热塑性复合材料夹芯结构熔融连接研究进展

面芯界面性能是复合材料夹芯结构发挥其力学/多功能优势的关键,热塑性树脂具有可熔融再造的特点,使热塑性复合材料夹芯结构(TPCSS)可在不引入新材料的前提下,形成连续可靠的面芯界面。对近年来热塑性复合材料夹芯结构熔融连接研究进展进行了梳理,总结了常见构型与所用材料,重点归纳了主要的熔融连接方法,包括热板焊接、模压成型、连续热压、面芯共编和增材制造等。基于国内外研究和应用现状,展望了熔融连接热塑性复合材料夹芯结构的未来发展趋势和应用前景。     

夹芯复合材料基座结构设计与强度分析

提出了两型夹芯复合材料基座结构的设计方案,建立了夹芯复合材料基座数值分析模型,通过理论分析确定了影响基座结构刚度和强度性能的主要参数;应用有限元法。分析了铺层方式、支撑厚度和骨架形式等对直支撑基座结构刚度和强度性能的影响规律,计算并讨论了曲率半径对弧形支撑式基座刚度和强度性能的影响;比较了5种夹芯材料基座的结构力学性能,并通过优化设计,确定了夹芯复合材料基座结构形式。     

复合材料蜂窝夹芯结构低速冲击位置识别研究

进行了碳纤维增强复合材料蜂窝夹芯结构的低速冲击实验,采用一种基于应力波和免疫遗传算法的冲击载荷定位方法对蜂窝夹芯结构上的低速冲击载荷进行分析和定位。首先,通过一组事先确定冲击位置的低速冲击载荷产生的冲击应力波实验数据,使用小波变换方法对其在时频域进行分析,获得多个频率上冲击应力波在蜂窝夹芯结构中的传播速度;然后在此基础上,考虑蜂窝夹芯结构中应力波的各向异性特性,采用免疫遗传算法对未知的低速冲击载荷进行位置识别。实验研究结果表明了该方法的可行性和有效性     

安静型夹芯复合材料舵设计及其力学性能分析

通过对夹芯复合材料各层材料的选择，以及夹芯复合材料舵壳的结构设计，提出了夹芯复合材料舵的设计方案和制作工艺。并利用有限元方法计算了复合材料舵壳在流体压力作用下的应力和变形，以及在瞬态载荷作用下舵壳的振动响应。计算结果表明，夹芯复合材料舵壳满足结构的强度和刚度的要求，同时振动水平与钢舵比较有很大的改善。     

复合材料夹芯结构非线性热传导分析

针对复合材料夹芯结构温度场分布的特点, 提出一种用于复合材料夹芯结构热传导精细分析的有限单元模型。这种单元模型为三维六面体模型, 单元模型厚度方向的插值函数在芯层和面板交界节点处温度值是连续的, 但温度变化率是不连续的, 而芯层内部节点处沿厚度方向温度值和温度变化率都是连续的。在考虑材料热传导参数随温度变化的情况下, 基于这种有限单元模型建立的复合材料夹芯结构瞬态温度场分析有限元方程为非线性方程。在求解此瞬态热传导非线性有限元方程时, 改进了常用的动力学平衡方程的解法, 改进后的动力学平衡方程解法避免了迭代运算, 提高了求解非线性动态平衡方程的效率。数值算例结果显示了该分析模型的有效性和可靠性。      

夹芯复合材料阻尼性能的研究进展

随着航空航天轻质高速化和精密仪器设备自动化的发展,振动问题日益凸显.夹芯复合材料比强度高、比模量大、减振性能优良,兼具结构和功能一体化的特性,成为航空航天领域研究的热点.从复合材料基体、增强体、界面3个方面阐述了复合材料的减振机理,介绍了目前研究热门的夹芯结构以及芯材、面板、结合界面及其相互作用对阻尼性能的影响规律,概述了夹芯复合材料阻尼改性的研究现状,最后对夹芯复合材料阻尼的研究方向进行了展望.     

夹芯复合材料结构阻尼特性研究

从粘弹性材料的本构关系出发,应用复特征值理论推导了夹芯复合材料结构阻尼的计算方法;同时基于能量损耗原理和阻尼的产生机理,研究了夹芯复合材料结构阻尼计算的模态应变能方法;提出了两种承载/减振夹芯复合材料结构模型,应用动态力学热分析方法测量了芯材的阻尼参数;应用两种阻尼计算理论和有限元数值分析相结合的方法研究了两种夹芯结构模型的损耗因子,并与试验结果进行了比较;分析了夹芯厚度对结构损耗因子的影响.     

复合芯材夹芯结构成型工艺研究

为了改善复合材料夹芯结构中芯材与面板界面结合强度,研制了一种新型夹芯结构,即复合材料柱/泡沫塑料复合芯材夹芯结构.该结构中用过渡层取代胶结层,使芯材和面板为一体,芯材由泡沫塑料和柱结构组成,其中柱结构是与面板同材质的纤维增强复合材料.通过该夹芯结构的芯材结构设计、加工工具的设计、加工工艺设计,使增强材料在法向上植入芯材中,并与上下面板的增强材料连通.由于在同一个工艺过程中固化成型,构成一个整体,没有界面,从根本上改善了面板与芯材之间粘接性能薄弱问题.试验结果表明,该结构具有较高的抗层间剪切、抗平压、抗剥离及抗疲劳性能.     

泡沫夹芯复合材料水声性能预测研究

针对泡沫夹芯复合材料声学测试的实际情况,建立了耦合声学有限元法的计算模型,针对计算模型进行了算例验证。结果表明,模型的预测值与试验值趋势吻合较好,计算方法是有效且可行的,可以用于预测泡沫夹芯复合材料的声学性能。同时,研究了与面板和芯材有关的四个参数对夹芯复合材料声学性能的影响规律。     

基于分层理论的螺栓连接夹芯复合材料加筋结构振动特性

针对采用螺栓连接方式固定的夹芯复合材料加筋结构,表层采用分层理论单元、芯层采用体单元,结合有限元方法计算固有频率和振型。通过试验验证,有限元计算结果与试验结果吻合,并得到了在有限元分析中模拟实际结构边界条件的处理方法。试验结果对比表明,与钢制结构相比,夹芯复合材料加筋结构前三阶固有频率提高2倍以上,夹芯复合材料加筋结构能大幅提高整体结构刚度,改善结构的振动特性。      

An analytical solution for the analysis of symmetric composite adhesively bonded joints

Analytical solutions for adhesively bonded balanced composite and metallic joints are presented in this paper. The classical laminate plate theory and adhesive interface constitutive model are employed for this deduction. Both theoretical and numerical (finite element analysis) studies of the balanced joints are conducted to reveal the adhesive peel and shear stresses. The methodology can be extended to the application of various joint configurations, such as single-lap and single-strap joints to name a few. The methodology was used to evaluate stresses in several balanced adhesively bonded metallic and composite joints subjected to the tensile, moment and transverse shear loadings. The results showed good agreements with those obtained through FEM.     

金属裂纹板复合材料单面胶接修补结构应力分析

考虑金属裂纹板复合材料单面胶接修补结构的几何非线性和边界条件,建立了考虑弯曲变形单面修补结构力学分析模型,计算出承受面内载荷时修补结构的弯矩和挠度,将补片自由端和金属板裂纹处的弯矩作为胶层应力控制微分方程的边界条件,推导出剪应力和剥离应力的解析解,及裂纹张开位移的表达式,并与有限元数值结果进行对比。分析结果表明,胶接修补结构应力分析理论模型和相关简化假设合理、正确。利用所建立的解析模型研究了金属裂纹复合材料单面胶接修补结构的应力分布特点及胶层主导破坏模式的失效机制,为胶接修补结构的承载能力分析以及结构改进设计提供了一定的理论依据。     

Analysis of adhesive bonded composite lap joints with transverse stitching

The effect of transverse stitching on the stresses in the adhesive is investigated using an adhesive sandwich model with nonlinear adhesive properties and a transverse stitching model for adhesive bonded composite single-lap and double-lap joints. Numerical results indicate that, among all stitching parameters, thread pretension and stitch density have significant effect on the peel stresses in the adhesive; increase in the thread pretension and the stitch density leads to a decrease in peel stress in the adhesive, while an increase in other parameters generally results in a negligible reduction in peel stress. The effect of stitching was found to be negligible on the shear stresses in the adhesive. Thus it is concluded that stitching is effective for the joints where peel stresses are critical and ineffective for those where shear stresses are critical.     

Elastic analysis of hybrid bonded joints and bonded composite repairs

The authors extend the closed-form bonded joint linear elastic analysis method of Delale et al. [Delale F, Erdogan F, Aydinoglu MN. Stresses in adhesively bonded joints: a closed-form solution. J Compos Mater 1981;15:249–71] and Bigwood and Crocrombie [Bigwood DA, Crocombe AD. Elastic analysis and engineering design formulae for bonded joints. Int J Adhes Adhes 1989;9(4):229–42] to include the composite deformation mechanisms and the thermal residual strains that arise in hybrid metal-composite joints such as those presented by bonded composite repairs applied to metallic aircraft structures. The analytical predictions for the adhesive stresses and the compliance are compared to the results of a linear elastic finite element model that has itself been validated by comparison with experimental results. The results are applied to the problem of coupled linear extension and bending of a bonded composite repair applied to a cracked aluminum substrate. The resulting stress intensity factor and crack-opening displacement in the repaired plate are compared to the results of a three-dimensional finite element analysis, and also exhibit excellent results. Throughout the text, observations are made regarding the practical application of the results to failure prediction in hybrid joints, whereby the authors demonstrate the need for consistency in the analytical methods used to determine the fatigue and failure of composites from the coupon level to the analysis of the final structural details.     

Fatigue performance of adhesively bonded single lap joints with non‐flat sinusoid interfaces

The role of a sinusoid interface shape on the load bearing capacity and fatigue life of adhesively bonded single lap joints (SLJs) was investigated numerically and experimentally. Aluminium adherends with wavy interfaces were tested under both quasi‐static and fatigue loading conditions. The experimental results showed that the non‐flat SLJs were indeed much stronger than the conventional flat joints. In order to fully demonstrate the advantage of the non‐flat sinusoid SLJ over the conventional SLJ, comparative fatigue tests with different loading levels were performed to determine the durability performance of the SLJs with non‐flat interfaces. The experimental results revealed that the non‐flat SLJ had considerably higher fatigue life than the conventional lap joint.     

Fatigue performance of a bonded wavy composite lap joint

A novel wavy lap joint design was further studied. Our previous studies using cross‐ply composite adherends showed that the new design was indeed much stronger than the conventional flat joint. In order to fully demonstrate advantage of the new wavy lap joint over the conventional single lap joint, comparative fatigue tests were performed to determine the durability performance of the wavy joint. In this study, a comparative static strength test of the conventional flat joint and the wavy joint was first carried out using unidirectional composite adherends. Then fatigue tests at different load levels and load frequencies were conducted. The test results showed that the wavy lap joint had a much longer fatigue life than the conventional lap joint.     

Failure analysis of adhesively bonded joints in composite materials

The present paper is concerned with a phenomenological model to perform the failure analysis of composite adhesive single lap joints with arbitrary glued area. The theory is conceived for joints composed by highly resistant elastic adherends bonded with brittle–elastic adhesives. It is shown that, under certain conditions, the rupture forces (in the case of monotonic loading) and lifetimes (in the case of cyclic loading) of two joints with different glued areas can be correlated using a shape factor. Results from experimental static and fatigue testing of joints with carbon/epoxy laminates bonded with epoxy adhesive and different bonding areas are compared with model prediction showing a good agreement.     

Damage modelling of adhesively bonded joints

A cohesive zone model (CZM) has been used in conjunction with both elastic and elasto– plastic continuum behaviour to predict the response of a mixed mode flexure and three different lap shear joints, all manufactured with the same adhesive. It was found that, for a specific dissipated CZM energy (Γ₀) there was a range of CZM tripping tractions (σ_u) that gave a fairly constant failure load. A value of σ_u below this range gave rise to global damage throughout the bonded region before any crack propagation initiated. A value above this range gave rise to a discontinuous process zone, which resulted in failure loads that were strongly dependent on σ_u. A discontinuous process zone gives rise to mesh dependent results. The CZM parameters used in the predictions were determined from the experimental fracture mechanics specimen test data. When damage initiated, a deviation from the linear load–displacement curve was observed. The value for σ _uwas determined by identifying the magnitude that gave rise to the experimentally observed deviation. The CZM energy (Γ ₀) was then obtained by correlating the simulated load-crack length response with corresponding experimental data. The R-curve behaviour seen with increasing crack length was successfully simulated when adhesive plasticity was included in the constitutive model of the adhesive layer. This was also seen to enhance the prediction of the lap shear specimens. Excellent correlation was found between the experimental and predicted joint strengths.     

Free vibration analysis of adhesively bonded single lap joints with wide and narrow functionally graded plates

This study investigates the three-dimensional free vibration behaviour of an adhesively bonded functionally graded single lap joint. The functionally graded plates of the adhesive joint are composed of ceramic (Al₂O₃) and metal (Ni) phases varying through the plate thickness. The effects of geometrical parameters, such as plate width, plate thickness and overlap length, especially the effect of the similar and dissimilar material composition variations through-the-thicknesses of both upper and lower plates on the natural frequencies and corresponding mode shapes of the adhesive joint were also investigated using both the finite element method and the back-propagation artificial neural network (ANN) method. A series of the free vibration analyses were carried out for various random values of the geometrical parameters and the through-the-thickness material composition so that a suitable ANN model could be trained successfully. The proposed ANN models indicated that increasing plate thickness and compositional gradient exponent resulted in increases in the first 10 frequencies whereas the overlap length has negligible effect. In contrast, the natural frequencies decrease suddenly with increasing the plate width. For the plate width >50 mm, the natural frequencies become very low and the effect of the other design parameters on the natural frequencies becomes minor. In case the upper and lower plates have similar or dissimilar material composition variations the mode shapes were affected considerably, but the natural frequencies.     

Numerical prediction of load–displacement behaviors of adhesively bonded joints at different extension rates and temperatures

The present work focuses on simulation of nonlinear mechanical behaviors of adhesively bonded DLS (double lap shear) joints for variable extension rates and temperatures using the implicit ABAQUS solver. Load–displacement curves of DLS joints at nine combinations of extension rates and environmental temperatures are initially obtained by conducting tensile tests in a UTM. The joint specimens are made from dual phase (DP) steel coupons bonded with a rubber-toughened adhesive. It is shown that the shell–solid model of a DLS joint, in which substrates are modeled with shell elements and adhesive with solid elements, can effectively predict the mechanical behavior of the joint. Exponent Drucker-Prager or Von Mises yield criterion together with nonlinear isotropic hardening is used for the simulation of DLS joint tests. It has been found that at a low temperature (−20 °C), both Von Mises and exponent Drucker-Prager criteria give close prediction of experimental load–extension curves. However, at a high temperature (82 °C), Von Mises condition tends to yield a perceptibly softer joint behavior, while the corresponding response obtained using exponent Drucker-Prager criterion is much closer to the experimental load–displacement curve.