Wenchun Jiang

Effect of notch position on creep damage for brazed joint

The creep failure is easy generate in surface notch.The far away notch is helpful to reduce the creep damage of filler metal.As H increases, the failure location moves from filler metal to base metal.As H increases, the failure time increases first then keeps stable.The failure time decreases with L increases while it increases with W increases. In this paper, we investigated the effect of notch position on creep damage for Hastelloy C276-BNi2 brazed joint. Three different types of notches locate in edge of base metal (base notch), edge of filler metal (surface notch) and center of filler metal (inside notch) were compared, and the influence of notch geometric parameters on creep damage was also investigated. The results show that the different notch position and dimension generate different creep damage distributions and have a great influence on creep life. The creep failure is the easiest to occur in surface notch, then the base notch, and the last is inside notch. The brazed joint with higher maximum principal stress and von Mises stress generates creep failure easier. For the base notch, the failure time increases with the increase of base notch distance and the creep failure location moves gradually from the center of filler metal to notch tip. The notch locating away from filler metal is beneficial to reduce the creep damage in filler metal and enhance the creep life. For the inside notch, the failure time decreases with notch length increases and the maximum creep damage locates at notch tip. With the increase of inside notch width, the failure time increases first and then keep steadiness, and the failure location moves away from notch tip. The effects of notch position and dimension should be fully considered in creep failure analyses and life assessments of brazed joints.

Neutron Diffraction Measurement and Numerical Simulation to Study the Effect of Repair Depth on Residual Stress in 316L Stainless Steel Repair Weld

study the effect of repair depth on residual stress in 316L stainless steel repair weld Wenchun Jiang, Yun Luo, BingYing Wang, Wanchuck Woo, S.T. Tu a College of Chemical Engineering, China University of Petroleum (East China), Qingdao, 266555, PR China b College of Mechanical and Electronic Engineering, China University of Petroleum (East China), Qingdao, 266555, PR China Neutron Science Division, Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong-gu, Daejeon, 305-353, South Korea Key Laboratory of Pressure System and Safety (MOE), School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237, PR China

Two-dimensional mapping of residual stresses in a thick dissimilar weld using contour method, deep hole drilling, and neutron diffraction

Residual stress variations were determined through the thickness of a 70-mm-thick ferritic–austenitic dissimilar steel weld using contour method, deep hole drilling, and neutron diffraction. The result shows that significant tensile stresses were distributed distinctly along the interface between ferritic and austenitic phases. The band of the large tensile stresses was about 8xa0mm wide and the magnitude reached 400xa0MPa, which is approaching 100xa0% of the yield strength of the base metal, near the top surface (about 15xa0% of the depth). It is attributed to the large difference (5.8xa0×xa010−6 1/°C) of the thermal expansion coefficient between ferritic and austenitic steels of the interface. The microstructure analysis elucidates that the martensitic phase prevailed near the interface and results in microhardness increases.

Effect of Impact Pressure on Reducing the Weld Residual Stress by Water Jet Peening in Repair Weld to 304 Stainless Steel Clad Plate

Stainless steel clad plate manufactured by explosive bonding is widely used in the chemical industry, but cracks are often initiated in the clad layer. Repair welding is a popular method to repair the cracked zone. But residual stresses are generated inevitably, which can lead to further cracking. How to decrease the residual stress is critical to ensure the structure integrity. This paper studies a method to reduce weld residual stresses by water jet peening (WJP) in 304 stainless steel clad plate. The effect of impact pressure is discussed. A sequential coupling finite element method is developed to simulate the as-welded residual stresses, which is validated by impact indentation measurement. Then, a user subroutine is developed to model the moving load generated by WJP. The results show that the WJP can introduce compressive stresses on the metal surface and thus decrease the as-welded tensile stresses. As the maximum impact pressure at the center of impact (P0) increases, the residual stresses are decreased greatly and even change to compressive stresses. There is a critical value P0, which changes the tensile stresses to compressive stresses. As P0 increases to 1.4 times the yield strength of 304 stainless steel, the initial tensile stresses on the surface have been decreased to compressive stresses. [DOI: 10.1115/1.4029655]

A New Connection Structure Between Hydrogen Nozzle and Sphere Head in a Hydrofining Reactor

This paper presents a study of the residual stress in the welding connection between hydrogen nozzle and spherical head in a hydrofining reactor. A sequential coupling finite element program is developed to analyze the residual stress in nozzle-to-sphere connection. The results show that large residual stresses are generated in the weld and weld/parent interface during the welding of hydrogen nozzle. Large axial stress is generated on the internal surface of hydrogen nozzle due to the angular deformation, which has a great effect on hydrogen induced cracking (HIC) and stress corrosion cracking (SCC). Based on the residual stress distribution character, a new connection structure between hydrogen nozzle and head is developed. A stressless flanging is proposed to insert into the nozzle to isolate the residual stresses, which can be useful to prevent HIC and SCC. To cover all the residual stresses effectively, the arc length of flanging should be not less than 80 mm.

Effect of geometrical parameters on the effective elastic modulus for an X-type lattice truss panel structure

Abstract The lattice truss panel structure (LTPS), which is a high strength material with high efficiency of heat transfer, has a good potential to be used as compact heat exchanger. The core of LTPS is a periodic porous structure, and the effective elastic modulus (EEM) will be different from the base material. It is essential to calculate the EEM for the design of this type of heat exchanger. This paper presents a study on the EEM of X-type LTPS by homogenization method, which has been verified by finite element method (FEM). It reveals that the effects of seven geometrical parameters of the X-type LTPS on EEM are not identical, and the relationship between the seven parameters and EEM has been established. Results calculated by homogenization method and FEM show a good agreement. The EEM decreases with the increase of truss length, stamping angle, shearing angle and node length, while it increases with the increase of truss width, truss thickness and face sheet thickness. Unlike the conventional foam material, there is no clear correlation between the EEM and the relative density, and a formula has been fitted to calculate the EEM of LTPS.

On residual stress and relief for an ultra-thick cylinder weld joint based on mixed hardening model: Numerical and experimental studies

Residual stress distributions as welded and after local post welding heat treatment (PWHT) of butted weld joint of a huge cylinder with ultra-thick wall were investigated by finite element (FE) simulations and measurement. Sequential coupling thermal-mechanical analyses were conducted with a generalized plane strain 2D model to simulate the welding procedure bead by bead, combining with 3D double-ellipsoid moving heat source and mixed isotropic-kinematic hardening plastic model. The simulation was validated by XRD measurements. Simulation results showed that local PWHT with heated band width of 0.5vRt can significantly reduce the residual stress on the outer surface of weld joint, but bring about harmful high tensile stress on inner surface due to bending moment induced by local radial thermal distortion. For the purpose to find out the appropriate heated band width of local PWHT, relations between stress relief and size of heated band were studied. Results show that the stresses on the inner surface reach a maximum value when the heated band width is less than 1vRt. Based on the simulation results and from the view point of lowering the stress level on the inner surface, the optimum width of 3vRt for heated band were proposed.

Effects of Inner Defects on Creep Damage and Crack Initiation for a Brazed Joint

Abstract In the brazing process, some brazing defects like semicircular or straight type are generated due to incomplete filling. In this paper, the creep damage and creep crack initiation (CCI) time of Hastelloy C276-BNi2 brazed joint with defects are investigated by a ductility exhaustion damage model. The effects of defect dimension and filler metal thickness are also discussed. The results show that the different defects have different creep damage distributions and CCI times. The maximum creep damage is located at the defect frontier due to the larger stress concentration. With the increase of semicircular defect radius and straight defect length, the CCI time decreases. The creep fracture is inclined to generate in semicircular defect for the smaller defect area ratio, while it is easy to generate in straight defect for the bigger defect area ratio. As the filler metal thickness increases, the CCI time increases. For the thicker filler metal, the creep crack is easy to initiate in semicircular defect.

Comparison of Brazed Residual Stress and Thermal Deformation between X-Type and Pyramidal Lattice Truss Sandwich Structure: Neutron Diffraction Measurement and Simulation Study

Abstract This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.