Delamination Fatigue Crack Growth in Unidirectional Graphite/Epoxy Laminates

Abstract

Delamination fatigue crack growth experiments were carried out on unidirectional T300/914 C Graphite/Epoxy laminates. Both mode I and mixed mode (mode I and mode II in combination) situations were investigated for the stress ratios R = 0.1, 0.3 and 0.5. Double Cantilever Beam (DCB) specimens were used for the pure mode I tests and Cracked Lap Shear (CLS) specimens were used for the mixed mode tests. The initial delaminations were produced by inserting 0.03 mm thick PTFE films during laminate layup. The cyclic loading of the specimens was carried out at a frequency of 5 Hz and with a constant stress ratio maintained throughout the test. It was found that the mode I cyclic crack growth rate yielded a power law relationship between da/dN and the cyclic variation in the energy release rate ΔGI. This relation was virtually independent of the stress ratio, at least for 0.1 < R < 0.5. The mixed mode results showed a similar power law relation between da/dN and Δ(G I + GII). Here a small stress ratio dependence was observed. The data were fitted to two alternative power law crack growth relations. Knowing the ratio of GIlGII and with the assumption that the mode I and mode II contributions of crack growth were additive, it was possible to formulate a crack growth relationship of:

Methods for the prediction of fatigue delamination growth in composites and adhesive bonds – A critical review

“…Gustafson and Hojo [50] suggested a similar relationship, but using ∆G rather than G max . Based on test results Russell and Street [101] developed the equation:…”

“…For f (∆G) Moroni and Pirondi compared three mixed mode models, viz: the model proposed by Kenane and Benzegaggh [102], the model proposed by Quaresimin and Ricotta [109], and what Moroni and Pirondi describe as "the simplified version of a model proposed by Abdel Wahab et al [ref: [144]]". In fact this third model goes back to the work of Ramkumar and Whitcomb [100] and Gustafson and Hojo [50]. Abdel Wahab et al [144] also proposed a model of this form, but using a sigmoidal formulation rather than simply G max [100] or ∆G [50].…”

“…In fact this third model goes back to the work of Ramkumar and Whitcomb [100] and Gustafson and Hojo [50]. Abdel Wahab et al [144] also proposed a model of this form, but using a sigmoidal formulation rather than simply G max [100] or ∆G [50]. In reference [188] Moroni and Priondi compare the results of their model with "analytical" results produced by using the normal, non-CZM, formulation of the models used in their CZM.…”

G-control fatigue testing for cyclic crack propagation in composite structures

“…These include the mode I DCB (Double Cantilever Beam) test [1], the mode II ENF (End Notched Flexure) test [2], and the MMB (Mixed Mode Bending) method for mixed mode I/II characterization [3]. The DCB and ENF tests have also been used to study cyclic delamination growth by several authors [4][5][6][7]. The DCB test has also become standard for initiation of cyclic delamination growth, ASTM D6115 [8].…”

Damage Accumulation in Graphite/Epoxy Laminates Due to Cyclic Gradient Stress Fields

“…A delamination crack growth threshold was found for Mode I and mixed mode (I and II) cyclic loading [19,20]. Above the threshold growth rate, crack propagation rate was expressed as a power function of the stress intensity range.…”