Mechanical Behavior Laboratory University of Nevada, Reno

Sergiy Kalnaus, Ph.D.

Sergiy Kalnaus

Sergiy Kalnaus, Ph.D.

Graduate Assistant

Mechanical Engineering Department,
MS 312, University of Nevada, Reno
Reno, NV, 89557, USA

Phone: 775-784-7028
Fax: 775-784-1701
Email: kalnauss@unr.nevada.edu

Education

Ph.D., Mechanical Engineering, University of Nevada, Reno, May 2009
Dissertation: Multiaxial Fatigue of Austenitic Stainless Steels, Advisor: Dr. Yanyao Jiang

M.S., Mechanical Engineering, 1998, Kharkiv State Polytechnic Institute, Kharkiv, Ukraine
B.S., Mechanical Engineering, 1996, Kharkiv State Polytechnic Institute, Kharkiv, Ukraine

Teaching

ME 303 Applied Numerical Methods. Fall Semester 2008, Fall Semester 2007.
ME 242 Dynamics. Fall Semester 2008, Spring Semester 2008.

Research




An ongoing research project dedicated to investigation of fatigue and stress corrosion behavior of Aerospace 4340 steel and 7075-T651 aluminum alloy in aqueous NaCl solutions. Both materials are used in aircraft engineering applications; 4340 steel is known for its high strength and used in parts of landing gear mechanisms and 7075-T651 possesses high strength to density ratio which makes this material ideal for structural components of an aircraft. It is generally recognized that stress corrosion cracking of high strength steels is driven by hydrogen diffusion near the crack tip or notch root. Experiments involving standard compact tension specimens subject to aqueous NaCl solutions of different concentration provide valuable information on influence of the concentration of sodium and chloride ions on the rate of stress corrosion cracking. Influence of orientation of the grains in the specimen, i.e. orientation with respect to direction of metalworking (rolling, extrusion, etc.) is also being investigated. 7075-T651 aluminum alloy show a very high degree of dependence of orientation on susceptibility to stress corrosion cracking.

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SCC Testing Equipment

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SCC Testing Equipment with QM100 Microscope

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SEM of an SCC Fracture Surface (7075-T651 Aluminum Alloy)

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The present work is focused on comparative investigation of fatigue properties of two alloys that belong to austenitic family of stainless steels: AISI 304L and AL6XN. Being classified into one category with austenitic primary phase, the alloys chosen for the investigation represent somewhat two branches in that category based on the stability of austenite under different temperatures and plastic deformation. Thus, the classical 304-type of steel with ?C ?18Cr?composition is often called a metastable austenitic alloy due to the fact that austenitic phase transforms into martensite under plastic deformation and the AL6XN alloy is termed as superaustenitic steel due to extreme stability of austenite. An extensive experimental study on fatigue and cyclic plasticity properties of two abovementioned alloys shows the differences in fatigue and fracture behavior and allows to develop stress intensity factor based model to describe the fatigue crack growth.

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Intragranular crack cgrowth from notch. Material: AL6-XN

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A critical plane multiaxial fatigue criterion was employed to predict the fatigue life of copper single crystals. The detailed stress-strain response was obtained through the constitutive modeling using a newly developed crystal plasticity theory. The constitutive model was capable of capturing the major deformation features of copper single crystals under cyclic loading including the cyclic stress-strain curves, cyclic hardening behavior, and the evolution of the hysteresis loops with increasing number of loading cycles. Fatigue life prediction of the single crystal copper was conducted based upon the stress-strain response obtained from the cyclic plasticity model. The fatigue criterion takes into account the plastic strain localization within a single crystal. The critical plane (cracking plane) was identified as the material plane where the fatigue damage accumulation first reached a critical value. For copper single crystals with the crystal orientations being within the standard crystallographic triangle, the fatigue criterion can predict both fatigue life and cracking direction consistent with the experimental observations. More importantly, the constants used in the fatigue criterion were found to be identical to those used for the pure polycrystalline copper with different grain sizes and texture.

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Schematics of Copper Single Crystal Showing the Region of Localized Plastic Deformation - Persistent Slip Band (PSB)

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Fatigue properties of carbon nano-fiber reinforced composite material and base epoxy polymer matrix have been studied in detail. Comparison of resulting strain-life curves and cyclic stress-strain curves allows to conclude that on average addition of nano-fibers to polymer matrix lowers the stresses during the fatigue loading, however at the same time it shortens the fatigue life of the material.

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Viscoelastic Response of Carbon Nano-Fiber Composite Under Cyclic Loading With Positive Mean Stress

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