In the past few years four-dimensional (4D) printing technologies have attained worldwide interest and they are now considered the "next big thing". The aim of this research is to provide three selected examples of stimuli-responsive polymer (SRP) applications additively manufactured (AM) by the fused filament fabrication (FFF) technique. To that end, a CCT BLUE filament of thermo-responsive polymer was chosen to produce a water temperature indicator, which changes colour from blue to white when temperature increases; a CCU RED filament of photo-responsive polymer was used to produce a sunlight / UV indicator bracelet; a transparent PLA CLEAR polymer, a CCU RED photo-responsive polymer, and an electrical conductive PLA polymer were selected to produce a smart business card stand. The temperature indicator capability was analysed based on examining colour changes as a function of temperature changes. The sunlight/UV indicator capability was analysed based on the inspection of colour change as a function of absorbed sun/ultraviolet light. The electrical conductivity of the conductive PLA polymer was examined by performing resistance measurements. All three objects were successfully produced and their functionality was demonstrated. We hope that these examples will catalyse the expansion of FFF 4D printed SRP applications, as much work remains to be done in designing the parts and developing FFF printing parameters that take advantage of the stimuli-responsive materials currently being developed for FFF technology.

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The effectiveness of the coordination process of the “engine-transmission” system is largely determined by the functional purpose of the car being designed. The solution to this problem is possible by choosing the optimal transmission parameters. Using a continuously variable transmission will make this process manageable. However, optimization is always performed according to a certain criterion. You can use its dynamic performance and fuel economy as an optimization criterion. The article presents a mathematical model for determining the current gear ratios of a continuously variable transmission of a vehicle depending on its mode of movement. The dependence of the transmission ratio of the vehicle on speed allowed us to find the mode of movement of the car with the minimum acceleration time. The dependence of the transmission ratio of the vehicle on the engine speed allowed us to find the driving mode with minimal fuel consumption. The recommendations received by the authors on the choice of transmission ratios can be used in the design of the control system. Automation of control will allow optimizing the pattern of change in the gear ratio of a continuously variable transmission depending on the mode of movement of the vehicle.

The 4D additive manufacturing processes are considered today as the "next big thing" in R&D. The aim of this research is to provide two examples of commercial PLA based shape memory polymer (SMP) objects printed on an open-source 3D printer in order to proof the feasibility of such novel 4D printing process. To that purpose, a PLA based filament of eSUN (4D filament e4D-1white, SMP) was chosen, and two applications, a spring and a vase, were designed by 3D-printing with additive manufacturing (AM) fused filament fabrication (FFF) technique. The 4D-printed objects were successfully produced, the shape memory effect and their functionality were demonstrated by achieving the shape-memory cycle of programming, storage and recovery.

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