Failure Characteristics of Rock-like Mortar Specimens with Arc-shaped Flaws under Freezing-thaw Cycles and Uniaxial Compression

To investigate the freeze-thaw(F-T)damages and failure characteristics of rock mass with arc-shaped joints in cold regions,three types of cement mortar specimens with different central angles and prefabricated arc-shaped flaws are subjected to uniaxial compressive tests under different F-T cycles.Experimental observations show that the uniaxial compressive strength of specimens are significantly influenced by F-T cycles and their failure modes are mainly affected by the central angleαof the prefabricated flaws.Unlike the specimens with a central angle of 60°,the specimens with a central angle of 120°and 180°have greater curvature of flaws,so tensile cracks occur in the arc-top area of their prefabricated flaws.According to experimental images observed by environmental scanning electron microscope(ESEM),as the number of F-T cycles increases,the deterioration effect of the specimen becomes more obvious,which is specifically reflected in the increase of the mass loss,peak stress loss,and damage variables as a power function,and the peak strain decreases as a quadratic polynomial.According to numerical results using two-dimensional particle flow code(PFC2D),it is found that F-T cycles cause more damage to the specimen in the early stages than in the later ones.The area of the concentrated compressive stress zone in the middle is decreased due to the increased number of F-T cycles,while the area of the surrounding tensile-shear stress zone is increased.The models appear different failure modes due to the release of concentrated stress in different tensile-shear zones.

The Origins of the Arc-Shaped Langshan Uplift and Linhe Trench

In the northern part of the Ordos Basin, there is a 325 km long arc-shaped Langshan uplift and a 15 km-deep Linhe Trench in front of Langshan, which are rare geological phenomena for which origins no one has explained. This article comprehensively analyzes the research achievements over the past 40 years of geology, geomorphology, seismic exploration, paleogeography, and oil and gas exploration in the Ordos Basin and Langshan. It recognizes that the northern part of the Ordos Basin experienced a meteorite impact in the Late Cretaceous period. The impact pushed the block northwest ward, subducting after colliding with igneous rocks in the north. This sudden event formed a clear arc-shaped mountain zone in the north and a wedge-shaped trench in front of the mountain. The chaotic layers, prolonged and continuous faults, and numerous thrust layers in the Langshan, a negative anomaly area in the center of the northern Ordos, abnormal orientation of crystalline basement structures in the north of Ordos, Moho uplift, and distribution of meteorite fragments in the northwest of Langshan, all of these geological phenomena support the occurrence of the meteorite impact event, forming the arc-shaped Langshan and the Trench.

Wave Diffraction on Arc-Shaped Floating Perforated Breakwaters

An analytical method is developed to study the sheltering effects on arc-shaped floating perforated breakwaters. In the process of analysis, the tloating breakwater is assumed to be rigid, thin, vertical, and immovable and located in water with constant depth. The fluid domain is divided into two regions by imaginary interface. The velocity potential in each region is expanded by eigenfunction in the context of linear theory. By satisfying continuity of pressure and normal velocity across the imaginary fluid interface, a set of linear algebraic equations can be obtained to determine the unknown coefficients for eigenfunction expansions. The accuracy of the present model was verified by a comparison with existing results for the case of arc-shaped floating breakwater. Numerical results, in the form of contour maps of the non-dimensional wave amplitude around the breakwater and diffracted wave amplitude at typical sections, are presented for a range of wave and breakwater parameters. Results show that the sheltering effects on the arc-shaped floating perforated breakwater are closely related to the incident wavelength, the draft and the porosity of the breakwater.

Numerical simulations of rip currents off arc-shaped coastlines

The rip currents induced by waves off arc-shaped coastlines are seriously harmful to humans, but understanding of their characteristics is lacking. In this study, the FUNWAVE model was used to calculate the wave-induced currents in the Haller experiment and the ideal arc-shaped coast similar to Sanya Dadonghai, Hainan Province,China. The results showed that the FUNWAVE model has considerable ability to simulate the rip currents, and it was used to further simulate rip currents off arc-shaped coastlines to investigate their characteristics. The rip currents were found to be stronger as the curvature of arc-shaped coastline increased. Coastal beach slope exerts a significant influence on rip currents; in particular, an overly steep or overly mild slope is not conducive to creating rip currents. Furthermore, the rip currents were found to become weaker as the size of arc-shaped coast decreased. When the height and period of waves increase, the strength of rip currents also increases, and, in some cases, wave heights of 0.4 m may produce dangerous rip currents.

Plastic Mechanism of Multi-pass Double-roller Clamping Spinning for Arc-shaped Surface Flange

Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency and the shape precision of final spun part. Based on ABAQUS/Explicit nonlinear finite element software, the finite element model of the multi-pass DRCS for the sheet metal is established, and the material model, the contact definition, the mesh generation, the loading trajectory and other key technical problems are solved. The simulations on the multi-pass DRCS of the ordinary Q235A steel cylindrical part with the arc-shaped surface flange are carried out. The effects of number of spinning passes on the production efficiency, the spinning moment, the shape error of the workpiece, and the wall thickness distribution of the final part are obtained. It is indicated definitely that with the increase of the number of spinning passes the geometrical precision of the spun part increases while the production efficiency reduces. Moreover, the variations of the spinning forces and the distributions of the stresses, strains, wall thickness during the multi-pass DRCS process are revealed. It is indicated that during the DRCS process the radical force is the largest, and the whole deformation area shows the tangential tensile strain and the radial compressive strain, while the thickness strain changes along the generatrix directions from the compressive strain on the outer edge of the flange to the tensile strain on the inner edge of the flange. Based on the G-CNC6135 NC lathe, the three-axis linkage computer-controlled experimental device for DRCS which is driven by the AC servo motor is developed. And then using the experimental device, the Q235A cylindrical parts with the arc-shape surface flange are formed by the DRCS. The simulation results of spun parts have good consistency with the experimental results, which verifies the feasibility of DRCS process and the reliability of the finite element model for DRCS.

Study on Submerged Upper Arc-Shaped Plate Type Breakwater

Based on the wave radiation and diffraction theory, this paper investigates a new type breakwater with upper arcshaped plate by using the boundary element method(BEM). By comparing with other three designs of plate type breakwater(lower arc-shaped plate, single horizontal plate and double horizontal plate), this new type breakwater has been proved more effective. The wave exiting force, transmission and reflection coefficients are analyzed and discussed. In order to reveal the wave elimination mechanism of this type of breakwater, the velocity field around the breakwater is obtained. It is shown that:(1) The sway exciting force is minimal.(2) When the ratio of the submergence and wave amplitude is 0.05, the wave elimination effect will increase by 50% compared with other three types of breakwater.(3) The obvious backflow is found above the plate in the velocity field analysis.

Coastline configuration and geomorphologic development mode of arc-shaped coast in South China

Coastline configuration indexes of 34 typical arc-shaped coasts in South China are investigated by the method of principal component analysis, and meanwhile deposition and geomorphologic features of arc-shaped coast are also analyzed. The results show: (1) The configuration of arc-shaped coast in South China is of the characteristic of variability and complexity. (2) The wave power and the openings of the bay are the decisive factors to result in the changes of the configuration of the arc-shaped coast in South China, however, incidence direction of the wave has no effect on configuration development of the coast. (3) Commonly, geomorphologic modes of the arc-shaped coast system in South China consist of barriers, lagoons and tidal-inlets, and can be divided into four types:the openings of the bay leaning to the east, the openings of the bay leaning to the south, the openings of the bay leaning to the west and the openings of the bay leaning to the north.

Numerical simulations of stress wave propagation and attenuation at arc-shaped interface inlayered SiC/Al composite

The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.

Hydrodynamic Performance of the Arc-Shaped Bottom-Mounted Breakwater

The problem of the hydrodynamic interaction with the arc-shaped bottom-mounted breakwaters is investigated theoretically. The breakwater is assumed to be rigid, thin, impermeable and vertically located in a finite water depth. The fluid domain is divided into two sub-regions of inner and outer by an auxiliary circular interface. Linear theory is assumed and the eigenfunction expansion approach is used to determine the wave field. In order to examine the validity of the theoretical model, the analytical solutions are compared to agree well with published results with the same parameters. Numerical results including wave amplitude, surge pressure, and wave force are presented with different model parameters. The major factors including wave parameters, structure configuration, and water depth that affect the surge pressure, wave forces, and wave amplitudes are discussed and illustrated by some graphs and cloud maps.

A DECAGONAL QUASICRYSTAL WITH AN ARC-SHAPED CRACK

A decagonal quasicrystal, which is weakened by an arc-shaped crackpenetrating through the solid in the period direction, and which is subjected to remote uniformphonon stresses, is investigated by applying the complex variable method which is just developed bythe authors. It is found that the phonon and phason stresses near the crack tips exhibit inversesquare root singularities. The four complex stress functions characterizing the phonon and phasonfields are derived. Explicit expressions for the phonon and phason stress intensity factors, crackopening displacements and energy release rate are also presented.

Determination of Wind Pressure Coefficients for Arc-Shaped Canopy Roof with Numerical Wind Tunnel Method

In this paper,the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method(NWTM) .Three-dimensional models were set up for the canopy roof with opened or closed skylights.The air flow around the roof under wind action from three directions was analysed respectively.Wind pressure coefficients on the canopy roof were determined by NWTM.The results of NWTM agreed well with those of wind tunnel test for the roof with opened skylights,which verified the applicability and rationality of NWTM.The effect of the closure of skylights was then investigated with NWTM.It was concluded that the closure of the skylights may increase the wind suction on the top surface of the roof greatly and should be considered in the structure design of the canopy roof.

气流辅助的静电纺丝技术研究进展

近年来,通过引入外部气流来增强静电纺使纳米纤维生产能力取得了显著进展,气流辅助不仅提高了静电纺丝效率,还改善了纤维的取向、堆积密度甚至形貌,已逐渐发展成为一种先进的纳米纤维制造方法。不同的气流施加方式,对静电纺丝过程具有不同的效果,结合不同的静电纺丝模式,使其展示独特优势,从而极大地丰富了静电纺丝技术。综述了气流辅助静电纺丝技术的研究进展,包括其基本原理、发展历程,讨论了具有代表性的气流辅助静电纺丝装置,如气流辅助的针型静电纺丝、气流辅助的无针静电纺丝、离心静电纺丝主要参数和理论模拟。对气流辅助静电纺丝技术存在的问题以及未来研究发展进行了展望。

干喷湿纺制备中空纤维膜的喷丝头结构优化模拟

在干喷湿纺法制备中空纤维膜的过程中,喷丝头作为关键的纺丝组件之一,其尺寸及内部几何形状对于聚合物分子链的取向和最终的膜形态有着重要影响,通过优化喷丝头结构有助于提高膜丝可纺性和产品质量。采用数值模拟的方法,建立三维喷丝头溶液流道模型,探讨了环隙直管长度、环隙间距、锥形流动角等流道结构参数对溶液在喷丝头内的剪切流动、出口挤出胀大以及气隙中拉伸流动的影响。模拟结果表明:纺丝液流经喷丝成型孔入口处的压力及压力降随着直管长度增加而增大,随环隙间距、锥形流动角的增大而减小,且环管流道越长,越有助于溶液流动充分发展;相比于直管长度,环隙间距和锥形流动角对溶液的挤出胀大行为影响更显著,随着环隙间距和锥形流动角的增大,挤出胀大现象减弱。直管长度和锥形流动角对气隙中的初生纤维外径分布影响不明显。增大直管长度和环隙间距、采用锥形环管,有利于增加膜丝取向度和强度、提高纺程中的流动稳定性。模拟优化得到的喷丝头结构为直管长度1.1 mm,环隙间距0.11 mm(即长隙比为10左右),锥形流动角大于30°。

湿法纺丝用喷丝头的结构与材质及性能

介绍了湿法纺丝用喷丝头的结构、材料及性能。湿法纺丝用喷丝头的形状主要为帽子形,孔径为0.05~0.12 mm,采用圆锥形和圆弧形两种孔形。喷丝头的材质主要为金、铂、铑、钽等,其中金铂合金喷丝头耐腐蚀性能好、强度和硬度高、纺丝质量好,但价格昂贵;钽喷丝头价格便宜,但硬度较低、使用寿命短、可纺性差。通过对钽喷丝头进行表面渗氮处理并镀膜的复合钽酸锂镀膜钽喷丝头、金刚石镀膜钽喷丝头已实现在不降低纺丝品质的前提下对金铂合金喷丝头的替代,并广泛应用于湿法纺丝,但在一些特种纤维、高端纤维领域,镀膜钽喷丝头依然无法取代金铂铑合金喷丝头。低成本、高硬度、抗腐蚀是未来湿法纺丝用喷丝头的研究发展方向。

33 dtex/36 f细旦有光波浪扁平涤纶FDY的生产工艺

讨论了熔体直纺33 dtex/36 f细旦有光波浪扁平涤纶全拉伸丝(FDY)纺制过程中喷丝板设计、冷却、上油、拉伸等工艺条件对纤维成形及产品质量的影响。在纺丝温度289~292℃,无风区高度55.5 mm,环吹风温度22℃、湿度90%、风速1.2 m/s,GR1速度2740 m/min,卷绕速度4100 m/min的工艺条件下,生产的涤纶FDY的断裂强度为4.06 cN/dtex,断裂伸长率为43.7%,异形度为54%,毛丝降等率为0.49%,生产作业性良好。

宽翼工字形涤纶的生产工艺

介绍了一种宽翼工字形涤纶全拉伸丝(FDY)的生产工艺,对喷丝板、纺丝工艺、热辊拉伸工艺等进行了调试,探索得到最佳工艺条件。试验表明:在纺丝温度为290~295℃,冷却风速为2.5 m/s,冷却风温为20℃,GR1速度为1 800 m/min、温度为91℃,GR2速度为4 370 m/min、温度为135℃,卷绕速度为4 300 m/min的工艺条件下,生产的工字形涤纶FDY的断裂强度为3.59 cN/dtex,10%模量为3.20 cN/dtex,条干不匀率在1.2%以下。该纤维抗弯性佳,且质轻、手感滑糯,具有特殊的光泽,可应用于割绒、貂绒、獭兔毛等起绒面料,具有很好的经济价值和推广价值。

喷丝板微孔全自动加工方案设计及微孔钻削技术

结合喷丝板微孔加工需求设计喷丝板微孔全自动加工方案,首先设计数字化控制精密机械加工机床的硬件结构及控制系统,为解决喷丝板微孔加工刀具磨损补偿不及时、扁钻易折断、盲孔钻屑不易排三方面问题,提出刀具磨损补偿、刀具破损在线监测、盲孔排屑三个功能设计方案,再从底孔工艺参数确定、切削参数优化、扁钻选材及孔底加工对比、扁钻加工问题优化四个方面展开微孔钻削技术应用优化,旨在实现喷丝板微孔全自动加工目标,提高喷丝板微孔加工的质量及效率。

功能性预取向丝134dtex/72f工艺研究

文章探讨了涤纶功能性预取向丝134dtex/72f的用途与性能,通过对工艺条件如纺丝温度、冷却上油条件、卷绕速度、喷丝板的设计等参数的最佳选择和设计,可以在聚酯直纺装置上生产出性能优异的三角形异性纤维134 dtex/72f产品。

纺丝用喷丝头受损分析及维护

为用好纺丝用喷丝头,保证纺丝质量,详述喷丝头的技术发展历程、制造要求、使用现状及微孔形状;从喷丝头运行中的问题表现出发,对4只已使用的镀膜钽喷丝头进行外观检验,分析其出丝面表面损伤、表面沉积物等受损情况;结合实践经验,对喷丝头的使用维护提出建议,总结轻微色斑或黑斑损伤的抛光处理方法。指出:喷丝头受损,会严重影响纺丝质量,应加强对喷丝头使用和维护方面的研究和管理,提高喷丝头的性能和可靠性。

不锈钢喷丝头表面镀DLC膜可行性探讨

为了提升化纤纺丝用喷丝头质量,介绍金铂合金、钽、不锈钢3种材质化纤喷丝头的优缺点;以SUS316L型不锈钢制作的PY35-2050-0.075型喷丝头为例,通过盐雾试验以及酸性溶液浸泡试验,对比分析其镀DLC膜前后的性能、质量及表面微观形貌变化。指出:以Cr+WC作为中间过渡层,能提高气相沉积DLC膜与不锈钢喷丝头基体的结合强度;镀DLC膜不锈钢喷丝头的硬度可达2000 HV,强度和耐酸碱腐蚀性均优于普通不锈钢喷丝头,使用寿命长,更适用于高温、高压以及酸碱腐蚀的纺丝环境。