Compressive and Diagonal Tension Strengths of Masonry Prisms Strengthened with Amorphous Steel Fiber-Reinforced Mortar Overlay

A technique for strengthening masonry walls by plastering with amorphous steel fiber-reinforced mortar (ASFRM) is investigated through compressive and diagonal tension tests for masonry prisms. The vertical joint between masonry units was not completely filled with mortar to mimic poor workmanship, which is typically reflected in low-cost buildings. The test variables include the number and thickness of mortar overlays, fiber volume fraction, and additional reinforcement using glass fiber mesh or shear connectors. In most strengthened specimens, the ASFRM is not damaged but separated from the masonry prisms after its maximum strength is reached. Additional tests for the bond strength between the ASFRM overlay and masonry surface are conducted to evaluate its contribution to the strengthening effects. Based on experimental observations, equations for predicting the compressive and diagonal tension strengths of masonry prisms strengthened with ASFRM are proposed. The compressive strength can be predicted more accurately by considering the asymmetrical distribution of compressive stress when strengthening is performed on only one side. The diagonal tension strength after strengthening can be predicted by incorporating the contribution of the bond strength between the ASFRM overlay and masonry prism to the initial strength.

Femtosecond Laser Trimming with Simultaneous Nanostructuring to Fine Piercing Punch to Electrical Amorphous Steel Sheets

A CVD (Chemical Vapor Deposition) diamond coated tungsten carbide (WC) and cobalt (Co) sintered alloy punch was trimmed by the femtosecond laser machining to sharpen its edge with about 2 μm and to simultaneously make nanostructuring to its side surface. In addition to the sharpened edge, its edge profile was formed to be homogeneous enough to reduce the damage layer width by piercing the electrical amorphous steel sheet stack. Each brittle sheet in the stacked work was damaged to have three kinds of defects by piercing; e.g., the droop-like cracking in the thickness and at the vicinity of hole, the wrinkling in peak-to-valley with partial cracking on the peaks, and the circumferential cracking. When using the WC (Co) punch with the inhomogeneous edge profile in the sharpened edge width, these three damages were induced into each sheet and the maximum damage width exceeded 80 μm. When using the punch with the sharpened edge and homogeneous edge profile, the wrinkling mode was saved and the total affected layer width was significantly reduced to less than 20 μm. Through the precise embossing experiments, this effect of punch edge profile condition to the induced damages was discussed with a statement on the nanostructuring effect on the reduction of damaged width in electrical amorphous steel sheets. The developed tool with the sharpened edge and homogenous edge condition contributes to the realization of a low iron loss motor with a reduced affected layer width.

Amorphous Steel Coatings Deposited by Cold-Gas Spraying

Cold-gas spray (CGS) deposition of amorphous steel coatings starting from a commercial feedstock powder containing boron, tungsten, and silicon was investigated. Microstructural characterization, carried out by X-ray diffraction (XRD), transmission electron microscopy, and backscattered electron diffraction (EBSD) analysis, confirmed the amorphous nature of deposited coatings. The amorphization phenomenon is related to high-strain/strain-rate deformation with shear instability caused by very high particle kinetic energy, with a mechanism that resembles the severe plastic deformation process. The CGS coatings were heat-treated at temperatures ranging from 650 to 850 °C to induce partial recrystallization. The effect of nanocrystal nucleation and growth on the hardness of the coatings was investigated, and the hardness of heat-treated samples was found to increase with respect to as-sprayed coatings, outperforming conventional high-velocity oxy-fuel (HVOF) deposits. Hardness was found to decrease after prolonged (<90 min) or higher temperature (>750 °C) exposures.