MODELLING OF SPALL IN AN ANISOTROPIC ALUMINIUM ALLOY
TOM DE VUYST
, RADE VIGNJEVIC
, NEIL K. BOURNE
and JAMES CAMPBELL
Structures and Materials Group, College of Aeronautics, Cranﬁeld University, Cranﬁeld, BEDS,
MK43 0AL, UK (E-mail: v.rade@cranﬁeld.ac.uk);
Royal Military College of Science,
Cranﬁeld University, Shrivenham, Swindon, SN6 8LA, UK (E-mail: N.K.Bourne@Cranﬁeld.ac.uk)
(Received 4 April 2002; Accepted 8 May 2003)
Abstract. Spall caused by hypervelocity impacts at the lower range of velocities could result in signiﬁcant
damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pro-
nounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a
consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation.
The material failure observed in plate impact was simulated using a number of spall models. The Hugoniot
elastic limit and spall strength have been studied as a function of orientation, and compared to experimental
Keywords: failure criteria, high velocity impacts, non-linear ﬁnite elements, space debris, spall
The effect of orientation on the mechanical properties of metals and alloys is well known
and has been studied extensively under quasi-static conditions. This can occur on three
levels, these being at the unit cell, the microstructural level (due to preferred orientation of
the grain structure) or the meso-scale due to either phase distribution or grain morphology.
Smallman (1985) gives a more complete discussion of such behaviour. In contrast, similar
measurements made at dynamic strain-rates are not as extensive. Gray et al. (2000) inves-
tigated two types of zirconium, a cold-rolled one and annealed one. Peak stresses in the
through-thickness direction were about 2.5 times greater when compared to the in-plane
direction for the same plate for quasi-static loading regimes. In the case of shock loading,
the variation of the Hugoniot elastic limit (HEL) was consistent with the quasi-static mea-
surements. Orientation had a signiﬁcant effect on damage evolution, but a minimal effect
on the spall was observed in rear surface visar traces. Similar measurements have also been
made on a eutectoid 1080 rail steel by Gray et al. (2001). This material is crystallographi-
cally isotropic, but possesses microstructural anisotropy due to the presence of manganese
sulphide (MnS) stringers that orientate themselves along the rolling direction. It exhibited
a signiﬁcantly lower spall strength when loaded transverse to the MnS stringers than when
loaded in parallel to them.
The behaviour of aluminium alloys under shock loading has been studied in some depth
by Moshe et al. (1998) and Zheng et al. (1995). Their low densities and (in some alloys at
least) high strengths has motivated their use as light-weight armours and airframes. Possibly
the most thorough study on a single alloy was made by Rosenberg et al. (1983). Here, they
Space Debris 2, 225–232, 2000.
© 2004 Kluwer Academic Publishers. Printed in the Netherlands.