Injection molded components made from fiber reinforced thermoplastics exhibit strong viscoelastic behavior. In the present study, the bending creep tests show that the 43‐wt% glass fiber reinforced polyamide 66 is highly stress‐dependent and requires a nonlinear viscoelastic representation. However, such representation is complex for isotropic materials and is even more arduous for composite materials. In order to overcome this complexity, an empirical approach is used herein to develop a viscoelastic model based on a simple power law with stress‐dependent parameters. The proposed model demonstrates high stress sensitivity and agrees with experimental data over a wide range of applied stress.
The creep test illustrates the tendency of materials to deform under constant loading; however, this test requires a very long testing time. The use of the time-stress superposition principle (TSSP) allows the prediction of the material performance very beyond the testing time by the construction of the creep master curve. Recently, a new accelerated creep testing method, called the stepped isostress method (SSM) was proposed. This technique requires specific handling of the test data in the construction of the master curve. Initially the method was used on technical yarns. This paper focuses on the effectiveness of this method for specimens having a large thickness. The considered material is a polyamide 6. A smooth creep master curve has been obtained. The obtained master curves by the SSM technique and the classical TSSP method are consistent. This result proofs the robustness of the SSM technique in the construction of the master curve.
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