A Methodology for Estimating the Delamination Growth Rate in Layered Composites under Tensile Cyclic Loading

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A METHODOLOGY FOR ESTIMATING THE DELAMINATION GROWTH RATE IN LAYERED COMPOSITES UNDER TENSILE CYCLIC LOADING

V. E. Strizhius*

Keywords: layered composites, tensile cyclic loading, delamination growth rate The main features of physical modeling of the delamination growth rate in layered composites in tensile loading are considered. To estimate this rate, an equation in the form of the well-known Collipriest equation, which is widely used in estimating the crack growth rate in metal materials, is proposed. The values of empirical constants of the equation for a quasi-isotropic [45/90/-45/0]S XAS/914 carbon/epoxy laminate in a tensile cyclic loading with R = 0.1 are obtained, and the S–N curve for it is constructed. A comparison of calculations with experimental data point to their acceptable accuracy.

Introduction. Delamination [1] is one of the most dangerous and difficult to control types of damage in layered polymer composite materials (PCMs). That is why the occurrence and growth of delaminations in PCMs arouses interest of many authors. It is known [2] that studies of the dominating fracture mode at the beginning and growth of delamination are focused on the mechanics of interlaminar fracture, within the framework of which it is required to determine, first of all, the change in the deformation energy per unit area of delamination increment. This parameter, G , is called the elastic energy release rate at the top of a crack. In order to clear up whether the delamination will grow or not at a static loading, the calculated values of G are compared with its critical values Gc . As a rule, considered are three fracture modes: mode I (opening mode), mode II (shearing mode), and mode III (tearing mode). Modes I and II are considered the most critical

Moscow Aviation Institute (National Research University), Russia * Corresponding author; e-mail: [email protected]

Translated from Mekhanika Kompozitnykh Materialov, Vol. 56, No. 4, pp. 781-790, July-August, 2020. Original article submitted May 30, 2019; revision submitted February 6, 2020. 0191-5665/20/5604-0533 © 2020 Springer Science+Business Media, LLC

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ones, and, therefore, the greatest attention in the development of calculation and test methods is focused exactly on them [3, 4]. Such an approach requires both computer modeling and determination of experimental characteristics. Another approach consists in estimating the growth of delaminations in cyclic (fatigue) loadings. In [3, 4], equations for estimating the delamination growth rate are presented for different fracture modes. In [4], the following equation for this rate is given in the case of the mixed (I+II) fracture mode: n

where

n

G 1 G 2 dL = m1  I  + m2  II  , dN  GIc   GIIc 

(1)

dL is the delamination growth rate in one fatigue loading cycle; GI and GII are the elastic energy release rates dN

in modes I and II, respectively, but GIc and GIIc are their critical values — the characteristic fracture resistances (they are determined experimentally and, as a rule, are s