Current Issue

2024, Volume 4,  Issue 2

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Abstract:

Electrification of Non-road mobile machinery (NRMM) is more and more urgent due to the demand of pollution reduction and energy conservation. In electrified NRMMs, electrohydraulic control system is still irreplaceable in many working conditions owing to its high power density and shock resistance performance. Meanwhile, electrohydraulic control systems are facing many opportunities to improve its energy efficiency by novel component and circuit design if the internal combustion engines (ICEs) and fossil fuel are replaced by electric motors (EMs) and energy storage devices. However, there are also a lot of challenges about controllability, compactness, lifetime and so on, due to the frequent variable load characteristic and wide speed regulation range of NRMMs. In this study, the technical opportunities and challenges of electrohydraulic control systems are reviewed and summarized in the electrification era of NRMM. Finally, the future directions are considered to improve the energy efficiency and electrification level of NRMMs.

Abstract:

Laser micromachining technology is widely used in various industrial fields because of its high machining accuracy, high machining flexibility, and low machining cost. However, the existence of thermal effects and recast layers on the machining surface has limited the further development of this technology. To improve the machining quality, laser-liquid composite micromachining technologies flourish, which has achieved brilliant results in recent years. Laser-liquid composite micromachining technology achieves improvement in surface quality and machining efficiency through the effects of cooling, flushing, dissolution and so on. This paper reviews the current research status of laser-liquid micromachining, mainly including the water guided laser machining technology, underwater laser ablation technology, water jet assisted laser machining technology, and laser-electrochemical composite machining. The mechanism of composite machining and the material removal process under the coupling of multiple energy fields are discussed. The existing problems and future development trends in various composite machining technologies are summarized.

Abstract:

The cyclic indentation effect is widespread in vibration-assisted grinding processes. The understanding of the material removal mechanism during cyclic indentation is scientifically important for the improvement of the quality of vibratory grinding. Therefore, in this paper, the cyclic indentation damage and crack extension mechanisms of quartz glass are investigated by experiments and finite element simulations. The evolution of surface cracks under cyclic loading from 0.203 N to 1.81 N is observed by scanning electron microscopy. The distribution of the maximum principal stress during cyclic indentation is simulated on the basis of a modified Drucker-Prager-Cap material ontology model. A combination of experiments and simulations reveals the crack evolution mechanism during cyclic indentation.

Abstract:

Most modern hydrophobic bionic surface preparations are generally plagued by chronic issues that limit their uses, which are always characterized by a difficult preparation procedure of high prices and environmentally unfriendly. This work reports the μ-SLA additive manufacturing microarray structure capable of achieving superhydrophobic wettability with the maximum contact angle of 157º for droplets. By means of the combination of wettability theory and experiment, conical microarray structures with different spacing are designed to analyze the wettability. The preparation method adopts the micro-nano additive manufacturing process that can be formed in a single step. This structure imitates the rough structure of biological surfaces through regular array structure, which can lead to a significant improvement in the superhydrophobic properties of solid surfaces.

Abstract:

Flexible and wearable sensors play a pivotal role in shaping advances in smart medical devices. However, the practicality and economy of current wearable flexible sensing devices have seriously hindered their wide application. Here, relying on the electrospinning method, material modification and triboelectric nanogenerator technology, we present a novel highly sensitive flexible triboelectric nanogenerator (TENG) sensor with the characteristics of flexible and sensitive. Through meticulous exploration of the exceptional triboelectric properties of polyvinylidene fluoride nanofiber and a rigorous investigation into the corresponding preparation processes, we have achieved remarkable results. The TENG created using positively polarized polyvinylidene fluoride nanofiber outperforms TENG created with electrospun polyvinylidene fluoride nanofibers, delivering output performance several times higher. Additionally, our fabricated highly sensitive flexible TENG sensor demonstrates exceptional sensitivity, achieving a response time of just 4 ms under controlled laboratory conditions—a notable improvement over previous iterations. Importantly, leveraging the excellent electrical output characteristics of TENG, we can generate a self-powered morse code producer system and the human motion sensor, which is demonstrates its wide application in the field of smart medical devices. Therefore, our research offers a groundbreaking avenue for developing high-output TENG and presents a pivotal solution for the design of innovative TENG applications.

Abstract:

In the present study, heat conductivity of an aircraft-grade BA9916 resin with high-toughness was characterized under the curing condition, so as to support curing modeling for this resin and its carbon fiber composites and avoid timeand labor-consuming experiments for manufacturing process design. Thermal-related properties, including density, curing kinetics, glass transition temperature, specific capacity and thermal diffusivity were measured to obtain thermal conductivity of the material. However, the BA9916 resin was toughened via addition of thermoplastic particles, resulting in much higher viscosity before completely cured than that of common epoxy resins. As a result, it was challenging to directly measure certain thermal properties of the neat resin. To settle this problem, the BA3202 unidirectional carbon fiber composite prepreg with the BA9916 resin was employed as a media to obtain corresponding properties of the resin through experiments and analytical calculation. Derived material properties of the resin were then input to the user-defined material subroutine UMAT to predict thermal response of the composite under various curing conditions, with the maximum error of 6.82% validated via experiments. Hence, the acquired characteristics can be utilized for numerical analysis of various composites composed of BA9916 resin, obviating the need for repeated physical experiments that are time- and resource-consuming.