Influence of loading rate on the delamination response of untufted and tufted carbon epoxy non crimp fabric composites: Mode I

Abstract

This research aims at the high speed Mode I delamination characterisation of carbon Non Crimp Fabric composites (NCF) with and without through the thickness reinforcement. The dynamic delamination response under Mode I is investigated using visual and force measurements as well as numerical analysis to minimize errors due to the dynamics of this test. For loading speed larger than 3 m/s the double cantilever beam (DCB) is subjected to mixed Mode loading (Mode I/II). This result is inherent to the nature of the test and the impactor that introduced the load in the lower DCB arm. Numerical simulations show that this effect would also occur for UD laminates. Consequently the validity of the tests is limited to loading speeds below 3 m/s until which pure Mode I loading is achieved. For those loading rates optical analysis shows rate effects only at the crack initiation state which are stronger for the tufted interface. To avoid mixed mode effects at higher loading rates (>3 m/s), the DCB specimen must be loaded at both arms simultaneously. Load cell recordings are not necessary as optical analysis is confirmed as a reliable technique for rate effect investigations

Coupon scale Z-pinned IM7/8552 delamination tests under dynamic loading

“…The influence of loading rate appears to be negligible. Similar results have been reported for other composite material systems from dynamic ELS and DCB tests [36,37]. The delamination response might be expected to change with loading rate, since the yield stress increases and the failure strain decreases with strain rate for epoxy materials [26].…”

Numerical evaluation of cohesive zone models for modeling impact induced delamination in composite materials

“…Here the trend is less clear than for the strength [2]. There is experimental evidence for positive strain rate effects (increase of fracture toughness with increase of loading rate) [3,4,5,6], negative strain rate effects (decrease of fracture toughness with increase of loading rate) [7,8,9,10], or no strain rate effect at all [10,11,12,13]. Cohesive zone models are a powerful tool for the design of damage-tolerant structures as they allow for modeling of damage initiation and evolution under quasi-static [14] or fatigue [15] loading conditions within a single, coherent analysis.…”

Loading rate effects on mode-I delamination in glass/epoxy and glass/CNF/epoxy laminated composites

“…Although no standard test procedure is introduced for dynamic loadings up to now, the DCB configuration has been the most common test set-up for the rate dependency examination of G IC at intermediate rates of loading [3][4][5][6][7][8][9]. This configuration has even been modified for further studies at higher loading rates [10,11]. Notwithstanding the number of previous researches on the rate dependency analysis of delamination in carbon fiber reinforced plastics (CFRPs), the available experimental data are rather controversial and there is no general agreement on the loading rate effects.…”