Single-family design allowables

A methodology is described that allows better performance to be achieved from previously characterized materials by appropriate statistical pooling of variance data from materials that are taxonomically grouped in the same ''family.'' A taxonomic hierarchical classification is defined from considerations of the reinforcing fiber and of the matrix. In the examples cited, one family is formed of material systems composed of PAN-precursor graphite fibers ranging from 220 GPa to 320 GPa in stiffness which are impregnated with 177 degrees C/0.7 MPa autoclave-cured epoxies. The appropriateness of data pooling is judged by a statistical equality of variance test. When the variance data is pooled, typically the design allowable values increase. An illustration shows that allowables may be increased by as much as 25 percent, achieving the effect of developing and qualifying an improved material without a large expense.