Development of a transparent indenter measurement system and indentation analysis for material mechanical property evaluation

Abstract

Since Tabor showed the application of the spherical indentation approach to obtain material post-yielding true stress-strain curves, the indentation technique has been investigated to determine mechanical properties besides hardness measurement. With the development of various thin film materials, depth-sensing indentation is often applied to evaluate mechanical properties of thin film materials. However, indentation testing is a complicate mechanical process and analytical solutions are difficult to obtain. As a result, much of the understanding of the indentation process has been acquired through experiments and finite element simulations. Thus accurate measurement of indentation parameters is critical in the determination of surface mechanical properties using indentation method. In this research, a Transparent Indenter Measurement (TIM) method was developed for material inspection and mechanical property measurement. The TIM method is capable of on-site, in-situ, (i) mechanical property measurement (hardness, Young's modulus, yield strength and post-yielding stress strain data) of material samples/machined parts and (ii) qualitative inspection of material surface conditions. The residual surface deformation after spherical indentations was first investigated on IN783 superalloy samples using phase-shifting moiré and Twyman-Green interferometry. The elastic-plastic boundary was identified based on the characteristic of the out-of-plane deformation fringe patterns. Then using the measured in-plane deformation, yield strength of the tested material was obtained. Using the TIM system, real-time in-situ measurement of indentation-induced out-of-plane deformation and contact radius are directly measured during an indentation process. Coupled with elastic recovery theories and 2D finite element analyses, a procedure was developed to determine the material stress-strain curve. It is also demonstrated that the TIM method is suitable for debonding inspection of thin film materials.

Precision inspection of transparent component quality

“…Nanoindentation refers to a hardness test with a load less than 1N and the size of the indentation is in the nanometer scale. Currently, Vickers, Knoop indenters are frequently used in microindentation tests [40].…”

Development of a Spherical Micro-Indentation Test Methodology for Creep Analysis and On-set of Tertiary Creep for Solder Alloys

“…Recently a Transparent Indenter Measurement (TIM) technique has been developed [7,8], by integrating a Twyman-Green type interferometer into the spherical transparent indenter head. This system measures the indentation-induced out of plane deformation as well as the indented surface which evaluates the young's modulus without unloading stiffness.…”

“…Load displacement curve for single point unloading algorithm.3.2.2 Multiple Partial UnloadingDeveloped at West Virginia University, the first generation of instrumented indentation analysis data reduction techniques required the use of transparent sapphire spherical indenter. This transparent indenter measurement (TIM) system, with phase shifting Twyman-Green and Moir interferometer techniques directly measures the out-of-plane deformation and contact radius throughout the indentation process[21]. This technique requires the use of sophisticated optical systems to continuously measure the contact radii, which provides the platform for elastic modulus and true stress strain relationship.…”

Progression in Non-Destructive Spallation Prediction and Elevated Temperature Mechanical Property Evaluation of Thermal Barrier Coating Systems by Use of a Spherical Micro-Indentation Method

“…Average APS TBC coefficient of variation in surface stiffness response measurement with 1σ (standard deviation) shown.Described as the ratio between standard deviation and mean, Equation(15), coefficient of variation along thermal cycles is shown to increase indicating the existence of a greater division between low and high residually stressed regions within the TBC system[117]. Furthermore, all locations within a single TBC system have been subjected to the same thermal environments and thus only the variations in residual stress across the coupon are capable of producing this effect.…”

“…Developed at West Virginia University, the first generation of instrumented indentation analysis data reduction techniques required the use of transparent sapphire spherical indenter. This transparent indenter measurement (TIM) system, with phase shifting Twyman-Green and Moiré interferometer techniques directly measures the out-of-plane deformation and contact radius throughout the indentation process[15]. The variation in out-of-plane deformation and continuously measured contact radii provide a platform on which the material's elastic modulus and true stress strain relationship are found.…”