PSI - Issue 28

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Author name / Structural Integrity Procedia 00 (2019) 000–000

744 D.A. Bondarchuk et al. / Procedia Structural Integrity 28 (2020) 743–751 This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo Keywords: composite;residual stress;defect; energy release rate;mathematical modeling,;Abaqus

1. Introduction The problem of the calculation of the structural strength of multilayered composite structures at the design stage has acquired a large relevance due to the increase in the use of these materials in many industries during last decades. Current trends in the aerospace industry are focused on the prediction of the structural strength of composite structures after loading taking in account possible manufacturing defects. This is especially actual in context of shortened development and production life cycles of composite structures upon implementation of new materials. Even though the capabilities of process modelling techniques have been improved over the past decades, the occurrence of localized manufacturing defects and residual stress distribution remains challenging to predict at the design stage due to insufficient development of the theoretical base, large number of input parameters (process/material) and lack of reliable scalable methodic. As a result, the manufacturing process of large composite structures still requires substantial investments in empirical optimization. One of the often greeted types of defect and at the same time one of the most crucial damage for impacted composite is delamination. Delamination can affect the compression strength of composite laminate, and it will slowly cause the composite to experience failure through buckling. The delamination phenomenon can be caused by concentration of interlaminar stresses that occur in the vicinity of free edges and due to mismatch of elastic properties between plies. There is a guess, that residual stresses near free-edge have a significant effect on further propagation of cracking. In research work, presented by Bondarchuk D.A. et al. (2019), it was shown that the fracture behavior of carbon-epoxy composite sample significantly changes when taking into account the influence of technological stresses. In the present study, the effect of presence of residual stresses inherited during manufacturing on delamination defect in carbon epoxy composite specimen is investigated during process of curing and after ideal cutout. In this way, an attempt has been made to fully evaluate the nature of the stress field and possible crack growth near the free edge over time. It is essential issue, in the evaluation of composite structures for durability and damage tolerance. The purpose of the current research can be formulated by following steps:  Developing of the modeling technique for prediction of stress-strain state distribution at the composite structure caused by manufacturing process.  Determine the strain-stress state in regular specimens near defect zone (free-edge) during cure cycle depending on the length of crack.  Determine the history of energy release rates under mode I, II ( G Ic , G IIc ) during process of polymerization and free edge cut. The problem of residual stress formation is complex as it depends on many factors and includes several sub problems. The analysis of sample with [0°/90°] n lay-up was selected for consideration in this work in terms of simplicity and as the first step of research. Since there is symmetry, the modeling can be provided in two-dimensional plane strain formulation. It is worth to note, effects of shape distortion and fracture effects become more evident for composites with [0°/90°] n lay-up due to maximum difference in anisotropic properties of each individual layer. The present work considers an example of AS4/8552-1 carbon-epoxy composite in view of popularity in engineering practice and availability of data in literature. The data (material properties) provided in Hexply AS4/8552 data sheet (2020) and in works conducted by Boyard N. (2016),Van Ee David and Poursartip Anoush (2020) and Parmentier A. et al. (2014). The study was conducted by means of general-purpose FE package ABAQUS and special constitutive material model was implemented in special user subroutine-UMAT. The model was previously described by A. Safonov et.al. (2017) and Bondarchuk D., Fedulov B. (2019).