1925, shortly after Li Minhua arrived in Shanghai, the May 30th Massacre happened. Young Li Minhua was deeply impressed by the fact that China people were killed by British patrols on the Shanghai beach and foreign warships swaggered on the Huangpu River. 193 1 year, Japanese invaders invaded three northeastern provinces of China. At that time, Li Minhua was studying in Wuben Girls' Middle School. The headmaster of the school is patriotic, encouraging students to take part in demonstrations and organizing military training. A music class happens to be May 4th. The music teacher told the students about his participation in the May 4th Movement in Beijing. Li Min stirred up a heat wave in her heart and decided to go to Peiping (Beijing) to study at a university after graduation.
1935, she was admitted to Tsinghua. Soon after, the "December 29th" student movement broke out. While actively participating in demonstrations with all patriotic youths, she studied harder and was determined to serve the motherland with what she had learned.
In the first year of college, Li Minhua met Wu Zhonghua. They have the same goal of "saving the country through science and technology" and the same hobbies of photography and music, which makes them good friends. During the period of War of Resistance against Japanese Aggression, he moved to Kunming with the school via Changsha, and was renamed Southwest United University. Under tough war conditions, study and life are tense and embarrassing.
1935- 1937 studied in Tsinghua University.
1937- 1940 studied in The National SouthWest Associated University department of aeronautics, and obtained a bachelor's degree.
1940- 1943 worked as a teaching assistant and teacher in the aviation department of Southwest Associated University. 1944, she went to the United States with Wu Zhonghua and studied at MIT. Soon, they had two sons. At that time, most American women took care of their children at home after giving birth, but Li Minhua was able to get a master's degree and a doctor's degree at 1945 and 1948 respectively. As a woman, it was very rare at that time. Li Minhua recalled: "The reason why I can study is because I firmly believe that I will return to China to serve after I finish my studies;" I can't do without Wu Zhonghua's help to take care of my children and housework. Only when we arrange our time reasonably, take care of our children and overcome all kinds of difficulties can we succeed. "Most of Li Minhua's master's thesis work is done in the evening, and Wu Zhonghua takes care of the children and burns the midnight oil.
At that time, the United States still discriminated against women. When she started studying for a doctorate, the professor in charge of undergraduate students in department of mechanical engineering, Massachusetts Institute of Technology said, "I can't see a female doctor in department of mechanical engineering." Fortunately, Professor Soderberg, who is in charge of graduate work, supported her. While studying for a doctorate, Li Minhua took a course in thermodynamics. Professor Keenen said in a test paper: "This exam is very difficult. Many people failed. Later, Professor Kenneng's wife said to Li Minhua at a tea party, "At first, Professor Kenneng didn't believe you, so I gave you a very difficult test. Only by passing this exam will Professor Ken believe it. "
Li Minhua's master's thesis is about "Solving axis torsion with scattered photons". First, she carefully read all the contents about scattered light in the optical book. Then, combining the characteristics of scattered light, the elastic principle of scattered light and the characteristics of axis torsion, a simple new method to solve the problem of elastic axis torsion of scattered light is proposed, and the strain distribution is obtained. Her doctoral thesis is subharmonic vibration. Instructor Den. Hartog pointed to a passage in his book Mechanical Vibration and said, "This is the topic of his doctoral thesis." And added: "The topic of doctoral thesis may not produce results." Dunhato himself wrote in the book: "Because this involves a nonlinear equation with variable coefficients, it is obviously extremely difficult to analyze this." At that time, after receiving his doctorate, Wu Zhonghua left the Massachusetts Institute of Technology to work at the NACA Lewis Engine Research Center in Cleveland. Li Minhua used the summer vacation to invite a middle school student to take care of the children so that she could write a paper. She consulted the literature on subharmonic vibration, and found that there are not a few literatures about subharmonic vibration in electronic system, but there is only one mechanical model to describe subharmonic vibration in mechanical system, and subharmonic vibration will only occur under certain initial conditions. She analyzed that the coefficient of electronic system changes in the process of oscillation, and sub-harmonic vibration will occur under certain conditions; These coefficients are fixed in mechanical systems, and only under certain initial conditions will subharmonic vibration occur. According to these understandings, she got the solution of subharmonic vibration and worked out an example. Professor Dunharto looked at her method and calculation results, and after a simple inspection, she was very happy and said to her, "You solved it!" " So, the tutor further asked her to calculate the whole range of initial difference. This job was done in the city where she worked with her two children in Wu Zhonghua. Li Minhua eventually became the first female doctor of engineering at MIT. When the Boston newspaper reported the graduation ceremony of MIT, it mentioned: "Li Minhua of China, the mother of several children, proved that women can get a doctorate as well as men."
In order to gain practical experience in scientific research, Wu Zhonghua and Li Minhua decided to work for a period of time before returning to China. Subsequently, Li Minhua also worked as a research scientist in the strength laboratory of NACA Lewis Engine Research Center, and conducted research work on plastic mechanics.
1944- 1948 studied in department of mechanical engineering, Massachusetts Institute of Technology, USA, and obtained master's and doctor's degrees.
1949- 195 1 worked as a research scientist in NACA Lewis engine research center.
1952- 1954 Professor of department of mechanical engineering Studies, Brookline Institute of Technology, USA. After the Korean War broke out, they immediately left Naka and went to school to prepare for returning to China. However, soon, the US government prevented China science and engineering students who worked in universities from returning to China. After several years of hard work and overcoming many difficulties, they finally left the United States in the summer vacation of 1954 and returned to the motherland by bypassing Western Europe and the Soviet Union.
After returning to China, young teachers of Huawei in CoCo Lee set up a course of plastic mechanics, and organized discussions on plastic theory and creep theory, which promoted the study of plastic mechanics in China. In the future, she will participate in basic research work in the aerospace field. 1959, she led the development of the newly developed high-temperature test of composite specimens and the experimental machine for transient heating and loading materials. In the mid-1970s, she participated in the aero-engine fault analysis meeting and undertook the stress analysis of the horn turbine shaft under the action of torque. This fault analysis will make her deeply feel the seriousness of the fatigue problem. Therefore, since 1980s, she has been engaged in fatigue research. At the same time, it initiated and organized a national academic conference on fatigue focusing on macro-research, which promoted academic exchanges.
After returning to China, Li Minhua successively served as a researcher and director of the solid mechanics research office in the Mechanics Group of the Institute of Mathematics of China Academy of Sciences and the Institute of Mechanics of Chinese Academy of Sciences. 1980 was elected as an academician of China Academy of Sciences.
1984, she joined the China * * * production party and realized her wish for many years.
1955- 1956 Researcher, Mechanics Research Office, Institute of Mathematics, China Academy of Sciences.
1956 researcher, deputy director and director of the institute of mechanics, Chinese academy of sciences. On the 90th birthday of Academician Li Minhua, the Institute of Mechanics of Chinese Academy of Sciences held a grand celebration. All-China Federation of Returned Overseas Chinese, United Front Work Department of the Central Committee, Beijing Branch and other relevant leaders attended the meeting to express their congratulations. Liu Yandong, Vice Chairman of Chinese People's Political Consultative Conference and Director of the United Front Work Department of the Central Committee, and Lu Yongxiang, Vice Chairman of the National People's Congress Standing Committee (NPCSC) and President of China Academy of Sciences, sent congratulatory letters to the Basic Science Bureau of China Academy of Sciences, China University of Science and Technology, Engineering Science College of University of Science and Technology of China and the Federation of Returned Overseas Chinese of China Academy of Sciences respectively. More than 60 relatives, friends and students of Academician Li Minhua attended the celebration meeting.
Congratulatory letters from Minister Liu Yandong and Chairman Lu Yongxiang were read out at the meeting. On behalf of the All-China Federation of Returned Overseas Chinese, Lin Shuniang, vice chairman of the All-China Federation of Returned Overseas Chinese, sent a deep blessing to Academician Li Minhua and presented a "peach blossom". Zhou Dejin, secretary of the Party Committee of the Institute of Mechanics, expressed congratulations and high respect to the academicians on behalf of the party and government leading bodies, and called on the younger generation of scientific workers to follow Mr. Li's example, learn from her rigorous academic spirit, practical work style, noble moral character of patriotic dedication and simple attitude towards life, and contribute their lives to developing the scientific cause of the motherland and rejuvenating China. Academician Li Pei, Academician Cai Ruixian and Academician Wu Xiaoping are close friends of Academician Li Minhua. They recalled their contacts with Academician Li Minhua and spoke highly of Academician Li Minhua's outstanding achievements and their sincere friendship. On behalf of the Institute of Engineering Thermophysics, Zhang Ping, Party Secretary of the Institute of Engineering Thermophysics, wishes Academician Li Minhua a happy birthday, health and longevity! Zhang Shuangyin, a researcher at the Institute of Mechanics, reviewed the hard work of Yan and his loving mother on behalf of graduate students, and Wu Ming, the son of Mr. Li, spoke on behalf of relatives. plastic mechanics
At the beginning of 1949, while working in NACA Lewis engine research center, Li Minhua made a plastic stress-strain analysis of circular thin film under lateral compression, considering material hardening. At that time, the work of plastic mechanics had just begun, and there were few solutions considering material hardening, so deformation theory was usually used to solve them iteratively. She used the deformation theory to express von Mises' yield condition with the angle α of elliptic equation and dimensionless effective strain γ/γ0. The problem is simplified from five unknown stress-strain components and unknown material parameters to two unknown variables α, γ/γ0 and unknown material parameters. Because α is known on the boundary, γ/γ0 is an unknown variable that changes with the strain component, and it still needs to be solved iteratively. Li Minhua introduces an arbitrary constant k to make the radius dimensionless as γ/k, so that the value of γ/γ0 is selected on a boundary, and the calculation is carried out along γ/k from this boundary until α meets another boundary value. At this time, the value of γ/k is equal to β/k, from which an arbitrary constant k can be determined, so that an accurate solution can be obtained without iteration. This method can be used for axisymmetric plane stress problems, which was very meaningful in the early 1950 s when computers were not developed. When discussing Li Minhua's article, E T Stowell wrote: "It is almost impossible to solve the plastic stress distribution of strain hardening materials accurately. For axisymmetric problems, the solution obtained by the author (Li Minhua) belongs to exact or nearly exact solution. ..... Even in the simple one-dimensional case of thin plates with circular holes, it is not easy to satisfy the compatibility equation, equilibrium equation, stress-strain relationship and boundary conditions at the same time. Because the author skillfully introduces any constant parameter, the author meets the above conditions quite accurately. " Finally, he said: "The author provided a series of examples of exact solutions, which is her special contribution."
Subsequently, Li Minhua extended it to the axisymmetric plane strain problem by calculation and to the plane stress problem by experiment. From the above work, she thinks that if the proportion of external load on the part increases, it can be applied to plastic large strain problem and deformation theory, and it also has the characteristics of plastic deformation mentioned above. When Feng Youlan visited the Institute of Mechanics in the late 1970s, he mentioned: "At the international academic conference on mechanics held last year, we also discussed Li Minhua's work." 198 1 year, J. Hutchinson and He Mingyuan of Harvard University also applied the plastic deformation theory.
aerospace industry
In 1959, she accepted the high-temperature experiment task of a newly developed composite specimen with stagnation temperature over 1000℃. As the deputy director of the research room, Li Minhua joined the research team and decided to use rocket engine for heating through research. Due to time constraints, it is impossible to develop a conventional rocket engine. She proposed to use incandescent body for ignition, which greatly shortened the design and processing cycle. In less than half a year, they realized the high-temperature experiment with stagnation point temperature exceeding 1000℃ for the first time in China, and the relevant departments of the Ministry of Space attached great importance to it, and specially organized a visit to imitate it.
Subsequently, Li Minhua joined the research group and established a material testing machine with instantaneous heating and loading. She put forward the strain measurement method, and decided the scheme after investigating several heating methods with the researchers in the group, and obtained the instantaneous uniform temperature of the test section of the specimen, and successfully developed the instantaneous heating loading material testing machine for the first time in China. This group was rated as the advanced group of the institute and obtained the certificate for this work.
In the early 1970s, Li Minhua undertook the stress analysis of the angular shaft under the action of torque in view of the failure of the turbine shaft of aero-engine. In view of the key points of the problem, it is necessary to obtain the stress and strain values of the high stress concentration area of the small groove. She proposed that the stress function be regarded as an unknown and calculated by the finite difference method of non-orthogonal curvilinear coordinates. In this way, the stress values of each point along the edge of the small groove can be directly obtained under the condition that the required computer capacity is not large. At that time, her youngest son was hospitalized with leukemia. She went to the hospital every other afternoon or evening and worked overtime on the other day, thus finishing the task on time. The relevant departments of the Ministry of Aviation said in the letter: "Compared with the results of finite element, photoelastic experiment and fatigue test of turbine shaft, the calculation results are more accurate. ..... This calculation can check the strength of any point on the outer surface of the shaft according to the needs of strength analysis, which is its main feature superior to the finite element method. This is exactly what the original fault research needs. " This work won 1978 China Academy of Sciences' major achievement award. Analysis of axisymmetric plane plastic stress in strain hardening range. NACA TR 102 1， 195 1。
2 Li Wumin. Linear solution and general plastic behavior of thin plates with circular holes in strain hardening range. NACA TN 230 1， 195 1。
3 lee Wu m H. general plastic behavior and approximate solution of rotating disk in strain hardening range. NACA TN 2367， 195 1。
A simple method for determining plastic stress and strain in a rotating disk with non-uniform metal characteristics. Doctor of applied mechanical law. 1952, 19(4):489~495.
Influence of stress-strain relationship of materials on solution of plane stress problem of large plastic deformation. International congress of applied machinery, 9th edition. Journal of Brussels University. The 9th International Conference on Applied Machinery. ),1957,8:156 ~165. See Journal of Mechanics, 65438+.
6 Li Minhua, Wang Ren. Overview of plastic stress-strain relationship. Journal of Mechanics,1958,2 (2):167.
7 Li Minhua. Study on axisymmetric plastic plane stress of hardened materials. Beijing: Science Press, 1960.
8 Li Minhua. A new solution to the torsion problem of circular shaft with variable cross-section by using non-orthogonal curvilinear coordinates. Journal of Solid Mechanics, 1980,1(2):159 ~169.