Fiberglass preforms or fabrics are the main structural form for making glass fiber reinforced plastics (abbreviated to FRPs). Once the fiber and matrix properties as well as fiber volume content are fixed, the mechanical properties of the FRP products are predominantly dependent on the structural parameters of the fabrics, i.e., fiber arrangement angles and areal weights. It is a difficult task to experimentally determine those parameters. Not only does high expenditure both in time and in money have to be spent, but also it is hardly possible to obtain an optimized design only through the trialand-error tests. This paper describes how to design the two structural parameters of any multiaxial fabric only based on the mechanical properties of the fiber and matrix materials. The load shared by any layer of the FRP is determined through the classical laminate theory, whereas the homogenized stresses in the fiber and matrix of this layer are calculated using micromechanics Bridging Model. The homogenized quantities are then converted into true stresses before compared with the fiber and matrix strength data to assess whether or not the layer is failed. If there is a fiber failure, or there is a matrix failure together with a maximum strain of the laminate which is greater than a critical value, the corresponding load applied on the FRP is defined as its ultimate strength. All of the design formulae involved are explicit and analytical, and the designed performances of the resulting FRPs agree well with the experimental counterparts. The present work provides an efficient methodology for engineering applications.

    The three-dimension integrated hollow sandwich composites is a novel sandwich structure material, which is obtained by interweaving the core material and the upper and lower panels together, and the core material and the panel become a unitary structure. The panel of the three-dimension integrated hollow sandwich composites is integrated with the core material and is formed by one-time curing, so that it has excellent properties such as resistance to delamination, impact resistance, and high damage tolerance. Studying the mechanical properties of three-dimension integrated hollow sandwich composites has important guiding significance for its structural design and application. In this paper, the research progress of mechanical properties of three-dimension integrated hollow sandwich composites in terms of flatwise compression, side compressive, shear, bending and impact properties were introduced in detail, and the existing problems are pointed out, to provide direction for future research.

3D printing is a layer-by-layer forming additive manufacturing technology. Fiber reinforced polymer composites are advanced structural materials with excellent mechanical performance. Combining 3D printing technology and fiber reinforced polymer composites, this paper proposes a novel composite preparation process which will certainly promote their development and applications. This paper reviews and analyzes the current research progress and difficulties of 3D printing for fiber reinforced polymer composites, and meanwhile, presents a new 3D printing process for continuous fiber reinforced thermosetting polymer composites. This process separated the whole preparation into three independent modules, including fiber impregnating, 3D printing and pre-formed sample curing. Relevant experimental equipments were designed and built independently, and the 3D printed samples were successfully fabricated. The mechanical test results showed that the tensile strength and tensile modulus of these (52% fiber content) specimens were 1325.14MPa and 100.28GPa, respectively. The flexural strength and flexural modulus were 1078.03MPa and 80.01GPa, respectively. The interlaminar shear strength was 58.89MPa. The mechanical performance had been greatly improved.

    Wing spar is the major load-carrying structure with large dimension and complex stress. Composite wing spar features weight reduction, load-carrying increase and long service life. To achieve the effective load carrying and transfer, and satisfy process coordination, composite wing spars are required to have accurate lay-up position and angle, and strictly controlled profile tolerance. However, due to complex lay-up and various sections of large composite wing spar, the traditional manual process of large composite components frequently brings about quality issues in the internal and unstable quality, which requires higher level of manufacturing process so as to satisfy engineering requirements. The digital technology adopted from design to manufacturing, and the automatic lay-up, cutting and forming of materials will contribute to the high quality forming of composite wing spar so as to satisfy all engineering requirements.

    The laminates of 6 different layers structure were designed and prepared, meanwhile the effects of the angle of different layer and different one-way zone volume mass fraction on the tensile properties of laminated plates were studied through the tensile test. The tensile ultimate strength, damage characteristics and load-displacement curves of 6 kinds of composite laminates under tensile test were obtained through experiments. The results show that the tensile strength of composite laminated plates decreases with the increase of eccentric axis angle. When the volume fraction of the 45° and 90° is the same, the tensile strength of the laminated plate in the 45° layer is higher than that of the laminated plate in the 90° layer. The delamination area can be effectively reduced on the surface of the [0°/45°] layer, and the layer is more prone to be layered because of the [0/90°] of internal shear. It is verified that the mechanical properties of composite laminated plates can be designed by changing the angle of lamination.

    This paper seeks to address practical experimental techniques on axial compression behaviors of flexible foldable lenticular composite tube (LCT) with ultra length. A testing system was designed and established to determine the axial compression behaviors of ultra-length LCT, and the axial compression stiffness and buckling load of LCT with the length of 6m were measured by this testing system. In order to verify the measurement from the novel experimental method, eigenvalue buckling FEA model of the LCT with the length of 6m was established to predict the axial compression buckling load that have a good agreement with the experimental data. It is shown that the new developed testing system can accurately and expediently determine the axial compression behaviors of ultra-length LCT .

    This essay studies the layout simulation evaluation technology of aeronautical composite production line, and constructs the digital model of aviation composite material process flow and production line layout. Based on actual projects of aeronautical composite materials digital production line, the simulation modeling and simulation experiment of the process layout of composite production line are completed. Through simulation technology, the process layout design of composite material production line has been quantitatively analyzed and demonstrated, so as to guide the instructand operation of composite production line.

    Automated fiber placement has been become the main manufacture method to produce airframes such as wings and fuselages, thus the research about automated fiber placement is more and more popular. The paper focuses on the common defects during automated fiber placement, including its types, its causes and its effects on mechanical properties. In the first section, the worldwide research about automated fiber placement is reviewed. Firstly, the summary of common
defects in practical placement experiment of our team is introduced, and its possible causes are analyzed, and the research object includes thermoset prepreg, dry fibers and thermoplastic materials. Secondly, a review about common defects in automated fiber placement is introduced. Thirdly, the defects in steering analysis is studied. Fourthly, the layup quality of automated fiber placement on curved panel is analyzed. Finally, the main defects in layup of sandwich structures is investigated, and the defects of dry fibers and thermoplastic prepreg are studied respectively. The introduction and summary should be benefit for the quality improvement in the future automated fiber placement.

    According to the characteristic of prepreg tow applied in grid automatic fiber placement, the prepreg by domestic T800/603B is slit into tows which is suitable for mesh laying width according to grid size. Taking slitting width of 5mm and 10mm prepreg tow for example, the preparation technology of which was researched. In addition the accuracy of slitting width, the strength of overlap joint and damage situation of slitting prepreg tow edge were studied. Results showed that different widths of the tows cut out can meet the requirements of prepreg tow applied in grid automated fiber placement.

    During the process of automatic fiber placement, aiming at the technological defects such as fiber folding and delamination in laying of resin-based fiber reinforced composites, this paper emphasizes on the advantages and disadvantages of different trajectory design methods (fixed angle, geodesic line, variable curvature) in technological defects. The different trajectory planning methods are compared. Finally, a trajectory design method for different surface characteristics and different wire laying process requirements is given.

    Curing-induced distortion in manufacturing processing, which is related to many different effect factors, has important influence on the dimensional accuracy of composite parts. The different effect factors can be classified as intrinsic or extrinsic factors. For intrinsic factors, these are with respect to material properties, stacking sequence of plies and geometry of structures, whereas extrinsic factors are generally related to the art of curing process and tooling properties. These factors could bring structures the process-induced residual stresses that will lead to the distortion after parts detooling. Through observing the current research results, the effects of these different factors on curing-induced distortion are concluded, then we can use these conclusions as the basis to predict and control the distortion of composite parts.

    To predict the springback of double curvature plates is difficult. Springback has negative effects on forming efficiency and quality. A series of experiments were carried out to study the springback problem of Invar alloy smooth mould plate forming process based on the flexible square pressure head technique. The experiment aimed at punching different sail and saddle shaped plates. Due to the complexity of the forming mechanical state of the equipment, springback has certain uncertainties, but there are clear rules: The distance from the edge of the plate has an important impact on the springback, the springback of plate at middle position is obviously smaller than the edge; The larger the curvature is, the springback is smaller, but not stable; The springback of saddle shape is smaller than that of the sail shape. The results are useful to guide the forming of smooth sheet products with uniform deformation by flexible die.