The influence of the fabrication process on the buckling of thin-walled steel box sections

Steel box sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which can influence their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The welding procedure and the behaviour of the box sections under load has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Modelling has been shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. A design method has been proposed.     

Criteria of dynamic buckling estimation of thin-walled structures

The paper deals with dynamic buckling of thin-walled structures (plates and beam-columns with open cross-section) subjected to compressive rectangular pulse loading. The local, global and interactive dynamic buckling was analysed. Author proposes the new criterion for critical amplitude of pulse loading leading to stability loss. The proposed criterion is a modification of quasi-bifurcation criterion formulated by Kleiber, Kotula and Saran. Results obtained using proposed criterion were compared with other well-known criteria (Volmir (V) and Budiansky–Hutchinson (B–H) criterion).     

Digital Twin-driven machining process for thin-walled part manufacturing

Thin-walled parts are widely used in the aerospace, shipbuilding, and automotive industry, but due to its unique structure and high accuracy requirements, which leads to an increase in scrapped parts, high cost in production, and a more extended period in the trial machining process. However, to adapt to fast production cycles and increase the efficiency of thin-walled parts machining, this paper presents a Digital Twin-driven thin-walled part manufacturing framework to allow the machine operator to manage the product changes, make the start-up phases faster and more accurate. The framework has three parts: preparation, machining, and measurement, driven by Digital Twin technologies in detail. By establishing and updating the workpiece Digital Twin under a different status, various manufacturing information and data can be integrated and available to machine operators and other Digital Twins. It can serve as a guideline for establishing the machine tool and workpiece Digital Twin and integrating them into the machining process. It provides the machine operator opportunities to interact with both the physical manufacturing process and its digital data in real-time. The digital representation of the physical process can support them to manage the trial machining from different aspects. In addition, a demonstrative case study is presented to explain the implementation of this framework in a real manufacturing environment.     

薄壁压力容器筒体纵焊缝角变形对应力的影响

提出压力容器简体纵焊缝产生角变形的模型。用简明的解析方法和有限元方法,探讨由变形引起的应力集中系数K_(ta)。结果表明,利用应力集中系数估算焊缝棱角对应力的影响是较合实际的,其公式为:K_(ta)=1+6E/S,式中E为棱角度,S为筒体壁厚。     

Direct laser fabrication of thin-walled metal parts under open-loop control

Direct laser fabrication (DLF) is an advanced manufacturing technology, which can build full density metal parts directly from CAD files without using any modules or tools. The investigation on the fabrication of thin-walled parts of nickel alloy using open-loop DLF process is introduced in this paper. The experimental setup consisted of a CO₂ laser, a 3-axis CNC table, a coaxial powder nozzle and a powder recycler. The 3D-CAD file of a thin-walled metal part was converted into the STL file format and imported into software HUST-RP to generate ‘pseudo-random’ scanning paths of laser beam. The influence of process parameters on the build height of thin-walled metal parts was studied by 1–10 layered single-bead stacks of nickel alloy. The result shows that the interference factors which affect the build height of thin-walled metal parts occur randomly during the process. For open-loop DLF process, thin-walled metal parts can achieve much better shape quality if the process parameters are suitable. Multilayer single-bead walls were built up with different scanning velocity to obtain the optimal process parameters of thin-walled parts of nickel alloy. It shows that thin walls of nickel alloy with uniform height can be built up layer by layer in a certain range of specific energy. However, it is difficult to control the build height of complex thin-walled metal parts in an accurate manner just using optimal parameters. A special coaxial powder nozzle was designed in this paper. In a certain range, the deposition thickness of the nozzle is nearly linearly increased with increase in the standoff distance between the powder focusing point of the nozzle and the deposition substrate. By means of the nozzle, a novel method to control the build height of thin-walled metal parts using open-loop DLF process was introduced. The difference in build height of a thin-walled part can be compensated automatically in one or several layers during the process. It is proved that the build height of a thin-walled metal part can be accurately controlled in theory using the nozzle. A complex single-bead part of nickel alloy whose geometry was designed to be the well-known Chinese ‘FU’ was fabricated and explained in this paper. The result shows that the shape quality of the sample is quite good, and actual build height of the sample is 53.54 mm while the designed value is 54 mm.     

内压支撑下薄壁管弯曲变形力学分析

管件内压弯曲又称为管件充液弯曲,具有减小截面畸变,延缓薄壁管内侧失稳起皱,提高弯曲成形极限等优点。支撑内压在其中起到了关键性的作用,对于环向和轴向的应力应变分量具有重要影响。采用塑性理论,对内压和弯矩共同作用下的薄壁管弯曲变形进行理论分析。考虑内压对微元平衡方程的影响,建立一个新的理论分析模型,通过求解非线性方程组,得到薄壁管应力应变的分布规律,定量分析内压对薄壁管应力应变的影响趋势。同时通过将有限元分析得到的应力应变分量的信息,与理论解进行对比发现,理论预测和模拟结果相符合,验证所建立的理论分析模型的可靠性。结果表明,轴向和环向应力随内压升高均大大提高,环向应变随内压升高线性递增,而厚向应变线性减小。     

Flexural buckling of simply-supported thin-walled columns with consideration of membrane shear deformations: Analytical solutions based on shell model

In this paper, flexural buckling of pin-ended thin-walled columns is discussed. The classical formulae for the critical force are based on a beam model. The simplest formulae use the classical Euler–Bernoulli beam theory, but solutions based on the shear-deformable beam theory are also known. In the presented research alternative formulae are derived. The column is modeled as a set of flat plane elements, and the in-plane membrane shear deformations are explicitly considered. The derivations can be carried out in various, slightly different ways, leading to different formulae. The derived critical force formulae are discussed through theoretical considerations and numerical studies.     

Cyclic axial response and energy dissipation of cold-formed steel framing members

This paper summarizes results from an experimental program that investigated the cyclic axial behavior and energy dissipation of cold-formed steel C—sections structural framing members. Fully characterized cyclic axial load–deformation response of individual members is necessary to facilitate performance-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). The cyclic loading protocol was adapted from FEMA 461 with target displacements based on elastic buckling properties. Cyclic response showed large post-buckling deformations, pinching, strength and stiffness degradation. Damage accumulated within one half-wave after buckling. The total hysteretic energy dissipated within the damaged half-wave decreased with increasing cross-section slenderness. More energy dissipation comes at the cost of less cumulative axial deformation before tensile rupture.     

A shear deformable theory for the analysis of steel beams reinforced with GFRP plates

A shear deformable thin-walled beam theory is developed for the analysis of steel beams reinforced with a GFRP plate to one of the flanges. Starting with the principle of stationary potential energy, the governing equilibrium equations and boundary conditions are formulated for the problem. The theory results in two sets of fully coupled systems of equilibrium equations. The first system describes the longitudinal-flexural response of the system and involves four generalized displacement fields and the second system governs the lateral-torsional response and involves six generalized displacement fields. The resulting coupled systems are then solved numerically for practical problems. Detailed comparisons with three dimensional and shell solutions under ABAQUS show that the present theory provides reliable predictions for displacements and stresses. A comparison with results from a non-shear deformable theory illustrates the necessity of incorporating shear deformation effects in cases involving predominantly twisting responses.     

薄壁包装盒底注塑模具设计

薄壁塑件的应用主要是节约材料,其模具设计与通常成型模具有着不同要求.包装盒壁厚仅有1.0mm,就盒底模具设计中结构设计、浇注、冷却、排气和脱模等部分进行了分析,并将设计方案作了详细的阐述.模具经过实践证明:结构合理,产品无变形等缺陷,受到用户的认同.