Fast prediction of the fatigue behavior of short-fiber-reinforced thermoplastics based on heat build-up measurements: application to heterogeneous cases

Abstract

International audienceShort-fiber-reinforced thermoplastics components for structural applications are usually very complex parts as stiffeners, ribs and thickness variations are used to compensate the quite low material intrinsic stiffness. These complex geometries induce complex local mechanical fields but also complex microstructures due to the injection process. Accounting for these two aspects is crucial for the design in regard to fatigue of these parts, especially for automotive industry. The aim of this paper is to challenge an energetic approach, defined to evaluate quickly the fatigue lifetime, on three different heterogeneous cases: a classic dog-bone sample with a skin-core microstructure and two structural samples representative of the thickness variations observed for industrial components. First, a method to evaluate dissipated energy fields from thermal measurements is described and is applied to the three samples in order to relate the cyclic loading amplitude to the fields of cyclic dissipated energy. Then, a local analysis is detailed in order to link the energy dissipated at the failure location to the fatigue lifetime and to predict the fatigue curve from the thermomechanical response of one single sample. The predictions obtained for the three cases are compared successfully to the Wöhler curves obtained with classic fatigue tests. Finally, a discussion is proposed to compare results for the three samples in terms of dissipation fields and fatigue lifetime. This comparison illustrates that, if the approach is leading to a very relevant diagnosis on each case, the dissipated energy field is not giving a straightforward access to the lifetime cartography as the relation between fatigue failure and dissipated energy seems to be dependent on the local mechanical and microstructural state

Fast screening of the fatigue properties of thermoplastics reinforced with short carbon fibers based on a heat build-up protocol

“…The experimental determination of the dissipated energy fields relies on the solving of the heat equation [21,44]. Under some classic assumptions (including adiabaticity) detailed in former publications [11,25,43,44], the heat equation can be written as…”

“…The approach considered in [11,25] consists in identifying regimes on the heat build-up curves based on a graphical analysis of the curve. This approach is possible only with a large amount of experimental data and thus a high number of blocks.…”

“…Short-fiber-reinforced thermoplastics (SFRT) provide a major opportunity today to obtain lightweight parts at a reasonable cost and have been widely investigated [1][2][3][4][5][6]. Over the last few years, this kind of materials has been used for structural components in the automotive industry to replace die casting aluminum or stamped steel parts [7][8][9][10][11]. The possible use of these materials for aeronautic applications is also under consideration.…”

“…This is explained mainly by the considerable development of thermography devices and analysis [16, 21, and 22]. The extension of the technique to other materials has also been tested [17] and is now applied, following different approaches, to rubbers [23][24][25], continuous fiber composites [26,27] and short fiber reinforced plastics [11,28,29]. All these approaches use the evolution of the sample temperature but can be quite different.…”

Fatigue Life Assessment of Filled Rubber by Hysteresis Induced Self-Heating Temperature

“…In recent years, rapid estimation methods for mean fatigue limits of metallic materials have been developed based on temperature measurements [9]. Some recent publications [10][11][12][13] proved that the characterization of the fatigue properties of fiber-reinforced thermoplastics can be very much accelerated by the use of the "heat build-up" approach. Le Saux and Marco, et al [14] tried to use this method for rubber-like materials.…”