Abstract. This paper presents an overview of mechanical properties and constitutive law for wood. Current research on the mechanical properties of wood have mostly focused on density, grain, moisture, and other natural factors. It has been established that high density, dense grain, and high moisture lead to higher strength. In most literature, wood has been regarded as an anisotropic material because of its fiber. A microscopic view is used in research of wood today, in this way, which has allowed for clear observation of anisotropy. In general, wood has higher strength under a dynamic load, and no densification. The constitutive model is the basis of numerical analysis. An anisotropic model of porous and composite materials has been used for wood, but results were poor, and new constitutions have been introduced. According to the literature, there is no single theory that is widely accepted for the dynamic load. Research has shown that grain and moisture are key factors in wood strength, but there has not been enough study on dynamic loads so far. Hill law has been the most common method of simulation. Models that consider high strain rate are attracting more and more attention.
The in-plane damage behavior and material properties of the composite material are very complex. At present, a large number of two-dimensional failure criteria, such as Chang-Chang criteria, have been proposed to predict the damage process of composite structures under loading. However, there is still no good criterion to realize it with both enough accuracy and computational performance. All these criteria cannot be adjusted by experimental data. Therefore, any special properties of composite material cannot be considered by these criteria. Here, in order to solve the problem that the criteria cannot be adjusted by experiment, new two-dimensional polynomial failure criteria with four internal parameters for composite laminates are proposed in the paper, which include four distinct failure modes: fiber tensile failure, fiber compressive failure, matrix tensile failure, and matrix compressive failure. In general, the four internal parameters should be determined by experiments. One example that identifies parameters of the new failure criteria is given. Using the new criteria can reduce the artificialness of choosing the criteria for the damage simulation of the failure modes in composite laminates.
Electroplating was employed to prepare Cu films on Fe substrates and Ni substrates. The average internal stresses in Cu films were measured in situ by cantilever beam test. The distribution of the internal stresses in Cu films was investigated. The results show that the average internal stresses and the distributed internal stresses in Cu films decrease abruptly with the increase of film thickness when the films are thinner. The interfacial stresses in Cu films are very large and growth stresses are very small. The average internal stresses in Cu films, which were caused by the adjustment of the electron densities at either side of the interface, were calculated roughly using a modified Thomas–Feimi–Dirac electron theory. For the same substrate and the same film, the theoretical value of the average internal stress in film is about equal to the experimental value. It shows that the theoretical calculation model of internal stress is of accuracy.
The influences of rare earth neodymium on microstructure and mechanical properties of as cast and hot rolled AZ31B wrought magnesium alloy were investigated. The results show that the mechanical properties of both as cast and hot rolled AZ31B alloys decrease due to Nd addition. Nd reacts with Al to form Al2Nd phase when Nd is added. Bulky and brittle Al2Nd intermetallic degrades the mechanical properties. Moreover, the addition of Nd weakens the grain refining effect of Al on as cast AZ31B alloy, resulting in grain coarsening. Coarse grains also cause the decline of the mechanical properties of as cast AZ31B–Nd alloy. The negative influence of the bulky and brittle intermetallics on mechanical properties of AZ31B alloy can be relieved by large deformation because the intermetallics can be sufficiently broken up during the deformation process.
In order to effectively describe the damage process of composite laminates and reduce the complexity of material model, a mixed damage model based on Linde Criteria and Hashin Criteria is proposed for prediction of impact damage in the study. The mixed damage model can predict baisc failure modes, including fiber fracture, matrix tensile damage, matrix compressive damage. Fiber damage and matrix damage in compression are described based on the progressive damage mechanics; and matrix damage in tension is described based on Continuous Damage Mechanics (CDM). Meanwhile, for interlaminar delamination, damage is described by cohesive model. A finite element model is established to analyze the damage process of composite laminate. A good agreement is got between damage predictions and experimental results.
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