冷轧制备碳纤维-铝合金层板及其弯曲力学性能

为研究铝合金/碳纤维预浸料轧制制备层板的可行性及力学性能,基于铝板不同表面处理工艺和轧制压下量,制备了碳纤维增强铝合金层板。结合三点弯曲试验分析了表面处理工艺和压下量对层板弯曲力学性能的影响。结果表明：铝合金表面处理工艺和轧制压下量对层板力学性能影响显著,经阳极氧化工艺处理后所得层板弯曲性能改善最为明显,弯曲强度和模量分别为573  MPa和80.9 GPa,相比表面未处理试样分别增加了65.9%和39.1%,界面结合性能明显优于化学清洗法和机械打磨法,层板破坏形式由纤维整体断裂和分层失效转变为纤维屈曲变形;当压下量为6.5%时,铝合金/纤维树脂界面整洁平齐,层板弯曲性能最优,表明适当的轧制压力有利于树脂流动浸润纤维,压实层间孔隙,促进树脂与铝合金表面形成稳定的机械咬合结构。     

缝合复材层板损伤后压缩强度的数值计算方法

缝合复合材料在复合材料的厚度方向加入了缝线,不仅提高了层板的层间强度,抑制了分层的扩展,而且提高了受冲击后的压缩强度。采用开口等效法来模拟层板的初始损伤,用三维实体单元模拟层板,空间三维杆单元模拟缝线的增强作用,采用三维Hashin判据作为压缩时层板渐近损伤的失效判据,模拟缝合复合材料层板受冲击损伤后的压缩过程;得到层板的剩余压缩强度,与试验结果吻合较好。     

复合材料层合板的极限强度分析与可靠性优化设计

研究层合板结构基于最终层失效准则的可靠性分析方法,在此基础上,对复合材料层合板可靠性优化设计的方法和算法进行讨论.层合板作为一个系统考虑,其可靠性分析含以下几个步骤:(1)随机载荷和强度参数作为随机变量,利用一次二阶矩法(first order reliability method, FORM)分析单层板的失效概率.(2)假定失效概率最大的单层板首先破坏,然后通过修改刚度矩阵对结构进行再分析,得到剩余结构各单层板的失效概率,从而建立主要失效序列.(3)计算系统的可靠度.在确立复合材料基于最终层失效准则的可靠性分析方法的基础上,以系统可靠度指标最大为目标,研究层合板的可靠性优化问题.建立和发展基于最终层失效准则的复合材料层合板可靠性优化方法以及相应的算法,并对比讨论单变量和多变量优化设计问题.     

基板宽度与铆钉高度对单搭自冲铆接头准静态力学性能的影响

自冲铆(SPR)是一种可以实现汽车车身结构轻量化重要薄板材料连接技术。为研究基板宽度与铆钉高度对自冲铆接头准静态力学性能的影响,测试获得最优铆接参数,制备两组均为单搭搭接长度20 mm基板宽度为20 mm的S(铆钉高度为5 mm)和SFX(铆钉高度为6 mm),一组搭接长度为40 mm基板宽度为40 mm的S-的5052铝合金自冲铆接头。基于准静态力学实验,分析各组接头的强度、刚度、失效形式以及能量吸收水平。结果表明:S-组失效载荷约为SFX组1.10倍,SFX组失效载荷约为S组1.24倍;S-组刚度大于SFX组,SFX组大于S组。三组自冲铆接头失效模式均为铆钉与上板从下板拉脱,铆钉头出现不同程度下陷;S-组能量吸收值约为SFX组的1.08倍,SFX组约为S组的1.76倍。     

动力蓄电池包挤压失效仿真与实验

为提高动力蓄电池包挤压仿真的精度,将延性损伤准则引入到有限元仿真,通过单轴拉伸试验、纯剪切试验与缺口件拉伸试验与有限元仿真,获得了某动力蓄电池包结构所用材料6061-T6铝合金的延性损伤参数。型材三点弯曲试验、动力蓄电池包挤压试验与有限元仿真的结果表明：输入延性损伤参数的有限元仿真结果与试验结果误差小,能较为准确地模拟铝合金损伤对结构承载性能的影响;不考虑材料失效的结果与试验结果误差较大。     

陶瓷基复合材料低循环拉—拉疲劳寿命预测

采用细观力学方法建立预测纤维增强陶瓷基复合材料低循环拉—拉疲劳寿命的模型。该模型考虑初始加载到疲劳峰值应力时,基体出现裂纹,纤维/基体界面发生脱粘,部分纤维将发生断裂,并采用统计方法得到初始加载到峰值应力时的纤维失效体积分数;在后续循环过程中,考虑纤维相对基体在界面脱粘区滑移造成界面切应力下降,纤维失效模型与Evans界面磨损模型相结合,得到循环过程中纤维失效体积分数与界面切应力、循环数之间的关系;当纤维失效导致剩余强度下降,并小于疲劳峰值应力时,判断材料失效。采用剩余强度方法对陶瓷基复合材料的S-N曲线进行预测,并将预测的S-N曲线与试验数据进行对比,结果吻合较好。     

铆速对SPR自冲铆接接头成形性能的影响

针对低碳钢340和铝合金6000的异种金属SPR自冲铆接接头,利用板材-铆钉-设备的设计思路,计算并选择合适的铆钉和铆接设备。采用五种不同的铆接速度进行该种接头的自冲铆接试验。观察各铆速下接头的截面成形形貌,并测得铆速增大时,接头底切量增大,底部厚度和剩余厚度均减小。通过测试接头的拉剪强度、脱落强度,发现两者均随铆速的增大而增大,且脱落强度增幅较小。接头失效形式主要为自锁失效和板材失效两种。铆速对接头成形性能的影响机理,主要由冲压载荷峰值变化和应变速率变化两方面组成。载荷峰值越大,接头成形性越好;应变速率越大,板材加工硬化程度越高且断裂应力越大。     

直升机传动系统复合材料尾传动轴铆接承载能力分析

复合材料具有比强度高和比刚度高的优点,应用于直升机传动系统尾传动轴可有效减轻结构重量。复合材料传动轴与法兰一般采用铆钉连接,铆接区域是尾传动轴的薄弱环节。利用Ansys ACP软件建立复合材料尾传动轴与法兰的铆接分析模型,铆接区域的失效判据采用Tsai-Wu失效准则。当铆接位置的失效区域超出垫片覆盖区域,认为铆接结构失去承载能力。通过与尾传动轴静扭试验结果对比,本文的计算结果与试验结果吻合的很好。     

细观力学模型预测复合材料横向强度性能研究

为了研究纤维增强复合材料在横向拉压载荷下的力学性能,采用细观力学有限元法与随机扰动法建立了表述复合材料微观结构的纤维随机分布代表性体积单元。对于界面脱粘与基体塑性变形这两种主要的损伤模式,分别用界面内聚力单元模型、基体Drucker-Prager弹塑性模型模拟,并结合塑性失效准则模拟基体的初始损伤与断裂,得出了材料在外载作用下的渐进损伤过程,并与试验结果进行了对比验证。此外,还总结了界面刚度、界面强度、界面断裂能等细观参数对损伤本构的影响规律。     

板厚对单钉单剪复合材料接头挤压强度和次弯曲效应的影响分析

接头设计是飞机、汽车和舰船等复合材料结构工程应用的重要内容。针对易发生次弯曲效应的复合材料单钉单剪机械接头,建立含沉头螺栓的机械接头有限元模型,在试验验证模型有效性的基础上,分析对比了层合板厚度对接头挤压失效和次弯曲的影响。发现了薄层合板接头的挤压失效载荷与厚层合板接头的挤压失效载荷相近。同时,在发生挤压失效时,出现了薄层合板接头的次弯曲现象没有厚层合板接头的次弯曲现象严重的现象。考虑到工程中机械接头一般设计为挤压失效模式,本研究所发现的接头失效特征可为工程结构充分发挥复合材料的减重潜力提供一定建议。     

Study of the impact of riveting sequence, rivet pitch, and gap between sheets on the quality of riveted lap joints using finite element method

Sheet metal parts are widely used in the assembly of aircraft. The most common method of joining sheet metal parts is through riveting. There are many parameters associated with a riveting process that affect the quality of rivets and the integrity of the final assembled product. This paper presents a study on the effect of some controllable process parameters in riveting (i.e., the sequence of riveting, distance between rivets (pitch), and gap between sheets) on the quality of riveted lap joints and the formed rivets. The study is performed on a one eight-inch nominal diameter flat head Tinner rivet and 0.064-in.-thick aluminum sheet. Finite element simulation is used as a means of modeling and analysis of the riveting process. Statistical design of experiment is employed to analyze the simulation data. A good combination of riveting process parameters is found which minimizes the residual stress in sheets and rivets, bulging and material growth in sheets, and which reduces the chances of postriveting clearance in a riveted lap joint.     

铝合金板材自冲铆接头的疲劳性能分析

介绍了自冲铆是一种无需预钻孔的薄板新型连接技术及自冲铆的工艺特点。参照国家标准疲劳试验方法,针对5052H32铝合金板材单搭自冲铆接头进行了疲劳试验,测得其疲劳强度为45．9MPa。分析了自冲铆接头的疲劳失效机理,发现微动磨损是导致其失效的主要原因。     

航空结构宽板铆接搭接件承载性能数值研究

为研究飞机蒙皮铆接搭接结构的力学特性,基于ANSYS软件建立宽板三排铆钉搭接件的三维有限元分析模型。考虑物面间的非线性接触、铆钉与板孔间的干涉配合、铆钉预紧力的影响,应用非线性有限元法对宽板铆接搭接件在恒定远端拉伸载荷作用下的承载性能进行计算。通过读取沿预设路径的位移分布数据,获得宽板搭接件产生的次弯曲和第三弯曲的变形趋势。从搭接板等效应力云图可以看出,靠近宽搭接板侧缘的沉头铆钉孔周围应力集中比较严重。计算每个铆钉的钉传载荷,获得宽板搭接件铆钉承载的分布规律。在调整铆钉预紧力和钉孔干涉配合量的情况下,给出三排铆钉载荷传递比的变化情况。针对宽板铆接搭接件的力学特性计算分析,可以为后续的搭接件结构多处损伤裂纹扩展和疲劳寿命研究奠定基础。     

Terahertz spectroscopy approach of the fiber orientation influence on CFRP composite solid laminates

Terahertz ray (T-ray) imaging applications have provided one of the most promising new powerful nondestructive evaluation techniques, and new application systems are under process development for area applications. Detecting flaws and defects in fiber reinforced plastic (FRP) composite laminates due to flaws in FRP composite laminate that affect laminate properties, including stiffness, strength, and thermal behavior, is very important. In this study, a new time-domain spectroscopy system was utilized for detecting and evaluating the flaws in FRP solid composite laminates. Extensive experimental measurements in reflection mode were made to map out T-ray images. In particular, electromagnetic properties, such as refractive index, were estimated in this characterization procedure. The estimates of properties were in good agreement with known data. Using these characteristic material properties, we successfully demonstrated the characteristics of the T-ray behavior propagating through FRP composites. Furthermore, layup effect and flaws of FRP composite laminates were observed in reflection mode, and limitations were discussed in the T-ray processing.     

Characterization of the residual mechanical properties of woven fabric reinforced composites after low-velocity impact

An investigation is undertaken to examine the residual mechanical properties of crowfoot-weave carbon/epoxy laminates subjected to a transverse central low-velocity impact load. It is found that the residual strength and stiffness of impacted laminates decrease with increasing impact damage area. Experimental data indicates that flexural stress constitutes the basis of a failure criterion that also describes damage severity, if localized damage at the region of impact is not serious. By formulating a simple model involving the motion of a rigid impactor, together with fundamental stress analysis of a transversely loaded plate, the effects of impactor mass, impact velocity, impactor tip radius, laminate thickness and lay-up on low-velocity impact damage are identified. Based on the experimental observations, it is found that the residual mechanical properties can be approximated by a linear relationship with a single damage severity parameter Q, where Q is a function of incident impact energy, impactor tip radius and laminate thickness. The theoretical results are verified by experimental data.     

搭接长度对平纹机织复合材料胶接结构连接性能影响的多尺度分析

针对平纹机织复合材料层合板,首先基于均匀化方法确定细观模型的性能参数,其次采用Hashin准则分析细观模型损伤过程,最后引入连续损伤力学模型和内聚力模型建立层合板胶接结构宏观模型。研究结果表明,平纹机织复合材料层合板的数值曲线与试验结果吻合较好,验证多尺度模型的有效性;搭接长度在5～15 mm时,随着搭接长度的增大,单搭和双搭胶接结构的极限失效载荷逐渐增大,并趋于稳定,而搭接剪切强度逐渐减小;单搭和双搭胶接结构的失效形式随着搭接长度的增大逐渐由胶层剪切失效过渡到层间分层失效;相同搭接长度下,与单搭胶接结构相比,双搭结构的极限失效载荷较大。基于均匀化方法、Hashin失效准则、内聚力模型和连续损伤力学模型,提出一种平纹机织复合材料多尺度模型,对结构性能设计和使用寿命具有重要意义。     

Effect of various surface preparation techniques on the delamination properties of vacuum infused Carbon fiber reinforced aluminum laminates (CARALL): Experimentation and numerical simulation

Carbon fiber reinforced aluminum laminates (CARALL) are one of the aluminum based Fiber metal laminates (FMLs) which, due to their high strength to weight ratio and good impact resistance are greatly replacing aluminum alloys in aircraft structures. In this research work, interlaminate shear strength of Vacuum assisted resin transfer molding (VARTM) manufactured CARALL has been investigated. Numerical simulation model incorporated with real time material data has been developed to predict the delamination behavior of CARALL laminates. Standard CARALL specimens with different surface morphologies were prepared by electric discharge machining, mechanical, chemical and electrochemical surface treatments. T-peel tests were carried out according to standard ASTM D1876-08 to find out inter laminate shear strength. FMLs made out of mechanically, chemically and electrochemically cleaned metal sheets depicted high interlaminate shear strength. SEM micrographs of failed surfaces verify the high adhesive strength of epoxy. Developed numerical simulation model accurately predicts the delamination behavior of CARALL as observed during experimentation.     

板料铆接方法及其装置的研究

铆接是一种重要的板料连接技术,开展板料铆接方法的研究具有重要意义。介绍了近年来国内外多种板料铆接的方法和装置,分析了它们的工作原理和特点,归纳了铆接技术目前存在的问题,并指出了其未来研究方向。     

22MnB5高强钢/7075铝合金热铆接冷模具淬火无铆钉铆接研究

针对目前车用22MnB5高强钢和7075铝合金板料在连接工艺上存在的问题,提出一种高强钢和铝合金异种材料车身零件的热铆接冷模具淬火（Hot riveting quenching, HRQ）无铆钉铆接工艺,利用22MnB5在高温下良好的成形性及易淬性,实现对22MnB5高强钢与7075铝合金的有效连接。通过建立HRQ无铆钉铆接的成形和淬冷有限元模型,证明了该工艺的可行性,使铆接后接头的高强钢具有全马氏体组织,保证了接头的强度。并从仿真和试验两方面研究高强钢铆接温度对接头尺寸颈厚值T_n、自锁值T_u的影响,发现在600～800 ℃区间内,T_n和T_u均呈现先上升后下降的趋势,T_u受温度影响更显著,两者均在700 ℃时获得最大值,表明700 ℃是高强钢板料的最佳铆接初始温度。