Mehdi Serati

The Brazilian disc test under a non-uniform contact pressure along its thickness

Using a three-dimensional analytical approach, the sensitivity of the Brazilian test to its standard testing recommendations was investigated. It was concluded that the tensile stress induced in a Brazilian disc is significantly affected by the distribution of the applied load along its thickness rather than its circumferential condition. Under a non-uniform contact pressure along the BTS thickness, it was evident that both the numerical value and the location of the maximum tensile stress varied as a function of the geometrical aspect ratio of the disc specimen. For test conditions in which load distribution in the contact region along the thickness does not follow the standards or the uncertainty of its exact nature is large, e.g. in testing of super hard materials with relatively high stiffness and hardness greater than the contact testing platens, great care should be taken in regard to the interpretation of the Brazilian test result.

Analytical and Numerical Study of Hard Rock Cutting With Roller Disc Cutters

Steel roller discs are an efficient mechanical tool for cutting soft to medium strength rocks in both civil and mining projects. However, their application for hard rock cutting has been hindered since steel discs wear quickly and fail prematurely due to high concentrated stresses generated at the sharp corners and thin elements of the disc. To overcome this problem, the current generation roller discs comprises a steel shaft connected to a tungsten carbide (WC) disc. In other words, while the material of the disc itself is replaced by a stronger WC material, steel continues to be used for the shaft body. In this paper, to comprehend the influence of material parameters on the induced stresses inside different parts of a roller cutter, an analytical closed-form solution and a series of finite element (FEM) numerical studies are performed. By considering the problem as a traction boundary-value problem in an elastic domain, the analytical solution is based on the Airy stress formulation in Cartesian coordinates with a Fourier series representing the boundary conditions. The analytical result is developed for both plane stress and plane strain conditions, encompassing all possible loading con?gurations and shaft geometries. To verify the numerical models, these results are also compared with laboratory experimental data obtained from cutting granite using mini discs for the penetration range 1 to 3 mm.

Roughness deterioration models for unsealed road pavements and their use in pavement management

ABSTRACT The present study aims to review the efficacy of three widely used roughness prediction models (Highway Development Model/HDM-4, Australian and South African) in the determination of blading frequencies to control roughness in the management of unsealed roads. The review comprises an assessment of the information used in the formulation of the models, the contribution of the input parameters and the effect if used in pavement management. The models are found to be based on dissimilar environmental and traffic conditions, to have relatively low coefficients of determination and variable contributions of the input parameters. The consequences are very diverse predictions of roughness and the determination of blading frequencies. The results of the assessment were used to develop blading frequency relationships using traffic volumes, rainfall category and blading cost as input for a range of commonly used models and two maintenance approaches, threshold level or user cost criteria. These relationships provide an alternative for the determination of blading frequencies if accurately calibrated models are not available.

Development and application of sustainability models for unsealed road pavements

Sustainability is a priority for most transportation and road agencies. Its measurement has progressed from a narrow environmental focus to the assessment of social, environmental, and economic outcomes. Although sealed-road sustainability assessment measures are available, measures have not been developed for unsealed road pavements despite the large networks of unsealed roads in many countries. The objective of this study was to develop models to capture sustainability measures for unsealed road pavements. This was done by relating unsealed road pavement characteristics to social (accidents and surface friction), environmental (emissions, dust pollution, and loss of resources), and economic (vehicle operating, accident, travel time, and maintenance costs) sustainability outcomes. Existing unsealed road surface characteristic prediction relationships, information presented in life-cycle cost analyses, and emissions studies were used to develop these models for rural unsealed roads. The models that were developed can be used in conjunction with existing pavement performance prediction models in life-cycle assessments, comparison of wearing course types, review of maintenance strategies, climate change consequence predictions, overall network sustainability performance reviews, and in pavement management. This paper contains a brief description of the approach, presents the models developed, and provides a number of examples of the application of the models to produce sustainability outcomes. The applications show that the models can effectively be used to quantify and compare sustainability outcomes. The applications highlight the dominance of aspects such as aggregate hauling distance in sustainability outcomes and the limitations of cost–benefit assessment procedures in which carbon emissions are not considered.

Hertzian contact damage in a hollow circular cylinder

This paper attempts to provide a theoretical framework for the determination of the stress state induced in a hollow cylinder (ring) under Hertzian compressions on its outer boundary. The solution is obtained using Airy stress functions, Michell-Fourier series expansions and Fourier-Bessel series expressions in polar coordinates. Parametric studies are also performed to investigate the influence of the loading angle and the geometrical aspect ratio of the ring on the induced stress tensor.