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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]

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]

• The objective were Hybrid Titanium Carbon Laminates as a second generation of FML. • The fibre orientation in HTCL has a significant influence on damage propagation. • Dominant failure occurs at the metal/composite and composite/composite interfaces. • HTCL can be an appropriate solution for materials under dynamic loads. Impact resistance is one of the more critical and important features of composite materials used in the aerospace industry. The objective of work was to evaluate the hybrid titanium carbon laminate resistance to dynamic loads. The paper utilizes numerous criteria for evaluation of impact behaviour of materials, including force change, energy absorption characteristics and failure identification. To thoroughly analyze the damage mechanism, a detailed fractography of laminate destruction was performed. Moreover, an empirical model for determining the universal impact behaviour coefficient of fibre metal laminate (FML) was proposed. The first significant force fluctuations prove to reach the laminate's impact resistance limit as caused by the initiation of cracking of respective layers and the consequent reduction of laminate rigidity. A growing proportion of absorbed energy in the case of growing impact energies, from some 50% in case of 2.5 J of energy, up to circa 80% in case of 30 J of energy was recorded. Reduction of interlayers with crossing fibers fosters the creation of cracks in the lower layer of titanium due to the limited capability of partial absorption of energy through delamination. [ABSTRACT FROM AUTHOR]

Post-impact strength and damage tolerance of composite structures stands as a paramount design consideration in the aeronautical industry. In the event of a low velocity impact, a set of damage manifestations within laminated structures are induced, including matrix cracking, delamination and fiber breakage. Despite the critical importance of discerning the influence of each damage type on post-impact compression strength, only a limited number of studies have endeavored to quantify these effects comprehensively. In response to this research gap, we have developed a novel methodology capable of mimicking damage extension and shape caused by a low-velocity impact, while preserving fiber integrity. This innovation is achieved through the application of induced electrical currents, thereby facilitating controlled damage simulation without compromising fiber structural integrity. Our investigation compares the residual stiffness and strength of AS4/PEEK laminates subjected to low velocity impacts and induction currents, under conditions of equivalent damage. Our findings reveal that fiber breakage significantly influences the loss of stiffness in the laminate, but not its strength. Moreover, our results confirm the role of delamination as the primary determinant of strength degradation in the damaged material. [ABSTRACT FROM AUTHOR]

• Use of thin-ply FMLs is a prospective material solution for innovative applications. • Thin-ply FMLs do not show a significant change in impact damage mechanisms. • Use of thin-ply carbon fibres in FMLs with not lead to higher impact resistance. • Thin-ply FMLs showed the brittle failure and in situ effect. This study present investigation on the low-velocity impact resistance of fibre metal laminates consisting of aluminium layers and a thin-ply carbon fibre reinforced polymer. A thin-ply effect is compared with fibre metal laminates consisting of conventional thickness plies. Low-velocity impact tests are conducted with impact energies ranging from 2.5 J to 30 J. The low-velocity impact behaviour of conventional and thin-ply laminates is estimated and compared by analysis of key characteristics describing impact during the impactor-laminate contact. In addition, impact damage of the laminates is analysed, focusing on the identification of dominant damage modes and locations. Results demonstrate that the use of a thin-ply carbon fibre reinforced polymer neither increases the low-velocity impact resistance of the laminates nor significantly changes their low-impact impact response as compared to the laminates with conventional ply thickness. Results demonstrate that the damage mechanism of the composite thin plies does not significantly differ from that of the conventional carbon plies. Results also confirm that the use of thin-ply fibre metal laminates is an interesting and promising materials solution. [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]