Mechanics of Time-Dependent Materials and Processes in Conventional and Multifunctional Materials

Experiments and Models for the Time Dependent Mechanics of Nanoscale Polymeric Structures and Nanocrystalline Metal Films

To date, micro and nanoscale experiments have been mostly focused on the length scale dependent mechanical behavior of nanostructures and nanostructured thin films but have not been able to address their time and rate dependence. This inefficiency stems from the use of high resolution electron microscopes which are slow imaging tools, and quite often are […]

Study of Damage Evolution in High Strength Al Alloy using X-Ray Tomography

Many micromechanics-based damage models were developed to mimic the macroscopic response of materials through matching measures such as toughness and failure strain [1]. However, there is a lack of microstructural experimental data to identify the roles of the initiation, growth and coalescence of voids to damage and failure. This paper is aimed to experimentally investigate […]

Corrosion Behavior of SS 304 with Ball Milling and Electrolytic Plasma Treatment in NaCl Solution

Abstract Electrolytic plasma process (EPP) was used as a fast annealing treatment on ball milled surfaces. With localized melting of EPP, the surface morphology and the chemical composition can be drastically changed. Annealed, ball milled and EPP treated stainless steel 304 samples were examined and EPP treatment has been shown to improve the overall corrosion […]

Experimental Studies of Phase Transformation in Shape Memory Alloys

ABSTRACT This paper presents experimental studies to examine stress-induced martensitic phase transformation during the superelastic deformation of the shape memory alloy Nickel-Titanium. The phase transformation, which is solid-to-solid and diffusionless, occurs between austenite, a B2 cubic crystal structure, and martensite, a monoclinic crystal structure during loading and unloading at constant ambient temperature. To examine the […]

Measurement of Energy Loss in Thin Films Using Microbeam Deflection Method Part 1

ABSTRACT A technique developed for studying the energy loss behavior of submicron to nanometer scale thin metal films on substrate is presented. The test microstructure was designed the triangular cantilever beam and fabricated by the standard CMOS processes, which can improve stress distribution non-uniform problem and the thickness regime of deposited metal thin film on […]

Measurement of Energy Loss in Thin Films Using Microbeam Deflection Method Part 2

Results and discussion The internal friction of film energy loss can be measured from the dynamic response of the paddle structure provided while testing it in high vacuum (10A-6 torr). In the absence of the air damping effects, measuring the resonant response from forced vibrations can thus reveal the dynamic inelastic behavior of materials. During […]

Multiscale Characterization of Water-, Oil- and UV-Conditioned Shape-Memory Polymer under Compression

ABSTRACT Shape memory polymers (SMPs) are an emerging class of active polymers that may be used for reconfigurable structures on air vehicles. In this study, epoxy-based SMPs were conditioned separately in simulated service environments relevant to Air Force missions, namely, (1) exposure to UV radiation, (2) immersion in jet-oil, and (3) immersion in water. The […]

Shape Memory Polymer based Cellular Materials

ABSTRACT We propose the concept of periodic cellular materials with programmable effective properties and present initial results from a computational study of a prototypical material that exhibits this behavior. Nonlinear FEA shows that programmed geometric imperfections at the cell level can be used to modify the effective compressive storage modulus of shape memory polymer (SMP) […]

Influence of Mechanical Properties and Loading Conditions on the Recovery of Shape Memory Polymers

Abstract This work presented a parameter study to investigate the influence of material properties and loading conditions on the recovery performance of amorphous shape memory polymers using a recently developed thermoviscoelastic model. The model incorporated the time-dependent effects of both structural relaxation—using a nonlinear Adam-Gibbs model—and viscoelasticity. The model can predict well the unconstrained strain […]

Fatigue Cycling of Shape Memory Polymer Resin Part 1

Abstract Shape memory polymers have attracted great interest in recent years for application in reconfigurable structures (for instance morphing aircraft, micro air vehicles, and deployable space structures). However, before such applications can be attempted, the mechanical behavior of the shape memory polymers must be thoroughly understood. The present study represents an assessment of viscoelastic and […]