Paul C. Lam

Influence of silicon carbide particulate reinforcement on quasi static and cyclic fatigue fracture behavior of 6061 aluminum alloy composites

In this paper, the quasi-static and cyclic fatigue fracture behavior of aluminum alloy 6061 discontinuously-reinforced with fine particulates of silicon carbide are presented and discussed. The discontinuous particulate-reinforced 6061 aluminum alloy was cyclically deformed to failure at ambient temperature under stress-amplitude controlled conditions. The influence of volume fraction of particulate reinforcement on high cycle fatigue response is presented. The underlying mechanisms governing the fracture behavior during quasi-static and cyclic fatigue deformation are discussed and rationalized in light of concurrent and mutually interactive influences of composite microstructural features, deformation characteristics of the metal matrix and reinforcement particulate, nature of loading and ductility of the microstructure.

An investigation of fusion zone microstructures of welded aluminum alloy joints

Abstract Fillet weld “T” joints were produced using dissimilar aluminum alloys by a manual arc welding process. In this study, a heat treatable aluminum–magnesium–silicon alloy and a non-heat treatable aluminum–magnesium alloy were joined. The microstructure of the fusion zone was characterized by optical microscopy. Results reveal that the manual welding process produces adequate fusion, while minimizing weld structure defects.

Nonlinear transient finite element analysis of rotor-bearing-stator systems☆

Abstract This paper extends the finite element scheme to handle the highly nonlinear interfacial fields generated in the fluid filled annulli of squeeze film and journal bearings so as to model the transient response of rotor-bearingstator systems. Since such simulations are highly nonlinear, direct numerical integration schemes are employed to generate the overall response. In this context, the paper gives consideration to such items as (i) numerical efficiency/stability, (ii) comparison of implicit and explicit schemes, (iii) determines extent of response nonlinearity as well as (iv) extensively benchmarks the overall concept/methodologies.

Increasing Diversity in Engineering Academics (IDEAs): Development of a Program for Improving African American Representation.

Ethnic minorities, especially African Americans, remain underrepresented in a number of occupations, including those which might be identified as high-technology areas. Engineering is one such area where African Americans and other minorities (defined here as Hispanics and Native Americans) have been traditionally underrepresented. In the United States, approximately 3.5% of all engineers are African American, while African Americans account for about 6.4% of the college degrees, 11% of the workforce, and 12% of the total population (National Science Foundation, 1992; U.S. Department of Commerce, 1993). In 1989, the year corresponding to the decision to initiate the program described in this paper, the minority rate had increased to 9.2%, although African Americans accounted for only about 4.5% of the Bachelors degrees in engineering (Carter & Wilson, 1992; National Science Foundation, 1992). A similar pattern emerges when analyzing the fields in which dagrees were obtained, approximately 6% of the bachelors degrees attained by African Americans were in engineering, compared to 9% for Whites and 20% for Asian Americans (National Center for Education Statistics, 1989). Thus, despite some recent progress, African Americans remain underrepresented in the engineering field. While a substantial body of literature now exists concerning the

Effect of Particulate Silicon Carbide on Cyclic Plastic Strain Response and Fracture Behavior of 6061 Aluminum Alloy Metal Matrix Composites

In this paper, the cyclic stress response and cyclic stress–strain response characteristics, cyclic strain resistance and low-cycle fatigue life, and mechanisms governing the deformation and fracture behavior of aluminum alloy 6061 discontinuously reinforced with silicon carbide (SiC) particulates are presented and discussed. Two different volume fractions of the carbide particulate reinforcement phase in the aluminum alloy metal matrix are considered. The composite specimens were cyclically deformed using fully reversed tension–compression loading under total strain-amplitude-control. The stress response characteristic was observed to vary with strain amplitude. The plastic strain-fatigue life response was found to degrade with an increase in carbide particulate content in the metal matrix. The fracture behavior of the composite is discussed in light of the interactive influences of composite microstructural effects, cyclic strain amplitude and concomitant response stress, deformation characteristics of the composite constituents and cyclic ductility.

Cyclic stress response characteristics of an aluminum–magnesium–silicon alloy

Abstract In this paper, the cyclic stress response characteristics of aluminum alloy 6061 is presented. Test specimens of the alloy were cyclically deformed using fully-reversed tension–compression loading under total strain amplitude control. The alloy showed evidence of initial hardening followed by progressive softening to failure. The stress response, deformation characteristics and fracture behavior of the alloy is interactively discussed in light of the competing influences of intrinsic microstructure contributions and deformation behavior arising from a combination of mechanical and microstructural contributions.

A study of fusion zone microstructures of arc-welded joints made from dissimilar aluminum alloys

Arc welding has proven itself to be an economically affordable and efficient method for the joining of a wide variety of aluminum alloy structures that find extensive use in the industries of ground transportation and building construction. Welded joints, having a “T” configuration, in dissimilar aluminum alloys were produced using the semiautomatic arc welding process. In this study, a combination of a non-heat-treatable aluminum-magnesium alloy and a heat-treatable aluminum-magnesium-silicon alloy was successfully welded. Optical microscopy was used to characterize the fusion zone microstructures of the fillet-welded T joints. The intrinsic microstructural features and the development and presence of defects are highlighted.

Engine Dynamic Analysis with General Nonlinear Finite Element Codes Part II:Bearing Element Implementation,Overall Numerical Characteristics and Benchmarking

Second-year efforts within a three-year study to develop and extend finite element (FE) methodology to efficiently handle the transient/steady state response of rotor-bearing-stator structure associated with gas turbine engines are outlined. The two main areas aim at (1) implanting the squeeze film damper element into a general purpose FE code for testing and evaluation; and (2) determining the numerical characteristics of the FE-generated rotor-bearing-stator simulation scheme. The governing FE field equations are set out and the solution methodology is presented. The choice of ADINA as the general-purpose FE code is explained, and the numerical operational characteristics of the direct integration approach of FE-generated rotor-bearing-stator simulations is determined, including benchmarking, comparison of explicit vs. implicit methodologies of direct integration, and demonstration problems.

The Fracture Behavior of a Ti-6242 Alloy Deformed in Bending Fatigue

In this paper, the fracture behavior of the Ti-6242 alloy subjected to bending fatigue deformation is presented and discussed. Samples of the alloy were deformed to failure in bending over a range of maximum load levels. The macroscopic fracture mode was found to be marginally different over the range of load levels examined. Microscopically the fracture surfaces revealed features reminiscent of locally ductile and brittle mechanisms. The kinetics governing crack advance and fracture is rationalized in light of maximum load, local stress concentration effects, and contributions from intrinsic microstructural features.

Lung-Diaphragm Behavior of the Respiratory System During Input From Excitation

A numerical behavior of a lung-diaphragm model of a respiratory system during input from mouth pressure and diaphragm excitation is being investigated. A lung-diaphragm is subject to constant inlet air-flow conditions into the respiratory system. The mouth pressure (Macia et. al., 1997) and diaphragm excitation (Ricci et. al., 2002) are described by a constitutive relations containing nonlinearities from rib cage muscles forces and inlet air-flow conditions. Within certain operating regimes, the model exhibits self-excited pulsatile periodic motion and the qualitative features of the response can be understood in terms of the underlying model. Further, the mathematical model is a more general approach and can be used to conduct parametric studies and determine the instability mechanisms involved in the modeling of lung-diaphragm behavior of the respiratory system during input from excitation.Copyright