Simulation of the Hybrid Carbon-Aramid Composite Materials Based on Mechanical Characterization by Digital Image Correlation Method

Effects of Rubber Core on the Mechanical Behaviour of the Carbon-Aramid Composite Materials Subjected to Low-Velocity Impact Loading Considering Water Absorption

The large-scale use of composite materials reinforced with carbon-aramid hybrid fabric in various outdoor applications, which ensures increased mechanical resistance including in impact loadings, led to the need to investigate the effects of aggressive environmental factors (moisture absorption, temperature, thermal cycles, ultra-violet rays) on the variation of their mechanical properties. Since the literature is still lacking in research on this topic, this article aims to compare the low-velocity impact behaviour of two carbon-aramid hybrid composite materials (with and without rubber core) and to investigate the effects of water absorption on impact properties. The main objectives of this research were as follows: (i) the investigation of the mechanical behavior in tests for two impact energies of 25 J and 50 J; (ii) comparison of the results obtained in terms of the force, displacement, velocity, and energy related to the time; (iii) analysis of the water absorption data; (iii) low-velocity impact testing of wet specimens after saturation; (iv) comparison between the impact behaviour of the wet specimens with that of the dried ones. One of the main findings was that for the wet specimens without rubber core, absorbed impact energy was 16% less than the one recorded for dried specimens at an impact energy of 50 J. The failure modes of the dried specimens without rubber core are breakage for both carbon and aramid fibres, matrix cracks, and delamination at matrix-fibre interfaces. The degradation for the wet specimens with rubber core is much more pronounced because the decrease in the absorbed impact energy was 53.26% after 10,513 h of immersion in water and all the layers were broken.

Characteristics of Carbon and Kevlar Fibres, Their Composites and Structural Applications in Civil Engineering-A Review

Kevlar and carbon fibres and fabrics have won a leading place in the structure market, although such materials are not cheap, and are increasingly used for reinforcing and strengthening structural elements in the civil engineering, automotive, aerospace and military industries, due to their superior mechanical properties, especially in terms of strength. The mechanical characteristics of such composite materials must be known in order to numerically simulate the mechanical behaviour of such structures in terms of the distribution of stresses and strains. It has also become a necessity to understand the effects of reinforcement with both types of fibres (carbon fibres and Kevlar fibres) on the mechanical properties, especially on the impact properties of such composites. This review aims to expose the main advantages and disadvantages of the hybridization of carbon and Kevlar fibres. For this reason, an overview is presented concerning the main characteristics (tensile strength, flexural strength, impact strength, coefficient of thermal expansion and so on) for carbon and Kevlar fibres and also for hybrid Kevlar-carbon composite materials to aid in the design of such hybrid composite materials. Finally, some civil construction rehabilitation and consolidation applications of the composites reinforced with carbon fibre, Kevlar fibre or with hybrid Kevlar-carbon fabrics are highlighted in the last part of the paper.

Mechanical Characteristics Evaluation of a Single Ply and Multi-Ply Carbon Fiber-Reinforced Plastic Subjected to Tensile and Bending Loads

Carbon fiber-reinforced composites represent a broadly utilized class of materials in aeronautical applications, due to their high-performance capability. The studied CFRP is manufactured from a 3K carbon biaxial fabric 0°/90° with high tensile resistance, reinforced with high-performance thermoset molding epoxy vinyl ester resin. The macroscale experimental characterization has constituted the subject of various studies, with the scope of assessing overall structural performance. This study, on the other hand, aims at evaluating the mesoscopic mechanical behavior of a single-ply CFRP, by utilizing tensile test specimens with an average experimental study area of only 3 cm². The single-ply tensile testing was accomplished using a small scale custom-made uniaxial testing device, powered by a stepper motor, with measurements recorded by two 5-megapixel cameras of the DIC Q400 system, mounted on a Leica M125 digital stereo microscope. The single-ply testing results illustrated the orthotropic nature of the CFRP and turned out to be in close correlation with the multi-ply CFRP tensile and bending tests, resulting in a comprehensive material characterization. The results obtained for the multi-ply tensile and flexural characteristics are adequate in terms of CFRP expectations, having a satisfactory precision. The results have been evaluated using a broad experimental approach, consisting of the Dantec Q400 standard digital image correlation system, facilitating the determination of Poisson’s ratio, correlated with the measurements obtained from the INSTRON 8801 servo hydraulic testing system’s load cell, for a segment of the tensile and flexural characteristics determination. Finite element analyses were realized to reproduce the tensile and flexural test conditions, based on the experimentally determined stress–strain evolution of the material. The FEA results match very well with the experimental results, and thus will constitute the basis for further FEA analyses of aeronautic structures.