Faculty and Staff
- Fumio Narita
We are performing the following studies on fracture and deformation of material systems in electromagnetic devices (macro-, micro-, and nano-systems) from both a theoretical and experimental point of view at some meso-scopic level.
In most of the applications as sensors and actuators in the field of microelectromechanical systems (MEMS) and smart devices, piezoelectric ceramics and magnetostrictive alloys are subjected to both high mechanical stresses and intense electromagnetic fields, hence, it is important for reliability and durability to investigate the mechanics and physics of piezoelectric/magnetostrictive material systems.
(a) Electric fracture mechanics and dynamics of piezoelectric material systems
Experimental data on the mechanical properties of piezoelectric ceramics and composites is presented considering the damage evolution, crack propagation and electromechanical behavior. From these measurements the influence of domain switching processes on the mechanical properties is deduced and a correlation between electromechanical behavior and microstructures is supposed. The experimental results are also modeled with a computer simulation of the ceramic microstructure and the observed properties for the piezoelectric ceramics and composites are reproduced by the simulation (Fig. 1).
(b) Fracture and deformation of magnetostrictive material systems
Crack tip deformations and fracture parameters in giant magnetostrictive alloys are evaluated by simulations based on the microstructural deformation and physical mechanism and by fracture experiments.
Design and development of superconducting structures require basic research on cryomechanics and magneto-solid mechanics.
(a) Electromagnetic fracture mechanics and material system design
There is a growing class of problems in solid mechanics related to new superconducting devices that employ high magnetic fields and high electric currents. The purpose of this study is to investigate some of the static and dynamic interactions that can occur between electromagnetic and elastic fields in cracked electromagnetic materials.
(b) Fracture behavior of structural alloys and weldments in cryogenic high magnetic field environments
When structural materials are subjected to magnetic field in service, the propagation of defects may result in premature failure of these materials. To prevent failure during service and to secure the structural integrity of magnetomechanical devices, understanding of the fracture behavior of structural materials is of great importance. In this study, the effect of magnetic field on the cryogenic fracture behavior of structural alloys and weldments is investigated. Mechanical tests are performed in the bore of a superconducting magnet and the magnetic fracture mechanics parameters are evaluated. The suitability of small size specimen techniques for cryogenic and magnetic fracture characterizations is also presented, and new computational techniques based on meso-scale model are proposed.
(c) Cryogenic fracture and mechanics of advanced composite materials
Glass-fiber and carbon-fiber reinforced polymer laminates are used in cryogenic devices, such as superconducting magnets in fusion energy power plants, liquid oxygen/hydrogen storage tanks in RLVs (reusable launch vehicles), etc. Understanding of the mechanical behavior of these composites at cryogenic temperatures will provide a basis for systematic development of material variants and of new materials to meet the needs of future designs. In this research, the non-linear fracture and deformation behavior of fiber-reinforced polymer laminates at cryogenic temperatures is discussed. In conjunction with the cryogenic mechanical testing, a meso- or micro-structure simulation is conducted to predict the fracture and damage properties (Fig. 2).