On the emergence and development of physical mechanics.
Abstract: Physical mechanics is mainly a micro-theoretical discipline that studies macro-mechanics. The main purpose of studying physical mechanics is to find out the calculation method of mechanical properties of media by understanding the interaction of microscopic particle properties, and then solve mechanical problems on the basis of microscopic analysis. This paper mainly discusses the emergence and development of physical mechanics, and provides theoretical basis for solving related problems of physical mechanics.
Keywords: physical mechanics; Produce; develop
First, analyze the problems that need to be solved in the development of physical mechanics.
In the development of physical mechanics, we need to solve two problems, one is about physical properties, and the other is about the law of motion. Physical mechanics is the basis of solving problems and establishing microscopic analysis mainly through microscopic analysis of physical properties and their laws of motion. Physical parameters are mainly the coefficients in the equation of motion, such as elastic coefficient, thermal conductivity, viscosity coefficient, sound velocity, specific heat and so on. In order to solve the equations of motion, we need to know their related values.
In traditional mechanics, the values of physical parameters need to be tested. In the physical mechanics we study, the numerical values of parameters are calculated by combining microscopic analysis with macroscopic data analysis. We study physical mechanics not only to find out the microscopic laws of material properties, but also to find a way to predict the properties of new materials.
In view of the related problems in the development of physical mechanics, let's first understand the example of shock wave structure. The state of matter will change greatly before and after the shock wave. Within a certain thickness of wavefront, matter is far from equilibrium. At this point, the parameters of the macroscopic state of matter are no longer applicable. Therefore, it needs to be described from the perspective of molecular application. For example, from the perspective of Boltzmann equation, and then directly solve it.
In the 1960s, a pair of problems affecting shock wave structures without internal degrees of freedom were further developed. Its development is mainly due to the development of computer technology, which can make Boltzmann equation, then get the mathematical equation of the model and find the exact solution. In addition, it can also measure the resolution of shock tube and rarefied gas wind tunnel in higher areas. Although the treatment of these problems is preliminary, it is indeed a great progress from the microscopic motion law of physical mechanics.
Another similar example is the study of the structure of detonation wave reaction zone. The research in this field is more complicated than the shock wave structure, and the difficulty in solving the problem lies in the complexity of theory and the lack of experimental experience. The non-balanced flow problem in the power laser of molecular gas is mainly due to the self-imbalance phenomenon caused by the nature of internal freedom of molecules in the expanding gas flow. In this rapidly expanding airflow, the degree of freedom of molecular vibration is unbalanced in two aspects and cannot be described by a unified temperature. Therefore, this is also a problem far from balance.
Second, new technologies constantly promote the development of physical mechanics.
The emergence and development of physical mechanics is not only an important trend of mechanical development, but also an important means to promote the development of modern engineering technology. Since the 1940s, due to the continuous development and progress of cutting-edge technology and basic science, mechanics has faced a lot of problems under special conditions such as ultra-high temperature and ultra-high pressure. Qian Xuesen, a famous Chinese mechanic, proposed to establish the discipline of physical mechanics in the early 1950s. His opinion grasped the general trend of machinery development and predicted the result of rapid development in the future.
The continuous development of human social science and technology provides more conditions for the study of physical mechanics. Looking at the development of physical mechanics in recent 50 years, it is worth mentioning that the liquid theory has made great progress. From 65438 to 0972, MacDonald and others calculated the isobar results and measured data of various liquids, which promoted the research of liquid theory. From 65438 to 0997, Wilson put forward the renormalization group theory to solve critical phenomena, and made great progress. In recent 20 years, the research of dissipative structure theory as a non-equilibrium system has also made breakthrough progress. Since 1950s, atomic and molecular physics has been paid more attention, especially the continuous application of computers has greatly promoted the development of this subject. Other techniques, such as molecular beam, light scattering and neutron diffraction, have become effective means to study the microstructure of solids and liquids. In addition, high-pressure technology can produce high-pressure conditions above10 million atmospheres, and atomic-scale phenomena can be observed by high-power electron microscope. New technologies and inventions provide favorable conditions for further study of physical mechanics.
This paper discusses the emergence and development of physical mechanics. Through the research of this paper, we know that when we study physical mechanics, we should make clear the purpose of physical mechanics research, and also fully adopt new technologies and inventions and constantly apply them to the research. As long as we keep exploring and practicing, we will certainly further promote the development of physical mechanics.
References:
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Physical Mechanics Part II Application Analysis of Mechanics in Machinery
Abstract: Mechanics is a science about force and motion. It is not only a basic science, but also a widely used science. Based on mechanics, the connotation and development process of mechanics are briefly discussed, and the application of mechanics in machinery is deeply discussed and analyzed.
[Keywords:] mechanics, elasticity, fracture mechanics, construction machinery
Mechanics is the science of force and motion, and its research object is mainly the macroscopic mechanical motion of matter. It is not only a basic science, but also a science with many applications and wide range. Mechanics, astronomy and calculus were born almost at the same time, which played a key role in the development of classical physics and promoted the development and progress of earth sciences, such as atmospheric physics and marine science. At the same time, mechanics plays an increasingly important role in machinery and is widely used.
I. Mechanics
Mechanics is an independent basic discipline, which mainly studies energy and force and their relationship with the balance, deformation or motion of solids, liquids and gases. It can be roughly divided into three parts: statics, kinematics and dynamics.
The development of mechanics has a long history. In ancient Greece, mechanics was attached to natural philosophy and later became a major branch of physics. 1687, Newton's three laws marked the beginning of the formation of mechanics as an independent discipline. Since then, with the development of capitalist production, by the end of 18, classical mechanics with dynamics and kinematics as its main features has become increasingly perfect. /kloc-in the 0/9th century, the production of large machines promoted the development of mechanics in engineering technology and application, and promoted the establishment of major branches such as structural mechanics, elastic solid mechanics and fluid mechanics. At the end of 19, mechanics has become a fairly developed and self-contained independent discipline.
Second, the application of mechanics in machinery
Mechanics is widely used in machinery, and its typical applications mainly include the following:
1. Application of elasticity in mechanical design
Elasticity, also known as elasticity theory, is an important branch of solid mechanics, which mainly studies the stress, strain and displacement of elastic body under the action of external factors such as external force or temperature change, so as to solve the strength and stiffness problems raised in structural or mechanical design. In the process of mechanical movement, many machines have high running speed and heavy load, and the influence of mechanical elastic deformation on the system can not be ignored, so the mechanical system must be analyzed and designed according to the elastic system. Therefore, elasticity is widely used in mechanical design. Generally speaking, elasticity is widely used in cam mechanism design, gear mechanism design and shaft design.
The knowledge of elastic mechanics is used in the design of gear mechanism. Involute, as a kind of tooth profile curve, has many advantages, but when it is analyzed with the knowledge of elastic mechanics, it will get some inherent defects, that is, when two gears are engaged, it can be obtained according to Hertz formula in elastic mechanics. Other things being equal, in order to reduce the maximum contact force of two gears at the contact point, it is necessary to increase the comprehensive curvature radius of the contact point tooth profile. For involute gear transmission, in order to increase the comprehensive curvature radius of the two-wheel tooth profile at the contact point, it is necessary to increase the size of the gear mechanism, but the range of increasing the comprehensive curvature radius of the two-wheel tooth profile at the contact point is limited, so it is difficult to further reduce the size of the gear mechanism and greatly improve the bearing capacity. At the same time, elasticity has many applications in shaft design. In order to avoid * * * vibration, it is particularly important to calculate the vibration of high-speed shafts, such as the main shaft of steam turbine and the crankshaft of engine. At this time, the knowledge of elasticity must be used.
2. The application of fracture mechanics in mechanical engineering.
Fracture mechanics is a new branch of solid mechanics, which mainly studies the strength and life of cracked members and is the theoretical basis of structural damage tolerance design. Fracture mechanics can be divided into linear elastic fracture mechanics and elastic-plastic fracture mechanics. The former is suitable for small-scale yield near the crack tip. The latter is suitable for large-scale yield near the crack tip. Fracture mechanics develops rapidly and is widely used in mechanical engineering, occupying an important position. The effective application of fracture mechanics in mechanical engineering can not only improve the performance and efficiency of machinery, but also prevent catastrophic fracture accidents of engineering equipment and ensure the safe, reliable and good operation of mechanical equipment.
First of all, China has made good achievements in establishing structural defect evaluation standards and safety design specifications by using fracture mechanics methods, such as pressure vessels, small but large liquefied petroleum gas cylinders, steam turbine generators and so on.
Secondly, probabilistic fracture mechanics is widely used in reliability design. The wide application of probabilistic fracture mechanics in reliability design promotes the rapid development of reliability design. Parameter distribution and safety margin are used to reflect the objective reality that can not be accurately reflected by conventional design and the real safety that can not be accurately reflected by safety factor in conventional design safety assessment. Because the second moment of stress intensity is considered in the safety margin, it reflects the essence of structural reliability, and at the same time, it considers the variation characteristics and average value, which is directly related to the failure distribution, making the safety design more reliable. Foreign countries have been fully applied to aircraft structures, such as probabilistic damage tolerance analysis, aircraft structure reliability and accident analysis, aircraft structure durability analysis and so on. The typical research in this field in China is the fatigue strength analysis of welded pipe joints of offshore oil platform jacket.
In addition, fracture mechanics method can be used to analyze the failure of mechanical products. Failure analysis refers to the side inspection and analysis after an accident or failure. The purpose is to find out the fault location, fault reason and mechanism, so as to grasp the product improvement direction and repair method, prevent similar problems from happening again, and promote the continuous progress of technology. Therefore, fault analysis technology has attracted the attention of all walks of life. Fracture mechanics plays an important role in the failure analysis of mechanical products. The main failure modes of mechanical products are: fracture, creep, fatigue, corrosion, wear and thermal damage. These can be solved by fracture mechanics method and fracture analysis technology, and fracture mechanics method is a powerful tool for failure analysis.
Finally, the application of fracture mechanics can guide the improvement of technology and the reasonable selection of materials, such as mold and welding technology, which can reduce the labor of workers.
3. The application of engineering mechanics in mechanical repair
Engineering mechanics involves many branches of mechanics and a wide range of engineering technical fields. It is a technical basic subject with strong theory and close connection with engineering technology. Theorems, laws and conclusions of engineering mechanics are widely used in engineering technology in all walks of life, which is an important basis for solving practical engineering problems. Dealing with a large number of damage problems in mechanical engineering is mostly based on mechanical knowledge to judge and analyze. For example, the damage analysis and repair of automobile parts in automobile maintenance are also the same. Among them, the whole process of judging the cause of automobile shaft sleeve fracture and determining the repair scheme embodies the application of engineering mechanics knowledge in automobile repair.
Third, the conclusion
Nowadays, science and technology are developing rapidly. Mechanics, as a basic discipline, is bound to get further development and progress, and will be widely and deeply applied in machinery.
refer to
[1] Lin Tongji, Puqun. Development of modern mechanics [J]. Mechanical progress, 1990, (1).
[2] Li. Application of Engineering Mechanics in Automobile Maintenance and Countermeasures [J]. Science and Technology Herald, 20 12, (32).
Hou yanbin. Application of elasticity in mechanical design [J]. Journal of Liaoning Normal University, 2005, (1).
Wu Qingke, Liu, Zhang. Application of fracture mechanics in mechanical engineering [J]. Mechanical strength, 1988, (6).