Fast screening of the fatigue properties of thermoplastics reinforced with short carbon fibers based on thermal measurements

L Leveuf,Y Marco,V Le Saux,L Navrátil,S Leclercq,J Olhagaray

doi:10.1016/j.polymertesting.2018.03.045

Abstract

The goal of this paper is to investigate the ability of the heat build-up technique to predict the fatigue lifetime of injected thermoplastic reinforced with short carbon fibers. Several commercial grades and filler ratios are considered in order to challenge the ability of the technique to capture the influence of these variations. First, the materials are investigated and the mechanical and thermal protocols are described. The way to build the heat-build-up curves is outlined. Then, the results obtained from the heat build-up and fatigue experiments are presented. The heat build-up curves are obtained both from measurements performed on the front surface of the sample and from the side surface. Finally, these results are used to discuss two main points. The first is the validity of the hypotheses needed to apply the approach, ranging from the evaluation of the dissipation to the fatigue response. The second is the capability to predict the fatigue curves accurately through an energetic criterion, and to identify the influence of the variations of matrix grade and fiber content on the fatigue properties. It appears that the predictions obtained match the results obtained from classic fatigue tests and validates the use of the technique for fast material screening.

Highlights

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]
It is necessary to check if the method can be applied, because a main difference of this approach compared to classic fatigue test is that it relates the response over a few initial cycles to the fatigue failure occurring after several days or weeks of testing
Evolution of the mechanical data during the fatigue tests The evolutions of the cyclic mechanical features were recorded during the fatigue tests

Summary

Introduction

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]. An even more desirable objective is to predict the full fatigue curve including the fatigue scattering from the heat build-up curve This has been proven to be possible on several metallic materials [18,19,20], by relating the dissipative energy to the damage mechanisms throughout a constitutive modeling including a probabilistic failure criterion. This last approach is clearly the most appealing but it faces several difficulties for short fibers reinforced composites. This could not be integrated in a fast testing approach

Objectives

Results

Conclusion