Poly(urea-formaldehyde) (PUF) microcapsules filled with dicyclopentadiene (DCPD) were prepared by in situ polymerisation and the effect of synthesis parameters, such as pH of the solution and agitation rate, on microcapsules size and shell thickness was evaluated. Scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR) were performed. Adjusted pH conditions (pH ¼ 3.5) and agitation rate (1350 RPM) were found using a design of experiments (DOE). SEM results indicated that microcapsule size was directly affected by agitation rate, whereas shell thickness was mostly affected by pH. After obtaining adjusted synthesis conditions, microcapsules presenting mean size of 60 mm and mean shell thickness of 4 mm were embedded in an epoxy matrix for evaluating the self-healing effect. FTIR and SEM analyses in damaged samples suggested that a healing agent was delivered to the crack location.

Composites are often employed as repair materials for steel pipelines in the oil industry. Nevertheless, it is known that polymer matrix composites age through service life due to exposure to environmental factors, leading to a decrease in the durability of these repairs. In this work, alterations in glass fiber–epoxy composites aged for 1440, 2880, and 4320 h were studied in two different aging conditions: an accelerated aging chamber (with alternate cycles of exposure to ultraviolet [UV] radiation and water condensation) and immersed in salt water. The effects of aging in the material were evaluated by Fourier‐transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), lap‐shear tests, permeability analysis, and scanning electron microscopy (SEM) and in terms of mass variation. The results show that chemical changes, as well as alterations in mass and fiber exposure, increases in glass transition temperature and permeability, and more pronounced debonding composite/metal after lap‐shear tests, as compared to unaged materials, occurred. In general, the cycles of UV and water condensation were found to be more harmful to the material than aging in salt water, for the same exposure period.

This study aimed to analyze the damage tolerance of a carbon/epoxy composite laminate (AS4/8552) impacted at low velocity, relating residual strength values with the impact energy and delaminated area. AS4/8552 laminated plates [0°3/90°/±45°]S were submitted to low-velocity impact tests with three energy levels: 30 J, 45 J and 74 J. Next, the test specimens were analyzed by X-ray computed tomography to check for cracks and delaminations, and compression after impact (CAI) tests conducted to assess their residual strength. The results indicate that above the minimum energy level of low-velocity impact to cause damage, the residual strength of the laminate may be related to the delaminated area.

A novel family of composite laminates with a simplified stacking sequence and double-double layup [±ϕ/±ψ] n has significant potential to reduce weight and increase strength, while facilitating design optimization and simplifying the manufacturing process. In this study, the low-velocity impact response of a double-double (DD) laminate and a quadriaxial (Quad) laminate of equivalent stiffness and thickness were compared. Carbon/epoxy laminates were produced with stacking sequences of [±0/±50]10 and [03/90/±45/02/±45]2S corresponding to double-double and quadriaxial varieties, respectively. Low velocity impact tests were conducted at 74 J of energy and damage areas were examined using X-ray computed tomography. Compressive strength and compression after impact (CAI) strength were equivalent for the two laminates. However, differences in impact damage morphology were observed and are discussed.