“Polarization increase reduces capacity” is frequently used to explain capacity fading in rechargeable batteries. To verify this empirical law, failure mode and effect analysis (FMEA) was used to identify capacity fade mechanism and derive the contribution of each failure mode in graphite–LiCoO2 cells cycled between 3.00 V and 4.35 V. The thermodynamic and kinetic attributes to the capacity fade at the material, electrode, and cell levels were quantified respectively. Loss of Li inventory dominates in the capacity fade, followed by the loss of active materials in the electrodes. The capacity loss due to the impedance increase in the cell was relatively insignificant, contrary to what often conceived. This work emphasizes the importance of using quantitative FMEA to assess cell degradation and conduct failure analysis so the contributions from material, electrode, to the cell level can be distinctly identified. The polarization increase does not affect the charge retention significantly.

No abstract

No abstract

In bidirectional ductile end diaphragm systems (EDSs) in which buckling restrained braces (BRBs) are used as the hysteretic devices to provide ductile responses to earthquake excitations, BRBs that connect the abutments to the bridge's superstructure span across the expansion joints. Therefore, these BRBs should not only be designed to resist significant forces from seismic excitations, but would also be expected to accommodate the displacements due to the expansion or contraction of the bridge as a consequence of temperature changes. Such displacement demands on the BRBs would produce cyclic stresses and strains in the BRB's core plate, and the BRB must be designed to ensure that the low-cycle fatigue of the BRB is prevented over the design life of the bridge (or periodically replaced if having shorter low-cycle fatigue life). In the absence of such a consideration, BRBs would have to be connected to the abutment in series with lock-up devices to allow thermal expansion and contraction of the bridge under normal conditions but engaged during earthquakes, which is not a desirable detail. In this study, the low-cycle fatigue analyses of BRBs across bridge expansion joints are performed by subjecting a bridge to temperature changes from various cities to determine recommended design parameters. Resulting from these analyses, the minimum ratio of BRBs' core plate yielding length over total bridge length is recommended as 3% to avoid low-cycle fatigue over 75 years of thermal changes on the bridge superstructure.

Quasi-static experiments were conducted to subject buckling restrained braces (BRBs) to a regime of relative end displacements demands to investigate if the BRBs' end connections could be able to sustain the required displacement demands when installed in bidirectional ductile end diaphragm systems (EDS). The loading protocols included the bidirectional displacement histories to be applied to the specimens for the cyclic inelastic test and the uniaxial displacement histories for the low-cycle fatigue test caused by temperature changes. Two types of BRBs with flat end plates and unidirectional pinholes, namely BRB-1 and BRB-2, were designed and tested. Four specimens of each type of BRB were tested under combinations of different displacement protocols, and the resulting BRBs' hysteretic behaviors were studied and compared. All the BRB specimens tested developed cumulative inelastic deformations of more than 200 times the BRB's axial yield displacement. The specimens were able to sustain multiple years of severe temperature cycles in addition to meeting the seismic qualification test criterion. Ultimately, as expected, all BRBs failed in tension after extensive cycles of inelastic deformations. No undesirable end-plate failure or instability was observed. A recommended design procedure for the EDS with BRBs in both straight and skew bridges was developed based on these experimental results.