复合材料板簧的模态预测与分析EI北大核心CSCD

为了能够对复合材料板簧的模态特性进行高效、准确的预测,基于经典层合板理论和微元法,建立了复合材料板簧的模态预测模型,并试制了玻璃纤维/环氧复合材料板簧对模型进行了验证。结果表明,该方法能够快速准确地预测复合材料板簧的垂向弯曲模态,有利于缩短复合材料板簧的开发周期。从复合材料的选材、铺层设计等角度出发,利用该模型分析了相关设计参数对板簧一阶弯曲模态频率的影响。分析结果表明,选用弹性模量较大、密度较小的复合材料、同时尽量增加簧身宽度、选择0°铺层方向角能够降低板簧与外界激励共振的可能性。该模型也能够对纤维增强型复合材料梁结构的模态预测提供参考。     

细编穿刺复合材料有效性能的有限元分析

根据细编穿刺复合材料的结构特点,提出了一个新的有限元模型,该模型较为真实地模拟了织物内纤维束的轮廓结构和走向.利用该模型采用有限元法,对穿刺纤维束间距接近于极限状态下的细编穿刺复合材料进行了有效性能的数值预报,并合理确定了复合材料内部应力场分布.通过理论计算结果与文献中结果的对比分析,验证了该模型的有效性.     

基于周期性边界条件的炭黑填充橡胶复合材料力学行为的预测

在分析炭黑填充橡胶复合材料的宏观与细观特征之间联系的基础上,提出了具有随机分布形态的代表性体积单元,推导并应用了周期性细观结构的边界约束条件,建立了三维多颗粒夹杂代表性体积单元的数值模型,对炭黑填充橡胶复合材料的宏观力学行为进行了模拟仿真。研究表明,该模型通过周期性边界条件的约束保证了宏观结构变形场和应力场的协调性;计算得到的炭黑填充橡胶复合材料的弹性模量明显高于未填充橡胶材料,并随着炭黑颗粒所占体积分数的增加而增大;该模型对复合材料有效弹性模量的预测结果与实验结果吻合较好,而且比Bergstrom三维模型的预测结果更好,证实了该模型能够用于炭黑颗粒增强橡胶基复合材料有效性能的模拟分析。     

2.5维编织复合材料力学性能的有限元分析

在已有研究的基础上,提出了一个新的2.5维编织复合材料有限元模型,该模型较为真实地模拟了织物内纤维束的轮廓结构和走向,可用于2.5维编织复合材料力学性能的有限元数值分析.利用该模型采用有限元法对2.5维编织复合材料进行了有效弹性性能的数值预报,并合理确定了复合材料内部应力场分布;同时提出经向纤维束横截面宽厚比是影响2.5维编织复合材料有效弹性性能的主要因素,分析了其影响情况.采用VARTM工艺制备了试验件,并对其进行力学性能测试.通过实验值和理论值的对比,结果表明:有限元计算得到的结果与实验值吻合较好,从而验证了该模型的有效性.     

三维四向编织复合材料力学性能的有限元分析

在已有研究的基础上,提出了一个新的三维编织复合材料单元胞体模型,该模型正确地反映了纤维束的交织方式,十分接近三维编织复合材料的真实结构,可用于三维四向编织复合材料有效模量的有限元数值预报,并合理确定复合材料内部全场应力分布。采用有限元软件对该模型进行了力学分析,得到了相关等效弹性性能参数。结果表明:有限元计算得到的三维编织复合材料的等效弹性性能与实验结果和理论预测值都吻合较好,从而验证了该模型的有效性。此外,基于新的单元胞体模型还确定了三维四向编织复合材料的应力场,为进一步的强度计算奠定了基础。      

层压复合材料分层扩展分析的虚拟裂纹闭合技术及其应用

提出一种基于虚拟裂纹闭合技术的界面元模型,用以模拟复合材料的分层破坏和预测结构的承载能力。界面元被嵌入在模型分层扩展路径上,计算结构的能量释放率,结合幂指数破坏准则,模拟复合材料的分层扩展。对由于裂尖单元长度不同所带来的分析误差进行了适当的修正,以降低网格粗细变化所带来的不利影响。为了检验该界面元的可靠性,分别将其应用于对双悬臂梁(DCB) 模型、端边切口(ENF) 模型和混合模式弯曲(MMB) 模型的分层扩展分析中。计算结果与解析解基本吻合,从而验证了采用该界面元模拟复合材料分层破坏的可行性。用该方法对3个含有不同初始损伤复合材料T型接头的界面拉脱分层破坏进行数值模拟,计算结果与试验数据吻合良好。      

圆柱形破片侵彻纤维增强复合材料三明治板的弹道极限模型EI北大核心CSCD

分析了圆柱形破片侵彻纤维增强复合材料三明治板的过程,基于能量守恒定律分别对圆柱形破片侵彻面板、复合材料夹层和背板三个阶段中消耗的能量进行了理论推导,建立了圆柱形破片侵彻纤维增强复合材料三明治板的计算模型,并得到了剩余速度的计算公式,令剩余速度等于零,即可得到弹道极限。将计算模型得出的结果与试验结果进行了对比,验证了计算模型的可行性与有效性。该计算模型可以为钢/纤维增强复合材料/钢复合装甲结构的抗侵彻设计提供指导。     

圆柱形破片侵彻纤维增强复合材料三明治板的弹道极限模型

分析了圆柱形破片侵彻纤维增强复合材料三明治板的过程,基于能量守恒定律分别对圆柱形破片侵彻面板、复合材料夹层和背板三个阶段中消耗的能量进行了理论推导,建立了圆柱形破片侵彻纤维增强复合材料三明治板的计算模型,并得到了剩余速度的计算公式,令剩余速度等于零,即可得到弹道极限。将计算模型得出的结果与试验结果进行了对比,验证了计算模型的可行性与有效性。该计算模型可以为钢/纤维增强复合材料/钢复合装甲结构的抗侵彻设计提供指导。     

随机短纤维增强复合材料弹性模量预测模型

为了研究纤维增强复合材料的力学性能, 借助混合率构造的Reuss-Voigt模型以及三维纤维取向简化模型, 建立了随机短纤维复合材料弹性模量预测模型。利用该模型对玻璃纤维增强尼龙6(PA6)复合材料进行弹性模量预测, 其预测结果与拉伸实验结果误差值小于5%, 表明该预测模型具有较好的准确性。     

异形截面木塑复合材料托盘的数值模拟与实验对比分析

利用有限元数值仿真技术,研究了具有异形截面的木塑复合材料托盘的承载能力。采用自定义截面梁单元建立木塑复合材料的异型截面梁模型;基于该异形截面梁模型,建立了托盘有限元模型,并进行承载能力计算;最后将数值计算结果与实验结果进行对比分析。研究结果表明：数值分析结果与实验结果有比较好的一致性;数值分析方法的计算精度满足实际工程需要。该方法用于具有复杂截面形状的木塑复合材料及制品的研究与开发,能节约实验及研发成本、缩短研发周期。     

Gaining knowledge on the processability of PLA-based short-fibre compounds – A comprehensive comparison with their PP counterparts

The present study provides a quantitative overview of bio-based compound processing compared to commonly used composites reinforced with short glass fibres (GF). Three reinforcing fibres were compounded with polylactide and polypropylene: abaca, man-made cellulose and conventional E-GF. The flow behaviour of corresponding melts was determined using melt flow rate (MFR) and online flow spiral test. The composite structures were analysed by means of SEM in order to investigate the fibre fracture during processing and the fibre/matrix bonding affinity. The fibre length distribution was correlated with the results from the melt flow experiments, and the structure–property relationships were determined using SEM images. It was confirmed that the fibre texture, interactions between fibres and fibre–matrix bonding are influenced by subsequent processing steps and have a substantial effect on the further composite melt processing.     

Determination of interfacial shear strength of white rot fungi treated hemp fibre reinforced polypropylene

Short untreated and white rot fungi treated hemp fibre, polypropylene (PP) and maleated polypropylene (MAPP) coupling agent were extruded and injection moulded into composite tensile test specimens. The tensile properties of untreated and treated fibre and their composites were measured. The fibre length distributions in the composite were obtained by dissolving the PP/MAPP matrix in boiling xylene to extract the fibre. Both the Single Fibre Pull-Out test and the Bowyer and Bader model were used to determine the interfacial shear strength (IFSS) of these composites. IFSS was found to be lower for the Single Fibre Pull-Out test, which was considered to be largely due to axial loading of fibre and the resulting Poisson’s contraction occurring during this technique. This suggests that the Bowyer and Bader model provides a more relevant value of IFSS for composites. The results obtained from both methods showed that IFSS of the treated fibre composites was higher than that for untreated fibre composites. This supports that the hemp fibre interfacial bonding with PP was improved by white rot fungi treatment.     

Development of a Model for Predicting the Transverse Coefficients of Thermal Expansion of Unidirectional Carbon Fibre Reinforced Composites

A model for predicting the transverse coefficients of thermal expansion (CTE) for carbon fibre composites is presented in this paper. The transverse CTE were calculated by finite element analysis using a representative unit cell. The analytical micromechanical models from literature were reviewed by comparing with the FEA data. It shows that overall Hashin model provides the best accuracy. However, the calculating process of Hashin model is very complicated and inconvenient for practical applications. By using FEA, Design of Experiments (DOE), and Response Surface Method (RSM), the transverse CTE of unidirectional carbon fibre composites were studied and a regression-based model was developed. The model was validated against the FEA and experimental data. It shows that the developed model offers excellent accuracy while reduces complicated computation process. The advantage of this model is that it provides a simple and accurate method for predicting the transverse CTE of composites, which helps effective and efficient design of composite structures.     

Thermal and dynamic mechanical analysis of polystyrene composites reinforced with short sisal fibres

The thermal behaviour of polystyrene composites reinforced with short sisal fibres was studied by means of thermogravimetric and dynamic mechanical thermal analysis. The thermal stability of the composites was found to be higher than that of sisal fibre and the PS matrix. The effects of fibre loading, fibre length, fibre orientation and fibre modification on the dynamic mechanical properties of the composites were evaluated. Fibre modifications were carried out by benzoylation, polystyrene maleic anhydride coating and acetylation of the fibre and the treatments improved the fibre-matrix adhesion. PS/sisal composites are thermally more stable than unreinforced PS and sisal fibre. The addition of 10% fibre considerably increases the modulus but the increase is found to level off at higher fibre loadings. The T_g values of the composites are lower than that of unreinforced PS and may be attributed to the presence of some residual solvents in the composites entrapped during the composite preparation. The treated-fibre composites show better properties than those of untreated-fibre composites. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. A master curve is constructed based on time-temperature superposition principle.     

Polyoxymethylene composites with natural and cellulose fibres: Toughness and heat deflection temperature

Cellulose and abaca fibre reinforced polyoxymethylene (POM) composites were fabricated using an extrusion coating (double screw) compounding followed by injection moulding. The long cellulose or abaca fibres were dried online with an infrared dryer and impregnated fibre in matrix material by using a special extrusion die. The fibre loading in composites was 30 wt.%. The tensile properties, flexural properties, Charpy impact strength, falling weight impact strength, heat deflection temperature and dynamic mechanical properties were investigated for those composites. The fibre pull-outs, fibre matrix adhesion and cracks in composites were investigated by using scanning electron microscopy. It was observed that the tensile strength of composites was found to reduce by 18% for abaca fibre and increase by 90% for cellulose fibre in comparison to control POM. The flexural strength of composites was found to increase by 39% for abaca fibre and by 144% for cellulose fibre. Due to addition of abaca or cellulose fibre both modulus properties were found to increase 2-fold. The notched Charpy impact strength of cellulose fibre composites was 6-fold higher than that of control POM. The maximum impact resistance force was shorted out for cellulose fibre composites. The heat deflection temperature of abaca and cellulose fibre composites was observed to be 50 °C and 63 °C higher than for control POM respectively.     

A study of the corrosion resistance of glass fibre reinforced polymers

Specific interactions between chemical environments (hydrochloric acid, sulphuric acid and distilled water) and glass fibre cause stress corrosion cracking in the glass fibre surface. The etching of the glass fibre gives rise to an extraction process. Axial or spiral cracks can then be observed. These effects depend on the fibre diameter, the etching time and the chemical environment and cause a drop in tensile stresses. The glass fibre crumbles with increasing etching time.Strict etching procedures lead to definite extraction processes and crack structures in the glass fibres and will be discussed in connection with strength tests.In addition to investigations of individual elements, e.g. glass fibres, it is also possible that whole glass fibre reinforced composites are damaged during service under the influence of aggressive surrounding media. In such cases, circular or spiral-shaped cracks can also be observed preferentially in the glass fibre. The fibres can then no longer contribute to an increase in strength and the result is the untimely failure of the composite material.     

Morphological investigations of injection moulded fibre-reinforced thermoplastic polymers

Fibres affect the matrix morphology in fibre-reinforced composites. Especially in semi-crystalline melts the fibres can act as nucleation rods causing a structure known as transcrystallinity. Transcrystalline structures are also found in injection moulded parts. They affect the structure of fracture surfaces especially in the case of long fibre-reinforced polymers with good fibre/matrix adhesion. Transcrystalline structures are usually generated and investigated in a microscope with a hot stage. For injection moulded parts this is an inadequate method. The morphological results presented here were obtained from plasma-etched inner surfaces and thin sections by means of light and contrast interference microscopy accompanied by scanning electron microscopy of fracture surfaces. Plasma etching is a well suited preparation technique to reveal both morphological superstructures and damage such as voids, debonding and fibre cracks in composites.     

Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites

In this work, flexural strength and flexural modulus of chemically treated random short and aligned long hemp fibre reinforced polylactide and unsaturated polyester composites were investigated over a range of fibre content (0-50 wt%). Flexural strength of the composites was found to decrease with increased fibre content; however, flexural modulus increased with increased fibre content. The reason for this decrease in flexural strength was found to be due to fibre defects (i.e. kinks) which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fibre treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fibre/matrix adhesion.     

The fibre distribution of Al2O3/Al–Cu alloy composites

Two methods which rely on direct microstructural measurements to assess the fibre distribution in alumina continuous fibre-reinforced Al–Cu alloy composites produced via an infiltration process, are outlined. The first is based on distance analysis, i.e. the distance distribution of nearest neighbours; and the second is based on fibre–cell structures. Specimens with two fibre volume fractions, 0.39 and 0.50, were employed in this study. It was found that the fibres in both kinds of specimen appear to have a rough thread-like distributions, and the local volume fraction of the fibres varies over a larger range in the specimen with lower fibre volume fraction than does that in the specimen with the larger one. Quantitative relationships between fibre distribution and the composite defects are deduced. Some data on the microsegregation of copper and the macrosegregation of eutectic phase are given in relation to the fibre distributions. The reasons for the uneven fibre distributions are also discussed.