Abstract
This study investigates the damage initiation in short glass fiber-reinforced polyamide 6.6 under fatigue loading using acoustic emission analysis. An optimized specimen geometry was developed to meet the specific requirements of this testing method, at the same time allowing further micromechanical studies. Specimens were preloaded with tensile–tensile fatigue loading, varying the maximum stress and the number of load cycles. Subsequently, the acoustic emission signals in residual strength tests were compared to those of undamaged specimens. The idea behind this approach is that only the damage that has not already occurred under fatigue load can be recorded in the residual strength tests. Using the analysis of acoustic energy, a stress threshold for damage initiation was identified. Furthermore, with tension–tension fatigue tests, the SN curve of the material was determined to estimate the lifetime for the identified stress threshold. The presented approach allows us to estimate a so-called endurance limit of short glass fiber-reinforced polyamide 6.6.
Highlights
Short glass fiber-reinforced thermoplastics (SFRT) are increasingly used in technical components thanks to their good mechanical properties and their flexible moldability.While their use was often limited to housings in the past, they are becoming more and more common in load-bearing components
The stress at the start of the acoustic activity and during the damage events exceeds the applied maximum stress of the fatigue loading. This means that in the residual strength tests, the damage events only start at a strain that is higher than the strain applied during cyclic preloading
In the the first first stage, stage, only only aa few few damage damage events events are are measured measured at at the the beginning beginning of of the the residual strength test. This suggests that fatigue loading with a number of load cycles residual strength test
Summary
Short glass fiber-reinforced thermoplastics (SFRT) are increasingly used in technical components thanks to their good mechanical properties and their flexible moldability While their use was often limited to housings in the past, they are becoming more and more common in load-bearing components. To the authors’ knowledge, Williams et al [25] were the first to overcome these challenges, recording AE data during fatigue tests for about 1.5 million cycles In this way, they were able to establish a correlation between AE and damage to continuous fiber-reinforced composite specimens. To overcome the difficulties mentioned above, the following study investigates correlations between the material behavior under static and under fatigue loading For this purpose, some of the test specimens were subjected to cyclic preloading, while the rest stayed unloaded. By comparing the AE data of unloaded and preloaded specimens, the damage state of the preloaded specimens could be evaluated
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