Synergistic effect of hybrid Himalayan Nettle/Bauhinia-vahlii fibers on physico-mechanical and sliding wear properties of epoxy composites

The cellulosic bast fibers are recognized as a justifiable and biodegradable substitute for producing moderate strength polymer composite materials because of their characteristics of renewability, eco-friendliness, and higher specific strength. Hence the aim of this research work is to fabricate Himalayan bast fibers (Nettle fiber (NF)/bauhinia vahlii fiber (BF)) based mono/hybrid epoxy composites at varying weight percentage of 2–6 wt% and evaluate the physical (void fraction and water absorption), mechanical (tensile strength, flexural strength, hardness) and sliding wear properties of as-fabricated composites. The 6 wt% NBF reinforced composites exhibited higher mechanical properties as compared to NF and BF composites with tensile strength of 34.04 MPa, flexural strength of 42.45 MPa, and hardness of 37.01 H_v respectively. The influence of various control factors (sliding velocity, NF/BF/NBF contents, normal load and sliding distance) on specific sliding wear rate of composites was evaluated by Taguchi (three factors at three levels) experimental design and the percentage contribution of these selected parameters on sliding wear performance was examined by Analysis of variance (ANOVA). The sliding wear property of as-developed composites was found to be greatly influenced by sliding velocity and the wear resistance was observed to be improved with the NF/BF/NBF contents. The wear mechanism of the as-fabricated composites has been elucidated by scanning electron microscopy analysis. The research outcomes demonstrated that the hybridization of Bauhinia vahlii fiber with Nettle fiber led to improve the mechanical and wear properties of epoxy composites.     

Kevlar fabric reinforced polybenzoxazine composites filled with silane treated microcrystalline cellulose in the interlayers: The next generation of multi-layered armor panels

The design of astonishing combinations of benzoxazine resins with various fillers is nowadays of great interest for high quality products, especially in ballistic armors. The objective of this study is to investigate a new hybrid material prepared as multi-layered composite plate by hand lay-up technique. Different composites were manufactured from Kevlar fabrics reinforced polybenzoxazine, which was filled with silane treated microcrystalline cellulose (MCC Si) at various amounts in the interlayers. The developed materials were tested for their flexural, dynamic mechanical and ballistic performance. The aim was to highlight the effect of adding different amounts of MCC Si on the behavior of the different plates. Compared to the baseline, the dynamic mechanical and bending tests revealed an obvious decrease of the glass transition of 21 °C and a notable increase in storage modulus and flexural strength of about 180 %and17%, respectively, upon adding 1% MMC Si as filler. Similarly, the ballistic test exhibited an enhancement in kinetic energy absorption for which the composite supplemented with 1% MCC Si had the maximal energy absorption of 166.60 J. These results indicated that the developed panels, with interesting mechanical and ballistic features, are suitable to be employed as raw materials to produce body armor.     

An investigation on anti-impact and penetration performance of basalt fiber composites with different weave and lay-up modes

The woven basalt fiber composites (WBFC) and the unidirectional [0°/90°/45°/-45°]_s basalt fiber composites (UBFC) were prepared by hot-pressing. Three-point bending test, low velocity impact test, and ballistic test were performed to the prepared composites. After the tests, the specimens were recovered and analyzed for micromorphology. Three-point bending tests show that both the bending strength and stiffness of the WBFC surpass those of the UBFC. Low velocity impact test results show that the low velocity impact resistance to hemispherical impactor of the UBFC is higher than that of the WBFC, but the low velocity impact resistance to sharp impactor of the UBFC is lower than that of the WBFC. For the ballistic test, it can be found that the ballistic property of the UBFC is higher than that of the WBFC. After the tests, microscopic analysis of the specimens was applied, and their failure mechanism was discussed. The main failure modes of the UBFC are delamination and fibers breakage under the above loading conditions while the main failure mode of the WBFC is fibers breakage. Although delamination damage can be found in the WBFC under the above loading conditions, the degree of delamination is far less than that of the UBFC.     

体内芳纶纤维筋梁受弯性能试验研究分析

通过钢筋混凝土梁与芳纶纤维筋梁的弯曲试验现象和结果,探讨了芳纶纤维筋梁的正截面受力性能和破坏模式,分析了芳纶纤维筋配筋率对混凝土梁的裂缝宽度、挠度和承载力等的影响,为今后进一步研究和设计AFRP筋受弯构件提供了参考。     

一种低黏度环氧树脂的制备及性能研究

采用一种新型增韧剂CC对环氧树脂进行增韧改性,获得一种低黏度中温固化环氧树脂体系。测试了树脂的力学性能,并通过红外光谱和动态热机械能分析等方法,对树脂的组织和性能进行了研究。结果表明：当CC的质量分数为19%时,环氧树脂的剪切强度和拉伸强度最大,分别为25.1 MPa和55.88 MPa;该环氧树脂具有较低的黏度;固化过程中各组分反应完全,树脂刚度较大,玻璃温度Tg达110.36℃。     

侧面封边对玻璃纤维增强环氧树脂基复合材料吸湿规律的影响

采用称量法和排水法联合,研究了侧面封边和未封边单向玻璃纤维增强环氧树脂基复合材料层合板试件的吸湿量和体积变化率与浸泡时间的关系,结果显示,复合材料侧面吸湿的速度远大于表面吸湿速度;侧面封边复合材料试件的饱和吸湿量为1.30％,而未封边试件的为2.26％,即与侧面封边试件相比,未封边试件的饱和吸湿量(质量比)增加了73....     

极性基团对环氧树脂基体力学性能及吸水特性的影响

研究了CYD- 128/THPA/DMP- 30 (CTD)、TDE- 85/THPA/DMP- 30(TTD)、CYD- 128/IPDA(CI)与TDE- 85/IPDA (TI)4种环氧树脂基体浇铸体的拉伸、弯曲和耐海水性能,分析了树脂、固化剂类型和分子结构对树脂基体性能的影响.结果表明,使用相同固化剂时,TDE...     

Investigation of normal,lateral, and oblique impact of microscale projectiles into unidirectional glass/epoxy composites

Spacesuits and spacecraft must endure high velocity impacts from micrometeoroids. This work considers the impact of 100 μm diameter projectiles into composite targets at velocities from 0.5 km/s to 2 km/s. This work begins by presenting an energy-based theoretical model relating depth of penetration (DoP) and impact force to impact velocity, characteristic time, and threshold velocity and force. Next, this work compares numerical simulations of normal impact on composites to the theoretical model. Numerical simulations are conducted with LS-DYNA and the well-known composite model, MAT-162. The numerical models consider unidirectional S2-glass fiber reinforced SC-15 epoxy composite laminates. The numerical model shows good correlation with the theoretical model. The numerical model also investigates lateral impact, parallel to the fiber direction, and oblique impact at angles from 30° to 82.5°. This work decomposes oblique impact into normal and lateral components, and compares them with normal and lateral impact results. The results show good correlation of the normal component of oblique results with the theoretical model. This numerical and theoretical study focuses on DoP, velocity, and penetration resistance force as functions of time. The theoretical model and numerical simulations are used to determine new DoP parameters: characteristic time of depth of penetration and threshold impact velocity. These models are a first step in developing the capability to predict DoP for oblique, microscale, high-speed impact on composite materials.     

石英纤维增强苯并噁嗪树脂复合材料研究

对苯并(啞心)嗪树脂应用于RTM工艺制备石英纤维增强复合材料进行了研究.系统考察了该树脂的工艺性能及力学性能,制备并测试了石英/苯并(啞心)嗪复合材料的力学性能及耐烧蚀性能,并将相关性能与钡酚醛与石英/钡酚醛进行了比较.结果表明,在85℃～145℃温度区间内苯并(啞心)嗪树脂粘度保持在800mPa·s以下,树脂具有较宽的低粘度温度平台和较长的低粘度保持时间.力学性能及耐烧蚀性能研究表明,石英/苯并(啞心)嗪复合材料的层间剪切强达到了61.5MPa,拉伸强度和弯曲强度显著优于石英,钡酚醛复合材料,质量烧蚀率和线烧蚀率分别为0.0510g·s-1和0.032mm·s-1.石英/苯并(啞心)嗪复合材料是一种可采用RTM工艺制备的耐烧蚀材料.     

双酚A环氧树脂改性二氧化双环戊二烯体系固化动力学分析及其性能研究

二氧化双环戊二烯(CDR -0122)环氧树脂固化物的耐热性较好,但脆性大.采用不同质量分数的环氧(E -51)改性CDR -0122.对不同的改性体系进行DSC分析,确定其活化能、反应级数和最佳固化工艺.对改性的CDR - 0122环氧树脂固化物进行力学性能和耐温性能测试.结果表明:当加入E-51的质量分数为30％时,CDR -0122的树脂体系的综合性能最优.相比改性前,改性后的树脂体系活化能略有下降,并且其拉伸强度和弯曲强度分别提高了52.38％和54.77％,但玻璃化转变温度略有下降.     

波速测量层合复合材料冲击损伤实验

在层合复合材料横向冲击试验中,用应变片记录层合板表层在冲击过程中的应变响应,根据波的传播理论和连续损伤力学,从波速变化间接测得冲击下材料的损伤及损伤率。通过实验测得玻璃纤维／环氧（ＧＥ）正交层合板的动态损伤阈值,并证实了ＧＥ复合材料在拉伸阶段比在压缩阶段有更快的损伤扩展速率     

Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites

The mechanical, thermal and ablation properties of carbon phenolic (C-Ph) composites (Type-I) rein-forced with different weight percentages of organo-modified montmorillonite (o-MMT) nanoclay have been studied experimentally. Ball milling was used to disperse different weight (wt) percentages (0, 1,2,4,6 wt.％) of nanoclay into phenolic resin. Viscosity changes to resin due to nanoclay was studied. On the other hand, nanoclay added phenolic matrix composites (Type-II) were prepared to study the dispersion of nanoclay in phenolic matrix by small angle X-ray scattering and thermal stability changes to the matrix by thermogravimetric analyser (TGA). This data was used to understand the mechanical, thermal and ablation properties of Type-I composites. Inter laminar shear strength (ILSS), flexural strength and flexural modulus of Type I composites increased by about 29％, 12％and 7％respectively at 2 wt.％ addition of nanoclay beyond which these properties decreased. This was attributed to reduced fiber volume fraction (％Vf) of Type-I composites due to nanoclay addition at such high loadings. Mass ablation rate of Type-I composites was evaluated using oxy acetylene torch test at low heat flux (125 W/cm2) and high heat flux levels (500 W/cm2). Mass ablation rates have increased at both flux levels marginally up to 2 wt.％ addition of nanoclay beyond which it has increased significantly. This is in contrast to increased thermal stability observed for Type-I and Type-Ⅱ composites up to 2 wt.％addition of nanoclay. Increased ablation rates due to nanoclay addition was attributed to higher insulation effi-ciency of nanolcay, which accumulates more heat energy in limited area behind the ablation front and self-propagating ablation mechanisms triggered by thermal decomposition of organic part of nanoclay.     

Residual Characteristic of High-Velocity Steel Fragments Penetrating UHMWPE FRP Laminates

The mechanical performance of ultra-high molecular weight polyethylene fiber (UHMWPE) and its composites were proposed. Penetrated properties of different thicknesses UHMWPE FRP laminates (URP) impacted by 3.3g cubic high velocity fragments were studied. According to the ballistic experimental results and theoretical analysis, the linear relation between ballistic limit vBL and area density AD was confirmed. The relative parameters of showing experientially residual velocity vr were expressed by the function of AD. In the end, versatile experiential expression between vr and AD was found. Prediction of vr and vBL using obtained expressions under the above stated condition of impacting URP was consistent with the experimentaled results. Consequently, the two experiential relations can be used to predict the residual velocity and ballistic limit of cubic high velocity fragments impacting URP. The residual characteristic of high-velocity steel fragments penetrating UHMWPE FRP laminates can be more exactly forecasted by the two derived experiential formulas.     

添加SiC微粉对硅树脂先驱体转化3D Cf/Si-O-C材料性能的影响

以三维碳纤维织物和廉价的硅树脂为原料,采用先驱体转化工艺制备3D G/Si-O-C材料,考察了浸渍液中添加SiC填料对材料微观结构、力学性能和抗氧化性能影响.结果表明:添加适量的SiC填料有助于减少基体孔隙,改善界面结合,从而提高材料的力学性能;而SiC含量过高时,容易在材料内部形成闭孔,从而导致材料力学性能下降.当SiC微粉含量为18.2%时,材料具有最好的力学性能,弯曲强度和断裂韧度分别为421.3MPa和13.0 MPa·m1/2;而材料的抗氧化性能随着SiC微粉含量的增加而增加,当SiC微粉含量为25.0%时,材料的弯曲强度保留率最高,达到了89.5%.     

Delamination process in cross-ply UHMWPE laminates under ballistic penetration

Cross-ply unidirectional laminates made of ultra-high molecular weight polyethylene fibers are widely used as components of bullet-proof vests. To simulate the delamination process of the material under penetration, we constructed a numerical mechanical model, which was validated by tests using 7.62 × 39 mm rifle bullets penetrating laminates of different thicknesses. The results show that the delamination region is essentially diamond-shaped. The simulated delamination region is in good agreement with the experimental data. It is found that the delamination region increases with the compression modulus along the fiber direction. The delamination region increases when the shear strength between the fabric layers decreases;However, it is little influenced by the normal strength. The delamination region of the front face of the laminate is little influenced by the failure strain of the material and the initial velocity of the bullet. The delamination region of the back face increases with the failure strain and decreases with the initial velocity.     

Enhancement of wear and ballistic resistance of armour grade AA7075 aluminium alloy using friction stir processing

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys,7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant Mo S2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.     

表面官能化对碳纳米管/环氧复合材料玻璃化转变温度及韧性的影响

通过碳纳米管的不同表面官能化,构造其与环氧树脂的不同界面。采用动态机械性能分析研究不同表面官能化碳纳米管对环氧树脂复合材料玻璃化转变温度的影响;采用摆锤冲击试验研究环氧树脂复合材料的韧性。结果表明:与纯环氧树脂相比,氨基化碳纳米管/环氧树脂复合材料的玻璃化转变温度升高,而羧基化碳纳米管/环氧树脂复合材料的玻璃化转变温度反而有所下降;碳纳米管/环氧树脂复合材料的冲击强度相比纯环氧树脂均提高了近一倍。复合材料性能的这些变化规律主要归因于不同表面官能化碳纳米管与环氧树脂基体间形成了不同的界面。     

Fabrication of AA7005/TiB2-B4C surface composite by friction stir processing: Evaluation of ballistic behaviour

The present work aims to enhance the ballistic resistance of AA7005 alloy by incorporating the TiB₂ and B₄C ceramic reinforcement particles. Surface composites with different weight fractions of TiB₂ and B₄C particles were processed by friction stir processing. Micro-hardness and depth of penetration tests were carried out to evaluate the ballistic properties of the surface composites. The surface hardness of the composite was found to be nearly 70 HV higher than base alloy. The depth of penetration of the steel projectile was 20–26 mm in the composites as compared to 37 mm in the base alloy. Ballistic mass efficiency factor of the surface composite was found to be 1.6 times higher than base alloy. This is mainly attributed to the dispersion strengthening from the reinforcement particles.     

FE modeling of concrete beams and columns reinforced with FRP composites

Compression and flexure members such as columns and beams are critical in a structure as its failure could lead to the collapse of the structure. In the present work, numerical analysis of square and circle short columns, and reinforced concrete (RC) beams reinforced withfiber reinforced polymer composites are carried out. This work is divided into two parts. In thefirst part, numerical study of axial behavior of square and circular concrete columns reinforced with Glass Fiber Reinforced Polymer (GFRP) and Basalt Fiber Reinforced Polymer (BFRP)bars and spiral, and Carbon Fiber Reinforced Polymer (CFRP) wraps is conducted. The results of the first part showed that the axial capacity of the circular RC columns rein-forced with GFRP increases with the increase of the longitudinal reinforcement ratio. In addition, the results of the numerical analysis showed good correlation with the experimental ones. An interaction diagram for BFRP RC columns is also developed with considering various eccentricities. The results of numerical modeling of RC columns strengthened with CFRP wraps revealed that the number and the spacing between the CFRP wraps provide different levels of ductility enhancement to the column. For the cases considered in this study, column with two middle closely spaced CFRP wraps demonstrated the best performance. In the second part of this research,flexural behavior of RC beams reinforced with BFRP, GFRP and CFRP bars is investigated along with validation of the numerical model with the experimental tests. The results resembled the experimental observations that indicate significant effect of the FRP bar diameter and type ont he flexural capacity of the RC beams. It was also shown that Increasing the number of bars while keeping the same reinforcement ratio enhanced the stiffness of the RC beam.     

SiCf/Si-O-C复合材料的抗氧化、抗热震性能研究

通过研究材料的氧化前后质量的改变和强度减少及氧化前后微观结构的变化,研究了先驱体转化法制备的SiCf/Si-O-C复合材料的抗氧化、抗热震性能。结果表明SiCf/Si-O-C复合材料具有良好的抗氧化、抗热震性能。对所得材料微观结构进行了分析讨论,发现界面结构的变化是影响SiCf/Si-O-C复合材料抗氧化、抗热震性能的主要原因。