It is now well established that adhesives and fibre-reinforced polymers (FRPs) can fail at far lower loads under fatigue loading than under quasi-static loading. Most of the work on the fatigue of these materials has been under constant amplitude (CA); however, recent work has shown that fatigue crack growth acceleration and unstable crack growth can be seen under conditions of variable-amplitude (VA) fatigue. In this paper, further evidence of this effect is given. This phenomenon is attributed to the influence of VA fatigue on the evolution of a damage zone ahead of the main crack front and results from the characterization of these damage zones are also presented. Finally, a simple fracture mechanics-based model for predicting crack growth under VA fatigue is proposed. This is shown to be entirely consistent with the experimental observations.
KinlochA. J.Adhesion and Adhesives, 1987 (Chapman and Hall, London).
6.
WangP. C.MaberyP.ChisolmC. K.Degradation of fatigue properties of weld-bonded aluminium exposed to moisture and elevated temperaturesJ. Adhesion, 1993, 43, 212–137.
7.
MostovoyS.CrosleyP. B.RiplingE. J.Use of crack-line-loaded specimens for measuring plane-strain fracture toughnessJ. Mater., 1967, 2, 661–681.
8.
KinlochA. J.ShawS. J.The fracture resistance of a toughened epoxy adhesiveJ. Adhesion, 1981, 12, 59–77.
9.
SchutzW.HeulerP.A review of fatigue life prediction models for the crack initiation and propagation phases In Advances in Fatigue Science and Technology, NATO Advanced Study Institute Series (Eds BrancoC. M.RosaL. G.), 1989, pp. 177–219 (Kluwer Academic, Alvor, Portugal).
10.
ErpolatS.AshcroftI. A.CrocombeA. D.Abdel-WahabM. M.A study of adhesively bonded joints subjected to constant and variable amplitude fatigueInt. J. Fatigue, 2004, 26, 1189–1196.
11.
HadaviniaH.KinlochA. J.LittleM. S.G.TaylorA. C.The prediction of crack growth in bonded joints under cyclic-fatigue loadingInt. J. Adhesion Adhes., 2003, 23, 449–461.
12.
PalmgrenA.Durability of ball bearingsZ. Vereins Dt. Ing., 1924, 68, 339–341.
13.
MinerM. A.Cumulative damage in fatigueJ. Appl. Mechanics, 1945, 12, 159–164.
14.
CrocombeA. D.RichardsonG.Assessing state and mean load effects on the fatigue response of adhesively bonded jointsInt. J. Adhesion Adhes., 1999, 19, 19–27.
15.
AshcroftI. A.GilmoreR. B.ShawS. J.Cyclic fatigue and environmental effects with adhesively bonded joints In Bolted/Bonded Joints in Polymeric Composites, AGARD-CP-590, 1997, pp. 14.1–14.9 (Advisory Group for Aeronautical Research and Development, Paris, France).
16.
BirtE. A.The applicability of X-radiography to the inspection of compositesInsight, 2000, 42, 152–157.
17.
Abdel WahabM. MAshcroftI. A.CrocombeA. D.ShawS. J.Diffusion of moisture in adhesively bonded jointsJ. Adhesion, 2001, 77, 43–80.
18.
ErpolatS.AshcroftI. A.CrocombeA. D.Abdel-WahabM. M.An investigation of crack growth acceleration in bonded joints subjected to variable amplitude fatigue loading. In Proceedings of the 26th Annual Meeting of the Adhesion Society, 2003, pp. 1086–9506 (Adhesion Society, Blacksburg, Virginia).
19.
Abdel-WahabM. M.AshcroftI. A.CrocombeA. D.Finite element prediction of fatigue crack propagation life-time in composite bonded jointsComposites A, 2004, 35, 213–222.
20.
RiceJ. R.A path-independent integral and the approximate analysis of strain concentration by notches and cracksJ. Appl. Mechanics, 1968, 35, 379–386.
21.
LandesJ. D.BegleyJ. A.A fracture mechanics approach to creep crack growth In Mechanics of Crack Growth, ASTM STP 590, 1976, pp. 128–148 (American Society for Testing and Materials, Philadelphia, Pennsylvania).
22.
XuX. X.CrocombeA. D.SmithP. A.Fatigue crack growth rates in adhesive joints tested at different frequenciesJ. Adhesion, 1996, 58, 191–204.
23.
Abdel WahabM. M.AshcroftI. A.CrocombeA. D.HughesD. J.ShawS. J.Prediction of fatigue threshold in adhesively bonded joints using damage mechanics and fracture mechanicsJ. Adhesion Sci. Technol., 2001, 15, 763–782.
24.
MallS.JohnsonW. S.Characterization of mode I and mixed-mode failure of adhesive bonds between composite adherends In Seventh Conference on Composite Materials: Testing and Design, 1986, ASTM STP 893, pp. 322–334 (American Society for Testing and Materials, Philadelphia, Pennsylvania).
25.
AshcroftI. A.ShawS. J.Mode I fracture of epoxy bonded composite joints. Part 2: Fatigue loadingInt. J. Adhesion Adhes., 2002, 22, 151–167.
26.
AshcroftI. A.Abdel-WahabM. M.CrocombeA.D.Predicting degradation in bonded composite joints using a semi-coupled FEA methodMechanics Advd Mater. Structs, 2003, 10, 227–248.
27.
ErpolatS.AshcroftI. A.CrocombeA. D.Abdel-WahabM. M.Fatigue crack growth acceleration due to intermittent overstressing in adhesively bonded CFRP jointsComposites A, 2004, 35, 1175–1183.
28.
Abdel WahabM. M.AshcroftI. A.CrocombeA. D.HughesD. J.ShawS. J.The effect of environment on the fatigue of bonded composite joints. Part 2: Fatigue threshold predictionComposites A, 2001, 32, 59–69.
29.
ParisP. CGomezM. P.AndersonW. E.A rational analytic theory of fatigue lifeTrend Engng, 1961, 13, 9–14.
30.
AshcroftI. A.Abdel WahabM. M.CrocombeA. D.HughesD. J.ShawS. J.Effect of temperature on the quasi-static strength and fatigue resistance of bonded composite double lap jointsJ. Adhesion, 2001, 75, 61–88.
31.
AshcroftI. A.Abdel WahabM. M.CrocombeA. D.HughesD. J.ShawS. J.The effect of environment on the fatigue of bonded composite joints. Part 1: Testing and fractographyComposites A, 2001, 32, 45–58.
