Papers by Keyword: Phenomenological Theory

Abstract: The presented paper delas with constitutive equations of the linear theory of viscoelasticity. The integral representations for homogeneous isotropic medium located in isothermal conditions are introduced. Relations are derived for the relaxation and creep processes, as well as relations between these functions in the Laplace images. In the solution we assume quasi-static external force loading under which the analyzed viscoelastic body in each time t shows infinitesimal deformations. General isotropic tensor of fourth degree G_ijkl (t) we use to derive the relationship between deviator stress and deformation, as well as the relations between stresses and distortions that produce volumetric changes. It is shown that for the linear viscoelastic problem can be used Stieltjes convolution and its algebraic properties. Derived relations and procedures followed to the results of differential-operator's representation of constitutive equations of linear viscoelasticity theory that have been published in the previous work of Authors.

Abstract: The titanium alloys containing the Nb transition elements have been investigated as the Ni-free shape memory and the biomedical alloys with a low elastic modulus. The mechanical properties of the alloys depended upon the meta-stable phases like the α`, α``, ω. To study the martensitic transformations from the β to α`` or α` the Ti-xNb (x=0 to 40 wt%) alloys were melted into the button type ingots using a VAR, and followed by the water-quenching after the soaking at 1000oC for 2hrs. The crystallography of the martensitic phases in the water-quenched alloys was analyzed using a XRD. The diffraction peaks of the orthorhombic martensites were identified by the crystallographic relationship with the bcc matrix. The lattice parameters of the orthorhombic martensites were varied continuously with the contents of the Nb elements. The martensitic transformations of the alloys were studied using the phenomenological theory of Bowles and Mackenzie.