引发机制对复合材料波形梁吸能性能的影响及其破坏形貌分析

复合材料正弦波形梁作为复合材料结构2功能一体化的典型构件 , 在结构高强、 高刚和稳定的前提下 ,其压溃峰值应力和稳态损毁吸能行为是设计结构件的关键性能指标 , 而这两个指标与梁的引发机制密切相关。本文中设计了根部打孔削弱机制、 根部预埋倒角机制、 根部非对称梯度削弱和根部对称梯度削弱机制等 3 种不同引发机制 , 通过对正弦波形梁的静态压溃实验及对压溃梁的宏观和微观形貌分析 , 发现引发机制对正弦波形梁的失效引发和稳态损毁模式影响很大 , 根部预埋倒角正弦波形梁的失效引发和稳态损毁吸能效果最好。     

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\     

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%。     

碳纤维截面特性对碳纤维/环氧树脂复合材料压缩强度的影响

基于压拉平衡为特征的新一代先进复合材料的需求,开展了碳纤维截面形状和尺寸对碳纤维/环氧树脂复合材料压缩强度的影响研究。有限元模拟和试验结果均表明,增大碳纤维直径可以提高复合材料压缩强度。另外碳纤维截面形状也对复合材料压缩强度有影响,圆形截面优于椭圆形截面。      

蠕变对SMC复合材料动态粘弹性能的影响

本文采用蠕变－振动实验方法，对一种ＳＭＣ短纤维增强复合材料，考察了在不同加载时间和温度下恒载蠕变对其动态力学参量的影响，拟合了该材料的本构关系。实验结果表明：经不同时间和温度下蠕变变形后，其动态弹性模量Ｅ都产生不同程度的下降，其损耗因子ｔｇδ都呈上升趋势。随着蠕变时间的延长和温度的提高，它们的相对改变量变化越大。但在常温下动态弹性模量随蠕变时间无明显变化；在随温度上升中，损耗因子对不同的蠕变时间…     

复合材料吸能圆管在半圆凹槽触发机制下的斜向压溃失效行为

有效的触发机制能诱导并改善复合材料吸能结构的轴向渐进压溃行为,但仍无法解决汽车吸能结构在斜向冲击载荷下的失稳问题。为了提出新的设计来改善失稳行为,对复合材料吸能圆管在半圆凹槽触发机制下的斜向压溃行为和失效机制进行研究。建立引入半圆凹槽触发机制的圆管有限元模型,采用界面和层内非线性损伤演化模型来模拟其真实的压溃失效模式。通过对比模拟和实验对应的轴向压溃载荷、吸能和失效模式来验证圆管的准静态压溃模型。进而,预测斜向压溃角度(10°～50°)对圆管在半圆凹槽触发机制下压溃行为的影响,并详细揭示其轴向和斜向压溃失效机制及其区别。结果表明,压溃载荷、吸能及失效面积随角度增大而明显减小,不稳定的压溃过程使材料失效耗能不充分。圆管在轴向压溃下表现为渐进破坏,而在斜向压溃下以“渐进破坏”向“失稳破坏”过渡为特征,导致斜向压溃载荷与吸能曲线均存在一个过渡。本研究加深了对圆管在外部触发机制下斜向压溃失效机制的理解,为改善斜向压溃失稳行为提供了一定的设计依据。     

碳/环氧管件的低温热膨胀系数测试研究

介绍了采用千分表测量碳/环氧复合材料管件低温热膨胀系数的测试方法,对于管件轴向和径向等不同方向的热膨胀系数测试,采用了不同的测试装置。叙述了测试过程及注意事项,指出了对管件进行热膨胀测试时,不应该采用传统的从管件取出小件试样进行测试的方法,两者数据存在较大差别。另外还讨论了管件低温热膨胀测试数据的规律、影响因素,分析了测量误差影响因素如顶杆带来的误差等,提出了解决方法。对于多次测量的碳纤维复合材料低温热膨胀测试数据逐渐减小问题,进行了初步探讨和分析。给出了某种工艺的碳纤维复合材料管件热膨胀系数与温度曲线。     

Al2O3涂层碳纤维/环氧基复合材料的性能研究

采用溶胶-凝胶法在碳纤维的表面涂覆了一层Al2O3涂层,透射电镜分析表明涂层中粒子的大小约为10nm,接触角分析表明涂层后碳纤维的表面张力有大幅提高.通过比较涂层前后碳纤维/环氧复合材料的力学性能发现,Al2O3涂层后复合材料的层间剪切强度,拉伸强度和弯曲强度分别提高了17.7%,4.8%和3.1%.扫描电镜分析表明,Al2O3涂层后的碳纤维与环氧树脂基体的结合更加紧密.且在碳纤维表面形成的Al2O3涂层在350℃～700℃能有效地减缓碳纤维环氧基复合材料的氧化失重速率.     

碳纤维/环氧超厚度复合材料壁板的固化工艺优化及性能

为制定适用于大厚度环氧基碳纤维增强复合材料的固化制度,首先采用热分析方法对预浸料的固化行为进行了详细的研究,结合预埋热电偶的方法在线监测了不同厚度的壁板在等速率升温条件下的固化过程,通过系统的研究,并提出了增加缓慢升温阶段的固化制度。文中对固化制度优化后的大厚度复合材料制件的进行了超声C扫描检测和内部微观结构等分析,结果证明,采用在120℃和150℃缓慢升温的方式可以有效地控制大厚度复合材料制件内部的固化集中放热现象,并可大幅度提高制造过程中的温度均匀性。采用上述工艺,有望得到质量优异的大厚度复合材料制件。     

On the Collapse of Cotton/Epoxy Tubes under Axial Static Loading

Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments.     

泡沫铝填充薄壁金属管结构冲击吸能特性研究

目的 为了研究静动态加载下泡沫铝填充薄壁金属管结构吸能特性随泡沫铝密度的变化规律。方法利用材料试验机对3种不同密度的泡沫铝填充薄壁金属管结构进行准静态压缩,利用Taylor–Hopkinson实验装置对相同结构进行动态压缩实验,基于电测和光测法获得结构的静动态压缩载荷位移曲线,对载荷位移曲线进行积分得到结构的静动态吸能特性。结果 准静态压缩下,随着泡沫铝密度的增加,泡沫铝填充薄壁管结构能量吸收能力近似成指数增加。动态压缩下,结构能量吸收能力随泡沫铝密度增加先保持不变后增加。结论 准静态压缩下,在薄壁金属管中添加泡沫铝能明显增加泡沫铝填充薄壁金属管结构能量吸收能力,但在动态压缩下,低密度泡沫铝的添加无益于增加结构的能量吸收能力,为增加薄壁金属管的吸能能力需要求泡沫铝的密度超过一定值。     

The Effects of Triggering Mechanisms on the Energy Absorption Capability of Circular Jute/Epoxy Composite Tubes under Quasi-Static Axial Loading

The usage of composite materials have been improving over the years due to its superior mechanical properties such as high tensile strength, high energy absorption capability, and corrosion resistance. In this present study, the energy absorption capability of circular jute/epoxy composite tubes were tested and evaluated. To induce the progressive crushing of the composite tubes, four different types of triggering mechanisms were used which were the non-trigger, single chamfered trigger, double chamfered trigger and tulip trigger. Quasi-static axial loading test was carried out to understand the deformation patterns and the load-displacement characteristics for each composite tube. Besides that, the influence of energy absorption, crush force efficiency, peak load, mean load and load-displacement history were examined and discussed. The primary results displayed a significant influence on the energy absorption capability provided that stable progressive crushing occurred mostly in the triggered tubes compared to the non-triggered tubes. Overall, the tulip trigger configuration attributed the highest energy absorption.     

薄弱环节对复合材料波纹梁吸能能力的影响

薄弱环节设置是复合材料吸能结构的关键技术,良好的设计可以使复合材料结构产生稳定的渐进压溃,从而吸收较多的能量.基于波纹梁准静态轴向压溃实验结果,运用MSC/DYTRAN有限元软件建立了三组不同尺寸的碳纤维-环氧树脂波纹梁的有限元模型,在数值模拟结果与实验结果基本吻合的基础上,分析了不同薄弱环节设置对复合材料波纹梁峰值载荷、吸能能力的影响,并进一步比较了不同薄弱环节设置的波纹梁在以6.5m/s的速度碰撞刚性地面时的能量吸能能力.     

碳/碳复合材料摩擦学性能及摩擦机制研究进展

碳/碳复合材料是一种性能优异的高温摩擦材料,作为刹车材料在航空工业已得到成功应用.但碳/碳复合材料的摩擦磨损性能强烈地依赖于试验条件和制备工艺.综述了各种因素对碳/碳复合材料摩擦磨损性能的影响,总结了碳/碳复合材料摩擦磨损机理,并指出了碳/碳复合材料摩擦学需进一步深入研究的问题及新的研究方向.     

圆形薄壁构件准静态径向压缩下的吸能特性分析

为探讨薄壁吸能构件径向压缩下的吸能防冲特性,以圆形薄壁构件为例,采用理论分析、数值模拟和实验研究方法,对构件径向压缩下的吸能防冲特性进行研究,得出以下主要结论:构件压缩过程中具有稳定的变形破坏模式和较为恒定的承载力。内径对载荷波动系数、冲程效率和总吸能影响较小,压溃峰值载荷、平均压溃载荷随内径增加而降低。构件压溃峰值载荷、平均压溃载荷和总吸能均随壁厚增加而增大,载荷波动系数和冲程效率随壁厚增加而降低。长度对载荷波动系数和冲程效率影响较小,构件压溃峰值载荷、平均压溃载荷和总吸能均随长度增加而增大。研究结果为圆形构件尺寸选取提供理论依据,为其它类型薄壁构件径向压缩吸能特性分析提供参考。     

复合材料结构-功能一体化技术与吸能结构的研究

复合材料的结构一体化技术包括结构整体化和结构-功能一体化两个方面.复合材料吸能结构属于典型的结构-功能一体化结构.以复合材料管形件为基础,发现提高管形件轴向性能如增加编织结构的轴向纤维纱数,或调整预浸料复合材料铺层尽可能地平行于轴向,或提高复合材料层间韧性(即高CAI值)等,都有利于提高吸能效果.在整体化制造方面,研制和验证了织物复合材料正弦波梁的液态成型制造技术.     

碳/碳复合材料的疲劳行为研究

碳/碳复合材料作为理想的高温结构材料,在服役过程中不可避免地涉及疲劳加载的情况,其疲劳行为的研究具有十分重要的意义.本文对近年来碳/碳复合材料疲劳行为的研究情况进行了综述,总结出了疲劳行为特点.提出了"界面控制"疲劳机理分析模型,并用此模型合理解释了碳/碳复合材料优异的抗疲劳性能以及异常的"疲劳强化"现象.并在此基础上,对今后的研究工作发表了一些看法.     

湿热环境对碳纤维环氧树脂复合材料弯曲性能的影响EI北大核心CSCD

采用不同温度下的三点弯曲测试方法,研究了湿热环境对机织碳纤维环氧复合材料吸湿前后弯曲性能的影响,分析了复合材料的吸湿量、断口形貌、动态力学性能及其加载曲线。结果表明:机织碳纤维环氧复合材料吸湿率较低,其饱和吸湿率仅为0.88%左右。湿热对复合材料弯曲强度的影响要大于对弯曲模量的影响。干态试样的断裂形式都为脆性断裂,湿态试样只有在高温下未发生断裂。吸湿后复合材料的玻璃化转变温度(DMA T_g)为125℃,比干态时下降了16℃。在弯曲变形的前期,载荷和位移曲线都成线性变化,干态试样在载荷达到峰值之前会出现小的波动。湿态试样的后期会有明显的弯折或塑变,而且随着温度的升高这种现象越明显。     

Buckling of Carbon/Glass Composite Tubes Under Uniform External Hydrostatic Pressure

Abstract: This paper describes an experimental and an analytical investigation into the collapse of 44 circular cylindrical composite tubes under external hydrostatic pressure. The results for 22 of these tubes were from a previous investigation and the results for a further 22 models are reported for the first time in this paper. The investigations concentrated on fibre‐reinforced plastic tube specimens made from a mixture of three carbon and two E‐glass fibre layers. The lay‐up was 0°/90°/0°/90°/0; the carbon fibres were laid lengthwise (0°) and the E‐glass fibres circumferentially (90°). The theoretical investigations were carried out using a simple solution for isotropic materials, namely a well‐known formula by ‘von Mises’. The previous investigation also used a numerical solution based on ANSYS, but this was found to be rather disappointing. The experimental investigations showed that the composite specimens behaved similarly to isotropic materials previously tested, in that the short vessels collapsed through axisymmetric deformation while the longer tubes collapsed through non‐symmetric bifurcation buckling. Furthermore, it was discovered that the specimens failed at changes of the composite lay‐up due to the manufacturing process of these specimens. These changes seem to be the weak points of the specimens. For the theoretical investigations, two different types of material properties were used to analyse the composite. These were calculated properties derived from the properties of the single layers given by the manufacturer and also the experimentally obtained properties. Two different approaches were chosen for the investigation of the theoretical buckling pressures, of the previously analysed models, namely a program called ‘MisesNP’, based on a well‐known formula by von Mises for single‐layer isotropic materials, and two finite element analyses using the famous computer package called ‘ANSYS’. These latter analyses simulated the composite with a single‐layer orthotrophic element (Shell93) and also with a multi‐layer element (Shell99). The results from Shell93 and Shell99 agreed with each other but, in general, their predictions were higher than the analytical solution by von Mises. The von Mises solution agreed better than the finite element solutions for the longer vessels, which collapsed by elastic instability, particularly when the experimentally obtained material properties were used. Thus, it was concluded that the results obtained from the finite element analyses predicted ‘questionable’ buckling pressures. The report provides design charts by all approaches and material types, which allow the possibility of obtaining a ‘plastic knockdown factor’ for these vessels. The theoretical buckling pressures obtained using the computer programs MisesNP or ANSYS can then be divided by the plastic knockdown factor obtained from the design charts, to give the predicted buckling pressures. It is not known whether or not this method can be used for the design of very large vessels.