Condition monitoring in polymer composites and structures based on continuous carbon fibers show overwhelming advantages over other potentially competitive sensing technologies in long-gauge measurements due to their great electromechanical behavior and excellent reinforcement property. Although carbon fibers have been developed as strain- or stress-sensing agents in composite structures through electrical resistance measurements, the electromechanical behavior under flexural loads in terms of different loading positions still lacks adequate research, which is the most common situation in practical applications. This study establishes the relationship between the fractional change in electrical resistance of carbon fibers and the external loads at different loading positions along the fibers’ longitudinal direction. An approach for real-time monitoring of flexural loads at different loading positions was presented simultaneously based on this relationship. The effectiveness and feasibility of the approach were verified by experiments on carbon fiber-embedded three-dimensional (3D) printed thermoplastic polymer beam. The error in using the provided approach to monitor the external loads at different loading positions was less than 1.28%. The study fully taps the potential of continuous carbon fibers as long-gauge sensory agents and reinforcement in the 3D-printed polymer structures.

The applications of acoustic focusing and acoustic asymmetric focusing (AAF) are severely constrained by the narrow frequency bandwidth. In this paper, we report broad bandwidth acoustic focusing lens and asymmetric acoustic focusing lens consisting of monolayer and dual-layer metamaterials, respectively. Additive manufacturing technology was utilized to fabricate the designed lens. Finite element analysis and experimental approaches are adopted to verify the performances of acoustic focusing and asymmetric acoustic focusing. The results demonstrate that the designed acoustic focusing lens can converge acoustic waves at the frequency from 4717 Hz to 7717 Hz. The excellent AAF effect can be realized at a large frequency range from 4717 Hz to 6717 Hz. The results of measurement are consistent well with the simulated ones. Besides, by changing the separation between the dual-layer metamaterials for the AAF lens, the focusing position can be controlled without changing the metamaterials structure. Our approach may offer an efficient method to design broadband acoustic focusing and AAF devices and promote the important applications in numerous practical fields, including acoustic absorption and noise reducing, acoustic energy harvesting, ultrasonic medicine and multifunctional materials.

CNC machine tools play an important role in manufacturing and are characterized by high total energy consumption and low energy efficiency. The energy consumption characteristics of the machine tool itself determine the total energy consumption and pollutant emission during its service life. Therefore, it is particularly important to design machine tools with energy consumption as the optimization target to analyze the composition of energy consumption and related characteristics, build a corresponding model based on reliability verification, guide the structural design and optimization according to the model, and ultimately use the evaluation system to evaluate and judge the overall energy consumption. In this paper, from four perspectives—the composition of the energy consumption of machine tools, modeling methods, design and optimization methods, and evaluation methods—with energy consumption optimization as the entry point, we analyze the research on CNC machine tools based on energy consumption around the world. The research results indicate that we should look forward to the role of energy consumption in the design of machine tools.