On the role of microstructure surface roughness and multiaxial loading on martensitic transformations in NiTi memory alloys

点击翻译按钮获取中文摘要

The objective of the research proposed here is to contribute to a better understanding of the relations between microstructural features and functional/mechanical properties of NiTi shape memory alloys. We intend to produce Ni-rich NiTi alloys with different microstructures and to study the functional and the mechanical properties of these alloys. The German partner will produce the alloys and characterize the materials in terms of differential scanning calometry (DSC) and quantitative metallography (optical microscopy, scanning electron microscopy and transmission electron microscopy). Both the German and the Chinese partner will characterise the mechanical and functional properties of the materials using miniature mechanical specimens including uniaxial tensile and compression specimens, double shear specimens, torsion specimens, torsion/compression specimens and circular notched specimens. Special emphasis will be placed on the microstructural aspects of strain and damage accumulation during mechanical testing and to the microstructural details of stress induced martensitic transformations under uniaxial and multiaxial stress states. The Chinese partner will calculate stresses and strains associated with mechanical loading of multiaxial specimens using the finite element method (FEM). To start off with the Chinese partner will implement state-of-the-art constitutive equations which allow to rationalize the shape memory behaviour into his FEM code (ABAQUS). Later, the Chinese partner will work on improved constitutive laws which will be validated on the basis of the available experimental results and which will reflect the important microstructural features.