Li Qing-fen

Experimental study on non-equilibrium grain-boundary segregation kinetics of phosphorus in an industrial steel

Abstract The non-equilibrium grain-boundary segregation level of phosphorus in an industrial steel, 12Cr1MoV, was measured. A non-equilibrium grain-boundary segregation kinetics curve of phosphorus is given, which provides direct evidence of the non-equilibrium grain-boundary segregation kinetic model proposed by Xu Tingdong.

The effect of plastic constraint on the initiation of ductile tears in shipbuilding structural steels

In this paper, the effect of plastic constraint on the initiation of ductile tears in four different shipbuilding structural steels has been experimentally studied by measuring the J-integral and crack opening displacement COD at initiation in three-point bend specimens with deep and shallow notches. Experimental results of seven groups of different strength alloy steels show that both δi and Jì values of ductile tear from the shallow crack specimens which have less constraint flow field are significantly higher than those of deeply notched specimens. Slip-line-field analysis shows that, for shallow crack, the hydrostatic stress is lower than that from standard deeply cracked bend specimen, which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will ensure an unduly conservative approach when applied to structural defects, especially if initiation values of COD and J-integral are used.

GRAIN-BOUNDARY SEGREGATION AND CO-SEGREGATION BEHAVIOR OF THREE ELEMENTS IN STEEL 2.25Gr1Mo *

Both thermally induced and stress-driven segregation behavior of P, Mo and Cr were experimentally studied in steel 2.25Cr1Mo. The relationship between Mo and P, Cr and P were analyzed. Results of specimens solution treated at 1050℃ and held at 540℃ show that the concentration of Mo at grain boundary increased with increasing concentration of P during aging, and that the experimental data dots of Mo and P relationship were distributed in a linear zone, whereas, the data dots of Cr and P relationship were scattered. It is concluded that the non-equilibrium grain boundary co- segregation (NGCS) of Mo and P occurred, and the NGCS of Cr and P did not occur during aging in steel with the above heat treatment history. Results of tension test show that both the NGCS of Mo and P, and NGCS of Cr and P occurred under low stresses 30MPa at 500℃. And the typical multi-elements NGCS of P-Mo-Cr occurred during aging. It is clear that the three elements P, Mo and Cr in steel 2.25Cr1Mo are interactional and inter-promoted.

Process Optimization of the Tube-Plate Welding Based on MARC

Three-dimensional thermo-mechanical FEM simulations are conducted for the tube plate welding. Different welding processes are simulated base on MARC. The optimization processes is evaluated by simulation results of welding residual stress distribution. The results shows that large welding seam, two sides alternative welding and TIG arc remelt weld toe can reduce stress center in X&Y direction. ultrasonic impact treatment has significant effects on the residual stress and introduces compressive residual stress in the welded joints.

A review of the effect of a/W ratio on fracture toughness (II) —experimental investigation in LEFM

In part I of this series, experimental investigation in EPFM (elastic-plastic fracture mechanics) had been discussed. In this paper, experimental investigation in LEFM (linear elastic fracture mechanics) is given. Fracture toughness tests had been carried out on three different strength steels, using both through-cracked specimens with different a/W ratio and semi-elliptical cracked specimens with variable crack size and shape. Results show that the fracture toughness KIC increases with decreasing a/W when a/W<0.3 for three-point-bend specimens, and that for a/W>0.3, it is independent of a/W. Shallow crack specimens, both through-cracked and surface-cracked, gave markedly higher values than deeply notched specimens. However, the effect of crack shape on fracture toughness is negligible. Results also show that the LEFM approach to fracture is not tenable for design stresses where ac is often very small, far less than 2.5(KIC/σy)2.

Study on J-integral with SENB specimens in a condenser material

A series of tests was performed with three-point single-edge-notched-bend (SENB) specimens in a condenser material (Titanium alloy). Results show that the J-integral values of welded joint and HAZ are obviously smaller than those of the base metal. It signifies that the welding process can result in a reduced toughness of Titanium alloy and the effect of crack orientation on toughness value is not negligible for engineering applications. Besides, the J-integral values of L-T direction specimens are much higher than those of L-S ones. The J-integral values of rolled ring are: JC-R>JC-L>JL-R.A series of tests was performed with three-point single-edge-notched-bend (SENB) specimens in a condenser material (Titanium alloy). Results show that the J-integral values of welded joint and HAZ are obviously smaller than those of the base metal. It signifies that the welding process can result in a reduced toughness of Titanium alloy and the effect of crack orientation on toughness value is not negligible for engineering applications. Besides, the J-integral values of L-T direction specimens are much higher than those of L-S ones. The J-integral values of rolled ring are: JC-R>JC-L>JL-R.

Knowledge-based system prototype in structural component design based on FM

A knowledge-based system in structural component design based on fracture mechanics is developed in this paper. The system consists of several functional parts: a general inference engine, a set of knowledge bases and data-bases, an interpretation engine, a bases administration system and the interface. It can simulate a human expert to make analysis and design scheme mainly for four kinds of typical structural components widely used in shipbuilding industry: pressure vessels, huge rotation constructions, pump-rod and welded structures. It is an open system which may be broadened and perfected to cover a wider range of engineering application through the modification and enlargement of knowledge bases and data-bases. It has a natural and friendly interface that may be easily operated. An on-line help service is also provided.A knowledge-based system in structural component design based on fracture mechanics is developed in this paper. The system consists of several functional parts: a general inference engine, a set of knowledge bases and data-bases, an interpretation engine, a bases administration system and the interface. It can simulate a human expert to make analysis and design scheme mainly for four kinds of typical structural components widely used in shipbuilding industry: pressure vessels, huge rotation constructions, pump-rod and welded structures. It is an open system which may be broadened and perfected to cover a wider range of engineering application through the modification and enlargement of knowledge bases and data-bases. It has a natural and friendly interface that may be easily operated. An on-line help service is also provided.