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[Display omitted] • This study proposes novel auxetic medical stents. • Two-dimensional metamaterials were fabricated through additive manufacturing technique. • Finite element analysis was employed to investigate the mechanical behaviour. • An excellent correlation was observed between the FEA and experimental results. • The modifications made to the rib-unit cells had a significant effect on the stent's recoil behaviour. Due to the significant mortality rate associated with atherosclerosis-induced cardiovascular disease, the utilization of advanced intravascular stents with superior mechanical performance is imperative for the restoration of obstructed arteries. This study proposes novel auxetic medical stents that aim to enhance critical parameters of biomedical stents. This includes load-bearing capacity, expanded opening percentage, and reduced recoil percentage. On this matter, the missing rib auxetic unit cell has been considered and geometrically modified to achieve these objectives. Two-dimensional (2D) metamaterials were fabricated through additive manufacturing technique and subjected to experimental testing. Then, finite element analysis (FEA) was employed to gain comprehensive insights into the mechanical behaviour of the proposed medical stents. Remarkably, an excellent correlation was observed between the FEA and experimental results, validating the high precision of the analysis. The findings reveal that the stents classified as "E-category" exhibit the highest final opening percentage while concurrently demonstrating the lowest recoil percentage. The base stent exhibited a relatively high recoil percentage of 15.56%, indicating a significant amount of recoil or spring-back after deformation. In contrast, the modified "E-category" stent displayed a substantially lower recoil percentage of 1.62%. This notable reduction in recoil percentage indicates that the modifications made to the rib-unit cells had a significant and beneficial effect on the stent's recoil behaviour and minimizing potential damage to arterial tissue during stent deployment (angioplasty) and balloon pressure. The modified design likely enhances the stent's ability to maintain its shape and resist recoil, making it more effective and reliable in its intended application. Additionally, more aspects of biomedical stents such as foreshortening, and dog-boning of the modified missing rib stents were meticulously examined through FEA. [ABSTRACT FROM AUTHOR]

Assessing, predicting, and controlling injection-induced seismicity is a major challenge for developing enhanced geothermal systems (EGS) due to the complexity of coupled thermo-hydro-mechanical (THM) processes. This study aimed to develop a fully coupled numerical model to assess the complex behavior of a low permeable matrix-fracture during non-isothermal single-phase fluid injection process. A thermo-poroelastic displacement discontinuity (DD) method combining with different forms of finite element method are implemented to encapsulate the fractured medium response and transport processes, respectively. The nonlinear characteristics of normal (changing the joint to hydraulic fracture status) and shear (changing the stick to slip fracture status) fracture deformation are taken into account through fracture constitutive relations. Developed numerical approach was applied to simulate cool water injection into fracture/matrix systems, analyzing the role of coupled processes on spatiotemporal variation of matrix-fracture stresses, temperature and pore pressure and assessing induced seismicity (slippage) and permeability alteration. Numerical simulations demonstrate a fully coupled relation between matrix dilation, shrinkage, and non-linear fracture deformation. The redistribution of dynamic and kinematic parameters along with non-linear fracture deformation showed that although the poroelastic effects are dominant in the early stages, thermoelastic effects dominate in the long-term injection stages. • A fully-coupled Thermo-Hydro-Mechanical approach was developed to model injection process in EGS. • Displacement discontinuity and finite element methods were combined to encapsulate fracture deformation and transport processes, respectively. • Fracture constitutive laws were implemented to model non-linear crack deformation. • Poroelastic effects are dominant in the early stages, and thermoelastic effects dominate in the long-term injection stages. [ABSTRACT FROM AUTHOR]

• A fully-coupled Thermo-Hydro-Mechanical approach was developed to study injection-induced seismicity and permeability enhancement in low permeable reservoirs. • Fracture deformation and transport processes were modeled using thermo-poroelastic displacement discontinuity method combined with Galerkin and Petrov Galerkin finite element methods. • Constitutive behavior of fault friction was captured using rate-and-state friction model incorporating aging law for history of sliding. • Traffic Light System-based injection protocols yield higher potential in enhancing the fault permeability. • Volume-Controlled fluid injection are far more effective in reducing the seismic risk. In recent years, there has been a substantial increase in the induced seismicity associated with geothermal systems. However, understanding and modeling of injection-induced seismicity have still remained as a challenge. This paper presents a two-dimensional fully thermo-hydro-mechanical (THM) coupled boundary element approach to characterize the fault response to forced fluid injection and assess the effect of different injection protocols on seismic risk mitigation as well as permeability enhancement. The laboratory-derived rate-and-state friction law was used to capture the frictional paradigm observed in mature faults produced in granite rocks. All phases of stick-slip cycles, including aseismic slip, propagation of dynamic rupture, and interseismic periods, were simulated. The modeling results showed that the residual values of effective normal stress and static shear stress after a particular event completely dominate the constitutive behavior of fault friction during the next seismic event. The seismic energy analyses indicated that there is a negative correlation between the seismic magnitude and the total injected volume, such that a prolonged monotonic injection eventually results in the steady slip, rather than the seismic slip. Several fluid injection protocols were designed based on a volume-controlled (VC) approach and traffic light systems (TLS) to explore their effectiveness on the seismic risk mitigation and permeability enhancement. The results showed that cyclic injection based on TLS is the most effective approach for irreversible permeability enhancement of faults through promoting slow and steady slips. Our numerical simulations also revealed that fluid extraction (backflow-fixing bottom hole pressure at atmospheric pressure), regardless of the injection style, can considerably reduce the seismicity-related risks by preventing the fast-accelerated fracture slip during the post-injection stage. This study presents novel insights into modeling the rate-and-state governed faults exposed to forced fluid injection, and provides useful approaches for shear stimulation of faults with reduced seismic risks. [ABSTRACT FROM AUTHOR]