Composite mechanics is an emerging branch of solid mechanics. It studies the mechanical problems of multi-phase solid materials composed of two or more materials with different properties on a macro scale, that is, composite materials. Composite materials have obvious non-uniformity and anisotropy, which is an important feature of composite mechanics. There are two most important types of modern composite materials: one is fiber-reinforced composite materials, mainly long-fiber layup composite materials, such as FRP; the other is particle-reinforced composite materials, such as coagulation, which is widely used in construction engineering. Fiber-reinforced composite material is a high-functional material, which is significantly better than a single material in mechanical properties, physical properties and chemical properties. A brief history of the development of composite materials mechanics In nature, there are a large number of composite materials, such as bamboo, wood, animal muscles and bones. From a mechanical point of view, natural composite materials are often ideal structures, which provide a bionic basis for the development of artificial fiber-reinforced composite materials. Humans have already created composite materials with mechanical concepts. For example, ancient Chinese and Jews used straw or wheat straw to reinforce mud bricks for building houses; two thousand years ago, China made raw lacquer lining for anti-corrosion; Chinese lacquerware made of thin silk and lacquer bonding is also modern fiber reinforced The prototype of the composite material, which reflects the mechanical advantages of light weight, strength and rigidity. In order to overcome the shortcomings of carbon fiber and boron fiber that are not resistant to high temperature and poor shear resistance, in the past two decades, people have developed metal-based and ceramic-based composite materials. The Chinese have made many contributions in the research of composite materials, but China's starting and level of research on composite materials mechanics is ten to fifteen years later than in Europe and America. After entering the 1960s, the development of composite mechanics accelerated. In 1964, Rosen proposed a method to determine the longitudinal compression strength of unidirectional fiber-reinforced composites. In 1966, Whitney and Riley proposed an independent model method to determine the elastic constants of composite materials. In 1968, after years of research by Cai Weilun and Hill, the Cai-Hill failure criterion was formed; in 1971, the Tensor-style Cai-Wu failure criterion appeared again. In 1970 Jones studied general multi-directional laminates and obtained simple and accurate solutions; in 1972 Whitney used double Fourier series to solve the deflection, buckling load and vibration of torsional coupling stiffness to anisotropic laminates The influence of the problem, the displacement solved by this method not only meets the natural boundary conditions, but also quickly converges to the exact solution; in the same year, Chamis, Hansen, and Serafini studied the impact resistance of the composite. In addition, Cai Weilun has done pioneering research on the analysis of the nonlinear deformation properties of unidirectional laminates, Adams on the mesomechanical theory of inelastic problems, and Soha Perry on the viscoelastic stress analysis of composite materials. In recent years, research on the mechanical properties of hybrid composites has attracted the attention of some scholars. Lin Yi first discovered in 1972 that the maximum strain corresponding to the straight part of the stress-strain curve of the hybrid composite material has exceeded the failure strain of the fiber with low elongation in the hybrid composite material. This incomprehensible phenomenon was discovered by Bansell and others in 1974, and was later called the "hybrid effect". Characteristics of composite materials The mechanical properties of the composite material can be designed, that is, the composite material member or composite material structure can meet the requirements of use by selecting appropriate raw materials and reasonable layup forms. For example, in a certain ply form, when the material is stretched in one direction and stretched, the material is stretched in the direction perpendicular to the tension, which is completely different from the performance of commonly used materials. Another example is to use the coupling effect of composite materials to make a laminate on a flat plate mold. After heating and curing, the board automatically becomes the required curved board or shell. Composite materials have good fatigue resistance. The fatigue strength of general metals is 40-50% of the tensile strength, and some composite materials can be as high as 70-80%. The fatigue fracture of the composite material starts from the matrix and gradually expands to the interface between the fiber and the matrix, without sudden changes. Therefore, the composite material has harbingers before it can be destroyed and can be inspected and remedied. Fiber composite materials also have good resistance to sound vibration fatigue performance. The helicopter rotor made of composite material has a fatigue life several times longer than that of metal. The vibration damping performance of the composite material is good. The fiber composite material has greater damping at the interface between the fiber and the matrix, so it has better vibration damping performance. Two beams of the same shape and the same size were used for vibration tests. The vibration attenuation time of carbon fiber composite beams is much shorter than that of light metal beams. Composite materials are usually able to withstand high temperatures. At high temperatures, the strength and stiffness of metals reinforced with carbon or boron fibers are much higher than the strength and stiffness of the original metal. When the ordinary aluminum alloy is at 400 ℃, the elastic modulus is greatly reduced, and the strength is also reduced. At the same temperature, the strength and elastic modulus of the aluminum alloy reinforced with carbon fiber or boron fiber are basically unchanged. The thermal conductivity of composite materials is generally small, so its instantaneous resistance to ultra-high temperature is better. The safety of composite materials is good. There are thousands of independent fibers in the matrix of fiber-reinforced composite materials. When a component made of this material is overloaded and a small number of fibers break, the load will be quickly redistributed and transferred to the undamaged fibers, so the entire component will not lose its load bearing capacity in a short time. The molding process of composite materials is simple. Fiber-reinforced composite materials are generally suitable for integral molding, thus reducing the number of parts, which can reduce the design calculation workload and help improve the accuracy of calculation. In addition, the step of making fiber-reinforced composite material parts is to bond the fiber and the matrix together, mold it first, and then heat and solidify. During the manufacturing process, the matrix changes from fluid to solid, which is not easy to cause micro cracks in the material. The residual stress after curing is very small. Research contents of composite materials mechanics Compared with the mechanics theory of conventional materials, the mechanics of composite materials has a wider scope and more research topics. First of all, the mechanical problems of conventional materials, such as the strength, stiffness, stability and vibration of structures under external forces, still exist in composite materials, but due to the uneven and anisotropic characteristics of composite materials, and The increase of variable factors such as material geometry (shape, distribution, content of each material) and layer geometry (thickness of each single layer, layer direction, layer order), etc. The above mechanical problems must be renewed in composite mechanics Research to determine whether the mechanical theories, methods, equations, formulas, etc. that are applicable to conventional materials are still applicable to composite materials, and if not, how to correct them. Secondly, there are many mechanical problems that do not exist in conventional materials in composite materials, such as interlayer stress (interlayer normal stress and shear stress coupling will cause complex fracture and delamination phenomenon), boundary effects and fiber degumming, fiber fracture, Problems such as matrix cracking. Finally, the material design and structural design of the composite material are carried out at the same time. Therefore, the material design of the composite material (such as the selection of materials and the determination of the combination method), the processing process (such as material layering, heating and curing) and the structural design process There are mechanical problems. At present, the research work on the mechanics of composite materials mainly focuses on the improvement and application of fiber-reinforced multi-layer laminate shell structures. This structure is formed by superimposing and bonding many unidirectional layer materials in different directions, so it is called a multidirectional layer material structure. The direction of the fiber in the unidirectional layer material is called the longitudinal direction; and the direction perpendicular to the fiber in the sub-plane of the unidirectional layer material is called the transverse direction. The longitudinal and lateral directions are collectively called the principal axis direction. Unidirectional layer materials are orthotropic materials, and its mechanical research and understanding of its performance parameters are the basis for the mechanical research of multidirectional layer materials and multidirectional layered plate and shell structures. The fiber direction of each unidirectional layer material in the multidirectional layer material is generally different. How to arrange these unidirectional layer materials should be based on the mechanical requirements of structural design. Copier Toner For Xerox,Compatible Printer Cartridge,Colorful Compatible Toner Cartridge,Custom Xerox Toner Cartridge jiangmen jinheng office equipment Co. Ltd. , https://www.jm-jinheng.com
The composite material is composed of a reinforcement and a matrix. The reinforcement plays a major role in bearing the load. Its geometric forms include long fibers, short fibers, and granules. The matrix plays a role in bonding, supporting, protecting the reinforcement, and transferring stress. Often used in the role of rubber, graphite, resin, metal and ceramics.
The development of fiber-reinforced composite materials is a scientific and technological issue that is currently highly valued internationally. Nowadays, in the field of military use, fiber-reinforced composite materials have been adopted for aircraft, rockets, missiles, satellites, ships, tanks, conventional weapons and equipment; for civilian use, transportation vehicles, building structures, machine and instrument components, chemical pipelines and containers , Electronic and nuclear energy engineering structures, as well as ergonomics, medical equipment and sports goods, etc. have gradually begun to use this composite material.
Modern composite materials marked by concrete appeared more than 100 years ago. Later, the original concrete structure could not meet the strength requirements of high-rise buildings, and the builders switched to reinforced concrete structures, where the steel bars increased the tensile strength of the concrete, thereby solving a large number of architectural problems.
In the early 20th century, in order to meet the requirements of military materials for mechanical properties, people began to develop new materials, and in the 1940s successfully developed glass fiber reinforced composite materials (ie, glass steel). Its appearance enriches the mechanics content of composite materials. In the 1950s, higher-strength carbon fiber and boron fiber composite materials appeared, and the research on the mechanics of composite materials has greatly developed, and a new discipline of mechanics, composite mechanics, has gradually formed.
The specific strength and specific stiffness of composite materials are higher. The strength of a material divided by density is called specific strength; the rigidity of a material divided by density is called specific rigidity. These two parameters are important indicators to measure the bearing capacity of the material. Higher specific strength and specific stiffness indicate that the material is lighter in weight, while greater strength and stiffness. This is an important requirement for materials for structural design, especially for aviation and aerospace structural design. Modern airplanes, missiles, satellites and other airframe structures are gradually expanding the proportion of fiber-reinforced composite materials.