Characteristics Of Residual Stress Distribution Research Articles

A framework for estimating residual stress profile in seam welded pipe and vessel components Part II: Outside of weld region

Part I of this study has identified two key parameters (r/t ratio and characteristic heat input Qˆ) that dominate important through-thickness residual stress distribution characteristics, with which a residual stress profile estimation scheme has been developed for weld region, i.e., at weld centerline and weld toe. In Part II, we present an analytical model for achieving residual stress profile estimation for through-thickness sections away from the weld region in seam welded pipe and vessel components. A curved beam bending theory based model is analytically constructed through an assembly of two parts: One is weld fusion zone region and the other is the rest of the component section along circumferential direction. The final assembly of the two parts leads to a closed form solution to both axial (longitudinal) and hoop (transverse) residual stress components as a function of circumferential angular position away from weld toe. The effectiveness of the full-field residual stress estimation scheme is demonstrated by comparing with finite element modeling results over a broad range of weld geometries and welding conditions. The present development should provide a consistent and effective means for estimating through-thickness residual stress profile as a continuous function of pipe geometry and welding heat input.

극후물재 용접부 내부잔류응력 측정기술 및 특성

Abstract Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW),especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficienttoughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thicknesswere compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the insideof the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.Key Words : Welding residual stress, Thick steel plate, Heat input, Fracture toughnessISSN 2466-2232Online ISSN 2466-2100

An IIW residual stress profile estimation scheme for girth welds in pressure vessel and piping components

Over the years, one major objective of IIW Joint Working Group (JWG) on residual stresses and distortion prediction (RSDP) has been the development of consistent residual stress profiles for supporting fitness-for-service assessment of welded components. As a result of the JWG activities and further in-depth investigations, this paper presents a major development on a novel full-field residual stress estimation scheme that can be used for describing through-thickness residual stress profiles not only within a weld region, but also at any location away from a weld in pressure vessel and piping components. Within weld region, a systematic parametric finite element analysis is used to establish key parameters that govern through-thickness residual stress distribution characteristics by introducing membrane, bending, and self-equilibrating based decomposition technique. Away from weld region, a shell theory based method is developed for describing through-thickness residual stress distribution at any distance away from weld toe. This paper presents detailed results for single “V” joint preparation with pipe wall thickness varying from 6.25 to 250 mm and wall thickness to pipe radius ratio (r/t) varying from 2 to 100. The residual stress estimation method can be applied for double V and narrow groove joint preparations for girth welded components since all three joint preparations have been shown to follow a similar functional form to that seen in single V joint preparation.

On residual stress prescriptions for fitness for service assessment of pipe girth welds

This paper aims to provide a detailed assessment of some of the existing residual stress profiles stipulated in widely used fitness-for-service assessment codes and standards, such as BS 7910 Appendix Q and API 579 RP Annex E, by taking advantage of some comprehensive residual stress studies that have recently become available. After presenting a case study on which residual stress measurements are available for validating finite element based residual stress analysis procedure, residual stress profiles stipulated in BS 7910 for pipe girth welds are selected for detailed evaluation by comparing residual stress distribution characteristics shown in parametric finite element results. A shell theory based full-field residual stress profile estimation scheme is then presented to illustrate how an improved estimation of residual stress profiles can be achieved in light of some of the deficiencies in BS 7910 and API 579 identified in this study.

The Research on Three-Dimensional Theoretical Model of Residual Stress on Cutting Surface

Two kinds of three-dimensional model of residual stress were discussed based on the three dimensional distribution characteristics of residual stress on machined surface, considering comprehensively the strain along the X, Y, Z three directions, to improve the two dimensional model of residual stress established by DL McDowell without considering the Z direction of the strain. As to the characteristics of milling force, strains of any point in the substrate surface along three directions can be calculated based on the elastic-plastic mechanics theory. With the improved models, both the distribution of residual stress on milled surface and the distribution of residual stress in subsurface layer can be obtained. By means of the examples of numerical calculation, the analytical result and simulation result are analyzed and compared. The improved model accorded better with the actual residual stress distribution on milled surface than original model.

Comparison of Measured Residual Stress Distributions in Extra-Thick Butt Welds Joined by One-Pass EGW and Multipass FCAW

This study is to measure the welding residual stress distributions in a 70 mm-thick butt weld by one-pass electron gas welding using both the inherent strain method and neutron diffraction method, respectively. Based on the measurement results, the characteristics of residual stress distribution through thickness were compared between one-pass electron gas welding and multipass flux-cored arc welding. Residual stresses in the specimens of electron gas welding measured by the inherent strain method and neutron diffraction method were well matched. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress in electron gas welding is tensile on both surfaces and compressive at the inside of the plate. The magnitude of residual stresses due to electron gas welding is lower than that due to flux-cored arc welding.

Numerical analysis of welding residual stress and distortion in laser+GMAW hybrid welding of aluminum alloy T-joint

A 3-D finite element model is developed to predict the temperature field and thermally induced residual stress and distortion in laser+GMAW hybrid welding of 6061-T6 aluminum alloy T-joint. And the characteristics of residual stress distribution and deformation are numerically investigated. In the simulation, the heat source model takes into account the effect of joint geometric shape and welding torch slant on the heat flux distribution and a sequentially coupled thermo-mechanical method is used. The calculated results show that higher residual stress is distributed in and surround the weld zone. Its peak value is very close to the yield strength of base metal. Besides, a large deformation appears in the middle and rear part of the weldment.

Surface Residual Stress Gradient Distribution in High Speed Milling of H13 Die Steel

High speed milling experiments are performed for hardened H13 die steel by using coated ball end milling cutter, the residual stress of the work-piece surface on the feed and cross feed direction are measured, and the distribution characteristics of residual stress is analyzed. The result shows that the residual stress presents gradient distribution on feed direction, and furthermore, the three-dimensional surface micro topography has no close relation with the residual stress. In addition, the cumulative effect is discussed for explaining the phenomena.

Finite element analysis of the effect of sequential cuts and tool–chip friction on residual stresses in a machined layer

A thermo-elastic–viscoplastic model using explicit finite element code Abaqus was developed to investigate the effect of sequential cuts and tool–chip friction on residual stresses in a machined layer. Chip formation, cutting forces and temperature were also examined in the sequential cuts. The affected layer from the first cut slightly changes the chip thickness, cutting forces, residual strain and temperature of the machined layer, but significantly affects the residual stress distribution produced by the second cut. Residual stress is sensitive to friction condition of the tool–chip interface. Simulation results offer an insight into residual stresses induced in sequential cuts. Based on simulation results, characteristics of residual stress distribution can be controlled by optimizing the second cut.