Dongil Son

Film-thickness considerations in microcantilever-beam test in measuring mechanical properties of metal thin film

Since metal thin films have broad applications in micromechanical devices, their mechanical properties are very important in designing and controlling such devices. In this study, the Young’s modulus and yield strength were estimated by using a microcantilever beam-bending technique. Al and Au cantilever beams of various thicknesses and lengths were fabricated by silicon bulk micromachining and were loaded in bending by a nanoindenter; displacement was simultaneously obtained at high resolution. The load–displacement data showed that the yield strengths of the two films increase with decreasing film-thickness. However, the Al and Au films showed different mechanical behaviors: the yield strength of the Au film followed the grain-size dependency of Hall–Petch type, but that of the Al film was not fully described by the grain-size effect alone. This difference arises mainly from the different surface conditions of each film. The effect of the surface on a film’s mechanical properties is discussed and a microstructure effect was suggested that a modified misfit dislocation theory used to predict the yield strength. 2003 Elsevier Science B.V. All rights reserved.

Assessing welding residual stress in A335 P12 steel welds before and after stress-relaxation annealing through instrumented indentation technique

Abstract Conventional nondestructive techniques for welding residual stress measurement have many disadvantages in the field because of poor repeatability, large scatter in data, complex procedures, inaccurate results, etc. To overcome these difficulties, an instrumented indentation technique was applied to evaluate the welding residual stress in A335 P12 steel welds in electric power-plant facilities before and after stress-relaxation annealing. Comparison of our results with stress values obtained from a destructive saw-cutting test showed that the instrumented indentation technique is very useful for quantitative/nondestructive evaluation of welding residual stresses in industrial facilities such as power-plants.

Evaluating the Mechanical Properties of MEMS by Combining the Resonance Frequency and Microtensile Methods

Tensile, fracture and fatigue properties of single- and polycrystalline silicon and LIGA-Ni were evaluated by the resonance frequency and microtensile methods. A new method for evaluating the fracture toughness that combines these two methods was proposed. A pre-crack was generated in an electrostatically driven test specimen and a load was applied by piezoelectrically driven microtensile equipment. Before the microtensile test, a new surface micromachining technique including a two-step sacrificial layer removal was used. The pre-cracked specimen was attached to microtensile equipment by a UV-adhesive glass grip. The fatigue pre-crack was successfully introduced and the fracture toughness could be derived on the basis of fracture mechanics. The fracture toughness of the pre-cracked specimen was relatively low compared with that of the notched specimen, so that we were able to determine the effect of the notch tip radius. The fatigue properties of LIGA-Ni film were also evaluated. A tensile-tensile fatigue load was applied by a piezoelectric actuator, and real-time load-displacement curves were displayed via computer. The dependence of S-N curves, crack propagation rates and fatigue-notch factor on the applied load for 10 μm Ni film was analyzed.

Evaluation of Welding Residual Stresses in Power Plant Facilities by Using a Newly Developed Indentation Technique

It is well known that residual stress is one of the important problems in welding design/fabrications and sound maintenance of welded structures. Thus, the demand for quantitative evaluation of welding residual stress has been increased. However, conventional non-destructive techniques for welding residual stress measurement have many difficulties in in-field applications according to poor repeatability, large scatter of obtained data, complex procedures, inaccurate results, and etc. To overcome these difficulties, a newly developed indentation technique was proposed in this study, and applied to evaluate the welding residual stress in electric power plant facilities. By comparing with the stress values obtained from the destructive saw-cutting test, it could be concluded that the new indentation technique is very useful for quantitative/non-destructive evaluation of welding residual stresses in industrial fields such as power plant facilities.© 2002 ASME

Advanced Indentation Techniques: NDE for Flow Properties and Residual Stresses of Pipelines

Structural integrity assessment is indispensable for preventing catastrophic failure of industrial structures/components/facilities that are faced with time-dependent and environmentally-accelerated degradation. This diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive and complex procedure of specimen sampling. So, an advanced indentation technique has been developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. Also the advanced indentation technique can evaluate residual stresses based on the concept that indentation load-depth curves were shifted with the direction and the magnitude of residual stress applied to materials. In this study, we characterized the tensile properties and welding residual stress of various Industrial pipeline steels through the new techniques, and the results are introduced and discussed.Copyright