The epoxy shape memory polymer (SMP) with adjustable phase transition temperature is a kind of high-performance shape memory polymer, which can change its phase transition temperature and improve its mechanical properties through the process of photo curing. An epoxy SMP constitutive model combining phase transition and viscoelasticity is established by discretizing the epoxy SMP into several glass phase units and rubbery phase units in this paper. The model includes the viscoelastic constitutive equations of glass phase units and rubber phase units, the parameter expression during shape memory process, and material parameter equation during photocuring process. And the stress relaxation behavior of epoxy SMP at different temperatures and the change of material parameters during the photo-curing process are simulated numerically, and the simulation results perform consistency with the experimental data. The model can not only relate shape memory effect and phase transformation in physics but also better characterize the viscoelastic properties of SMP and predict the shape memory response of SMP. Graphical abstract

It is significant to numerically investigate thermo-mechanical behaviors of shape memory alloy (SMA) structures undergoing large and uneven deformation for they are used in many engineering fields to meet special requirements. To solve the problems of convergence in the numerical simulation on thermo-mechanical behaviors of SMA structures by universal finite element software. This work suppose a finite element method to simulate the super-elasticity and shape memory effect in the SMA structure undergoing large and uneven deformation. Two scalars, named by phase-transition modulus and equivalent stiffness, are defined to make it easy to establish and implement the finite element method for a SMA structure. An incremental constitutive equation is developed to formulate the relationship of stress, strain and temperature in a SMA material based on phase-transition modulus and equivalent stiffness. A phase-transition modulus equation is derived to describe the relationship of phase-transition modulus, stress and temperature in a SMA material during the processes of martensitic phase transition and martensitic inverse phase transition. A finite element equation is established to express the incremental relationship of nodal displacement, external force and temperature change in a finite element discrete structure of SMA. The incremental constitutive equation, phase-transition modulus equation and finite element equation compose the supposed finite element method which simulate the thermo-mechanical behaviors of a SMA structure. Two SMA structures, which undergo large and uneven deformation, are numerically simulated by the supposed finite element method. Results of numerical simulation show that the supposed finite element method can effectively simulate the super-elasticity and shape memory effect of a SMA structure undergoing large and uneven deformation, and is suitable to act as an effective computational tool for the wide applications based on the SMA materials.

The discrete element method (DEM) has been widely used to investigate the mechanical properties of gas hydrate-bearing sediments (GHBS). However, a flexible membrane boundary has not been incorporated into three-dimensional DEM modelling. Moreover, the roles of hydrates in stress transmission have not been comprehensively interpreted from a particulate scale point of view. This study adopted the finite difference method (FDM)-discrete element method (DEM) coupling method to establish the flexible boundary condition to capture the failure modes of GHBS and categorized the overall contact set into three contact subsets (i.e., soil-soil, soil-hydrate and hydrate-hydrate contact subsets) in a way that the stress transmission characteristics of hydrates can be identified. The simulated macroscale mechanical responses demonstrate a favourable agreement against the experimental results. The results show that the sample with a low hydrate saturation shows a single slant shear failure zone, while the sample with a high hydrate saturation shows an X-shape shear failure zone. The particulate scale analysis shows that the soil-hydrate contact subset not only plays a critical role in stabilizing the strong force chains but also has a significant contribution to the deviatoric stress. By contrast, the hydrate-hydrate contact subset accounts for a small contribution to the deviatoric stress.

A semianalytical coupled reservoir/wellbore model based on the volumetric source for horizontal wells of sulfur gas reservoirs is presented, which considers sulfur deposition and permeability heterogeneity. Compared to the results without considering the sulfur deposition effect, the results of this paper model is better fitted to field production data and average relative errors of two simulated results are 8.37% (considering sulfur deposition) and 23.38% (not considering sulfur deposition). Based on the model, we perform sensitivity in terms of various sulfur depositions, producing pressure drop, and permeability contrast. Results show that the production decreases with increased sulfur deposition, and the flow rate along the wellbore in the horizontal well decreases because of sulfur deposition. The production without and with sulfur deposition increases with increased producing pressure drop, while the production without sulfur deposition is higher. Also, higher producing pressure drop causes a higher nonuniform inflow profile along the horizontal well. Sulfur deposition can reduce a nonuniform biased inflow profile along the horizontal well in heterogeneous sulfur gas reservoirs, but the horizontal well production is reduced. Therefore, sulfur deposition is crucial for the production prediction and inflow profile along the horizontal well in heterogeneous sulfur gas reservoirs.