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Matt Pharr's picture

Variation of Stress with Charging Rate due to Strain-Rate Sensitivity of Silicon Electrodes of Lithium Ion Batteries

Silicon is a promising anode material for lithium-ion batteries due to its enormous theoretical energy density. Fracture during electrochemical cycling has limited the practical viability of silicon electrodes, but recent studies indicate that fracture can be prevented by taking advantage of lithiation-induced plasticity. In this paper, we provide experimental insight into the nature of plasticity in amorphous LixSi thin films. To do so, we vary the rate of lithiation of amorphous silicon thin films and simultaneously measure stresses.

Scanning AC nanocalorimetry study of Zr/B reactive multilayers

The reaction of Zr/B multilayers with a 50 nm modulation period has been studied using scanning AC nanocalorimetry at a heating rate of approximately 1,000 K/s. We describe a data reduction algorithm to determine the rate of heat released from the multilayer. Two different exothermic peaks are identified in the nanocalorimetry signal: a shallow peak at low temperature (200 - 650°C) and a sharp peak at elevated temperature (650 - 800°C).

Gi-Dong Sim's picture

High-temperature tensile behavior of freestanding Au thin films

In this paper, the mechanical behavior of freestanding thin sputter-deposited films of Au is studied at temperatures up to 340°C using tensile testing. Films tested at elevated temperatures exhibit a significant decrease in flow stress and stiffness. Furthermore the flow stress decreases with decreasing film thickness, contravening the usual notion that “smaller is stronger”. This behavior is attributed mainly to diffusion-facilitated grain boundary sliding.

This paper has been accepted by Scripta Materialia.

Widusha Illeperuma's picture

Force and stroke of a hydrogel actuator

Hydrogels that undergo a volume phase transition in response to an
external stimulus are of great interest because of their possible use as
actuator materials. The performance of an actuator material is normally
characterized by its force–stroke curve, but little is known about the
force–stroke behavior of hydrogels. We use the theory of the ideal
elastomeric gel to predict the force–stroke curves of a
temperature-sensitive hydrogel and introduce an experimental method for
measuring the curve. The technique is applied to PNIPAm hydrogels with
low cross-link densities. The maximum force generated by the hydrogel
increases with increasing cross-link density, while the maximum stroke

Kamyar M Davoudi's picture

Dislocation Climb in Two-Dimensional Discrete Dislocation Dynamics

In this paper, dislocation climb is incorporated in a two-dimensional discrete dislocation dynamics model. Calculations are carried out for polycrystalline thin films, passivated on one or both surfaces. Climb allows dislocations to escape from dislocation pile-ups and reduces the strain-hardening rate, especially for fully passivated films. Within the framework of this model, climb modifies the dislocation structures that develop during plastic deformation and results in the formation of pile-ups on slip planes that do not contain any dislocation sources.

Gi-Dong Sim's picture

Fatigue of polymer-supported Ag thin films

The fatigue behavior of Ag films on polyethyleneterephthalate substrates was studied using electrical resistance measurements.
Scanning electron microscopy images showed two types of failure: typical fatigue failure with extrusion–intrusion pairs, and ductile
failure with local necking. Once through-thickness cracks are formed in the metal layer, cracks propagate and the resistance increases abruptly for both failure modes. The effect of adhesion on fatigue life is discussed in terms of concurrent delamination, crack initiation and propagation.

Gi-Dong Sim's picture

Improving the stretchability of as-deposited Ag coatings on poly-ethylene-terephthalate substrates

In this paper, we report that silver films evaporated on poly-ethylene-terephthalate (PET) substrates coated with an acrylic primer can be stretched beyond 70% without fracture. As-deposited films show a larger failure strain than annealed coatings. These observations are rationalized in light of a ductile fracture mechanism where debonding from the substrate coevolves with strain localization. The results of this study indicate that PET substrates coated with an acrylic primer layer may be suitable for stretchable electronics.

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