Yarn damage during braiding of reinforcement fibers for composites

Fiber damage and impregnation during multi‐die vacuum assisted pultrusion of carbon/PEEK hybrid yarns

“…Chen and Ma, in their study on pultruded glass fiber, aramid fiber and carbon fiber reinforced polyurethane (PU), reported that fiber damage occurred only during the manufacturing using carbon fibers . Carbon fibers exhibit high modulus, high strength and low ultimate strain, making them fragile and prone to damage . Prior to pultrusion, several operations have to be performed, such as yarn commingling, bobbin rewinding, and yarn insertion into the dies.…”

“…Prior to pultrusion, several operations have to be performed, such as yarn commingling, bobbin rewinding, and yarn insertion into the dies. The manipulations can cause fiber damage . During pultrusion, the damaged fibers will accumulate in the die tapered inlet , and their presence in the backflow will generate more friction on the yarns which could lead to the halting of the process.…”

Optical inspection of the braid formation zone during manufacturing of preforms from reinforcement fibers for defect detection purposes

“…More specifically, braiding of reinforcement fibers in order to manufacture preforms for composite parts has well-known applications in the automotive [e.g., pillars for passenger compartments (Hill, 2003;Bulat et al, 2016)], aviation [e.g., helicopter landing gears (Thuis, 2004a;2004b)], space [e.g., rocket nozzles (van Ravenhorst and Akkerman, 2016b;van Ravenhorst, 2018)] as well as in the sports and leisure industry [e.g., lightweight bicycle rims (Kind and Drechsler, 2015;Bulat et al, 2016;Zuurendonk, 2018)]. During braiding of these often hollow structures that may be curved and show a varying cross-section, typical defects such as a generally "fuzzy" braid due to frictional yarn abrasion, yarn loops due to a loss in tension of a single yarn or local yarn gaps and yarn breakages due to an increased tension of an individual yarn may occur (Ebel et al, 2013;Ebel et al, 2016). A particular process anomaly, namely the fibrous ring, is regarded as the most relevant cause for braiding defects.…”

“…A particular process anomaly, namely the fibrous ring, is regarded as the most relevant cause for braiding defects. A fibrous ring is an accumulation of broken carbon filaments at the bobbin (braiding spool) which impedes the yarn from unwinding properly from the spool (Ebel et al, 2016;Mierzwa et al, 2016). This causes an increase in tension of the respective yarn that may eventually lead to a distortion of the regular braid structure in the form of a local yarn gap and eventually to a breakage of the yarn.…”

“…In case of a rigid upper tooling (here: RTM tool), a local yarn gap did not cause additional fiber undulation and hence no significant knock-down in strength. Ebel et al (2013); Ebel et al (2016) conducted endurance braiding tests in order to quantify the extent of machine downtime due to the necessity of manually rethreading yarns that had broken because of fibrous rings at the braiding spools. In an extreme case scenario with unsuitable parameters during rewinding of the yarns on the braiding spools, they observed a downtime of 26% of the total duration of a test.…”