PSI - Issue 47

Mikhail Bannikov et al. / Procedia Structural Integrity 47 (2023) 685–692 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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elements [1-3]. To adequately describe the stress-strain state and parameters of fracture mechanics and crack resistance, two approaches can be used [4]. The first approach involves determining the crack resistance of a non standard sample with a crack-like defect that reflects the stress-strain state of the structural element [5]. The second approach involves creating a model that transforms the crack resistance of a standard sample into the crack resistance of a structural element by introducing an additional criterion parameter that reflects the triaxial stress state. The transition from damage to failure can be divided into stages based on the degree of locality, which can be interpreted using self-similar solutions reflecting the distribution of stress and damage fields. Understanding this transition can help create models and formulate fracture mechanics criteria. To determine the stages of damage accumulation during cyclic testing of unidirectional composites, an analysis of acoustic emission signals and DIC data is planned. This analysis will help in further model building and the determination of PCM failure criteria, allowing for the creation of criterion equations that describe the generalized crack resistance diagram [6-8]. 2. Materials and experimental conditions We studied two types of specimens: unidirectional polymer composite materials (PCM) in the form of a strip 2 mm thick, 20 mm wide and 200 mm long [9] and woven composite material with 25 mm wide and 250 mm with a concentrator in the form of a hole in the center (fig. 1.b). Cyclic loading of PCM specimens was carried out on an electroresonant type testing machine - Testronic-50 with a maximum allowable working load of 50 kN (Fig. 1) and by servohydraulic machine Biss 10kN.

( а ) (b) Fig. 1, a) Experimental complex for testing: general view of the experimental complex: 1 - resonant testing machine Testronic-50, 2 - thermal imaging camera NECTH9100, 3 - LED lamp, 4 - camera of the LaVision digital image correlation system, 5 - fan, 6 - sample, 7 - microphones of the acoustic emission system AMSY-6. b) Schematic image of specimen (size in mm) During the tests, standard samples - 6 (Fig. 1) were placed in hydraulic grips for flat samples, which ensured that the plane of the sample and the vector of application of static and dynamic loads coincided. The tests were carried out using an air-cooled fan, and were accompanied by recording the temperature field of the sample using an infrared camera NEC TH9100 WR - 2 (Fig. 1). The evaluation of dynamic deformation fields was performed using the digital image correlation (DIC) method implemented in the LaVision - 4 system (Fig. 1). To do this, a speckle structure was applied to the front surface of the sample before testing. Acoustic emission signals were recorded using piezoceramic microphones - 7 by Vallensysteme, model AE204A, with a frequency measurement range of 180-700 kHz and a capacitance of 46 pF. The overall dimensions of the sensors used were 8x18 mm, and the weight