Ian W. Johnston

Bio: Ian W. Johnston is an academic researcher from University of Melbourne. The author has contributed to research in topics: Heat pump & Geothermal energy. The author has an hindex of 25, co-authored 102 publications receiving 2413 citations. Previous affiliations of Ian W. Johnston include Monash University & Monash University, Clayton campus.

Emerging geothermal energy technologies

Abstract: Geothermal energy, whether as a source of electricity or to heat or cool buildings, has an enormous potential as a renewable energy source. This paper presents a broad overview of geothermal energy, with a focus on the emerging technologies of Enhanced Geothermal Systems (EGS) and Ground Source Heat Pumps (GSHPs). EGS and GSHP systems are important because of their potential for widespread use, as opposed to traditional geothermal energy systems which are generally limited to tectonically active regions. Commercial application of EGS technology is some years off but its enormous potential demands investment for further research. GSHP heat pump technology is available now — policy makers need to be educated and the potential of GSHPs demonstrated. Research should focus on optimising the design of the in-ground component of GSHP systems to maximise their economic, as well as environmental, benefits.

Constant normal stiffness direct shear testing for socketed pile design in weak rock

Abstract: It is demonstrated that the development of side shear resistance of piles socketed in weak rock can be controlled by conditions of constant normal stiffness. To model this behaviour and to provide ...

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

Abstract: Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

Virtual crack closure technique: History, approach, and applications

Abstract: : An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

On the micromechanics of crushable aggregates

Abstract: This paper presents a study of the micromechanical behaviour of crushable soils. For a single grain loaded diametrically between flat platens, data are presented for the tensile strengths of particles of different size and mineralogy. These data are shown to be consistent with Weibull statistics of brittle fracture. Triaxial tests on different soils of equal relative density show that the dilatational component of internal angle of friction reduces logarithmically with mean effective stress normalized by grain tensile strength. The tensile strength of grains is also shown to govern normal compression. For a sample of uniform grains under uniaxial compression, the yield stress is related to the average grain tensile strength. If particles fracture such that the smallest particles are in geometrically self-similar configurations under increasing geotoscopic stress, with a constant probability of fracture, a fractal geometry evolves with the successive fracture of the smallest grains, in agreement with the a...

ISRM-Suggested Method for Determining the Mode I Static Fracture Toughness Using Semi-Circular Bend Specimen

Abstract: The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular bend specimen is herein presented. The specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The specimens are tested in three-point bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum specimen size requirements are satisfied.