An experimental study on the impact behavior of cavitation inside tip clearance of a hydrofoil

Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.

Acute histopathological responses and long-term behavioral outcomes in mice with graded controlled cortical impact injury

While animal models of controlled cortical impact often display short-term motor dysfunction after injury, histological examinations do not show severe cortical damage. Thus, this model requires further improvement. Mice were subjected to injury at three severities using a Pin-Point^(TM)-controlled cortical impact device to establish secondary brain injury mouse models. Twenty-four hours after injury, hematoxylin-eosin staining, Fluoro-Jade B histofluorescence, and immunohistochemistry were performed for brain slices. Compared to the uninjured side, we observed differences of histopathological findings, neuronal degeneration, and glial cell number in the CA2 and CA3 regions of the hippocampus on the injured side. The Morris water maze task and beam-walking test verified long-term(14–28 days) spatial learning/memory and motor balance. To conclude, the histopathological responses were positively correlated with the degree of damage,as were the long-term behavioral manifestations after controlled cortical impact. All animal procedures were approved by the Institutional Animal Care and Use Committee at Shanghai Jiao Tong University School of Medicine.

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

Wear behavior of bainite ductile cast iron under impact load

The dry impact wear behavior of bainite ductile cast iron was evaluated under three different impact loads for 30000 cycles. The strain-hardening effects beneath the contact surfaces were analyzed according to the surfaces＇ micro-hardness profiles. Scanning electron microscopy （SEM） and X-ray diffraction （XRD） were used to observe the wom surfaces. The results indicated that the material with the highest hardness was the one continuously cooled at 20℃, which exhibited the lowest wear rate under each set of test conditions. The hardness of the worn surface and the thickness of the hardened layer increased with the increases in impact load and in the number of test cycles. The better wear performance of the sample cooled at 20℃ is attributed to its finer microstructure and superior mechanical properties. All the samples underwent the transformation induced plasticity （TRIP） phenomenon after impact wear, as revealed by the fact that small amounts of retained austenite were detected by XRD.

Firm embedding behavior of annular grooved projectiles impacting ductile metal targets

Annular grooved projectiles(AGPs)have drawn ongoing concerns as an advanced penetrator for their excellent anti-rebound capability in impacting metal plates.They could become embedded solidly in the target surface during low-velocity impact.In this investigation,the firm embedding behavior of AGP was observed by impact experiments.Corresponding numerical simulations provided a better understanding of this process.Experimental and numerical results indicated that the firm embedding behavior of AGP was mainly due to the filling-material in the groove rather than the friction between the projectile and target,unlike traditional shape such as conical projectile.According to observation,firm embedding process can generally be subdivided into four stages:initial-cratering stage,groove-filling stage,fillingmaterial failure stage and rebound vibration stage.Moreover,the damage mechanics of target material around crater was obtained through microscopic tests.A comparison of the cross-sectional figures between the experiment and simulation proved that the analysis and the proposed method were reasonable and feasible,which further demonstrated that the firm embedding behavior has application potential in new concept warheads.

The Impact Compression Behaviors of Silica Nanoparticles—Epoxy Composites

The compressive properties of epoxy with different silica nanoparticles (SiO2 nanoparticles) contents at quasi-static and high strain rates loading were investigated via experiment. This article evaluates the compressive failure behaviors and modes at different SiO2 nanoparticles contents and different strain rates. The results indicated that the stress strain curves were sensitive to strain rate, and the compressive failure stress of composites with various SiO2 nanoparticles contents increased with the strain rates, and it increased along with SiO2 nanoparticles contents and then declined. The compressive failure stress and the compressive failure modes of the composites were apparently different from the change of SiO2 nanoparticles contents.

Effect of maleic anhydride grafted styrene-ethylene-butylene-styrene （MA-SEBS） on impact fracture behavior of polypropylene / wood fiber composites

MA-SEBS 作为 compatibilizer；影响修饰词被合并到聚丙烯 / 木头纤维(PP/WF ) 提高接口粘附；影响力量合成。PP/WF composites 的影响破裂行为上的 MA-SEBS 内容的效果被学习。有 8% MA-SEBS 的 composites 的影响性质到达了最大的价值。并且到 10% 的 MA-SEBS 内容的进一步的增加没改进破裂坚韧，但是由直接存储器存取分析改进 composites 的僵硬。这被归因于改进 PP/WF 粘附。因为 MA-SEBS 内容是超过 8% ， PP 的分子相互作用；WF 被期望到比更低的 MA-SEBS 强壮的大部分。扫描电子显微镜学(SEM ) 被执行分析影响破裂表面；为木头表面显示出一种更强壮的亲密关系。

Influence of Pseudoelasticity on Mechanical Behavior of TiNi Alloy under Dynamic Impact Loading

The mechanical behavior of TiNi alloy and Cr12MoV alloy under dynamic impact loading was investigated with a self-made impact testing system. The real-time contact force was measured with a piezoelectric force sensor and digital signal processing system during impact. Equations for predicting instantaneous velocity anti displacement were presented. The results showed that the TiNi alloy exhibited a plateau of maximum contact force with increasing impact height. At the plateau stage, TiNi alloy in the parent phase can absorb impact energy and keep the maximum contact force nearly identical due to its pseudoelasticity.

Fracture Behavior of CrN Coatings Under Indentation and Dynamic Cycle Impact

Fracture behavior of CrN coatings deposited on the surface of silicon and AISI52100 steel by different energy ion beam assisted magnetron sputtering technique （IBAMS） was studied using indentation and dynamic cycle impact. It is found that, for the coatings on silicon substrate, the cracks form in the indentation corners and then propagate outward under Vickers indentation. The coating prepared using ion assisted energy of 800 eV shows the highest fracture resistance due to its compact structure. Under Rockwell indentation, only finer radial cracks are found in the CrN coating on AISI 52100 steel without ion assisting while in the condition of ion assisting energy of 800 eV, radial, lateral cracks and spalling appear in the vicinity of indentation. The fracture of CrN coatings under dynamic cycle impact is similar to fatigue. The impact fracture resistance of CrN coatings increases with the increase of ion assisting energy.

A STUDY ON THE COUNTER-INTUITIVE BEHAVIORS OF PIN-ENDED BEAMS UNDER PROJECTILE IMPACT

The counter-intuitive behaviors of pin-ended beams under the projectile impact axe investigated with ANSYS/LS-DYNA in this paper. It studies in detail their displacement-time history curves, final deformed shapes, energy relationships and projectile impact velocity ranges related to their counter-intuitive behaviors. The influences of the impact positions on their counterintuitive behaviors are also discussed. The results show that no matter where the impact position on the beam is, the counter-intuitive behaviors of pinned beams will occur as long as the impacting velocity lies within a proper range. Corresponding to the occurring of the counter-intuitive behaviors, the rebounding number in the displacement history curves of the beams decreases from a few times to zero with an increase of the impact velocity. The final deformation modes of the beam corresponding to the counter-intuitive behaviors will appear in symmetrical and unsymmetrical forms no matter where the impact position is; the impact velocity of the first-occurring of the counter-intuitive behaviors of the beam increases slowly with the deviation of the impact position away from the mid-span.

信息化教学技术对高职生学习行为的影响研究——以云班课为例

文章以云班课为例,探索信息化教学环境如何影响学生的课程学习行为,进而为提升课程教学效果起技术支撑作用。文章构建了结构模型;研究验证了信息化技术支持的教学环境对学生课程学习表现的显著影响;感知云班课APP的易用性和感知云班课学习内容的有用性是高职学生对信息化教学环境感知的关键要素;感知云班课系统的易用性对感知云班课课程学习内容的有用性有显著影响;利用云班课学习课程的态度倾向和学习知觉控制在云班课教学环境影响课程学习表现的路径中起到重要的中介作用。结合研究,文章提出了有关信息化教学工具的开发与选择、线上教学内容的设计、学习态度和知觉行为控制引导的建议。

基于IMPACT模式的护理管理结合低升糖指数膳食管理对2型糖尿病患者饮食行为及自护能力的影响

目的分析基于IMPACT模式的护理管理结合低升糖指数膳食管理对2型糖尿病(T2DM)患者饮食行为及自护能力的影响。方法选取2021年1月至12月收治的100例T2DM患者为研究对象,按照随机数字表法将其分为对照组与观察组,各50例。对照组采用常规护理干预,观察组在对照组基础上加基于IMPACT模式的护理管理结合低升糖指数膳食管理。比较两组的饮食行为、自护能力以及血糖控制水平。结果干预后,观察组的饮食行为量表各维度评分高于对照组,差异具有统计学意义(P<0.05)。干预后,观察组的自我护理能力测定量表(ESCA)各维度评分高于对照组,差异具有统计学意义(P<0.05)。干预后,观察组的空腹血糖(FBG)、餐后2 h血糖(2 h PBG)水平低于对照组,差异具有统计学意义(P<0.05)。结论基于IMPACT模式的护理管理结合低升糖指数膳食管理不仅能够改变患者饮食行为,还能加强其自护能力,以此提高血糖控制水平,值得推广。

论过程性行政行为不可诉规则之突破——以出口退税疑而缓退为切入点

税务机关在办理出口退税业务中如果发现纳税人有骗税嫌疑,则将开展疑点调查、暂缓出口退税。在实务中,税务疑点调查并无时限要求,导致税务机关可以无限期调查,形成事实上的疑而不退,而法院也大多以该疑而缓退行为属于过程性行政行为而认定其不具有可诉性,造成纳税人无以救济的诉权困局。为了实质性化解疑而缓退的可诉性争议,宜针对“过程性行为”与“不产生实际影响的行政行为”的狭隘理解,将疑而缓退界定为“复合型过程性行为”,并对“实际影响”作出“权益增减变动型”与“权益限制型”的二元划分,并通过建构法定的暂缓退税时限制度,对税务机关施加法定时限这一程序限制,用以保障“权益限制型的复合型过程性行为”下纳税人在事实上的出口退税利益。

液滴在柔性辣椒叶片表面撞击行为研究

液滴撞击叶片时会使叶片发生弯曲变形,这种变形会对液滴的撞击行为产生影响。基于前人液滴撞击刚性表面的理论模型,探究了液滴撞击柔性辣椒叶片时叶片弹性系数对液滴撞击行为的影响,考虑叶片弹性势能、液滴和叶片重力势能,建立了液滴撞击柔性辣椒叶片最大扩散因子数学预测模型。以液滴粒径、撞击速度、撞击点到叶尖距离占比为试验因素,对数学模型进行了合理性验证。结果表明:3个因素对液滴粘附和飞溅均有显著性影响(P<0.05)。数学模型对液滴撞击柔性辣椒叶片最大扩散因子预测误差在10%以内,但此误差会随着叶片弹性系数的增加而减小。液滴撞击柔性辣椒叶片没有发生反弹,和理论模型预测结果一致。液滴粘附时,叶片弹性系数与液滴达到最大扩散的时间呈负相关,与撞击刚性固定叶片相比,达到最大扩散的时间增加量在0.5 ms以内,最大扩散因子减小率在25%以内,传递给叶片弹性势能占初始总能量的比随着叶片弹性系数的增加呈现先减小后增大趋势。液滴飞溅时,在到叶尖距离占比的20%、40%、60%、80%处,与刚性叶片相比,飞溅临界值Kcrit分别增加16.202%、10.515%、6.508%、4.467%,说明叶片越靠近弹性系数小的区域,液滴越不容易飞溅。本文为液滴在柔性植物叶片上的撞击行为研究和喷雾参数选择提供了一种方法。

Experimental investigation on enhanced damage to fuel tanks by reactive projectiles impact

Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel tank is a rectangular structure,welded by six pieces of 2024 aluminum plate with a thickness of 6 mm,and filled with RP-3 aviation kerosene.Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s,and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed.However,the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene.Based on the experimental results,the radial pressure field is considered to be the main reason for the shear failure of weld.For mechanism considerations,the chemical energy released by the RMP enhances the hydrodynamic ram(HRAM)effect and provides additional ignition sources inside the fuel tank,thereby enhancing both rupture and ignition effects.Moreover,to further understand the enhanced ignition effect of RMP,the reactive debris temperature inside the kerosene is analyzed theoretically.The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene,resulting in the enhanced ignition of the kerosene.

双酚G对斑马鱼神经行为的影响及机制研究

使用双酚G(BPG)慢性染毒成年斑马鱼,以评估其毒性效应和作用机制.结果表明,50μg/L BPG染毒组显著降低了斑马鱼的移动距离和上下水层切换频率,在底部累积时间增加了22.7%,表现出显著的行为异常;5和50μg/L染毒导致社交距离分别增加了126.8%和151.2%,社交累积时间分别减少了80.1%和73.7%,表现出显著的社交障碍.切片染色显示脑结构和肠道绒毛受损以及肠道杯状细胞数量和粘液分泌增加,表明潜在的肠道炎症以及神经疾病的发生.进一步的靶向代谢组学显示肠脑神经递质水平紊乱,色氨酸、GABA、谷氨酰胺、去甲肾上腺素、胆碱和组胺等水平显著改变;KEGG通路富集分析表明,苯丙氨酸、酪氨酸和色氨酸生物合成,缬氨酸、亮氨酸和异亮氨酸生物合成,精氨酸生物合成及苯丙氨酸代谢是主要受影响通路且存在性别差异,这些通路通过干扰神经递质转运和稳态,调控斑马鱼行为.BPG染毒,斑马鱼表现出显著的神经行为毒性效应和肠脑神经递质代谢紊乱,肠脑调节可能参与介导该效应.