层合板复合材料的层间剪切强度评价方法及其改进研究

针对国际上目前主要使用的双切口拉伸/压缩式层间剪切试验方法存在的问题,吸收了拉伸与压缩式试验方法各自的优点,对试验夹具及试验片形状与尺寸进行了改进设计,提出了双切口开孔拉伸式新的层间剪切强度测试、评价方法.以玻璃纤维平纹织物/环氧树脂复合材料层合板为试验材料对改进后的试验方法进行了实验及有限元分析.实验发现,表观层间剪切强度随槽间距的减小而有增大的趋势.通过有限元分析,对实验结果进行了解释,并确立了可获得真实层间剪切强度的最佳试验片尺寸.     

胶层中间隙长度及位置对接头剪切强度的影响

研究了在单搭接接头上、胶缝中预留的不同长度间隙对接头剪切强度和剪切应力分布的影响。结果表明，随着间隙长度的增加，接头的承栽能力趋于减小，但接头的实际剪切强度却持续上升．当间隙长度再继续增加时，接头的实际强度趋于下降。研究中还发现间隙所处的位置对接头的剪切强度有较大的影响，胶层端部预留间隙使接头的承载能力和实际强度均显著下降。有限元数值分析的结果表明，间隙长度超过某特定值后，胶层中的应力集中系数会急剧上升，间隙位于端部时胶层中的应力集中程度明显高于位于中部处。     

胶层厚度对拉伸试样应力分布影响的数值分析

运用弹塑性有限元法研究了胶层厚度对承受拉伸载荷的对接接头胶层内应力分布的影响．三维有限元法数值分析的结果表明，随胶层厚度减小，胶层中正应力SZ与剪应力SYZ的分布趋于均匀；而对正应力SY而言，胶层厚度为0．15mm时，其边缘峰值应力最低。     

基于TOM理论的金属裂纹板复合材料胶接修补胶层应力分析

针对复合材料胶接修补结构,基于TOM理论,提出了一种改进的Rose L R F胶层剪应力分析方法。该方法考虑了金属母板厚度方向上的剪切应力变化,认为剪应力沿厚度方向呈线性变化,并通过有限元数值方法进行了验证,分析了不同厚度的金属裂纹板组成的修补结构中的胶层剪应力。结果表明,当金属板厚度较薄(板厚与板长之比小于0.1)时,该方法得到的剪应力比Rose L R F给出的结果更接近于有限元解。     

单面和双面复合材料粘接修理胶层中的应力分析

胶层在复合材料粘接修理结构中起着载荷传递作用,采用有限元分析方法,研究了单面和双面粘接修理胶层中的应力分布特点,比较了2种不同修理形式胶层的VonMises应力、剥离应力和剪切应力的分布。结果表明,相同载荷下,单面修理的胶层VonMises、端部的剥离应力都较大,受剪切也比较严重。还研究了补片尺寸对胶层应力的影响。     

铺层结构对树脂基复合材料层间剪切强度影响的研究

主要目的在于利用双切口剪切强度试验法验证手糊成型的玻璃钢层合板铺层顺序以及单向布的相对体积含量对层间剪切强度的影响。实验中六种玻璃钢层合板的铺层方式分别为(UF)_5、(UF,CSM,UF,CSM,UF)、(CSM,UF,CSM,UF,CSM)、(UF,CSM,CSM,CSM,UF)、(CSM,UF,UF,CSM,CSM)、(CSM)_5。单向布相对体积含量依次为100%、60%、40%、40%、40%、0%。通过实验结论发现,单向布相对体积含量对层合板层间剪切强度影响较大,其中铺层方式为(UF)5的层合板通过双切口法得到的层间剪切强度高达40.768 MPa,而铺层方式为(CSM)_5的层合板在双切口法中所测得的层间剪切强度却只有15.867 MPa。相对而言,铺层顺序对层合板的层间剪切强度影响相对较小。同时利用数理统计方法"秩和检验法"对大量实验数据进行了离散性分析,结果表明,在同一种铺层方式下,尽管因为不同失效形式导致数据具有较大的离散性,但这些数据仍然可以作为一个整体进行分析。     

多层筛板流化床料层高度均匀性研究

通过测定流化床料层压差,研究了多层流化床顶层进料均匀性、进气及排气方式对多层流化床流化料层高度均匀性的影响。结果表明,布料越均匀,上中二料层高度越接近,且在低气速下易于形成较良好的流化层,但随着气速增大,其影响逐渐减弱;在低气速下进气方式对中下二料层均匀性有较大影响,但随气速增大影响也减弱,底部进气方式更易达到较好的料层均匀性;流化床的排气方式对流化料层基本无影响。因此均匀的布料和较均匀的进气预分布有助于均化各料层高度,并拓宽多层流化床的操作弹性。     

塑料黏度和制品壁厚对夹芯注射芯层穿透效果的影响研究

通过Moldflow软件对桶形塑件进行了夹芯注射模拟仿真分析，研究了芯/壳层材料黏度比和制品壁厚对夹芯注射制品芯层穿透长度、芯层厚度和芯层分布均匀性的影响。结果表明，在成型工艺参数相同的情况下，随着芯/壳层黏度比的增大，芯层穿透长度比按照1.41 %~1.67 %的倍率对应减小，芯层厚度因子均值按照1.76 %~2.28 %的倍率对应增大，芯层厚度因子偏差按照1.91 %~2.66 %的倍率对应增大，芯层厚度分布均匀性有所下降；制品壁厚每增加1 mm，芯层穿透长度比减小1 %~2 %，芯层厚度因子均值增大6 %左右，芯层厚度因子偏差增大10 %左右。     

基体条件对Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力的影响

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力分布进行了数值仿真。结果表明:基体厚度不同时,涂层界面Sm2Zr2O7/YSZ及界面YSZ/NiCoCrAlY对应应力及应力梯度基本不变,表明应力及应力梯度与基体厚度无关;但基体材质热膨胀系数对涂层系统界面的径向、轴向及剪切应力梯度有决定性的影响,且各应力梯度随金属基体的热膨胀系数差异增加而增大,表明基体材质是影响涂层界面径向残余热应力及应力梯度的根本原因。采用多层陶瓷结构并合理选择各层材质的热膨胀系数将更加有利于降低涂层应力梯度,进而改善涂层性能,延长涂层寿命。     

多层复合膜彩虹效果的研究

对多层复合薄膜产生的彩虹效果进行了研究，进行了材料的选择，研究了材料的流动性、薄膜的透明性及加工工艺条件等对多层复合膜彩虹效果的影响，结果表明：两种树脂熔融速率越相近，所生产的多层复合膜的彩虹色彩越均匀；随着单膜透明性的增加，多层复合膜的彩虹效果更好；复合膜厚度增加，色彩变化明显；保护层的厚度占整个复合膜厚度的20％～40％。     

An experimental and numerical investigation of adhesive bonding strengths of polymer materials

We employed the Iosipescu shear specimens and butt-joint specimens to measure the shear and tensile strengths of five types of adhesive bonds for brittle poly(methyl methacrylate) and Homalite polymers. In order to examine the possible stress singularities due to property mismatch between the adhesives and polymers, and ensure uniform stress distributions along the bonded interfaces, two optical techniques, photoelasticity and coherent gradient sensing, were employed to record full field, in situ fringe patterns until specimens failed. Direct comparison of finite element analysis and experimental stress analysis of Iosipescu shear specimens showed that along the polymer/adhesive/polymer interface, only a very weak stress singularity existed. Consequently, the stress distributions were quite uniform. Butt-joint tensile experiments verified negligible stress singularities and uniform stress distributions along the interface. However, for some shear specimens with strong bonds, the final failure occurred in a tensile mode at the upper edge, rather than a shear failure mode in the gauge section. Hence, only the lower limits of the shear strength rather than the actual magnitude could be measured.     

Effects of imperfect adhesion on thermal micro-residual stresses in polymer matrix composites

This paper investigates the influences of imperfect bonding between the fiber and matrix on thermal micro-residual stress fields in polymer matrix composites. For this purpose, a representative volume element consisting of a three-phase composite material subjected to a uniform temperature change is considered. Based on the energy method, a three-dimensional closed-form solution for micro-residual stresses is obtained. Besides, a finite element model is developed and the results are compared with the analytical solution. Both the energy method and finite element analysis show similar trend for thermal stress distribution along the fiber length, while due to the stress singularity, the interfacial shear stress from the finite element solution cannot satisfy the stress-free condition at the fiber end. The analysis shows that the magnitude of thermal stresses and their distribution mainly depend on the bonding efficiency parameter. An increase in thermal and elastic properties bonding efficiencies leads to a considerable decrease in composite axial and shear residual stresses, while the Poisson's ratio bonding efficiency does not affect the thermal stress fields. The interfacial radial residual stress distribution is approximately independent of the bonding conditions. Inefficient bonding may result in higher residual stresses in comparison with the perfect bonding condition. It means that in cases of low bonding efficiency conditions, the ability of composites to sustain and transmit load decreases drastically. Thermal stress concentration occurs at the vicinity of the fiber ends, although peak values depend on the bonding efficiency value.     

Fatigue Failure Criterion of Adhesively-Bonded Joints Under Combined Stress Conditions

A study was conducted to investigate fatigue failure criteria for adhesively-bonded joints under combined stress conditions. Two types of adhesively-bonded joint specimens were used: the scarf joint and the butterfly-type butt joint. Both types of joints have considerably uniform combined stress distributions in the adhesive layer. Furthermore, the stress distributions of these joints were analyzed by a finite element method. The results showed that the maximum principal, the von Mises equivalent and the maximum shear stresses in the uniform stress region of the adhesive layer at the endurance limit are correlated with the principal stress ratio.     

On the Uniformity of Stresses in Some Adhesive Deformation Specimens

The stress distributions within napkin-ring, cone-and-plate and stiff-adherend specimens were determined under shear, bond-normal and thermal loadings using linear elastic finite element analysis. Modifications to adherend edges were also considered in order to improve uniformity. The stiff-adherend specimen showed the most promise for use as a specimen for determining the deformation behavior of adhesives in-situ. A stiff-adherend specimen having rounded adherends provided the most uniform stress state, free from any stress concentrations, a result that was qualitatively confirmed in experiments.     

胶瘤中嵌入金属对单搭接接头的影响

研究了在胶瘤中嵌入金属对单搭接接头强度的影响,结果表明,金属嵌入后均能显著提高接头的强度.但随三角形锲块入射角度的增大,接头强度提高幅度逐渐降低.有限元数值分析的结果显示,三角形金属楔块使端部应力峰值和平均应力均大大降低,剥离应力降低明显.     

基于ANSYS的两种胶黏剂劈裂接头数值模拟

采用有限元分析软件ANSYS，对钢制劈裂接头上胶层中部的正应力和剪切应力的分布进行了弹塑性有限元数值模拟与分析。分别考察了由弹性模量相差较大的丙烯酸酯胶和环氧树脂胶黏剂时制备的单一胶或处于不同部位的两种胶黏剂所得到的混合胶层与45钢形成的劈裂接头中的应力分布情况。结果表明，对于由单一胶形成的劈裂接头来说，采用弹性模量较低的丙烯酸酯胶黏剂所形成的接头中的正应力分布更为均匀；而混合胶所形成的劈裂接头的应力集中程度通常高于单一胶。     

胶瘤中嵌入金属块对单搭接接头强度的影响

研究了在胶瘤中嵌入三角形金属楔块对单搭接接头强度和应力分布的影响,结果表明,金属楔块能显著提高接头的强度。但随三角形锲块入射角度的增大,接头强度提高幅度逐渐降低。有限元数值分析的结果表明,三角形金属楔块使端部应力峰值和平均应力均大大降低,剥离应力降低明显。     

On the Uniformity of Stresses in Some Adhesive Deformation Specimens

The stress distributions within napkin-ring, cone-and-plate and stiff-adherend specimens were determined under shear, bond-normal and thermal loadings using linear elastic finite element analysis. Modifications to adherend edges were also considered in order to improve uniformity. The stiff-adherend specimen showed the most promise for use as a specimen for determining the deformation behavior of adhesives in-situ. A stiff-adherend specimen having rounded adherends provided the most uniform stress state, free from any stress concentrations, a result that was qualitatively confirmed in experiments.     

Three dimensional finite element analysis of bi-adhesively bonded double lap joint

Hybrid-adhesive joints are an alternative stress reduction technique for adhesively bonded joints. The joints have two types of adhesives in the overlap region. The stiff adhesive should be located in the middle and flexible adhesive at the ends. In this study, the effect of the hybrid-adhesive bondline on the shear and peeling stresses of a double lap joint were investigated using a three-dimensional finite element model. We developed a three dimensional model of the double lap joint based on solid and contact elements. Contact problem is considered to model the interface as two surfaces belonging to adherend and adhesive. Finite element analyses were performed for four different bond-length ratios (0.2,0.4,0.7 and 1.3). The results show that the stress components can be optimized using appropriate bond-length ratios. To validate the finite element analysis results, comparisons were made with available closed-form solutions. The numerical results were found in good agreement with the analytical solutions.     

有限元分析在37.00R57巨型工程子午线轮胎结构优化中的应用

利用ABAQUS软件建立轮胎静态三维有限元模型,对采用不同设计方案的37.00R57巨型工程子午线轮胎进行了静负荷工况下的受力分析。以期通过分别调整胎肩部位两个尼龙包布的宽度,来降低轮胎肩部的最大剪应力,利用Tresca屈服准则和Mises屈服准则来判断,从而得到最优方案,提高轮胎性能。