Fabrication of Wear-Resistant Ti3AlC2/Al3Ti Hybrid Aluminum Composites by Friction Stir Processing

Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result...     

Multi Response Optimization and Experimental Investigations into the Impact of Wire EDM on the Tribological Properties of Ti–6Al–4V

Titanium (Ti) alloy, Ti–6Al–4V (commonly known as Ti64), is employed in numerous applications due to their superior strength to weight ratio, low cost to performance ratio, tensile strength, and corrosion resistance properties. However, due to its poor tribological (friction and wear) properties and difficult-to-machine material, its implementation in the intended applications is limited. Nevertheless, Ti64 can be accurately machined using wire electrical discharge machining (WEDM) and further, this process develops a recast layer on the surface of Ti64, which posses larger percentage of oxygen. Therefore, in the present work, it is hypothesized that, the presence of the recast layer on the surface of Ti64 may enhance its tribological properties. To validate the proposed hypothesis, pins of (1) pure Ti64 and (2) WEDMed Ti64 were slided against EN32 steel disc on a pin on disc experimental setup for load of 50 N, rotational speed of 200 rpm and sliding distance of 500 m. In-situ analysis (scanning electron microscope and energy dispersive spectroscopy) and mechanical properties (nano-hardness and elastic modulus) were performed on the pin’s surface, to identify the change in properties. Obtained results indicated significant increase in the oxide layer formation, consequently enhanced the tribological properties of WEDMed Ti64 compared to pure Ti64. To understand the tribological behavior of WEDMed Ti64 at other rotational speed and load, second set of experiments was performed by varying load (50, 70 and 90 N) and rotational speed of (200, 400 and 600 rpm). It was observed that wear values were not proportional to increase in load and speed. To identify the condition favoring the tribological behavior, multi-response optimization technique was performed and the identified load and speed values for the optimum tribological behavior were estimated.     

Silver: An extensible attribute grammar system

Attribute grammar specification languages, like many domain-specific languages, offer significant advantages to their users, such as high-level declarative constructs and domain-specific analyses. Despite these advantages, attribute grammars are often not adopted to the degree that their proponents envision. One practical obstacle to their adoption is a perceived lack of both domain-specific and general purpose language features needed to address the many different aspects of a problem. Here we describe Silver, an extensible attribute grammar specification system, and show how it can be extended with general purpose features such as pattern matching and domain-specific features such as collection attributes and constructs for supporting data-flow analysis of imperative programs. The result is an attribute grammar specification language with a rich set of language features. Silver is implemented in itself by a Silver attribute grammar and utilizes forwarding to implement the extensions in a cost-effective manner.     

On the Modeling of Adhesive Wear with Consideration of Loading Sequence

Established models for predicting adhesive wear in sliding tribo-systems are based on the assumption that applied load remains constant. However, in many applications, load rarely remains constant—changing from low-to-high and high-to-low, or always fluctuating. Hence, the applicability of the existing wear models for prediction purposes becomes questionable. In the present work, an attempt is made to develop a wear model using the principles of thermodynamics to address this drawback. The proposed wear model establishes a relationship between the so-called degradation coefficient, load-dependent friction force, and the contact temperature. Efficacy of the proposed wear model is demonstrated by considering four cases of published data with variable loading sequence as well as additional series of ball-on-disk experiments conducted as a part of this study to validate the theory. A detailed explanation is provided to illustrate how a constant degradation coefficient value could predict the cumulative wear volume in applications dealing with variable loading while the Archard wear coefficient could not.     

Using Verified Data-Flow Analysis-based Optimizations in Attribute Grammars

Building verified compilers is difficult, especially when complex analyses such as type checking or data-flow analysis must be performed. Both the type checking and program optimization communities have developed methods for proving the correctness of these processes and developed tools for using, respectively, verified type systems and verified optimizations. However, it is difficult to use both of these analyses in a single declarative framework since these processes work on different program representations: type checking on abstract syntax trees and data-flow analysis-based optimization on control flow or program dependency graphs.We present an attribute grammar specification language that has been extended with constructs for specifying attribute-labelled control flow graphs and both CTL and LTL-FV formulas that specify data-flow analyses. These formulas are model-checked on these graphs to perform the specified analyses. Thus, verified type rules and verified data-flow analyses (verified either by hand or with automated proof tools) can both be transcribed into a single declarative framework based on attribute grammars to build a high-confidence language implementations. Also, the attribute grammar specification language is extensible so that it is relatively straight-forward to add new constructs for different temporal logics so that alternative logics and model checkers can be used to specify data-flow analyses in this framework.     

Silver: an Extensible Attribute Grammar System

Attribute grammar specification languages, like many domain specific languages, offer significant advantages to their users, such as high-level declarative constructs and domain-specific analyses. Despite these advantages, attribute grammars are often not adopted to the degree that their proponents envision. One practical obstacle to their adoption is a perceived lack of both domain-specific and general purpose language features needed to address the many different aspects of a problem. Here we describe Silver, an extensible attribute grammar specification language, and show how it can be extended with general purpose features such as pattern matching and domain specific features such as collection attributes and constructs for supporting data-flow analysis of imperative programs. The result is an attribute grammar specification language with a rich set of language features. Silver is implemented in itself by a Silver attribute grammar and utilizes forwarding to implement the extensions in a cost-effective manner.