复合材料的Ⅰ型层间断裂韧性

本文采用铰链式双悬臂梁试件对碳/双马来酰亚胺复合材料的Ⅰ型层间断裂韧性进行了研究,分析比较了层间断裂韧性G_IC的表达方法,用三次多项式和幂函数拟合实验柔度的方法得到的结果比较满意,实验结果表明纤维桥连对单向层合板的G_IC的影响是显着的,用刀片切割桥连纤维后G_IC值下降百分之二十,分散性也有显着下降。另外发现G_IC值随试件厚度增加而增大。     

环氧玻璃钢层合板冲击破坏及其断口微观特征的研究

S-GF/Ep648复合材料层合板[0₉°/θ]_s冲击抗力试验的结果表明其冲击抗力值与铺层角θ无关,只受浸水时间的影响;而另一种铺层形式[+θ₈/-θ₈]的复合材料层合板,在落重冲击试验中却发现:在相同的冲击能量下,θ越大,分层破坏越严重,损伤区面积也越大。利用SEM-505扫描电子显微镜对发生穿透性断裂、层间分层断裂或仅出现冲击损伤等破坏形式的断口表面进行了观察和分析,讨论了影响该复合材料冲击断裂和冲击损伤性能的因素。     

CF/PEEK复合材料界面层结构与性能关系研究

本文根据聚醚醚酮(PEEK)在碳纤维表面形式的横晶层的结构特征分析,建立了CF/FEEK复合材料界面层微观力学性能的理论方程,计算了界面层的杨氏模量.通过超声浸渍法测量复合材料的力学性能验证了计算结果,证明所进行的分析合理.计算结果表明,PEEK界面横晶层在垂直于纤维方向的杨氏模量E_r随PEEK结晶度的增大,或随横晶中PEEK晶片长度的增大而增大,并随晶片厚度的增大而减小.该界面层的上述模量值始终高于界面层附近球晶的模量值E_s,两者之间的比值E_T/E_s;依赖于横晶及球晶中的晶片长度b、厚度c和宽度a.由于界面层的模量高于非界面层的模量,当复合材料中纤维表面形成横晶时,复合材料将有较高的刚性.     

Al与γ－Al2O3润湿角的计算

本文应用金属的形核理论对目前无法用实验进行准确测定的易氧化金属Al与γ-Al₂O₃的润湿角进行了计算。计算结果发现Al与γ-Al₂O₃的润湿角在30°到50°这一范围之间,即30°<θ≤50°。     

复合材料层板+θ/-θ层间断裂韧性研究

本文讨论了纤维增强复合材料层板沿+θ/-θ层间断裂韧性的研究方法;提出在满足一定力学条件时,可沿用机械载荷实验方法测得G_C中“纯机械部分”G_m;结合数值方法计算得出“纯温度部分”G_T,从而得到G_C.给出一个针对DCB试验的充分条件,据此设计铺层并对T300/648和T300/QY8911进行试验和分析(θ=0～30°)、讨论了大变形的影响并提出一个新的修正系数.结合θ对G_C的影响及断口微观形貌作了进一步讨论.     

复合材料对称层合板特征值问题的灵敏度分析

由于复合材料层合板的横向剪切模量较低,因此基于克希霍夫理论而计算的层合板特征值及其灵敏度与实际情况相差较大。本文采用层合板的一阶剪切变形理论,将纤维铺设角、材料参数和从层合板的中面到第K层板上表面的距离Z_K视为设计变量,研究了对称层合板特征值的灵敏度计算问题。     

Kinetics of Technetium Reactions: XV. Tc(IV) Oxidation with Persulfate Ions in HClO<Subscript>4</Subscript> Solution

Tc(IV) is oxidized with persulfate ions in HClO₄ solution by reactions with both S₂O ₈ ²⁻ ion and product of its thermal decomposition, Caro acid, H₂SO⁵. The reaction rate at 35°C and solution ionic strength μ = 1 is described by the equation d[Tc(IV)]/dt = k ₁[Tc(IV)][S₂O ₈ ²⁻ ] + k ₃[Tc(IV)][HSO ₅ ⁻ ]/[H⁺], where k ₁ = 0.88±0.04 l mol⁻¹ min⁻¹ and k ₃ = 110±5 min⁻¹. With increasing ionic strength to μ = 2, both rate constants decrease (k ₁ = 0.58±0.08 l mol⁻¹ min⁻¹ and k ₃ = 52±2 min⁻¹ at 35°C). The activation energy of the overall reaction is 77.7±8.1 kJ mol⁻¹. The mechanisms of both reactions are discussed. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 145–149. Original Russian Text Copyright ? 2005 by V. Koltunov, Gomonova, G. Koltunov.     

[±θ/902]碳/环氧层板横向裂缝与分层的测试及分析

本工作对[±θ/90₂]_S和[0_n/90₂]_S两系列碳/环氧层板在拉仲载荷下的横向裂缝与分层损伤,进行了实验研究和有限元分析.采用声发射技术跟踪配合显微观测多向层板损伤过程,分析了θ角变化与力学性能、初始损伤、累积等的关系.表明实测横向开裂与分层结果和采用能量判据有限元计算预测比较,符合良好.同时在扫描电镜内进行各类层板压缩试验,动态观测破坏形貌,讨论了不同θ铺层角的微观破坏机理.     

Kinetics of Reactions of Np and Pu Ions with Hydrazine Derivatives: XVIII. Reaction between Np(V) and Hydroxyethylhydrazine

The Np(V) reduction with hydroxyethylhydrazine is described by the equation −d[Np(V)]/dt = k ₁[Np(V)][HOC₂H₄N₂H ₄ ⁺ ] + k ₂[Np(V)][Np(IV][H⁺]^1.8, reflecting its main and autocatalytic pathways. The rate constants are k ₁ = 0.31±0.04 l mol⁻¹ min⁻¹ and k ₂ = 4.04±0.11 l^2.8 mol^−2.8 min⁻¹ at 80°C and ionic strength μ = 4. The activation energies are E ₁ = 90±6 and E ₂ = 116±4 kJ mol⁻¹, respectively. The autocatalytic pathway is limited by the reaction between hydroxyethyldiazenium ions, HOC₂H₄N₂H ₂ ⁺ and protonated Np(V) ions. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 150–153. Original Russian Text Copyright ? 2005 by V. Koltunov, Baranov, G. Koltunov.     

碳纤维复合材料的微波反射特性研究

研究了各种铺层（０°、０°／９０°、±３０°、±４５°、±６０°）方式碳纤维复合材料（ＣＦＲＰ）的皮反射特性。结果表明,单向纤维铺层ＣＦＲＰ的反射率与纤维方向及层板厚度有关;交叉铺层ＣＦＲＰ的反射率很大,但比金属略小,喷涂了防雷击层的单向纤维铺层ＣＦＲＰ,电性能基本上各向员性;喷涂了防雷击层的０°、±４５°、０°／９０°ＣＦＲＰ的反射率比喷涂前有所降低。     

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.     

Influence of intralaminar cracking on the apparent interlaminar mode I fracture toughness of cross‐ply laminates

One of the major difficulties in interlaminar fracture tests of multidirectional laminates is the high tendency for intralaminar cracking and the resulting wavy crack propagation. Experimental work showed that this occurred in double cantilever beam (DCB) tests of cross‐ply laminates having a starter crack on a 0°/90° interface. Moreover, under steady‐state propagation conditions, the apparent values of the critical strain energy release rate G_Ic were two times higher than those of 0°/0° specimens. In this paper, a finite‐element‐based progressive damage model was used to simulate crack propagation in cross‐ply specimens. The results showed that transverse cracking alone cannot be responsible for the above difference of G_Ic values. Therefore, the higher propagation G_Ic values for cross‐plies must be attributed to the more extensive fibre bridging observed and to plastic deformations of the 90° interfacial ply.     

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。     

Embedded flaws for crack path control in composite laminates

An experimental investigation was conducted on using small flaws purposefully introduced into composite laminates to control growth of interlaminar cracks and through-thickness crack branching. Mode I crack growth specimens were used to study branching through 0°, 90° and 45° plies. The results showed that crack growth through 0° plies could be promoted by a ply gap, but this was not as controllable as combining a ply gap with a pre-crack to create a “crack branch flaw”. Crack branching through 45° plies could be controlled using crack branch flaws, and also promoted controllably using ply gaps. Crack branching through 90° plies was seen without any flaws, but was better controlled with embedded delaminations. Using these outcomes, crack branching through two quasi-isotropic laminates was demonstrated. The results have application to improved damage tolerance and fracture toughness, by taking advantage of high toughness crack growth mechanisms.     

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.     

碳纤维复合材料层合板低速冲击损伤应力分析

目的 为掌握碳纤维复合材料板在低速冲击载荷作用下的损伤规律,延缓失效破坏,对其冲击损伤的应力状态进行研究。方法 基于ABAQUS平台,建立碳纤维复合材料层合板低速冲击有限元模型,采用Hashin失效准则和VUMAT用户子程序,对碳纤维复合材料层合板的冲击过程进行数值模拟,同时考虑层合板层内与层间失效,以此来研究低速冲击条件下复合材料的损伤机理,分析冲击损伤过程中的应力变化趋势,讨论应力的分布状态。重点研究铺层角度及铺层距离冲头远近对应力的影响。结果 不同角度铺层的应力传播轨迹均沿着纤维方向和垂直于纤维方向同时扩展,应力均先增加至极限值而后迅速下降;铺层角度越大,板料的承载能力越弱,0°铺层的极限应力为1 432 MPa,而90°铺层的极限应力降至1 206 MPa;离冲头越远的铺层应力越小,达到峰值的时间更早且率先下降,说明远离冲头的铺层更早发生失效。结论 揭示了碳纤维层合板在低速冲击载荷作用下的应力状态及其对损伤的影响规律,能够为复合材料层合板零件设计提供参考。     

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.     

Damage Assessment of CFRP [90/±45/0] Composite Laminates over Fatigue Cycles

The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) [90/±45/0] composite laminates with various stacking sequences. The damage model is constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional plies of 90°, 0° and angle-ply laminates of ±45° as the number of cycles progresses. The proposed model accumulates damages of constituent plies constructing [90/±45/0] laminates by means of weighting factor η ₉₀, η ₀ and η ₄₅. These weighting factors were defined based on the damage progress over fatigue cycles within the plies 90°, 0° and ±45° of the composite laminates. Damage model has been verified using CFRP [90/±45/0] laminates samples made of graphite/epoxy 3501-6/AS4. Experimental fatigue damage data of [90/±45/0] composite laminates have fell between the predicted damage curves of 0°, 90° plies and ±45°, 0/±45° laminates over life cycles at various stress levels. Predicted damage results for CFRP [90/±45/0] laminates showed good agreement with experimental data. Effect of stacking sequence on the model of stiffness reduction has been assessed and it showed that proposed fatigue damage model successfully recognizes the changes in mechanism of fatigue damage development in quasi-isotropic composite laminates.     

Analysis of first ply failure in composite laminates

The mechanics of transverse cracking in an elastic fibrous composite ply is explored for the case of low crack density. Cracks are assumed to initiate from a nucleus created by localized fiber debonding and matrix cracking. It is found that cracks may propagate in two directions on planes which are parallel to the fiber axis and perpendicular to the midplane of the ply. In general, crack propagation in the direction of the fiber axis controls the strength of thin plies, while cracking in the direction perpendicular to the fiber axis determines the strength of thick plies. The theory relates ply thickness, crack geometry and ply toughness to ply strength. It predicts a significant increase in strength with decreasing ply thickness in constrained thin plies. The strength of thick plies is found to be constant, but it may be reduced by preexisting damage. Results are illustrated by comparison with experimental data.     

Damage characterisation of thermally shocked cross-ply ceramic composite laminates

Damage due to thermal shock in cross-ply Nicalon/calcium aluminosilicate ceramic matrix composites has been investigated. Heated specimens of two simple [(0°/90°)_s and (90°/0°)_s] and two multi-layer [(0°/90°)_3s and (90°/0°)_3s] materials were quenched into water at room temperature. Crack morphologies were assessed by reflected light microscopy and scanning electron microscopy. The use of image assembling software allowed the generation of reflected light microscopy images of all of the thermally-shocked surfaces onto which the crack patterns were then superimposed. This allowed clear identification of damage mechanisms and accurate quantification of damage accumulation with increasing severity of thermal shock. Damage was first detected in the central plies of each composite. Composites with 0° central plies exhibited slightly higher resistance to thermal shock than their counterparts with 90° central plies. Although damage extended to the outer plies as the severity of the shock increased, crack density was found to vary with position at every shock: it was highest in the central plies and gradually reduced towards the outer plies. Multiple matrix cracking perpendicular to the fibre direction was the damage mode identified in 0° plies, while 90° plies contained cracks that ran along the ply length. At more severe shocks the morphology of these crack patterns was affected in significantly different ways. In addition, the thinner, simple cross-ply composites exhibited much higher resistance to thermal shock than their multi-layer counterparts.