缝合复合材料层板低速冲击损伤数值模拟

建立了缝合复合材料层板在低速冲击载荷下的渐进损伤分析模型。模型中采用空间杆单元模拟缝线的作用;采用三维实体单元模拟缝合层板,通过基于应变描述的Hashin准则,结合相应的材料性能退化方案模拟层板的损伤和演化;采用界面单元模拟层间界面,结合传统的应力失效判据和断裂力学中的应变能释放率准则判断分层的起始和扩展规律。通过对碳800环氧树脂复合材料（T800/5228）层板的数值仿真结果和试验结果相比较,验证了模型的正确性,同时讨论了不同冲击能量下缝合层板的损伤规律。研究结果表明：缝线能够有效地抑制层板的分层损伤扩展;相同冲击能量下缝合与未缝合层板的基体损伤和纤维损伤在厚度分布上相似,缝合层板的损伤都要小于未缝合层板。     

复合材料层合板低速冲击逐渐累积损伤预测方法

针对复合材料层板在冲击载荷下,各种损伤的产生和扩展是一个随载荷、时间和空间而演变的过程,发展了复合材料层合板低速冲击逐渐累积损伤预测方法.采用刚度退化技术和改进的Chang-Chang失效准则、显式有限元法来模拟复合材料层合板受到低速冲击下逐渐损伤过程.使用所发展的方法分析了[0m/90n/0m]铺层的复合材料层合板在低速冲击过程中的逐渐损伤扩展,结果表明本文的方法能较好地模拟复合材料层板在低速冲击下的损伤扩展及变形过程,计算结果与实验结果吻合较好;对不同冲击能量下层合板损伤扩展研究表明,冲击能量与分层损伤面积成线性关系.     

缝合泡沫夹芯复合材料低速冲击的多尺度数值方法

为了发展缝合泡沫夹芯复合材料低速冲击损伤的多尺度分析方法, 建立了缝合泡沫简化力学模型, 将缝合泡沫等效为缝线树脂柱增强的正交各向异性芯材, 其材料参数由各组分性能及所占体积分数根据均一化理论计算得出; 同时, 建立冲击试验有限元模型, 通过界面元模拟面板与芯材之间的层间分层。采用GENOA渐进损伤分析模块对缝合结构冲击动态响应过程进行数值模拟, 并将计算结果与试验记录进行对比分析。结果表明: 缝合可以减小面板破坏面积, 抑制面板与泡沫分层的扩展; 但缝纫会对结构造成初始损伤, 较高的缝合密度使芯材刚度增加, 不利于泡沫结构的缓冲吸能。数值模拟结果与试验记录吻合良好, 验证了多尺度分析方法的正确性。     

基于连续介质损伤力学的复合材料层合板低速冲击损伤模型

基于连续介质损伤力学（CDM）方法,建立了分析复合材料层合板低速冲击问题的三维数值模型。该模型考虑了层内损伤（纤维和基体损伤）、层间分层损伤和剪切非线性行为,采用最大应变失效准则预测纤维损伤的萌生,双线性损伤本构模型表征纤维损伤演化,基于物理失效机制的三维Puck准则判断基体损伤的起始,根据断裂面内等效应变建立混合模式下基体损伤扩展准则。横向基体拉伸强度和面内剪切强度采用基于断裂力学假设的就地强度（in-situ strength）。纤维和基体损伤本构关系中引入单元特征长度,有效降低模型对网格密度的依赖性。层间分层损伤情况由内聚力单元（cohesive element）预测,以二次应力准则为分层损伤的起始准则,B-K准则表征分层损伤演化。分别通过数值分析方法和试验研究方法对复合材料典型铺层层合板四级能量低速冲击下的冲击损伤和冲击响应规律进行分析,数值计算和试验测量的接触力-时间曲线、分层损伤的形状和面积较好吻合,表明该模型能够准确地预测层合板低速冲击损伤和冲击响应。     

一种改进的内聚力损伤模型在复合材料层合板低速冲击损伤模拟中的应用

针对传统内聚力损伤模型(CZM)无法考虑层内裂纹对界面分层影响的缺点,提出了一种改进的适用于复合材料层合板低速冲击损伤模拟的CZM。通过对界面单元内聚力本构模型中的损伤起始准则进行修正,考虑了界面层相邻铺层内基体、纤维的损伤状态及应力分布对层间强度和分层扩展的影响。基于ABAQUS用户子程序VUMAT,结合本文模型及层合板失效判据,建立了模拟复合材料层合板在低速冲击作用下的渐进损伤过程的有限元模型,计算了不同铺层角度和材料属性的层合板在低速冲击作用下的损伤状态。通过数值模拟与试验结果的对比,验证了本文方法的精度及合理性。     

缝合泡沫夹层复合材料低速冲击数值模拟及实验

在ABAQUS分析平台中建立了缝合泡沫夹层复合材料在低速冲击下的动力学有限元模型,采用杆单元模拟缝线树脂柱的作用,基于Hashin破坏准则模拟层板面内损伤,通过各向同性硬化本构模型利用等效塑性变形模拟泡沫夹芯损伤演化。针对相同铺层的缝合和未缝合泡沫夹层结构,模拟了相同冲击能量下的低速冲击响应过程及面板、泡沫的损伤情况,数值结果与实验结果吻合较好,证明了该方法的有效性和准确性。研究结果表明,在低速冲击下,泡沫夹层结构引入缝线后虽然降低了泡沫缓冲吸能的作用,使得面板表面受到较大的冲击破坏,但增强了整体刚度,增大了面板抵抗弯曲变形的能力,减小了内部面板的损伤,使其在改善复合材料面板易分层缺陷的同时还依然拥有优良的面内性能。     

含缺陷的复合材料层合板低速冲击过程的有限元模拟

用自编的动态有限元分析程序APIC 对含缺陷的复合材料层合板的冲击损伤问题进行了模拟计算。该程序采用三维20 节点超单元分析了复合材料层合板内的应力分布, 通过修正后的C. T. Sun 的接触定律建立了冲击物和层合板的运动状态与冲击接触力之间的关系, 采用Wilson-θ法求解层合板和冲击物的运动微分方程。在处理层间分层缺陷问题时, 采用拉格朗日乘子法使预制分层缺陷界面上满足不可互相贯穿条件。对本文中的计算结果和试验结果进行比较表明: 模拟计算结果与试验结果有良好的一致性。相对于无缺陷层合板, 含预制分层缺陷的复合材料层合板在分层部位遭受冲击时, 分层缺陷对冲击损伤扩展有一定的抑制作用。     

基于改进Hashin准则的复合材料低速冲击损伤研究

针对复合材料力学性能的分散性和传统模型中退化系数选取的随意性问题,将退化系数与复合材料强度的威布尔分布参数相结合,采用改进的三维Hashin准则建立了复合材料低速冲击渐进损伤模型。考虑复合材料非线性剪切行为改进了Hashin准则,将原始准则中的剪切项用应变能替代,并采用最大应变准则判断剪切失效,避免了应力准则导致的变形不连续。采用该模型对三种能量下的T300/3501复合材料层合板低速冲击过程进行了仿真分析,计算得到的冲击响应曲线、层内和层间分层损伤结果与实验结果吻合良好,表明建立的模型适用于复合材料层合板低速冲击损伤预测。     

缝合对泡沫夹芯复合材料低速冲击性能的影响EI北大核心CSCD

为了研究缝合对泡沫夹芯复合材料抗低速冲击的影响,以未缝合、全厚度缝合和冲击面纤维面板三类缝合碳纤维泡沫夹芯复合材料板为研究对象,采用落锤冲击试验机对泡沫夹芯复合材料板进行10J能量的冲击试验。然后使用水浸超声波扫描成像系统对冲击后的复合材料板进行损伤检测,得出泡沫夹芯复合材料板内部不同深度层的损伤情况。采用ABAQUS有限元软件对上述三类泡沫夹芯复合材料板进行有限元模拟,得出了低速冲击响应过程及面板的损伤情况,并进行了实验与数值模拟结果对比分析。研究结果表明,缝合会使得各铺层的损伤趋向均匀化,能够大幅提高层合板的整体性使各铺层之间的衔接更加紧密。在较小冲击能量下,全厚度缝合与冲击面纤维面板缝合都能够抑制分层的破坏,并且抑制分层的效果相差不大,且靠近冲击面的层与层之间更加容易产生分层的破坏。     

缝合对泡沫夹芯复合材料低速冲击性能的影响

为了研究缝合对泡沫夹芯复合材料抗低速冲击的影响,以未缝合、全厚度缝合和冲击面纤维面板三类缝合碳纤维泡沫夹芯复合材料板为研究对象,采用落锤冲击试验机对泡沫夹芯复合材料板进行10J能量的冲击试验。然后使用水浸超声波扫描成像系统对冲击后的复合材料板进行损伤检测,得出泡沫夹芯复合材料板内部不同深度层的损伤情况。采用ABAQUS有限元软件对上述三类泡沫夹芯复合材料板进行有限元模拟,得出了低速冲击响应过程及面板的损伤情况,并进行了实验与数值模拟结果对比分析。研究结果表明,缝合会使得各铺层的损伤趋向均匀化,能够大幅提高层合板的整体性使各铺层之间的衔接更加紧密。在较小冲击能量下,全厚度缝合与冲击面纤维面板缝合都能够抑制分层的破坏,并且抑制分层的效果相差不大,且靠近冲击面的层与层之间更加容易产生分层的破坏。     

Finite element model for compression after impact behaviour of stitched composites

A finite element (FE) model using coupling continuum shell elements and cohesive elements is proposed to simulate the compression after impact (CAI) behaviour and predict the CAI strength of stitched composites. Continuum shell elements with Hashin failure criterion exhibit the composite laminate damage behaviour; whilst cohesive elements using traction-separation law characterise the laminate interfaces. Impact-induced delamination is explicitly modelled by reducing material properties of damaged cohesive elements. Computational results have demonstrated the trend of increasing CAI strength with decreasing impact-induced delamination area. Spring elements are introduced into the model to represent through-thickness stitch thread in the composite laminates. Results in this study validate experimental finding that CAI strength is improved when stitching is incorporated into the composite structure. The proposed FE model reveals good CAI strength predictions and indicates good agreement with experimental results, making it a valuable tool for CAI strength prediction of stitched composites.     

整体缝合夹芯结构复合材料压缩性能

设计了一种新型整体缝合夹芯结构。采用真空导入模塑工艺(VIMP)制备整体缝合夹芯结构复合材料,研究其在平压载荷作用下的力学性能和破坏模式,建立其有限元模型,研究缝合纱线用量对整体缝合夹芯结构复合材料平压力学性能的影响。结果表明:该新型整体缝合夹芯结构复合材料能够在提高缝合纱线数量的同时避免一般斜缝方式引起纤维交叉损坏的弊端。整体缝合夹芯结构复合材料的压缩强度和压缩模量随着缝合纱线数量的增加而增大,但缝合纱线含量较高时,比压缩强度有所下降。数值计算结果与试验结果对比分析,验证了所建立有限元模型的合理性,说明该模型可用于预测其压缩模量。     

缝纫泡沫夹芯复合材料板的稳定性分析

整体屈曲是缝纫复合材料夹芯板的一种重要失效模式.考虑到缝纫夹芯复合材料板一般较厚且面板与芯层厚度相差较大,缝纫工艺对夹芯板刚度影响较大的特点,基于高阶剪切理论,编制了缝纫泡沫夹芯复合材料板稳定性分析的有限元程序.利用该程序对多个算例进行了计算,所得临界屈曲应力与文献及试验结果吻合很好.同时,讨论了不同边界条件下缝纫泡沫...     

含分层损伤缝合复合材料层板的剩余压缩强度

基于渐进损伤方法,研究了含单脱层缝合复合材料层板在压缩载荷下的剩余强度。通过商用软件ABAQUS建立了含单脱层缝合复合材料层板剩余压缩强度计算模型,考虑了子层屈曲和分层扩展对剩余强度的影响。通过UMAT子程序实现了层板失效、层间失效和缝线失效的模拟。通过嵌入式杆单元结构模拟了缝线桥联作用及失效。采用Hashin准则及刚度折减法对纤维拉压、基体拉压失效进行了模拟。通过渐进损伤分析,揭示了缝合情况下含单脱层复合材料层板的失效机理,讨论了缝合参数对剩余压缩强度的影响。所预测的破坏模式和剩余强度结果与实验能较好地吻合。分析表明缝合可以明显提高含分层损伤复合材料层板的子层屈曲载荷,抑制分层扩展,并提高层板的剩余压缩强度。     

缝合参数对复合材料T型接头拉脱承载能力的影响

利用二维平面应变模型对缝合增强试验件进行失效分析,采用内聚力模型模拟界面的破坏情况,通过在分层的上下界面加入非线性弹簧元来模拟缝线的增强作用,非线性弹簧元的力学性能(桥联律)由细观力学方法获得。有限元分析结果与试验值吻合较好。在此基础上,对缘条区的缝合增强进行缝线的材料、直径和缝合密度的参数化分析,研究各参数对T型接头拉脱承载能力的影响。结果表明:缝合可显著提高T型接头的拉脱承载能力,同时能使其在较大的加载位移下仍保持较高的承载性能。T型接头的拉脱承载能力随缝线直径和缝合密度的增大而增大,且直径和密度的影响显著。缝线的拉伸强度是影响缝线性能最主要的因素,T型接头的拉脱强度随缝线拉伸强度的升高而升高。T型接头的拉脱强度随缝线拉伸模量的降低而升高,但拉伸模量的影响较拉伸强度的影响小。     

Impact damage evaluation on advanced stitched composites by means of acoustic emission and image analysis

Polymeric composites that are stitched reinforced show dissimilar behaviours with respect to regular ones. In this paper the mechanical characteristics and different behaviours of stitched reinforced polymeric composites after impact tests are investigated using an alternative approach. Several factors such as grid size, stitching scheme and voids content modify the composite performances and the interlaminar delaminating processes. If, on the one hand, the stitching technique is used to prevent delaminating damage phenomena, then, on the other hand, the process itself introduces a sort of damage into the layers during the assembled preform, that has to be taken into account. Delaminating processes due to impact loads are considered and the post-impact behaviours and damage tolerance are investigated. Impact tests were performed at several energy levels known to have an appreciable damage on the specimens. Damage evaluation analysis was performed on post-impacted specimens using different techniques: as a first step, using a digitalised image technique, the damaged area was measured and different zone shape was evaluated, further compression tests were done to evaluate the material residual properties after impact. The results coming from compression tests do not reveal the better awaited behaviour of the stitched composites with respect to regular ones. On the other hand, the acoustic emission technique is capable of evidencing the different aspects of the stitching wire. The image acquisition technique represents a new experimental method able to fully characterise damage zones and gives more information on the interlaminar behaviour of composite material. This new technique joined to acoustic emission measurements allows important results on the residual life prediction of materials mechanical properties to be obtained.     

Effect of stitch density and stitch thread thickness on compression after impact strength and response of stitched composites

In this paper, the damage failure and behaviour of stitched composites under compression after impact (CAI) loading are experimentally investigated. This study focuses on the effect of stitch density and stitch thread thickness on the CAI strength and response of laminated composites reinforced by through-thickness stitching. Experimental findings show that stitched composites have higher CAI failure load and displacement, which corresponds to higher energy absorption during CAI damage, mainly attributed to greater energy consumption by stitch fibre rupture. The coupling relationships between CAI strength, impact energy, stitch density and stitch thread thickness are also revealed. It is understood that the effectiveness of stitching has high dependency on the applied impact energy. At low impact energy range, CAI strength is found to be solely dependent on stitch density, showing no influence of stitch thread thickness. It is however observed that stitch fibre bridging is rendered ineffective in moderately stitched laminates during compressive failure, as local buckling occurs between stitch threads, resulting in unstitched and moderately stitched laminates have similar CAI strength. The CAI strength of densely stitched laminates is much higher due to effective stitch fibre bridging and numerous stitch thread breakages. At high impact energy level, CAI strength is discovered to be intimately related to both stitch density and stitch thread thickness. Since CAI failure initiates from impact-induced delamination area, stitch fibre bridging is considerable for all specimens due to the relatively large delamination area present. Stitch threads effectively bridge the delaminated area, inhibit local buckling and suppress delamination propagation, thus leading to increased CAI strength for laminates stitched with higher stitch density and larger stitch thread thickness. Fracture mechanisms and crack bridging phenomenon, elucidated by X-ray radiography are also presented and discussed. This study reveals novel understanding on the effectiveness of stitch parameters for improving impact tolerance of stitched composites.     

T300帘子布/QY9512缝纫含孔板拉伸性能

针对T300 帘子布/ Q Y9512 缝纫含孔板的面内拉伸性能, 进行了实验研究, 并考虑到缝纫对含孔层合板面内性能的影响建立了有限元分析模型。结果表明, 该模型能有效地分析缝纫含孔板的拉伸性能, 缝纫后含孔板拉伸强度没有变化或略有提高, 而缝纫方向对孔板的拉伸强度无明显影响。