Matrix-dominated tensile behaviour of unidirectional T300/914 and structural modelling of the material

Unidirectional T300/914 carbon epoxy composite has been tested under transverse tensile loading at various temperatures and test rates. The test programme revealed a different viscoelastic response for the bulk resin modulus from that of the composite modulus and associated fractographic examination showed the structures of the resin and composite to be complex. The resin consisted of an epoxy-based particulate phase embedded within a thermoplastic-based connecting phase. The addition of carbon fibres resulted in the formation of an irregular epoxy-based interphase region. A parameter, , has been defined that easily characterizes the viscoelastic behaviour of the composite. Structural models have been successfully developed for both the resin and the composite and a cure mechanism suggested. Any plastic deformation occurring on failure was within the connecting phase and the weakest point of the composite was identified as being the particle/interphase boundary. Property modelling has successfully accounted for the interphase influence on the transverse tensile modulus and the composite transverse tensile strength was found to be higher than the bulk resin tensile strength.     

Artificial Neural Network Prediction of Ultimate Strength of Unidirectional T-300/914 Tensile Specimens Using Acoustic Emission Response

Acoustic Emission (AE) Monitoring was used to evaluate unidirectional carbon epoxy specimens when tensile loaded with a 100 kN Universal Testing Machine. A series of eighteen samples were loaded to failure to generate AE data for this analysis. After data acquisition, AE response from each test was filtered to include only data collected up to 50% of the actual failure load for further analysis. Amplitude, Duration and Energy are effective parameters utilized to differentiate various failure modes in composites viz., matrix crazing, fiber cut, and delamination with several sub categories such as matrix splitting, fiber/matrix debonding, fiber pull-out etc. The ultimate strength prediction was performed with an Artificial Neural Network Back propagation algorithm. Peak Amplitude values varying from 35–100 dB were taken as the input to the network. The impact of signal amplitudes due to different failure mechanism to the ultimate strength was mapped using a supervised network having a middle layer with 45 neurons and actual failure loads were supplied as target values during training phase. The network finally trained with twelve specimens was able to predict failure loads of remaining six specimens with in the acceptable error tolerance.     

T300／4211复合材料的使用寿命评估

选用Ｔ３００．４２１１环氧基碳纤维增强复合材料，应用半经验数学模型，结合短期不同气候区的自然老化数据和人工加速老化数据，预测其长期使用下（５１年和３０年）力学性能的变化，估算复合材料结构的工作寿命，为复合材料飞机构件的性能评定提供参考依据。     

Modeling and testing strain rate-dependent compressive strength of carbon/epoxy composites

A technique for testing high modulus fiber-reinforced composites in compression at different strain rates is investigated. The rate-dependent compressive behavior of unidirectional AS4/3501-6 carbon/epoxy composite is characterized by using off-axis specimens. It is found that, in the compression test, a titanium coating applied at the contact ends of the off-axis specimen can greatly reduce contact frictions, allowing a fully developed extension–shear coupling so that a state of uniform stress in the specimen can be achieved. A rate-dependent nonlinear constitutive model and a dynamic compressive strength model (fiber microbuckling model) for the unidirectional AS4/3501-6 composite are established based on the low strain rate off-axis test data. Model predictions and experimental data including high strain rate data are in very good agreement indicating that the constitutive model and compressive strength model obtained with low strain rate data are valid for high strain rates as well. A technique is also developed to extract the longitudinal compressive strength of the composite from those of the off-axis specimens.     

T300/5405复合材料的吸水特性研究

通过对Ｔ３００／５４０５复合材料在６０℃,８０℃、１００℃水中近９００ｈ的浸水试验研究,给出了Ｔ３００／５４０５复合材料的吸水曲线,分别确定了扩散系数、平衡吸湿量与水温的关系。从而为深入研究Ｔ３００／５４０５复合材料的吸湿行为奠定了基础。     

国产CCF300/双马树脂层合板高温拉伸与压缩性能试验研究

对碳纤维(CCF300)/双马树脂(GW-300)复合材料层合板进行了200 ℃和300 ℃高温环境下的拉伸和压缩性能试验, 研究其在不同温度环境下基本力学性能的变化。研究结果表明, 由基体控制试件在高温下的拉伸强度和模量比由纤维控制试件降低的比例大; 随着温度的升高, 厚试件的压缩强度比薄试件的压缩强度提高幅度明显; 高温下, 拉伸性能保持率较高, 而压缩性能保持率较低; 300 ℃下基体控制试件和纤维控制试件的拉伸强度保持率分别达70%以上和90%以上, 而厚试件和薄试件的压缩强度保持率都只略高于30%。      

猪股骨常应变率动态压缩试验方法研究

准确的骨骼材料响应对于模拟交通事故、战争和跌落中的人体损伤机制作用重大,但上述工况所对应的皮质骨动态力学响应还没有在常应变率条件下被规范测量。为在动态压缩试验中实现和维持不同的恒定应变率,建立针对皮质骨的重复性良好的霍普金森杆动态材料测试方法,并测试大应变率范围内的骨骼材料力学参数。首先测试纯铝整形器尺寸和子弹撞击入射杆速度对入射脉冲形状的改变效果,并在此基础上不断改变入射脉冲形状直至满足常应变率条件,随后对32个加工规则的猪股骨中轴皮质骨试样按照应变率范围进行分组测量。当入射波平台部分斜率与透射波上升沿斜率相等时,试样以常应变率变形,此时常应变率产生的变形超过总应变量的70%。猪股骨皮质骨在200～1 500 s~(-1)应变率间极限应力和极限应变增大(分别为10.2%与25.0%),弹性模量减小(7%)。结果表明,相对于杆材料更软的塑性金属作为整形器能使骨骼在需要的应变率范围内保持应变率恒定,且重复性良好,适宜进一步用于人骨测试。     

T300/QY8911 π/4层压板机械连接干涉疲劳

本文对T300/QY8911π/4层压板机械连接干涉配合进行了静拉伸挤压和拉-拉疲劳试验。与滑配合比较,干涉使静挤压强度略有提高,但能使疲劳寿命增加数倍。文中用有限元方法计算了两种配合的孔边应力分布。并对疲劳损伤用X射线作了检测,初步分析了干涉配合的增寿原因。      

碳/双马来酰亚胺层板加压冲击后的损伤研究

本文对预压碳/双马来酰亚胺层板进行了冲击试验.运用超声C扫描,金相技术和揭层法对冲击损伤进行了细致观察与描述,得到了较全面的细观损伤面貌.研究表明,分层是其主要损伤形式,并几乎分布在所有界面上.分层的形状不规则,但主方向均沿着界面下层纤维方向.分层面积与相邻两层的铺层方向间的夹角及铺层顺序有关.预加压对其内部分层分布有较大影响,最大的分层处于层板背面部分接近中面的界面上.     

Temperature dependence of mechanical and thermal expansion properties of T300/5208 graphite/epoxy

The elastic constants, ultimate strengths and thermal expansion behaviour of T300/5208 graphite/epoxy laminates of differing lay-ups have been determined in the temperature range 116 K to 394 K. Most of the properties exhibit nearly linear temperature dependences. However, the transverse modulus and the axial thermal expansion vary non-linearly with temperature, their values changing by an order of magnitude over the temperature range considered.     

应变率对T300/Al(L2)复合丝拉伸性能的影响

利用MTS810试验机和自行研制的冲击拉伸试验装置对T300／Al复合丝实施了不同应变率下的拉伸试验,获得了材料从0．001s^-1到1300s^-1应变率范围内完整的应力应变曲线。结果表明：T300／Al是一种应变率敏感复合材料,随着应变率的提高,材料的拉伸强度、失稳应变均相应提高,具有明显的应变率强化效应和动态韧性现象,这主要是由铝基体的应变率强化效应和应变率历史效应引起的。根据材料在不同应变率下的试验结果以及对其不同变形阶段机理的分析,提出了弹塑性复合丝束模型,并由此建立了相应的应变率相关的一维统计损伤本构方程,模型拟合结果与试验结果一致。     

T300和T700炭纤维的结构与性能

利用SEM、元素分析、XRD和激光Raman光谱研究了T300和T700的形貌、化学组成和微观结构参数。结果发现:T700炭纤维表面光滑,而T300炭纤维的表面有大量的沟槽。表明前者是用干喷湿纺原丝,后者是用湿法纺丝原丝。两种纤维的断面均呈现出颗粒状特征。T700的含碳量高于T300,含氮量低于T300。两者的微观结构参数(d002、La和Lc)差异佐证了T700的炭化温度高于T300。T700的择优取向角Z比T300小2.3°,是石墨微晶致密有序排列的反映,因而使其体密度比T300高2.27%,空隙率低7.54%。所以致密化赋予了T700较高的拉伸强度。     

T300/648复合材料迭层板接头挤压疲劳累积损伤问题的实验研究

本篇论文根据“剩余强度,剩余刚度”理论,讨论了碳纤维增强复合材料迭层板承载孔的挤压疲劳损伤,应用孔的永久变形描述损伤的产生和扩展,提出了“损伤函数”的定义和测定方法,并提出了新的“疲劳损伤点”的概念。实验还研究了温度对连接孔静挤压强度和疲劳寿命的影响。实验结果表明,温度的影响尤为重要。对损伤失效试件,采用“揭层方法”、“X射线”及“SEM方法”进行检测和损伤机理的研究。     

T300/BPM316复合材料层合板的载荷放大系数确定

在加速飞机复合材料结构耐久性验证的试验过程中,载荷放大系数(LEF)的求解精度对试验持续时间有着重要的影响。以铺层方式为[45/-45/0/0/-45/90/0/90/45/0]_s 的T300/BPM316 复合材料层合板为研究对象,采用改进的联合威布尔分布分析复合材料的疲劳寿命分散性,并运用MATLAB 软件编写程序,计算得到其部件的载荷放大系数。结果表明:在该文研究范围内,T300/BMP316 复合材料层合板的载荷放大系数随试验持续时间的增加而减小;部件试验件数对耐久性验证试验的可靠性影响很小,对载荷放大系数的影响可忽略不计;验证了采用改进的联合威布尔分布的联合载荷放大系数法的正确性,并发现其不受原始载荷放大系数法的求解限制,具有推广应用价值。     

Transverse tension fatigue life characterization through flexure testing of composite materials

The transverse tension fatigue life of S2/8552 glass–epoxy and IM7/8552 carbon–epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass–epoxy laminates. Results showed that 90-degree flexure specimens with polished machined edges and polished tension-side surfaces had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law were examined using the carbon–epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S–N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S–N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives of heterogeneous, fiber reinforced, polymer matrix composites.     

T6热处理对复式连通双连续相SiC/Al复合材料性能的影响

研究了T6热处理(固溶处理 时效)对复式连通双连续相SiC/A1复合材料的组织和压缩性能的影响.结果表明,经T6热处理后,复合材料基体中第二相共晶硅从粗大的针状变成了细小的粒状,增强了弥散强化效果,时效析出相Mg2Si强化了基体;界面附近的基体中残余应力增大,使复合材料的压缩强度显著提高,材料的弹性模量和塑性稍稍降低.随着固溶时间的延长,复合材料的压缩强度先升高后降低.其影响机制是,随着固溶时间的延长共晶硅扩散充分,球化完全,继而粗化长大,从而提高了弥散强化效果.随着时效时间的延长,材料中的残余应力减小,位错密度降低,时效强化相Mg2Si的强化能力减弱,使复合材料的压缩强度降低.     

T300/Al复合丝中纤维就位强度的测试与表征

以萃取法、纤维束拉伸试验技术以及纤维强度的应变率和温度相关的统计本构理论为基础，形成了纤维增强金属基复合材料中纤维就位强度的测试与表征方法，利用该方法获得了T300／Al复合丝中纤维的就位强度的所有确定性参数和统计参数。结果表明，在经过与铝基体的高温复合以后，T300纤维的模量、强度均有不同程度的降低，工艺过程中纤维表面损伤加剧是造成纤维就位强度降低的主要原因。     

Time-Dependent Deformation of Stitched T300 Mat/Urethane 420 IMR Cross-Ply Composite Laminates

This article concerns certain aspects of the time-dependent response ofcross-ply polymeric composites consisting of stitched graphite fiberstrands embedded in urethane resin. Experimental data were collected atseveral levels of stress and temperature, as well as at various loadorientations. The time-dependent strains were shown to consist of thesum of a fully recoverable viscoelastic component and a permanentportion, which could be expressed empirically. The utility andshortcomings of the power-law creep form are being examined, suggestingthat its validity for making long term predictions may require that`short time' data must be collected over durations that exceed a certaintime-span.The article presents several results that demonstrate thepredictive capabilities of some of the formulations employed therein.