Ograniczanie wyników
Czasopisma help
Autorzy help
Lata help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 410

Liczba wyników na stronie
first rewind previous Strona / 21 next fast forward last
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  naprężenie
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 21 next fast forward last
PL
Zarówno podczas eksploatacji samolotów i śmigłowców, jak również w badaniach elementów innych struktur cienkościennych obserwuje się wiele interesujących zjawisk zachodzących w połączeniach nitowych, jak na przykład odkształcenia plastyczne, fretting itp., które wpływają ujemnie na trwałość połączenia, powodując inicjację pękania pokrycia. W artykule zaprezentowano wyniki badań dotyczących wizualizacji pól naprężeń metodami analizy MES oraz optycznymi połączeń nitowanych oraz wskazano na możliwość wykorzystywania tego rodzaju metod w badaniach odkształceń występujących w tych połączeniach.
EN
During the exploitation of aircraft and helicopters, as well as in the study of elements of other thin-walled structures, many interesting phenomena are observed in riveted joints, such as plastic deformations, fretting, etc., which negatively affect the durability of the joint, causing the initiation of cracking of the covering. The paper presents the results of research concerning the visualization of stress fields by FEM analysis methods and optical methods of riveted joints and indicates the possibility of using such methods in studies of deformation occurring in such type of joints.
EN
In galleries digged for different type of uses, but mostly for extracting coal, hydrotechnical adduction galleries but also for tunnels, after the dislocation of the rocks is done, the tenssions in the rock changes massively. We take for example a metallic structure used as provisory structure until the rock pressure stabilize and used in Petroșani Romania, coal mines. The galleries are digged with explosives and the shockwave gives excessive cracks and disturb the rock pressure and its characteristics. The space between the metallic structure, rock walls and bolt is filled with wood, but this article suggests a rubber band material so the rock pressure to be distributed uniformly and not concentrated in the contact points between the wood and metal profile.
PL
W wyrobiskach wybranych do różnego rodzaju zastosowań, głównie do wydobycia węgla, budowli hydrotechnicznych, tuneli, po zakończeniu wydobycia skal napięcie w skale zmienia się ogromnie. Jako przykład pokazano stabilizowanie się ciśnienia w wyrobiskach w kopalni węgla Petroșani w Rumunii Eksploatacja jest prowadzona za pomocą materiałów wybuchowych, fala uderzeniowa powoduje nadmierne pęknięcia i zaburza ciśnienie w skałach. Przestrzeń między obudowa a górotworem metalową jest wypełniona drewnem, ale w tym artykule przedstawiono zastosowanie gumy dla uzyskania równomiernego nacisku skały.
PL
Omówiono problematykę projektowania drewnianych belek dwutrapezowych z otworami w strefie kalenicy. Przedstawiono zagadnienia normowe oraz obliczenia numeryczne za pomocą metody elementów skończonych, z uwzględnieniem zbrojenia wzmacniającego. Zamieszczono rekomendacje dotyczące położenia otworów i stosowanego zbrojenia.
EN
The paper is dedicated to design of timber double tapered beams with openings in the apex area. Standard design regulation as well as computational analysis by the finite element method with the influence of reinforcement are presented. The work is supplemented with recommendations regarding the location of openings and the reinforcement used.
EN
A relation connecting stress intensity factors (SIF) with displacement intensity factors (DIF) at the crack front is derived by solving a pseudodifferential equation connecting stress and displacement discontinuity fields for a plane crack in an elastic anisotropic medium with arbitrary anisotropy. It is found that at a particular point on the crack front, the vector valued SIF is uniquely determined by the corresponding DIF evaluated at the same point.
6
EN
The problem of gap estimation for a break of a continuous welded rail is studied. The track is represented as a semi-infinite rod on elastic-based damping. Static and dynamic solutions are obtained. It is shown that during the rail break, the dynamic factor does not exceed 1.5. We derive equations for thermal deformation of the welded rail of jointless track on an elastic foundation in the presence of the insert into the base with another characteristic stiffness. It is shown that the presence of the insertion of up to 20% of the length of the rail, with both large and small stiffness, has a little effect on the stress-strain state (SSS) of the track. The presence of a rigid insert may increase the clearance of an accidental break of the rail, which has a negative effect on traffic safety.
EN
Finite element and response surface methods were utilized to investigate the stress concentration factor induced in isotropic rectangular plates with two identical countersunk rivet holes due to uniaxial tension. In this investigation, the finite element model was constructed using ANSYS software and used to produce stress concentration factor (SCF) data. Additionally, the response surface method (RSM) was implemented to characterize the influence of the problem geometric parameters on the SCF. Besides, RSM combined with least squares regression methods were employed to formulate a simple and effective equation to mathematically compute the stress concentration factor […] value. This equation was consequently verified with finite element analysis (FEA) results. Lastly, an optimum plate and holes configuration that minimizes the SCF was suggested and hence recommended.
PL
Przedmiotem rozważań zaprezentowanych w pracy są przemieszczenia i naprężenia w elementach stalowych dźwigarów kratowych, spowodowane zmianami temperatury zewnętrznej i nierównomiernym rozkładem temperatur wewnątrz hali. Wielodniowe pomiary przemieszczeń stalowych, kratowych dźwigarów dachowych dużej rozpiętości połączone z pomiarami temperatury w przestrzeni hali i w różnych punktach dźwigarów wykazały znaczący wpływ nierównomiernego rozkładu temperatur na przemieszczenia. Zmierzone wartości przemieszczeń zostały porównane z przemieszczeniami otrzymanymi drogą symulacji numerycznych, w których danymi wejściowymi były pomierzone temperatury. Poza przemieszczeniami w pracy przeanalizowano także wzrost naprężeń w wybranych elementach dźwigara kratowego, spowodowany nierównomiernym rozkładem temperatur. Oceniono destrukcyjny wpływ temperatury na stan wytężenia analizowanych stalowych dźwigarów kratowych.
EN
The subject of considerations presented in the work are displacements and stresses in steel elements of truss girders, caused by changes in the external temperature and uneven distribution of temperatures inside the hall. Multi-day measurements of displacement of steel, large-span truss roof girders combined with temperature measurements in the hall space and at various points of the girders showed a significant influence of uneven temperature distribution on the displacements. The measured displacement values were compared with the displacements obtained by numerical simulations, in which the input data were measured temperatures. In addition to displacements, the increase of stress in selected elements of the truss girder, caused by uneven temperature distribution, was also analyzed in the paper. The destructive effect of temperature on the strain and stress state of the analyzed steel truss girders was assessed.
9
Content available remote Deflection of an eccentric crack under mixed-mode conditions in an SCB specimen
EN
Crack propagation under mixed-mode (I + II) conditions has been investigated in a semicircular disc where various levels of mixed-mode can be achieved by means of different geometry configurations. The research has been performed on a novel cementitious material, alkali-activated concrete. Its main advantage is that it is environment-friendly. On the other hand, its fracture mechanical properties, as of yet, have not been described sufficiently. Therefore, a fracture analysis has been performed. The crack deflection under three point bending conditions has been investigated numerically as well as experimentally. The numerical approach is based on a combination of the common finite element analysis and a multi-parameter form of the maximum tangential stress criterion. This generalized method is suitable especially for materials with specific (elasto-plastic, quasi-brittle etc.) fracture behaviour. The over-deterministic method together with the Williams expansion is applied to approximate selected stress tensor components around the crack tip. In this work, the influence of the eccentric crack is also discussed. In the conclusions, several recommendations about using single-parameter/multi-parameter fracture mechanics are stated.
EN
Thermal barrier coating (TBC) with Al2O3 and 8YSZ as topcoat constituents has been developed. The commercially available 8YSZ (80% wt.), Al2O3 (17 and 19% wt.) and multiwall carbon nanotubes (MWCNT) (3% and 1% wt.) were plasma sprayed to produce composite coatings. A stress relaxation technique using a slow-speed diamond cutter has been used to relax the strain and determine the through-thickness residual stress in the coatings. A 3D finite element model was developed, the model was experimentally validated, and the model was used to establish a relationship between applied stress and relaxed strain. The addition of alumina increased the compressive residual stress on the surface of the coating by 42%, the addition of 1% MWCNT had a negligible effect on the residual stress on the coating surface. The further addition of MWCNT (3% wt.) resulted in tensile residual stress in the coating as a result of MWCNT agglomeration.
11
EN
A method has been developed for determining residual stress based on displacement fields near drilled holes analyzed using 3D digital image correlation. Finite element modeling was used to determine corrections for analytical equations describing displacement fields near the blind holes, which made it possible to determine the residual stress distribution over a wide range of hole depth-to-hole diameter ratios and various areas of displacement field measurements using inverse method iterative calculations. The proposed method eliminates many drawbacks of traditional procedure based on strain gauges as hole eccentricity sensitivity and requirement of the relatively large span between holes. The method and testing setup, build-up of generally available components, were used to determine the residual stress distribution for 316 LVM samples processed by two methods from the large deformation group: hydrostatic extrusion (HE) and high-pressure torsion (HPT), by drilling 1.75 and 0.58-mm-diameter blind holes, respectively. In the case of the measurements performed on the surface of a HE-processed 16 mm bar cut along its diameter, a gradual change was revealed-from a compressive to a tensile residual stress distribution (from ~ − 300 MPa in the center to 400 MPa in 4 mm distance from the edge) in the longitudinal direction, with near-zero values in the radial direction. Moreover, the method was also adapted to perform measurements on the outside surface of the bar, which gave results consistent with those taken along the radius profile (~ 600 MPa longitudinal stress). Measurements on the top surface of a cylinder 10 mm in diameter and 1 mm high processed by HPT showed a high compressive residual stress in the center and a dominant shear component for the holes drilled at different distances from the center.
EN
The paper presents the results of experimental investigations of total tensile stresses in a gyroplane’s rotor during flight. The research aimed to determine which flight maneuvers induce the greatest stress in the rotor blade and the hub bar. The object of research was an ultralight gyroplane Tercel by Aviation Artur Trendak equipped with a rotor by the same manufacturer. Measurements were taken a) at the root of the rotor blade in the longitudinal direction, at the rotor blade’s lower surface in the point where the blade is attached to the hub bar, and b) in the hub bar, on its lower surface also in the longitudinal direction. To measure the stress, the author constructed an original measuring system based on the strain gauge bridge circuit mounted on the rotor head. The tests were carried out in a wide range of maneuvers within the gyroplane’s flight envelope. The highest value of tensile stress was found to occur while rapidly reducing the horizontal velocity in steep descent.
13
Content available Fatigue testing machines and apparatus
EN
This paper presents selected examples of construction and applications of fatigue test stands. The authors made a review of universal fatigue machines and test stands, made specifically for own and individual programs to research fatigue material properties. The publication contains the developed procedures to determine the fatigue life of materials. The authors also describe how to implement these procedures to control and measurement systems in research stands. The article briefly reviews the history of the development of fatigue testing methods, with respect to industrial needs. Moreover, it presents selected examples of solutions and applications systems for fatigue testing, available in scientific
PL
W artykule przedstawiono wybrane przykłady budowy i zastosowań stanowisk do badań zmęczeniowych tworzyw konstrukcyjnych. Autorzy dokonali przeglądu uniwersalnych maszyn zmęczeniowych i stanowisk testowych, jak również urządzeń stworzonych specjalnie dla indywidualnych programów badania własności zmęczeniowych materiałów. Autorzy opisują również, jak wdrożyć te procedury do układów sterowania i pomiarów w stanowiskach badawczych.. W artykule przedstawiono historię rozwoju metod badań zmęczeniowych w odniesieniu do potrzeb przemysłu. Ponadto zaprezentowano wybrane przykłady rozwiązań i ich aplikacji do badań zmęczeniowych, dostępnych w nauce.
EN
The article is devoted to solving the fundamental and applied problem of nonlinear structural me-chanics of machines by introducing into the drum two additional stop cylinders with supporting rollers at the end and adjustable length, providing a given elliptical or circular shape of a flexible shell with a smoothly variable geometry in the area of its contact with compacted pavement material. Compaction of soil, gravel and asphalt concrete in the sphere of road is not only an integral part of the technological process of the roadbed, road foundation and surface construction, but it is actually the main operation to ensure their strength, stability and durability. The quality, cost and speed of road construction, the possibility of using fundamentally new technologies, structures and materials is largely determined by the availability of modern road machinery.
EN
The lack of a common methodology on compaction theory stimulates developers of road construc-tion equipment to create various approximate methods for their calculation, the number of which, at the present time, is comparable with the nomenclature of the proposed designs of rollers. The article presents the analysis of the deformable shell behavior of a road roller, and the compacted material under its compacting roller, in a situation when a rigid circular shell of the roller is replaced by a forcefully deformable elliptical shape, which, unlike the circular design, allows variation, adjustment and optimization of the road roller impact on the material to be compacted.
PL
W artykule przedstawiono wyniki badań naprężeń wewnętrznych w szynach kolejowych i w zgrzewanych połączeniach szyn. Badano przebieg naprężeń w złączach szynowych po zgrzewaniu oraz po badaniach zmęczeniowych. W badaniach naprężeń zastosowano tensometryczną metodę niszczącą. Porównano kształtowanie się naprężeń w szynach oraz złączach szynowych wykonanych ze stali gatunku R260 oraz gatunku R350HT. Metodę pomiaru naprężeń oparto na wymaganiach zawartych w normie PN EN 13674-1:2011+A1:2017.
EN
Purpose: The aim of the study was to determine forces which are transferred to supporting teeth during the treatment with the midpalatal device with Hyrax screw and to evaluate orthodontic and orthopaedic effects based on displacement analysis. Design/methodology/approach: The finite element method (FEM) was used to simulation the midpalatal expansion forces activated by the screw pre-loaded during a turn of 180° which corresponds to daily recommended value. Distribution of expansion forces of Hyrax device was calculated as reaction forces on elastic supports with stiffness corresponding to the teeth working on periodontal ligament in alveolar bone. Findings: On the basis of the displacement analysis was observed the movement of supporting teeth by a value higher than 0.1 mm which corresponds to the recommended daily value. The midpalatal suture splitting forces were determined on the first premolars with a value of 32.8 N and on the first premolars of 44.2 N. Research limitations/implications: The studies did not take into account the shape of palate other craniofacial bones and their stiffness. Practical implications: Adjusting the stiffness of the device to degree of ossification midpalatal suture and teeth mobility. Searching for new solutions which eliminate the negative phenomenon of tilting teeth during the expansion of maxilla and recommending a surgically assisted techniques. Originality/value: The simulation confirmed that treatment with Hyrax screw gives a uniform expansion with values of forces corresponded to stiffness of premolar and molar teeth. The studies have indicated a possibility of tendency to tilting the supporting teeth what is a negative phenomenon.
PL
Przedstawiono rozwiązania analityczne wpływu pierwotnych i wtórnych efektów skurczu na stan naprężenia i odkształcenia w stalowo-betonowych belkach zespolonych. W belkach swobodnie podpartych skurcz betonu powoduje dodatkowe ugięcia oraz naprężenia, a w wieloprzęsłowych belkach statycznie niewyznaczalnych wtórne efekty skurczu betonu - dodatkowo powstanie wzbudzonych sił wewnętrznych.
EN
The article presents analytical solutions of the infuence of the primary and secondary effects of concrete shrinkage on stress and strain state in steel-concrete composite beams. In sigle-span simply supported beams shrinkage of concrete causes additional deflections and self-equilibrated stresses. In multi-span statically indeterminate beams the secondary effects of shrinkage also give rise to induced cross sectional forces.
EN
In the present paper, we have studied the temperature and pressure dependent creep stress analysis of spherical shell. The review is critical to enhance the warm resistance of spherical shells in high-temperature conditions. The effect of different parameters was studied and it was noticed that the parameter n has a significant influence on the creep stresses and strain rates. Creep stresses and strain rates are ascertained on the premise of summed up strain measures and Seth’s transition hypothesis. This investigation is completed to demonstrate the impacts of temperature on the creep stresses and strain rates in the spherical shell. The resulting quantities are computed numerically and depicted graphically. It has been watched that the spherical shell made of an incompressible material is on more secure side of configuration when contrasted with the shell made of a compressible material.
first rewind previous Strona / 21 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.