the friction coefficients. The material that showed lower wear rate was the ASI304 stainless steel. To prevent wear, the wire and the brackets have high hardness values and in the same order of magnitude., Peer Reviewed, Postprint (published version)

In this paper LDPE/silica nanocomposites are foamed by two different processes. First one is the pressure quench method which is based on the use of a physical blowing agent and second one is the improved compression moulding technique. As the latter process uses a chemical blowing agent, both types of foamed nanocomposites will provide very useful information about the relationship between foaming process-microstructure and macroscopic properties. Results have revealed how silica nanoparticles are able to act as nucleating sites during foaming step in both processes; however, the optimum amount of particles strongly depends on the foaming route. Thermal and mechanical properties of solid and foamed nanocomposites have been analyzed by means of thermogravimetric analysis and compression tests. Results have revealed that nanosilica particles act as effective nucleating agents, not only reducing cell size and increasing cell density but also achieving more homogeneous cellular structures. Thermal and mechanical properties are improved due to the presence of silica nanoparticles. It has been found that the improvement degree reached for samples produced using chemical blowing agents is greater than that achieved for samples produced using physical blowing agents., Peer Reviewed, Postprint (published version)

Dos tipos de espumas flexibles de baja densidad . basadas en polipropileno y producidas por dos métodos diferentes de espumación (espumación física y espumación química) .se han caracterizado utilizando el concepto del trabajo esencial de fractura (EWF), con particular atención a la influencia de la densidad relativa de la espuma y a su estructura celular en los valores de los parámetros característicos. Se ha propuesto un procedimiento de corrección basado en la relación de expansión de la espuma y en la estructura celular, con el objetivo de tener en cuenta su complejidad estructural en los parámetros de fractura . Se encontraron diferencias significativas en los parámetros del EWF entre los dos tipos de espumas producidas por métodos diferentes, derivados de las diferencias en su estructura celular (tamaño, número y orientación de las celdas). En general. el término esencial específico de fractura se vio incrementado con la densidad celular de las espumas, principalmente en las espumas con una orientación celular predominante en la dirección del flujo de extrusión. En ambos tipos de espuma, los valores de los parámetros de fractura resultaron considerablemente inferiores en dirección perpendicular al flujo de extrusión. mostrándose así que el comportamiento de fractura de estos materiales resulta considerablemente anisotrópico, como consecuenci a de su estructura celular., Peer Reviewed, Postprint (published version)

In the present work polyurethane foams containing variable concentrations of nano-sized clay and esparto wool were prepared and studied, with the objective of developing new multi-scalar rigid foams. The addition of montmorillonite clay favoured foaming and the formation of finer and homogeneous cellular structures, resulting in foams with compressive elastic moduli and collapse stresses lower than that of the polyurethane foams. Nevertheless, a comparative analysis versus the foams’ relative density demonstrated that both properties follow one single trend for the two materials. The combination of esparto and montmorillonite further reduced the cell size of foams, at the same time promoting higher open cell contents, resulting in the foams with the lowest mechanical properties. Although no important differences in thermal conductivity were found with adding montmorillonite, its value decreasing with reducing the relative density, the incorporation of esparto led to higher thermal conductivities, independently of the relative density. The combination of esparto and montmorillonite resulted in foams with thermal conductivities halfway between the esparto-reinforced and the montmorillonite-reinforced foams, related to a higher open cell content., Peer Reviewed, Postprint (published version)

Low-velocity impact properties of shape memory alloy (SMA) wires and carbon fi ber reinforced poly (butylene terephthalate) obtained by resin transfer molding were characterized. At the subcritical regime the dissipated energy is not affected by the presence of the wires. However SMA has a positive effect on the maximum absorbed energy, since the maximum allowable load is higher. The contribution of the SMA wires to the higher impact performance of the hybrid composite is suggested to be due to their energy absorbing capability, and also to the high reversible force that acts as a healing force., Peer Reviewed, Postprint (published version)