3. Compressive Properties 　 We understand that COMPRESSIVE behaviors are rather different from those of tensile properties. When compressive load is applied in parallel with fiber axis, either fiber micro-structure disintegration or composite buckling (rupture of matrix or fiber-matrix interface rupture) occurs at break. (Fig. 3-1, 3-2) Fig. 3-1  Composite compression failure models (By Thomas Hahn) The tests of compressive property are usually so difficult that the coupon test- although very practical - cannot always tell the real status. Thus, bigger sized test object of which construction and dimensions are closer to the actual part is desirable in order to estimate the compressive behavior more accurately. Fig. 3-2 Micro-buckling of fibers in a shear crippling zone (by Thomas Hahn) Fig.3-3 shows tensile and compressive strength of various fibers (coupon). As you can see, increase of tensile strength of TORAYCA (from T300 to T800H) cannot simply assure compressive strength increase. Fig. 3-3  Tensile/Compressive strength balance Against this fact, we obtained information that a single fiber compressive strength measured by single fiber loop test increases as fiber tensile strength becomes higher. Then large discrepancies between compressive strength of single fiber and that of composite are observed There is an opinion that bigger diameter carbon fiber could show higher compressive strength. Our experiments have not confirmed this fact, but rather indicate that modest fiber diameter difference will not affect on the compressive strength (Fig.3-4) We have found that compressive strength decreases as anisotropy of fiber increases. Fig. 3-5 indicates this fact. Here, as a parameter of anisotropy Ef/Gf (fiber tensile modulus/torsion modulus) is selected