Microstructure dependent fatigue life prediction for short fibers reinforced composites: Application to sheet molding compounds

Abstract

Because of the high variability of SMC microstructure due to material flow during thermoforming, fatigue life prediction in real automotive structure represents a huge challenge. In this paper, we present a two-step microstructure selection involving an original ultrasonic method which is briefly presented. Then, on the basis of four selected microstructure configurations, an accurate experimental damage analysis is performed including both monotonic and cyclic loading. The high microstructure dependence of the obtained Whöler curves is demonstrated. Moreover, an experimental link between monotonic damage and fatigue life is emphasized. Then, a new fatigue life prediction methodology based on the later is proposed. This methodology also uses a micromechanical damage model in which a local damage criterion is involved for monotonic loading damage prediction. A very good agreement between experimental and predicted Whöler curves is demonstrated for all studied microstructures and three working temperatures. Finally, the model allows building a microstructure dependent Whöler curve abacus which may be very useful for SMC structures design.

A novel energy‐based framework for characterizing the strain‐softening behavior of CFRP composites using cyclic loading

“…From a microscopic point of view, strain-softening behavior is closely related to the initiation and propagation of micro-cracks in CFRP composites, and then it is manifested as material stiffness degradation on the macroscopic level. [40] Besides, the initiation of localized deformation, which usually occurs in the matrix or material interface, is caused on the material's microscale. The microscopic behavior is governed by the occurrence, growth, and interaction of cracks and voids, leading to eventual damage on the macroscale.…”

“…To solve the problem that the progressive damage in the fiber direction (dominated by fiber failure) is difficult to be accurately simulated, the equivalent principle of strain dissipation energy proposed by Pfanner [38] is introduced in this work. [14,[38][39][40][41][42] The core of the equivalent principle of strain dissipation energy is that the damage state (residual stiffness and residual strength) is only dependent on the dissipated energy in the progressive damage process, while has nothing to do with the specific macroscopic loading history: quasi-static loading, high-speed loading or cyclic loading. Pfanner's theory has been successfully employed in fatigue research of composite, [39][40][41][42] but to the best of the our knowledge, it is the first time used in the quasistatic progressive failure analysis.…”

“…[14,[38][39][40][41][42] The core of the equivalent principle of strain dissipation energy is that the damage state (residual stiffness and residual strength) is only dependent on the dissipated energy in the progressive damage process, while has nothing to do with the specific macroscopic loading history: quasi-static loading, high-speed loading or cyclic loading. Pfanner's theory has been successfully employed in fatigue research of composite, [39][40][41][42] but to the best of the our knowledge, it is the first time used in the quasistatic progressive failure analysis. [14,[38][39][40][41][42] The work aims to obtain a refined strain-softening model of plain woven CFRP composites through experimental methods and apply it to the PDA of corresponding components.…”

“…Pfanner's theory has been successfully employed in fatigue research of composite, [39][40][41][42] but to the best of the our knowledge, it is the first time used in the quasistatic progressive failure analysis. [14,[38][39][40][41][42] The work aims to obtain a refined strain-softening model of plain woven CFRP composites through experimental methods and apply it to the PDA of corresponding components. Meanwhile, the core of the objective is to solve the problem that performing progressive failure analysis in the fiber-dominant direction is challenging due to the poor toughness of the fibers.…”

Sheet Molding Compound Automotive Component Reliability Using a Micromechanical Damage Approach

“…Several studies have been conducted concerning the mechanical behaviour of several SMC composites formulations [13,[21][22][23][24][25]. The focus has been on the multi-scale experimental analysis and modelling of the mechanical behaviour and damage of this class of composites materials [27,28]. It has been demonstrated that the non-linear behaviour of a standard SMC (such as the one in study) is mainly governed by fibre-matrix interface failure [21][22][23].…”