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The prototype of removable visual impact indicator for thermoset polymer composite materials is developed, and its characteristics are experimentally determined. The indicator is a fabric tape glued by epoxy to the surface of the polymer composite. The tape is impregnated with a composition that provides a visual response at the place of an impact on the composite surface. Ball-drop tests demonstrated the increase of the magnitude of the visual response with the impact energy at different substrate hardnesses. The shelf-life and mode of the tape storage until commissioning are determined. Peel tests showed the ability to remove a used indicator without damaging the surface of the composite.

A simple and prompt method to determine the mechanical properties of industrial multilayer extrusion polypropylene pipes for a gravity sewer network is suggested. The engineering formulas included for calculating the permissible thickness and relative position of a foam core in the pipes are based on a linear-elastic approximation and the rule of mixtures. The applicability of the approximation was justified experimentally during investigation of the effective tensile characteristics of single- and multilayer pipes and each layer specimen by using traditional tests and finite-element calculations. The results obtained were used to formulate engineering recommendations for calculations of this type.

A system of pultruded carbon fibre-reinforced plastics micro-tubes is used for self-healing simulation in laminated polymer composite. The system consists of a package of micro-tubes, placed in the symmetry plane of the GFR/epoxy laminate stack. Healing agent is a mixture of the epoxy resin and hardener. The healing agent releases and penetrates into the cracks after the composite is damaged by the quasi-static indentation. The specimens are healed at 30℃ for 24 h. Rectangular specimens notched under ASTM D2733 have been subjected to tensile test to determine interlaminar shear strength. Shear strength of specimens has been compared in three states (virgin, damaged and healed) for various ways of healing. After the most effective self-healing, the interlaminar shear strength has been recovered to 70 ± 15% of those for virgin specimens that almost twice exceeds the residual strength of the damaged specimens.

A method for the manufacture of a glass-fiber-reinforced plastic (GFRP) containing a sensitive layer with a damage visualization capability is developed. The layer is based on a glass fabric impregnated with a mixture of three components — microcapsules with a leuco dye, a dye developer, and a polymer adhesive. Specimens of the GFRP epoxy composite with an integrated damage-indicating layer were manufactured by the method of vacuum-assisted resin transfer molding. It was established that both the shear and compression strains above the threshold of sensitivity of the layer led to a change in color of the specimen. The kinetics of the halochromiс transformation in room conditions was estimated in series of quasi-static compression and shear strength experiments. The effect of the integrated damage indicating layer on the interlaminar shear strength of the composite was estimated in a series of test on double-notch specimens.

A concept of a composite possessing a biomimetic function of visual response in the form of a “bruise” to an external mechanical action has been developed. The concept is implemented by creating a model layered epoxy composite. Methods for creating a sensitive layer, containing microcapsules with a leuco dye and particles of a developer, and a composite including this layer are described. The threshold of a visual response, i.e., the sensitivity of the composite to a local indentation load is controlled by means of a protective epoxy coating of various thickness. Series of mechanical tests with a gradually increasing load and subsequent digital image analyses were carried out. The data obtained were used to determine the required thickness of the epoxy coating in relation to the desirable threshold of visual response to an indentation load. The Hertz theory was used to analyze the resulting stresses in the coating in the elastic approximation. The experimental results allowed us to determine the normal threshold pressure causing the action of a sensitive layer embedded into the epoxy composite.

For damage indication needs in polymer composites, three smart acrylic coatings based on microencapsulated crystal violet lactone leuco dye with embedded developer silica gel and methyl 4-hydroxybenzoate were elaborated. Damage visualization ability upon duralumin substrates was tested. Indentation tests were conducted in the interval of 0.0005–0.55 J of mechanical work. Digital image analysis was used for evaluation of the visual response in the form of “bruise” spots. The measure of response intensity was relative excess of blue color above achromatic gray in the scanned images of the “bruise” spots. This technique allowed detecting influence of the coating formulations onto the substrate damage visualization.

This research aimed to realize experimentally the facilevascular self-healing system in epoxy glass fibre reinforced composite. Using flexiblepolytetrafluoroethylene tubes as removable preforms, the channels were embeddedinto both neat epoxy resin and unidirectional glass-fibre reinforced epoxy laminate.Room temperature curable epoxy resin with a surfactant and an amine-basedhardener were the components of the binary healing agent. The specimens oftapered double cantilever beam geometry were subjected to Mode I fracture tests.Fracture of specimens released the healing agent from channels and triggeredself-healing process of the crack. Tested neat epoxy resin specimensdemonstrated recovery of fracture toughness ca. 70 % after 24 h of self-healingat 50°C. Unidirectional laminate specimens (250×23×1.2 mm) were made by vacuuminfusion method from two layers of glass yarns with 5 embedded channels aligningto reinforcing fibers. The channels were alternately filled with components of thehealing agent and then sealed. It was revealed that the embedded vascularchannels in specimens had very little effect on their elastic modulus. Theexperimental program included multiple three-point bending tests of specimensfor their initial damage and self-healing of specimens during their heat treatmentand following exposure at room temperature. Static and dynamic flexural moduli ofelasticity were determined by three-point bending and cantilever beam vibrationat all stages of the test program. The healing efficiency was evaluated as a relativechange of elastic modulus. The efficiency ca. 30 % was reached during 24 h at50°C and additionally increased up ca. 40 % after more than 3 weeks of roomtemperature exposure. The sealed healing agent was capable of maintaining thecapacity for self-healing for at least six months. The research resultsdemonstrated capacity of the macro-channel approach for self-healing realizationin multifunctional polymer composite materials.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5354