In situ computed tomography for the characterization of the fatigue damage development in glass fiber-reinforced polyurethane

Abstract

Fiber-reinforced polymers show a continuous material degradation under cyclic loading, which is why damage development has to be investigated for an exact assessment of fatigue properties. In order to obtain information on damage in the internal volume, conventional mechanical test methods require accompanying support by further developed techniques. In this study, a methodology for in situ computed tomography has been developed and applied to glass fiber-reinforced polyurethane. Polyurethane has advantages over epoxy in terms of impact strength, damage tolerance and abrasion, which are important for various applications. Fatigue properties, on the other hand, are largely unknown. Optimized imaging parameters for computed tomography have been established in order to obtain detailed 3D volume images suitable for analysis. The 3D volumes of the damage state were recorded according to defined fatigue load steps and used to evaluate and correlate the damage development with the mechanical properties. The results confirm known damage characteristics of fiber-reinforced composites but also show material and structure-related differences in crack formation and propagation.

MIST – Mechanical In-situ Stage with Temperature control for X-ray computed tomography

“…As consequence, its damage mechanism can be different for high or low temperature applications -e.g., earlier development of defects such as pores and cracks (and therefore higher stress) in case of low temperatures or only plastic deformations (and therefore much lower stress) of the polymer due to high application temperatures. In the last few years in-situ investigations have become of great importance [1][2][3][4]. Various research groups developed novel methods and test rigs for such investigations.…”

Constant Temperature Approach for the Assessment of Injection Molding Parameter Influence on the Fatigue Behavior of Short Glass Fiber Reinforced Polyamide 6

“…Since failure occurs as a process of a sum of interaction between local damage spots [ 41 ], rather than a dominant crack, µCT enables a holistic analysis. The reliable qualitative and quantitative visualization of inner structures such as fibers, agglomerations, and voids enable expanded ways of damage characterization [ 42 , 43 , 44 , 45 ]. Further improvement is possible by extending µCT with in situ testing.…”

“…With the use of digital volume correlation (DVC), deformation and strain in the material inner can be analyzed and correlated to the damage state recorded through µCT, extending the possibilities even further. In this regard, relaxation and creep of the material need to be taken into account, since µCT scans can take several hours and therefore lead to a blurred image and inaccurate representation of the material state [ 45 , 46 ].…”

In Situ Characterization of Polycaprolactone Fiber Response to Quasi-Static Tensile Loading in Scanning Electron Microscopy

“…On the other hand, it impairs SEM imaging. Furthermore, polymers are vulnerable to creep and relaxation depending on load mode, i.e., constant strain or constant stress, at intermittent in situ testing [ 27 , 28 ].…”