Papers by Keyword: Creep Test

Abstract: One of the main problems with the use of steels for elevated temperatures is their limited weldability. This is mainly due to the fact that these materials may contain in their chemical composition. Due to the susceptibility to cold cracking, PWHT is necessary, especially in high-stiffness welded structures. In addition, depending on the condition after heat treatment or in the absence of heat treatment, precipitates may appear in the microstructure of the steel, affecting its mechanical properties. It is important in this case to ensure the high quality of welded joints, which means that the manufacturer has to demonstrate a very high technical culture. Currently, thin-walled pipe butt joints are welded manually using a tungsten electrode with solid wire material (TIG method). One of the solutions that can significantly speed up the welding process of components for work at elevated temperatures is the use of an electron beam welding. In addition, the ability to make welded joints without the use of filler material and to achieve narrow heat-affected zones may find application in the welding of modern materials used in the power industry. This paper presents the welding experience of materials assigned for the power industry (TEMPALOY AA1 and T92) by use of electron beam. In this article authors present the results of tests gained during first steps of welding welded joints. The article also includes preliminary results on the service life of the fabricated joints.

Abstract: In order to study the effect of temperature-confining pressure coupling on the creep behavior of rock-like specimen with precast internal fissures, the creep tests under different temperatures and confining pressures are carried out. The test results show that the rock presents primary creep stage and steady creep stage at low stress levels. Under the condition of high stress, the creep process of rock shows an obvious accelerated creep stage. The curve of accelerated creep stage of rock gradually smoothing with the increase of confining pressure, and the corresponding creep failure time gradually increases. The failure under low confining pressure is mainly tensile failure. The high confining pressure is the shear failure, or even the mixture of shear and plastic failure.

Abstract: Conventional long-term creep test (CCT) to the rupture and so called accelerated creep test (ACT) of the dissimilar weld joint made of FB2 and F martensitic steels and of the base materials were carried out at temperatures ranging from 550 °C to 650 °C in the stress range from 70 to 220 MPa. Assessment of microstructure development and changes of hardness was correlated with the creep strength. During creep at temperatures above 575 °C Laves phase precipitated in all parts of the weld joint and especially in the heat affected zones. Coarse Laves phase particles and their clusters with chromium carbides served as nucleation centers for cavities. As the fine grained heat affected zone of F steel was the softest part of the weld joint, many cavities originated and cause failure of samples. The aim of this paper is to compare results and possibilities of the “standard” methods and advanced scanning electron microscopy performed by instrument equipped with a concentric backscatter electron detector (CBS). Filtering of the signal enables improving and/or diminishing of selected type of contrast caused by various types of particles of secondary phases. The images were used as an input data for image analysis and developments of microstructures during CCT and ACT were compared. Results have shown that specimens after ACT contains significantly lower content of the Laves phase.

Abstract: The fracture characteristics of two AISI 316 austenitic stainless steels, creep-tested at constant load and temperatures of 600 and 800°C, were studied by scanning electron microscopy. The morphological aspects of the fracture were analyzed and correlated to the ductility level attained under creep. In one of the 316 steels, a marked change from ductile to intergranular mode of fracture was observed in going from 600 to 800°C. It is proposed that the condition for crack nucleation at precipitates as well as grain boundary oxidation are responsible for these microstructural changes.

Abstract: High-water material is a kind of new inorganic nonmetal material which mainly used in coal mine goaf filling. In order to simulate the real stress conditions of this material in goaf filling, the creep tests of high-water material in real pressure water environment were conducted and the creep laws were also researched. The results showed that water environment was conductive to maintaining and developing the strength of high-water material, and pressure water environment can improve the carrying capacity and long-term strength of high-water material. The deformation of steady creep period decreased while water pressure increased. And strain increasing caused by axial compression was less than strain increasing caused by water pressure. The time needed from starting to steady creep period was longer when water pressure was bigger.

Abstract: This research focuses on predicting long-term behavior of unsaturated polyester resin (UP) and kenaf unsaturated polyester composite. The objectives of these tests are to establish a relationship between stress, strain and time at constant loading and temperature. The results obtained from these tests are used in predicting the life and strength of the polymer material. Based on the 1,000 hours experimental data, curve fitting and Findley Power Law models are employed to predict long-term behavior of the material. The results showed that curve fitting model accurately predicted the non-linear time dependent creep deformation of these materials with acceptable accuracy.

Abstract: The creep characteristic of saturated silt soil was studied by k₀ consolidation creep test through two stress paths of axial loading and lateral lightening. According to test datas, some conclusions were submitted. First, the axial creep laws between the two stress paths were consistent on drainage conditions. Volume strains were much smaller than Axial strains. Volume strains presented alternation characteristic between shear shrinkage and shear dilatancy along with time extension. The silt soil creep constitutive model was presented. The results suggested combining the NHRI model describing the transient elastic-plastic strain with the creep empirical formula describing creep strain to establish the creep constitutive model.

Abstract: Steel CB2 developed in frame of the COST actions belongs to the most promising steel for production of cast turbine components working at ultra-supercritical steam conditions. VZÚ Plzeň has participated on assessment of original trial melt CB2 as well as on testing of samples coming from one of pilot valves produced of steel CB2 in full scale. Recently VZÚ Plzeň has cooperated with Doosan Škoda Power in development of weld processes of advanced power energy steels including steel CB2. This contribution deals with a comparison of properties of the steel CB2 produced by four various steelmakers from point of view of their microstructure in relation with their mechanical and creep resistant properties. Evaluation is focused on chemical heterogeneity, porosity, content of non-metallic inclusions, in particular on an occurrence of coarse NB, microstructure and substructure using methods of light and electron microscopy.

Abstract: The concrete creep effect is a peculiar phenomenon of concrete material, it has a significant effect on the deformation and internal force redistribution of concrete member, besides, it may cause the loss of prestress , it may have serious consequences especially on complex structure such as long-span bridges. So it must be considered in bridge design and construction. Based on the subject of CYSG deformation monitoring and 32m precast PC simply supported box girder, the method of creep test has been researched and determined in this paper firstly, then the laws of the development of the creep has been summarized, and the influencing factors of concrete creep has been concluded. Using the finite element software ANSYS and the APDL language, theoretical analysis of creep has been carried on in this paper. In conclusion, This paper analyzed the influencing factors of concrete creep and provided the basis for long-term deformation control of creep by comparing the theoretical results with the experimental data.

Abstract: In this present investigation, the mechanical properties of industrial drawn copper wires have been studied by creep tests, tensile tests and hardness Vickers. The effect of prior heat treatments at 500°C for different time on the drawn wires behavior was the main goal of this investigation. We have found that these heat treatments influenced the creep behavior of drawn wires and recorded shape curves. The creep tests were applied under ambient atmosphere at 240 °C. The creep duration before rupture decreased with the prior heat treatment time. The creep tests results were confirmed by tensile tests. A relationship between the hardness and the ultimate tensile strength of this industrial material has been established. Optical and scanning electron microscopy observations have been also used. Cross section observations of the wire after tensile or creep-rupture tests have shown that the mechanism of rupture was mainly controlled by the void formation.