Filament wound composite fatigue mechanisms investigated with full field DIC strain monitoring

Abstract

Fatigue of filament wound materials was investigated using Digital Image Correlation DIC monitoring every 50th cycle of a high cycle fatigue test of a split disk ring sample. The ring was cut from a filament wound glass fiber reinforced polymer pressure vessel and had a hole. The strain field redistributed over time, lowering and moving strain concentrations. The redistributive behavior was most extensive in areas that later developed local fiber failure, which soon led to catastrophic failure. Microscopy was carried out on partially fatigued material. Damage evolved as matrix cracks and matrix splitting of groups of fibers and complete debonding of single fibers. This occurred at borders of voids and matrix cracks, easing progressive fiber failure. It was concluded that fatigue in filament wound composites has an extensive matrix damage phase before final failure. Fibers could locally withstand strains close to and above the static failure strain for considerable number of cycles if little local strain field redistribution was observed. The used method was able to detect changes in the strain fields that preceded catastrophic failure. It was concluded that DIC combined with the post processing methods presented may serve as a valuable tool for structural integrity monitoring of composite pressure vessels over time.

Progressive Fatigue Failure Analysis of a Filament Wound Ring Specimen with a Hole

“…With increasing number of cycles, the average strain increases but the strain concentration diminishes or moves even to the outer edge of the specimen. This effect is due to matrix damage spreading in the material changing the constitutive properties of the material [29]. Intuitively there should be only two regions that concentrate strain, one on each side of the hole at the equator.…”

“…Good correlation was found between model and experiment using the local fiber properties. The DIC methods used in this study have been elaborated in two articles explaining how to trace progressive failure in composites [29] and how to estimate a local S-N curve using DIC data [30]. DIC has recently been proven to be a valuable tool in estimating material parameters such as the fracture toughness [31] by tracing crack propagation visually.…”

Progressive Fatigue Failure Analysis of a Filament Wound Ring Specimen with a Hole

“…With increasing number of cycles, the average strain increases but the strain concentration diminishes or moves even to the outer edge of the specimen. This effect is due to matrix damage spreading in the material changing the constitutive properties of the material [42]. Figure 19 Microscopy of the split disk specimen.…”

Estimating degradation of strength of neat PEEK and PEEK-CF laminates under cyclic loading by mechanical hysteresis loops

“…Typically, contact crack opening gauges are used for this purpose, but they cannot be implemented or does not provide the required accuracy in some cases (for a number of reasons). As a worthy alternative, non-contact (remote) techniques are well suited, including the digital image correlation (DIC) method, which was deployed for studying laminated fiber (fabric)reinforced PCMs [4][5][6][7]. It is known that laminated reinforced PCMs are designed for operation under severe loads, determined by high strength of reinforcing fibers.…”