Experimental Study on Mechanism and Shape Characteristics of Suspended Flexible Dam

Hydraulic structures such as groin, longitudinal dike and seawall are common in water conservancy and water transportation engineering projects at home and abroad, which have long been dominated by solid mass structural form. With brush and stone as building materials, this kind of structure has an obvious engineering effect. However, it not only requires huge capital investments, but also has negative impacts on the ecological environment. The suspended flexible dam is an innovative engineering measure, and few theoretical and experimental researches of this type dam can be found at present. This paper studies the mechanism and shape characteristics of this dam and obtains the dynamic equilibrium equation of flexible dam, the float buoyancy expression, and the condition for transformation among three forms of the underwater shape of the dam. The results are valuable in engineering application and can be used as the reference for the future work due to the distinctive design philosophy, the small negative effects on environment and the consistency for sustainable development.

Formation Mechanism of Curved Martensite Structures in Cu-based Shape Memory Alloys

The curved martensite structures have been observed in CuZnAI-based shape memory alloys by both transmission electron microscope and optical microscope. It was found that the curved martensite structures observed in as-solution treated, as-aged and as-trained alloys usually occurred around dislocation tangles or precipitate, at the plate boundary or grain boundary, and when the growing plates collided with each other or alternate mutually.

Linear Shaped Charge Cutting Property and Charge Cutting Mechanism of Mg-Gd-Y-Zn Alloy

The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.

Review on structural fatigue of NiTi shape memory alloys:Pure mechanical and thermo-mechanical ones

Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.

Flap side-edge noise mechanism and shape modification noise reduction design

Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Large Eddy Simulation （VLES）. Two kinds of flap side-edge shape modifications are proposed, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings （FW-H） acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the development of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can reduce the overall sound pressure level （OASPL） by 1 to 2 dB without decreasing the lift and drag aerodynamic performances.

Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology （especially the shape） and, consequently, density and compression properties of in situ Ti-TiB composite materials produced by selective laser melting （SLM） technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium （CP-Ti） and 5 wt% titanium diboride （TiB2） powders and subsequently milled for two different times （i.e. 2 h and 4 h）. The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti-TiB composite samples prepared from 2 h and 4 h milled Ti-TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those （883 MPa and 5.5%, respectively） for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density （i.e. increasing porosity level） of the Ti-TiB composite materials and their mechanical properties.

World’s first spaceflight on-orbit demonstration of a flexible solar array system based on shape memory polymer composites

With a 10%reversible compressive strain in more than 10 deformation cycles,the shape memory polymer composites(SMPCs)could be used for deployable structure and releasing mechanism.In this paper,without traditional electro-explosive devices or motors/controllers,the deployable SMPC flexible solar array system(SMPC-FSAS)is studied,developed,ground-based tested,and finally on-orbit validated.The epoxy-based SMPC is used for the rolling-out variable-stiffness beams as a structural frame as well as an actuator for the flexible blanket solar array.The releasing mechanism is primarily made of the cyanate-based SMPC,which has a high locking stiffness to withstand 50 g gravitational acceleration and a large unlocking displacement of 10 mm.The systematical mechanical and thermal qualification tests of the SMPC-FSAS flight hardware were performed,including sinusoidal sweeping vibration,shocking,acceleration,thermal equilibrium,thermal vacuum cycling,and thermal cycling test.The locking function of the SMPC releasing mechanisms was in normal when launching aboard the SJ20 Geostationary Satellite on 27 Dec.,2019.The SMPC-FSAS flight hardware successfully unlocked and deployed on 5 Jan.,2020 on geostationary orbit.The triggering signal of limit switches returned to ground at the 139 s upon heating,which indicated the successful unlocking function of SMPC releasing mechanisms.A pair of epoxy-based SMPC rolled variable-stiffness tubes,which clapped the flexible blanket solar array,slowly deployed and finally approached an approximate 100%shape recovery ratio within 60 s upon heating.The study and on-orbit successful validation of the SMPC-FSAS flight hardware could accelerate the related study and associated productions to be used for the next-generation releasing mechanisms as well as space deployable structures,such as new releasing mechanisms with low-shocking,testability and reusability,and ultra-large space deployable solar arrays.

Physical study on the vibrated packing densification of mono-sized cylindrical particles

Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and spheric- ity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains con- stant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.

Bioinspired Adaptive Gel Materials with Synergistic Heterostructures

In nature, many biological soft tissues with synergistic heterostructures, such as sea cucumbers, skeletal muscles and cartilages, exhibit high functionality to adapt to complex environments. In artificial soft materials, hydrogels are similar to biological soft tissues due to the unique integration of ＂soft and wet＂ properties and elastic characteristics. However, currently hydrogel materials lack their necessary adaptability, including narrow working temperature windows and uncontrollable mechanics, thus restrict their engineering application in complex environments. Inspired by abovementionedbiological soft tissues, researchers have increasingly developed heterostructural gel materials as functional soft materials with high adaptability to various mechanical and environmental conditions. This article summarizes our recent work on high-performance adaptive gel materials with synergistic heterostructures, including the critical design criteria and the state-of-the-art fabrication strategies of our gel materials. The functional adaptation properties of these heterostructural gel materials are also presented in details, including temperature, wettability, mechanical and shape adaption.

Generalized Coherent States for Position-Dependent Effective Mass Systems

A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of the system which are obtained using the concepts of supersymmetric quantum mechanics and the property of shape invariance. In order to exemplify the general results and to analyze the properties of the coherent states, several examples have been considered.