G.G.W Mustoe

Finite element modeling of the stresses, fracture and delamination during the indentation of hard elastic films on elastic–plastic soft substrates

In this work, the mechanical behavior of hard films on soft substrates was studied based on the finite element analysis of an indentation with normal forces. As an attempt to reproduce situations found in practice, defects were considered during the preparation of the finite element mesh, both in the film and at the interface. A sequence of steps was considered during the loading sequence applied in the models. Initially, the deposition (intrinsic) and thermal (extrinsic) stresses were introduced to account for all residual stresses present in thin films deposited by processes such as sputtering. Later, a normal load of 50 N was applied on the pre-stressed system. The effects of a crack that propagated along the film/substrate interface was studied directly, by calculating the normal and shear stresses that develop at the film surface and the film/substrate interface, and indirectly, by looking at the behavior of cracks located at the film surface and propagating perpendicular to the interface. The results indicated that the suppression of the constraint imposed by the interface resulted in a decrease in the stresses in the film. However, the crack at the interface apparently did not interact with the stresses responsible for the array of circular cracks usually observed at the contact edge of the indentation of coated systems with soft substrates.

Mechanical properties of Ti-B-C-N coatings deposited by magnetron sputtering

Abstract This work investigated structure, mechanical properties and tribological performance of the Ti–B–C–N thin films deposited using RF magnetron sputtering in different argon–nitrogen atmospheres from a TiB2–TiC composite target synthesized by a one-step SHS-consolidation technique. Quasi-amorphous nano-composite films were deposited using RF power density of 11.2 W/cm2 and a substrate bias of −50 V. In this paper, the mechanical properties of the composite films, including nanohardness, Youngs modulus, film adhesion and residual stress, are presented together with their tribological behavior. The best properties and performance were achieved by depositing the film with a 50-nm-thick titanium interlayer and using a substrate bias of 50 V. The nitrogen content in the deposition atmosphere changed the film properties and performance slightly. The Ti–B–C film and the Ti–B–C–N film deposited in an argon–nitrogen atmosphere with 10% nitrogen exhibited the best adhesion to substrate, lowest residual stress, and best tribological performance. In general, these Ti–B–C–N thin films appear to be a promising composite film system suitable for engineering wear applications.

Finite-element modeling of the stresses and fracture during the indentation of hard elastic films on elastic-plastic aluminum substrates

Abstract In this work, a three-step finite-element analysis was conducted to study the behavior of wear-resistant coatings on soft substrates. Initially, a mesh simulating a system with one hard and elastic film on an elastic-plastic aluminum substrate was developed considering the presence of cracks in the film. A sequence of loading steps was then applied to simulate the deposition (intrinsic) stresses, thermal (extrinsic) stresses and contact stresses during the indentation with normal forces, respectively. Crack propagation was allowed during the indentation step. The influence of film thickness, fracture toughness and elastic modulus was studied based on the radial and shear stresses that developed at the film surface and at the film/substrate interface. The results indicated that, under the conditions studied, film cracking was favored in systems with lower thickness and high elastic modulus. The effect of film cracking was also analyzed and a good qualitative comparison was obtained with results found in the literature.

Finite element analysis of a coating architecture for glass-molding dies

Finite element analysis (FEA) is being used as an integral part of an overall research program that is being conducted to develop a non-sticking, oxidation- and wear-resistant coating system for glass-molding dies and forming tools. This non-linear thermomechanical FEA consists of two parts: (1) a global analysis using a coupled thermomechanical model of the complete die to predict the locations where the die experiences extreme stress/strain condition during molding cycles; and (2) a local analysis of the die coating used to protect the die at those positions where extreme conditions were predicted by the global analysis, to analyze the stresses generated in the coating system during a simulated glass-molding process. This paper outlines the methodology developed in this work, which can be used to explore the effects of die geometry, die material, and coating materials on the integrity, reliability and performance of a coated die. This methodology may also be helpful for investigation of the mechanisms relating to the thermal fatigue problem. The preliminary results presented here demonstrate that it is possible to find an optimized coating architecture with optimal stress transition from the substrate to the outmost working layer by selecting appropriate coating materials and engineering the compositional gradients of the functionally graded material (FGM) intermediate layer.

Understanding the Soil Contact Problem for the LWD and Static Drum Roller by Using the DEM

The estimation of the elastic soil modulus from many in situ field test devices currently rely on the continuum theory and assumptions about linear elasticity that are somewhat ill-posed. To improve the understanding of in situ field measurement of elastic modulus using intelligent roller compactors and light-weight deflectometers (LWDs), a complete understanding of the contact problems formed through the use of these devices is needed for a wide range of soils. The varying material properties of cohesionless and cohesive soils can have dramatic effects on the assumed stress distributions, contact areas, and surface deformations. Investigations are conducted by using the discrete-element method (DEM) to investigate the relationships between soil properties and the mechanical responses for both plate (simulated LWD) and drum-roller loading. Simulations of purely cohesionless granular soils are shown to exhibit substantially different stress and strain fields compared to simulations of cohesive soils. This ...