No abstract

An increase in interfacial properties between the matrix, a polyurethane cellular foam, and the reinforcement, a short carbon fibre, led to improved mechanical properties of a lightweight composite. The carbon fibre surface modification was designed with two aims: to impart magnetic properties so the discontinuous fibres could be aligned on-demand during the manufacturing process using a weak magnetic field, and to promote interfacial adhesion between the matrix and the reinforcement. After surface treatment, functionalising and coating with magnetite nanoparticles created and deposited in situ via electrodeposition prior to their deployment, the fibres were susceptible to magnetic manipulation and orientation within the reacting foam. The fibre coating contributed to interfacial compatibilization between the matrix and the reinforcement. Comparing the results between unreinforced, reinforced with untreated fibre, and reinforced with magnetised fibre, the results show that: foam reinforced with a low %vol content, i.e., from 0.1%vol to 0.4%vol, of any of the fibres improved specific strength, stiffness and toughness in tension relative to the unreinforced cellular polymeric matrix without densification, modification of cell size or compromising their lightweight properties. The magnetised fibre-containing composites showed significantly improved mechanical properties overall in tension, when compared to the untreated fibres, due to their enhanced interfacial adhesion and their alignment in the matrix. Results in compression yielded improvement only in compressive strength, with other properties being similar to the unreinforced matrices. No significant differences were observed between the magnetised (aligned fibres) and the untreated (randomly distributed) configurations in compression.

Because the susceptibility of plate material to lamellar tearing is believed to be related to the amount of reduction of area measured by a tension test specimen oriented in the through-thickness (Z) direction, tests were conducted to determine the influence of specimen dimensions on the tensile properties of ASTM A36, A588, and A514 Grade F steels for the two types of specimens commonly used for testing in the Z-direction. The first is the standard specimen with the length of the reduced section shortened so that the overall length of the specimen is equal to the thickness of the plate (stub specimen). The second is the standard specimen machined from a blank that has been prepared by welding prolongations to the plate surfaces so that the plate forms a full-plate-thickness insert at the midlength of the specimen (tab specimen). Because the intent was to compare only the trends in the changes of the tensile strength values and the reduction-of-area values for the different specimens, and because variability obtained in the longitudinal direction is less than that obtained in the through-thickness direction, the specimens were oriented in the longitudinal direction of the plate. The results indicated a significant decrease in the reduction of area and a significant increase in the tensile strength of both types of specimens as the thickness of the insert or the length of the reduced section is decreased to less than two specimen diameters. These trends are due to constraint in plastic flow caused by the higher strength of the weld area of the tab specimens or by the shoulders of the stub specimens.