The properties and mechanisms of fracture of hybrid composite materials (HCMs) based on flexible and brittle matrices reinforced with hybrid fibers of carbon, aramid, and ultrahigh molecular weight polyethylene (UHMWPE) are studied by the method of impact break (IB) under low speed impact. The composition of the hybrid fiber and the plasticity of the matrix have an effect on the properties and fracture mode of the HCM. It is established that the combination of carbon and aramid fibers in a hybrid fiber for reinforcing a flexible matrix (FM) makes it possible to create a material with delayed failure. It is shown that the impact fracture of the HCM with a flexible matrix requires a load twice as large as the load required for specimens with a brittle matrix. Hybrid composite materials in which there is a joint deformation of the matrix and the reinforcing fiber at all stages of loading up to failure have the highest strength. The mechanism of deformation and destruction of anisotropic HCMs upon impact is associated with the stepwise behavior.

A universal method “Break upon Impact and in Static Conditions” (BIS) has been developed for the experimental determination of the ultimate strength properties of polymer composite materials based on multifilament nanocrystalline ultrahigh molecular weight polyethylene (UHMWPE) fibers, which differs in the method of fixing the sample in a testing machine. The method is carried out using a uniform BIS sample with an intermediate matrix at the ends and equipment for its attachment to the platforms of testing machines. The sample is a round composite rod composed of the fibers and matrices under investigation, which is held in the tooling by an additional matrix that fixes it under various loading rates. The BIS method was used to study the properties and mechanisms of destruction upon impact and in a static situation of anisotropic polymer and hybrid composite materials (PCM and HCM) based on flexible and rigid matrices reinforced with hybrid fibers of carbon, aramid, and UHMWPE fibers activated by nonequilibrium low-temperature plasma. The breaking loads under low-velocity impact and static bending conditions, relative deformation, specific absorbed-in-fracture energy, work of adhesion, shear strength, and other properties are determined. It was found out that the plasticity of the matrix and the hybrid fiber composition affect the properties and fracture mode of PCM and HCM. For the destruction of HCM with a flexible matrix upon impact, a load is required by a factor of two larger as for composites with a rigid matrix. HCMs have the highest strength, in which at all stages of loading up to failure joint deformation of the matrix and the reinforcing fiber occurs. The mechanism of deformation and destruction of anisotropic HCM upon impact is stepwise, while the nature of the deformation curve is zigzag. In static conditions, the deformation proceeds smoothly. By changing the ratio of carbon and UHMWPE fibers during hybridization, it is possible to control the properties of HCM and improve its specific properties. The combination of carbon and UHMWPE fibers in a hybrid fiber for reinforcing a flexible matrix makes it possible to create a material with a delayed fracture. It has been established that, for HCM based on a flexible matrix reinforced with a hybrid fiber combining 20% carbon and 80% UHMWPE fiber, the fracture load increases by a factor of 2, the specific fracture work (absorbed-in-fracture energy) increases by 42%, and relative deformation increases by 68%.

Молекула СВМПЭ с насыщенными ковалентными химическими связями обладает низкой поверхностной энергией (≈ 33 мДж/м2). Этим объясняется инертность СВМПЭ-волокон к взаимодействию с полимерными матрицами при получении композитных материалов (КМ). В пучке нанокристаллических многофиламентных СВМПЭ-волокон содержится от ∼ 900 до 2000 и более филаментов (мононитей). Благодаря малому диаметру филаментов, волокно имеет огромную межфазную поверхность, основная часть которой находится внутри волокна [1, 2].

Волокнистые материалы на основе полиэтилена находят все большее применение в различных отраслях промышленности. Особенно выделяются волокнистые материалы на основе сверхвысокомолекулярного полиэтилена (СВМПЭ), обладающие высокими удельными прочностными характеристиками.

The low-velosity impact properties and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) fiber (Dyneema®SK-75) and a composite material (CM) based on it with the rigid and flexible matrices were investigated by the “Impact Break” (IB) method. A fundamental difference in deformation behavior and failure mechanisms upon impact on the UHMWPE-fiber and on the CM based on this fiber has been investigated experimentally. It is shown that impact has a little effect on the properties of UHMWPE-fiber, since it is an isotropic material. It has been established that upon impact, the properties of a fiber without a matrix were significantly higher than the properties of CM based on it. Impact action stimulates the interaction between CM components (fibers and matrix). Mechanism of stepwise deformation of anisotropic CM is occurred, which begins from the first moment of impact and ends with the destruction of the CM. A “stairway of deformation” behavior is observed in anisotropic materials. Stepwise deformation is the main form of deformation and the basic mechanism of failure of anisotropic composite materials upon impact.

Methods for the creation and characteristics of composite materials reinforced with carbon, aramid and UHMWPE-fibers based on polymer matrices are considered. The properties of more than 50 composite materials are given. Technologies for their production from wound nonwoven and woven fiber reinforcements are proposed, with regulation of activation, composition and arrangement of components in the material. Experimental methods for studying polymer com- posites, such as wet-pull-out (W-P-O), full-pull-out (F-P-O) and impact break (IB) have been deve­loped. It allows one to study the interfacial interaction of components during the creation of CM, regulate the activation of fibers by non-equilibrium low-temperature plasma and fluo­ rination, and analyze mechanisms of deformation and destruction of CM, in statics and upon impact with the help of uniform universal samples. Monograph – reference book is intended for scientific and engineering staff, teachers, stu- dents, graduate students, and inventors involved in the development, production and use of poly­ mer composite materials.

The processes that occur during loading and destruction of composite materials (CMs) are studied by the full pull-out method. The mechanisms of load and deformation transfer in CM and the effects of the plasma activation of fibers and of the matrix properties on them are ascertained. It is established that the transfer and distribution of load and deformation among fibers in CM occur via two adhesive joints of fibers with the matrix layer. Reinforcing fibers activated by nonequilibrium low-temperature plasma increase the specific absorbed-in-fracture energy from 26 to 44 J/cm2, the shear strength from 7.1 to 10.4 MPa, and the strain from 1.8 to 2.33%. When the maximum load and strain are reached, the CM is destroyed and the fiber is fired from the matrix. In the case of nonactivated fiber reinforcement, destruction of the CM occurs in two stages: first, the strength and deformation reach the limiting values and the fiber then begins to shift in the matrix, which causes stress relaxation and a sharp drop in strength of the CM. Further deformation occurs as a result of pulling fibers out of the matrix at low load. Plasma activation of reinforcing fibers leads to an increase in properties of the CM.

Abstract Regulation of carbon fiber reinforced plastic (CFRP) properties and failure mode upon low-velocity impact by hybridization of the reinforcing fibers is discussed. Effect of the ratio of carbon fiber (CF) and plasma-activated ultra-high molecular weight polyethylene (UHMWPE) fiber contained in a hybrid fiber on the ultimate tensile strength and impact properties et al. properties of the hybrid composite material (HCM) has been investigated by impact break (IB) method. It was found out that at the ratio of CF:UHMWPE-fiber = 20:80, the carbon and UHMWPE-fibers in HCM are no longer deformed and broken down simultaneously. At first carbon and then UHMWPE-fiber are broken down. At this ratio the HCM values of ultimate tensile strength and specific absorbed-in-fracture energy were increased by the factors of 1.65 (from 594 to 986 MPa) and 1.98 (from 47 to 89 J/cm2), respectively. The detected effect of the delay in the destruction of HCM can be used to create aircraft and other impact-resistant structures.

The effect of rigid and flexible matrices on the properties of carbon fiber reinforced plastics has been studied using the impact break method at different rates of loading the composite material (CM). It has been established that the strain of CM under static loading conditions has a smooth character and is generally tensile. For this reason, CM with a plastic matrix under static loading conditions has higher properties, such as the maximum specific absorbed-in-fracture energy α = 154 J/cm2 and the maximum strength σ = 524 MPa at a greater relative strain ε = 6%. The fracture mechanism of carbon fiber reinforced plastics (CFRPs) abruptly changes upon an impact. The fracture of CMs is initiated by an impact at the first moment of its action. The entire process of CM strain until fracture is accompanied by fiber filament breaks. Load fluctuations occur due to filament breaks and are reflected in the strain curves in the form of peaks. The processes of filament break and crush are superimposed on the overall process of multistage CM tensile strain at a higher level. The accumulation of fiber crushes and breaks decreases the strength of CMs. This leads to fast fracture at lower strain in comparison with the case of static loading conditions. The specific absorbed-in-fracture energy α of CFRPs with a flexible matrix decreases upon an impact by a factor of 3.4, from 154 to 45 J/cm2, relative to the specific absorbed-in-fracture energy of CM in the static case; the material is fractured at a smaller relative strain ε = 1.7% and a lower strength σ = 496 MPa.

A new approach toward understanding failure mechanisms of anisotropic fiber-reinforced composite materials due to low velocity impact is discussed. The dependence of failure mechanisms and mechanical properties of such composites on loading velocity are examined by Impact Break method. It has been shown experimentally that especially large change in the CM properties occurs in the transition from static to impact loading conditions. CM destruction was observed at the first moment of a shock load application. The relaxation of the stresses in CM and the energy dissipation from breaking fibers are limited the short duration of impact value equal to 1-2 ms. Failure mechanism is based on the fibers stretching and stress-wave propagation through the CM under impact. The processes of multi-breaking and crushing of the filaments are imposed on the process of multi-stage stretching deformation. It led to decrease CM properties as compared with that under static. In a static situation, the deformation of CM is mostly stretching deformation. It gradually grows as the load increases. It has been found out that specific absorbed-in-fracture energy of CFRP and OFRP under impact loading conditions is significantly reduced by factors of 3.7 and 3.2, respectively, as compared with that under static ones. As a result, the choice of CM to create structures based only on the static properties of the material does not guarantee the impact resistance of structures upon low-velocity impact.

The properties and failure mechanisms of anisotropic polymer composite materials in configuration of a single bundle of filaments microcomposite reinforced with carbon and aramid fibers under impact and static loading conditions are investigated by impact break method. Various failure mechanisms of the CM affected on their properties under static and impact loading conditions. The destruction processes in dynamically loaded CM are multistage. Failure mechanism is based on the multifilament fiber stretching and stress‐wave propagation through the CM. The processes of multibreaking and crushing of the filaments are imposed on the process of multistage stretching deformation. It led to a sharp decrease of the CM properties on impact as compared with that CM tested under static loading conditions. It has been found out that specific absorbed‐in‐break energy of CFRP and OFRP under impact loading conditions is significantly reduced by a factor of 3.1 and 4.1, respectively, as compared with that under static ones. POLYM. ENG. SCI., 57:693–696, 2017. © 2017 Society of Plastics Engineers

A method for investigation of impact toughness of anisotropic polymer composite materials (reinforced plastics) with the help of CM model sample in the configuration of microplastic (micro plastic) and impact pendulum-type testing machine under static and dynamic loadings has been developed. The method is called "Break by Impact" (Impact Break IB). The estimation of impact resistance CFRP by this method showed that an increase in loading velocity similar to 10(4) times the largest changes occurs in impact toughness and deformation ability of a material.