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It is not feasible for an engineer to develop a solution that accounts for all the worst case scenarios. Otherwise the developed product would became so expensive that it would not be competitive or its functioning costs would be astronomical.
Normally an engineer siezes/designs a product so that it could bear the most probable phenomenons.
Ivo is of course correct, materials for building aircraft were designed for their strength and lightness but these two features were meant purely to withstand the tests of flight and natural phenomena not the destructive power of explosives! It is also an unfortunate fact of life that if you invent something which should deter terrorists they will find a way to negate that deterrent! Presently the only answer is to keep upgrading aviation security and work towards prevention until such time as technology can produce materials with the elements required to enable flight but withstand terrorist attacks.
A very interesting question! day by day brings us new materials that are cutting edge and incredibly resilient to a lot of natural and man made phenomenon, aviation is also adapting these new materials with cautious optimism these days, i.e. carbon fiber composites, and advanced ceramics, these materials provide much better results than the existing metals and alloys but are also expensive to introduce when it comes to an assembly line environment, mainly due to the fact that they aren’t mass produced, and most of the time are made to specifications which makes them unique. plus these newly evolved materials needs to be thoroughly tested to the aviation standards, which would take time and money to achieve certification, having said that a direct answer to whether a completely impervious material will be developed or not should be left to the ambiguous, because safety is not dependent on a single new metal or a breakthrough composite. It is a combination of right practices, elimination procedures and technology ( also a sane mind ! :-) )which will reduce the risk to an acceptable percentage than completely eliminating it.
bullect reflector and bullet effect absorber are the two solutions, can solve this problems.
Composite material is used as a replacement of aluminium
The designer of composite aircraft simply uses fibers in the desired direction exactly where and in the amount required. The fibers are embedded in resin to hold them in place and provide the required support against buckling. Instead of plywood or sheet metal which allows single curvature only, the composite designer uses cloth where the fibers are laid in two directions .(the woven thread and weft) also embedded in resin. This has the advantage of freedom of shape in double curvature as required by optimum aerodynamic shapes and for very appealing look (importance of esthetics).
Today's fibers (glass, nylon, Kevlar, carbon, whiskers or single crystal fibers of various chemical composition) are very strong, thus the structure becomes very light. The drawback is very little stiffness. The structure needs stiffening which is achieved either by the usual discreet stiffeners, -or more elegantly with a sandwich structure: two layers of thin uni- or bi-directional fibers are held apart by a lightweight core (foam or "honeycomb"). This allows the designer to achieve the required inertia or stiffness.
From an engineering standpoint, this method is very attractive and supported by many authorities because it allows new developments which are required in case of war. (The U.S. having no titanium or chromium needs to develop practical alternatives.) But this method also has its drawbacks for homebuilding: A mold is needed, and very strict quality control is a must for the right amount of fibers and resin and for good adhesion between both to prevent too "dry" or "wet" a structure. Also the curing of the resin is quite sensitive to temperature, humidity and pressure. Finally, the resins are active chemicals which will not only produce the well known allergies but also the chemicals that attack our body (especially the eyes and lungs) and they have the unfortunate property of being cumulatively damaging and the result (in particular deterioration of the eye) shows up only years after initial contact.
If an aircraft has to fly then there is no material that can be used which can withstand the strongest terrorist attack. Unfortunately terrorists can even use the aircraft itself as a bomb so the most effective way is to improve on security. Even if titanium was to be used to build the whole plane it is still prone to destruction by very strong bombs. Answer is NO, unless if you want to build a concrete aircraft....
Titanium is often used in specific parts of an aircraft, for example the fan blades of the jet engines. Yet this would be very inefficient if used for the major construction of the aircraft for its weight and cost.
Yes Kevlar. Or many composite varieties. And Titanium.
