Vacuum drying stress

    Vacuum drying is different from atmospheric drying in that the material will not produce drying shrinkage during vacuum drying. On the contrary, many materials will have volume expansion after drying, and the size of the expansion is often related to the type of material, moisture content, drying speed, drying temperature and vacuum degree. Expansion is anisotropic and often presents different laws. Currently, there is no unified method and formula to describe the expansion coefficient. Since there is drying deformation, drying stress will be generated, and the calculation method of drying stress is not mature. Here, we will use the method of material mechanics to explain briefly.

    Metal materials can be divided into brittle materials and plastic materials. The brittle material has no obvious residual deformation when it is loaded to the fracture, while the plastic material will appear large plastic deformation after the elastic limit is loaded, until the fracture limit, the wet material generally has no obvious boundary between elastic and plastic deformation, and its stress The strain curve can continue to extend to the ultimate load until the specimen breaks.

    The purpose of studying vacuum drying is to dry large-scale materials that may produce stress and deformation, which will adversely affect product performance and use. For example, vacuum drying wood, drying stress will cause the wood to warp or crack, which will affect the use value of the wood. The stress-strain analysis of vacuum drying of large and irregularly shaped wet materials is a difficult mechanical problem, which is usually solved by finite element method.

(Huiputech)