Z-pin参数对复合材料T型接头拉脱承载能力的影响

利用二维平面应变模型对Z-pin增强T型接头试样进行失效分析,采用内聚力模型模拟界面的破坏情况,通过在分层的上下界面加入非线性弹簧元模拟Z-pin的增强作用,非线性弹簧元的力学性能(桥联律)由细观力学方法获得,数值结果与试验值吻合较好。在已验证有限元方法的基础上,研究了Z-pin直径、密度及植入角度等对T型接头拉脱承载能力的影响。结果表明:Z-pin增强可显著提高T型接头的拉脱承载能力,与未Z-pin增强的T型接头相比,Z-pin增强明显延缓了掉载;T型接头的拉脱承载能力随Z-pin直径和密度的增加而增大,随植入角度的增大而减小;在所研究的角度范围内,当植入角度为60°时,T型接头的拉脱承载能力最好;Z-pin直径和密度对拉脱承载能力的影响远比植入角度的影响显著。     

Z-pin/缝合对复合材料T型接头剪切承载能力的影响

利用三维有限元模型对Z-pin/缝合增强试验件进行有限元分析,采用内聚力模型模拟界面的破坏情况,通过在分层的上下界面加入非线性弹簧元来模拟Z-pin/缝合的增强机制,非线性弹簧元的力学性能（桥联律）由细观力学方法获得。通过与试验结果的对比发现,由于未进行界面增强的T型结构的剪切承载能力已较高,Z-pin/缝合增强较难提高T型接头的剪切承载能力。从少数几种可提高T型接头的剪切承载能力的增强方案中可看到,应选择拉伸强度较高而拉伸模量较低的缝线来进行T型接头剪切界面增强设计。     

填充物、胶膜和Z-pin对复合材料T型接头强度影响对比

为提高复合材料T型接头结构的拉伸强度,对接头中胶膜属性、圆弧区填充物属性和Z-pin增强三种结构参数对T型接头强度的影响进行了研究。设计了两种不同胶膜属性、两种不同填充材料和有无Z-pin的同尺寸试验件,完成拉伸试验,测得极限位移和极限拉伸强度,并进行了对比分析,同时研究了不同T型接头的损伤演化过程。结果表明：J299胶膜复合材料T型接头的极限位移和极限载荷相比于J116B胶膜分别提高了57.8%和64.7%;ZXC195增强芯复合材料T型接头的极限位移和极限载荷相比于单向带材料分别提高了51.7%和30.3%;Z-pin钉对复合材料T型接头的极限位移和极限载荷分别提高了190.8%和31.9%。三种结构参数均只影响接头的极限载荷和极限位移的大小,接头的整体刚度没有改变。胶膜属性对接头极限载荷的提高影响最大,而Z-pin对接头的极限位移提高影响最大。     

Z-pin增强树脂基复合材料单搭接头弯曲性能

为了研究Z-pin对单搭接头弯曲性能的影响,制备了不同参数Z-pin增强单搭接头试样,研究了Z-pin单搭接头在三点弯曲载荷下连接性能.结果表明:Z-pin(直径0.5mm)体积分数从0％～1.5％时,弯曲载荷随Z-pin体积分数的增加而增加,体积分数在1.5％～3.0％范围内时,试样的弯曲载荷随Z-pin体积分数的增加而下降,Z-pin体积分数为1.5％时达到最大值1303.2N;Z-pin直径为0.3～0.7mm时(体积分数1.5％),峰值载荷随着直径的增加而增加,0.7mm增强接头的弯曲载荷比0.3mm增强接头高出27.9％.Z-pin植入角度对单搭接头弯曲性能影响不大.另外,随着搭接长度的增加,单搭接头的弯曲性能提高.     

基于NCF技术的RTM成型复合材料T型接头高效制造与验证

选用多层非屈曲经编织物(NCF)作为增强体, 提高了预成型体的铺覆效率及准确性, 同时根据T型接头的结构特点将其组合成工字梁形式并依此设计成型模具, 采用树脂传递模塑(RTM)成型工艺实现了复合材料T型接头的高效制造, 并对其拉伸和压缩力学性能进行了试验研究。结果表明: T型接头拉伸破坏由孔边蒙皮纤维拉断和腹板分层拉脱造成; 而压缩破坏则由腹板翻边分层屈曲和接头中部蒙皮纤维压断造成; T接头拉伸破坏载荷高于其压缩的破坏载荷。     

缝合复合材料T型加筋壁板的抗剪与抗弯性能

为了防止复合材料T型加筋壁板在服役过程中因剪切和弯矩作用而发生筋条与蒙皮的脱粘失效,引入了缝合技术来提高筋条-蒙皮界面的结合性能.采用自主研发的单线弯针缝合设备来缝合干纤维,通过真空辅助树脂灌注技术(VARI)固化成型,脱模后制成缝合T型加筋壁板试样.通过对试样进行剪切和弯曲试验,研究缝合的增强机理以及缝线细度对T型接头性能的影响规律.结果表明:在剪切应力作用下,缝合试样的峰值载荷比未缝合试样有明显提高,随着缝线细度增大,T型接头的峰值载荷升高,缝线细度增大到1 500 D时,峰值载荷提高55. 0% .在弯曲应力作用下,随着缝线细度的增大,T型接头的峰值载荷先升高后降低.缝合对T型接头在两种不同应力下的初始损伤载荷均无明显影响.     

X状Z-pin增强泡沫夹层结构的剪切性能

通过不同Z-pin角度(15°和25°)和夹芯厚度(8mm和12.7mm)的X状Z-pin增强泡沫夹层材料的剪切性能试验, 与相同材料同尺寸的未增强件进行对比, 考察X状Z-pin对泡沫夹层结构的增强作用。试验结果表明, X状Z-pin增强使材料的剪切强度和刚度都有较大幅度的提高; 同时, Z-pin的加入使该结构具有与传统泡沫夹层材料不同的剪切破坏形式。在此基础上, 结合空间网架结构和等效夹杂方法, 提出了X状Z-pin增强泡沫夹层结构剪切刚度模型, 计算结果与试验值符合良好。结果表明, X状Z-pin增强不仅能大幅度提高泡沫夹层结构的剪切性能, 并具有良好的可设计性, 可以通过改变Z-pin角度和材料等改变其力学性能。      

Z-pin增强复合材料层合板断裂韧性试验研究

针对Z-pin增强复合材料层合板, 开展了断裂韧性的试验研究。研究选取了3种Z-pin直径(0.28、 0.52、 0.80mm)且每种直径下分别以3种分布形式(5×5、 8×8、 10×10)排布Z---pin的增强方式, 为了确定比较基准, 试验中同时测试了不含Z-pin的复合材料层合板试样。通过Z-pin拔出试验测试了3种直径Z-pin从基体拔出过程中的载荷位移关系。利用双悬臂梁试验和端部开口弯曲试验分别测试了不含Z-pin和含Z-pin试样的Ⅰ型断裂应变能释放率G_ⅠC、 Ⅱ型断裂应变能释放率G_ⅡC。试验结果表明:? 与不含Z-pin的结构相比, Z-pin增强试样的Ⅰ型断裂应变能释放率G_ⅠC增大了83%~1110%, Ⅱ型断裂应变能释放率G_ⅡC增大了23%~438%; 在相同Z-pin体积含量下, 与增大Z-pin直径相比, 增大Z-pin分布密度能更有效地提高复合材料层合板的断裂韧性。      

复合材料蜂窝夹层结构T型接头拉伸性能研究

通过试验测量了复合材料蜂窝夹层结构T型整体接头的拉伸性能,得到其拉伸强度与破坏模式。建立了接头结构有限元模型,利用分类损伤判据、失效准则与刚度退化准则对结构的损伤情况进行模拟,研究了接头的拉伸破坏行为。有限元分析结果与试验结果吻合良好。研究结果表明,结构的薄弱点位于腹板内靠近蒙皮的位置。蜂窝在此处发生面外拉伸破坏,从而导致结构的最终破坏。腹板上的拉伸载荷主要通过过渡区填料传递给蒙皮,腹板与蒙皮间的搭接段对载荷传递的贡献较小。参数研究表明,对于复合材料蜂窝夹层结构T型接头,搭接段长度对结构的强度几乎没有影响,而增大蒙皮蜂窝的高度或采用低模量蜂窝可以提高结构强度。     

RTM成型非对称复合材料T型接头的拉伸失效机制

采用树脂传递模塑(RTM)工艺制备了结构对称和非对称两种复合材料T型接头试样,并对其进行了静态拉伸力学试验,对比分析了两种结构的拉伸破坏模式、结构刚度及破坏载荷。同时基于T接头内聚力模型(CZM),研究了两种不同结构T型接头的拉伸破坏过程及失效机制,并对比分析了不同偏转角下T接头的层间应力。结果表明：不同结构T型接头的拉伸破坏模式不同,偏转角的存在使结构非对称T型接头夹角大侧圆弧受力明显高于小侧圆弧,导致接头首先在大侧夹角圆弧与三角区界面定向萌生初始裂纹,随后裂纹主要沿大侧腹板翻边与蒙皮的界面扩展,进而导致接头最终破坏,最终失效载荷较对称T型接头提高了15.3%,且结构刚度更大。有限元结果表明T型接头三角区的初始失效主要由层间正应力及剪应力引起,有限元分析的失效模式与试验一致,结构对称及非对称T型接头最终失效载荷与试验值均吻合较好;且随着偏转角的增加,腹板圆弧处层间应力逐渐减小,初始失效载荷将随之增大;初始破坏位置将转移至大侧夹角圆弧末端。     

Strengthening mechanics of thin and thick composite T-joints reinforced with z-pins

This paper presents an experimental and analytical study into the importance of the skin–flange thickness on the strengthening mechanics and fracture modes of z-pinned composite T-joints. The structural properties of unpinned and z-pinned carbon fibre–epoxy T-joints that had skin–flange thickness values between 2 mm (thin) and 8 mm (thick) were determined under tension (stiffener pull-off) loading. Experimental testing revealed that the capacity of z-pins to improve the structural properties was strongly dependent on the T-joint thickness. The joint properties increased at a quasi-linear rate with the skin–flange thickness, and z-pin pull-out tests showed that this was due to the increased crack bridging traction load and traction energy. The increase to the structural properties of the z-pinned T-joints with increasing thickness is explained using the bridging traction laws for z-pinned laminates.     

工艺参数对聚甲醛微注塑制品力学性能的影响机理EI北大核心CSCD

基于单因素实验,研究工艺参数对不同厚度聚甲醛(POM)微注塑制品屈服应力、弹性模量、断裂强度和断裂伸长率等力学性能指标的影响,并基于制品形态结构分析工艺参数对制品力学性能的影响机理。实验结果表明,随着注射速度的增大,1.0mm厚微制品的皮层厚度减小,过渡层厚度增加,结晶度增大,综合效应使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小;0.2mm厚微制品的皮层厚度占主导地位,其力学性能是由皮层的力学性能决定,皮层厚度先增大后减小使得屈服应力、断裂强度和弹性模量先增大后减小,断裂伸长率先减小后增大。随着熔体温度的升高,1.0mm厚微制品的分子链取向度减小,皮层厚度减小,收缩量增大,使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大;而0.2mm厚微制品的皮层减小,但过渡层增加,结晶度增大,且补料更充分,综合作用使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小。随着模具温度的升高,1.0mm厚微制品的皮层比例减小,结晶度增大,结晶度影响占主导,使得屈服应力、断裂强度和弹性模量逐渐增大,断裂伸长率减小;而0.2mm厚微制品的皮层厚度占主导,皮层厚度明显减小使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大。     

负载条件下CFRP加固轴心受压钢管短柱受力性能研究

该文以试验、有限元与理论相结合的方法研究CFRP(碳纤维)布加固轴心受压钢管短柱构件;以不同负载百分比、不同CFRP粘贴方式为对比参数,研究了加固后构件的受力性能。主要讨论了对于不同负载程度、CFRP粘贴方式对加固后构件极限承载力和破坏形态的影响。通过试验与有限元数值模拟及参数分析,得到随着负载百分比的增大,加固后构件极限承载力呈下降趋势,在极限状态下,构件的破坏形态主要为端部局部屈曲破坏;在构件端部粘贴CFRP的加固效果优于中部加固效果;随着CFRP加固层数的增大,构件极限承载力随之增大,但增大百分比在达到一定程度后呈现下降趋势;随着构件厚度的增大,负载百分比和CFRP层数对构件承载力的影响呈下降的趋势,通过理论与试验和有限元结果的对比分析,得出采用该文所推导的理论可以用于负载条件下加固构件的承载力计算。     

Indentation study of Z-pin reinforced polymer foam core sandwich structures

Z-pin reinforced foam core sandwich panels with composite face sheets, supported on a rigid base and subjected to quasi-static indentation using spherical indenter was studied in this paper. The effects of configurations of Z-pin, including inclination angle and pinning density, on the load–indentation response were studied, and the resulting damage modes were investigated. The effect of inclination angle of pin on the load–indentation behavior is not notable compared with those of Z-pinning density and Z-pin configuration. The collapse of Z-pinned foam core is due to the buckling of pin, and the pin buckling is significantly dependent on the location of indenter. An approximate solution was developed based on the principle of minimum potential energy to simulate the indentation damage response of Z-pin reinforced foam core sandwich. The analytical predictions compare well with the experimental results.     

Numerical analysis of ductile failure of undermatched interleaf in tension

Ductile failure of an interleaf tension specimen consisting of a metal interleaf bonded between two elastic substrates, with a crack located in the centre of the metal, is studied by means of detailed finite element (FE) analyses. The rate-independent version of the Gurson model is used. This accounts for ductile failure mechanisms of micro-void nucleation, growth and coalescence within the framework of a finite deformation plasticity theory. Also, the rapid evolution of void density due to coalescence, which leads to ultimate failure, is considered. The effect of the interleaf thickness on failure (crack initiation and limited amount of crack growth) is investigated. The results show that the interleaf thickness affects crack initiation only slightly. For all specimens considered, crack initiation takes place at the crack tip. However, after crack initiation, the interleaf thickness affects stress and strain distributions significantly. Reducing the interleaf thickness significantly increases the load-carrying capacity. Moreover, reducing the interleaf thickness increases the maximum hydrostatic stress in the interleaf, which is no longer developed at the crack tip but at a distance far away from the crack tip. The resulting fracture toughness thus decreases as the interleaf thickness decreases. The shielding of the crack tip due to constrained plasticity is observed at higher load levels for interleaf specimens. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modeling and predicting the compression strength limiting mechanisms in Z-pinned textile composites

Motivated by experimental results on Z-pinned plain weave glass fiber textile composites that show kink banding of fiber tows to be a strength limiting mechanism of failure in compression, computational results are presented for the effects of Z-pin diameter and Z-pin density on compression strength. Distortion to the textile fiber tows introduced by the insertion of Z-pins is found to be the dominant cause for initiating kink bands while the type of bond between the Z-pin and the surrounding matrix is found to influence the post-kinking response. When the Z-pin diameter remains unchanged, the composite strength decreases as the Z-pin density increases, while, when the Z-pin density is fixed, the composite strength decreases as the Z-pin diameter decreases in agreement with experimental observations.