We investigated fatigue properties and crack initiation behavior in galvanized steel when fatigue tests were conducted under conditions with controlled humidity（RH＝30% and 80%）. The fatigue strength in the low cycle（Nf ≤ 105cycles）did not increase in response to increments in humidity. However, the fatigue strength in the high cycle（Nf > 105 cycles）at RH＝80% was higher than that of RH＝30%, which was attributed to the humidity dependence of crack initiation behavior. That finding indicates that fatigue cracking is inhibited at RH＝80%. When fatigue strength was independent of humidity, several crack initiation sites were formed in the surface during the low cycle. However, when differences in fatigue strength were between RH＝80% and RH＝30%, only one crack initiation site occurred at RH＝80%, with numerous such sites at RH＝30%. These findings suggest that cracking is prone to occur at RH＝30%. Several subcracks were found in the test piece at RH＝80%. Furthermore, the subcrack number and length decreased as the number of cycles to failure increased. Some subcracks on test pieces that reached fatigue limits were closed by corrosion products consisting of ZnO and Zn（OH）2. Results show that increased fatigue strength of galvanized steel resulted from corrosion products ZnO or Zn（OH）2, which caused the cracks to close under high humidity, thereby delaying crack propagation.
This study analyzed holed structures formed in lithium iron phosphate（LiFePO4; LFP）cathodes and graphite anodes with a picosecond pulsed laser, which can remarkably improve the material’s high-rate performance. The holes in the structure have tapered shapes. During hole formation in the LFP cathode layer, a minute amount of LFP was transformed to Fe2O3 through LFP oxidation by laser irradiation. Additionally, results demonstrated that percussion drilling by the laser beam increased the LFP cathode layer porosity because the strong effect of the laser on the LFP layer evaporated the Al current collectors. After laser ablation, Al deposits formed on the hole sidewalls because of the cooling Al vapors. The increased LFP layer porosity increases the permeation of Li＋-containing electrolyte solutions into LFP layers. The three-dimensional（3D）electron pathway formed by the Al deposits on the sidewalls of holes and the Al current collector plane were regarded as improving its high-rate performance.