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This paper describes the development of electrically insulating hybrid steel–composite cross-arm for medium-voltage overhead distribution power lines with three conductors. The main goal was to achieve substantial weight savings compared to a common steel cross-arm with three ceramic insulators widely used in the Czech Republic. The structure has been designed as a combination of two main composite components – a pultruded horizontal profile and a braided vertical conical tube. These components are connected by a steel locking component which also serves for attaching the whole cross-arm to common concrete utility poles. The hybrid cross-arm is conceived to insulate electrical current in the default configuration thanks to the properties of the glass fiber reinforced composite materials, yet additional insulating elements can be used to further increase the electrical insulation distance. The materials and components used for the construction are chosen by combining finite element simulations of mechanical and electrical behavior with experimental testing and verification of important characteristics on selected substructures. The final design of the cross-arm is then manufactured and subjected to long-term testing in real-life environmental conditions. The achieved reduction of weight exceeds 50% while maintaining the mechanical rigidity and strength of the steel solution as well as the required insulation properties. The future trend of the cross-arm development is aiming at the weight reduction and increase of manipulation capabilities resulting in lowering many additional costs. In this work the designed cross-arm has half the weight of the original one. [ABSTRACT FROM AUTHOR]

Abstract The effect of impact load with low velocity in thin-walled plates and profiles has been investigated. The paper deals with the relation between damage propagation, size and shape as a function of boundary conditions, layer arrangements and impact energy. The structures under consideration were made of eight-layer Glass Fiber Reinforced Polymer (GFRP) laminate with a quasi-isotropic, quasi-orthotropic and angle ply arrangement of layers. The standardised plates predefined to CAI tests and channel section profiles have been subjected to impact load. Based on the performed tests, the impact characteristics have been obtained and compared with the theoretical model (one degree of freedom mass-spring system). Further, despite it not being mentioned in the ASTM 7136 standard, characteristic curves were identified. It was noted that the impacts introducing matrix damages and the partial fracture of the fibres significantly change the course of the Force-Time histories, particularly after the maximum impact force is reached. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the feasibility of improving structural performance of composites in the presence of stress concentrators. Matrix grading through local deposition of additive-enhanced matrices and fibre steering by varying fibrous architecture are examined independently and in combination on a glass-fibre triaxial braided composite subjected to open hole tensile test. Stiffened and toughened matrices were incorporated through precise point-wise injections of liquid reactive resin into dry preforms (Liquid Resin Printing). Fibre steering was implemented by varying the braiding angle along the length of the braided sleeve. It has been shown that these novel forms of architecture modification enable a significant improvement in composite strength through a variety of deformation mechanisms. This includes local stiffening of composite in the direct vicinity of the stress concentrator and damage accumulation away from the stress concentrators. The experimental observations are explained by using simple finite-element models. [ABSTRACT FROM AUTHOR]

Composite materials provide high strength and stiffness-to-weight ratios and adjustable directional material properties. As a result, a growing application of composite materials in weight-relevant and complex-loaded structures is noticeable, especially, for the production of high-speed rotors. However, their material complexity, their parameter scatter and unpredictable impact events contribute to the prediction uncertainty of the operational capability. The in situ measurement of damage-sensitive features can provide information for reliable simulation models. Such models are a prerequisite for the analysis of the damage behaviour in practice-relevant loading scenarios. For this purpose, a novel optical measurement system is introduced measuring the rotor deformation. The system offers a measurement rate of 1.6 kHz with an 7 μm error independent on the rotational speed. Furthermore, the rotor vibration response was identified using a combined excitement-measurement system for different rotational speeds. Both measurement systems were successfully applied on a glass fibre-reinforced composite rotor. Based on the experimental results, a simulation model was adjusted using an advanced mixed numerical–experimental technique. A good compliance between experimental and simulation results was identified for rotor-typical stress states. In addition, the rotor temperature is shown to have a significant influence on the model accuracy and has to be incorporated in future models. [ABSTRACT FROM AUTHOR]

Abstract: In this study, edge-cracked aluminum plates repaired with one-sided composite patches were investigated experimentally for their response to Charpy impact test. Two different materials were used for composite patches, in one the reinforcement was woven glass–fibres while the other had woven carbon fibres as the reinforcement. Further, in each case, two lay-ups were used, viz. 3-ply and 5-ply. Also, the aluminum specimens had edge-cracks of three different lengths. In each case, the energy absorbed during the impact test, when the specimen had a crack of known length and reinforced with patches, was determined and compared with the energy absorbed during impact of the corresponding specimen without crack. It was observed that for a given crack length, the 5-ply patch of carbon fibres performed better than all other patches. For example, when the ratio of the crack length to the specimen width, i.e. l/w is 0.5, the percentage of the absorbed energy for the specimen repaired with 5-ply carbon fibre patch is 2-times as compared to the specimen repaired with 5-ply glass–fibre reinforced patch. [Copyright &y& Elsevier]

Abstract: The influence of laminate thickness on the resistance to repeated low energy impacts of glass, carbon and aramid fabrics reinforced composites, was evaluated for two levels of energy of impact. The results obtained show that below a certain energy level the cross section of the laminate is the most relevant variable that determines the impact resistance. Under these conditions the experimental points of all tested laminates fall on a single curve, irrespective of the reinforcing fiber used. When the energy level of the impactor is increased, fiber characteristics became relevant. The glass fabric reinforced composite showed the steepest increase on the impact resistance with increasing laminate thickness. This behavior was attributed primarily to the higher areal coverage of the glass fabric used. The isotropic behavior of glass fibers in relation to the anisotropic character of aramid and carbon fibers was also of relevance. A quadratic equation was shown to provide a best fit to the experimental points, and the coefficient of the quadratic term was shown to reflect the increase of the impact resistance with laminate thickness. [Copyright &y& Elsevier]