Kevlar缠绕增强机匣包容过程研究

开展轻质复合材料风扇包容机匣的研究,对大型民用涡扇发动机的减重设计具有重要意义。为研究Kevlar纤维束编织布缠绕增强机匣的包容过程,在立式试验台上进行高速旋转平板叶片撞击Kevlar缠绕增强铝合金内层机匣的包容试验,并采用显式瞬态动力学软件LS-DYNA对撞击过程进行数值仿真。结果表明:叶片撞击机匣的过程可分为3个阶段,其中包括两次主要的撞击;断叶的冲击动能大部分由Kevlar纤维束编织布吸收;断叶包容过程中外层纤维布会产生较大的鼓包变形,鼓包的大小和位置随叶片运动而改变。     

纤维织物增强复合材料微观应力场的有限元分析

应用有限元法对一种平面编织玻璃纤维复合材料层板在拉伸载荷下的微观应力场作了详细的计算分析。分析结果清晰揭示了微观应力场的概貌, 尤其是材料结构中的强度薄弱点。      

平面三向织物复合材料增强体顶压性能有限元分析

借助绘图软件PRO/E构建用于研究顶压性能的平面三向织物、平纹织物和冲头的结构模型,并利用有限元软件ANSYS对其力学性能进行模拟分析。分别表征平面三向织物和平纹织物的形态变化、应力及应变分布情况,并研究平面三向织物相对平纹织物性能优势及织物的顶压破坏形式。结果表明:在同样载荷作用下同样面密度的平纹织物的形态位移变化是平面三向织物的2倍,平面三向织物抵抗顶压的能力好于平纹织物;在同样载荷作用下同样面密度平纹织物的最小顶压应力和应变均大于平面三向织物,表明平面三向织物分散载荷效果好于平纹织物。     

起圈织物增强层合板层间力学性能有限元分析与实验研究

建立了一种起圈织物增强层合板的平拉单胞模型,通过有限元计算预测其平拉强度。研究起圈织物增强层合板的复合成型工艺,制作了符合要求的实验件。对该种材料的短梁剪切、平拉、双面剪切性能进行了实验研究,获得了该材料主要层间力学性能参数,并与传统复合材料层合板的力学性能进行了对比,得出了一些有益的结论,为该材料的性能分析和结构优化奠定了基础。     

厚壁管温热缩口与管壁增厚的数值模拟研究

目的主要研究厚壁管两端同时温、热锥形缩口工艺的特点,以及缩口过程不同工艺参数对壁厚增厚的影响。方法通过选择合理的材料模型与热力耦合等温度场模拟参数,建立了有限元模型,使用DEFORM体积成形软件对厚壁管两端同时温热缩口工艺进行了分析,探究了温、热缩口两种条件下应力应变分布特点。结果模拟实验获得了管材缩口系数、模具半锥角、t/d0值、摩擦因子、成形温度等工艺参数,在温、热两种条件下对壁厚增厚量的影响曲线。结论管材缩口过程具有典型的变形阶段:入锥弯曲阶段、反弯曲阶段和缩口稳定阶段;管材高温下缩口变形特点为周向、轴向的压缩变形和径向的增厚变形;厚壁管缩口的增厚变形量随着模具半锥角的增大和缩口系数的减小而增大,同时受摩擦因子、成形温度、管材壁厚的影响较大。研究结果为管材缩口壁厚增厚工艺提供了基础技术数据。     

木质平托盘抗冲击性能有限元分析及试验研究

目的 以木质平托盘为对象,通过有限元仿真和试验分析影响木质平托盘抗冲击性能的主要因素。方法 用SolidWorks建立木质平托盘的3D模型,利用Abaqus有限元软件,以GB/T 4996—2014为依据进行角跌落试验仿真,分析木质平托盘上木质构件以及托盘钉上产生的应力和位移。为了进行对比,在实验室进行木质平托盘产品的角跌落试验,观察木质平托盘的破坏形式,并测量其对角线长度。结果 有限元仿真与实验室实物试验结果相吻合,验证了有限元仿真分析的正确性和有效性。有限元仿真分析发现钉孔处木质构件和托盘钉产生应力集中并逐渐发生塑性变形,且应力和变形数值随跌落次数的增加而增大,仿真和试验均表明跌落侧纵梁向内侧凹陷且变形最为明显,木质平托盘对角线变化量受跌落次数逐渐变大。结论 木质平托盘抗冲击性能随跌落次数的增加而下降。木质平托盘中木质构件、托盘钉的性能,以及托盘钉紧固件与木质构件的连接强度是决定木质平托盘抗冲击性能的关键因素。     

Nylon-230T/TPU织物蒙皮撕裂性能的数值模拟和试验研究

针对每平方厘米由230根尼龙纱平纹编织并复合热塑性聚氨酯（Nylon-230T/TPU）的织物蒙皮,通过数值模拟和撕裂试验研究了预制裂纹对其撕裂性能的影响,主要包括裂纹长度、裂纹倾斜角度和裂纹位置对蒙皮撕裂强度的影响,通过数字图像相关技术（DIC）获取蒙皮撕裂过程中的应变场,研究了撕裂过程中蒙皮应变场变化规律;分别利用扩展有限元法（XFEM）、内聚力单元法（CZM）及虚拟裂纹闭合技术（VCCT）对预制裂纹Nylon-230T/TPU织物蒙皮的裂纹扩展过程和路径进行了数值模拟,模拟结果与试验结果吻合较好。研究结果表明：Nylon-230T/TPU织物蒙皮的撕裂强度与预制裂纹长度、裂纹倾斜角度及裂纹位置都密切相关;裂纹极大地影响了蒙皮的应变场分布;本文数值模拟方法能够准确预测织物蒙皮裂纹的扩展过程和路径。     

三软复杂地质条件提高机械化采煤技术的研究分析

清水营煤矿地质条件复杂，地质构造多变，煤层倾角大，特别是2层煤属于三软煤层：煤质软、顶板软、底板软，给煤矿安全生产及高产高效带来了很大技术难度。本文通过对该矿复杂地质现状的研究分析，提出了相应的应对措施，取得了良好效果。     

扁平管膨胀性能仿真及实验研究EI北大核心CSCD

分离结构是航天运载器上十分关键的部位,膨胀管分离装置作为一种清洁的分离结构,被广泛应用于航天运载器的分离部位。使用LS-DYNA中的流固耦合算法对扁平管组件(扁平管、填充物、炸药索)进行了有限元仿真分析,并进行了实验验证,仿真与实验结果吻合较好。在此基础上,分别改变扁平管的壁厚,填充物的密度、弹性模量,通过有限元仿真分析了扁平管上两个特征点的膨胀速度、膨胀位移及扁平管动能的变化规律,获得各参数对于扁平管膨胀变形的影响,对于设计扁平管组件具有很大的指导意义。     

高聚物熔体锥形收敛流场分布的影响因素数值分析

在入口收敛流基本方程基础上,通过建立锥形入口结构和有限元网格模型,运用数值仿真方法,采用Cross本构方程和壁面无滑移模型,速度采用二次插值、压力采用线性插值和黏度牛顿迭代的有限元计算方法,对影响广义等温流动熔体在口模入口和出口区域的压力、速度和剪切速率分布的熔体材料、工艺参数和口模形状等因素进行了数值分析。研究结果表明,压力分布与熔体黏度、流动指数、松弛时间、入口流率和流道压缩比等有直接关系,而法向速度和剪切速率仅受入口流率的影响较大。通过对多个因素量化分析表明,压力分布随着熔体黏度、入口流率和流道压缩比的增大而增大,而随着流动指数和松弛时间的增大而减小,法向速度和剪切速率随着入口流率增大而增大;这些影响因素使得口模出口处压力、法向速度和剪切速率均不为零,从而引发离模膨胀等问题。     

浸轧压力对STF-Kevlar织物高速冲击性能影响研究

为研究浸轧压力对剪切增稠液体(STF)增强Kevlar织物高速冲击性能的影响,分别采用50 kPa,100 kPa,200 kPa的压力浸轧STF-Kevlar织物,并使用钛合金模拟叶片弹体开展打靶试验.研究结果表明:STF表现出明显的剪切增稠现象,增稠范围为169 ～1 500 s-1,增稠比为56.4;Kevlar...     

Kevlar纤维织物的性能研究

通过电子织物强力仪、万能试验机、圆盘式平磨仪、广角X-射线衍射(WAXD)、示差扫描量热(DSC)、红外光谱(IR)、热失重分析(TG)对对位芳纶纤维(Kevlar Twaron)织物进行表征,分析了热处理前后KevLar纤维织物的取向结晶行为和热性能.结果表明,KevLar单纱的断裂强力为693.82 cN/tex,...     

Development of reliable modeling methodologies for engine fan blade out containment analysis. Part II: Finite element analysis

In the first part of the paper [Naik D, Sankaran S, Mobasher B, Rajan SD, Pereira M. Development of reliable modeling methodologies for fan blade-out containment analysis. Part I: experimental studies. Int J Impact Eng, in press], details of the experiments to characterize the behavior of dry fabrics including Kevlar^®49, and ballistic tests involving the fabric were presented. In this second part of the paper, we discuss the development and verification of a constitutive model for dry fabrics for use in an explicit finite element program. The developed constitutive model is implemented as a user-defined subroutine in LS-DYNA, a commercial finite element program. It is then used to simulate a suite of ballistic tests [Naik D, Sankaran S, Mobasher B, Rajan SD, Pereira M. Development of reliable modeling methodologies for fan blade-out containment analysis. Part I: experimental studies. Int J Impact Eng, in press] that replicate conditions seen in an engine fan blade out (FBO) event. A qualitative and quantitative comparison of the deformation shape of the fabric containment system and a quantitative comparison of the absorbed energy are carried out. Results indicate that the developed constitutive model provides a very encouraging start in modeling these high-speed events and could provide as Federal Aviation Administration (FAA) desires, an attractive complement to full-scale engine FBO tests.     

Finite element modeling of ballistic impact on multi-layer Kevlar 49 fabrics

This paper presents a material model suitable for simulating the behavior of dry fabrics subjected to ballistic impact. The developed material model is implemented in a commercial explicit finite element (FE) software LS-DYNA through a user defined material subroutine (UMAT). The constitutive model is developed using data from uniaxial quasi-static and high strain rate tension tests, picture frame tests and friction tests. Different finite element modeling schemes using shell finite elements are used to study efficiency and accuracy issues. First, single FE layer (SL) and multiple FE layers (ML) were used to simulate the ballistic tests conducted at NASA Glenn Research Center (NASA-GRC). Second, in the multiple layer configuration, a new modeling approach called Spiral Modeling Scheme (SMS) was tried and compared to the existing Concentric Modeling Scheme (CMS). Regression analyses were used to fill missing experimental data – the shear properties of the fabric, damping coefficient and the parameters used in Cowper-Symonds (CS) model which account for strain rate effect on material properties, in order to achieve close match between FE simulations and experimental data. The difference in absorbed energy by the fabric after impact, displacement of fabric near point of impact, and extent of damage were used as metrics for evaluating the material model. In addition, the ballistic limits of the multi-layer fabrics for various configurations were also determined.     

碳纤维-玻璃纤维混杂增强环氧树脂复合材料低速冲击性能及其模拟

本文基于实验和数值模拟方法研究了碳纤维-玻璃纤维混杂增强环氧树脂复合材料低速冲击性能.采用商业有限元软件ABAQUS建立了层间/层内两类混杂复合材料低速冲击模型,采用基于应变形式的Hashin失效准则模拟面内损伤;零厚度Cohesive内聚力单元预测层间分层;编写VUMAT子程序定义渐进失效过程,并结合C扫和Micro...     

复合材料层合板低速冲击损伤的有限元模拟

建立了用于预测复合材料层合板在低速冲击作用下损伤的3D有限元模型。采用应变描述的失效判据来判断铺层层内的各类损伤, 如纤维断裂、 纤维挤压、 基体开裂、 基体挤裂, 并结合相应的刚度折减方案对失效单元进行刚度折减。使用界面元模拟层间区域, 结合传统的应力失效判据和断裂力学中的能量释放率准则来定义分层损伤的起始和演化规律, 提出了一种界面元损伤起始强度沿厚度方向的分布函数。通过对数值仿真结果和实验结果的比较, 验证了模型的合理性和准确性。      

基于镀银纱线的电加热织物温度场模拟与电热性能

运用ANSYS有限元模拟软件对镀银纱线在织物中加热过程进行数值模拟,并通过调整镀银纱线之间的距离和施加电压分析不同条件下加热织物内部和周围空气中热场分布情况。根据模拟结果制备镀银纱线加热织物,验证模拟结果并研究电加热织物电热性能。结果表明,随着电压的增加,镀银纱线平衡温度升高,当输出电压为7V时,镀银纱线在织物中实测温度可达109.7℃。设定镀银纱线间距为3mm,使镀银纱线在较低成本下获得较高的表面温度均匀性。加热织物的升温速度和平衡温度随着功率密度的增加而增加,模拟结果与实测结果趋势一致且结果偏差小于4.5%,说明有限元分析结果能够作为镀银纱线加热织物制备的重要参考依据。     

Multiscale modeling of the impact of textile fabrics based on hybrid element analysis

In this work, a multi scale modeling approach has been developed to simulate the impact of woven fabrics using a finite element (FE) analysis. A yarn level of resolution is used in the model. This approach, referred to as the hybrid element analysis (HEA) is based on decreasing the complexity of the finite element model with distance away from the impact zone based on the multiscale nature of the fabric architecture and the physics of the impact event. Solid elements are used to discretize the yarns around the impact region, which transition to shell elements in the surrounding region. A new method for modeling the shell yarns is incorporated that more accurately represents the contours of the yarn cross section. Impedances have been matched across the solid–shell interface to prevent interfacial reflections of the longitudinal strain wave. The HEA method is validated by first applying it to the FE model of a single yarn for which an analytical solution is known. The HEA method is then applied to a woven fabric model and validated by comparing it against a baseline model consisting of yarns discretized using only solid elements.     

预制破片对厚壁圆管的横向高速冲击作用研究

为了获得厚壁圆管在横向高速冲击下的响应规律,进行了预制破片冲击圆管试验,得到不同冲击速度作用下圆管的响应模态及侵彻深度,并采用LS-DYNA对整个动态变化过程进行了仿真研究,获得了侵彻过程中预制破片的速度变化规律及圆管壁厚和预制破片长径比对极限穿透速度的影响规律。结果表明侵彻深度与冲击速度线性相关;圆管壁厚在7mm-8mm之间时对圆管极限穿透速度影响最大;预制破片长径比低于1.5时,对圆管极限穿透速度有显著影响,但其影响效果随自身的增大而逐渐削弱,当达到3.5左右时极限穿透速度不再变化。     

An experimental and numerical investigation on tyre impact

A key issue in the design of tyres is their capability to sustain intense impact loads. Hence, the development of a reliable experimental data basis is important, against which numerical models can be compared. Experimental data on tyre impact in the open literature is somewhat rare. In this article, a specially design rig was developed for tyre impact tests. It holds the test piece in a given position, allowing a drop mass with a round indenter to hit pressurised tyres with different impact energies. A high-speed camera and a laser velocimeter were used to track the impact event. From the laser measurement it was possible to obtain the impact force and the local indentation. A finite element study was then conducted using material properties from the open literature. By comparing the experimental measurements with the numerical results, it became evident that the model was capable of predicting the major features of the impact of a mass on a tyre. This model is therefore of value for the assessment of the performance of a tyre in extreme cases of mass impact.