The figure shows (i) the theoretically estimated maximum values of strength for each strengthening method applied and (ii) the strength of steel and non-ferrous metals that are used in actual structures.

Strength is the most important factor for a structural material, because higher strength makes it possible to reduce the weight of the structure. However, the strength of a material is not the sole factor that determines which material should be used. Other factors, such as corrosion resistance and formability, may determine the choice of the material. In addition, the final characteristics may differ from those of the original material after the processing and assembling.

Some examples are described below:
(i) Bend forming, press forming and weld joining are used with steel materials for structures, machinery, and automobiles. It is important that these processes should not introduce defects such as cracks. In general, the formability and weldability of steel materials tend to decrease with increasing strength.

(ii) The strength values obtained by the uniaxial tensile test are not the only criteria used to evaluate the breakage of steel materials. Under some conditions, materials will fracture under stresses which are considerably lower than the static strength value. Well-known examples include the fatigue failure under repeated loading, creep rupture under constant stress at high temperatures, brittle fracture at low temperatures, and delayed failure due to hydrogen embrittlement.

(iii) During manufacture, the characteristics of parts subjected to cold processing and welding undergo a change from those of the original material and, in general, tend to deteriorate.

(iv) Although the design thickness of a plate can be reduced by using high strength materials, the stiffness of the resulting structure may sometimes become insufficient. In this case, stiffeners need to be used and the total weight of the structure is not significantly reduced.

In choosing the material to be used for a structure, it is necessary to take the above-mentioned factors into consideration.