Papers by Keyword: Stress Concentration

Abstract: Failure analysis of condensate pump shaft used in power generation plant was investigated. After 5 years of operation, the pump shaft fabricated from free-machining 416 martensitic stainless steel was suddenly ruptured into two parts. Detailed study was carried out using VT, PT together with microstructure investigation using optical and scanning electron microscope (SEM), fractography, chemical analysis and hardness testing to find out the cause of shaft failure. Failure analysis investigation revealed that the shaft was failed by torsion fatigue. Rupture was initiated from the sharp edge of the shaft outer surface at which sulphide inclusions were existed The failure is attributed to simultaneous action of both stress concentration resulted from sharp corner (design fault) and sulphide inclusions that segregate in 416 free-machining martensitic stainless steel base alloy near shaft surface (metallurgical fault). To overcome the shaft failure, sharp corner must be smooth turned and eliminate sulphide segregation by appropriate heat treatment.

Abstract: Presently in rules for fatigue assessment of structures subjected to intensive alternating service loading the Stress-Life (S-N) criteria are recommended in versions of the Nominal stress approach, Hot-spot stress and Notch-stress approach based on using the stress range a representative of the current damage. The criteria and approaches provide assessment of fatigue properties of structures accompanied with a series of approximations and uncertainties. A physically and mechanically more correct procedures might be provided by the Strain-life and Inelastic strain energy criteria for fatigue failure and approaches, although specific with intrinsic sources of approximations. The nature of approximations in the approaches is briefly commented and feasible means of improvement the fatigue assessment procedures and applications are presented.

Abstract: The composite materials are widely used nowadays as major parts of structures in many industries like aerospace, marine, automobile, space vehicles and also for the repair and replacement of civil infrastructures. Stresses are vital parameters considered in the design of structures. Any irregularities in shape, materials, or the presence of cut-outs create localized stress concentration and reduce the capacity of the material to take loads. The anisotropic behaviour of composite structures also makes the analysis more complex. Shear loading often exists in the engineering practices such as in aerospace due to heavy aerodynamic loads. So in the present study the effects of different parameters like layup sequences, number of plies, proximity of cut-outs, shapes and arrangements of cut-outs under in-plane shear loading on the glass fibre reinforced polymer (GFRP) plate with multiple cut-outs are studied using ABAQUS. The results from the study show that all the parameters considered for the study affects the stress concentration considerably. The observations are analysed then and the final conclusions are presented.

Abstract: Aspect ratio of crack is one of key factors of fatigue strength prediction in engineering design and civil structures using fracture mechanics and nondestructive inspection. However the author proposed the method to predict crack shape, it has the error caused by stress distribution of notch. In this study, in order to investigate the relationship between predicted crack shape and empirical observed it, the aspect ratio of cracks at notch root was observed, analyzed and discussed. We obtained the two important conclusions which are between predicted crack shape and empirical observed it. Predicted aspect ratio of crack was 17% bigger than that of observation result. The aspect ratio of crack should be defined considering scale of crack and notch shape.

Abstract: The objective of the study is to reduce the stress created in the root fillet region as the maximum stress concentration in gears occurs in the fillet. Therefore, stress relieving features have been created at an offset distance from the root fillet to reduce the stress. A Spur gear with involute profile is taken for the study. The application taken for the study is the gear used in terrain vehicles. The material of the gear is EN-353 grade Steel. Based on the compressive strengths and bending strengths, the spur gear is designed to the required application. The gear is modelled using the specifications obtained from the design calculations. The forces acting on the gear is calculated considering the application in which it is used. The gear is then analysed using the ANSYS WORKBENCH 14.0 software. It has been found that the maximum stress acts near the root fillet region. Hence, stress relieving features of circular and elliptical shapes are created at an offset distance from the root fillet. It has been found that the gear with elliptical stress relieving hole has the minimum stress than those of gears with other combinations. The next objective which is to reduce the mass of the gear is done by creating larger holes in the lower stress regions of the gear. The mass reducing features are created in the gears with stress relieving features and each gear has been subjected to analysis for the minimum amount of stress. It has been found that the value of stress is less in the gear with mass reducing holes but with no stress relieving feature. Thus, the stress acting on the root fillet region has been reduced by 20% by creating circular and elliptical holes. The other objective of mass reduction is satisfied by creating larger holes.

Abstract: In the paper, the Metal Magnetic Memory Testing signal of pipeline crack is extracted. The BP neural network is constructed and trained. The experiment shows that the BP neural network can effectively identify the crack parameters of oil and gas pipeline in quantitative.

Abstract: Aspect ratio of crack is one of key factors of fatigue strength prediction in engineering design and civil structures using fracture mechanics. Their empirical shapes are changed by stress concentration. However, it was not clear how stress concentration affects empirical results including crack shape and size. In this study, in order to investigate the relationship between stress concentration and crack geometry, the aspect ratio of cracks at notch root was observed and discussed. We succeeded to capture two important relationships which are between stress concentration and crack shape, and between crack initiation point at notch root and crack shape, respectively.

Abstract: Plates are the important structural members finding applications in the field of structural engineering, ship technology and aerospace engineering. Holes are often provided in the plates for the purpose of services and aesthetics. Pitting corrosion can also induce holes on the plates, thereby inducing stress concentration and redistribution of stress around the hole. In this paper, the popular finite element software ANSYS is used for the static analysis of thin plates with holes. The influence of shape and size of the hole on the stress distribution of plate is also analysed. The study can form foundation for strength assessment of steel plates with holes, especially residual strength of plates subjected to pitting corrosion.

Abstract: Under the suspended crane loading, the key to the fatigue of the grid structure with bolt-sphere joints is the fatigue of the higher strength bolt. By now, there are not any research reports about the fatigue properties of M27 higher strength bolt at home and abroad. With the aid of the fatigue-testing machine and the loading device, this paper will have 8 constant amplitude fatigue experiments on test-piece, and will get the S-N curve of the higher strength bolt. With the aid of the metallographic analysis, this paper studies the mechanism and influencing factors of the fatigue failure; and with the aid of the finite element software ABQUAS, it analyzes and gets the stress concentration factor of the M27 higher strength bolt, and verifies the position of the fatigue failure.

Abstract: In this paper, the author uses ANSYS, the software of finite element analysis, to establish the finite element model, the hot spot stress value of different connection structures of steel tube-welded hollow sphere under uniaxial elongation has been analyzed, the theoretical stress concentration factor of this joint has been obtained. Through the static test on the four typical test-piece, 26 steel tube-welded hollow spherical nodes in total, the actually measured stress concentration factor of the joints has been obtained. The theoretical analysis basically coincides with the law of stress concentration factor obtained from the test results.