W. Błażejewski

Optical fiber sensors integrated with composite material based constructions

In the present work we demonstrate measurements obtained using optical fiber head sensors for high pressure composite vessel, composite strengthened concrete beam and the high-voltage composite insulator.

Application of Optical Fibre Sensors to Measuring the Mechanical Properties of Composite Materials and Structures

The role of polymer composites in mechanical structures has been steadily increasing. The key factor here is the coefficient of specific strength, i.e. a ratio of tensile strength to specific gravity. As compared with metals, this coefficient assumes a high value for composites, including the polymer ones. Other major factors determining the choice of materials are: the product price, mass manufacturability, high strength and durability, corrosion resistance, material production and machining energy consumption and a few more. Also the latter criteria increasingly favour composites. Materials engineering as applied to composites offers the possibility of creating entirely new materials and modifying the traditional materials, which in both cases better meet designers’ expectations. The ever increasing popularity of composite structures is first of all due to the considerable reduction in weight in comparison with metal structures, at a sufficiently high mechanical durability. Nevertheless, the safety requirements require that the stress-strain state of composite structure be monitored. Standard NDE methods such as radiography, interferometric holography, ultrasonic scanning or visual inspection are usually not effective in on-line monitoring. Even if they were used for periodic checks, they would not be able to detect promptly defects critical to the condition of the monitored structure. Moreover, conventional measurement devices, such as electrical resistance strain gauges, often get damaged in adverse environmental conditions. State-of-the-art measuring methods based on optical fibre technology are increasingly often used to monitor the structural health of industrial objects. Optical fibre sensors have many advantages over the conventional devices. The obvious one is that they can work at high levels of electromagnetic interference and in other adverse conditions (high dust concentration, high temperature, high pressure, significant deformations). Moreover, such sensors are characterized by high (deformation and temperature) measuring sensitivity in a wide measuring range. Owing to their small geometric dimensions and a relatively small weight they can be installed inside a structure (e.g. by embedding them in the composite material) or on its surface. Thanks to their high potential for multiplexing it is possible to create a nervous system of the object being monitored, enabling health and damage assessment. In addition, optical fibre based sensors ensure spark-proof safety which is an important consideration for inflammable applications.

SMART composite high pressure vessels with integrated optical fiber sensors

In this paper application of integrated Optical Fiber Sensors for strain state monitoring of composite high pressure vessels is presented. The composite tanks find broad application in areas such as: automotive industry, aeronautics, rescue services, etc. In automotive application they are mainly used for gaseous fuels storage (like CNG or compressed Hydrogen). In comparison with standard steel vessels, composite ones have many advantages (i.e. high mechanical strength, significant weight reduction, etc). In the present work a novel technique of vessel manufacturing, according to this construction, was applied. It is called braiding technique, and can be used as an alternative to the winding method. During braiding process, between GFRC layers, two types of optical fiber sensors were installed: point sensors in the form of FBGs as well as interferometric sensors with long measuring arms (SOFO®). Integrated optical fiber sensors create the nervous system of the pressure vessel and are used for its structural health monitoring. OFS register deformation areas and detect construction damages in their early stage (ensure a high safety level for users). Applied sensor system also ensured a possibility of strain state monitoring even during the vessel manufacturing process. However the main application of OFS based monitoring system is to detect defects in the composite structure. An idea of such a SMART vessel with integrated sensor system as well as an algorithm of defect detection was presented.

Application of Optical Fiber Sensors for Damage Accumulation Monitoring in Composite Structures

In this paper a study of damage accumulation evaluation of highly stressed composite layer using acoustic emission method and local strain measurements by optical fiber based sensors in form of Fiber Bragg Grating (FBG) is presented. The study was carried out using composite NOL-ring specimens. These kind of specimens can simulate behavior of the cylindrical part of the pressure vessel. Quasistatic and creep tests of CFRC made NOL specimens were performed. It has been shown that there is a correlation between changes in the strain field of composite material, detected by FBG optical sensors, and changes in acoustic emission signals. The possibility of a kind of calibration of composite material strain state monitoring system by AE measurements and at the same time evaluation of damage accumulation was confirmed.

Fatigue crack growth rate in CFRP reinforced constructional old steel

Purpose The purpose of this paper is twofold: first, to observe an influence of different Composite Fibre-Reinforced Polymer (CFRP) patches, whose application to metals is very easy, in suppling and significantly elongating the service time; and second, the numerical calculation of the reduced stress intensity factor (SIF) range for strengthened cracked steel specimens. Design/methodology/approach One of the successful strengthening methods is the CFRP patching along the fatigue crack paths. The presented approach has been studied and discussed in this paper on the background of the numerical and experimental data. As it was expected, the proposed strengthening method is efficient and promising in case of the “immediate” repairs of critical members with cracks. The manufacturing process of specimens and test methodology as well as numerical approach to calculate SIFs for various reinforcements of steel specimens are presented. For this purpose, the Extended Finite Element Method was involved and described. Findings The main mechanism of fatigue crack growth retardation is associated with local ΔK reduction due to CFRP patches; any type of reinforcement results in an increase in af and a significant decrease in SIF values. The beach-marking method is described as a good, reliable and comprehensive method to capture the crack propagation in structures consisting of various materials and could be applied successfully for mixed mode testing. Originality/value A detailed experimental-numerical approach for fatigue crack growth in long-term operated structures made of steel is presented. The strengthening methodology is presented with consideration of the various CFRP patches configurations.

Calculations with the Finite Element Method During the Design Ballistic Armour

For protection against projectiles with higher impact speed (up to 1000 m/s) a type of a ballistic sandwich shield can be used—which is a monolithic combination of ballistic laminates with additional materials, typically hard layers made of ceramic in the form of plates or spheres of oxides, carbides and nitrides. The authors of this paper, by using FEM to optimize defined material sets to fire the cartridge 7.62 × 54R mm, give a range of results which are compared with tests of ballistic firing on the shooting range.