Patricio F. Mendez

Strain energy distribution in ceramic-to-metal joints

Abstract This work introduces a framework for evaluating the strength characteristics of ceramic-to-metal joints with multiple interlayers. Strain energy in the ceramic is used as a strength metric instead of maximum tensile stress. Based on the FEM analysis and order of magnitude scaling (OMS), simple analytical formulations between the strain energy and material properties are developed, which provide a guideline in designing multiple interlayers. Our analysis reveals the important role of multiple interlayers, which reduce the strain energy in the ceramic, increasing the strength of the joint. Based on the proposed design rule, Si 3 N 4 to Inconel 718 joints have been brazed with single, double and triple interlayers and the joint strength was evaluated using a shear test. The experimental results support the design rules and confirm that strain energy is a good strength metric.

Materials Informatics

An improved semiconductor device and method of manufacturing employs interconnecting films on film circuit as ground lines which extend to the periphery of the film circuit where there is a further connection to a conductive reinforcing plate 25. Advantageously, the conductive reinforcing plate reduces electrical noise from interfering with the semiconductor device and prevents the semiconductor device from radiating undesired signals. The interconnecting films also reduce cross-talk between signal lines of the semiconductor device.

Constants for hot deformation constitutive models for recent experimental data

Abstract This paper presents previously unavailable constants for the Sellars and Tegart constitutive model for hot metalworking. The materials considered are aluminium alloys 2024, 5083, 6061, 7050, 7075 and 356, carbon steel 1018, stainless steel 304, titanium alloy 6Al–4V, and magnesium alloys AZ31 and AZ61. These materials and their mechanical properties at high temperature are of great interest for latest generation manufacturing processes involving deformation to accomplish solid state joining, such as friction stir welding, cold spray and magnetic impulse welding. The results are also useful to model established processes, such as hot rolling, forging and creep. The methodology used to obtain the constants consists on non-linear regressions based on partial data sets as it was conducted previously. The input data were obtained from published values for hot compression experiments. All regressions presented here have a coefficient of determination R 2>0·95. When possible, the results obtained were compared to previous published regressions.

Humping mechanisms present in high speed welding

Abstract As welding speeds continually increase owing to automation and newer processes, a common defect that occurs is humping. Humping is the periodic occurrence of beadlike protuberances. The objective of the present investigation is to review current and previous researches that were made on humping, including both experimental and theoretical studies. It is found that humping can be classified into two distinct categories of formation: gouging region morphology and beaded cylinder morphology. Various theories that explain the two types of humping formation are examined. Experimental data compiled from many sources are presented to verify the models and explain the fundamental mechanisms of humping morphology. Humping prevention measures that can be applied directly to industrial fabrication are also included. The direct benefit is increased travel speeds that reduce production costs.

Scaling Laws From Statistical Data and Dimensional Analysis

Scaling laws provide a simple yet meaningful representation of the dominant factors of complex engineering systems, and thus are well suited to guide engineering design. Current methods to obtain useful models of complex engineering systems are typically ad hoc, tedious, and time consuming. Here, we present an algorithm that obtains a scaling law in the form of a power law from experimental data (including simulated experiments). The proposed algorithm integrates dimensional analysis into the backward elimination procedure of multivariate linear regressions. In addition to the scaling laws, the algorithm returns a set of dimensionless groups ranked by relevance. We apply the algorithm to three examples, in each obtaining the scaling law that describes the system with minimal user input.

Characteristic Values in the Scaling of Differential Equations in Engineering

This work introduces, for the first time, a formal approach to the estimation of characteristic values of differential and other related expressions in the scaling of engineering problems. The methodology introduced aims at overcoming the inability of the traditional approach to match the exact solution of asymptotic cases. This limitation of the traditional approach often leaves in doubt whether the scaling laws obtained actually represent the desired phenomena. The formal approach presented yields estimates with smaller error than traditional approaches; these improved estimates converge to the exact solution in simple asymptotic cases and do not diverge from the exact solution in cases in which the error of traditional approaches is unbounded. The significance of this contribution is that it extends the range of applicability of scaling estimates to problems for which traditional approaches were deemed unreliable, for example, cases in which the curvature of functions is large, or complex cases in which the accumulation of estimation errors exceeds reasonable limits. This research is part of a larger effort towards a computational implementation of scaling, and it is especially valuable for approximating multicoupled, multiphysics problems in continuum mechanics (e.g., coupled heat transfer, fluid flow, and electromagnetics) that are often difficult to analyze numerically or empirically.

Non-wetting behaviour of tungsten carbide powders in nickel weld pool: new loss mechanism in GMAW overlays

Abstract This paper presents a new mechanism, observed directly for the first time, to explain low carbide fractions in Ni–WC overlays produced with GMAW. In this loss mechanism, a significant amount of powder loss is a consequence of the non-wetting behaviour of tungsten carbide. High speed videography and quantitative metallography of weld deposits are used to identify this mechanism. The non-wetting mechanism found acts simultaneously with the carbide dissolution mechanism, which until now was the only suggested cause of low carbide fraction in GMAW Ni–WC overlays. The non-wetting behaviour is observed in both short circuit and free flight metal transfer, accounting for carbide losses between 20 and 70% in the experiments performed. Low carbide fraction has prevented the mainstream use of GMAW for Ni–WC overlays, despite the advantages of simplicity, capability of in situ repair, and low capital costs. The findings presented here have a potential large impact for further consumable and process development.

3D microstructure reconstruction of chrome carbide weld overlays

Abstract This paper addresses a current debate about the morphology of M7C3 phase in the chrome carbide overlay (CCO) and white iron community. This morphology was investigated using a serial sectioning technique in combination with computer post-processing software. A 600×600×300 μm volume of CCO was reconstructed in three dimensions (3D) to determine the difference between blade and rod-like carbide morphologies. The 3D analysis revealed that the two carbides morphologies correspond to the same hexagonal rod-like structures, but are oriented in different directions relative to the sectioning plane.

Advanced Scaling Techniques for the Modeling of Materials Processing

This paper presents a formalism to automate portions of the traditional scaling procedure. This formalism, called here Order of Magnitude Scaling (OMS), captures essential components of the governing equations into a set of matrices and arrays amenable to computer implementation using standard linear algebra tools. This approach is valid and specially useful for large systems of multicoupled equations. The matrix approach proposed enables one to automate operations such as normalization, dominant balance, obtention of characteristic values, and check for self-consistency. Also, automation permits an exhaustive exploration of all possible balances and the discovery of unsuspected scaling laws. As an example, OMS is applied to the analysis of the viscous boundary layer with no external pressure gradient. The obtained scaling laws for boundary layer thickness and transverse velocity are the same as those obtained with traditional scaling, and in addition, a meaningful estimation for pressure variations within the boundary layer is obtained; this last estimation is typically not addressed in the manual analysis.

Issues associated with welding and surfacing of large mobile mining equipment for use in oil sands applications

Abstract Welding for large mobile mining equipment commonly used in the oil sands mining industry represents a unique aspect of the construction and mining heavy equipment industries. Low volume, high production capacity dominates, differing from the high volume, low production typical of the on-highway cartage automotive industry. The use of robotic welders is increasing but remains predominantly avoided due to the high cost associated with fixturing and positioning of large structural components, compounded by tolerance concerns. The main issues facing weld performance are fatigue and wear. A large portion of the ultraclass large mobile mining equipment industry focuses on fast field repair techniques, dominated by shielded metal arc welding, while in shop repairs, gas metal arc welding remains the preference.