Papers by Keyword: Yield Strength

Abstract: Wire arc additive manufacturing (WAAM) of titanium parts shows promising potential for aerospace application due to its high deposition rates allowing a fast and economical production of large integral parts. However, due to the demands of aerospace industry an extensive qualification procedure is necessary to enable the parts as ready to fly. Nowadays, qualification for additive manufactured parts is a time-consuming process, so the advantages in additive manufacturing cannot be fully utilized. For this reason, a complete process qualification for WAAM would reduce the costs drastically in contrast to qualifying manufactured parts individually. As a first step the robustness and reproducibility of the energy reduced WAAM process was investigated. Thick-walled samples are manufactured layer by layer with an oscillating welding head motion. The mechanical properties of the samples are compared on an adequate statistical basis. Microstructural-and computer tomography analysis are conducted to comprehend shown interactions. The reproducibility is investigated in dependence of different heat treatment states, different directions of mechanical testing and two manufacturing systems of the same type.

Abstract: This work evaluates the microstructure and the yield strength under compression at room temperature and at 800°C of specimens prepared with AISI 310 stainless steel powder (D50 = 10 μm), manufactured by gelcasting. Parts were vacuum sintered in a single batch at 1280°C. At room temperature, specimens presented average yield strength of 270 MPa, and at 800°C, 105 MPa. Microstructure analysis involved the measurement of grain size along the vertical axis of cylindrical specimens, with special attention to the effect of particles settling, and was conducted using scanning electron and optical microscopy, and X-ray diffraction. Settling effect was assessed considering the position where the specimen was taken and was negligible: both density and yield strength did not vary significantly along the vertical axis.

Abstract: High strength can be achieved by severe plastic deformation but at the cost of ductility. A novel strategy, which named multiple surface rolling was applied on a homogeneous annealed pure copper to break the strength and ductility trade-off. A combination of high strength and acceptable ductility was achieved in copper strips after submitted to multiple surface rolling. The detail microstructure evolution rolled samples were characterized by EBSD observation and compared with the initially annealed ones. The average grain size does not show significant deviation in both initially annealed and multiple surfaces rolled copper. Detailed observations show a heterogeneous distribution of low angle grain boundaries through thickness direction. The low angle grain boundaries and misorientations revealed the potential strengthening mechanisms in the material. Both microstructural characterization and numerical simulations indicate that multiple surface rolling contributes to strain hardening at the sample surface, while the interior layer was undergoing elastic deformation or partial plastic deformation. This heterogeneous deformation renders copper sheet with a combination of high strength and ductility.

Abstract: 7075 alloy is the most typical Al-Zn-Mg-Cu alloy and widely used in industry. In the present study the regularities of the change for the size and volume fraction of the precipitates in the retrogression process and the effects of aging time on strengthening of spray formed 7075 alloy were investigated based on the thermodynamics, aging kinetics and hardening theory. The results show that there was a relationship between the parameters of retrogression treatment and yield strength of the alloy. A unified model is presented to establish the quantitative relations between the retrogression process and the yield strengths of spray formed 7075 alloy from the perspective of combining micro and macro.

Abstract: The problems of improving operating procedures and diagnosing the bearing capacity of metal structures designed and operating in the Arctic and subarctic regions of the country with a long period of low climatic temperatures remain unresolved. The paper notes that the development of digital methods of non-destructive testing, primarily X-ray diffractometry methods, can provide technical diagnostics of structures by identifying the features of the deformation of the crystalline structure of structural materials in an elastic stress-strain state. It is shown that the application of the method of X-ray diffractometry of complex polycrystalline structural steels has sufficient resolution to detect changes in the fine structure under the elastically stressed state of the samples. The broadening of the diffraction line (B) profile characterizes the effect of the elastically stressed state of steel samples 08 ps and 09Г2С on the course of microdeformation processes in the surface layers of the metal. The effect of periodic annual temperature fluctuations on the profile characteristics of the diffraction lines of 08 ps structural steel samples was studied experimentally. It is established that low climatic temperatures contribute to the elimination of individual instrumental errors due to the design conditions of the experiment. A sharp change in the true half-width of the profile of diffraction lines (В) at stresses σ ≥ 0.5 σ_т indicates the minimum possible value of the allowable stress [σ] for structural steel 08 ps.

Abstract: By using X-ray diffractometry, it was determined how short-term stresses, being within the limits of the offset yield strength σ_s, influence changes in the diffraction line profile characteristics resulting from static tension in plate specimens of 09G2S (09Г2С) structural steel. Microstructural changes in the surface of 09G2S steel specimens considered in this work were studied at different levels of elastic stress. The special aspects of changes in the diffraction line profile characteristics are presented and discussed, specifically, a broadening of the profile maximum half-width (B), as a response to the external mechanical impact on the surface layers.

Abstract: An artificial neural network (ANN) model has been developed for the analysis and simulation of the correlation between the chemical composition and mechanical properties of high strength low alloy (HSLA) steel X70. The input parameters of the model consist of the base metal chemical composition (C, Si, Mn, the sum of Cr+Cu+Ni+Mo, the sum of Nb+Ti+V, carbon equivalent CEpcm) and the yield strength (YS). The outputs of the ANN model include the ultimate tensile strength (UTS) of the test material. Scatter plots, correlation coefficient (R) and mean relative error (MRE) were used to assess the performance of the developed neural network. Interestingly, the model output is efficient to calculate the mechanical properties of high strength low alloy steels, especially the ultimate tensile strength as a function of chemical composition and yield strength of the used material. The obtained results are in a good agreement with experimental ones, with high correlation coefficient and low mean relative error. The predictions accuracy of the developed model also conforms to the results of mean paired T-test.

Abstract: The cables are widely used in mechanical, electrical and civil engineering applications, as they are flexible and highly resistant. In this paper, the behavior of the elastic limit of straight central core strands is studied. In this study, we focus on the elastic limit’s behavior of straight central core strands. That is, we investigate 27 cores with different configurations. They generally consist of 7 wires (1+6) belonging to wire ropes of type 19x7 subjected to static axial loads. The numerical study is performed using finite element method (FEM). The main results are compared with experimental data. Finally, to determinate the impact of three parameters: the basic material constituting the strands, the winding angle of wires and the diameter of strands on the yield strength of the core strands, we apply a design of experiments (DOE) analysis by YATES’ method.

Abstract: The present research includes the analysis of mechanical properties of A356/ hybrid metal matrix composite. The mechanical behaviour - hardness, ductility, tensile and yield strength were studied. Reinforcement of these composite specimens were with a weight percentage of (wt - %) 10%, 20% and 30%. The microstructure of these specimens at different wt - % of reinforcements were viewed under an optical metallurgical microscope. It was observed that at 30 wt - % of reinforcement addition, there was a finer distribution of reinforcement particles and as the wt - % decreased, much leaner distribution was observed. The hardness test was carried out using a Vickers Hardness Tester. From the experiment it was noted that with an increase in the amount wt - % of reinforcement, there is a subsequent increment in the mechanical properties except in the case of percentage elongation, which was observed to decrease with an increase in the reinforcement content.

Abstract: The presented work reviews the research in the field of production of nanostructured composite materials based on copper, reinforced with carbon nanostructures. Particular attention is paid to the use of composites with high thermal conductivity as structural materials. The method of manufacturing a composite material based on copper is described in detail: modes of preliminary annealing, pre-pressing, hot isostatic pressing. The characteristics of the matrix and alloying components are given, and also preliminary treatment of copper powder and carbon nanotubes is described. Different mechanisms of component mixing are considered, the process of mechanical alloying in a planetary mill is described in detail, the results of measuring the thermal conductivity of samples are given. The mechanical characteristics of the samples are considered in detail: ultimate strength, yield strength, elongation. The degree of influence of surfactants on the uniformity of the distribution of alloying components and the mechanical properties of the composite material is determined.