Metal Foams: A Design Guide

Cyclic loading of fasteners
Cutting, finishing and joining 199
Cyclic loading leads to a response typified by Figure 15.6. At peak cyclic
loads, Fmax, below the monotonic pull-out load, Ff, the response (both for
pull-out, Equation (15.3), and for bearing loads, Equation (15.6)) is essentially
elastic until, at a critical number of cycles which depends on Fmax/Ff, the
displacement per cycle increases dramatically. This response parallels that
for fatigue of plain specimens (Chapter 8). Figure 15.7 shows a plot of load,
normalized by the monotonic pull-out load, versus number of cycles to failure,
defined as the number of cycles at the knee of the curves of Figure 15.6, for
an embedded fastner subjected to cyclic pull-out loads. It resembles the S–N
curves for metal foams, but the slope is slightly steeper, suggesting that damage
accumulates slightly faster than in the cyclic loading of plain specimens.
F max
F p
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
1
Wood screw
(Dry)
A = 0.92, α = 0.06
F max /F p = A N f −α
Wood screw
(Epoxy)
A = 1.07
α = 0.055
Insert
(Epoxy)
A = 1.10
α = 0.065
10
Number of cycles to failure, Nt 3 104 105 106 107 102 101 Figure 15.7 Cyclic peak-load plotted against number of cycles to failure for
embedded fasteners
References
Burzer, J., Bernard, T. and Bergmann, H.W. (1998) Joining of aluminum structures with
aluminum foams. In Shwartz, D.S., Shih, D.S., Evans, A.G. and Wadley, H.N.G. (eds), Porous
and Cellular Materials for Structural Application, Materials Research Society Proceedings,
Vol. 521, MRS, Warrendale, PA, USA
Olurin, O.B. Fleck, N.A. and Ashby, M.F. (1999) Joining of aluminum foams with fasteners and
adhesives. To appear in J. Mat. Sci.
Sedliakova, N., Simancik, F., Kovacik, J. and Minar, P (1997) In Banhart, J. (ed), Metallschäume,
Fraunhofer Institut für Angewandte Materialforschung, Bremen, MIT Press, pp. 177–185.