Mixed-Mode Interlaminar Fracture Toughness of Glass and Carbon Fibre Powder Epoxy Composites—For Design of Wind and Tidal Turbine Blades

Abstract

Powder epoxy composites have several advantages for the processing of large composite structures, including low exotherm, viscosity and material cost, as well as the ability to carry out separate melting and curing operations. This work studies the mode I and mixed-mode toughness, as well as the in-plane mechanical properties of unidirectional stitched glass and carbon fibre reinforced powder epoxy composites. The interlaminar fracture toughness is studied in pure mode I by performing Double Cantilever Beam tests and at 25% mode II, 50% mode II and 75% mode II by performing Mixed Mode Bending testing according to the ASTM D5528-13 test standard. The tensile and compressive properties are comparable to that of standard epoxy composites but both the mode I and mixed-mode toughness are shown to be significantly higher than that of other epoxy composites, even when comparing to toughened epoxies. The mixed-mode critical strain energy release rate as a function of the delamination mode ratio is also provided. This paper highlights the potential for powder epoxy composites in the manufacturing of structures where there is a risk of delamination.

Powder Epoxy for One-Shot Cure, Out-of-Autoclave Applications: Lap Shear Strength and Z-Pinning Study

“…The powder epoxy (PE6405) used in this study was developed by Swiss CMT AG (Siebnen, Switzerland) and produced by Freilacke (Bräunlingen-Döggingen, Germany). The powder system has multiple advantages, such as a low curing exotherm [14,15], which reduces the risk of thermal runaway during manufacturing of thick sections, and a low minimal viscosity [14,15] for optimal wetting and minimal porosity, leading to superior mechanical properties [16][17][18][19].…”

“…The powder epoxy has also been shown in previous work to have improved interlaminar fracture toughness [19] compared to untoughened liquid epoxy resins, which is very interesting as there is a linear correlation between fracture toughness and lap shear strength [20].…”

“…A summary of the manufacturing process is provided in Figure 2. Firstly, glass fiber-reinforced plastic and powder epoxy plates were produced using a previously developed manufacturing process [19].…”

“…Due to the low minimum viscosity of powder epoxy prior to gelation, the resin tends to bleed out of the composite during the sintering/curing stage. This can cause some variability in the fiber volume fraction (FVF) of the manufactured plates [19]. To solve this, a previously manufactured steel frame was used (8 mm thick, inner dimensions of 300 mm × 280 mm) along with two steel caul plates.…”

“…This behavior highlights the superior adhesive properties of the powder epoxy system for out-of-autoclave (OOA) manufacturing purposes. Indeed, the powder epoxy system was previously shown to have high fracture toughness [19] compared to standard epoxy prepregs. Additionally, the very low melt viscosity allowed for a homogeneous adhesion consolidation.…”