三维角联锁机织复合材料弯曲抗疲劳性能有限元分析

使用三维绘图软件PRO/E 5.0绘制出三维角联锁机织复合材料结构模型,借助有限元软件ANSYS Workbench对该结构模型的弯曲疲劳性能进行分析。在复合材料弯曲静力学分析的基础上,添加疲劳工具对复合材料的抗疲劳性能进行分析,通过复合材料纤维、树脂各自的寿命、损伤分布云图分析复合材料的抗疲劳性能。结果表明:弯曲载荷作用下,复合材料与弯曲压头接触的位置表现出更大的弯曲应力;这些位置在较小循环载荷作用下较早发生破坏;与测试方向平行的纬纱较经纱发生更严重的破坏。     

三维机织间隔复合材料结构对其力学性能的影响

以玻璃纤维为原料,设计3种不同结构的三维机织间隔织物,采用手糊成型工艺制备三维机织间隔复合材料,研究了其在压缩、剪切、弯曲等载荷作用下的力学特性,并分析了材料结构对其力学性能的影响。结果表明,相同高度(20 mm)、相同间隔(30 mm)的3种三维机织间隔复合材料的压缩强度和剪切强度均表现为:三维纤维间隔复合材料<"X"型间隔复合材料<三维织物间隔复合材料,其压缩强度分别为0.52,0.72,1.66 MPa,剪切强度分别为0.22,0.28,0.36 MPa;3种三维机织间隔复合材料的弯曲强度基本相同,均为4.30 MPa左右。     

三维中空夹芯复合材料侧压性能的有限元分析

本文利用有限元软件ANSYS,建立三维中空夹芯复合材料的结构模型,进行侧压性能研究。利用该模型,探讨了材料在1mm侧压位移载荷作用下复合材料中纤维、树脂和材料本身的应力、应变分布。结果表明,三维中空夹芯复合材料在侧压载荷作用下,上下面板中经、纬纱线交织处应力最大,最容易发生侧压破坏;芯材应力最小,不容易发生侧压破坏;复合材料在承受侧压载荷作用时,纤维起主要承载作用,树脂起次要作用;材料的破坏模式主要为树脂破裂。     

不同结构纺织复合材料准静态侵彻实验分析及有限元模拟

本文研究了两种不同结构三维结构纺织复合材料——三维正交机织玻璃纤维,不饱和树脂复合材料和双轴向纬编针织玻璃纤维／不饱和树脂复合材料在MTS材料试验机上的准静态侵彻测试。以纯铝MTS实验数据为标定,分析了准静态侵彻载荷一位移曲线及其破坏机理,比较了不同结构纺织复合材料以及纯铝的位移一载荷曲线,由此计算得到位移与吸能关系曲线。同时根据复合材料各自织物中纤维束排列及织物成型特点,分别建立了复合材料的细观结构模型和单胞模型。编写用户子程序（VUMAT）,用ABAQUS软件进行了有限元模拟。结果表明：三维纺织复合材料各自损伤结果和载荷-位移曲线与实验结果吻合较好,证明有限元的有效性。三维正交结构复合材料抗侵彻能力优于双轴向纬编针织复合材料,但是破坏过程中其抗侵彻能力幅值变化差异大,没有针织复合材料抗侵彻能力稳定。     

三维角联锁机织复合材料低速冲击破坏的有限元计算

测试三维角联锁机织复合材料低速冲击性能,得到复合材料在低速冲击过程中的载荷－位移曲线等。结合采用冲击接触定律、单元失效准则和材料刚度退化技术,建立复合材料低速冲击的三维有限元单胞模型。运用商业有限元软件ABAQus／Explicit,联合用户子程序（VUMAT）计算复合材料低速冲击破坏过程。比较有限元计算结果和实验结果,发现二者在载荷一位移变化规律和复合材料破坏形态上较为吻合。     

三维浅交弯联复合材料结构与力学性能研究

以2400tex的玻璃纤维为原料,在SGA598型三维织机上,织制出三层和六层两种三维浅交弯联机织物作为三维机织复合材料预制体,将两块三层三维浅交弯联机织物层叠在一起以保持两种机织物的纬纱层数一致。将环氧树脂E51与聚醚胺WHR-H023以质量比为3∶1的比例混合后制成树脂基体,采用手糊成型的方式将预制体与树脂基体按照质量比为1∶1的比例复合成型,制备出两种三维浅交弯联机织复合材料。借助Instron 3385H型万能材料试验机对材料的拉伸及弯曲力学性能进行测试;通过实验过程及对破坏断面的观察比较两种复合材料的力学性能。实验结果表明,三维浅交弯联机织复合材料在承受拉伸及弯曲载荷时,主要表现为脆性破坏模式;六层三维浅交弯联机织物作为复合材料的预制体时,该复合材料的弯曲性能和拉伸性能均优于两块三层三维浅交弯联机织物层叠在一起作为增强体的复合材料;且六层机织物可以更好地保护复合材料,提高其使用寿命。     

三维正交机织复合材料准静态侵彻实验和有限元模拟

用钢制侵彻体对三维正交机织复合材料在MTS材料试验机上作准静态侵彻测试，得到的准静态侵彻位移一载荷曲线用来研究材料的能量吸收和破坏模式。根据三维机织复合材料的细观结构建立单胞模型，结合应力更新原理编写用户子程序（VUMAT）。利用ABAQUS有限元软件及用户子程序模拟实验过程，得到的位移一载荷曲线与实验对比，可以看出有限元计算得到的结果与真实实验比较吻合，表明单胞的建立和用户子程序的编写是正确的。     

三维角联锁机织复合材料三点弯曲疲劳的细观结构效应

依据层层接结三维角联锁机织复合材料的结构特点,建立能真实反映细观结构特征的大型精细实体几何结构模型;基于非弹性滞后能疲劳破坏准则,用有限元法计算三维角联锁机织复合材料在三点弯曲低周交变循环载荷下的变形和刚度降解,揭示疲劳过程中三维角联锁机织复合材料内部应力分布特征和变形特征,分析纱线与树脂的破坏机理,阐述该复合材料在循环载荷下发生疲劳破坏的结构效应。结果表明,经纱在疲劳过程中承担大部分的载荷,且不同的组分呈现不同的破坏扩展过程。本文研究结果和研究方法将可进一步扩展至三维机织复合材料工程结构设计。     

三维机织复合材料力学性能分析与研究

通过对三维机织复合材料几何细观结构的研究,分析了三维机织复合材料的力学性能,采用椭圆形纤维束截面假设并结合实际的纱线形态建立了一种新的三维机织复合材料力学模型,对三维机织复合材料的拉伸、压缩和层间剪切强度进行了理论分析,并与实验结果进行了对比,验证了力学模型的正确性。     

国产T800级S型与H型碳纤维对于三维机织复合材料风扇叶片的适用性研究

针对国产T800级S与H型碳纤维对于三维机织复合材料风扇叶片的适用性开展试验研究,试验结果表明S型纤维具备更高的拉伸断裂强度,但其三维机织复合材料疲劳性能较差,适用于非疲劳高承载结构;而H型纤维三维机织复合材料的拉伸强度略低于S型纤维,但相同载荷条件下其疲劳寿命比S型纤维高108.91%,相比之下,H型纤维更适用于航空发动机风扇叶片。     

Effect of different fiber orientations on compressive creep behavior of siC fiber-reinforced mullite matrix composites

The compressive creep behavior of monolithic mullite and a composite made of mullite reinforced by 40 vol% SiC fiber were investigated at temperatures from 1100 to 1200°C and under stresses from 5 to 55 MPa in air with a loading direction parallel and perpendicular to the fiber direction. For both situations the composite exhibits better creep resistance than monolithic mullite, although there is a creep anisotropy. The improvement in creep resistance when the fibers are parallel to the loading directions is due to the shedding of the applied stress on the SiC fibers, and the improvement in creep resistance when the fibers are perpendicular to the loading direction occurs because the fibers inhibit the lateral deformation of the mullite matrix along the fibers. The improvement mechanisms of the composites were confirmed further by their creep-recovery study, which indicated that the two types of composite specimens exhibit both an apparent creep-recovery behavior on load removal, due to the relaxation of the residual stress state between the mullite matrix and the SiC fibers after unloading. ©     

Compressive test and numerical simulation of center‐notched composite laminates with different crack configurations

Experimental and computational studies of the composite laminates with thin center notches under axial compressive loading are carried out. A series of compressive testing of the composites with different crack lengths and angles between the loading vector and 0° fiber direction were conducted. The damage mechanisms as well as load–displacement curves are obtained from the test to analyze the effects of crack dimensions on stress distribution and ultimate load. It was shown that the compressive strength of composites drastically reduces when the crack angle goes from 0° to 90°. By studying the fracture surfaces of the tested specimens, all initial cracks within the laminates are found to extend without a straight crack path until fibers fracture simultaneously. Cases that involve crack propagation are modeled for different crack dimensions with a 3D progressive damage finite element analysis using the Abaqus. Numerical simulations qualitatively reproduce the general observations made in the laboratory experiments. POLYM. COMPOS., 38:2631–2641, 2017. © 2015 Society of Plastics Engineers     

Stress dependence of the coefficient of moisture diffusion in composite materials

A model for the effect of external loading on diffusion into the bulk resin matrix of unidirectional composite materials is proposed. The model attributes the effect to a change in the free volume of the resin matrix, which is equal to its volume strain. The latter is calculated by substracting the volume strain of the fibers from that of the composite. The ratio of the diffusion coefficients in the stressed and unstressed states is expressed as a function of the stress level, the volume fraction of the fibers, and the angle between the applied stress and the fiber direction. Calculations for a glass-fiber-reinforced epoxy composites are presented.     

制备工艺对C3D/EP复合材料力学性能的影响

本文采用了两种工艺制备三维编织碳纤维增强环氧树脂基(C3D/EP)复合材料,并对其力学性能和微观结构进行了研究和分析.结果表明,孔隙对复合材料的影响较大,相对RTM工艺制备的复合材料,真空浸渍法制备的复合材料有较高的空隙率,较低的弯曲强度和弯曲模量、较好的冲击性能.     

Transverse compression failure of unidirectional composites

The mechanical response of unidirectional composites subject to uniaxial transverse compressive loads was measured and analyzed by finite element simulation. Consistency in failure plane orientation was observed when comparing simulated matrix shear band angle to measured crack angle. A model based on hexagonal packing of fibers was proposed and the shear band angle was shown to depend on the fiber volume fraction. The effects of strong and weak fiber–matrix interfaces were considered using models with randomly distributed fibers for a valid statistical analysis. The results of these models showed that the composite compressive strength increased with the fiber loading for the strong interface case, while the strength was independent of the fiber loading for the weak interface case because of interface debonding. POLYM. COMPOS., 36:756–766, 2015. © 2014 Society of Plastics Engineers     

深潜壳体用高模量树脂基体的研究——基体模量对复合材料抗压抗剪性能的影响

制备了高模量树脂基单向复合材料，测试了单向复合材料的纵向压缩性能和平面剪切性能。研究了基体模量对单向复合材料抗压强度及复合材料平面剪切性能的影响，结果表明：单向复合材料的抗压强度与基体模量成线性比例关系，随基体模量的提高而提高，复合材料的平面剪切性能与基体模量基本上呈线性关系，平面剪切强度亦随基体模量的提高而提高。以模量达５．３６ＧＰａ的环氧树脂作为复合材料的树脂基体制备的，单向玻璃纤维增强复合材料其抗压强度高达１．２９５ＧＰａ，碳纤维增强的复合材料抗压强度高达１．３７２ＧＰａ，与普通环氧树脂的单向复合材料相比，分别提高了５５％和４５．８％；复合材料的平面剪切强度达６４．５ＭＰａ，比普通环氧树脂复合材料的平面剪切强度提高了４４．３％，满足了深潜壳体对复合材料抗压强度的要求。     

In situ preparation of intrinsic flame-retardant urea formaldehyde/carbon nanotubes nanocomposite foam: structure and reinforcing mechanism

ABSTRACT

Urea-formaldehyde (UF)/carboxylated carbon nanotubes (CNTs-COOH) nanocomposite foams were prepared via in-situ polymerization. Chemical bonding and hydrogen bonding interactions formed between CNTs-COOH and UF matrix. UF resin adhered onto the ektexine of CNTs-COOH and grafting ratio of 496.41% was achieved. UF/CNTs-COOH foam showed smaller cell size, narrower cell size distribution and lower water absorption compared with UF foam. Introduction of 0.25 wt% CNTs-COOH resulted in 58.43% increase in compressive strength. CNTs-COOH were pulled out with surface covered with UF resin under stress and the failure mode was the destruction of matrix around interfacial layer. UL-94V-0 rating was achieved for the composite foams.     

铺层结构对三维中空夹层复合材料压缩性能的影响

采用手糊成型制备了双夹层三维中空夹层复合材料,重点研究了厚度为5 mm和8 mm的三维中空织物ZK5和ZK8铺层顺序对复合材料压缩强度的影响,并从树脂含量、织物厚度匹配性角度进行分析。结果表明,随树脂含量增加,三维中空夹层复合材料的压缩强度明显提高;双夹层三维中空夹层复合材料中,下层的树脂含量明显高于上层;ZK5和ZK8织物铺层顺序对双夹层中空复合材料的压缩强度影响较大,其中将ZK8置于ZK5下层时复合材料的压缩强度为ZK8置于ZK5上层时的1.7倍,即在三维中空夹层复合材料总厚度不变的情况下,将高厚度中空织物置于下层的结构明显优于将其置于上层的结构。通过这一概念可以在保证三维中空夹层复合材料整体厚度尺寸不变、质量不增加的条件下通过铺层结构的匹配设计,最大限度地提高复合材料的力学性能。     

The moisture and temperature effect on mechanical performance of flax/starch composites in quasi‐static tension

The effect of temperature and moisture on mechanical behavior of flax fiber/starch based composites was investigated experimentally. Elastic modulus, the nonlinear tensile loading curves, and failure strain were analyzed. Neat matrix and composites with 20 and 40% weight content of fibers were tested. It was found, performing tests with different amplitudes, that microdamage development with stress is rather limited and the related elastic modulus reduction in this type of composites is not significant. It was shown that the composite elastic modulus and failure stress are linearly related to the maximum tensile stress in resin. The sensitivity of the maximum stress of the resin with respect to temperature and moisture is the source of composites sensitivity to these parameters. Constant interface stress shear lag model for stress transfer assuming matrix yielding at the fiber/matrix interface has been successfully used to explain the tensile test data. It indicates that the sensitivity of the used composite with respect to the matrix properties change could be significantly reduced by increasing the average fiber length from 0.9 mm to 1.5 mm. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers