军用涤纶长丝面料热转移印花及功能整理研究

介绍涤纶长丝面料分散染料热转移印花工艺,包括工艺流程、主要技术创新、产品应用等方面。阐述涤纶长丝面料阻燃涂层整理技术,并讨论阻燃剂用量、涂层增重量对整理效果的影响。总结防热红外侦察整理、防雷达波侦察整理、多功能迷彩面料生产及要点。文章表明,化纤长丝纺织产品的发展与国防建设是密切相关、相互促进、相辅相成的。以化纤长丝为基材生产的系列化军用产品是建设强大国防的重要保障。不断深化化纤长丝面料的功能性深度加工具有非常重要的意义。     

棉麻织物阳离子改性工艺及栀子黄染色研究

文中采用浸轧法对棉麻织物进行阳离子改性,探讨改性剂用量、处理液pH值、焙烘温度、焙烘时间对阳离子改性后栀子黄染色效果的影响。通过正交试验得出最佳棉麻织物阳离子改性工艺并进行栀子黄直接染色,并与未改性织物直接染色法和硫酸铝钾后媒法进行对比。结果表明:采用浸轧法改性,阳离子改性剂用量10.00 g/L,pH值=10,两浸两轧(轧余率75%),焙烘温度115℃,焙烘时间120 s时阳离子改性效果最佳;与后媒法和直接染色法相比,阳离子改性后直接染色织物染色性能最佳,染色牢度提高明显,其中耐湿摩擦色牢度3~4级,耐皂洗牢度色牢度4级,耐日晒色牢度3~4级。     

Voids and their effect on the strain rate dependent material properties and fatigue behaviour of non-crimp fabric composites materials

The manufacture of composite structures is inevitably linked to the formation of voids. Several non-destructive techniques are potentially able of detecting defects, but just the exact knowledge of the effects of defects on the mechanical properties allows the definition of thresholds for the purpose of quality management. In this paper an experimental program for characterizing the effect of voids on the composite materials behaviour is presented. Therefore glass fibre non-crimp fabric reinforced epoxy composites were produced using vacuum assistant resin transfer moulding. For obtaining various void contents specially modified process parameters were used. Nominally defect free specimens are compared with flawed specimens. Tensile testing at different loading speeds and fatigue tests in tension-compression loading are performed.     

Effect of inter-ply sliding on the quality of multilayer interlock dry fabric preforms

Forming thick, complex shapes with several layers is needed in high technology fields. During forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows that, when working with dry fabric forming, the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies. In addition, to reduce the number and amplitude of defects, the layers subjected to severe defects can be placed in the inner position where they are subjected to the compression applied by the upper layers.     

Influence of the tufting yarns on formability of tufted 3-Dimensional composite reinforcement

In aerospace industry, thicker and more complex composite parts are needed. Multilayered reinforcement is largely used as the traditional method. Recently, three-dimensional (3D) fabrics are developed to replace the multilayered reinforcements in certain applications to increase the performance in thickness direction of part, e.g. interlock structure. Currently, the development of tufting technology can be employed to produce the 3D textile composite reinforcements. The tufting parameters, such as tufting density, tufting length and tufting yarn orientations, can be completely controlled by user. In order to improve the understanding of formability of the tufted 3D fabric during manufacturing, the present work analyzes the preforming behaviours of tufted 3D reinforcement in the hemispherical stamping process. Also the preforming behaviours are compared with the samples of the multilayered forming. The experimental data demonstrated the influence of tufting yarns on the material draw-in, interply sliding, and winkling phenomenon during forming. Furthermore, the orientations of tufting yarn affected the forming results, which leaded to misalignment defect in the zone of strong in-plane shear.     

In-situ damage sensing of woven composites using carbon nanotube conductive networks

We report an in situ analysis of the microstructure of woven composites using carbon nanotube (CNT)-based conductive networks. Two types of specimens with stacking sequences of (0/90)_s (on-axis) and (22/85/−85/−22) (off-axis) were manufactured using ultra-high-molecular-weight polyethylene fibers and a CNT-dispersed epoxy matrix via vacuum-assisted resin transfer molding. The changes in the electrical resistance of the woven composites in response to uniaxial loading corresponded to the changes in the gradient of the stress–strain curves, which is indicative of the initiation and accumulation of microscopic cracking and delamination. The electrical resistance of the woven composites increased due to both elongation and microscopic damage; interestingly, however, it decreased beyond a certain strain level. In situ X-ray computed tomography and biaxial loading tests reveal that this transition is due to yarn compaction and Poisson’s contraction, which are manifest in textile composites.     

Numerical simulation of the impact behaviors of shear thickening fluid impregnated warp-knitted spacer fabric

The impact behavior of warp-knitted spacer fabrics (WKSFs) impregnated with shear thickening fluid (STF) under low-velocity impact loadings have been investigated from experimental and finite element analyses (FEA) approaches. From the experimental approach, the impact load–displacement curves have been obtained. It was observed that the WKSF impregnated with the STF composite material (the WKSF/STF composite) shows a higher stiffness and lower peak force than those of the WKSF under the same impact loadings. In FEA approach, the geometrical models of the WKSF and the WKSF/STF composite material were established based on the WKSF fabric architectures. The dynamic responses including the impact load–displacement curves and impact deformation of the samples were predicted based on finite element analyses at the microstructure level. It was found that the STF and the coupling effect between the STF fluid and fiber tows are the key factors which influence the cushioning behaviors of the composite. The energy absorption mechanisms include the buckling of the spacer finer tows and the thickening effect of the STF under impact loading. The WKSF/STF composite could be expected as a damping or energy-absorptive materials under impact loading.     

Inter-ply stitching optimisation of highly drapeable multi-ply preforms

An efficient finite element model has been developed in Abaqus/Explicit to solve highly non-linear fabric forming problems, using a non-orthogonal constitutive relation and membrane elements to model bi-axial fabrics. 1D cable-spring elements have been defined to model localised inter-ply stitch-bonds, introduced to facilitate automated handling of multi-ply preforms. Forming simulation results indicate that stitch placement cannot be optimised intuitively to avoid forming defects. A genetic algorithm has been developed to optimise the stitch pattern, minimising shear deformation in multi-ply stitched preforms. The quality of the shear angle distribution has been assessed using a maximum value criterion (MAXVC) and a Weibull distribution quantile criterion (WBLQC). Both criteria are suitable for local stitch optimisation, producing acceptable solutions towards the global optimum. The convergence rate is higher for MAXVC, while WBLQC is more effective for finding a solution closer to the global optimum. The derived solutions show that optimised patterns of through-thickness stitches can improve the formability of multi-ply preforms compared with an unstitched reference case, as strain re-distribution homogenises the shear angles in each ply.     

Nesting effect on the mode II fracture toughness of woven laminates

The mode II fracture toughness is evaluated for carbon fibre T700-epoxy reinforced woven laminates using the end notch flexure set-up. The analysed woven composites have a different tow size (3K/12K). Three different nesting/shifting configurations are applied to the plies at the fracture surface. Corrected Beam Theory with effective crack length method (CBTE) and Beam Theory including Bending rotations effects method (BTBE) are evaluated for obtaining mode II fracture toughness. During data post-processing, the importance of the bending angle of rotation and the test configuration is observed to be important. The results show that crack propagation under mode II is more stable if the matrix is evenly distributed on the surface. The nesting does not significantly affect mode II fracture toughness values, although a greater presence of matrix on the delaminated area increases its value.     

Comparison between voxel and consistent meso-scale models of woven composites

The applicability of voxel meshes to model the mechanical behavior of woven composites at the mesoscopic scale is studied and compared to consistent Finite Element (FE) meshes. The methods are illustrated by mechanically modeling a Representative Unit Cell (RUC) of a composite made of four layers of glass fiber plain weave fabric embedded in an epoxy matrix. Mesh convergence is studied to determine the minimum element size necessary to obtain a correct yarn volume fraction. The comparison between both methods is based on (i) homogenized macroscopic elastic properties, (ii) local stress fields, and (iii) first damage prediction. Even if a good agreement is obtained for the elastic properties, the stress concentrations due to the steplike shape of voxels induce significant differences between both methods in terms of first damage prediction.