Page 290 - Mechanics Analysis Composite Materials

Chapter 6. Failure criteria and strength of laminates 215

I --
I -02

02
Fig. 6.5. Failure surface corresponding to maximum stress criterion.

It can be expected that the maximum stress criterion describes adequately the
behavior of the materials in which stresses 61, a;?,and 2];?are taken by different
structural elements. A typical example of such a material is a fabric composite layer
discussed in Section 4.6. Indeed, warp and filling yarns (see Fig. 4.80) working
independently provide material strength under tension and compression in two
orthogonal directions (1 and 2), while the polymeric matrix controls the layer
strength under in-plane shear. A typical failure envelope in plane (al,~;?)for a
glass-epoxy fabric composite is shown in Fig. 6.6 (experimental data from
G. Prokhorov and N. Volkov). The corresponding results in plane (q,~n),but
for a different glass fabric experimentally studied by Annin and Baev (1979) are
presented in Fig. 6.7. As follows from Figs. 6.6 and 6.7, the maximum stress
criterion provides a satisfactory prediction of strength for fabric composites within

-1'o:H:oo
o,,MPa

CT,,MPa

00

-200
-300

Fig. 6.6. Failure envelope for glassepoxy fabric composite in plane (a,,uz). (-) maximum stress
criterion. Eqs. (6.2); (0)experimental data.