Charakteristiky impaktního poškození a ponárazové pevnosti vláknových plastových kompozitů s různou architekturou skelné výztuže

Fiber-reinforced plastics (FRP) are nowadays used commonly for constructions subjected to impacts of different energies and velocities; therefore, the problem of impact resistance is crucial. This paper presents the results of high-velocity impact tests and post-impact evaluation of damage in glass-fiber-reinforced plastics, depending on the architecture of reinforcing material (different woven fabrics, mat). Composites reinforced with continuous-filament mat, woven roving, roving fabric and twisted-yarn fabric were prepared and subjected to intermediate- and high-velocity impact. After the ballistic impact, damage extent and residual strength, as well as water leakage through the composites, were evaluated. The damage was also investigated under a microscope. The damage extent was confirmed to be linearly dependent on impact energy. The addition of rubber was found to decrease damage extent and increase post-impact residual strength, as well as decrease water leakage rate.Plasty vyztužené vlákny (FRP) jsou v současné době hojně používány pro konstrukce vystavené nárazům o různé energii a rychlosti. Z tohoto důvodu je řešení problematiky odolnosti proti nárazu klíčové. Tento článek prezentuje výsledky vysokorychlostních nárazových zkoušek v případě plastů vyztužených skelnými vlákny v závislosti na architektuře matrice (různé druhy tkanin). Kompozity vyztužené spojitými vlákny s různým zpracováním byly posléze podrobeny nárazovým zkouškám s různou rychlostí indentoru. Po nárazu byl zkoumán rozsah poškození, reziduální pevnost a také intenzita úniku vody skrz poškozenou oblast, která byla dodatkově analyzována s využitím mikroskopu. Zkoušky potvrdily lineární závislost mezi rozsahem poškození a nárazovou energií. Přidáním kaučuku do základní matrice došlo ke zvýšení zbytkové pevnosti kompozitu včetně snížení intenzity úniku vody skrz poškozený kompozit

Characteristics of Impact Damage and Post-Impact Strength in Glass-Fibre-Reinforced Plastics with Different Reinforcement Architecture

Fiber-reinforced plastics (FRP) are nowadays used commonly for constructions subjected to impacts of different energies and velocities; therefore, the problem of impact resistance is crucial. This paper presents the results of high-velocity impact tests and post-impact evaluation of damage in glass-fiber-reinforced plastics, depending on the architecture of reinforcing material (different woven fabrics, mat). Composites reinforced with continuous-filament mat, woven roving, roving fabric and twisted-yarn fabric were prepared and subjected to intermediate- and high-velocity impact. After the ballistic impact, damage extent and residual strength, as well as water leakage through the composites, were evaluated. The damage was also investigated under a microscope. The damage extent was confirmed to be linearly dependent on impact energy. The addition of rubber was found to decrease damage extent and increase post-impact residual strength, as well as decrease water leakage rate

Static and Flexural Fatigue Behavior of GFRP Pultruded Rebars

This paper presents the experimental results of composite rebars based on GFRP manufactured by a pultrusion system. The bending and radial compression strength of rods was determined. The elastic modulus of GFRP rebars is significantly lower than for steel rebars, while the static flexural properties are higher. The microstructure of the selected rebars was studied and discussed in light of the obtained results—failure processes such as the delamination and fibers fracture can be observed. The bending fatigue test was performed under a constant load amplitude sinusoidal waveform. All rebars were subjected to fatigue tests under the R = 0.1 condition. As a result, the S-N curve was obtained, and basic fatigue characteristics were determined. The fatigue mechanism of bar failure under bending was further analyzed using SEM microscopy. It is worth noting that the failure and fracture mechanism plays a crucial role as a material quality indicator in the manufacturing process. The main mechanism of failure under static and cyclic loading during the bending test is widely discussed in this paper. The results obtained from fatigue tests encourage further analysis. The diametral compression test reflects the weakest nature of the composite materials based on the interlaminar compressive strength. The proposed methodology allows us to invariantly describe the experimental transversal strength of the composite materials. Considering the expected durability of the structure, the failure mechanism is likely to significantly improve their fatigue behavior under the influence of cyclic bending. The reasonable direction of searching for reinforcements of composite structures should be the improvement of the bearing capacity of the outer layers. In comparison with steel rebars (fatigue tensile test), the obtained results for GFRP are comparable in the HCF regime. It is worth noting that in the near fatigue endurance regime (2–5 × 106 cycles) both rebars exhibit similar behavior

The Mechanical Investigation of Filament-Wound CFRP Structures Subjected to Different Cooling Rates in Terms of Compressive Loading and Residual Stresses—An Experimental Approach

Although cooling at ambient temperature is widely used and is said to be safe and convenient, faster cooling may have an influence not only on the time of the manufacturing process but also on the mechanical response, especially the residual stress. The study aimed to investigate the influence of the cooling rate after curing on the mechanical response of filament-wound thick-walled carbon fiber reinforced polymer (CFRP) rings. Three cooling rates were taking into consideration: cooling with the oven, at room temperature, and in the water at 20 °C. The splitting method was used to examine the residual strains. In the radial compression test, the mechanical response was investigated between the rings with different cooling regimes. The FEM analysis of the compression test in elastic range was also performed. Both the splitting method and the radial compression test showed no significant difference in the mechanical response of the CFRP rings. The presented results showed that the fast-cooling rate slightly decreases the mechanical performance of the filament-wound rings

A novel design of a low-pressure composite vessel with inspection opening – design, manufacturing and testing

Composite structures, especially pressure vessels, pipelines, and additional components such as tees, reductions, or inspection openings are more and more willingly used in the chemical industry. In this research, a novel design of a low-pressure composite vessel with an inspection opening is presented. The vessels are unsymmetrical considering the domes. On one side the opening is considerably bigger, around half of the cylindrical diameter of the vessel. This design requires a new approach to manufacturing such structures. In this study, a two-step analysis was performed. Firstly, small-size pressure vessels (S) were manufactured and the design of dome reinforcement was validated. Then, the final design of vessel (M) was produced, with a volume of around 700 litres. The vessels were initially calculated for 21 bars of burst pressure. During burst pressure tests, the strains were measured with optical fibres (FBG) and strain gauges. Additionally, the acoustic emission was utilized to predict the damage modes and locations. Finally, a microscopic evaluation of the specific parts of the vessels was performed. Conclusions were drawn, that the proposed novel design of dome reinforcement around the inspection opening fulfilled the strength and stiffness requirements

Improvement of Interaction in a Composite Structure by Using a Sol-Gel Functional Coating on Carbon Fibers

The modification of carbon fibers for improving adhesion between fibers and an epoxy resin in composite materials has become the focus of attention. In this work the carbon fiber coating process has been devised in a way preventing the stiffening and clumping of fibers. To improve interactions between coated fibers and a resin in composites, four types of silica coatings with different organic functional groups (3-aminopropyl–coating 1, 3-mercaptopropyl–coating 2, 2-(3,4-epoxycyclohexyl) ethyl–coating 3, methyl–coating 4) were obtained. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to distinguish the changes of a carbon fibers surface after coating deposition. The thickness of the obtained coatings, including the diversity of thickness, was determined by transmission electron microscopy (TEM). The increase in surface free energy (SFE) of modified fibers, including the distinction between the polar and dispersive parts, was examined by wettability measurements using a tensometric test. The developed coating preparation process allowed to cover fibers separately with nanoscale silica layers, which changed their morphology. The introduction of organic functional groups resulted in surface free energy changes, especially an increase in specific polar surface energy components