Mei Yao

Quantitative description of temperature- and strain rate-dependence of yield strength of structural steels

A quantitative description of temperature- and strain rate-dependence of yield strength of structural steels was proposed and experimentally verified with enough accuracy.

The physical nature of drop-weight-test NDT

Abstract Based on a correlation study on the series-temperature fracture behavior of a precracked Charpy specimen with sufficient plastic constraint and a drop-weight specimen of a C-Mn steel, both in static and impact loading conditions, it is found that the Nil-Ductility Transition temperature, NDT, in its nature, is the characteristic transition temperature of brittleness, T*, and reflects the transition behavior of crack arrestability, of the base metal in impact loading conditions.

Determination of characteristic transition temperature of low-temperature brittleness in mild steel

By means of the finite element method, the stress distributions below the notch root of some typical notch bending test specimens were analyzed in detail to obtain the numerical solution of the maximum principal stress intensification Qmax at the edge of the “effective yield zone”, which is an important parameter characterizing the characteristic transition temperature of low-temperature brittleness Tc∗. The present work lays a theoretical foundation for determining the temperature Tc∗ using only series-temperature plain-tension test results.

Ductile/brittle transition condition in Charpy V-notch impact test in structural steel

Abstract Instrumented impact tests of standard Charpy V-notch specimens of structural steel were carried out over a temperature range from 223 to 353 K. The results show that as in slow notch-bend, the cleavage-characteristic stress Sco also plays a controlling role in the critical condition for the ductile/ brittle transition in the Charpy V-notch impact test in structural steel.

Numerical analysis of strain rate field below notch root of Charpy V-notch test specimen under impact loading condition

Abstract By using the ADINA (Automatic Dynamic Incremental Nonlinear Analysis) program, numerical analysis of the strain rate distribution below the notch root of a Charpy V-notch test specimen under the impact loading condition was made in detail. Some useful results were obtained which are very important for the analysis of the critical ductile/brittle transition condition of the Charpy V-notch test in structural steel.

Cleavage characteristic stress Sc0: a new parameter of microscopic resistance to cleavage fracture

Abstract In this paper, studies on a new parameter characterizing the microscopic resistance to cleavage fracture, S c0 , named the ‘cleavagecharacteristic stress’, are reviewed, with emphasis on its physical nature and application in analysis of the typical ductile/brittle transition (DBT) behavior of steels.

The generalized characteristic transition temperature of brittleness-II. Thermal activation analysis

Abstract The ductile/brittle transition behavior was analyzed by means of the dislocation thermal activation mechanism. Besides, a relationship between the nominal loading rate and intrinsic transition temperature of brittleness, T c ∗ , was established.

Critical crack size for low-temperature brittleness of mild steel in tension of center-cracked sheet

Abstract The present paper deals with the fracture behavior of mild steel vs temperature using experimental results of a center-cracked sheet in tension at various temperatures. It is indicated that, for this specimen geometry and loading mode, there also exists a critical crack size for the occurence of low-temperature brittleness, ac, below which the corresponding component should maintain its integrity as regards its low-temperature service. The theoretical expression of ac has been derived and its validity verified by data of the simulating test. Thus the research extends the adaptability of the model of ac to conditions other than notch-bend.

Effect of precipitation and grain size on the ductile-to-brittle transition in mild steels

Abstract The ductile-to-brittle transition behavior was studied for mild steels in annealed and aged states as weil as with different grain sizes, using plain tension and notchbending tests at various temperatures. For evaluating the transition here new parameters, the cleavage-characteristic stress S co and the cryogenic brittleness-characteristic temperature T ∗ c , were adopted. It is indicated that the shift of T ∗ c with variation of microstructure is determined by the resultant change in the combination of S co and yield strength σ y . The elevation of T ∗ c for aged steel is mainly due to an increase in σ y since precipitation exhibits little effect on S co . However, a decrease in grain size makes an increment of both σ y and S co , and the increment of S co predominates over that of σ y , thus leading to a decrease in T ∗ c .