F. Segovia

Influence of processing variables on mechanical characteristics of sunlight aged polyester–glass fibre composites

Abstract Unsaturated polyester–glass fibre reinforced composites have been exposed to sunlight radiation by means of special lamps. Tensile mechanical properties decrease with exposure time. The evolution fits a damped exponential model. Ageing degree varies between 15 and 56%, depending on composite and mechanical property. The influence of cure temperature, kind of resin and reinforcing fabric has been investigated. Toughness property losses are greater than strength ones. The kind of resin had a very small influence on losses in the orthophthalic polyester family. Higher cure temperature decreased losses, mainly in toughness properties. Fabric type showed no influence on strength properties losses but taffeta reinforcement showed higher loss of toughness properties.

Effects of Long-term Exposure on E-glass Composite Material Subjected to Stress Corrosion in a Saline Medium

This work provides an insight on very long-term degradation of polyester-fiber glass composites immersed more than 30,000 h in saline medium under service stresses. Samples were loaded under bending conditions with stresses both in the elastic and plastic fields, with the result that characteristics in a flexural mode were able to be determined and the ensuing decrease in characteristics was fitted to an exponential model. The degree of losses ranged from 25 to 31% for the bending modulus, from 28 to 35% for the flexural strength, and from 40 to 51% for the specific fracture energy. The most notable losses were for specimens immersed in artificial sea water under a continuous stress of 140 MPa, corresponding to the plastic behavior of the material. Although the existence of matrix plasticization is doubtful, the osmotic effects of the diffusion on the matrix and the junction to the fibers, the presence of microcracks, and the effects of chemical ions in the medium on the surface fiber composition became evident in the strength degradation of the material.

Surface Modification of Ti-35Nb-10Ta-1.5Fe by the Double Acid-Etching Process

Surface topography and composition influence the osteoblastic proliferation and osseointegration rates, which favor the biomechanical stability of bone anchoring and implants. In recent years, beta titanium alloys have been developed, and are composed of biocompatible elements, have low elastic modulus, high corrosion resistance, and mechanical properties to improve the long performance behavior of biomaterials. In the present research, the influence of the acid-etching process was studied in Ti6Al4V ELI and Ti35Nb10Ta1.5Fe. Samples were etched in a two-step acid treatment. Surface roughness parameters were quantified under a confocal microscope, topography was studied by scanning electron microscopy, and surface composition was analyzed with energy dispersive X-ray spectroscopy. The results revealed that the two-step acid treatment changes the topography of the β alloy, increases the surface area, and changes the chemical composition of the surface. Two differentiated regions were identified in the Ti35Nb10Ta1.5Fe alloy after the acid-etching process: The α + β region with higher values of mean roughness due to the lower chemical resistance of this region; and the β region with lower values of roughness parameters.