缝合复合材料层合板疲劳寿命预测

复合材料层合板疲劳损伤机理和寿命预测是关系到现代航空结构损伤容限设计的关键问题。通过对复合材料层合板疲劳损伤特征研究,从应变等效性出发,结合经典刚度降法,建立层合板疲劳寿命预测两阶段宏观唯象模型,弥补了经典刚度降法和S-N曲线模型的不足。应用此模型对新型的缝合复合材料层合板进行了相关分析与研究,并将预测结果与试验结果进行了对比。结果表明,所建立的疲劳寿命预测模型结果与试验结果吻合良好,可为缝合复合材料的失效分析与工程应用奠定一定的理论基础。     

含低速冲击损伤复合材料层合板的压缩失效

通过含低速冲击损伤的两种平面编织复合材料层合板（G803／5224、G827／5224层合板）的压缩试验,研究了低速冲击损伤对复合材料层合板失效行为的影响。试验后采用超声c扫描检测、外观检查与断口侧面宏观观察方法对损伤与失效特征进行了对比分析。结果表明,两种含低速冲击损伤层合板被压缩时,G803／5224层合板冲击背面首先发生子层微屈曲,微屈曲沿着垂直于压缩方向扩展,最后剪切分层失效;G827／5224层合板冲击背面首先发生子层屈曲分层,屈曲分层也是沿着垂直于压缩方向扩展,最后剪切屈曲失效。两种层合板低速冲击后压缩的失效模式与光滑板压缩失效模式基本相同。     

含穿透损伤复合材料桨叶结构静强度分析

受弹伤后桨叶结构的静强度、动态特性和剩余寿命等是复合材料直升机旋翼桨叶结构损伤容限设计必须研究的问题.选取某直升机复合材料桨叶靠近桨根的翼段结构,利用CATIA建立三维实体模型,并导入ANSYS软件建立有限元分析模型,分别对翼段不同位置、不同方向的穿透损伤情况进行桨叶结构静强度分析.应用APDL参数化设计语言,开发了计...     

复合材料层合板雷击烧蚀损伤影响因素分析

通过复合材料层合板雷电流冲击的热-电耦合分析,建立复合材料层合板烧蚀的三维有限元模型,研究复合材料层合板在不同材料属性下的瞬态热传递和热解作用规律,进行雷击复合材料损伤机理和损伤模式分析,根据烧蚀后的温度分布评估雷电流烧蚀尺寸变化规律,得出复合材料烧蚀损伤与材料性能的关系,结果表明电导率对烧蚀形貌的发展变化产生很大影响,热导率变化时烧蚀结果并没有发生显著改变。比热只有增加到一定程度烧蚀损伤才会降低。     

直升机旋翼桨叶的红外检测

采用便携式红外无损检测系统对直升机旋翼桨叶的不锈钢前缘包片、桨叶前“Z”形梁和后缘条等部位进行了红外检测研究。在主动热激励方式下,由于内部材料的阻热与吸热特性不同将导致表面温度场分布不均,使红外热图像能够清晰显示出桨叶漆层下的内部结构特征或损伤情况。检测结果表明,主动红外检测技术完全可用于直升机复合材料结构的内部分层、脱粘和漆层下腐蚀等的快速检查,在直升机日常和应急维护保障中的应用前景广阔。     

复合材料层合板低速冲击后压缩损伤特征研究

试验研究了5224/G803和5224/G827两种复合材料层合板低速冲击及冲击后压缩载荷作用下的损伤特征.结果表明,两种层合板低速冲击损伤特征基本相同,均存在分层、纤维断裂与基体裂纹.5224/G803层合板冲击正面和背面在压缩载荷作用下的损伤特征相同,均为纤维基体剪切断裂.而5224/G827层合板冲击正面在压缩载荷作用下为纤维基体剪切断裂失效,冲击背面则以分层损伤为主.     

低速冲击下CFRP层合板的损伤分析与数值模拟

为研究碳纤维层合板在低速冲击载荷下的损伤过程，按照国家标准测定了平纹编织碳纤维层合板的冲击强度，并设定不同冲击能量进行冲击试验，分析层合板的损伤形式及演化过程。根据冲击试验条件，利用Abaqus软件建立了层合板的复合材料有限元模型，基于Hashin失效准则和渐进损伤演化理论，模拟层合板在不同冲击能量下的层内损伤和层间损伤。结果表明，随着冲击能量增大，基体拉伸损伤与纤维压缩损伤最容易发生，但基体压缩损伤最先完全失效，宏观表现为局部凹陷；分层损伤最先出现在冲击表面，以松树型损伤模式逐步向背面扩展。     

复合材料层合板分层损伤动态检测方法

针对复合材料层合板在加工、服役过程中经常发生分层损伤的问题,提出了基于曲率模态参数的损伤评价方法。运用有限元理论对层合板不同损伤状态下的振动特性进行数值模拟;再基于计算所得参数,运用中心差分法分别计算其均布载荷的曲面值曲率和振型曲率;最后将此曲率参数与未损伤模型参数作差分以辨别损伤。数值计算结果表明,运用均布载荷的曲面值曲率和振型曲率均可有效识别损伤位置和损伤数量,且损伤所处层的位置会影响损伤识别指标的大小。     

复合材料层合板疲劳损伤研究

结合基于基体和纤维断裂能的Peter Linde失效准理论完成了层合板疲劳损伤子程序的开发,子程序可调整层合板刚度降参量k的设定来有效减少层合板疲劳计算量.进行了子程序的可靠性验证.从最终的损伤演化分析结果来看,层合板疲劳损伤子程序不仅可较好完成层合板疲劳损伤模拟及寿命估算,且能给出不同循环周次的损伤状态.     

层合板静压痕及压缩强度试验与其数据统计分析

复合材料层合板在低速能量冲击后的压缩强度变化是航空器结构设计应用的重要依据。本研究运用标准静压痕及冲击后压缩强度试验方法,对工程中两类典型的碳纤维及玻璃纤维树脂基复合材料层合板进行了静压痕及压缩强度试验研究,并采用数理统计方法,对试验数据进行了处理,给出了冲击后有效弹性模量及压缩极限强度的分散性表征及其拟合分布,计算了A、B基准值。研究结果表明:冲击后两类复合材料层合板的有效模量与强度特性仍遵从正态分布的概率推断;但较玻璃纤维增强的树脂基复合材料层合板, 碳纤维增强复合材料呈现更明显的脆性。     

The extent of laser-induced thermal damage of UD and crossply composite laminates

Composite materials exhibit poor quality cut surfaces due to spalled fibres, fuzzing, and delamination when routed by conventional tools. Laser beam cutting offers an ideal means for the cutting of fibre composite materials, being a non-contact and virtually force-free manufacturing method. However, in the shaping operation of composite materials after curing, thermal damage associated with laser energy can be produced. It leads to poor assembly tolerance and long-term performance deterioration. In the current investigations, 3-dimensional anisotropic heat conduction models based on moving point heat source for thermal analysis are presented to predict heat affected zone (HAZ). Also, the conductivity models allow to consider the anisotropic heat conductivity for unidirectional (UD) and [0/90] laminates. Taking the immersing heat source and Mirror Image Method into account would further improve the prediction of HAZ. Extensive experiments were conducted on composite materials to examine HAZ, and compared with experimental results. The analytical results show a good agreement with experiments.     

超声椭圆振动切削技术及装置应用研究现状及进展

首先,阐述了超声椭圆振动切削技术、原理及其装置特点,着重论述了装置各构成部分的特点及其主要应用类型与材料。其次,分析了国内外学者在双激励、单激励方式下实现纵弯、纵扭、双弯曲和弯扭等复合超声振动装置结构设计及其优化方面的研究成果与进展,并且比较了超声椭圆振动切削与传统加工在加工性能、工件表面质量和加工精度等方面的加工优势与适用范围,以及不同超声振动装置在各切削加工中所能获得的加工效果。最后,对超声椭圆振动切削装置的发展趋势进行了总结和展望,指出该装置发展将朝着结合能场的方向发展。     

Mechanical model for predicting thrust and torque in vibration drilling fibre-reinforced composite materials

Delamination is a dramatic problem associated with drilling fibre-reinforced composite materials (FRCMs), which, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long-term performance deterioration. The key to solving the problem lies in reducing the thrust force of drilling. In this paper, a theoretical analysis for predicting mean values of thrust and torque in vibration drilling FRCMs is presented. The model is based on mechanics of vibration cutting analysis and the continuous distributions of thrust and torque along the lip and the chisel edge of a twist drill. The result of a simulation study has shown a very good agreement between the theoretical predictions and the experimental evidence. On the same cutting conditions, the thrust and the torque by the vibration drilling method are reduced by 20–30 percent, compared with conventional drilling.     

复合材料桨叶鼓包变形分析

复合材料桨叶设计重点考虑其疲劳性能和环境老化性能,变形失效问题则很少涉及.通过对处于不同变形损伤阶段的桨叶结构和复合材料损伤情况进行观察分析,对复合材料桨叶的变形失效问题进行了分析和讨论.结果表明:桨叶叶根材料在叶根套离心力压迫、离心应力及循环载荷下出现塑性变形损伤累积,使得玻璃纤维织物和泡沫塑料出现鼓包堆积,最终导致...     

Comeld～TM Joints: A Novel Technique for Bonding Composites and Metal

Current and future structural applications for composite laminates frequently involve design solutions combining composite laminates and metal; the materials must be joined. Two conventional means of joining are available: mechanical joining and adhesive bonding. Both methods have critical disadvantages. A novel surface treatment for metals developed at TWI, Surfi-Sculpt, leads to the formation of surface protrusions on metal surfaces. These protrusions are typically 1.0 mm high and 0.6 mm in diameter. The...     

NDE of smart structures using multimode fiber optic vibration sensor

There are many conventional methods which may be used to monitor the health of structures — of which vibration monitoring is effective and can be used for special structures such as aircraft wings. A smart structure system based on fiber optic vibration sensors has been developed to monitor structural damage. A method based on the detection of spatial speckle of a multimode optical fiber is described. A multimode optical fiber with a diameter of 200/230 μm is used in the present experiment. The theoretical analysis and the experimental tests are described. The fiber optic sensors have been embedded in the carbon/epoxy composite specimens and surface mounted on the surface of aluminum specimens. Furthermore, experiments to examine the different types of damage to these specimens have been carried out. The results show that this kind of multimode fiber optic sensor can be used in the non-destructive evaluation of smart materials.     

A coefficient clustering analysis for damage assessment of composites based on pulsed thermographic inspection

This paper introduces a coefficient clustering analysis method to detect and quantitatively measure damage occurring in composite materials using pulsed thermographic inspection. This method is based on fitting a low order polynomial model for temperature decay curves, which (a) provides an enhanced visual confirmation and size measurement of the damage, (b) provides the reference point for sound material for further damage depth measurement, (c) and reduces the burden in computational time. The performance of the proposed method is evaluated through a practical case study with carbon fibre reinforced polymer (CFRP) laminates which were subjected to a drop impact test with varying energy levels. A novel method for reducing an entire thermogram sequence into a single image is introduced, which provides an enhanced visualisation of the damage area.