Papers by Keyword: Residual Stress

Abstract: Based on finite element method, the FEA model used for analyzing fatigue properties of sample treated by laser shot peening (LSP) was established. In order to research the influence of material intensity on LSP effect, two kinds of wrought magnesium alloys AZ31B and ZK60 with different intensity were chosen as object, the compressive residual stress and fatigue life after LSP were analyzed. After spring back analysis the elastic strain is released in material inner, the value of compressive residual stress was reduced; after LSP with 3 times, the fatigue life gains of AZ31B and ZK60 were 105% and 163%, respectively. The results show that strengthening effect of high intensity material treated by LSP is better than that of low intensity material.

Abstract: An orthogonal cutting model was presented，and the cutting process was simulated by a finite element software based on the thermal-elastic-plastic FEM theory and updated Lagrange method.We obtained the distributions of residual stresses in machined layer of NAK80 mold-steel.The effects of cutting speeds，cutting depths and tool geometry on residual stress distributions were investigated. Comparing to experimental results，the conclusions are more accurate.

Abstract: TiN coating is often coated on fine blanking tools made of with the powder metallurgy high speed steel S790 by Multi-arc ion plating. The phase variation, residual stress and microhardness of TiN coatings were respectively analyzed by X-Ray Diffraction(XRD) and Vickers hardness tester in this research. The result shows that: there is obvious preferred orientation in the crystal surface (1 1 1) and (2 2 2) of TiN coating, the residual stress of TiN coating ranges from -2 347 MPa to -1 920 MPa, and that of the substrate from -154.9 MPa to -69.21 MPa, both of which decrease with the increasing of coating thickness. The TiN coating on the S790 substrate was annealed at temperature 500°C for one hour. It was revealed that the stress state of TiN coating was better and thus the properties of the TiN coating were improved.

Abstract: The crankshaft fillet rolling process is one of the commonly adopted methods in engineering to improve fatigue life of the crankshaft. The crankshaft fillet rolling process was simulated based on the explicit dynamic calculation in this paper. After the data acquisition program was compiled, the distribution of the crankshaft surface stress could be obtained. Coupling calculation between the operating stress at different bending moments and the rolling residual stress was based on the Smith-Watson-Topper (SWT) modle. After the simulation on the crankshaft fillet rolling process was carried out, which was based on optimization rolling parameters, the crankshaft fatigue strength was improved by 8.6%.

Abstract: The stress field of compound cast rollers during centrifugal casting process was investigated in this work. A finite element (FE) model was built to simulate the internal stress fields during cooling process, in which phase transformation was considered. The mechanical parameters employed in stress numerical simulation were measured by using thermal/mechanical simulator. The residual internal stress of the compound cast roller by centrifugal casting method was measured by using X-ray stress analyzer. The simulated results are in agreement with the measured ones very well. According to this model, the temperature and stress fields of the compound cast roller during centrifugal casting process were simulated.

Abstract: Fatigue fracture is the main failure form of welded structures. Fatigue strength of welded joints is far below that of base metal under the combined effect of stress concentration, molten slag defects in weld toe and residual tensile stress. Fatigue damage mechanism and main factors that affect fatigue strength of welded structures are analysis and summarized respectively. This paper emphasizes on introducing the research progress of various measures to improve the fatigue properties, including weld toe grinding, TIG dressing, local-heating and local extrusion method, hammering and shot blasting and ultrasonic peening treatment.

Abstract: Deformation mechanism of low-rigidity thin part caused by clamping force is studied in this paper. A coupled thermo-mechanical simulation process of aluminum alloy 6061 is developed using the finite element method with Abaqus. The results of simulation are verified by experimental measurements of cutting force and surface residual stress. Then using the model investigates the effect on residual stresses along the thickness of aluminum alloy 6061 load and unloadthe clamping forces. The deformation condition is also studied after removing fixing.

Abstract: Nickel-hardened gold and silver coatings were brush-plated from a commercial SIFCO Dalic Solution (Gold Hard Alloy), Code SPS 5370, and Silver Hard Heavy Build, Code SPS 3080, on unclosed thin-walled copper ring substrates. To determine residual stresses, the conventional curvature method (common among the electrodeposition methods) was applied, where the substrate was coated with certain thickness and then the slit increment (bending deflection) of the substrate was measured as an experimental parameter. Residual stresses on gold coatings were also determined by X-ray diffraction (XRD) based on the sin2 method. The values of residual stresses determined by the curvature method and by the XRD technique were comparable. Relaxation of residual stresses was observed. An equation for approximation of the change of residual stresses was applied assuming that the dependence of residual stresses on relaxation time is linear-fractional. The surface morphology and microstructure of the coatings was studied by means of scanning electron microscopy (SEM). The magnitudes of the modulus of elasticity and of the nanohardness of the coatings were obtained by instrumented indentation.

Abstract: Residual stresses have a fundamental effect on the operational behaviour and lifetime of industrial products. The fatigue resistance of machine parts can be increased by introducing residual compressive stresses into the surface region. For certain machine parts especially in the vehicle industry the residual stress is strongly demanded by the quality control. For this reason, measuring the stress accurately is becoming increasingly important. The Almen test, which only gives a qualitative result, is widely used in the industry. Shot peening and rolling are methods which are suitable for creating elastic residual stresses. This paper examines the technologies used by Rába Futómű Nyrt. to increase the lifetime by means of residual stress. We performed analysis of the residual stress of samples shot peened the same way but under different heat treatment states. We compared the residual stress values of burnished and hardened shaft joints, and the residual stress states of gear made of hardened alloy, comparing the carbonized ones to ones which were shot peened under small intensity.

Abstract: Residual stresses and residual plastic strains of the welded structures are the products of nonlinear behaviors during welding. The residual stresses will cause errors during the assembly of the structure and injure the beauty of appearance of the structure. Based on an elastic-plastic-model, finite element numerical simulation of a representative tube sheet penetration assembly with loop welding line joined by multi-pass welding is carried out and the influence of welding conditions on residual stresses of the tube sheet welds is studied in this paper. Nonlinear three dimensional transient temperature fields and real-time dynamic stresses field are analyzed by FEM. The heat source is modeled as a moving heat flux following a double ellipsoid distribution and the temperature-dependent properties of materials are considered. The method of birth and death of element in finite element analysis is applied to simulate the gradual growth of weld pass metal. It is shown that welding sequence, size of groove welding and weld toes dressing will obviously change the magnitude of the residual stresses of tube sheet welds.