Probabilistic Modelling of Fracture Toughness of Composites with Discontinuous Reinforcement.

The results presented in the paper are related to the prediction of the effective fracture toughness of particulate composites (KICeff). KICeff was determined using a probabilistic model supported by a cumulative probability function qualitatively following the Weibull distribution. Using this approach, it was possible to model two-phase composites with an arbitrarily defined volume fraction of each phase. The predicted value of the effective fracture toughness of the composite was determined based on the mechanical parameter of the reinforcement (fracture toughness), matrix (fracture toughness, Young's modulus, yield stress), and composite (Young's modulus, yield stress). The proposed method was validated: the determined fracture toughness of the selected composites was in accordance with the experimental data (the authors' tests and literature data). In addition, the obtained results were compared with data captured by means of the rule of mixtures (ROM). It was found that the prediction of KICeff using the ROM was subject to a significant error. Moreover, a study of the effect of averaging the elastic-plastic parameters of the composite, on KICeff, was performed. The results showed that if the yield stress of the composite increased, a decrease in its fracture toughness was noticed, which is in line with the literature reports. Furthermore, it was noted that an increase in the Young's modulus of the composite affected KICeff in the same way as a change in its yield stress.

Composites in Vehicles Brake Systems-Selected Issues and Areas of Development.

Modern composite materials, thanks to their excellent properties, are widely used [...].

The Computational Fluid Dynamics (CFD) Analysis of the Pressure Sensor Used in Pulse-Operated Low-Pressure Gas-Phase Solenoid Valve Measurements.

This paper presents a flow analysis of the original pressure sensor used to determine times until full opening and closing of the pulse-operated low-pressure gas-phase solenoid valve. The sensor in question, due to the fast variation of the process lasting several milliseconds, has high requirements in terms of response time and ability to identify characteristic parameters. A CFD code has been employed to successfully model the flow behavior of the original pressure sensor used to determine times until full opening and closing of the pulse-operated low-pressure gas-phase solenoid valve at different inlet flow conditions, using the Eulerian multiphase model, established on the Euler-Euler approach, implemented in the commercial CFD package ANSYS Fluent. The results of the modelling were validated against the experimental data and also give more comprehensive information on the flow, such as the plunger displacement waveform. The flow calculations were dynamic in nature; therefore, the experimental plunger displacement waveforms were entered as input in the software for dynamic mash implementation. In identifying the times until full opening and closing, the characteristic points of the pressure waveform on the pressure sensor plate were adopted. CFD flow calculations confirmed the accuracy of identifying the times until full opening and closing by relating them to the results from the plunger displacement sensor. The validation of the results of calculations with the analyzed sensor and the original stand also confirmed the correctness of the use of this type of method for the assessment of gas injector operating times. In the case of time until full opening, the CFD calculations were shown to be consistent with experimental tests, with only a few cases where the relative difference with respect to the displacement sensor reached 3%. The situation was slightly worse in the case of time until full closing, where the results of CFD calculations were in agreement with the displacement sensor, while the experimental test stands had a relative difference of up to 21%. It should be remembered that the sensor evaluates times below 5 × 10-3 s, and its construction and response time determine the use depending on the adopted level of accuracy.

Application of Smart Materials in the Actuation System of a Gas Injector.

This paper presents the results of research related to the selection of materials for passive and active components of a three-layer piezoelectric cantilever converter. The transducer is intended for use in a low-pressure gas-phase injector executive system. To ensure the functionality of the injector, its flow characteristics and the effective range of valve opening had to be determined. Therefore, a spatial model of the complete injector was developed, and the necessary flow analyses were performed using computational fluid dynamics (CFD) in Ansys Fluent environment. The opening and closing of the injector valve are controlled by a piezoelectric transducer. Thus, its static electromechanical characteristics were found in analytical form. On this basis, the energy demand of the converter, required to obtain the desired valve opening, was determined. Assuming a constant transducer geometry, 40 variants of material combinations were considered. In the performed analyses, it was assumed that the passive elements of the actuator are made of typical materials used in micro-electromechanical systems (MEMSs) (copper, nickel, silicon alloys and aluminum alloys). As for the active components of the converter, it was assumed that they could be made of polymeric or ceramic piezoelectric materials. On the basis of the performed tests, it was found that the energy demand is most influenced by the relative stiffness of the transducer materials (Young's modulus ratio) and the piezoelectric constant of the active component (d31). Moreover, it was found that among the tested material combinations, the transducer made of silicon oxide and PTZ5H (soft piezoelectric ceramics) had the lowest energy consumption.

Investigation of the Near-Tip Stress Field of a Notch Terminating at a Bi-Material Interface.

The article deals with the problem of a sharp corner, the tip of which is located on the bi-material interface. The paper presents a qualitative and quantitative description of singular stress fields occurring in the tip area of such a stress concentrator. The qualitative description was obtained by solving the problem of the plane theory of elasticity with appropriately defined boundary conditions. To obtain a quantitative description, it was necessary to determine the values of generalised stress intensity factors (GSIFs). The GSIFs were determined using the developed analytical-numerical method. The calculations were made for various load variants (uniaxial/biaxial tension load, shear load) and notch positions (single/double edge-notched plate, centre-notched plate). Additionally, the impact of notch geometry (height and opening angle) and relative stiffness (Young's moduli ratio of both components of bi-material) on GSIFs was investigated. It has been noticed that with a decrease in the relative stiffness and an increase in the notch angle or its height, the normalised GSIFs values increased. The obtained results were compared with the data available in the literature and their satisfactory agreement with those presented by other scientists was found.

Static Electromechanical Characteristic of a Three-Layer Circular Piezoelectric Transducer.

The paper presents research related to the functional features of a novel three-layer circular piezoelectric actuator/sensor. The outer layers of the transducer are made of non-piezoelectric material. The middle layer comprises two elements-a piezoelectric disk, and a ring made of non-piezoelectric material. The additional external passive layer has a very important function; it protects the transducer's electrical components against damage caused by external factors. Also, if sparking on the transducer wires or electrodes occurs, this layer prevents fire. So far, there is no analytical model for such a transducer. Closed-form analytical equations are important tools for predicting and optimizing the operation of devices. Thus, using both the Plate Theory and constitutive equations of piezoelectric materials, an analytical formula describing transducer deflection as a function of electrical loads has been found (electromechanical characteristic of the transducer). In addition, it is worth noting that under certain assumptions, the developed analytical model can also be used for two-layer transducers. The tests carried out show satisfactory compliance of the results obtained through the developed solution with both literature data and numerical data. Moreover, based on the obtained analytical model, the effect of selected non-dimensional variables on the actuator performance has been examined. These parameters include dimensions and mechanical properties of both piezoelectric disk and passive plates and strongly influence the behavior of the transducer.