An accurate evaluation of fluid density and bulk modulus is essential for predicting the operation of hydraulic systems and components. Among the models reported in literature to describe fluid properties, of particular success in the fluid power field are the continuous methods that assume the gas and liquid phases to be the same fluid. However, these models are typically based on steady-state equilibrium relations and, consequently, they fail in correctly predicting the dynamic features of both air release and air absorption processes. These phenomena are particularly important for machines based on open-system hydraulic circuits, in which a significant part of the system can operate with a fluid below the saturation pressure. This paper addresses this topic by proposing a novel approach suitable to describe the dynamic features of both vaporization and air release processes. The approach is based on simplified transport equations to evaluate the phase change rate and the air release/dissolve rate. These transport equation are obtained from the well-known theoretical “full cavitation model” previously developed for computational fluid dynamics (CFD). Specific tests were performed to validate particularly as concerns the air release/absorption features using a standard ISO32 mineral oil. Comparisons between model predictions and measurement data are presented for compression/decompression cycles as concerns transient fluid density and bulk modulus, and a good agreement between the two trends is found, showing the potentials of the new approach to describe typical cavitation phenomena in hydraulic systems.
The fabrication of a single polymer
network that exhibits a good
reversible two-way shape memory effect (2W-SME), can be formed into
arbitrarily complex three-dimensional (3D) shapes, and is recyclable
remains a challenge. Herein, we design and fabricate poly(thiourethane)
(PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary
reconfigurability, and good recyclability via the synergistic effects
of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane
bonds). The PTU samples with good mechanical performance simultaneously
demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a
high strain of 474.8 ± 7.5%. In addition, the fraction of reversible
strain of the PTU with 20 wt % hard segment reaches 22.4% during the
reversible 2W-SME, where the fraction of reversible strain is enhanced
by self-nucleated crystallization of the PTU. A sample with arbitrarily
complex permanent 3D shapes can be realized via the solid-state plasticity,
and that sample also exhibits excellent reversible 2W-SME. A smart
light-responsive actuator with a double control switch is fabricated
using a reversible two-way shape memory PTU/MXene film. In addition,
the PTU networks are de-cross-linked by alcohol solvolysis, enabling
the recovery of monomers and the realization of recyclability. Therefore,
the present study involving the design and fabrication of a PTU network
for potential applications in intelligent actuators and multifunctional
shape-shifting devices provides a new strategy for the development
of thermadapt reversible two-way shape memory polymers.
Stimulus-responsive hydrogels are of great significance in soft robotics, wearable electronic devices, and sensors. Near-infrared (NIR) light is considered an ideal stimulus as it can trigger the response behavior remotely and precisely. In this work, a smart flexible stimuli-responsive hydrogel with excellent photothermal property and decent conductivity are prepared by incorporating MXene nanosheets into the physically cross-linked poly(N-isopropyl acrylamide) hydrogel matrix. Because of outstanding photothermal effect and dispersion of MXene, the composite hydrogel exhibits rapid photothermal responsiveness and excellent photothermal stability under the NIR irradiation. Furthermore, the anisotropic bilayer hydrogel actuator shows fast and controllable light-driven bending behavior, which can be used as a light-controlled soft manipulator. Meanwhile, the hydrogel sensor exhibits cycling stability and good durability in detecting various deformation and real-time human activities. Therefore, the present study involving the fabrication of MXene nanocomposite hydrogels for potential applications in remotely controlled actuator and wearable electronic device provides a new method for the development of photothermal responsive conductive hydrogels.
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