Papers by Keyword: Stiffness

Abstract: The paper considers issues the nonlinear behavior of shear bonds affecting the changes in the distribution of stresses and strains in vertical structures, as well as to compare these stresses and strains with the linear statement of the problem solution in which the compliance of the bonds is constant. In a complex multiconnected system of the multistory building, the new redistribution of stresses arises, which does not coincide with the original distribution of stresses. To correct the stiffness value for the bonds, the experimental data of MGSU were used. A secant module was used to determine the stiffness for links such as lintels. Loading was performed by the step method. Redistribution of stresses in the load-bearing elements of the building showed their significant leveling. The issue of ultimate deformations of shear bonds limiting the process of redistribution of stresses and deformations requires discussion.

Abstract: Investigation of the effect of low-pressure NLTP in nitrogen, argon, propane-butane and air on the properties of a multilayer medical-purpose material based on polypropylene used for the manufacture of sanitary-hygienic and medical products. It is shown that after plasma treatment of argon, nitrogen, propane-butane, the surface polarity of the CMC material changes significantly, as evidenced by a decrease in the wettability angle and an increase in capillarity. The most significant changes in indicators are observed in the case of plasma treatment in argon and nitrogen. However, in the case of argon, less processing time is required to achieve the effect. Plasma treatment leads to a slight decrease in tensile strength, no more than 10-15%. It is also shown that when plasma is treated in an argon atmosphere, such characteristics of a nonwoven material as air permeability, hygroscopicity increase, and a decrease in rigidity is observed. The study of the structure of the material (pore size) showed that the treatment with NLTP leads to a significant decrease in the size of large pores and an increase in the size of medium and small pores

Abstract: Sustainability calls for reduction in the use of natural resources and man-made materials. In light of this, the present study demonstrates the potentials of the reduction of transverse reinforcement in structural walls. A structural wall 1.7 m long was designed following the Greek Code for Reinforced Concrete (GCRC). This wall was then constructed and tested under cyclic loading. The theoretical value of the uncracked stiffness was four times greater than the value calculated after the experiment. The wall was also designed according to the Compressive Force Path method (CFP), which allowed for a significant reduction in the transverse reinforcement for the same target values.

Abstract: Composite columns are generally installed in high-rise buildings and bridges. As well as being smaller and lighter than conventional reinforced concrete columns, composite columns offer high efficiency and ductility. In this research, experimental and analytical studies were carried out to investigate the optimal distribution of the ‎total steel area of the Concrete-Filled Hollow Steel Tube (CFHST) columns; the experimental program included 20 CFHST columns. ‎The main variables of the experimental study were the distribution of the total steel cross-sectional area over the internal concrete core (steel reinforcement) and the external steel tube, the cross-sectional shape, the width-to-breadth ratio t/b, and the presence or absence of shear connectors. In addition, using equations of different codes, comparison was conducted between the experimental and analytical results. For a constant steel cross-sectional area, the use of internal steel bars and external steel tubes, together with the use of shear connectors, was found to exhibit a better ultimate load capacity, stiffness, and ductility for the CFHST columns.

Abstract: The use of ultrasonic smoothing methods for metal sheet materials opens up new opportunities for improving their performance properties. The paper considers the possibility of increasing the axial stiffness of aluminium thin-walled machine parts by reducing the size of their grains and creating conditions for obtaining nanostructured formations. It has been found that the yield strength of the 8011 grade foil treated with two-way ultrasonic smoothing, depending on the depth of the hardened layer, microstructure and grain size, initially decreases to the middle section, and then increases to its largest value. According to a similar relationship, the relative elongation, i.e. the plasticity of a thin-walled part, changes which also confirms the possibility of formation of nanostructures in the studied layers. Experimental studies have established that the two-way ultrasonic treatment of multilayered plates made of aluminium 8011 grade foil with a thickness of 0.42 mm allows to provide high plasticity and to increase its axial rigidity up to 20.6%, thereby improving the manufacturability of complex machine parts from thin-walled plates by the methods of cold treatment.

Abstract: Granulated iron oxide particles were incompletely reduced to structured particles comprised metallic iron and residual iron oxides. Structured particles were pressed into prismatic compacts and sintered. Some of sintered specimens were subsequently phosphatized and calcined. Specimens with an iron phosphate coating were found stiffer than specimens without coating. In Hanks' solution, a galvanic corrosion was induced by more noble iron oxides coupled to a less noble metallic iron. This could explain higher corrosion potentials and higher rates of iron dissolution in comparison with a pure iron. The coating of specimens with iron phosphates shifted corrosion potentials towards more negative values and slowed down the dissolution of iron. This was most likely caused by a reduction in oxygen flow through the coating to iron-oxide cathodes, which has enhanced the influence of diffusion control on the kinetics of reduction reaction.

Abstract: Five engineered cementitious composite mixtures were adopted in this study with five different contents of 0, 0.5, 1.0, 1.5 and 2.0% of untreated low cost PVA fiber. Four different test specimens were prepared from the five mixtures to conduct several tests. Abrasion tests were conducted using 300 mm discs for six time steps each of 12 hours, while 100 mm cubes were used to evaluate the compressive strength. Cylinders with 100 mm diameter and 200 mm depth were adopted for splitting tensile strength, while four-point bending tests were conducted using small concrete beams with a span of 210 mm. The modulus of rupture was calculated from the tested beams, while the stiffness and elastic energy were calculated based on the load and deflection records of the beams. The tests showed that compressive strength did not affected noticeably by fiber inclusion, while all other mechanical quantities in addition to abrasion resistance exhibited significant improvement due to PVA fiber effect. The stiffness, splitting tensile strength, modulus of rupture and elastic energy exhibited maximum developments of 45, 134, 287 and 1181%, respectively, due fiber addition to the mixture. Quadratic formulas were found to be very accurate to correlate the relationship between abrasion depth in millimeters and each of splitting tensile strength, modulus of rupture and elastic energy, where R² values of these relations were between 96.7 and 99.5%.

Abstract: Nowadays, it is important to select the proper material for parts of the car-body’s deformation zones in terms of passenger safety. Due to wide range of high-strength steels on the market, the article presents the way of selecting the material by determining the deformation work and the stiffness constant, both measured by the stretch-bending test. The procedure was verified on a high-strength micro-alloyed steel HSLA, high-strength multi-phase steels DP 600 and TRIP, and an austenitic stainless steel AISI 304. The results indicate the austenitic steel is better to use in the deformation zones for the frontal impact, while multi-phase steels are more suitable for deformation zones at the lateral impact. The regression model describing the dependence of the deformation work measured at the stretch-bending test and the deformation work measured at uniaxial tensile test was defined as well. The model allows predicting the deformation work at stretch-bending test based on the mechanical properties measured by the tensile test.

Abstract: It is presented the study of the beam samples reinforced with metal armature, BFRP armature and beams with hybrid reinforcement using metal and BFRP armature. Half of the tested samples of beams were manufactured on concrete with river sand, as a fine aggregate. The others were made on concrete with fractionated fine wastes of Mining and Beneficiary complex (MBC) instead of the river sand. The tests were carried out by static loading of the scheme of a single-run free beam loaded in the thirds of gear. It was established that the beams reinforced with BFRP armature and the beams with hybrid reinforcement showed an increase of strength, about 40%, compared with the beams reinforced with metal reinforcement. The deflections of the beams reinforced with BFRP armature were 315% -331% higher than the deflections of the beams reinforced with metal reinforcement and 165% -205% higher than it is allowed by standards. The use of hybrid reinforcement allowed reducing their deflections in two times compared to the beams reinforced with BFRP armature. At a load level of 60% of the destructive, the deflections of beams with hybrid reinforcement BFRP and metal armature did not exceed the maximum permissible norm. When concrete samples manufactured, the substitution of the river sand with fine fractionated wastes from the Mining and Beneficiary complex (MBC) did not affect their durability and deformability (the difference between the values according to these indicators is within the statistical error).

Abstract: In orthodontics, nickel-titanium wires are used for teeth alignment and leveling. For leveling the curve of Spee, reversed curve archwires are often used to increase the vertical force needed to correct a deep bite.Objectives: The aims of this study were to investigate and compare the mechanical properties (unloading force, stiffness, springback, and surface hardness) of the pre-formed plain and reversed curved NiTi archwires.Materials and Methods: NiTi wires of dimensions 0.016x0.022 inch were divided into two groups, Group 1 - plain and Group 2- reversed curve NiTi archwires. For each type of the archwire, load-deflection curve obtained from a three-point bending test, performed by a Texture Analyser (TA.XT.plus, Stable Micro System, United Kingdom) with 5 kg load cell at room temperature, was used to analyze unloading force, springback, and stiffness. Surface hardness was measured by Vickers micro-hardness tester. Kruskal-Wallis test was used to analyze the variables of this study.Results: The results showed that the unloading force of each deflection point of the reversed curve NiTi archwire was more than the plain archwire. The means of unloading force, stiffness, and springback were 2.42 N, 2.76 N; 0.28 N/mm, 0.49 N/mm; and 2.94 mm, 2.98 mm for the plain archwire and reversed curve NiTi archwire, respectively. The properties of reversed curve NiTi archwire were significantly higher (p<0.05) than the plain NiTi archwire, except the springback. The surface hardness of the plain archwire was significantly higher (p<0.05) than reversed curve NiTi archwire in each segment.Conclusion: The reversed curve NiTi archwire had more unloading force and stiffness than plain NiTi archwire. For the correction of deep curve of Spee in orthodontic treatment, clinicians must be aware of the vertical force needed during intrusion of lower incisors or the wires should be used in the later leveling and aligning stage.