Viscous Inner and Outer Pressure Forming Method of Thin-walled Tube and Its Application

Aiming at overcoming the difficulties in integral forming of thin-walled tubes with complex shapes, a novel forming method by inner and outer pressure through viscous was proposed. In this method, by dividing large deformation of the part into inner and outer pressure forming deformations, the limit deformation of tube part can be increased by several times. Meanwhile, the principle of viscous inner and outer pressure forming was provided, and key problems during the forming process such as reduction of the wall-thickness and instability wrinkling were analyzed. Thereby, the complex curved surface super-alloy GH3044 thin-walled tube with varying diameter ratio of 1.35（the ratio between the maximum and minimum diameters of the part） can be integrally formed by this method. The experimental surface of the formed part is superior in quality and the wall-thickness distribution is uniform. The results show that the viscous inner and outer pressure forming can provide a new approach for integral forming of thin-walled tubes with complex shapes.

Inner and outer pressure forming of nickel based super-alloy thin-walled part with variable diameter sections

A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room temperature,and the principle of the method was provided.Experiments and FE simulations were carried out to analyze the deformation characteristics for the part with larger variable diameter ratio(35%).The results show that visco-elasto-plastic pressure-carrying medium can meet the requirements of the room-temperature deformation condition for nickel based super-alloy sheet.The inner and outer pressure forming with the visco-elasto-plastic pressure-carrying medium can meet the requirements of dimensional accuracy for the thin-walled part with variable diameter sections.The thinning of wall-thickness is less than 4%.This method provides a new approach for near-net shape forming of nickel based super-alloy thin-walled parts with variable diameter sections.

Mechanical properties and microstructure evolution in incremental forming of AA5754 and AA6061 aluminum alloys

This study performs single point incremental forming(SPIF)on two aluminum alloys(i.e.AA5754 and AA6061),and analyzes their post forming mechanical properties and microstructure evolution.The forming parameters namely wall angle(35°-55°),feed rate(1-4 m/min),spindle rotational speed(50-1000 r/min),and lubricant(grease and hydraulic oil)are varied to probe detailed processing effects.The pre-and post-SPIF mechanical properties and microstructures are characterized by conducting tensile tests and optical microscopy,respectively.It is shown that an increase in the wall angle,feed rate and rotational speed causes microscopic variations in the alloys such that the grains of AA5754 and the second phase particles of AA6061 elongate.As a result,the ultimate tensile strength of the formed parts is increased by 10%for AA5754 and by 8%for AA6061.And,the ductility of AA5754 is decreased from 22.9%to 12%and that of AA6061 is decreased from 16%to 10.7%.Regarding the lubricant effect,it is shown that the mechanical properties remain insensitive to the type of lubricant employed.These results indicate that SPIF processing modifies the microstructure of Al alloys in a way to enhance the strength at the cost of ductility.

Novel approach for analysis of deformation behavior of thin-walled tube in free hydro-bulging process

Based on the assumption that profile of thin walled tube in free hydro-bulging process is a quadratic curve and any point on the profile moves vertically to the profile, mathematical models were deduced for analyzing the deformation behavior. The critical pressure and the maximum bulge coefficient(height) at bursting can be determined based on the models, in which a shape factor a is introduced to tightly communicate the material property and geometric parameters to plastic deformation. Free hydro-bulging experiments of stainless steel and low carbon steel tubes were conducted to validate the models, and the experimental data indicate that the theoretical predictions are reliable and accurate. The results display that the profile, dependent on the material and geometric parameters, can be hyperbola, parabola, arc and ellipse or alternative among them; moreover, the forming pressure and forming limit are both closely connected with material and geometric parameters.

Study on Effectiveness of Solitary-Wave-Like Form Based on Overtopping Data from Irregular Wave Tests

The previous study conducted by Li(2022)demonstrates that the Goda graph can be adequately represented by a solitary-wave-like form across the entire range of relative water depth,with the exception of the extremely shallow zone.However,it remains uncertain whether this form is equally effective when applied to test data generated by irregular waves,as the Goda graph was initially developed based on overtopping data from regular wave tests.Additionally,it is unclear whether this form is suitable for formulating overtopping discharge at composite vertical walls.In order to address these questions,a 2D overtopping experiment was conducted,incorporating both simple and composite types of vertical walls,with various relative water depths across the entire range,excluding the extremely shallow zone.A novel analysis procedure was developed,which proved to be highly productive and can be considered a general method for data fitting.Ultimately,the study yielded two conclusions:(1)the solitary-wave-like form is remarkably effective in formulating overtopping test data generated by irregular waves,regardless of whether the vertical wall is simple or composite,and(2)the resulting formulas exhibit definitely better performance compared with existing formulas.

HYGROTHERMAL PERFORMANCE ASSESSMENT OF ICF WALLS WITH DIFFERENT MOISTURE CONTROL STRATEGIES AND WALL DESIGNS

The initial high moisture content of concrete and the low vapor permeability of insu-lation layers on both sides of the concrete complicate the drying process of Insulated Concrete Forms(ICF).In order to facilitate the moisture transport and enhance the drying process,different moisture control stratcgics and wall designs can be implc-mented.The application of an air and vapor barrier is one of the most common moisture control stratcgics.In this paper,the impact of vapor permcance of an air and vapor barriers on the hygrothermal performance of an ICF wall in three differ cnt cold and wet climates is examined using a validated Hcat-Air-Moisture transfer model.The hygrothermal performance of an ICF wall assembly with different types of barriers and locations in the wall system for scveral wall designs is invcstigated.Results indicate that a smaller thickness of insulation on the outside facilitates remov-ing the moisture towards the outside and installing low permcance air/vapor barrier systems on the outside prohibits drying and drives the moisture to the inside.Our findings also show that with the proper sclection of insulation thickncss and vapor control stratcgy moisture-related problems can be avoided.

Fibre glass reinforced plastics bolt's application in coal wall support of stoping tunnel

This article set forth two types of destructive form of stopping tunnel coal wall: destructive form in coal and destructive form in interface of coal layer. In addition, the mechanism of destruction in stopping tunnel coal wall is analyzed.

Springback of thin-walled tube NC precision bending and its numerical simulation

The springback is one of the key factors which affect the forming quality of thin-walled tube NC precision bending. The elastic-plastic finite element method was proposed to study the springback process of thin-walled tube NC precision bending and the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to solve the whole process of thin-walled tube NC precision bending. Then, the 3D elastic-plastic finite element model was established based on the DYNAFORM platform, and the model was verified to be reasonable. At last, the springback rule of thin-walled tube NC precision bending and the effect of geometry and material parameters on the springback rule of thin-walled tube NC precision bending were studied, which is useful to controlling the springback of thin-walled tube NC precision bending, and the numerical simulation method can be used to study other effect of parameters on the forming quality of thin-walled tube NC precision bending.

Approach Based on Response-Surface Method to Optimize Lining of Dies Used in 3D Free-Bending Forming Technology

In three-dimensional free-bending forming(3D-FBF),the tube is not overly constrained,and the plastic deformation behavior and forming quality of the bent tube are significantly affected by the critical structure of the forming die lining.However,the effects of die-lining structural parameters on the tube quality,and a method to determine the combination of die-lining structural parameters is yet to be devised.This study aims to propose a new framework that allows one to understand the effects of various die-lining structural parameters on tube quality and to propose the best combination of die-lining structural parameters.First,finite-element modeling is performed to simulate 3D-FBF and examine the effects of individual die-lining structures on the quality of tube formation.The simulation results show that the deformation-zone length and die gap are positively correlated with the tube-section distortion and wall-thickness variation,whereas it shows an opposite trend with respect to the bending radius.Additionally,the lining chamfer radius of the bending die and the guide lining chamfer radius minimally affect the tube forming quality.Subsequently,the optimal die-lining structure is obtained using the response-surface method.The tube cross-sectional distortion rate reduced from 2.73 to 2.53%after the die lining is optimized.Additionally,the average inner-wall thickness reduced to 1.06 mm,whereas the average outer-wall thickness increased to 0.97 mm.This paper proposes a method for optimizing the forming-die-lining mechanism and for improving the tube forming quality in 3D-FBF.

Construction of Thin Concrete Lined Walls for Three Gorges Shiplock

With high rock slope in shiplock area, thin reinforced concrete lining walls are constructed for the shiplock system. The construction technology involves much complicated structures in formwork, frequent interference due to crossover working procedures, tight time schedule, high quality of reinforced concrete and showcase appearance requirements, hidden troubles affecting construction safety. With above-mentioned factors in consideration, a single-side-separated sliding formwork technology advanced from past sliding formwork experiences has been developed and applied successfully. This new technology is beneficial in quick and safe operation, capable to assure best quality and appearance of shiplock concrete works, and has filled up the gap in terms of construction sliding formwork in our country.

Experimental Study of Sand Bed Configurations in Front of a Vertical Wall Under Wave Action

When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.

装配式混凝土剪力墙结构接缝连接研究进展

装配式剪力墙结构拼装时存在大量的水平接缝和竖向接缝,由于剪力墙的刚度较大,接缝连接处易存在刚度不足引起的损伤集聚问题,成为影响结构整体性和抗震性能的决定性因素。总结了国内外正在发展的预制装配式剪力墙结构水平和竖向接缝的连接形式,并对各类连接形式的构造特点、抗震性能、应用优势和技术瓶颈进行了系统阐述和分析,在此基础上探讨了装配式剪力墙结构接缝连接技术的发展方向。结果表明:目前湿式连接技术已较为成熟且被广泛应用,但仍存在现场湿作业量大、质量不易检测和控制等问题;干式连接技术工业化程度高,但对施工精度的要求也高,可能产生的螺栓松动、锈蚀以及磨损问题限制了其工程应用;将消能减震技术融入竖向接缝连接,利用超高性能混凝土实现水平接缝连接,并结合可恢复功能防震技术,是未来装配式剪力墙结构高质量发展的新增长点。

Thin-walled aluminum alloy tube NC precision bending based on finite element simulation

Elongation and springback are the bottleneck problems of thin-walled aluminum alloy tube NC precision bending. So thin-walled aluminum alloy tube NC precision bending based on finite element simulation is put forward. The finite element model of thin-walled aluminum alloy tube NC bending is established based on the DYNAFORM platform. The process of thin-walled aluminum alloy tube NC precision bending is simulated with the model and the elongation and springback of tube bending can be gained. A new method of measuring the elongation of thin-walled tube NC precision bending named 'pressure die measuring method' is put forward and the computing equations of bending angle, bending radius, blanking length and initial bending section based on elongation and springback angle are derived. The bending angle, bending radius, blanking length and initial bending section of tube bending can be gained with these equations based on the elongation and springback angle from the simulation. The study can be used to control the quality of thin-walled aluminum alloy tube NC bending so that precision bending without redundance can be realized.

嵌套加强的LQ550高强冷弯薄壁C型钢连续檩条受力性能研究

为提高LQ550级高强冷弯薄壁C型钢连续檩条的承载能力,采用在支座处嵌套的方法来加强连续檩条。对未加强和采用两种嵌套方式加强的檩条共7组试件进行三点受弯试验,得到了试件的承载性能和破坏形态,试验结果表明加强后的试件出现跨中局部屈曲和嵌套端部局部屈曲两种破坏形态。采用ABAQUS软件建立了非线性有限元模型对嵌套加强的檩条进行数值模拟,有限元分析得到的承载力和破坏形态与试验结果吻合良好,验证了有限元模型的准确性。基于验证的有限元模型,分析了两种嵌套方式和不同嵌套长度对檩条承载力的提升,且表明嵌套檩条的长度宜取为连续檩条跨度的1/5~1/4。

筋材布设方式对加筋土挡墙动力响应的影响

针对目前加筋土挡墙设计和施工中筋材布设方式大多为等长形的问题,提出一种倒梯形的筋材布设方式,并基于挡墙位移分区理论和有限差分Flac^(3D)数值模拟,建立加筋土挡墙三维分析模型,探讨不同峰值加速度下3种加筋土挡墙对位移、水平土压力、筋材拉应力及潜在破裂面的影响。结果表明,随峰值加速度增大,挡墙位移逐渐增大,同一荷载作用下,改变筋材布设方式,侧向水平位移减少9.3%,竖向沉降减少5.3%;3种形式挡墙水平土压力相差不大,最大水平土压力分布在挡墙的中下部;筋材拉应力随峰值加速度的增大,沿墙高从单峰型转化为双峰型分布,最大值位于挡墙中下部;潜在破裂面填土区破裂带的形状与筋材的布设方式有关。所提出的倒梯形筋材布设方式对加筋土挡墙的抗震效果更好,可为施工设计中加筋土挡墙筋材布设提供参考。

模块化冷弯薄壁型钢结构体系低层村镇住宅设计研究

在传统冷弯薄壁型钢结构体系的基础上,从模块化、装配化角度出发,提出了一种适用于低层村镇住宅的新型结构体系——模块化冷弯薄壁型钢结构体系。首先,简述了墙体模块单元的构成,给出了7种通用标准化墙体模块单元,并介绍了基于通用标准化模块单元的村镇模块化户型构建原则及过程;其次,详述了便于快速装配安装的标准墙体单元间模块化连接方式,对模块连接节点进行了受力分析及数值模拟,并给出了模块化冷弯薄壁型钢结构体系构建的原则;最后,重点介绍了适用于所有冷弯薄壁型钢结构体系的抗剪墙长简化设计方法以及基于模块化冷弯薄壁结构体系的抗剪墙长设计方法,并通过实际案例详述了墙长确定过程,同时对比了不同计算方法的抗剪墙长,进一步验证了所提出的抗剪墙长简化设计方法的可行性。结果表明:所提出的模块化冷弯薄壁型钢结构体系可大幅提高冷弯薄壁型钢结构低层村镇住宅的工业化和产品化水平,大幅缩减了工期;所提出的抗剪墙长简化设计方法可显著降低设计门槛,便于该类体系的推广应用。

柱脚不同连接形式钢框架-摇摆墙结构抗震性能对比分析

增设摇摆墙后框架结构地震下柱脚仍会发生一定程度的塑性损伤,将柱脚设置为铰接或提离后有望减轻上述缺陷。以三层、六层和九层钢框架为基准模型,分别建立柱脚固接、铰接及提离三种框架-摇摆墙结构模型并进行动力弹塑性时程分析,对比各结构最大侧向位移、层间位移角、峰值加速度、层间剪力、墙体剪力和弯矩等;进一步建立耗能连梁固接和铰接的对比模型,研究连梁连接方式对结构抗震性能的影响。结果表明:三层模型中柱脚固接时侧向位移、层间位移角、加速度、层间剪力及摇摆墙墙体剪力的控制效果最优,六层、九层模型中分别对应柱脚提离和柱脚铰接效果最好;摇摆墙墙体剪力图和弯矩图分别呈现“C形”和“反C形”,柱脚固接时墙体弯矩均为最小,与层数无关。柱脚固接耗能连梁两端采用固接最优,柱脚铰接和柱脚提离时耗能连梁两端采用铰接形式效果更优。此分析可为框架-摇摆墙结构进一步推广应用提供参考。

Forming Characteristics of Al-alloy Large-diameter Thin-walled Tubes in NC-bending Under Axial Compressive Loads

Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.

送进式焊剂片约束电弧超窄间隙焊接工艺参数匹配

为探究送进式焊剂片约束电弧超窄间隙焊接的工艺参数匹配,自主设计制作了一套送进式焊剂片约束电弧超窄间隙焊接装置,以提高焊接过程稳定性和自动化水平。利用瞬间中断电弧的方法保留了熄弧位置处焊缝形态和焊剂片末端熔化形貌,发现焊接电压和焊剂带送进速度都是通过改变焊剂片对电弧的作用长度来影响焊缝成形,焊剂片对电弧的作用长度可表现为焊剂片对电弧固壁约束面积。通过改变焊剂带送进速度和焊接电压进行了试验研究,结果表明,当焊剂片对电弧固壁约束面积适中时,电弧集中加热区域会下移至间隙底部和侧壁根部,获得根部熔合良好的焊缝;当焊剂片对电弧固壁约束面积较大时,电弧受约束程度过强,电弧加热区域集中在间隙底部,分布于侧壁根部电弧热量很少,焊道上部会有熔池堆积;当焊剂片对电弧固壁约束面积较小时,电弧受约束程度较弱,会沿侧壁攀升导致加热区域集中在两侧壁上,很难在坡口根部形成有效熔池,最终形成孔洞焊缝。确定了最佳的焊接电压范围为21.5~24.5 V,焊剂带送进速度2.1~2.6 mm/s,利用该参数进行超窄间隙单道多层焊接可以获得成形良好的焊缝。

冷弯薄壁型钢-结构防火一体板自攻螺钉连接性能试验研究

开展冷弯薄壁型钢-结构防火一体板自攻螺钉连接抗剪性能试验研究,完成35个典型试件单调拉伸及低周往复加载试验,分析结构防火一体板厚度、螺钉直径、螺钉端距及加载角度等因素对其抗剪性能的影响。结果表明:不同加载角度及螺钉端距的试件呈现不同的破坏模式,主要包括板材端部撕裂破坏、板材孔壁承压破坏、板材被拉断破坏等,且破坏时试件的自攻螺钉存在不同程度的倾斜。对于试验端分别采用直径为4.8、5.5 mm螺钉的试件,试件的峰值荷载及延性系数与螺钉直径无明显相关性,弹性刚度随着螺钉直径增大而显著提升;随着螺钉端距由15 mm增大至25 mm,试件的弹性刚度无明显变化,而峰值荷载和延性系数提高了约35%;随着板厚由12 mm增大到20 mm,试件的峰值荷载提高了约40%,弹性刚度提高了约90%,延性系数降低了约30%;与加载角度为0°的试件的特征参数相比,加载角度为45°时,试件弹性刚度提高了约100%,峰值荷载及延性系数无明显差别;加载角度为90°时,试件弹性刚度及峰值荷载无明显差别,延性系数降低了约40%。