Damage Assessment of Concrete under Wind-Sand Load

In this paper, a numerical model of wind-sand flow is established to explore the influence of wind-sand flow parameters on the stress state of the concrete. According to the contact mechanics theory, the wind erosion critical pressure of concrete members and the corresponding stress state of concrete are analyzed. A wind erosion damage assessment index based on stress fatigue theory is proposed.

An Integrated Study of Water Weakening and Fluid Rock Interaction Processes in Porous Rocks: Linking Mechanical Behavior to Surface Properties

We investigated the impact of water weakening on the mechanical behavior of Obourg Chalk and Ciply Chalk (Mons Basin, Belgium). Different mechanical tests were conducted to estimate the unconfined compressive strength (UCS), tensile strength, Young’s modulus, mechanical strength under triaxial loading, critical pressure, fracture toughness, cohesion, and internal friction coefficient on samples either dry or saturated with water or brine. This extensive dataset allowed us to calculate wet-to-dry ratios (WDR), i.e., the ratio between any property for a dry sample to that for the water-saturated sample. For both chalks, we found that water has a strong weakening effect with WDR ranging from 0.4 to 0.75. Ciply Chalk exhibits more water weakening than Obourg Chalk. The highest water weakening effect was obtained for UCS, critical pressure, and Young’s modulus. Weakening effects are still present in brine-saturated samples but their magnitude depends on the fluid composition. The mechanical data were correlated to variations in surface energy derived from three different methods: fracture mechanics, contact angle goniometry, and atomic force microscopy. Water weakening in the tested chalks can be explained by a clear reduction in surface energy and by the existence of repulsive forces which lower the cohesion.

Analysis of leakage characteristics for bent-axis piston pump based on elastohydrodynamic deformation

Purpose This paper aims to revel the leakage characteristics of the bent-axis piston pump considering elastohydrodynamic deformation via a dynamic leakage model. Design/methodology/approach A dynamic leakage model of bent-axis piston pump based on elastohydrodynamic lubrication theory is proposed, which is used to present the leakage characteristics of bent-axis piston pump. The model is composed of three parts. First, the dynamic gap in the piston ring-cylinder bore interface (PRCB) is described via the elastohydrodynamic lubrication equations. Then, the PRCB leakage is presented based on the dynamic gap. Finally, combined with leakage equation of the valve plate-cylinder block interface (VPCB), the total leakage model is proposed. Through the numerical simulation and experiment, the leakage characteristics of bent-axis piston pump considering elasto-hydrodynamic deformation are studied. Findings The PRCB leakage is negatively correlated with VPCB leakage under the range of 800–1400 r/min and 1–25 MPa. When the discharge pressure is less than the critical pressure, the PRCB leakage is the main factor affecting the total leakage in bent-axis piston pump. On the contrary, the VPCB leakage is the main factor. The critical pressure increases with increasing speed Originality/value The effect of operating parameters has a significant effect on the elastic deformation of piston ring without considering wear of friction pairs in bent-axis piston pump. There is a critical phenomenon in the leakage, which is related to the operating parameters, and provides a novel idea for extracting wear information from leakage and evaluating the status of bent-piston pump.

Application of mathematical modelling in the process of design and production of pressure vessels

The paper presents the engineering practice, which the company “Regeneracija” Ltd. Velika Kladuša – Bosnia and Herzegovina uses to perform preliminary experimental testing and measurements, followed by mathematical modeling of critical pressure of these vessels, in order to obtain the projected quality of pressure vessels made of composite materials. The paper will confirm the hypothesis that it is possible to relate mathematical connection and dependence of the critical pressure of vessels of composite materials (Pkr) with mechanical characteristics of vessel material (σM), vessel diameter (D), and vessel wall thickness (s). In this way, by varying the mentioned parameters, it is possible to achieve the desired product quality in the production of composite material containers by achieving the projected critical and thus working pressure. Generally speaking, the mathematical model of critical pressure obtained in this way will be a good indicator for design engineers to know how much critical pressure a given vessel can withstand, and based on that to take quick control of working or projected pressure, but also for designing completely new vessels made of composite materials as a substitute for the expensive experimental testing.

The influence of friction on gas parameters in the minimum section of nozzles

Processes of gas flow in nozzles, accompanied by the release of frictional heat, are presented in the form of polytropic processes. The polytropic process index n determines the degree of irreversibility of the gas flow process caused by the release of frictional heating. Relations are obtained to calculate the flow rate and thermodynamic properties of gas in the minimum section of the Laval nozzle and in the outlet section of the convergent nozzle at a pressure behind the nozzle less than the critical pressure. The gas calculated parameters (pressure, temperature, specific volume, velocity, cross-sectional area) in the minimum cross-section differ from the recommended values in the reference literature [1]. In particular, the gas pressure in the minimum cross section turns out to be higher than the critical pressure recommended in [1].