Numerical and experimental investigation of manufacturing and performance of metal inserts embedded in CFRP

Due to their outstanding specific mechanical properties, carbon fibre reinforced plastics (CFRP) exhibit a high application potential for lightweight structures. With respect to multi-material design and to avoid drilling of structural CFRP parts to join them to other components, embedded metal elements, so called inserts, can be used. The inserts consist of a shaft and a baseplate which is embedded between the fibre layers. So far, only punctiform inserts have been subject to research. One feasible geometry are linear inserts which have not been studied yet. In this work, the performance of two different types of linear inserts will be investigated. The shapes are based on a punctiform insert which is made out of a threaded shaft welded onto a baseplate whose performance under different types of loading has been investigated before. The first type of linear inserts has the same cross-section as the reference punctiform insert but is of a linear form. The second type is a quasi-linear insert which consists of a baseplate with the same dimensions as the first linear inserts and three threaded shafts welded onto it. All samples are manufactured by resin transfer moulding (RTM). Depending on the geometry of the insert and the preforming concept it is potentially possible to maintain the fibre continuity. For the inserts with a continuous shaft and in the proximity of the insert, it is necessary to cut fibres of the top layers which are aligned perpendicular to the shaft. For the quasi-linear insert, it is possible to maintain the fibre continuity as the fibres are guided around the circular shafts. Additional to mechanical tests that are carried out, mould-filling and curing simulations are performed for different inserts to analyse the influence of the process parameters onto the part quality. In the main series of tests, the specimens are characterized regarding their failure behaviour and load bearing capacity under quasi-static loads. The results of the experiments show that, compared to the punctiform reference insert, the linear load introduction elements exhibit higher load bearing capacity. However, the linear load introduction elements are inferior regarding specific load bearing capacity and furthermore increase process complexity during preforming and production.     

Experimental and numerical appraisal of self-piercing riveting

Self-piercing riveting (SPR) has become an interesting alternative joining technique for difficult to weld materials. A limitation of this technology is still the heavy experimental procedure needed for joint optimisation. In this paper, an experimental activity on Al6082-T4 sheet metal samples has been conducted to achieve a better understanding of the process. The joining process and the tensile tests have then been simulated using a FE code to predict deformed shape, failure mechanism (e.g. crack propagation, rivet pull-out) and shear resistance of the joint. Results show how this procedure can be a powerful tool for joint optimisation.     

具有复合型织构的水润滑轴承的摩擦学性能研究

目的 提升水润滑轴承的摩擦学性能.方法 采用流固耦合的方法,对具有该复合型织构的水润滑轴承进行研究,将拥有仿生硅藻的多孔结构(矩形-半球型复合型织构)应用在轴承的高压区位置.分析具有矩形-半球型的复合织构的水润滑轴承在不同载荷、织构宽度以及间距的作用下,其摩擦学特性的变化.结果 通过与光滑轴承和单层织构轴承进行对比可知,随着载荷的增大,矩形-半球型复合型织构轴承的承载力随之增加,摩擦系数随之减小,并且有最大的轴承承载力和最小的摩擦系数.随着第一层及第二层织构宽度的增加,复合型织构轴承的承载力虽有复杂波动,但总体呈现上升趋势,摩擦系数呈现下降趋势.在间距较小时,复合型织构轴承的摩擦学性能更优,在间距一定的情况下,存在最优的织构个数,使得轴承的摩擦系数最小.结论 具有矩形-半球型复合织构的水润滑轴承适合在重载条件下工作,织构尺寸较大时,能产生较好的摩擦学性能;在间距较小时,复合型织构的摩擦学性能较为优异,且存在最优的织构个数.     

微孔节流气体静压止推轴承跨缝过程时变特性研究

目前,大型气浮平台均采用花岗岩平台拼接而成,平台拼缝会对实验效果产生一定影响。针对上述问题,以微孔节流气体静压轴承运动中经过平台拼缝时的时变特性为研究对象,建立微孔节流止推轴承物理模型,并使用CFD软件与UDF相结合的动网格技术实现轴承跨越平台拼缝的动态过程仿真,研究不同气膜厚度、进气口压力、平台拼缝位置对轴承承载力和压力分布的影响。结果表明：当平台拼缝到达微孔分布圆附近时承载力急速下降,且平台拼缝到达轴承中心时承载力下降到最小值;随着气膜厚度的增加,轴承承载力的最大损失比例随之增加,并最终稳定到0.6;平台拼缝位于供气孔分布圆之外时,轴承边缘与平台拼缝之间的承载面将失效;通过增加进气口压力,轴承承载力整体有明显提升,但承载力损失速度也明显加快。     

–50 ℃冷风条件下抛光硬质合金刀片加工TC4钛合金的表面粗糙度分析

目的提高硬质合金刀片加工TC4钛合金的表面质量。方法利用化学机械抛光技术对传统磨削的硬质合金刀片分别进行粗抛、半精抛和精抛处理,运用正交试验法,在常温干切和–50℃冷风条件下,分别采用传统磨削的硬质合金刀片(磨削刀片)与化学机械抛光的硬质合金刀片(抛光刀片)进行切削TC4钛合金正交试验,利用方差分析法分析切削参数对已加工表面粗糙度Ra的影响。运用多元线性回归方法建立磨削刀片、抛光刀片在常温干切和–50℃冷风条件下切削TC4钛合金已加工表面粗糙度Ra的经验预测模型。结果硬质合金刀片前刀面通过粗抛、半精抛和精抛后,刀片前刀面的表面粗糙度Ra为19 nm。当切削参数相同时,磨削刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度,比常温干切条件下平均降低了35.9%;抛光刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度,比常温干切条件下平均降低了43.5%。在常温干切条件下,抛光刀片比磨削刀片切削TC4钛合金的已加工表面粗糙度平均降低了19.2%;在–50℃冷风条件下,抛光刀片比磨削刀片切削TC4钛合金的已加工表面粗糙度平均降低了28.7%。抛光刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度Ra,比磨削刀片在常温干切条件下切削TC4钛合金的已加工表面粗糙度Ra平均降低了54.4%。结论采用对硬质合金刀片表面进行化学机械抛光技术和以–50℃冷风为切削介质的组合工艺,可有效降低TC4钛合金已加工表面粗糙度。     

泡沫铝填充金属波纹夹芯梁弯曲破坏模式研究

为了提高金属波纹结构的承载效率,充分发挥泡沫铝在能量吸收方面的优势,本文设计了泡沫铝填充金属波纹三明治夹芯梁。针对波纹结构各向异性的特点,本文对其横向和纵向两个方向在三点弯曲载荷作用下的力学响应及破坏模式进行了试验研究。研究表明,泡沫铝的填充可以有效改变金属波纹夹芯梁的弯曲破坏模式,其弯曲刚度和峰值载荷均得到了大幅提升。和横向弯曲相比,金属波纹夹芯梁在纵向弯曲时具有更强的承载能力,且泡沫铝填充的增强效果更加显著。纵向弯曲时载荷在达到峰值后并不会突然下降而是呈现出很长的平台区,表现出更强的后屈曲承载能力。     

Hydrogen embrittlement of nodular cast iron

Ferritic nodular cast iron, intended for use as the material for inserts of canisters for long-term geological disposal of spent nuclear fuel, was studied for hydrogen sensitivity. In the canisters, the insert provides the mechanical strength against external loads. Hydrogen was charged from 0.1 N H₂SO₄ solution in free-corrosion tests and under controlled cathodic potential. Hydrogen uptake and trapping were then measured using thermal desorption spectroscopy. The hydrogen desorption rate after hydrogen charging manifests two distinct peaks. Plastic deformation during hydrogen charging increases the hydrogen uptake considerably. Hydrogen reduces the elongation to fracture and time to fracture in slow strain rate testing and constant load testing (CLT), respectively. Especially, the strain rate in CLT is dramatically increased. The appearance of hydrogen-induced cracking in the ferrite phase changes from ductile dimple fracture to brittle cleavage fracture due to hydrogen charging, which initiates from the interphases of the graphite nodules. The results are discussed in terms of the role of hydrogen and the graphite nodules in hydrogen embrittlement of ductile cast iron.     

Joining metal-polymer sandwich composite sheets with mechanical nuggets

This paper presents a new joining by forming process to produce lap joints in metal-polymer sandwich composite sheets. The process involves drilling a blind hole in each sheet for removing the upper metal skin and the polymer core layer, and fixing them together by compressing a metal insert placed in-between to obtain a form-fit mechanical nugget. The cross-section of the joint resembles that of resistance spot welding, with the cold formed insert (‘nugget’) hidden inside the sheets. The geometry and size of the inserts are analysed by finite elements and experimentation to determine the effectiveness and performance of the new joints.     

高炉标准载荷下炉身段不同开孔率对炉顶封罩受力性能影响

利用有限元ANSYS软件建立大型高炉局部模型,对炉身段不同开孔率对炉顶封罩开孔受力性能的影响进行了数值模拟.结果表明,标准荷载下,模拟条件的炉身各开孔率均使炉顶封罩孔洞周边处于弹性状态;将炉身段30％开孔率时产生的底部径向位移线性化处理后,作为炉顶封罩局部模型的径向边界约束,在标准荷载下模拟炉顶封罩的受力性能是完全可行的.     

Use of thin adherends in adhesively bonded joints under different loading modes

Abstract

The adhesive bonding technique is especially suited to the joining of thin materials. An adhesive joint consists of a structural adhesive and an adherend. When designing the joint, focusing on the behaviour of the adhesive is important. However, if the material to be joined is thin, then it becomes much more important to concentrate on the material properties. In the present work, two adhesives with different mechanical behaviour and two thin adherend materials, steel and aluminium, were selected for the production of adhesive joints. The single lap joint configuration was subjected to tests under bending load and also under tensile load. The results show that adherend plasticity plays an important part in the joint failure; specimens under bending load experienced high plastic deformation of adherends, depending on the strength of the adherend material. Overlap increase did not seem to affect the joint strength. When the joints were tested under tensile loading, it was observed that the load bearing capacity of adhesives was an important parameter influencing the joint strength, and that an increase in overlap seemed to contribute to the joint performance. In general, the results obtained imply that it is vital that the adherends used remain in their elastic deformation region to obtain a joint strength that reflects the mechanical behaviour of the adhesive used.     

工件材料可切削性对可转位硬质合金刀具加工经济性影响规律研究

用2种不同牌号和不同槽型的硬质合金刀具分别对优质中碳钢45#和GCr15轴承套进行切削实验,通过应用金属切削原理结合加工经济学分析方法,对零部件的可切削性对生产效率、生产成本的作用机制进行研究,从而揭示其对后两者的影响规律性;通过切削实验,探究刀具使用寿命、工件可切削性系数和整体硬度的内在联系。研究表明:当工件可切削性系数提高、刀具使用寿命延长以及工件硬度降低时,其加工成本将呈指数化降低,同时生产效率也会成倍提高。研究获得刀具使用寿命与加工经济性的量化关系曲线,从而实现切削过程最优化的可量化目标。研究数据和研究方法可为切削过程优化、刀具设计与优选提供方法和数据支撑。      

纤维从弹性基体中的脱粘和拔出

本文分析了纤维从弹性基体中的脱粘与拔出,得到纤维初始脱粘应力。完全脱粘应力和纤维拔出应力与嵌入纤维长度的非线性函数关系,该理论经钢丝一环氧拔出试验验证,结果表明,当嵌入纤维长度较大时纤维初始脱粘应力趋向于一常数;完全脱粘应力随嵌入纤维长度的增加而增加,最后达到一个稳定状态:纤维拔出应力随嵌入纤维长度非线性地增加。     

不锈钢在Cl^- ＋H2SO4溶液中轻载下的腐蚀磨损

从腐蚀磨损速率、钝化膜承载能力以及点蚀与腐蚀磨损的关系等方面，研究Cl对不锈钢在H2SO4溶液中轻载下的腐蚀磨损行为的影响，在自然电位下，Cl对腐蚀磨损存在一临界载荷，低于此载荷腐蚀磨损速率略有降低：高于此载荷，腐蚀磨损率增加，轻载下磨痕内的点蚀坑较多而深，高载下点蚀坑少且浅，在钝化区，Cl将降低钝化膜的承载能力，使腐蚀磨损率增加。     

Design and mechanical characterisation of a layer wise build AFP insert in comparison to a conventional solution

Joining methods that present a detachable connection of thin walled fiber reinforced plastic (FRP) structures greatly increase the proliferation of lightweight FRP-parts. This paper describes the design of a new layer wise build insert solution named multilayer insert (MLI) in a comparative study in terms of mechanical performance. The MLI is designed to be easily integrable into existing automated fiber placement processes. The mechanical characteristics and damage behavior of the MLI is compared with a commercially available insert serving as reference. Comparable results are obtained by testing the specimen in the same test setup. Both, the results of the MLI and the reference specimen show that a geometrical optimization is able to change the failure modes of the connection thereby keeping the surrounding FRP intact while improving the mechanical performance of the entire component.     

飞机强度试验结构单点大载荷加载技术研究及应用北大核心

某型飞机弹射试验中单点集中载荷较大,受试验场地条件和试验设备能力等因素限制,现有加载方式难以满足试验集中大载荷加载要求。因此,综合考虑试验载荷大小、方向、加载位置、地轨承载能力、加载装置强度、质量、减载载荷等因素,通过多参数目标优化,得到满足试验需求的单点大载荷加载装置的最佳设计尺寸。研发的加载装置通过航向载荷主动卸载及垂向载荷卸载接口将大载荷优化分配,确保承载系统安全,实现集中大载荷的精准施加。所设计的单点集中大载荷加载系统已成功应用于某型飞机弹射载荷静力试验,试验加载中加载装置保持平稳,未发现破坏及目视可见变形,且试验测量数据与目标值相吻合,试验加载稳定性、重复性良好。     

Multi-scale structuring for thermoplastic-metal contour joints of hollow profiles

In contrast to common and classical joining technologies for composite/metal hybrid structures such as bonding and riveting, profile and contour joints offer a promising potential for novel lightweight hybrid structures. Contour joints with form locking elements on multiple scale levels enable to pass very high loads into rod- and tube-shaped fibre reinforced structures and promise high degrees of material utilization for the composite part. This paper demonstrates the advantage of multi-scale structured load introduction elements. First the intrinsic manufacturing process, whereas the thermoplastic tape braided preform is simultaneously consolidated and formed into the metallic load introduction element is shown. Numerical investigations on the macro- and generic microscale demonstrate the potential to trigger cohesive or adhesive failure by appropriate designed form locking elements. The extensive experimental investigation of meso-, macro- or combined-structured tubular specimen shows the beneficial effect of multi-scale structuring to increase the joining strength. Concluding advises for the contour joints’ design are given.     

残余应力对液压油缸缸筒承载能力影响的有限元分析

为了获得残余应力对液压油缸缸筒承载能力的影响规律,利用有限元的方法,建立了缸简的力学模型,通过计算获得了缸筒残余应力与载荷之间的关系,分析了残余应力对承载能力的影响。结果表明,残余应力在很大程度上影响着缸筒的承载能力,残余压应力可以抵消一部分载荷产生的应力,从而可以提高缸筒的承载能力,而残余拉应力刚好相反。所以适当的残余应力的存在有助于提高缸筒的承载能力。     

铝钢点焊铆接复合连接技术

提出了一种点焊与铆接复合进行铝钢连接的技术,即在待焊试样区域预制工艺孔,将铆钉铆入孔中,利用铆接力实现试样的预连接.然后使用点焊机在铆接位置进行点焊,实现铆接与点焊的复合连接,称为"点铆焊".文中分析了该方法的力学性能、微观组织、断裂模式,并同纯点焊与纯铆接进行了比较.结果表明,点铆焊的抗拉强度比纯点焊提高了23.8%,比纯铆接提高了28.7%,失效前吸收功比纯点焊提高211%,比纯铆接提高67%.虽然在点铆焊过程中也会产生脆性金属间化合物,但这些区域并不是主要的承载部位,点铆焊为塑性断裂模式.     

泡沫铝填充双层金属点阵结构增强效应及吸能特性

通过激光焊接获得3种不同几何构型的双层金属点阵结构,再将闭孔泡沫铝切割后填充到其孔隙当中获得一种新型泡沫铝填充双层金属点阵结构。采用实验和有限元模拟的方法研究其准静态面外压缩载荷作用下的承载能力、吸能特性及机理、变形破坏模式等。结果表明,泡沫铝的填充能够有效改变空心点阵结构的后屈曲行为,提高点阵芯体单元的屈曲稳定性,具有明显的耦合增强效应,表现在承载及能量吸收效率的大幅提升,可达到对应空心结构的10倍以上。     

Φ177.8mm偏梯形螺纹接头套管脱扣原因分析

对Φ177.8mm偏梯形螺纹接头套管脱扣原因进行了详细的试验分析,认为套管脱扣与套管材质无关也不是过载所致。模拟现场脱扣时的受载情况,采用套管实物进行验证试验。通过对套管脱扣之前的上扣配合状态、脱扣时所受载荷和实物验证试验的综合分析,认为套管脱扣的原因是由于上扣不到位,在后续洗井作业过程中套管接头受到振动等载荷后首先发生松动,随后在碰压作业过程中发生脱扣。