A Robust Numerical Methodology for Fatigue Damage Evolution Simulation in Composites

Abstract

Composite materials, like metals, are subject to fatigue effects, representing one of the main causes for component collapse in carbon fiber-reinforced polymers. Indeed, when subject to low stress cyclic loading, carbon fiber-reinforced polymers exhibit gradual degradation of the mechanical properties. The numerical simulation of this phenomenon, which can strongly reduce time and costs to market, can be extremely expensive in terms of computational effort since a very high number of static analyses need to be run to take into account the real damage propagation due the fatigue effects. In this paper, a novel cycle jump strategy, named Smart Cycle strategy, is introduced in the numerical model to avoid the simulation of every single cycle and save computational resources. This cycle jump strategy can be seen as an enhancement of the empirical model proposed by Shokrieh and Lessard for the evaluation of the fatigue-induced strength and stiffness degradation. Indeed, the Smart Cycle allows quickly obtaining a preliminary assessment of the fatigue behavior of composite structures. It is based on the hypothesis that the stress redistribution, due to the fatigue-induced gradual degradation of the material properties, can be neglected until sudden fiber and/or matrix damage is verified at element/lamina level. The numerical procedure has been implemented in the commercial finite element code ANSYS MECHANICAL, by means of Ansys Parametric Design Languages (APDL). Briefly, the Smart Cycle routine is able to predict cycles where fatigue failure criteria are likely to be satisfied and to limit the numerical simulation to these cycles where a consistent damage propagation in terms of fiber and matrix breakage is expected. The proposed numerical strategy was preliminarily validated, in the frame of this research study, on 30° fiber-oriented unidirectional coupons subjected to tensile–tensile fatigue loading conditions. The numerical results were compared with literature experimental data in terms of number of cycles at failure for different percentage of the static strength. Lastly, in order to assess its potential in terms of computational time saving on more complex structures and different loading conditions, the proposed numerical approach was used to investigate the fatigue behavior of a cross-ply open-hole composite panel under tension–tension fatigue loading conditions.

Numerical Assessment on the Fatigue Behavior of Composite Open‐Hole Tensile Specimens

“…The generalized residual material properties degradation model, developed by Shokrieh and Lessard, [10,11] has been implemented in the Ansys Mechanical software and employed to study the effect of the thickness and the stacking sequence variation on composite material open-hole coupons under tensile cyclic load. The proposed parametrical numerical tool allows to easily assess the fatigue fracture behavior of composite structures, which can be useful in the preliminary design stage.…”

“…The expression of the residual strength of a unidirectional lamina under general uniaxial cyclic loading conditions is defined in Equation ( 1), where R 0 is the static strength, 𝜎 is the state of stress in the lamina, and 𝛼 and 𝛽 are fitting parameters derived from experimental tests, as described in ref. [11]. The residual strength is a function of the number of cycle n, the state of stress 𝜎, and the stress ratio k.…”

“…, while the parameters f, A, and B are curve fitting parameters that can be experimentally defined as explained in ref. [11].…”

CFRP Fatigue Damage Detection by Thermal Methods

“…In [ 25 ], material property degradation was determined by measuring the change in specimen stiffness to analyze the progression of fatigue damage which is correlated to micro- and macroscale damage mechanisms and biaxial fatigue loading parameters. Russo et al [ 26 ] studied the fatigue response of composite materials using numerical methods with Shokrieh and Lessard’s residual strength material property degradation model. A finite element methodology was implemented in the commercial software ANSYS MECHANICAL.…”

Modelling pre-fatigue, low-velocity impact and post-impact fatigue behaviours of composite helicopter tail structures under multipoint coordinated loading spectrum

“…Turon et al [29] employed a controlled damage variable level to determine the number of cycle increments in the constitutive fatigue damage model, which is used to predict the delamination in composites under fatigue load. Based on the hypothesis that the stress redistribution due to the fatigue-induced gradual degradation of the material properties can be neglected before sudden damage onset, Russo et al [30] introduced a smart cycle strategy in the numerical model to investigate the fatigue damage evolution of composite under tension-tension fatigue loading conditions. Moreover, Russo et al [31] used the increment in the delaminated area to calculate the number of cycle increments in the FaTigue-SMXB approach.…”