Residual Resistance Change Research Articles

Low-strain sensor based on the flexible boron-doped diamond-polymer structures

A free-standing high boron-doped diamond nanosheet (BDDNS) has been fabricated for the development of a flexible BDDNS strain senor. High boron-doped diamond was initially grown on a tantalum substrate in a microwave plasma-assisted chemical vapor deposition method, and was then transferred to a Kapton polymer substrate to fabricate the flexible BDDNS/Kapton device. Before performing the transfer process, the thin BDDNS’s morphology and bonding structure on the top and bottom surfaces were investigated using scanning electron microscopy and Raman spectroscopy. The contact potential difference and work function values of the BDDNS top and bottom surfaces were measured using a Kelvin probe atomic force microscope. Significant electrical conducting properties were observed from the resistance mapping of the BDDNS foil, and the average resistance value of 31 Ω attained from the top surface of the BDDNS foil. The electrical response of the BDDNS/Kapton device was investigated using a custom-made measurement system and a positive residual resistance change with strain was observed. The developed BDDNS/Kapton device was able to sustain for measuring up to 0.55% of strain, which indicates it may have great potential to be utilized in low-strain sensor applications.

Correlating Electrical Resistance Change with Mechanical Damage in Woven SiC/SiC Composites: Experiment and Modeling

Silicon carbide (SiC) fiber‐reinforced SiC matrix composites are inherently multifunctional materials. In addition to their primary function as a structural material, the electric properties of the SiC/SiC composites could be used for the sensing and monitoring of in situ damage nucleation and evolution. To detect damage and use that information to further predict the useful life of a particular component, it is necessary to establish the relationship between damage and electrical resistance change. Here, two typical SiC/SiC composites, melt infiltrated (MI), and chemical vapor infiltrated (CVI) woven SiC/SiC composites, were tested to establish the relationship between the electrical response and mechanical damage in unload–reload tensile hysteresis tests. Compared to the 55% resistance increase seen for CVI composites, the MI SiC/SiC composites exhibit a maximum resistance change in 450% in response to mechanical loading (damage), which is the highest sensitivity known among various composites. An analytic model accounting for fiber breakage and matrix cracks was developed to link the electrical resistance to mechanical damage in the composites. The predictions from the models agree well with the experimental data for both composites with high and low conductive matrices. The residual resistance change after unloading is also correlated to the loading history by the analytical relationship. This study demonstrates that resistance change is sensitive to damage in a predictable manner and can be used to improve the reliability of damage assessment of SiC/SiC composites.

Using controlled disorder to distinguishs±ands++gap structure in Fe-based superconductors

We reconsider the effect of disorder on the properties of a superconductor characterized by a sign-changing order parameter appropriate for Fe-based materials. Within a simple two band model, we calculate simultaneously $T_c$, the change in residual resistivity $\Delta \rho_0$, and the zero-energy density of states, and show how these results change for various types of gap structures and assumptions regarding the impurity scattering. The rate of $T_c$ suppression is shown to vary dramatically according to details of the impurity model considered. We search therefore for a practical, experimentally oriented signature of a gap of the $s_\pm$ type, and propose that observation of particular evolution of the penetration depth, nuclear magnetic resonance relaxation rate, or thermal conductivity temperature dependence with disorder would suffice.

Piezoresistance Behaviour of CFRP Cross-Ply Laminates with Transverse Cracking

This paper describes the piezoresistance behavior in CFRP cross-ply laminates with transverse cracking loaded in tension. The resistance change due to transverse cracking and the gage factor (the rate of resistance change per mechanical strain) for each transverse crack density were experimentally measured during loading/unloading cycles. The resistance change-strain curves in the unloading/ reloading processes show the bilinear behavior where two gage factors are defined as the slopes of the bilinear curve. The residual resistance change after full unloading increases almost linearly with the mechanical strain while the gage factors do not always increase with the strain. The residual resistance change and gage factors are associated with transverse crack density on the basis of an equivalent resistance circuit.

A Model for Piezoresistance Behavior in a CFRP Cross-Ply Laminate with Transverse Cracking

An electromechanical model is proposed for predicting the resistance change in CFRP cross-ply laminates with transverse cracking loaded in tension. A one-dimensional equivalent circuit model was established for describing the relation between the resistance change and mechanical strain at a given transverse crack density. A shear lag model was employed for obtaining the mechanical strain distribution. The relative resistance change-strain curve was measured for various transverse crack density and the slope and secant of the curve were defined as the gage factor and residual resistance change, respectively. Unknown functions in the model were determined using the measured residual resistance changes. The model can predict the bilinear behavior in the relative resistance change-strain curves during loading/unloading. It is found that the second residual resistance change can be the parameter for predicting transverse crack density because it increases monotonically with transverse crack density compared with the gage factors.

Anomalous Pressure Dependence of the Kadowaki-Woods Ratio and Crystal-Field Effects in Mixed-ValenceYbInCu4

The mixed-valence compound was investigated by electrical resistivity and ac specific heat at low temperatures and high pressures. At atmospheric pressure, its Kadowaki-Woods (KW) ratio A/gamma2 is 16 times smaller than the universal value RKW(=1.0x10(-5) microOmega.cm.mol2.K2.mJ-2), but sharply increases to 16.5RKW at 27 kbar. The pressure-induced change in the KW ratio and deviation from RKW are analyzed in terms of the change in f-orbital degeneracy N and carrier density n. This analysis is further supported by a dramatic change in residual resistivity rho0 near 25 kbar, where rho0 jumps by a factor of 7.

Pressure dependence of the electrical residual resistivity of disordered alloys.

The pressure dependence of the electrical residual resistivity was calculated for a series of disordered Au-Pd alloys by using the Korringa-Kohn-Rostoker coherent-potential approximation and the Kubo-Greenwood equation. The changes of the density of states and of the Fermi surface caused by an external pressure applied to the alloy are discussed and related to the change in residual resistivity. The volume coefficient of the residual resistivity is calculated from the pressure-dependent resistivity and found to be in accordance with experimental findings. \textcopyright{} 1996 The American Physical Society.

Piezoresistance response of ytterbium foil gauges shocked to 45 kbar in fused silica matrix

Resistance change at peak stress and the residual resistance change of ytterbium foil gauges embedded at different depths in fused silica matrix were determined under shock loading to a stress of 45 kbar. The results show that for a given peak stress, the gauge response was unchanged for an order of magnitude variation (103–104 kbar/μs) in the loading rate. Measured resistance change at peak stress and upon unloading agree very well with the analytic model calculations for stresses up to 30 kbar in the fused silica. Peak resistance change values in the present work have been reconciled with earlier ytterbium data in a polymethylmethacrylate (PMMA) matrix on the basis of differences in longitudinal stress in the gauge foils for the two materials (polymethylmethacrylate and fused silica) and differences in the electromechanical constants of the two sets of foils. Above 30 kbar stress in the fused silica, measured resistance values are lower than the calculated values. This difference is attributed to changes in the ytterbium as a result of the initiation of the fcc to bcc phase transition. The resistance change-time profile from the 45-kbar experiment shows a strongly time-dependent behavior suggesting that a significant fraction of the material has been transformed.

Scattering of conduction electrons by localised moments in metals

The scatiering of conduction electrons from localized ionic moments in metals was studied by observing the change in residual resistivity of samples of pure lutetiurn, into which were dissolved small amounts of magnetic rareearth metals. The results indicate that the exchange scattering of the conduction electrons is proportional to the factor (g-1)/sup 2/J(J + 1), where J is the localized ionic moment of the solute and g is the Lande factor. The magnitude of the exchange scattering is comparable with that caused by the change in the electrostatic lattice potential, due to the impurity ion. (H.D.R.)

A Study of the Annealing Kinetics in Cold Worked Copper

The resoftening kinetics for cold work in copper have been studied using residual resistance as a measure of the degree of recovery. The specimens were quickly heated to the annealing temperature, held at temperature for a measured time, and quenched for measurement. It was assumed that the cold work could be characterized by a number of lattice defects n and that the residual resistance change produced by these defects obeyed Matthiessen's rule. It was found that the resoftening could be represented by a single process of activation energy 28.3 kilocalories per mole. The complete annealing kinetics are described by a fourth-order reaction, dn/dt=−vn4e−E/RT.