Dynamic mixed-mode I/II delamination fracture and energy release rate of unidirectional graphite/epoxy composites

• Published in: Engineering fracture mechanics Vol. 72; no. 10; pp. 1531 - 1558
• Main Authors: Wosu, Sylvanus N., Hui, David, Dutta, Piyush K.
• Format: Journal Article
• Language: English
• Published: Tarrytown, NY Elsevier Ltd 01.07.2005; Oxford Elsevier
• Subjects: Applied sciences; Composites; Delamination; Dynamic interlaminar fracture; Energy release rate; Exact sciences and technology; Forms of application and semi-finished materials; Fracture mechanics (crack, fatigue, damage...); Fundamental areas of phenomenology (including applications); Mixed mode; Physics; Polymer industry, paints, wood; Solid mechanics; Split Hopkinson pressure bar; Structural and continuum mechanics; Technology of polymers; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Energy release rate; Split Hopkinson pressure bar; Mixed mode; Delamination; Dynamic interlaminar fracture; Total energy; Energy release; Mode coupling; Epoxy resin; Energy level; Composite material; Fragmentation; Graphite fiber; Energy dissipation; Kinetic energy; Fracture energy; Scanning electron microscopy; Notched test piece; Unidirectional fiber material; Notch; Experimental study; Plate; Low energy; Hopkinson bar; Fracture surface; Energy absorption; Fracture mode; Structural analysis; Mechanical shock; Bending test
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2004.08.008

Mixed-mode open-notch flexure (MONF), anti-symmetric loaded end-notched flexure (MENF) and center-notched flexure (MCNF) specimens were used to investigate dynamic mixed I/II mode delamination fracture using a fracturing split Hopkinson pressure bar (F-SHPB). An expression for dynamic energy release rate G d is formulated and evaluated. The experimental results show that dynamic delamination increases linearly with mode mixing. At low input energy E i ⩽ 4.0 J, the dynamic ( G d) and total ( G T) energy rates are independent of mixed-mode ratio. At higher impact energy of 4.0 ⩽ E i ⩽ 9.3 J, G d decreases slowly with mixed I/II mode ratio while G T is observed to increase more rapidly. In general, G d increases more rapidly with increasing delamination than with increasing energy absorbed. The results show that for the impact energy of 9.3 J before fragmentation of the plate, the effect of kinetic energy is not significant and should be neglected. For the same energy-absorption level, the delamination is greatest at low mixed-mode ratios corresponding to highest Mode II contribution. The results of energy release rates from MONF were compared with mixed-mode bending (MMB) formulation and show some agreement in Mode II but differences in prediction for Mode I. Hackle (Mode II) features on SEM photographs decrease as the impact energy is increased but increase as the Mode I/II ratio decreases. For the same loading conditions, more pure Mode II features are generated on the MCNF specimen fractured surfaces than the MENF and MONF specimens.