No abstract

Glasses and transparent plastics are used as daylighting face materials in buildings and vehicles. However, these transparent materials are mechanically inferior to other structural members such as metals, concretes, and fiber-reinforced plastics and have no contribution to the load-bearing capacities of whole structures incorporating them. Herein, we report clearly transparent and mechanically strong plate materials (haze 8%, strength 256 MPa) comprising solely wood-derived cellulose nanofibers (CNFs) with carboxy functionality. These plates have a millimeter thick laminated structure and are united by self-adhesive forces of the CNFs. Their strength is comparable to those of lightweight structural materials, such as aluminum alloys and glass fiberreinforced plastics, while the CNF plates are even lighter. The plates feature excellent flame self-extinguishing properties due to the carboxylate structure of CNFs and further show anisotropic thermal conduction between the in-plane and out-of-plane directions. A strategy for overcoming the high water absorption, a major issue of CNF materials, through the counterion design of carboxy groups is also demonstrated.

Thermal residual stresses developed at the time of semiconductor molding may cause serious problems both in their structural and functional performance; therefore, residual stress assessment in microelectronic devices is a mandatory evaluation step. Fluorescence piezo-spectroscopy was applied to evaluate residual stresses with a microscopic resolution inside a semiconductor encapsulant. In order to obtain reliable stress information, a low fraction of alumina powder, as a fluorescent sensor, was embedded into the silica/epoxy molding compound. Residual stress was transferred from the molding compound to the alumina phase and could be monitored by recording the shift of the sharp and intense fluorescence spectrum of Cr3+ in alumina. Two-dimensional residual-stress maps, recorded near the edge of the silicon chip, revealed a strong stress concentration in the molding compound. Experimental results were compared with calculations obtained by the linear finite element method. Such a comparison showed that the experimental stress values were systematically larger than the corresponding calculated values due to local delamination at the chip edge.

Glasses and transparent plastics are used as daylighting face materials in buildings and vehicles. However, these transparent materials are mechanically inferior to other structural members such as metals, concretes, and fiber-reinforced plastics, and have no contribution to the load-bearing capacities of whole structures incorporating them. Herein, we report clearly transparent and mechanically strong plate materials (haze 8%, strength 256 MPa) comprising solely wood-derived cellulose nanofibers (CNFs) with carboxy functionality. These plates have a millimeter-thick laminated structure and are united by self-adhesive forces of the CNFs. Their strength is comparable to those of light-weight structural materials, such as aluminum alloys and glass fiber-reinforced plastics, while the CNF plates are even lighter. The plates feature excellent flame self-extinguishing properties due to the carboxylate structure of CNFs and further show anisotropic thermal conduction between the in-plane and out-of-plane directions. A strategy for overcoming the high water absorption, a major issue of CNF materials, through the counterion design of carboxy groups is also demonstrated.

For quasi-isotropic CFRP laminates, the elastic stress-strain behavior is expected to be the same in any loading direction and stacking sequence of laminate. But fracture and strength of them may strongly depend on the loading direction and stacking sequence of laminate. The laminate has structurally made up many interfaces and the lamina in the laminate is anisotropic due to embedded fiber. Therefore, once matrix cracking or delamination takes place in the loading laminate, the laminates change into anisotropic ones. In this paper, the tensile tests were carried out in the constant displacement velocity for the specimens, cut out in several directions from each laminate, to investigate the influence of loading direction and stacking sequence on the damage pattern and tensile strength. A FEM code was used to analyze the stresses in the specimens, and the comparison between the calculated stressstrain curves and experimental ones was attempted.In addition, using Tsai-Wu failure criterion, the strength of the laminates were predicted in the various loading directions. And the correlations between the predicted results and experimental one are discussed.