Abstract: Based on the twin shear unified strength theory and formaterials with different elastic moduli in tension and compression, thispaper derives unified solutions for the stress and displacementfields in a thick spherical shell in expansion. The influences of severalfactors are analyzed, including different elastic moduli in tension andcompression, different parameters in models and the development of plasticzone. The results show that the elastic ultimate expansion pressure, stressand displacement fields depend on the elastic moduli, and the modelparameters. If \alpha is less than 1, the elastic limit pressure (p_e) can be increasedsignificantly. The plastic ultimate pressure (p_r) is not related withelastic moduli, it depends on parameter (\eta) in models, and increasesfirst and then decreases with the increasing \eta . Large errors may beresulted if the classical elastic theory and the single model are adopted and thestrain-softening properties are neglected.