This paper presents an analytical technique for determining the stress-strain response up to ultimate laminate failure for a laminated composite consisting of orthotropic lamina with nonlinear stress-strain behavior. The procedure, which has been programmed for a digital computer, will produce a laminate stress-strain curve up to ultimate failure. The technique is restricted to the prediction of ultimate strength for plane anisotropic laminates with midplane symmetry sub jected to biaxial membrane loads. Comparisons are made between analytical predictions and experimental results. The basic concepts of ultimate and limit strength design as applied to an advanced com posite structure are discussed.

A simple and relatively inexpensive technique is presented for determining the inplane shear stress-strain response of unidirectional composites. The method utilizes the stress-strain results from an uniaxial test on a ±45-deg laminate which is symmetrically laminated about the midplane. Through the use of relations derived from laminated plate theory, expressions are presented which allow the inplane laminae shear stress-strain curve to be incrementally reproduced from the ±45-deg laminate stress-strain curve. The simple coupon and uniaxial sandwich beam specimens, which may be utilized to obtain the data, are described. Comparisons are presented between boron/epoxy and graphite/epoxy shear stress strain curves obtained by this technique and the curves from cross-sandwich beam tests.

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The size evolution of niobium carbonitrides Nb(C,N) and the evolution of the composition of an austenitic matrix in 316Nb stainless steel were simulated using DICTRA software. For the first time, the complete nine-element composition of steel was taken into account during isothermal and even anisothermal heat treatments. A reduced model was then proposed to optimize the calculation time for complex heat treatments. The change in the mean Nb content in austenite due to Nb(C,N) evolution during different heat treatments was studied. It qualitatively agrees with experimental data as obtained by electron probe microanalysis. Furthermore, the model was successfully applied to explain the effect of heat treatments on the recrystallization behavior of 316Nb steel during hot torsion tests. Moreover, the effect of the thermodynamic database and the number of alloying elements chosen was discussed. We showed that taking into account seven or even nine elements greatly improves the accuracy compared to usual simplified compositions. The proposed method can be useful in designing heat treatments promoting or conversely hindering recrystallization for a wide variety of Nb-bearing steels.

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