Albert S. Kobayashi

Bio: Albert S. Kobayashi is an academic researcher from University of Washington. The author has contributed to research in topics: Fracture mechanics & Crack closure. The author has an hindex of 35, co-authored 202 publications receiving 5021 citations.

Handbook on experimental mechanics

Abstract: The "Handbook on Experimental Mechanics" is a comprehensive reference in the field. Since 1950, new experimental techniques, such as holography, laser speckle interferometry, optical heterodyning and modal analysis, have emerged as practical tools in the broader field of experimental mechanics. The emergence of new materials and new disciplines, such as composite materials and fracture mechanics, resulted in the evolution of traditional experimental techniques to new fields such as orthotropic photoelasticity and experimental fracture techniques. The new revised edition of the handbook includes, among other things, one new chapter on digital image processing; key sections of the handbook have been entirely rewritted or updated. The handbook should be useful to any mechanical engineer or anyone interested in stress analysis of materials.

Toughening of a Particulate-Reinforced Ceramic-Matrix Composite by Thermal Residual Stress

Abstract: The micromechanics involved in increased crack growth resistance, KR, due to the addition of TiB2 particulate in a SiC matrix was analyzed both experimentally and theoretically. The fractography evidence, in which, the advancing crack was attracted to adjacent particulates, was attributed to the tensile region surrounding a particulate. Countering this effect is the compressive thermal residual stress, which results in the toughening of the composite, in the matrix. This thermal residual stress field in a particulate-reinforced ceramic-matrix composite is induced by the mismatch in the coefficients of thermal expansion of the matrix and the particulate when the composite is cooled from the processing to room temperature. The increase in KR of the composite over the monolithic matrix, which was measured by using a hybrid experimental-numerical analysis, was 77%, and compared well with the analytically predicted increase of 52%. The increase in KR predicted by the crack deflection model was 14%. Dependence of KR on the volume fraction of particulates, fp, and of voids, fv, is also discussed.

Mechanics of crack curving and branching — a dynamic fracture analysis

Abstract: A comparative study on crack curving and branching criteria in dynamic fracture mechanics shows that the criteria based on “advanced cracking” concept correlated best with available experimental data. The crack branching criterion requires as a necessary condition, a critical dynamic stress intensity factor, K Ib, and a sufficient condition involving the crack curving criterion. The criteria are used to predict crack curving and crack branching in dynamic photoelastic experiments involving Homalite-100 and polycarbonate fracture specimens, as well as bursting steel and aluminum pipes.

Indentation Fracture Toughness of Sintered Silicon Carbide in the Palmqvist Crack Regime

Abstract: The fracture toughness of a sintered dense alpha-SiC was estimated by the Vickers indentation microfracture method in the low-load Palmqvist crack regime. It was observed that the use of simultaneously obtained Vickers hardnesses does not yield reliable fracture toughness values, nor does application of the median-crack-derived equations. It is necessary to utilize a load-independent, crack-free hardness value with this toughness estimation method. Although several of the curve-fitting equations yield similar toughnesses, it is concluded for the Palmqvist crack system in this alpha-SiC that the Niihara-Morena-Hasselman (1982) equation is the only one which yields fracture toughness values in agreement with conventional measurement techniques.

Review of low-velocity impact properties of composite materials

Abstract: This paper is a review of low-velocity impact responses of composite materials. First the term ‘low-velocity impact’ is defined and major impact-induced damage modes are described from onset of damage through to final failure. Then, the effects of the composite's constituents on impact properties are discussed and post-impact performance is assessed in terms of residual strength.

Review: Current international research into cellulosic fibres and composites

Abstract: The following paper summarises a number of international research projects being undertaken to understand the mechanical properties of natural cellulose fibres and composite materials. In particular the use of novel techniques, such as Raman spectroscopy, synchrotron x-ray and half-fringe photoelastic methods of measuring the physical and micromechanical properties of cellulose fibres is reported. Current single fibre testing procedures are also reviewed with emphasis on the end-use in papermaking. The techniques involved in chemically modifying fibres to improve interfacial adhesion in composites are also reviewed, and the use of novel fibre sources such as bacterial and animal cellulose. It is found that there is overlap in current international research into this area, and that there are complementary approaches and therefore further combining of these may make further progress possible. In particular a need to measure locally the adhesion properties and deformation processes of fibres in composites, with different chemical treatments, ought to be a focus of future research.

Vibration–based structural damage identification

Abstract: Many aerospace, civil and mechanical systems continue to be used despite ageing and the associated potential for damage accumulation. Therefore, the ability to monitor the structural health of thes...