典型螺栓连接CFRP薄壁C型柱轴压失效行为:试验及数值模拟

为了研究典型螺栓连接碳纤维增强树脂复合材料(CFRP)薄壁C型柱的轴压失效模式及吸能特性,进行了5组不同铺层方式C型柱的准静态轴压试验,即[0/90]_4s、[±45]_4s、[±45/90₂/0₄]_s、[±45/90/0₂/90/0₂]_s、[90/±45/0]_2s,获得其失效形貌及载荷-位移曲线。采用Lavadèze单层壳单元模型、Puck-Yamada失效准则、层间胶粘单元及螺栓模型,建立C型柱层合壳模型进行轴压仿真,并与试验失效形貌、载荷-位移曲线及吸能特性评估指标进行对比分析。结果表明:0°、±45°、90°纤维可以显著影响C型柱轴压失效模式及吸能特性。在轴压载荷下,±45°纤维铺设C型柱发生局部屈曲失效模式,吸能特性差。±45°纤维铺设在外部,0°和90°纤维交替铺设在内部的C型柱,其轴压失效过程平稳,吸能特性好。与C型柱轴压试验结果相比,层合壳模型获得的整体变形和局部失效形貌吻合较好,载荷-位移曲线变化趋势和吸能特性评价指标基本一致。研究结果对CFRP薄壁C型柱吸能设计具有一定的指导意义。      

纤维铺层角度对复合材料薄壁圆管轴向压溃吸能特性影响研究

研究T700/3234复合材料薄壁圆管轴向压溃吸能特性受纤维铺层角度变化的影响规律。开展复合材料力学性能试验和薄壁圆管轴向准静态压溃试验。通过对比圆管轴向压溃峰值载荷及比吸能等指标的试验结果,验证建立的复合材料圆管有限元模型和分析方法。基于验证的有限元分析方法,探讨了复合材料纤维铺层角度的变化对薄壁圆管轴向压溃吸能特性的影响规律。结果表明,在准静态轴向压缩载荷下,随着纤维铺层角度的增大,比吸能先增大后减小;纤维角度为±45°时,初始峰值载荷最低,载荷效率最高,圆管易于进入渐进破坏吸能阶段。研究结果可为复合材料纤维铺层角度设计及复合材料薄壁结构有限元建模提供参考。     

复合材料层合结构破坏机理及压溃吸能特性分析

针对纤维增强复合材料层合试验样件,对[90]_(16)和[0]_(16)试验样件分别进行拉伸、压缩试验,对[±45]_(4s)试验样件进行剪切试验,分析其破坏模式,通过SEM扫描电镜观察试验样件断口微观形貌,揭示其细观破坏机理。针对纤维增强复合材料层合薄壁结构,对[±45/0/0/90/0]_s圆管、[0/90]_(3s)圆管、[0/90]_(3s)方管和[±45]_(3s)方管进行准静态轴向压溃试验,分析其宏观破坏模式及吸能特性。结果表明:宏观破坏模式是多种细观破坏机理共同作用的结果,包含纤维断裂、基体变形与开裂、层间与层内裂纹扩展等;[±45/0/0/90/0]s圆管为横向剪切破坏模式,比吸能最大;[0/90]_(3s)圆管为层束弯曲失效模式,比吸能次之;[0/90]_(3s)方管为层束弯曲失效模式,比吸能第三大;[±45]_(3s)方管为局部屈曲失效模式,比吸能最小。不同铺层方式复合材料层合薄壁圆管和方管压溃破坏失效模式差异较大,比吸能差距也较大,通过合理设计可以改变复合材料层合薄壁结构破坏模式,改进其吸能特性。     

复合材料层合板端部压溃试验研究EI北大核心CSCD

通过对T800复合材料层合板进行一系列的端部压溃试验,重点研究了长度、厚度、铺层顺序、触发角以及胶结压力等因素对复合材料层合板破坏模式和力学性能的影响。分析复合材料板在端部压溃过程中的载荷-位移曲线和观察试验样件端部破坏形貌,揭示其破坏机理。结果表明:复合材料平板的端部压溃过程为非稳态脆性断裂模式,而含45°触发角的复合材料层合板的端部压溃过程为层束弯曲破坏模式;在端部压溃试验中复合材料平板压缩强度随着厚度的增加逐渐上升,而长度的增加会减少其压缩强度,同时[45°/0°/-45°/0°]_(3s)铺层比[45°/90°/-45°/0°]_(3s)铺层拥有更好的抗轴向承载能力;触发角的加入会改变试件在压溃过程中的破坏模式并极大降低试件压溃时的压缩强度,是影响复合材料结构吸能能力的关键因素;研究还发现不同胶结压力下,复合材料层板的力学性能随着胶结压力的增加逐渐提高,但达到一定胶结压力值后,继续增加胶结压力力学性能反而下降。     

变刚度碳纤维/环氧树脂复合材料薄壁圆管轴向压溃响应与破坏机制

通过控制缠绕线型改变轴管纤维角度,制备了一种轴向刚度渐变、压溃稳定的碳纤维增强树脂基复合材料(CFRP)变刚度薄壁圆管。对变刚度、[±45°]_n以及[90°]_n三类CFRP缠绕轴管进行轴向准静态压缩测试,结合数字图像相关技术(DIC)及有限元结果,对比三类结构压溃初始应变模式、损伤演化与应力状态结果,研究了变刚度结构的压溃响应与破坏机制。结果表明:不同纤维角度CFRP轴管因轴向刚度不同,压溃的初始破坏与损伤演化过程相异,三类结构产生不同的压溃响应与破坏模式。变刚度区连续变化的大角度纤维能有效地引发分层和"开花式"混合破坏,缓慢释放应变能,使变刚度CFRP轴管吸能效果明显优于其他两类结构。其峰值载荷为66.97 kN,压溃效率为50.8%,比吸能为10.1 kJ/kg,相对于[±45°]_n结构比吸能提升156.35%,压溃效率提升518.76%,相对于[90°])n结构比吸能提升16.9%,压溃效率降低27.3%。     

不同粒子改性环氧树脂基碳纤维复合材料低速冲击及冲击后压缩性能

使用单层纳米氧化石墨烯(GO)、纳米SiO2、陶瓷粉对环氧树脂进行改性处理,采用真空辅助树脂传递模塑成型(VARTM)工艺分别制备了[±45/0/90]S、[908]T、[08]T三种铺层角度下的碳纤维增强复合材料(CFRP)层合板.通过落锤冲击实验、超声C扫描检测、冲击后压缩实验等对不同粒子改性CFRP进行实验研究.结果表明:纳米粒子改性可以显著提升CFRP的抗冲击性能及冲击后压缩性能,与其他铺层角度相比,[±45/0/90]S铺层CFRP有效抑制了冲击裂纹的扩展,且单层纳米GO改性下的[±45/0/90]S铺层层合板最大冲击载荷及冲击后压缩强度分别达到3470 N、124.8 MPa,冲击损伤面积仅有580 mm2.与无粒子改性同种铺层层合板相比,最大冲击载荷及冲击后压缩强度相应提高了30％、47.3％,冲击损伤面积减小了15.5％.     

复合材料翼面壁板剪切稳定性

基于长桁铺层数不同的两块复合材料翼面T型加筋壁板试件SS-1和SS-2开展剪切稳定性试验。试件SS-1和SS-2的L型层合板铺层分别为11层和14层,腹板铺层分别为22层和28层,缘条铺层分别为15层和18层。采用提出的工程方法进行壁板的剪切屈曲应变分析,方法中考虑了长桁尺寸和铺层数的影响,并应用有限元弧长法进行试件屈曲载荷、后屈曲承载能力及剪切屈曲模态分析。试验结果表明,屈曲发生之前试件蒙皮处于均匀纯剪切应变状态,后屈曲阶段试件发生了长桁-蒙皮脱粘破坏失效,长桁铺层数较多的试件SS-2具有更高的屈曲载荷和蒙皮局部屈曲应变。工程方法计算得到试件SS-1和SS-2的剪切屈曲应变相对于试验结果的误差分别为–14.9%和–9.2%。有限元弧长法分析得到试件SS-1的屈曲载荷和屈曲应变误差分别为1.9%和2.7%,且剪切屈曲模态与试验结果一致。弧长法对不同长桁铺层数的研究结果表明,长桁铺层较少时,壁板发生整体失稳的材料破坏,而长桁铺层数较多时,更容易发生长桁与蒙皮的脱粘失效。      

复合材料波纹板准静态轴压性能试验及数值模拟

以[+45/-45]_(4s)和[0/+45/-45/0]_(2s)碳纤维增强复合材料波纹板为研究对象,通过准静态轴压试验获得其失效形貌及载荷-位移曲线;通过CT扫描分析其破坏机理,基于吸能特性评价指标进一步研究其吸能特性。针对[0/+45/-45/0]_(2s)波纹板,建立考虑层间模型的多层壳模型进行轴压仿真,通过对比失效形貌、载荷-位移曲线及吸能特性评价指标来验证有限元模型。试验结果表明:[+45/-45]_(4s)波纹板出现整体失稳现象,材料利用率较低导致其吸能特性较差,且试验获得的比吸能的离散系数大于15%,试验重复性较差。[0/+45/-45/0]_(2s)波纹板为典型的层束张开失效模式,材料利用率较高导致其吸能特性较好,吸能特性评价指标的离散系数均小于15%,具有良好的轴压稳定性与可重复性。在±45°纤维铺层中增加0°纤维铺层,可改变其轴压失效模式,并显著提升其轴压吸能特性。仿真结果表明:多层壳模型能较好地复现[0/+45/-45/0]_(2s)波纹板轴压过程及层束张开失效模式;同时仿真获得的比吸能比试验均值高2.27%,能较好地复现[0/+45/-45/0]_(2s)波纹板轴压吸能特性,从而验证了多层壳模型。     

铺层顺序对复合材料薄壁圆管轴向压溃吸能特性的影响研究

采用仿真和试验相结合的方法探讨复合材料薄壁圆管在准静态轴向压缩载荷下的失效吸能特性和吸能机理。首先,建立复合材料薄壁圆管\     

UHMWPE波纹结构复合材料抗压及抗冲击性能研究

以超高分子量聚乙烯(UHMWPE)UD布为原料,采用模压成型工艺制备UHMWPE波纹结构复合材料。研究不同工艺下复合材料的界面强度、结合载荷-位移曲线及试样的损伤模式,分析不同铺层方式对试样压缩和冲击性能的影响。结果表明,UHMWPE波纹板吸能的主要方式是整体结构屈曲变形,[0°/90°]铺层数量的增多能够提高波纹板的整体承载能力,通过波纹板内部加入[45°/-45°]铺层可增加波纹板的吸能能力。     

Piezoresistive effect of plain-weave CFRP fabric subjected to cyclic loading

The present study deals with electrical resistance changes in woven-fabric CFRP during loading. Four kinds of plain weave woven-fabric CFRP laminated specimens are prepared and subjected to cyclic tensile loading that does not cause any damages, and the electrical resistance changes of the specimens are measured experimentally by the four-probe method. As a result, the present study shows that the electrical resistance of a specimen comprised of six ±45° plies decreases remarkably with increasing number of loading cycles. The decrease is caused by shear plastic deformation of ±45° plies. The thickness shrinkage caused by shear plastic deformation increases the number of fiber contacts, and this decreases the interlaminar contact resistance between the plies. For a single ±45° ply, the same electrical resistance decrease caused by the shear plastic deformation is observed, and the magnitude of the decrease is smaller than that of the six-ply laminate tested. This is because the effect of interlaminar contact resistance decrease does not exist for a single ±45° ply. For the six 0°/90° plies, the present study shows that electrical resistance in the through-thickness direction is decreased by out-of-plane plastic deformation of carbon fiber and misalignment of the plies.     

Failure mechanisms of a notched CFRP laminate under multi-axial loading

A quasi-isotropic CFRP laminate, containing a notch or circular hole, is subjected to combined tension and shear, or compression. The measured failure strengths of the specimens are used to construct failure envelopes in stress space. Three competing failure mechanisms are observed, and for each mechanism splitting within the critical ply reduces the stress concentration from the hole or notch: (i) a tension-dominated mode, with laminate failure dictated by tensile failure of the 0° plies, (ii) a shear-dominated mode entailing microbuckling of the −45° plies, and (iii) microbuckling of the 0° plies under remote compression. The net section strength (for all stress states investigated) is greater for specimens with a notch than a circular hole, and this is associated with greater split development in the load-bearing plies. The paper contributes to the literature by reporting sub-critical damage modes and failure envelopes under multi-axial loading for two types of stress raiser.     

Static Behaviour of Transversely Loaded CFRP Laminate Panels Subject to In-Plane Tension

Abstract: Static tests with various in-plane loads from 0 to 30 kN were conducted, to study in- plane load effects on the static behaviour of CFRP laminated composite panels when subjected to transverse load. The panels were 32 ply with the unidirectional carbon epoxy plies in a quasi-isotropic lay up. It is shown that panel stiffness and maximum load increase with increasing in-plane load and that a failure mode transition occurs with increasing in-plane load. It is also shown that the energy absorbed by the panel to failure is approximately constant with respect to in-plane load. Experimental information on load v deflection histories, surface strain histories and different failure modes together with material properties are presented in the paper, which could be used for analytical and numerical simulations of the problem.     

铺层取向误差对CFRP可折叠管件半片变形影响的数值分析与试验研究

以单层厚度为0.04mm的碳纤维/树脂(T300/5228,CFRP)超薄单向预浸料,采用真空袋-固化炉成型方法制备了一系列不同铺层复合材料"Ω"型可折叠管件半片,并采用ANSYS软件进行了有限元分析,通过实验和数值模拟方法研究了铺层方式及取向误差对变形的影响,制备的四种铺层方式制件实验测量其变形趋势与相应模拟分析结果一致,得到了铺层取向误差对变形影响较小的铺层方式。研究发现:±45°铺层比0°铺层的铺层取向误差对变形影响更大,增加90°铺层可以在一定程度上控制因铺层取向误差导致的可折叠管件半片的变形。研究结果表明通过铺层设计可以在一定程度上实现对CFRP可折叠管件半片变形的控制。     

飞机用复合材料斜胶接修补结构的冲击损伤

高传力效率的斜面式胶接在飞机复合材料传力接头和修补中被广泛使用,但该结构的低速冲击损伤阻抗和损伤容限未在飞机结构设计中考虑。本文研究了低速冲击下的较厚的复合材料斜胶接板的力学性能及损伤失效。在胶接区域布置不同冲击点,寻找最敏感位置,在该位置进行冲击能量变化研究,通过冲击响应（冲击载荷、挠度、能量等）及冲击损伤两个方面获取其规律和失效机制。小能量和大能量冲击结果表明,胶接区域5个典型冲击位置中,中心位置冲击损伤最大,冲击敏感性最高,因此中心点为冲击损伤阻抗最小位置。中心点不同能量冲击时,冲击响应研究揭示了冲击过程中冲击载荷具有典型的4阶段行为。冲击载荷还具有双峰值力的现象。冲击后沿试样中心线切开的显微损伤图揭示了该结构有两种损伤模式,包括复合材料损伤及胶层损伤。复合材料的损伤包含90°和45°层基体的开裂和0°与90°层之间的层间损伤。胶层损伤出现在试样冲击点正下方背部的复合材料斜接尖端部位。进一步通过考虑复合材料层内、层间损伤及胶层损伤的渐进损伤模型对试验进行仿真研究,找出导致第Ⅱ阶段冲击载荷突降的主要原因为复合材料层间损伤,第Ⅳ阶段冲击载荷再一次突降是由于胶层出现了损伤。     

The effect of environment on the compression strength of notched CFRP — a fractographic investigation

Compression strength tests were carried out on notched 0° ± 45° CFRP coupons under various environmental conditions. In addition, the fracture of a number of specimens was arrested to minimize post-failure damage and thus facilitate fractographic analysis. The investigation revealed three basic environment-related failure modes. Significant compressive notch sensitivity occurred only under hot-wet conditions and, apart from this condition, laminates in which axial plies were distributed singly were weaker than those in which the 0° plies were in groups of two or three.     

含拼接铺层碳纤维增强树脂复合材料拉伸破坏机制

对于尺寸较大或形状复杂的结构,通常需要在纤维增强树脂（FRP）复合材料内部对铺层进行拼接处理。铺层拼接会在材料内部引起复杂的应力分布,具有突出的安全隐患。以同一位置处出现不同层数铺层拼接的单向碳纤维增强树脂（CFRP）复合材料为研究对象,重点分析了铺层拼接对材料拉伸力学性能的影响机制。通过拉伸实验,测试了拼接对其力学强度的影响;用相机记录了破坏过程,并结合数字图像相关技术（DIC）对拼接位置附近的应变场进行了监测。利用有限元模型（FEM）模拟和分析结构的破坏机制,采用3D-Hashin准则和渐进损伤模型对CFRP复合材料铺层进行模拟;采用内聚力模型对胶层失效行为进行描述。实验结果表明,拼接结构的引入大幅降低了材料的抗拉强度。FEM模拟与实验测试结果吻合度高,说明了模型的有效性。综合实验结果和模拟分析得到,铺层拼接处产生应力集中,造成被拼接的两部分分离并伴随拼接铺层和连续铺层的层间剪切破坏;层间破坏发生后,拉伸载荷完全由连续铺层承载。因此,材料的最终承载能力由材料中连续铺层数决定。      

Full-field assessment of the damage process of laminated composite open-hole tensile specimens. Part II: Experimental results

The present paper deals with the investigation of the damage process of glass–epoxy quasi-isotropic laminated open-hole tensile test specimens. The effect of the scaling of ply thickness was also studied, comparing two lay-ups with the same global thickness, with ply-level scaling (PL) [−45₄/90₄/45₄/0₄]_s and sublaminate scaling (SL) [−45/90/45/0]_4s. The grid method was used to provide full-field displacements and strains at the surface of the specimen. It was shown that the cracks could easily be picked up by the method and that it was possible to follow the crack opening as a function of load as the tests proceeded. Moreover, processing the strain maps, it was possible to detect a non-linear behaviour of the material caused by the onset of subsurface cracks in the 90° plies. Finally, the difference between the two lay-ups was underlined. The PL specimens sustained much lower loads to first surface cracking than the SL specimens. It was clearly shown for both specimen types that before the onset of surface cracking, significant subsurface cracking occurred at the hole in the 90° plies. However, because of the higher loads sustained by the SL specimens, subsurface cracking in the 90° plies occurred not only at the hole but also away from the hole.     

Prediction for progression of transverse cracking in CFRP cross-ply laminates using Monte Carlo method

This study predicted transverse cracking progression in laminates including 90° plies. The refined stress field (RSF) model, which takes into account thermal residual strain for plies including transverse cracks is formulated, and the energy release rate associated with transverse cracking is calculated using this model. For comparison, the energy release rate based on the continuum damage mechanics (CDM) model is formulated. Next, transverse cracking progression in CFRP cross-ply laminates including 90° plies is predicted based on both stress and energy criteria using the Monte Carlo method. The results indicated that the RSF model and the CDM model proposed in this study can predict the experiment results for the relationship between transverse crack density and ply strain in 90° ply. The models presented in this paper can be applied to an arbitrary laminate including 90° plies.