Studies on the impact response of carbon-epoxy laminates with and without buffer-strip layers

The work looks at the dynamic behaviour of laminated carbon-epoxy (C-E) composites with inserted interleaf material. Instrumented impact tests were performed to study the impact response of C-E system containing the interleaved PTFE-coated fabric material. Significant differences were noticed in the trend of the load-time plots. It was inferred that the introduction of small amounts of less adherent layers of material at specific locations causes a decrement in the load carrying capability of this material. An attempt to correlate these trends with the post impact observed failure features has been made in this work.     

The Effects of Morphological Properties of Henequen Fiber Irradiated by EB on the Mechanical and Thermal Properties of Henequen Fiber/PP Composites

The aim of this study was to investigate the effects of electron beam (EB) irradiation on the morphological properties, crystallinity and surface area of henequen fiber and on the mechanical and thermal properties of henequen fiber reinforced polypropylene (PP) composites. The structure of henequen fiber was characterized by X-ray diffraction, mercury porosimetry and BET surface area analysis. The EB irradiation of 10 kGy led to the increasing of crystalline and surface pore area of henequen fiber, which contributed to the number of interlocking places with PP. From the results of tensile and impact strength tests, the highest value was observed for the composite reinforced with the henequen fiber treated with EB dose of 10 kGy, decreasing overall as EB dose increased. This tendency was also shown by coefficient of thermal expansion (CTE) measurements, but the value of CTE decreased until 50 kGy, meaning that a large total surface area can provide many interlocking places and so improve adhesion between fiber and matrix. Therefore, it can be concluded that the optimum pore surface area by 10 kGy irradiation contributes to successful mechanical interlocking between fiber and matrix and consequently enhances the mechanical and thermal properties of the composites.     

Effect of Rubber Content of ABS on the Mechanical Properties of ABS/Clay Nanocomposites

One approach to improve the impact strength of acrylonitrile–butadiene–styrene (ABS)/clay nanocomposites is to increase rubber content. To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, other parameters were fixed and ABS/clay nanocomposites containing various rubber contents were prepared in this study. Also the effect of the UV stabilizer on the mechanical properties of ABS/clay nanocomposite was studied. For addition of 3 wt% clay, ABS nanocomposite with 35 wt% content of rubber displayed the highest reinforcement ratio for tensile properties and impact strength.     

Study of impact properties and morphology of unidirectional bamboo strips–polyester composites: effect of mercerization

Composites were fabricated with alkali (10%, 15% and 20%) treated bamboo fibers incorporated to the extent of 50% (by volume) and polyester resin. Impact test was made on bamboo strips and composites samples. It was observed that the fracture energy undergoes an increase from untreated to alkali treated bamboo strips. Alkali treated bamboo fiber composites show higher fracture energy value than the untreated bamboo fiber composites. The phenomenal change was quite evident from scanning electron micrographs of the fractured surface. Considering the effects of all factors, the work of fracture shows maximum value in the case of 20% alkali treated bamboo strip composites. It was also observed that the rate of increase of work of fracture value is much higher in the case of composite samples than the bamboo sample. It was explained on the basis of synergism obtained by improved interfacial adhesion between fiber and matrix, and removal of hemicellulose from the bamboo itself, which was evident from the intermolecular H-bonding formation studied by FT-IR.     

水雷冲击掩埋的一维-三维模型预测

当圆柱体或非圆柱体海军水雷通过空气、水和沉积物下落时,水雷冲击掩埋状态预测模型建立了一段时间历程.模型的输出是预测水雷在空气和水柱中的运动轨迹、在沉积物中的掩埋深度和方向,以及雷体在掩埋物中凸出部分的高度、面积和体积.模型的输入包括环境、水雷特征和初始释放状态等参数.综述近30年来水雷冲击掩埋预测模型从一维到三维的发展情况:(1)一维模型预测了在水雷降落角度恒定时的水雷质心的垂向位置;(2)二维模型预测了水雷质心在(x,z)二维平面中的位置以及绕y轴的旋转情况;(3)三维模型预测了水雷质心在(x,y,z)三维空间里的位置以及绕x,y和z轴的旋转情况.这些模型均通过从水雷冲击掩埋试验中获得的实验数据进行了验证.一维模型只求解了在沿z轴方向运动的一个动量方程,它不能很好地预测水雷的运动轨迹和掩埋深度.二维模型仅限于水雷在(x,z)平面中的运动状态预测,而且要求雷体周围的流体是静止的,另外,使用了不准确的阻尼系数和不精确的沉积物动力学.因此,二维模型在水雷的运动轨迹和埋藏深度的预测上误差很大(比在Monterey湾砂底观察的深度大6～10倍).三维模型能很好地预测圆柱体、近圆柱体以及实验用的Manta和Rockan等水雷的运动轨迹和掩埋深度.     

Impact response in glass-epoxy system with and without perforated PTFE-bearing material at the mid-thickness

The work looks at the differences in impact response between plain glass fabric-epoxy and the same system containing PTFE-bearing layer having regular circular perforations inserted at the entire mid-thickness position during fabrication stage of the laminate by the hand lay-up technique. Instrumented impact data showed a drop in maximum load, total energy and ductility index following the insertion. There was a difference in the way the load–time data appeared between the plain and the mid-layer inserted PTFE bearing material cases. The plain ones showed a sharp drop after the peak whereas such a feature was absent for the mid-layer material inserted ones. Also noticed were the changes in the number of steps seen both before and after peak load following the insertion of the PTFE bearing material. These features are analyzed with the help of optical microscopy, which showed a delamination exactly at the PTFE inserted interface region while for the plain, i.e.for the non-mid-layer inserted cases, the separation seemed to occur along the ply that had the poor bonding. These and other features are analyzed in this work.     

Interfacial activity of styrene-butadiene block copolymers in low-density polyethylene/polystyrene blends

The effect of molecular structure of styrene-butadiene (SB) block copolymers on their interfacial activity in low-density polyethylene/polystyrene (LDPE/PS) (4/1) blends was studied. It was found that addition of some SB copolymers, which are localized in brittle PS particles, leads to a decrease in the blend impact strength in spite of the fact that these SB improve the toughness of both the blend components. Comparison with our previous results showed that the distribution of SB copolymers between the interface and bulk phases and their supermolecular structure in LDPE/PS (4/1) blends strongly differs from those in LDPE/PS (1/4) blends.     

Thermal Degradation Behavior,Permeation Properties and Impact Response of Polyethylene/Organo-montmorillonite/(Ethylene Methacrylic Acid) Ternary Nanocomposites

Through this work we explored the effect of melt compounding a commercial grade of HDPE with organoclays of different precedence using EMAA as compatibilizing agent on the thermal behavior, barrier properties and biaxial impact response of composites. Morphology was examined by XRD and TEM. Crystalline structure was examined by DSC. Thermal behavior was evaluated by TGA. Barrier properties to low-molecular-weight penetrants were experimentally determined employing a gravimetric technique. Mechanical properties under impact conditions were evaluated by instrumented puncture tests. Intercalated nanocomposites were obtained. Throughout the thermal degradation of the nanocomposites in oxidant atmosphere a charring process of the PE, which is normally a non-char-forming polymer, was observed. The addition of OMMT improves barrier properties due to its contribution to tortuosity path and to the reduction of molecular mobility. Impact properties were only slightly reduced by nanocomposite formation. Results demonstrate that EMAA did not improve exfoliation, but it enhanced polymer–organoclay interactions giving rise to better thermal and permeation properties, without detriment of impact response.     

芳香族硝基炸药感度和安定性的量子化学研究I.苯胺类硝基衍生物

运用HMO 和CNDO/2方法, 研究了二十多种苯胺类硝基衍生物的安定性. 随着分子中C-NO2 键级的增大, 其撞击感度减小丶热它定性增强. 以孤立双键为参考基准的离域能判据, 不能反映分子中基团位置对称定性的影响; 它的运用只能局限在基团相互位置影响不大的共轭体系中, 作为本系列化合物它性的影响; 它的运用只能局限在基团相互位置影响不大的共轭体系中.作为本系列化合物它定性的判据, C-NO2 键级较通常的离域能更为适用和直观; C-NO2 键级判据也符合炸药起爆和热分解机理, 且与Delpuech 的 判据相一致.     

EFFECT OF PROCESSING METHOD ON THE IMPACT STRENGTH OF POM/TPU/CaCO3 TERNARY COMPOSITES

Polyoxymethylene （POM）/elastomer/filler ternary composites were prepared, in which thermoplastic polyurethane （TPU） and inorganic filler, namely, CaCO3, were used to achieve balanced mechanical properties of POM. The dispersion and phase morphology of POM/elastomer/filler composites were found to depend largely on processing method, CaCO3 content in masterbatch and the filler size. Two processing methods were employed to prepare POM/elastomer/filler ternary composites. One is called the one-step method, in which elastomer and the filler directly melt blended with POM matrix. The other is called the two-step method, in which the elastomer and the filler were mixed to get masterbatch first, which was then melt blended with pure POM of different content. The effect of phase morphology and processing method on impact strength was investigated. It was found that the two-step method results in an increase in impact strength but not for the one-step method. Additionally, the impact strength of POM ternary composites decreases with the increase in the size of CaCO3 particles.