Showing papers by "Giuseppe Catalanotti published in 2017"

The effect of the through-the-thickness compressive stress on mode II interlaminar fracture toughness

Abstract: Abstract The effect of through-thickness compressive stress on mode II interlaminar fracture toughness is investigated experimentally and replicated numerically. The modified Transverse Crack Tensile specimen recently proposed by the authors is used, together with an experimental device designed to apply a constant transverse compressive stress on the surface of the specimen. Experiments are conducted using IM7/8552 specimens for different compressive stresses, ranging from 0 to 100 MPa, covering all the practical applications commonly encountered in the aeronautical industry (e.g., tightened filled holes or bolted joints). It is shown that mode II interlaminar fracture toughness increases with the applied compressive through-thickness stress. Finally, experiments are replicated using appropriate numerical models based on cohesive elements that take into account frictional effects. A good agreement between numerical predictions and experiments is found.

Synthesis and testing of a conducting polymeric composite material for lightning strike protection applications

Abstract: Lightning strike protection is one of the important issues in the modern maintenance problems of aircraft. This is due to a fact that the most of exterior elements of modern aircraft is manufactured from polymeric composites which are characterized by isolating electrical properties, and thus cannot carry the giant electrical charge when the lightning strikes. This causes serious damage of an aircraft structure and necessity of repairs and tests before returning a vehicle to operation. In order to overcome this problem, usually metallic meshes are immersed in the polymeric elements. This approach is quite effective, but increases a mass of an aircraft and significantly complicates the manufacturing process. The approach proposed by the authors is based on a mixture of conducting and dielectric polymers. Numerous modeling studies which are based on percolation clustering using kinetic Monte Carlo methods, finite element modeling of electrical and mechanical properties, and preliminary experimental studies,...

Studies on the effects of lamina thickness and orientation on the shear response of composite laminates

Abstract: With the growing application of carbon-fibre reinforced polymers (CFRPs) in lightweight aerospace and transportation structures, it is essential and urgent to develop a comprehensive understanding of their response under various loading conditions to determine the design constraints. Under longitudinal tensile and compressive loading, the material behaviour is dominated by the fibre and presents a predominantly linear response. In contrast, transverse and shear loading may result in large nonlinear deformation prior to polymer matrix damage. Compared to fibre dominated behaviour, a response dominated by the matrix under shear loading can considerably limit the load-bearing capability and restrict the utilisation of composite materials. In the design of composite structures, lamina thickness and orientation are specified to meet the requirements of the working environment. In order to attain a detailed comprehension of the shear response of these parameters, an investigation into the effects of lamina thickness and orientation on the shear response of composite laminates was carried out in this work. Different ply thickness and ply orientation were represented by four composite lay-ups to characterise the material response of composite laminates under shear loading. The geometry of a V-notched rail shear specimen and testing method, presented in the American Society for Testing and Materials (ASTM) standard D7078/D7078M-05, was employed to perform the physical compact shear tests. A Digital Image Correlation (DIC) system was used to observe the strain evolution of the compact shear specimens. The load versus displacement and nominal stress versus strain curves were obtained from the experimental data. In addition, the nonlinear shear stress profile was defined using an exponential model based on the calculated nominal stress and measured strain. The shear modulus, shear strength and nonlinear shear response obtained from different composite lay-ups were compared. A good understanding of the relationship between shear response and lay-up thickness and orientation was achieved based on experimental and analytical results obtained in this study. Furthermore, the measured shear properties of the composite laminates were used to verify a high-fidelity computational damage model through the modelling of virtual v-notched rail tests. Good correlation was obtained between experiment and simulation results.

Structural response of aerospace-grade thin-ply woven and non-crimp fabrics

Abstract: The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained more interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements. In the present work, an experimental test campaign was carried out to study the structural response of aerospace-grade plain weave STFs of different areal weights, and NCFs with different levels of 0° ply blocking. The results show that multidirectional thin-STF laminates exhibit an improved tensile unnotched strength over the thick-STF laminate, and similar tensile notched strengths. In compression, the thin-STF laminate performed substantially better in both unnotched and notched configurations, but exhibited a similar bearing response. In the case of the thin-ply NCFs, the results show that, by grouping together the 0° plies in thicker blocks, an improved structural response was obtained on scaled coupons, as well as on mechanically fastened joints, without compromising the superior unnotched tensile and compressive strengths intrinsic to thin-ply laminates.