PSI - Issue 18

Ekaterina M. Zubova et al. / Procedia Structural Integrity 18 (2019) 843–848 Zubova et al. / Structural Integrity Procedia 00 (2019) 000–000

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There are various monitoring and diagnosing methods of accumulation damage process in composites including methods of monitoring during operation. One such method is the acoustic emission technique (AE). AE refers to the generation of transient elastic waves produced by a sudden redistribution of stress in a material. AE testing is a powerful method for examining the behavior of materials deforming under load. The AE technique is a promising method for damage monitoring of composite materials, as it can provide important information about the initial stage of loading, the rate of damage accumulation during loading, and the dominance of various damage mechanisms in composite materials with different structures. The study of damage accumulation in composite materials at an initial stage of deformation by using the AE technique is described in papers [Bourchak et al. (2013) and other]. The technique for evaluation the structural integrity of the composite structure and determining the location of damage by the using of the AE technique is presented in paper [Sikdat et al.]. AE signal parameters such as hits number, energy and amplitude were analyzed in [Barile et al. 2019] to study the damage initiation and control the delamination process. This paper is devoted to studying the damage initiation process in a carbon fiber reinforcement polymer (CFRP) at an initial stage of deformation by using the AE technique. Experimental studies include mechanical testing of CFRP samples with different types of reinforcement for uniaxial tension with simultaneous registration of AE. AE comparative analysis is provided. In this work, the 3D digital image correlation system Vic-3D was used to monitor the initiation and development of crack-like defects in a composite material based on an analysis of the evolution of heterogeneous displacements and strain fields during loading of specimens. 2. Materials and methods 2.1. Materials end experimental procedure In this work CFRP samples based on preforms, obtained by the 3D weaving method with various weave patterns (type 1 and 2), layered (type 3) and layered samples reinforced in the transverse direction using the Tufting method (type 4) were investigated. The geometry of the specimens is shown in Fig. 1.

Fig. 1. Geometry of the specimens.

Uniaxial tension mechanical tests (ASTM D3039) of CFRP specimens with simultaneous registration of AE were carried out at room temperature and at the rate of 2.0 mm/min. Electromechanical testing system Instron 5882 was used for loading composite samples. The AE system Vallen Systeme AMSY-6 (Germany) was used to study the damage initiation. The wide band sensors AE105A (frequency range 450-1150 kHz) and preamplifiers (40dB) were used for testing. The sensors were attached to samples using a Wacker Silicon vacuum silicone grease and rubber bands. The photo of the sample in the grips of the testing machine and sensors' location is shown in Fig. 2. The images were captured with a pair of two high-resolution cameras (Prosilica, 16 Mp) at an imaging frequency of 3.5 Hz. The captured images were processed using the criterion ‘normalized sum of squared differences’; the strain fields were calculated using the Lagrangian finite strain tensor.