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EN
High strength low alloy (HSLA) steels are a new generation of plain carbon steels with significantly improved mechanical properties while maintaining good weldability with common commercial techniques. Residual stress and microstructural analysis of welded HSLA Strenx 700 MC was carried out in this research. Results have shown that the welding process causes significant grain coarsening in the heat affected zone. The microstructural changes are also accompanied with creation of tensile residual stress field in the weld metal and heat affected zone, reaching up-to depth of 4 mm. Tensile residual stresses are well known for acceleration of fatigue crack initiation and together with coarse grains can lead to significant decrease of the fatigue properties of the welded structure.
EN
Industries that rely on additive manufacturing of metallic parts, especially biomedical companies, require material science-based knowledge of how process parameters and methods affect the properties of manufactured elements, but such phenomena are incompletely understood. In this study, we investigated the influence of selective laser melting (SLM) process parameters and additional heat treatment on mechanical properties. The research included structural analysis of residual stress, microstructure, and scleronomic hardness in low-depth measurements. Tensile tests with specimen deformation analysis using digital image correlation (DIC) were performed as well. Experiment results showed it was possible to observe the porosity growth mechanism and its influence on the material strength. Specimens manufactured with 20% lower energy density had almost half the elongation, which was directly connected with the porosity growth during energy density reduction. Hot isostatic pressing (HIP) treatment allowed for a significant reduction of porosity and helped achieve properties similar to specimens manufactured using different levels of energy density.
EN
In the current research the hydrostatic extrusion (as one of the most common method of grain refinement) of the commercial 1.4462 duplex stainless steel was carried out using several reduction stages leading to a cumulative deformation strain ɛ = 1.4, and then ɛ = 3.8. The extrusion process has led to a change of microstructure and texture of the investigated material as was expected. Moreover, these changes were accompanied by improvements in mechanical properties measured by the nanohardness. The aim of this research was the characterization of the texture, residual stress and mechanical properties after subsequent stages of deformation.
EN
The results of experimental studies on the dependence of the thickness of amorphous-crystalline Zr-Al-B coatings on the value and level of distribution of type 1residual stresses were presented. It was demonstrated that residual compressive stresses arise in the surface layers of coatings, which in absolute value are not significant for its integrity and quality. It was established that the amorphous-crystalline composition, under the conditions of minimizing residual stresses and the optimal combination of the volume fraction of components, the structure and morphology of their components, has the best surface strength and wear resistance under friction compared to tungsten carbide and iron coatings
EN
In this study, the influence of thermomechanical coupling effect - the effect of thermal expansion due to dissipation of the energy of plastic deformation, with and without taking into account the stored energy of plastic deformation (SEPD) for the distribution of stresses, strains, temperature, the applied pressure and the residual stresses is examined. The residual stresses remain in a thick-walled tube (a cylindrical thick-walled tank) after removing the internal pressure in the process of purely elastic unloading. The analysis is made on the example of an analitycal solution for a thick-walled tube subjected to a quasistatically increasing internal pressure for the case of adiabatic processes (without heat flow). Since the loading with internal pressure is quasi-static (monotonic), then neglecting the process of heat flow can lead to some different results in calculated stresses, deformations, temperature, internal pressure and residual stresses. The calculations for isothermal type of processes of deformations (without heat or ideal cooling) are also performed for the estimation of these differences. The results calculated for the process with heat flow should be intermediate between the values obtained for isothermal and adiabatic processes.
EN
The paper deals with the measurement of the residual stresses in P91 welded pipe using the blind hole drilling technique. The P91 pipe weld joints were prepared using gas tungsten arc welding process. The residual stress measurement was carried out using the strain gauge rosette that was associated with the plastic deformation of material and stress concentration effect of multi-point cutting tool. Strain gauge response was estimated experimentally using the tensile testing for the uniaxial loading while finite element analysis was performed for biaxial loading. Gas tungsten arc welds joint was prepared for conventional V-groove and narrow groove design. The corrective formulation was developed for calculating the corrected value of residual stresses from the experimentally obtained strain value. The corrected and experimental induced residual stresses values as per ASTM E837-13 were calculated for both V-groove and narrow groove design. Post weld heat treatment (PWHT) of P91 welded pipe was also conducted to study their effect on residual stresses.
EN
The purpose of this paper was to analyse the structure and the state of residual stresses in the samples made of rolled AW-2024 and AW-7075 aluminium alloy plates, prior to machine cutting and after the process of milling under various machining conditions. The state of stresses was evaluated on the basis of measurements by means of sin2vF X-ray diffractometry and layer removal method. Furthermore, top layer microstructures were compared in half-finished product, machined product, and core material samples.
EN
The bead blasting process is widespread in both the automotive and aerospace industry and is performed in order to improve the fatigue strength of various components. Bead blasting is a cold plastic forming process during which the surface of the material processed is hit by small, hard particles consisting of steel pellets, bearing balls or glass beads. It increases the hardness of the outer layer and establishes compression stresses inside it, which is why this processing is often used to improve fatigue strength. Contrary to other peening methods, bead blasting does not result in a reduction in the height of the processed surface’s unevenness in most cases. Shot peening changes the residual tensile stresses into residual compression stresses, thanks to which, the lifetime of the parts processed is extended and their carrying capacity is increased. The double shot peening process proposed by the authors consists in a two-stage bead blasting process. The first stage consists in blasting with round cast steel pellets, pellets cut from wire or cast iron pellets. During the second stage the same samples underwent glass bead blasting. The tests conducted on the RSA-501 aluminum alloy indicate that as a result of the processing medium’s impact in the form of glass beads or pellets of different diameter and shape, a permanent plastic deformation of the material surface occurs. On the basis of the obtained results it is possible to infer that the choice of parameters of both conventional shot peening and the double shot peening determine the impact thereof on the material’s mechanical properties. Thanks to the application of the double shot peening process there is a noticeable decrease in value of the Ra parameter, by about 40% on average. When analyzing the compressive stress results it is possible to state that after the first blasting process the value of stress was increasing when moving deeply into the sample from its surface, while after the glass bead blasting the value of compressive stress was significantly higher already near the surface. Double shot peening results in an increase in the value of compressive stresses by 40-50% when compared to conventional blasting.
9
Content available remote Structure studies on the AK7-SiC composite after machining
EN
The paper presents results of the structural studies on the composites of alumina matrix after machining processes. There were used two different methods: Electrical Discharge Machining (EDM) and Abrasive Water Jet (AWJ). The phase composition of the composite was carried out by X-ray diffraction (XRD). In order to investigate the heterogeneity of the material there were conducted additional measurements using the Grazing Incident X-ray Diffraction (GIXD) for angles of 1°, 3°, 5°, 9° and 12°. Residual stresses were determined based on the sin2ψ and grazing (g-sin2ψ) methods for the main components of the composite - alumina and silicon carbide. Analysis of the diffraction patterns performed for different X-ray penetration depths, showed that the tested material was inhomogeneous. Furthermore, depending on the treatment method (EDM or AWJ), the tested materials were shown the differences, both in the phase composition and the residual stresses values, as well.
PL
W pracy przedstawiono wyniki badań strukturalnych stopów z układu AK7-10% obj. SiC, po procesie obróbki ubytkowej z wykorzystaniem dwóch metod: elektroerozyjnej i wodnościernej. Badania składu fazowego oraz jego zmian przeprowadzono metodą dyfrakcji rentgenowskiej (XRD) w geometrii Bragga-Brentano. W celu zbadania niejednorodności materiału przeprowadzono dodatkowe pomiary w geometrii stałego kata padania (SKP – Grazing Incident X-ray Diffraction) dla kątów padania promieniowania rentgenowskiego: 1°, 3°, 5°, 9°, 12°. Przeprowadzono pomiary naprężeń własnych dla głównych składników stopów, tj. Al i SiC, które wyznaczono w oparciu o metodę g-sin2ψ. Analiza dyfraktogramów wykonanych przy różnych głębokościach wnikania promieniowania rentgenowskiego wykazała, iż badany materiał kompozytowy jest wielofazowy i niejednorodny. Ponadto, w zależności od zastosowanej metody obróbki badanych materiałów (EDM i obróbka wodnościerna), wystąpiły różnice, zarówno w składzie fazowym, jak i w wielkościach wyliczonych naprężeń własnych.
EN
Thermal barrier coatings (TBCs) are widely used on different hot components of gas turbine engines such as blades and vanes. Although, several mechanisms for the failure of the TBCs have been suggested, it is largely accepted that the durability of these coatings is primarily determined by the residual stresses that are developed during the thermal cycling. In the present study, the residual stress build-up in an electron beam physical vapour deposition (EB-PVD) based TBCs on a coupon during thermal cycling has been studied by varying three parameters such as the cooling rate, TBC thickness and substrate thickness. A two-dimensional thermomechanical generalized plane strain finite element simulations have been performed for thousand cycles. It was observed that these variations change the stress profile significantly and the stress severity factor increases non-linearly. Overall, the predictions of the model agree with reported experimental results and help in predicting the failure mechanisms.
EN
Estimation of residual stress in drawn wires is an important issue in contemporary metallurgy. The present paper considers the possibility to use a non-destructive method based on magnetic measurements for this purpose. The Jiles-Atherton-Sablik model is used for the description of hysteresis loop.
PL
Oszacowanie poziomu naprężeń szczątkowych w drutach podczas procesu ich wytwarzania jest istotnym zagadnieniem we współczesnej metalurgii. W niniejszej pracy rozważono możliwość wykorzystania do tego celu metody nieniszczącej, opartej na pomiarach magnetycznych. Model Jilesa-Athertona-Sablika wykorzystano do opisu pętli histerezy magnetycznej.
EN
High temperature MgO-ZrO2 insulation coatings were grown on long-length Stainless-Steel (SS) tapes by reel-to-reel sol-gel method for applications of High Temperature Superconductor/Low Temperature Superconductor (HTS/LTS) coils and magnets. The residual stresses were investigated analytically at various temperature ranges, 580°C to 25°C (room temperature) and -196°C (liquid helium temperature), and 630°C to 25°C and -196°C for different thicknesses to be 13, 12, and 7 μm. The maximum stress values were obtained to be 1.92 GPa in tension for SS substrate with the 13 μm coating and -2.42 GPa in compression for the 7 μm MgO-ZrO2 coating in the temperature range between 630°C and liquid helium temperature. The surface morphologies and microstructure of sample were also characterized using a scanning electron microscope (SEM). SEM observations revealed that MgO-ZrO2 coatings have a mosaic like crack structure.
PL
Wysokoemperaturowe powłoki izolacyjne MgO-ZrO2 wytworzono na długich taśmach ze stali nierdzewnej metodą reel-toreel zol-żel dla zastosowań w cewkach i magnesach typu wysokotemperaturowy nadprzewodnik/niskotemperaturowy nadprzewodnik. Naprężenia badano analitycznie w różnych zakresach temperatur, 580°C do 25°C (temperatura pokojowa) i -196°C (temperatura ciekłego helu), oraz 630°C do 25°C i -196°C dla różnych grubości powłoki: 13, 12 i 7 μm. Maksymalne wartości naprężeń otrzymano w zakresie temperatur pomiedzy 630°C a temperatura ciekłego helu: 1,92 GPa (rozciągające) dla podłoża ze stali nierdzewnej z powłoką o grubości 13 μm oraz -2,42 GPa (ściskające) dla powłoki MgO-ZrO2 o grubości 7 μm. Morfologia powierzchni i mikrostruktura próbek zostały również scharakteryzowane za pomocą skaningowego mikroskopu elektronowego (SEM). Obserwacje w SEM wykazały, że powłoki MgO-ZrO2 mają strukturę pęknięć podobną do mozaiki.
EN
The paper deals with estimation of a stress concentration factor in the hole area during tensile loading. The load carrying capacity and fatigue performance of sheet samples (made of 2024 aluminium alloy) with open and riveted holes are compared. Tests confirm the insignificant influence of riveting on ultimate strength, however, it strongly affects fatigue life. The material cold working around the hole causes a decrease in maximum principal stress values as well as stress concentration moves away a few millimetres (about half a rivet radius length) from the hole. During tensile loading the maximum stress values increase slower around the riveted hole than at the open one and consequently in the former case the yield stress is achieved later.
EN
The influence of long-term ageing in NaCl on the passivity and the electrochemical behaviour of UNS S32304 is studied. The passive film thickness, the Cr/Fe ratio and the chloride content were significantly increased after ageing. The chloride distribution depends on residual stresses, sample microstructure and surface preparation.
PL
W pracy badano wpływ długiego czasu starzenia w roztworze NaCl na pasywację i elektrochemiczne zachowanie się stali UNS S32304. Wykazano, że po długim czasie starzenia znacząco wzrasta grubość warstwy pasywnej, stosunek Cr/Fe i zawartość chlorków. Rozkład zawartości chlorków zależy od rozkładu naprężeń szczątkowych, mikrostruktury i przygotowania powierzchni.
PL
W pracy zbadano wpływ parametrów technologicznych natryskiwania oraz grubości powłok uzyskiwanych łukowo na powstawanie w nich naprężeń oraz na zmianę naprężeń w procesie sezonowania wysokotemperaturowego przy temperaturze 400 -600 0C w czasie 100 - 2000 h. Stwierdzono, że naprężenia szczątkowe w powłokach powstają w wyniku dwóch konkurencyjnych, równolegle przebiegających procesów, a mianowicie: procesu wydzielania faz dyspersyjnych, któremu towarzyszy wzrost naprężeń rozciągających oraz wewnętrznego utleniania fazowego, któremu towarzyszy wzrost naprężeń ściskających.
EN
Influence of technological parameters of arc spraying and of obtained coating thickness on creation of internal stress and its changes during 100 - 2000 h aging in high temperature of 400 -600 0C have been investigated. It was concluded that residual stress in coatings are caused by two parallel processes: first one produce residual phases and increase of tensile stress and the second one is internal phase oxidation and it increases compressive stress.
EN
The paper presents the results of studies on the effect of heat treatment and cyclic deformation on the properties of the magnesium alloy AZ91. The alloy was subjected to heat treatment by solutioning and ageing (420 °C/24 h/powietrze+210 °C/4 h/powietrze) and then to cyclic uniaxial zero-start pulsating loads. The maximal amplitudes of cyclic loads 54 and 74 MPa were lower than the offset yield strength of the alloy. The microstructure of the alloy is presented, while the properties of the alloy before and after cycling loading (up to 50 and 70 cycles) are determined by measurements of residual stress made by the X-ray method of sin2fi. It has been found that cyclic deformation causes the strengthening of the alloy AZ91. The strengthening of the alloy is found to increase with increasing loading amplitude and number of cycles, with the greatest strengthening effect occurs in the first three loading cycles.
PL
W pracy przedstawiono wyniki badań wpływu obróbki cieplnej i cyklicznego odkształcania na własności stopu magnezu AZ91. Stop poddano obróbce cieplnej przesycania i starzenia (420 stopni C/24 h/powietrze+210 stopni C/4 h/powietrze) a następnie cyklicznym jednoosiowym obciążeniom odzerowo tętniącym. Maksymalne amplitudy cyklicznych obciążeń 54 i 74 MPa były niższe od umownej granicy plastyczności stopu. Przedstawiono mikrostrukturę stopu, a własności stopu przed i po cyklicznym obciążaniu (po 50 i 70 cyklach) określono przez pomiary naprężeń szczątkowych metodą rentgenowską sin2 fi. Stwierdzono, że cykliczne odkształcanie powoduje umocnienie stopu AZ91. Wykazano, że umocnienie stopu zwiększa się wraz ze wzrostem amplitudy obciążania oraz z liczbą cykli, a największy efekt umocnienia występuje w pierwszych trzech cyklach obciążania.
17
Content available remote Residual stresses and plastic zones' boundaries in two-dimensional elements
EN
In the paper, author presents the analysis of the elastic-plastic residual stresses and the boundaries of plastic zones in two-dimensional model with central circular hole. The experimental testing was carried out by photoelastic coating method. The duralumin model was loaded within the overelastic range by uniformly distributed tensile stresses. For various levels of loading, the photographs of isochromatic pattern were taken. The residual stresses along the axis of symmetry perpendicular to the stretching direction were calculated by the characteristics method, using multisectional schematization of sigma - epsilon relation for the material. The boundaries of plastic zones in the loaded model were obtained on the basis of the Treska-Coulomb yield condition directly from the isochromatic pattern. The analysis and discussion of the test results is presented.
PL
W pracy została przedstawiona analiza naprężeń własnych i granic stref plastycznych na przykładzie płaskiego modelu elementu konstrukcyjnego z otworem kołowym. Model wykonany z duraluminium został obciążony równomiernie rozłożonymi na końcach naprężeniami rozciągającymi wywołującymi częściowe uplastycznienie materiału. Do badań doświadczalnych zastosowano metodę pokryć optycznie czynnych. Na wybranych poziomach obciążenia w zakresie sprężysto-plastycznym zostały zarejestrowane obrazy izochrom, które posłużyły do wyznaczenia granic obszarów uplastycznionych oraz określenia wartości naprężeń własnych na osi symetrii prostopadłej do kierunku rozciągania. Granice obszarów plastycznych zostały wyznaczone metodą izochromy granicznej. Do rozdzielenia odkształceń wykorzystano metodę charakterystyk, a naprężenia zostały wyznaczone na podstawie przyjętego wieloodcinkowego modelu zależności sigma - epsilon dla materiału elementu. W pracy została przeprowadzona dyskusja otrzymanych wyników.
18
EN
Purpose: A parametric model is adopted and the technique of element "birth and death" is used to estimate the effect of thermal properties and weld efficiency on residual stresses in butt weld joints. Design/methodology/approach: Residual stresses and distortions on butt welded joints are numerically evaluated by means of finite element method. The FE analysis allows to highlight and evaluate the stress field and its gradient around the fusion zone of welded joints, higher than any other located in the surrounding area. Findings: The main conclusion is the significant effect of varying the value of the conductivity on residual stresses. Practical implications: Several experimental destructive and non destructive techniques for directly measuring residual stress have been developed. However, the application of these methods in practice is usually limited by either cost or accuracy. Numerical simulation based on finite element techniques, therefore, offers a comprehensive solution for the prediction of residual stress and strain as well as welding distortion in complex welded structures. Originality/value: In this study it is shown that the technique of element "birth and death" can be usefully applied to welding process in order to take into account the effect of the thermal properties of materials.
EN
Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cutting depth and tool radius nose) on the cutting forces (cutting force, feed rate cutting force and penetration cutting force) as well as on the residual stresses, in conical bearings made of steel DIN 100 CrMn6 hardened (62 HRc), searching correlations between the residual stresses and the cutting forces. Design/methodology/approach: A complete factorial planning was used to establish the correlations. At the same time, the cutting parameters influence in the microstructure of the material and it's correlation with the residual stress was studied. A turning center machine and CBN inserts was employed for the tests. To the cutting force measurements was carried out using a piezoelectric dynamometer. The residual stresses measurements were carried out by X-ray diffractometry. Findings: The penetration cutting force was the most important factor in the residual stress generation, and it was influenced by the feed rate and the cutting depth. A correlation between the cutting depth and the residual stresses was established. The results do not showed any changes in the microstructure of the material, even when the greater cutting parameters were used. Research limitations/implications: The residual stress is one of the major causes of failures in bearings by contact fatigue, keeping this on mind, this work helps the developer to select correct cutting parameters in order to increase the machined workpiece life in service. Originality/value: This work were based on the real components (conical bearings), real cutting conditions and with these results were possible to make greater improvements in the manufacturing and in the quality of the studied parts.
20
Content available remote Residual stresses in the strips from copper-based alloys
EN
Purpose: The aim of this work was to define the stress state in the strips from copper-based alloys with an account of the parameters of rolling and flattening. Design/methodology/approach: Samples of thin strips from three commercial copper-based alloys, i.e. CuSn6, CuZn33 and CuNi18Zn27, and from copper 99.98% in purity, were examined. The stress analysis was performed using X-ray diffraction method. The macro-stresses were determined by the measurements of the changes in a lattice constant and by the "square sin psi" technique. The micro-stresses were measured by the diffraction line broadening method. Findings: It was found that the residual stresses, measured at both surfaces of the cold rolled strip, depend strongly on the rolling conditions and on rolling gap geometry. Considerable differences between these surfaces have been observed before and after the flattening process. However, they can be significantly reduced by suitably conducted flattening process. Research limitations/implications: Further studies are necessary to assess the possibility of reducing stresses on both surfaces of a strip in the case of non-ideal shape of rolls in a rolling mill. Practical implications: Modification of technological flowchart for rolling strips from hardly-deformable copper-based alloys enables obtaining the required dead flatness of the strips. Originality/value: The results from this work can be used to improve the technology of rolling and flattening thin strips from copper and copper-based alloys.
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