Determining the Stages of Deformation and Destruction of Composite Materials in a Static Tensile Test by Acoustic Emission

Composite materials are used in many industries. They are construction materials that are being used more and more often, which makes it necessary to accurately identify the process of their destruction. Recent decades have resulted in an intensive increase in diagnostic tests of structures and mechanical elements. Non-destructive testing (NDT) represents a group of test methods (surface and volumetric) that provide information about the properties of the tested element without changing its structure. The method of acoustic emission (AE) is also being used more frequently. Thanks to the ability to detect and locate signal sources, as well as to perform tests during operation, it is a method that is increasingly used in industry. In this article, the acoustic emission was used to analyze the changes occurring in composite materials. Obtained parameters helped to determine the signals originating from fibre delamination, fibre cracking, etc., as well as the starting point of these changes and the stress values at which these changes occurred. The analysis of acoustic emission signals recorded during the tests helped to determine the values of amplitudes characteristic for the destruction mechanisms of considered composite materials. Signals with an amplitude in the range of 30–41 dB may indicate elastic–plastic deformation of the matrix. Signals with an amplitude in the range of 42–50 dB indicate matrix cracks with the accompanying phenomenon of fibre delamination. Signals with amplitudes greater than 50 dB indicate fibre breakage. Based on the test results, the permissible stress was determined; when exceeded, the mechanisms of damage to the structure of composite materials accumulate. This stress limit for the tested material is 70 MPa. The use of the acoustic emission method in mechanical tests may contribute to a greater knowledge of composite materials used as a construction material, as well as determine the stresses allowable for a given structure.

Development of a Double Row Tractor Operated Yam Minisett Planter

Drudgery in manual yam minisett planting was identified as a major constraint facing yam cultivation in Ghana. The main objective of the study was to develop a double row yam minisett (DRYM) planter using Finite Element Analysis (FEA). A potato planter was adopted and modified to suit the design of DRYM planter. The main task was to perform 3D modeling of the planter major components using FEA method. Analysis of systems (ANSYS) software was used for FEA. Minisett and soil physical properties were factored into the design processes. Total deformation and equivalent (Von-Mises) stress were 0.442 mm and 7.37 MPa for hopper; 0.01 mm and 9.18 MPa for ridger bottom and that of furrow opener were 1.8-0.6 mm and 6.27 MPa, respectively. Maximum total deformation and equivalent (Von-Mises) stress were below material specification of 50 mm and 250 MPa for structural steel, and 20 mm and, 440 MPa for mild steel, respectively. The study concluded that the entire design was within the material property and permissible stress limits of the materials used. Yam planter development will enhance farmer satisfaction.

ЗНИЖЕННЯ МЕТАЛОМІСТКОСТІ РОТАЦІЙНО-ПРОФІЛЬОВАНИХ КОЛІСНИХ ОБОДІВ РІЗНИХ ТИПІВ І ТОВЩИНИ

The research carried out made it possible to develop a new scheme for the process of rotary profiling of wheel rims, which allows to reduce the specific quantity of metal for parts. The essence of the solution lies in the fact that at the second step the jet central section is additionally made more powerful. This allows to change the nature of the deformation after the second step and to eliminate unnecessary thickening of the jet base. With an increase in the jet depth the edge sections are subjected to insignificant tensile stresses, while the stress-strain state of the part remains symmetric and constant at each point. The worked out sequence of calculating a new technological process allows calculating all technological parameters: width and length of a flat workpiece; maximum permissible stress in the workpiece material; a profiling route; as well as to identify deformations and stresses for edge elements and in hazardous areas. Further, taking into account the elastic deformations of the workpiece, the profile of the rollers was built, and then optimal deformation force along the transitions was calculated, then feed and the number of revolutions of the rollers were assigned. The new scheme made it possible to reduce metal consumption for parts and obtain a significant economic effect. Ovality of the part and multiple repeated deformation of the same sections of the workpiece are eliminated, and the degree of strengthening of the material is also reduced.

THE SAFETY FACTORS OF PROBABILITY REACHING LIMITING STATES OF NPP EQUIPMENTS AND PIPELINES DURING DIFFERENT OPERATING MODES

Reliability theory makes it possible to determine the probabilities of destruction, reaching limit states, equipment and pipeline failures (E&P). Normative documents, as a rule, define requirements for integral indicators of reliability or safety of objects, but do not establish requirements for admissible values of probabilities for individual systems and data elements of objects. This article proposes the approach for determining the permissible values of the probabilities of reaching the yield stress or ultimate strength by operating stresses on the basis of design data on loads and data from certificates on the mechanical properties of metal. During operation, the achievement of the working stresses in metal of E&P value of the permissible stress values is a probabilistic event, in this fact, the probabilistic approach has been developed to obtain the safety factor of probability reaching limiting states. The developed approach is based on the methods of strength science, statistical analysis and probability theory. The object of application of the developed approach is thermal mechanical equipment used in different branches of technology. Using the example of the main circulation pipeline of the NPP with WWER-440, the presence of a reserve in the probability of reaching the limit state is shown and a relationship is established between the stress variation coefficient and the calculated probability for normal operation and abnormal operation. This approach determines the reserve for the probability of destruction, which will justify the extension of the resource or optimize the operating parameters of the objects under consideration.

Establishing the value of the deflection of the soil-piercing working body with an asymmetric tip when correcting the airway of movement

Trenchless laying of engineering communications is actively used in all countries of the world. Among the existing methods of formation of wells for the implementation of these technologies, the most popular is the method of ground penetration. The main disadvantage of this method is the poor accuracy of movement of the piercing head in the array. This requires constant adjustments to the trajectory of its movement. This process can be controlled by using a head with an asymmetrical tip and acting on it with translational and rotational motion. The transmission of these movements from the power unit by means of type-setting push rods. Therefore, it is important to choose a trajectory such that the deflection of the bar will be within the permissible stress range. If the bend goes beyond these limits, the rod may break and the puncture process will be interrupted. The conducted studies have established the regularities of the process of puncturing the soil with a head with an asymmetric tip in the form of an inclined flat surface. It has been established that the greatest deviation of the head from the action of the transverse component of the soil resistance force, which occurs when moving such a working body in the soil, will occur at an angle of inclination of the front surface of 25º, and the smallest deviation will occur at an angle of 55º. In addition, it was found that in heavy clay, deflection will occur almost 3 times worse than in a soup and 1.4 times worse than in a loam. It has been experimentally confirmed that at a distance of 10 m the puncture with a head with an inclined forehead surface in sandy loam was 40 mm, and in clay 20 mm. At an angle of inclination of 70º, a constant core of soil compaction is formed and the process of controlling the movement of the head stops.

Assessment and rehabilitation of a deteriorated heat pipeline overpass

A deteriorated heat pipeline overpass was subjected to assessment and rehabilitation. Lack of technical documentation, increased loading, and changing design codes had to be taken into consideration. The numerous damages and their origin were identified. Special attention was paid to corrosion at the connection zones, being the result of inadequate paint coating, aggressive environment, and leakages for technological installations. The structure was originally designed according to the design code PN-62/B-03200 from the 1960’s using the permissible stress method. After rehabilitation it was supposed to fulfil current requirements of Eurocodes. Static strength analyses were performed for both codes and the differences between them were noted. The methods for rehabilitation were limited by the requirement of limited intervention and maintaining the structure under service. The applied solution for the strengthening in form of the steel profiles welded to the existing structure is described.

Microgripper Based on Simple Compliance Configurations, Improved by Using Parameterization

The design of a novel electrothermal microgripper device is shown, which is based on an improved chevron type actuator developed considering their elements parameterization, whose resistive model is also provided. The performance of the microgripper’s parameters, such as displacement, force, and temperature distribution, with convection for the voltage range from 0 up to 5 V, is evaluated through numerical and analytical simulation. Microgripper design was also improved with aid of parameterization. The effect on the microgripper performance due to its thickness is also analyzed, finding a considerable increment in force, when thickness increases. Its main advantage is given by the simplicity of the compliance arrangement of the microgrippers jaws. Considering convection, when 5 V are applied, 37.72 °C was generated at the jaw’s tips of the Improved Microgripper 2 (IMG2), implemented with silicon, this relatively low temperature increases its capabilities of application. When the IMG2 is implemented with polysilicon, its response is competitive comparing with a more complex microgripper, increase of displacement (50%) is shown, but a decrement of force (30%). The diameters allowed for the subjection objects are found between 84.64 µm and 108 µm, with weights lower than 612.2 µg. Some tests of subjection were performed using microcylinders of Au, glass ceramic, polycarbonate and carbon fiber, showing a permissible stress on them, considering its Young’s modulus, as well as the total reaction force induced. All simulations were done on Ansys software. The results demonstrate the feasibility of the future microgripper fabrication.

Influence of Tightening Torque of Emergency Cooling Heat Exchanger Flange Studs on Strength

Previous efforts on assessing static strength of the flange joint components of the emergency cooling heat exchanger 08.8111.335 SB (ECHE) performed using the finite element method (FEM) revealed that there is an excess of permissible stress values for flange joint components of heat exchanger Dn2130 and Dn2080. These static strength calculations considered the design values for tightening of flange studs. Failure to meet the strength conditions flange joint components is due to the fact that the effect of «protrusion» under pressure of the bottom and shell attached to the flanges, as well as depending on the tightening force of the studs, the system of equilibrium applied force changes. This, in turn, leads to deformation of flange joint components. The paper presents an approach to reducing stress in flange joint components of ECHE first used at ZNPP-4. As a result of additional iterative calculations, the boundary conditions under which the strength conditions in all flange joint components of the heat exchanger are met are determined. In addition, the compliance with tightness condition for flange connections is considered. Thus, the analysis of the calculations established that when the tightening value of flange connection Dn2080 studs equal to 6800 kgf (corresponding to the torque on the key of 65 kg ∙m), the strength conditions for all groups of reduced stresses in all elements of the flange unite. In addition, at this value of stud tightening, the tightness of the flange connection Dn2080 is maintained. Analysis of similar iterative calculations of flange connection Dn2130 shows that for this flange connection it is recommended to reduce the tightening of the flange connection studs to the value of 14600 kgf, which is equal to the torque on the key of 145 kg ∙ m.

Finite Element Analysis (FEA) Based Frequency Optimization of Vertical Storage Column

The ethanol containing vertical storage column is typically a leak proof tank which is used to store the liquid and fine powder. To exploit the storing capability, these columns are generally precise high normally above 27meters with a circular cross section. The task arranged is that the agitator and the vertical pole are necessary to be on the equal podium. Due to this the pole is predisposed to vibrations from the Campaigner. This was needed to optimize the natural frequency of the column. Stiffeners /Support are fond of to the column plate to reinforce the column counter to pressure force, to minimize the vibrations of the plate and to become rigid plate against buckling. Stiffeners must be set apart at some suitable positioning so that plate stress is low than permissible stress. If column panel tallness or breadth is less than acceptable plate span then according to assumption column doesn’t requires stiffeners/support. Though if column lifted or handles in one piece then, some stiffening may be required to keep column shape. Rise the stiffness by growing stiffeners/supports leads to load increase so no actual variance in rate of recurrence. By reducing mass of column and that can be possible only by selecting proper material. The objective of entire effort is to design of the vertical column in such a way that the natural frequency of the column can be optimized. As number of supports (horizontal) are increasing the natural frequency of column is also increasing, but at same time weight is also increased. So in order to optimize design the weight of column provided by support must be reduced. After optimize the structure of support and carrying out pre stressed modal analysis the targeted natural frequencies (>16 Hz) is obtained in the structure.