Papers by Keyword: Fatigue Performance

Abstract: This study investigates the fatigue performance of additively manufactured H13 hot work tool steel (AM-H13 TS) produced using the laser powder bed fusion (L-PBF) process with two distinct build orientations: vertical (V-BO) and diagonal with 45° (D-BO). A fixed volumetric energy density of 57.3 J/mm³ was employed for fabrication. The study compares the as-built AMH13 TS to its surface-finished counterpart, focusing on fatigue life and damage under fully reversed tension-compression loading conditions. The surface finishing processes involved electropolishing using commercial DLyte 100HF+ equipment, followed by mechanical surface refinement. The surface topography and roughness characteristics of the as-built and post-polished specimens were comprehensively analyzed using laser confocal scanning microscopy (LCSM). Scanning electron microscopy (SEM) was utilized to examine the microstructural features and fatigue mechanisms. The as-built AM-H13 TS exhibited high surface roughness due to the presence of satellites and partially melted particles, which are inherent to the L-PBF process. The surface-finishing approach substantially mitigated these surface imperfections, resulting in significantly improved surface quality and reduced roughness. As a result, the fatigue performance of surface-finished AM-H13 TS showed remarkable enhancement. The fatigue limit increased fivefold, from 100 MPa in the as-built condition to 500 MPa after surface finishing. SEM analysis revealed that the improved fatigue strength was primarily attributed to the reduction in surface roughness and the elimination of surface flaws, which acted as crack initiation sites in the as-built condition.

Abstract: During heavy oil production, the performance of casing varies with temperature in the service environment. The tensile test of N80Q Steel and 80SH Steel were carried out to evaluate the mechanical properties during the service. The results indicated that the grain size of 80SH steel was relatively uniform and the grain boundary was relatively obvious compared with N80Q steel. A qualitative analysis was performance by relating the tensile properties with different temperature. The results showed that the yield strength, the tensile strength and elongation of N80Q and 80SH steels decreased with increasing temperature, but the degree of decline was limited. The observation of the tensile fracture revealed that the characteristics of the radiation zone of N80Q steel were obvious compared with 80SH steel at 20°C.

Abstract: The welded joint of a S890QL grade steel pipes containing 1.2% Ni have been prepared to characterize the use performance under high cycle fatigue test. It has been found that the fatigue strength of the welded joint is 290MPa with a fatigue life of more than 10 million cycles, and the obtained Basquin equation is σa=488*(2N)-0.02758 . It is found that the steel exhibits the whole bainite microstructure when the cooling rate is less than 1°C/s. The welded joint is divided into the weld zone, the coarse grain zone, the fine grain zone, the softening zone and the matrix. The fine grain characteristic in the welded area determines the good anti fatigue performance of the investigated steel.

Abstract: Based on the fatigue damage mechanism, fatigue life, stiffness degradation, crack width change, bending, shear fatigue properties and other aspects, this paper introduces the research progress of the fatigue properties of ordinary reinforced concrete beams. And the existing reinforced concrete beam flexural, shear fatigue properties of research ideas, methods and results are summarized, providing the basis for further study on the fatigue performance of reinforced concrete beams. At present, the research results show that the fatigue damage of reinforced concrete beam is basically in accordance with the law of the three stages. In the early stage of fatigue, the tensile concrete cracks and exits, and the damage develops rapidly. In the middle of fatigue crack growth, fatigue damage is developed into a more moderate linear growth. In the late stage of fatigue, fatigue fracture occurs in the steel bar, and the bearing capacity of the beam is quickly lost.

Abstract: In this paper, the fatigue performance of X65 marine pipeline is domestically studied by means of full-scale fatigue tests (four-point bending + inner pressure), in which all the influencing factors, such as welding residual stress, stress concentration, initial defects, internal pressure shutdown and pressure fluctuation are taken into consideration comprehensively. Consequently, the fatigue cycles under different stress amplitude can be derived and applied to predicting the full-scale fatigue life of pipes quantitatively. Additionally, the test results are compared with the recommended data of international general standards, such as BS 7608 and DNV C203, by which the fatigue safety of pipes could be evaluated. Therefore, this study is not only beneficial to the accumulation of full-scale fatigue data of pipes, but also can provide quantitative basis for evaluating the fatigue life and ensuring the safety operation cycles of pipes.

Abstract: A number of different semi-rigid pavement structure models are established to perform calculation and the results are led into the calculation software nSoft to analyze and acquire the fatigue property of different semi-rigid pavement structure models. The grey relational analysis of different semi-rigid pavement structure models fatigue properties are done based on the grey system theory to gain the key influence parameter on semi-rigid pavement structure fatigue performance. The research conclusion has certain instruction function to design pavement structure with excellent anti-fatigue performance.

Abstract: Based on the fatigue test of 6 stainless steel reinforced concrete beams, number of stress cycles, dropping-coefficient of stiffness and crack width are studied. This paper mainly discussed, under different stress states and reinforcement ratio, the influence of the reinforced concrete beam with stainless steel rebar on crack development, deflection and fatigue life. It can be concluded that, the fatigue life of the stainless steel reinforced concrete beam will go up as the stress decreases. Based on the analysis of the test results, the S-N curve can be deduced.

Abstract: A tension-compression cycle fatigue test was performed in order to study the fatigue property of C50 concrete with pre-cracks in cyclic loading. The stress ratio was-1 and the amplitude was 0.2 MPa ~1.30 MPa. The results show that the modified coefficient of fatigue strength is 0.198~0.265 and the infinite life fatigue strength is below 0.45MPa. While the log value of fatigue life is approximately linear with the amplitude of fatigue load stress, the discreteness of fatigue life, the particularity of concrete, has little to do with the amplitude. The S-N, P-N fatigue life curves and the constant fatigue life diagram of pre-crack concrete are obtained.

Abstract: The characterization of microstructure and basic properties of domestic butyl rubber 1751 ( IIR 1751) was performed with different testing , such as 1H-NMR spectrum, gel permeation chromatography, dynamic mechanical analysis, thermal gravimetric analysis and differential scanning calorimeter. And the comparison with Butyl 268 and Butyl 301 was made. The results showed that IIR1751 had a narrower molecular mass distribution, lower number-average molecular mass and lower weight-average molecular mass. The unsaturation degree of IIR1751 was close to Butyl 268 and Butyl 301. Its thermal stability was higher than the other and its ash content and volatile matter content was lower. Its glass transition temperature was same to Butyl 268’s, which was slightly higher than the Butyl 301. Dispersion of carbon black in IIR1751 vulcanizates was poor, but IIR1751 vulcanizates had good processing property, had a longer scorch safety period and fast curing rate. Its fatigue performance was good and its mechanical properties can achieve a better balance.

Abstract: The study on power steering gear is less than other auto parts at home or abroad. Compared with developed countries, the independent design and manufacture of power steering starts late, and lacks practical and effective evaluation standards. The combination of the theoretical analysis, numerical calculation and experimental verification is the key technology to optimize the design or test to evaluate the power steering gear’s function and performance. In this paper, the power steering gear’s finite element analysis(FEA) model was built to analyse the fatigue stress and fatigue life of the power steering gear’s components, such as housing, input shaft and output shaft. and the fatigue test of the power steering gear was also designed and implemented. Research showed that, the power steering gear fatigue properties of FEA and reliability test have the same results. The total damage of 4 A-B-C event cycles is less than 1, the steering gear system is judged safe after 4 event cycles per design requirements. Each component of the power steering gear has different maximum average stress. The stress of the sector shaft, the piston and the screws is very close to the yield stress, which is much larger than the other components, and needed to be treated with caution The maximum stresses of the gear housing are a little over the yield strengths at the stress of 6,118 lbs, which is more dangerous than the other components, and great attention should be paid to it.