基于NASTRAN的复合材料层合板层间应力分析

基于MSC.PATRAN/NASTRAN软件,采用一种准三维混合有限元模型,计算了复合材料层合板的层间应力,得到了层间应力对层合板面内应力分布的影响规律,为合理设计层合板,优化层间剪切强度,扩大层合板的应用范围,提供了分析手段和理论依据；这种准三维混合模型的有限元计算方法,提高了复合材料层合板的分析效率和分析精度,也为其他复合材料结构分析提供了新的分析思路和途径.     

缝合/RTM复合材料层合板的力学性能研究

分别采用高强玻璃纱、Kevlar-29纤维和T300 3K纤维为缝合线对玻璃纤维方格布进行缝合,研究了缝合/RTM复合材料层合板的面内拉伸性能和层间剪切性能.研究结果表明,与未缝合复合材料层合板相比,缝合复合材料层合板面内拉伸性能有所降低(碳纤维缝合复合材料除外),在给定缝合密度下最大降幅为14%;缝合复合材料层合板的层间剪切性能较未缝合层合板都有不同程度的提高,在给定缝合密度下最大达到了40%,缝合可显著提高复合材料层合板的层间性能.     

铺层拼接层合板的抗拉强度

针对复合材料结构设计中遇到含铺层拼接的层合板强度预测问题,本文设计了含铺层交错拼接区的碳/双马复合材料层合板试件,采用拉伸试验方法测定了该材料的力学性能,得到了不同拼接长度层合板的抗拉强度。试验结果表明,铺层拼接状态差异对复合材料层合板的承载能力有显著影响,文中根据试验结果建立了抗拉强度随拼接长度变化的经验公式,为复合材料层合板结构的铺层设计和强度分析提供了理论依据。     

Z-pin增强酚醛复合材料层合板的层间拉伸性能

本文探索研究了Z-pin的植入对酚醛复合材料层合板层间拉伸性能的影响。通过向酚醛复合材料层合板中植入体积分数为0.78%(植入间距5mm×5mm)的石英/酚醛Z-pin,对其进行层间拉伸性能测试,结果表明,随着Z-pin的植入,层合板的层间拉伸性能显著提高,并伴随破坏模式的变化、材料韧性的增加。最后,根据复合材料力学,建立Z-pin增强层合板的简单力学模型,通过桥率试验与层间拉伸试验,对其进行验证和修正,得出Z-pin植入对层合板的层间性能的影响规律。     

表面带金属层的复合材料层合板低速冲击数值模拟

使用Abaqus/Explicit建立表面带金属层的复合材料层合板和复合材料裸板低速冲击有限元模型,与已有文献对比验证结果的可靠性,研究结果对复合抗弹结构有很好的借鉴和参考价值.采用Johnson-Cook本构关系模拟铝合金和钛合金层的力学行为,选用Hashin准则对复合材料层内损伤进行失效判断,用二次应力准则来模拟粘结层Cohesive单元的层间失效.结果表明,相同铺层与冲击能量下,表面带铝合金层合板对内部纤维的保护性能优于表面带钛合金层合板,表面带钛合金层合板的抗冲击性能优于复合材料裸板;[§/0°/90°/0°/90°/0°]s铺层层合板的抗冲击性能优于[§/-45°/90°/0°/45°/-45°]s铺层层合板的抗冲击性能;在子弹刚冲破层合板与子弹完全离开层合板阶段,表面带铝合金层合板对子弹动能吸收率最大.     

缝合层合板的I型层间断裂韧性研究

通过缝合的方法改善织物增强复合材料层合板的层间断裂韧性.采用双悬臂梁(DCB)试验测试和研究了缝合层合板的层间断裂韧性与断裂行为.为了评价缝合工艺参数(缝合密度)对层间断裂韧性的影响, 用改进的插入型夹具在实测不同缝合工艺层合板的I型层间断裂韧性值(GIC)的基础上, 分析和阐明了缝合工艺参数(缝合密度)与GIC间的关系; 以提高层合板的平均层间断裂韧性值为目标, 以拉伸和弯曲强度为约束条件优化了缝合工艺; 采用摄影显微镜对分层断裂面进行了观察, 分析和考察了缝合对其它性能的影响.结果表明 改进的插入型夹具可方便地完成缝合层合板的I型层间断裂韧性测试; 缝合后裂纹不连续扩展, 缝合密度对裂纹扩展行为有较大影响; 随着缝合密度的增大, 层间断裂韧性值增大, 但拉伸和弯曲强度降低, 缝合密度存在最佳值.     

传递矩阵法分析复合材料层合板的传声损失

为了得到不同频率下正交各向异性复合材料层合板的传声损失,基于传递矩阵的方法,推导出层合板的传声损失计算公式。通过建立复合材料层合板的传声计算模型,研究了层合板铺设角度、板厚度和板密度等结构参数对层合板的传声损失影响。计算结果表明：复合材料的密度与传声损失之间没有明显的线性关系,而是随着频率的增加而上升;层合板的总厚度越大,传声损失也越大,而且各层之间厚度不同,也会引起传声损失的较大改变;层合板铺层角度越大,传声损失也越大。采用传递矩阵法能充分考虑复合材料层合板的铺设方式和铺层角度等因素的影响,利用层合板层间的速度和应力连续边界条件,准确的反应复合材料层合板隔声性能。     

复合材料层合板脱层诊断的实验研究

利用动态特性对复合材料层合板的脱层损伤进行无损检测,是一种方便、实用的方法.复合材料层合板发生脱层损伤时,其内部微观结构、应力分布以及材料性能参数都会发生变化,这些变化会引起材料的动态特性发生显著的变化.因此,分别研究层合板在健康状态下和损伤状态下的动态特性,就可以分析建立脱层损伤的诊断知识规则.     

复合材料层合板接触损伤问题的分析

将连续介质损伤力学的分析计算方法与复合材料层合板无损伤接触问题的分析相结合, 分析了层合板在接触载荷作用下的损伤问题。采用逆解法得到复合材料层合板无损伤接触问题的解。在进行接触损伤分析时, 考虑到实际应用中层合板的层间相对容易发生损伤, 同时为了简单起见, 不计复合材料铺层的损伤演化, 只计层间胶层的损伤, 并将层间胶层的损伤演化视为各向同性。通过胶层材料的疲劳性能实验曲线拟合得到损伤演化参数。采用附加载荷法与迭代法求解层合板接触损伤分析时应力场与损伤场的互耦问题, 得到了层间胶层的损伤度分布及应力分布。计算结果显示, 该方法收敛性好, 求解简单。     

含缺陷的复合材料层合板低速冲击过程的有限元模拟

用自编的动态有限元分析程序APIC 对含缺陷的复合材料层合板的冲击损伤问题进行了模拟计算。该程序采用三维20 节点超单元分析了复合材料层合板内的应力分布, 通过修正后的C. T. Sun 的接触定律建立了冲击物和层合板的运动状态与冲击接触力之间的关系, 采用Wilson-θ法求解层合板和冲击物的运动微分方程。在处理层间分层缺陷问题时, 采用拉格朗日乘子法使预制分层缺陷界面上满足不可互相贯穿条件。对本文中的计算结果和试验结果进行比较表明: 模拟计算结果与试验结果有良好的一致性。相对于无缺陷层合板, 含预制分层缺陷的复合材料层合板在分层部位遭受冲击时, 分层缺陷对冲击损伤扩展有一定的抑制作用。     

A detailed fractographic analysis of cleavage steps in silicon

A detailed analysis of cleavage steps present on fracture surfaces in pure silicon has been carried out using scanning electron microscopy. The results indicate that the mechanisms involved in both the formation of unfractured ligaments, produced when adjacent cleavage facets overlap, and the subsequent fracture of these ligaments to form cleavage steps, are quite complex. Specifically it is shown that, during ligament formation, the local crack fronts are deflected from their preferred (1 1 1) cleavage plane and that the fracture of these ligaments to form cleavage steps occurs in a very complex fashion producing very small microcleavage steps. It is shown that these latter steps are consistent with cleavage along both {1 1 1} and {0 1 1} planes.     

Cleavage step deformation in brittle solids

The nature and origin of sub-surface deformation associated with steps on cleavage surfaces of brittle solids is investigated. The geometrical configuration of step formation during cleavage is first discussed in terms of an interaction between crack segments propagating on adjacent planes. Observations of cleavage surfaces, using optical microscopy, scanning electron microscopy, and X-ray topography, are then described. It is concluded that the cleavage steps form primarily according to a mechanism in which adjacent crack segments first overlap to produce a connecting cleavage sliver, and subsequently join at one end (sometimes both ends) of the sliver to complete the separation of the cleavage halves. The slivers close in imperfect registry with the underlying parent material, thereby leaving a residual gap or dislocation network beneath the undercut steps. This mechanism is in accord with previous observations of step-associated deformation, hitherto taken as evidence of local plasticity.     

Fractography and structure of the subsurface cleavage zone in molybdenum

Transmission electron microscopy of thin foils was used to examine the structure of fracture surfaces of single crystals of molybdenum failed by cleavage along different crystallographic planes, and the dislocation structure of the zone adjacent to the fracture surface was also studied. The results show that cleavage steps are the main characteristic element in failure along any plane in the group of the examined planes ({100}, {110}, {211}, {123}). The number, dimensions, and crystal geometry of the cleavage steps depend on the cleavage plane. The primary cleavage elements are steps of the minimum size (height 8–17 nm). The results also show that with an increase of the work used in failure in transition from one cleavage of macroplane to another the thickness of the zone with high (in comparison with the initial value) dislocation density increases together with the dislocation density directly on the fracture surface.Translated from Problemy Prochnosti, No. 1, pp. 58–63, January, 1991.     

重组植物毒素gelonin的纯化及性质研究

采用pET28a载体系统在E.coli BL21中进行了植物毒素gelonin的原核表达，产物经SP-Sepharose，Superdex 75二步纯化，获得了电泳纯的重组植物毒素gelonin。将重组的gelonin与从植物种子中提取的天然gelonin进行了Western blot，ELISA，无细胞体系中蛋白质合成抑制实验以及超螺旋DNA裂解研究。结果都表明，重组植物毒素gelonin与天然gelonin具有相似的生物活性。     

The nucleation and growth of thin films on sodium chloride cleavage steps

In the present investigation we used scanning and transmission electron microscopy to study the cleaved sodium chloride surface. Several metals with different melting points were used to decorate the cleavage steps. It was observed that step decoration can be achieved with epitaxial, polycrystalline and amorphous thin films. The difference in the nucleation density at steps and edges and the nucleation density at smooth surfaces is attributed to the smaller activation energy required to nucleate an island in the former case. The pitting on NaCl could be caused by a contaminated vacuum system or by the exposure of the cleaved face to air.     

Fracture of high carbon high strength anchor rods

During a heavy windstorm, there was failure of anchors supporting transmission towers. We were given the mandate to examine the reasons for the failure of the anchor rods and suggest measures to prevent such failures from occurring. The study involved the in-depth examination of the chemical composition, microstructures, mechanical properties and fracture morphologies of specimens from failed anchors. Results indicated that the chemical composition, yield and tensile strengths of the anchor rods are within the norm of ASTM standard A722. The chemical composition corresponds to that of AISI 1070 with slightly higher manganese and silicon levels. Microstructure is ferrite–pearlite with dominance of pearlite due to the relatively high carbon content. Fracture surfaces of failed anchor rods exhibited pronounced cleavage facets (cleavage steps and river pattern) indicating that failure mode is brittle and the mechanism of fracture is cleavage. There were no signs for the occurrence of fatigue – any beach mark or striations. Final area of fracture showed traces of ductility (small shallow dimples). To prevent brittle failure of anchor rods, their toughness has to be improved. To achieve this, the potentiality of applying HSLA steel technology of micro alloying and TMCP (thermo mechanical control process) has been suggested.     

Surface aggregation of impurity in manganese-doped alkali halide crystals

The technique of surface decoration using a vacuum-evaporated thin gold layer is shown to be a powerful means of investigating the distribution of impurities on the surface of NaCl crystals containing manganese impurity. The method has been applied to the study of the diffusion of manganese from the bulk to the surface. The topography of the impurity aggregation centres is deduced from the interaction with slip and cleavage steps, which are also revealed by the decoration process.     

Cleavag Fracture Criterion of Low Alloy Steal and Weld Metal in Notched Specimens

The cleavage fracture criterion of low alloy steel and weld metal in notched specimens is investigated in detail based on a great number of experimental data. It has been found that the most cleavage fractures initiate at a distance shorter (left side) than that of the peak stress location below a notch root, and the cleavage fracture in notched specimens must satisfy a dual criterion, i.e., a critical plastic strain (ε_p ≥ ε_pc) for initiating a crack nucleus, and a critical tensile stress (σ_yy ≥ σ_f) for its propagation. According to the dual criterion model, the great number of experimental data of 4PB (four-point bending) tests for the low alloy steel and weld metal and their statistical distribution are explained. The effects of temperature , the local fracture stress σ_f and the critical plastic strain ε_pc on the locations of cleavage initiation sites and the controlling steps of cleavage fracture process are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响

对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。     

Sensitive and homogeneous protein detection based on target-triggered aptamer hairpin switch and nicking enzyme assisted fluorescence signal amplification

Specific and sensitive detection of proteins in biotechnological applications and medical diagnostics is one of the most important goals for the scientific community. In this study, a new protein assay is developed on the basis of hairpin probe and nicking enzyme assisted signal amplification strategy. The metastable state hairpin probe with short loop and long stem is designed to contain a protein aptamer for target recognition. A short Black Hole Quencher (BHQ)-quenching fluorescence DNA probe (BQF probe) carrying the recognition sequence and cleavage site for the nicking enzyme is employed for fluorescence detection. Introduction of target protein into the assay leads to the formation change of hairpin probe from hairpin shape to open form, thus faciliating the hybridization between the hairpin probe and BQF probe. The fluorescence signal is amplified through continuous enzyme cleavage. Thrombin is used as model analyte in the current proof-of-concept experiments. This method can detect thrombin specifically with a detection limit as low as 100 pM. Additionally, the proposed protein detection strategy can achieve separation-free measurement, thus eliminating the washing steps. Moreover, it is potentially universal because hairpin probe can be easily designed for other proteins by changing the corresponding aptamer sequence.