Multiaxial fatigue models for short glass fibre reinforced polyamide. Part II: Fatigue life estimation

Abstract

WOSInternational audienceComponents made of short fibre reinforced thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response. As the cyclic behaviour of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a preliminary step for confident fatigue design. Constitutive equations for the cyclic behaviour, developed and validated by the authors in Part I of this paper [Launay et al., Int J Fatigue, in press], are applied to the mechanical analysis of fatigue campaigns carried out by Klimkeit et al. and De Monte et al. on specimens made out of polyamide 66 reinforced with 35 wt.% of short glass fibres. Both studies are performed at room temperature, with material conditioned at the equilibrium with air containing 50% of relative humidity (RH50) or dry-as-moulded (DAM). Post-processing the cyclic response in steady-state allows the comparison of several fatigue criteria. The fatigue databases involve various loadings, including the study of multiaxiality and mean-stress effects on different microstructures. Among all physical quantities, the dissipated energy density per cycle ΔWdiss displays the best correlation with the fatigue life

Multiaxial fatigue models for short glass fiber reinforced polyamide – Part I: Nonlinear anisotropic constitutive behavior for cyclic response

“…Therefore, the need for a method to design those components against fatigue failure has become a serious issue during the last years, when different authors began addressing the problem. For example, in Part II of this work [1], De Monte's and Klimkeit's recent fatigue experiments give the basis for a comparative study of different fatigue criteria [2,3].…”

“…The second step of our approach, i.e. the proposition of an appropriate fatigue lifetime model for SGFR polyamides, is the topic of Part II [1]. This work will be conducted from the analysis of fatigue databases published by De Monte et al [2] and Klimkeit [3].…”

Phenomenological multi-mechanisms constitutive modelling for thermoplastic polymers, implicit implementation and experimental validation

“…iii) The model, integrating temporal effects on several time ranges, can provide a basis for modelling high cycle fatigue. Of course, such fatigue analyses require model reduction techniques (Cojocaru and Karlsson, 2006;Haouala and Doghri, 2015) that enable simulations on long time periods, as well as advanced fatigue theories for polymers (Nouri et al, 2009;Launay et al, 2013b).…”

Micromechanical Fatigue Visco-Damage Model for Short Glass Fiber Reinforced Polyamide-66

“…This method has been extensively used by many authors to obtain the effective behavior of composite materials [6,9,11,15]. The Eshelby tensor has been numerically evaluated by the method defined by Lagoudas and Gavazzi [8].…”

“…Phenomenological approaches have been frequently adopted to simulate the cyclic behavior of PA66/GF30 composite structures. Recently, a constitutive model has been developed by Launay et al [14,15] to take into account the elasto-viscoplatic nature of polyamide matrix reinforced by glass fibers. This model does not take into account the evolution of damage.…”