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Fibre metal laminates (FML) are the modern hybrid materials with potential wide range of applications in aerospace technology due to their excellent mechanical properties (particularly fatigue strength, resistance to impacts) and also excellent corrosion resistance. The study describes the resistance to low velocity impacts in Ti/CFRP laminates. Tested laminates were produced in autoclave process. The laminates were characterized in terms of their response to impacts in specified energy range (5J, 10J, 20J). The tests were performed in accordance with ASTM D7137 standard. The laminates were subjected to impacts by means of hemispherical impactor with diameter of 12,7 mm. The following values have been determined: impact force vs. time, maximum force and the force at which the material destruction process commences (Pi). It has been found that fibre titanium laminates are characterized by high resistance to impacts. This feature is associated with elasto-plastic properties of metal and high rigidity of epoxy - fibre composite. It has been observed that Ti/CFRP laminates are characterized by more instable force during impact in stage of stabilization of impactor-laminate system and stage of force growth that glass fibre laminates. It has been observed more stable force decrease in stage of stress relaxation and withdrawal of the impactor. In energy range under test, the laminates based on titanium with glass and carbon fibres reinforcement demonstrate similar and high resistance to low-velocity impact, measured by means of failure initiation force and impact maximum force. [ABSTRACT FROM AUTHOR]

Results of a study of silica and silica–titania sol–gel coatings for the creation of intermediate interfaces between commercially pure Ti or titanium alloy Ti6Al4VELI and dental porcelain are presented. Coatings of SiO2 on Ti6Al4V alloy and SiO2–TiO2 on Ti were deposited using sol–gel method. Surface microstructures and wear behaviour of the coatings were studied by using scanning electron microscopy with electron diffraction spectroscopy and pin-on-disc method. It is found that (1) Ti6Al4V/SiO2 and Ti/SiO2–TiO2 coatings obtained by the sol–gel method are compact, chemically homogeneous and relatively rough, and (2) the smaller wear of SiO2 coatings than that of SiO2–TiO2 coatings is associated with differences in their microstructure and roughness. [Copyright &y& Elsevier]

The load dependence of the Vickers microhardness of some cobalt-based alloys subjected to heat treatment at different temperatures for various durations, investigated using Hanemann’s method and a PMT-3 hardness tester, has been discussed. The experimental results show that: (1) the indentation size effect is best revealed by the proportional specimen resistance model of Li and Bradt, and (2) the plot of the ratio of indentation load P to indentation diagonal d against d for a sample exhibits two different slopes b with a transition in the slopes occurring at an indentation diagonal d lying between 9 and 20 μm. Analysis of the results revealed that: (1) the origin of indentation size effect is associated with the processes of relaxation of indentation stresses, (2) the load-dependent quantity a and load-independent quantity b for cobalt-based alloys are intimately connected with the grain size and defect structure of the alloys, and the grain-size dependence of their microhardness qualitatively agrees with the modified Hall–Petch relation, (3) in the range of high indentation loads the microhardness of cobalt-based alloys, as determined by using the proportional specimen resistance model, is practically independent of the applied load, and (4) the origin of a critical indentation diagonal dc*≈15 μm, when a change in the slope of the plot of a against b occurs, is associated with the value of indentation diagonal d when frictional resistance begins to contribute to the values of a. [Copyright &y& Elsevier]

The load dependence of the Vickers microhardness of some cobalt-based alloys subjected to heat treatment at different temperatures for various duration has been investigated using Hanemann’s method and a PMT-3 hardness tester. It is found that even for the same sample Hanemann’s method shows a decrease in microhardness with applied load (i.e., normal indentation size effect) while the PMT-3 hardness testing exhibits a reverse effect. The experimental data were analysed using Meyer’s law, Hays–Kendall’s model, the elastic/plastic deformation model of Bull et al., the proportional specimen resistance model of Li and Bradt and the energy balance approach of Bu¨ckle. The analysis of the experimental data revealed that: (1) the Meyer hardness index n decreases linearly with logarithm of the so-called standardised hardness constant A, (2) within the limits of experimental errors, the load-independent microhardness of a given sample predicted by the other models used is constant, (3) the quantities contributing to the load dependence of hardness are inversely related with the constants describing the load-independent hardness, (4) the quantities contributing to the load dependence of hardness are related with the Meyer hardness index n and (5) the constants of the energy balance approach are mutually related but the load-independent microhardness predicted by this approach is erratic with respect to that obtained by the other models. [Copyright &y& Elsevier]

The purpose of this paper is to investigate the impact behaviour and damage characterization of carbon fibre reinforced aluminium hybrid laminates (Al/CFRP) in comparison to classic carbon fibre reinforced polymer (CFRP) at low-velocity and low-energy impact. Impact damage characteristic with damage initiation and progression, internal failure modes and understanding of the role of the metal layers in the impact behaviour under low-energy were examined and discussed. The damage mechanism of the tested laminates is very complex. There is an internal degradation of the material, with the plastic deformation in case of fibre metal laminates. Characteristic matrix cracks (bending and shearing cracks) running at the fibre–matrix interface in composite layers are the first damage mode. The critical damage mode is delaminations observed between composite layers with different orientation as well as delaminations at the metal–composite interface in fibre metal laminates. For the tested materials, particularly carbon fibre reinforced composites, the absorbed impact energy is mainly connected with elastic response and damage of the laminate. In case of fibre metal laminates the absorbed energy is also connected with plastic deformation of the laminate, occurring especially in the metal layers. High impact resistance of fibre metal laminates indicates that metal (aluminium) layers may prevent delamination propagation and impactor penetration. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a numerical analysis of damage of composite materials with polymeric matrix reinforced with carbon fibres subject to static tension. Verification of numerical analyses was conducted with experimental methods – strength tests and microstructural observations. The methodologies applied were: the material damage modelling methodology based on XFEM (eXtended Finite Element Method) and contact interactions in a fibre–matrix connection layer using the CZM method (Cohesive Zone Method – Surface-based Cohesive Behaviour). ABAQUS/Standard software was the applied numerical tool. Microstructural analysis and numerical simulations indicate the fact that initiation of composite material damage takes place at the interface as a result of cracking and loss of fibre/matrix connection. This results in weakening of the composite microstructure in this area through the initiation of a reinforcement cracking process, which leads to further structural degradation, consisting in propagation of matrix cracking and, as a result, complete damage of the composite structure. The presented research of carbon/epoxy composite damage confirmed the adequacy of the prepared numerical model. [Copyright &y& Elsevier]