New Science of Strong Materials: or why your feet dont fall through the floor, a book by J E Gordon.
"Like boron, this fibre has suffered from a great deal of irresponsible Government publicity.
Although frequently described by the newspapers and on television as a wonderfibre of exceptional strength, carbon fibres are not in fact, particularly strong; if anything they are a little weaker than glass fibres. They are however, for their weight, something like eight times as stiff as either glass or the normal engineering metals. As might be expected the resin-fibre composites made from carbon fibres are very stiff but not especially strong in tension. They are also, at present, rather inconveniently weak in compression. While it might be possible, in theory, to put up the compressive strength of carbon fibre composites by using a metal matrix, this does not usually work in practice because of the chemical reactions which occur between the carbon and the metal.
However, for many purposes where weight saving is important but where the strength requirements are not too critical – such as artificial limbs, golf clubshafts or the stiffening of car bodies – carbon fibre composites have been very successful.
When we turn to more exacting applications, like aircraft parts, the trouble is generally lack of toughness. When the composite is made in the conventional way the work of fracture whichis actually achieved is not far short of the calculated theoretical limit – but unfortunately this is, in practice, not sufficiently high."
Yes cynic_al aluminium has limited physical properties (toughness)
Higher strength aluminium alloys do not always have higher FRACTURE TOUGHNESS.
http://emeraldinsight.com/Insight/viewContentItem.do;jsessionid=B098E158DF7197C11F7B9EA2CEB39EA8?contentType=Article&contentId=1682514
"THE highest strength wrought aluminium alloys currently available are based on the aluminium-zinc-magnesium-copper system, and such alloys offer considerable potential for weight savings in airframe structures. However, these alloys have presented problems in service, arising from deficiencies in fracture toughness and fatigue crack propagation resistance together with a susceptibility to exfoliation corrosion and stress-corrosion, which have led to restrictions being placed on their use by individual aircraft companies and by procurement authorities in a number of countries. This situation has led to the wide-spread use in the UK and continental Europe of lower strength alloys of the aluminium-copper-magnesium-silicon type, even though significant weight penalties are incurred in the process. There has been a more general acceptance of the high strength aluminium-zinc-magnesium-copper alloys in the USA, where problems associated with their use have been partially alleviated by a willingness to replace components at short intervals, but even so during recent years a trend has developed there towards the use of lower strength versions of these alloys in attempts to improve airframe durability and reliability. "
