结构力学（structural mechanics）Structural mechanics is a branch of solid mechanics, which mainly studies the laws of force and force transfer of engineering structures, and how to optimize the structure. The so-called engineering structure refers to the system that can bear and transfer the external load, including the rod, plate, shell and their combinations, such as aircraft fuselage and wing, bridge, roof truss and load-bearing wall.The task is to study structural mechanics in engineering structure under external load stress, strain and displacement law; analysis of different forms and different materials of engineering structure, analysis method and calculation formula for engineering design; engineering structure subjected to external forces and transfer; research and development of new engineering structure.The natural structure observed in nature, such as roots, stems and leaves of plants, animal bones, egg shell, can find their strength and stiffness related not only to material, but also closely related with their shape, many engineering structures are natural structures created out of inspiration. The structure design should not only consider the strength and stiffness of the structure, but also to do material saving and light weight. The weight is particularly important for some projects, such as aircraft weight can make the aircraft flight range, rising quickly, high speed and low energy consumption.A brief history of structural mechanicsHumans began to manufacture all kinds of artifacts in ancienttimes, such as houses, boats and bow, musical instruments, these are simple structure. With the progress of society, people for structural design patterns and the strength and stiffness of the structure has been gradually recognized, and accumulated experience, which is reflected in the brilliant achievements of ancient buildings, such as Egypt, Pyramid, China the Great Wall, Zhaozhou Anji bridge, Beijing the Imperial Palace. Despite the presence of mechanics in these structures in knowledge, but did not form a discipline.As far as the basic principles and methods are concerned, structural mechanics is developed simultaneously with theoretical mechanics and material mechanics. Therefore, structural mechanics is integrated with theoretical mechanics and material mechanics in the initial stage of development. By the early nineteenth Century, due to the development of industry, people began to design a variety of large-scale engineering structures, the design of these structures should be more accurate analysis and calculation. Therefore, the analysis theory and analysis method of engineering structure began to be independent. By the middle of the nineteenth Century, structural mechanics began to become an independent discipline.Many computational theories and methods of structural mechanics appeared in the nineteenth Century. At France in 1826 proposed a normal method for solving statically indeterminate structure problems. From 1830s onwards, due to the bridge by train, not only need to consider the bridge under static load problems, must also be considered to withstand the dynamic load, because the bridge span increases, the metal truss structure.In the decades since 1847, scholars have studied the force analysis of statically determinate truss structures by means of graphic method and analytic method, which laid the foundation of truss theory. In 1864, Maxwell established the unit load method and the displacement reciprocal theorem, and calculated the displacement of the truss by the unit load method. Thus, scholars finally got the method to understand the statically indeterminate problem.After the establishment of the basic theory, the new structure and its corresponding theory have been continuously developed while solving the problems of the original structure. From the late nineteenth Century to the early twentieth Century, scholars carried out a lot of mechanical research on the ship structure, and studied the dynamic theory of the beam under the moving load, as well as the problems of free vibration and forced vibration.In the early twentieth Century, the development of Aeronautical Engineering promoted the stress and deformation analysis of thin-walled structures and stiffened plates and shells, and studied the stability problems. At the same time, bridges and buildings started to use a large number of reinforced concrete materials, this requires scientists to study systematically the steel structure, the displacement method was founded in Germany in 1914 of the Dixon, for solving the problem of rigid frame and continuous beam etc.. Later, in the 20~30 century, some simple calculation methods were put forward for the complex statically indeterminate bar structures, so that the general designers could master and use them.By 1920s, people have put forward the idea of honeycomb sandwich structure. According to the concept of limit state of structure, scholars have come up with a new design and calculation theory for beams, plates and frames on elastic foundations. The mechanical problems of structures subjected to various dynamic loads (especially the action of earthquakes) have been studied in many aspects, such as experiment and theory. With the development of structural mechanics, fatigue problems, fracture problems and composite structure problems have entered the field of structural mechanics.In the middle of the twentieth Century, the advent of electronic computers and finite element methods made it possible to make complex calculations of large structures, thus bringing the level of research and application of structural mechanics to a new level.The discipline system of structural mechanicsThe general structural mechanics according to the different nature and its research object is the static structure, structural dynamics, theory, structure, fracture and fatigue theory of rod structure theory, theory of thin-walled structure and overall structure theory etc..Structural statics is the first branch of structural mechanics. It mainly studies the elastic-plastic deformation and stress state of engineering structures under static loads, and the structural optimization problems. Static load refers to the load that does not change with time, the load that changesslowly, and also can be regarded as static load approximately. Structural statics is the basis of other branches of structural mechanics.Structural dynamics is a branch of study on the response and performance of engineering structures under dynamic loads. Dynamic load refers to the load that changes with time. Under dynamic load, the stress, strain and displacement in the structure must be the function of time. Because of the time factor, the research content of structural dynamics is generally more complex than that of structural statics.The theory of structural stability is the branch of study on the stability of Engineering structures. Slender and thin structures are widely used in modern engineering, such as thin rods, thin plates and thin shells. When they are compressed, they will lose stability (wrinkling or buckling) when the internal stress is less than the yield limit, that is to say, the structure produces too large deformation, thus reducing and even completely losing the bearing capacity. Large deformation also affects other requirements of structural design, such as aerodynamic performance of aircraft. The most important content of structural stability theory is to determine the critical buckling load of structures.Structural fracture and fatigue theory is the study of engineering structures are inevitable because of internal crack, crack under external load expansion caused by fracture, caused by fatigue failure would be expanded subject in smaller amplitude under alternating load. Now, the research history of fracture and fatigue is not long and imperfect, but the theoryof fracture and fatigue is developing very fast.In structural mechanics, theoretical and experimental studies on various engineering structures, based on the research object also formed some research fields, which are the main truss structure theory, the theory of thin-walled structures and the overall structure of the theory of three categories. The whole structure is made of raw materials, machined by mechanical milling or by chemical etching. It is especially suitable for some boundary conditions and is often used as variable thickness structure. With the development of science and technology, many new structures emerge, such as sandwich structure and composite structure appearing in the middle of twentieth Century.The research methods of structural mechanics mainly include three kinds of analysis, experimental research, theoretical analysis and calculation of Engineering structure. In the structural design and research, these three aspects are often alternate and complement each other.The use analysis is in the structure use process, carries on the analysis, the comparison and the summary to the structure appears, this is easy and reliable one kind of research method. The use analysis plays an important role in the evaluation and improvement of structure. The newly designed structures also need to be used to test the performance.The experimental research can provide an important basis for the identification of structure, which is also the main means to test and develop the theory and calculation method ofstructural mechanics. The experimental research can be divided into three types: model experiment, real structural component experiment and real structure experiment. For example,Aircraft ground failure test, flight test and vehicle collision test, etc..The mechanical structure usually takes more manpower, material and financial resources, so only to a limited degree, especially in the early stages of the structural design, generally rely on theoretical analysis and calculation of the structural components.In the field of solid mechanics, provides the basic knowledge necessary for the development of material mechanics, structural mechanics, elastic mechanics and plastic mechanics is the theoretical basis of structural mechanics, structural mechanics is also combined with other physical disciplines form many interdisciplinary, such as fluid elastic force etc..Structural mechanics is an ancient discipline, and it is also a rapidly developing subject. A large number of new engineering materials and new engineering structures have provided new research contents and new requirements for structural mechanics. The development of computer provides a powerful computational tool for structural mechanics. On the other hand, structural mechanics also plays an important role in the development of mathematics and other subjects. The emergence and development of the finite element method is closely related to the study of structural mechanics.。
