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Abstract Bis-maleimides (BMIs) exhibit healing functionalities on polymer level. In the current investigation, BMI self-healing (SH) resin based on Diels-Alder (DA) reaction mechanism (identification code: BMI pp) was integrated into high performance aerospace carbon fiber reinforced plastics (CFRPs). The effect of BMI pp as self-healing agent (SHA) into CFRPs is assessed. More precisely, open-hole reference and BMI pp modified CFRP samples having [45/-45/0/90] 2S stacking sequence, with similar fiber volume fractions have been tested under quasi static tensile and tension-tension fatigue loading conditions. According to quasi static experimental results, it was shown that the incorporation of the BMI pp SHA did not deteriorate the in-plane mechanical properties of the entire composite. In addition, tension-tension fatigue tests revealed that the incorporation of the BMI pp SHA into composites architecture made composites to slightly extend their fatigue life. Finally, the activation of the healing functionality of BMI pp modified composites at certain number of fatigue cycles significantly extends their fatigue life of about 75%. For all fatigue tested material sets a three-stage pattern of stiffness degradation was observed. [ABSTRACT FROM AUTHOR]

The electrical conductivity of the dry carbon fibre multidirectional thin layers (without resin matrix material) can be expressed by an equivalent EC tensor. The flow of the electric current inside the material is depended, mainly, upon the material’s microstructure and specifically upon the interlaminar microstructure. In the case of the multidirectional carbon fibre composites, two different methodologies were used in order to elucidate the EC behaviour of the multidirectional laminates both quantitatively and qualitatively. The first experimental setup was used in order to compare the measured electrical resistance to the calculated equivalent EC tensor. Also, the temperature field changes according to the equivalent EC tensor of each laminate and the second methodology was utilized in order to elucidate the validity of equivalent EC tensor indirectly, comparing the temperature field of the electro-thermal numerical models and the measured temperature field. [ABSTRACT FROM AUTHOR]

The preparation procedure of epoxy and benzoxazine multi-walled carbon nanotube buckypaper composites is described. The morphology of the buckypaper is characterized by scanning electron microscopy and porosimetry, revealing a non-uniform porous structure. The wetting behavior of epoxy and benzoxazine resins in the buckypaper surface is studied by contact angle measurements. Scanning electron microscopy photographs of the composites obtained by infiltration of the buckypaper with epoxy and benzoxazine resins and subsequent curing reveal that a good impregnation is achieved. Thermal conductivity results reveal higher values for pristine buckypaper than for the composites, which is explained by the extremely small thermal conductance of the nanotube–polymer interface. The thicker resin layer surrounding the nanotubes observed in the buckypaper/epoxy composite justifies its lower conductivity, as compared with the buckypaper/benzoxazine composite. [ABSTRACT FROM AUTHOR]

The present work deals with the development and verification of a set of analytical solutions for the bearing failure of single lap composite joints, which are applied on a composite joint tested experimentally. The stress field originating from the solution is calculated and progressive failure criteria are applied, verifying their applicability as a fast way of calculating bearing failure of a joint. Additionally, the extracted stress field from the results is introduced as a load to the finite element model of the joint under evaluation, and the equivalency of this method is compared and proven against typical implicit non-linear contact analysis. The major advantage of the proposed methodology is that the highly non-linear contact problem is circumvented using the stress distribution at the hole boundary as an actual load and thus transforming the analysis to a linear one, providing considerable agreement to the exact high-cost numerical solution. [ABSTRACT FROM AUTHOR]

Abstract: Conductive fibrous porous materials present strong anisotropy in electrical conductivity. The electrical conductivity of continuous carbon fiber composites is a function of carbon fiber electrical conductivity, fiber direction, preform thickness, fiber volume fraction, length to width ratio and temperature. Along the fiber direction, the conductivity of the composite depends upon the carbon fiber conductivity and on the fiber volume fraction. In the transverse to the fiber direction, the electrical conductivity of the unidirectional (UD) preform depends upon the random fiber-to-fiber contact. The aim of this study is to develop a robust methodology for the prediction of the electrical conductivity of UD carbon preforms taking into consideration material properties and geometrical parameters (fiber direction, length to width ratio) at a given temperature, under constant and uniform pressure. The variation of electrical conductivity as a function of preform thickness (number of plies) for different fiber direction was also investigated. Finally, a mathematical expression was extracted that correlates the preform electrical conductivity to the thickness, length to width ratio and fiber direction. Predictions using the mathematical expressions are in excellent agreement to the measured experimental data. [Copyright &y& Elsevier]