Nondestructive Testing and Characterization of Residual Stress Field Using an Ultrasonic Method

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel（12%C） as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave（LCR wave） is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designed to conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.

QUASI-PERMUTATION REPRESENTATIONS OF ALTERNATING AND SYMMETRIC GROUPS

The quantities c（G）, q（G） and p（G） for finite groups were defined by H. Behravesh. In this article, these quantities for the alternating group An and the symmetric group Sn are calculated. It is shown that c（G） = q（G） = p（G） = n,when G = An or Sn.

21世纪哈斯宝人物论研究综述(2000-2019)

Hasboo,Oglige-e Bayasqulant Geriin Ejen,Behd Hobdog Hobuun,was a Mongolian scholar of theDream of Red Mansion Dream and literary critic in the Qing Dynasty.He translated one hundred and twentychapters of Dream of Red Mansion into forty chapters in classical Mongolian,and left 43 valuable articles,setting a precedent for Mongolian people to read and study A Dream of Red Mansion.Throughout Hasboo’sliterary theory,the comments on the characters in the book are the most classic.This paper intends to sum-marize the research on Hasboo’s character theory by combing the 21 st century Hasboo’s character theory re-search and also analyzes the characteristics of Hasboo’s character theory research.On the basis of theachievements and deficiencies in the field,the trend of the future research on Hasboo’s character theory isproposed.The study of Hasiboo’s literary theory is an important part of the study of Mongolian literary theo-ry,and it is one of the indispensable contents of the study of the related area and even the theory of ancientChinese novels.By summarizing and analyzing the academic circles’research on Hasboo’s literary theory,it has enriched Hasboo’s research and research of the Dream of Red Mansion,and it has certain practicalsignificance in promoting the relationship between Mongolian and Chinese literature.

Groups with One or Two Super-Brauer Character Theories

A super-Brauer character theory of a group G and a prime p is a pair consisting of a partition of the irreducible p-Brauer characters and a partition of the p-regular elements of G that satisfy certain properties.We classify the groups and primes that have exactly one super-Brauer character theory.We discuss the groups with exactly two super-Brauer character theories.

Effects of Cooling Rate and Component on the Microstructure and Mechanical Properties of Mg–Zn–Y Alloys

The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y（wt%） alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing（SDAS） of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates（Rc） from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0：45：45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction（Vf） of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.