Effect of the structural parameters on the mechanical properties of cross-reinforced composites

Abstract

The problem of creating a composite material which has defined properties is related to the optimum selection of its structural components, ioeo, fibers and matrix, and the directions of the reinforcement. The corresponding selection of the binder plays an important role in ensuring the maximum strength characteristics of the composite. The features of failure of unidirectional carbon plastics which differed with respect to the properties of the structural components were investigated in [i]. It was shown that the deformation properties of the matrix have an important effect on the strength of the carbon fibers in the composite and as a consequence, a material with weaker fibers can be stronger than material with stronger fibers and a matrix with a low maximum elongation. The problems related to improving the manifestation of the strength of carbon fibers in a composite are also examined in [2, 3]. The features of the behavior of a unidirectional layer in a cross-reinforced carbon plastic in uniaxial extension were investigated and the properties of the matrix which cause the best manifestation of its strength in a stack were determined in the present study. Two types of carbon fibers: CF I and CF=, and two types of matrices: thermoplastic M I and epoxy M2, were selected for the analysis (Tables 1 and 2). Two types of carbon plastics (subsequent material I: CF I + M I and material 2: CF 2 + M 2) were prepared from these fibers and matrices. Material 1 was a carbon plastic based on ELUR-0.08P carbon tape and polysulfone thermoplastic binder and was prepared by laminar alternation of the intermediate product with subsequent molding of the stack by direct pressing. The following types of stacking were realized; [0~ 13 layers; [0 ~ +45 ~ , 90 ~ , -45~ 16 layers; [+45 ~ , -45~ 24 layers; [90~ 13 layers. Material 2 is a carbon plastic based on UKN-P/5000 complex carbon fiber and epoxy binder, and it was prepared by laminar alternation of the intermediate product in the form of unrolled tape with subsequent molding of the stack by the direct pressing method. The following types of stacks were realized: [01]: nine layers; [0 ~ +45 ~ , 90 ~ , -45~ eight layers; [90~ nine layers. The average values of the dimensions of material 1 for all directions of reinforcement except for [90 ~ are the following: width of 9.75 mm, thickness of 1.25 mm; samples reinforced at an angle of 90~ 20 and 2.75 mm, respectively. The samples of material 2 with stacking of [0 ~ and [0 ~  ~ 90 ~ ] had a width of 9.75 mm and a thickness of 1.25 mm, and the samples reinforced in the transverse direction had dimensions of 19.90 and 3.3 mm, respectively. The data on the mechanical properties of materials 1 and 2 in uniaxial extension are reported in Table 3. Special experiments on extension with monotonic static loading on an Instron universal machine (model TT-Dm-10t) with a loading rate of 5 mm/min were conducted to determine the mechanical characteristic of materials 1 and 2. The samples were brought to failure with measurement of the longitudinal (on a 50 mm base) and transverse deformation. The effect of the reinforcement scheme of the carbon plastic on its mechanical properties is shown in Fig. i. The strain diagrams of material 1 are shown as an example, and the dependences of the deformation of the material on the reinforcement scheme are similar for material 2. Deviation of the strain diagram from the linear for a load level of approximately 90% of the limiting level is observed in materials reinforced in the transverse direction. This effect can be attributed to cracking of the binder, which results in a decrease in the rigidity of the material. A comparison of the characteristics of the carbon plastics