Mechanical Behavior of Single Patch Composite Repaired Al Alloy Plates: Experimental and Numerical Analysis.

In this paper, glass fiber reinforced polymer (GFRP) materials were used to repair cracked Al plates. In order to study the influences of resin properties and repair configurations, three resins and two patch configurations were selected to manufacture six groups of specimens. It turned out that only little differences (less than 3%) were found in tensile strength among the six groups. Compared with the parent plates, the strength recovery ratio was higher than 80% after the GFRP repair, representing excellent repair efficiency. Moreover, a finite element model (FEM) was established to analyze the failure process of the repaired structure under tensile loading. The FEM results show good agreement with the experimental results, indicating good precision. Both the experimental and numerical work found that the damage initiated in the plies adjacent to the crack surface and the failure modes was mainly delamination and fiber breakage. This work will be meaningful for the future application of GFRP in metallic structures.

Preparation and properties studies of UV-curable silicone modified epoxy resin composite system.

INTRODUCTION: Modified epoxy suitable for ultraviolet (UV) curing is prepared by using organic silicon toughening. The curing kinetics of the composite are studied by dielectric analysis (DEA), and the two-phase compatibility of the composite is studied by scanning electron microscopy (SEM). METHODS: The tensile properties, heat resistance, and humidity resistance of the cured product are explored by changing the composition ratio of the silicone and the epoxy resin. RESULTS: SEM of silicone/epoxy resin shows that the degree of cross-linking of the composites decreases with an increase of silicone resin content. Differential thermal analysis indicates that the glass transition temperature and the thermal stability of the composites decrease gradually with an increase of silicone resin content. The thermal degradation rate in the high temperature region, however, first decreases and then increases. In general, after adding just 10%-15% of the silicone resin and exposing to light for 15 min, the composite can still achieve a better curing effect. CONCLUSIONS: Under such conditions, the heat resistance of the cured product decreases a little. The tensile strength is kept constant so that elongation at breakage is apparently improved. The change rate after immersion in distilled water at 60°C for seven days is small, which shows excellent humidity resistance.

[Analysis of hydrogen bondings in polyurethane urea cured in graded temperature field by FTIR].

Hydrogen bondings in polyurethane urea elastomer, which reflect the microphase separation, have an important effect on the properties of the elastomer. The polyurethane urea elastomers, whose degree of microphase separation changed gradually, were prepared in the graded temperature field. Hydrogen bondings in them were investigated by FTIR technology. The discussions about C=O, NH, and -O- stretching vibration spectra were given. The percentage of hydrogen bonded carbonyl groups increases with the increase in the curing temperature in the thickness direction, which indicates the increase in the degree of microphase separation in it. The degree of hydrogen bonded ether oxygen atoms exhibits obvious difference in polyurethane urea with different crosslinking degree. It is this difference that leads to a contrast changing trend of the percentage of hydrogen bonded NH in different samples. Three-dimensional hydrogen bonding between urea carbonyl and NH is stronger than the hydrogen bonding between ether oxygen atoms and NH. The stretching vibration of hydrogen bonded ether group is at about 1 076 cm(-1).