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With the aim of describing and explaining the creep tensile property of shape memory polymers (SMPs) better, a variable--order fractional creep constitutive model with fewer parameters and good simulation performance was constructed on the basis of existing constitutive models. The consists of a Hookean spring connected in series with a Newtonian dashpot was employed to propose a new variable--order fractional Maxwell model for SMPs. Drawing support from the Laplace transform, we derive the analytical solution of this novel model. The verification of the obtained theoretical results with the creep test data for different fiber weight fractions and stress levels available from the literature reveals their satisfactory agreement. It can be concluded that the developed variable--order fractional constitutive model can better describe the complex viscoelastic relationship of shape memory polymers which is difficult to be described by the classical integer order derivative, and obtain a more accurate constitutive model of shape memory polymers with fewer parameters.

[Objective] National parks take ecological protection as their primary function and give consideration to the comprehensive coordination of regional economy and society. Promoting regional coordinated development is the mandate and important way of national park development. This article aims to explore the coordination relationship and driving mechanism between national park construction and regional ecology, economy, and society. [Methods] Taking Shennongjia Forest District as an example and based on the regional ecological-economic-social evaluation systems, comparative analyze Shennongjia Forest District’s ecology, economy, and society before and after the construction of Shennongjia National Park, and discuss the relationship and driving mechanism between national park construction and the forest’s development with coupled and coordinated development model. [Results] The results show that: (1) During the study period from 2014 to 2020, the ecological, economic, and social conditions of Shennongjia Forest District were significantly improved, and the evaluation index values increased from 0.132, 0.107, and 0.166 to 0.438, 0.213, and 0.240, indicating the positive impact of national park construction on forest’s development; (2) The coupling degree of the ecological, economic, and social systems in the forest district remained at a high level with an average value of 0.988, and the coordination level had been improved from initial uncoordinated to somehow coordinated (from 0.359 to 0.551), indicating that the construction of the national park had promoted the coordinated development of the ecology, economy, and society in the forest district; (3) The reform of the national park system had promoted the optimization of the spatial and structural allocation of forest land, resource utilization methods, and investment priorities, and had been constantly coupled with regional ecological, economic, and social developments in terms of ecological protection, community development, and cultural service function construction. The improvement of the service function of the national park had also promoted the coordinated development of the region. [Conclusion] This research verified the positive impact of national park construction on regional coordinated development, and provides a scientific reference for national park construction and regional coordinated development.

Based on the fracture mechanics theory of the isotropic Hoek-Brown strength criterion, this paper established the initiation conditions of the bifurcated microcrack along bedding which begins with the meso-fracture mechanism of laminated rocks. Then the author substituted the critical angle which indicates that the initial crack most likely causes the fracture of the rock into above established conditions and derived the anisotropy expression of the parameter m1 for the weak plane of bedding leading to the crack deflection. Through introducing the correction coefficient for the mixed fracture of the rock along the bedding and the matrix, this paper obtained the anisotropic modified model of Hoek-Brown strength criterion. Compared with the established anisotropic Hoek-Brown model and shale triaxial test results, the validity of the model was proved. The modified model inherits the fracture mechanics analysis of the isotropic Hoek-Brown strength criterion for the selection of rock failure characteristic quantity, and reflects the microscopic failure mechanism of the rock, also considers the effect of bedding anisotropy. The parameters in the modified criterion have a clear physical meaning. The parameter m in the model is related to the angle of the bedding plane, the tensile strength, compressive strength and friction coefficient of bedding and matrix. The change in the friction coefficient of the bedding plane will cause the position of the minimum value of m and the rock strength characteristics changed.