IN718 alloy clad coating cooled in liquid nitrogen was fabricated by high power diode laser. The microstructure of the coating was investigated using SEM equipped with energy disperse spectroscopy, and the precipitation phase was analysed using TEM after standard heat treatment. The results showed that the liquid nitrogen provided the clad coating an ultrarapid cooling rate during laser cladding. Laves in the ultrarapid cooled clad coating was refined, and Laves concentration and dendritic space were decreased compared with the air cooled clad coating. The ultrarapid cooling rate reduced the constitutional supercooling and restrained Nb segregation in the Laves during solidification. More Nb was distributed in austenite and precipitated as c0-Ni 3 Nb during the standard heat treatment to improve the mechanical properties of the clad coating.
On the basis of the existence of strong bonding between carbon nanotubes (CNTs) and polymer matrix, and considering the axial and radial thermal expansion coefficients of CNTs as nonlinear functions of temperature changes, this article presents an analytical method to investigate hygrothermal effects on the interfacial stress transfer characteristics of single-multiwalled CNTs-reinforced composites system under hygrothermal loading by means of thermoelastic theory and conventional fiber pullout models. According to the known literature, the thermal expansion coefficient of CNTs is considered as transverse isotropy, and is a nonlinear function of temperature changes. The thermal expansion coefficient of polymer matrix is isotropy, and is a linear function of temperature changes. Numerical examples show that the interfacial shear stress transfer behavior can be described and affected by several parameters such as the temperature changes in CNTs–polymer composite, the moisture concentration changes in polymer matrix, the layer numbers, volume fractions, and chiral vectors of CNTs. From the results obtained it is found that mismatch of the thermal and moisture expansion coefficients between the CNTs and polymer matrix may be more important in governing interfacial stress transfer characteristics of CNTs-reinforced composites system.
The response histories and distribution of dynamic interlaminar stresses in laminated plates with one side fixed support and others simply supported, under free vibration and thermal environment is investigated based on thermally dynamic differential equations. The layer number and stacking sequence of the laminated plates may be arbitrary. The dynamic mode of displacements takes account of the triangle series. First, the plane stresses are calculated by using geometric equations and generalized Hooke’s law. Then, the interlaminar stresses are derived by integrating the 3-D equations of dynamic equilibrium, and utilizing the given complexes boundary conditions and the continuity conditions between layers. The response histories and distribution of interlaminar stress in the laminated plates under thermal environment are presented considering various vibration modes and stacking sequence. In example calculations, some results are carried out and discussed. From the knowledge of the response histories of interlaminar stresses in the laminated plates under thermal environment, we can evaluate the interlaminar intensity of various composite laminated structures under various vibration modes, stacking sequence, and thermal environment.
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