The aircraft was designed for a 30,000 hour service life over 15 years. Airframe heating and the high temperature properties of the primary structural materials, which were aluminum alloys, set the maximum speed at Mach 2.2.:p.49 15% by weight was titanium and 23% non-metallic materials. Titanium or stainless steel were used for the leading edges, elevons, rudder and the rear fuselage engine-exhaust heat shield.
Among metal-based biomaterials, chromium, titanium, and tantalum are to mention. The high durability of metals is exploited especially in joint prostheses, hearth valves and dental implants [91,92]. These metals are bioinert but in some cases they induce immunological responses, including allergies. Another disadvantage is that they are not biodegradable [93,94]. 1e1e36bf2d