PSI - Issue 17

Elena M. Strungar et al. / Procedia Structural Integrity 17 (2019) 965–970 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

966

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The purpose of this work is to conduct a complex study of polymer composite materials samples based on preforms to obtain the mechanical material properties and to assess the effect of various weave patterns on mechanical characteristics.

2. Experimental part

Within the framework of the complex tests, experimental studies of tensile, tensile/ compression of samples with a hole, bent beam four-point bending, impact and compression after impact, non-uniform separation, and shear in the plane were carried out. A total of 6 weave patterns of 3D woven performs and two types of layered samples reinforced in the transverse direction are considered. This paper presents experimental studies of tensile strain of solid samples and with a hole. The test equipment complex, which is part of the Center for Collective Use of the Experimental Mechanics Center of the Perm National Research Polytechnic University, includes the following systems: Instron 5882 universal electromechanical system (100 kN), equipped with an Instron AVE non-contact video extensometer; universal electromechanical system Instron 5989 (600kN); Vic-3D digital optical system for analyzing deformation fields, designed for contactless measurement of deformations over the entire surface of a material during sample testing or operation of structural elements. It allows to research different materials, including anisotropic or composite materials, to check numerical solutions results. The measurement accuracy of displacements is 0,01 P, the shooting speed is 15 fps, the resolution of DCP cameras is 4.0 MP; synchronization with the controller of the test system; the software mathematical apparatus is based on the method of correlating digital images. The speed of the rolling grip when testing for uniaxial tension of composite samples was 2 mm / min. When measuring the mechanical characteristics of structural materials, as a rule, devices are used that determine the displacements at two points. This information can be obtained using optical methods for measuring strain, namely the method of correlating digital images and is based on analysis of the region of interest from a pair of digital photos taken before and after deformation of the sample. In preparing the surface of the sample, a contrasting fine stain was applied to the surface using white and black matte spray paint. To do this, first applied a white matte base on the surface of the samples, after which a set of black dots was applied. To determine the elastic modulus and Poisson's ratio on samples without a hub, an additional module of the optical video system software “virtual extensometer” was used. The principle of its operation is simi lar to the mounted extensometer and consists in tracking the mutual displacement between two points on the sample surface in accordance with the applied force. The main advantages of using a “virtual extensometer (T)” is the contactless recording of deformations, thereby eliminating the mechanical effect on the sample surface. The average values of the elastic modulus and Poisson's ratio for 10 samples obtained in the experiment for each type of reinforcement are presented in Table 1 and are given in relative units. Measuring base hinged extensometer was 100 mm. 3. Property definition

Table 1. Main mechanical characteristics of composite samples Type of reinforcement 1 2 3 4

5

6

Elastic modulus, GPa

0.9

1.0

0.7

0.8

0.5

0.6

Poisson's ratio

0.16 0.14 0.63 0.09 0.47 1.00

According to the results of tests on uniaxial tension, it can be concluded the samples with reinforcement type 1 and 2 have the highest mechanical characteristics. To assess the inhomogeneous deformation fields obtained using the video system, a sample of the type of reinforcement 2, which has the highest modulus of elasticity, was considered. When calculating the fields of longitudinal (  yy), transverse (  xx) and shear deformations (  xy), the finite deformation tensor in the Lagrange