Hw Bonin

Radiation effects on aluminum-epoxy adhesive joints

Two epoxy adhesive types, Cole-Parmer and Devcon, were used for preparing aluminum-epoxy bondings. The adherend surfaces, of 30 mm in diameter, were prepared using grits of 120, 240, and 320 followed by a final grit of 400, according to the ASTM D897 standard. The curing was set at 72 h at room temperature. The samples were submitted to irradiation for different times in the pool of a SLOWPOKE-2 reactor which produced thermal neutrons, fast neutrons, and γ rays. The tensile properties of nonirradiated and irradiated samples were obtained with an Instron Tester, model 4206. The failure stress, about 11 MPa for nonirradiated samples, had a large decrease after a short period of irradiation and then constantly increased for longer irradiation periods. This may be explained by a predominant effect of crosslinking over chain scissions for higher irradiation doses. The density data and tensile properties of the bulk cured epoxy (Devcon) also supported the above findings. The presence of water on the bonding joints had an effect of exaggerating the irradiation effects on the strength of joints. The use of the adhesive failure modes to group the results into subgroups has permitted the reduction of the spread of the results from the tensile tests.

Physicochemical and Adhesion Characteristics of High-Density Polyethylene when Treated in a Low-Pressure Plasma under Different Electrodes

ABSTRACT The present investigation studys the effects of different electrodes such as copper, nickel, and stainless steel under low-pressure plasma on physicochemical and adhesion characteristics of high-density polyethylene (HDPE). To estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to low-pressure plasmas have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that the surface energy and its polar component increase with increasing exposure time, attain a maximum, and then decrease. The increase in surface energy and its polar component is relatively more important when the polymer is exposed under a stainless-steel electrode followed by a nickel and then a copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the HDPE is exposed under these electrodes, single crystals of shish kebab structure form, and the extent of formation of crystals is higher under a stainless-steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under low-pressure plasma has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. Furthermore the ESCA studies strongly emphasize that higher incorporation of oxygen functionalities are obtained when the polymer is exposed to low-pressure plasma under a stainless-steel electrode followed by nickel and then copper electrodes. These oxygen functionalities have been transformed into various polar functional groups, which have been attributed to increases in the polar component of surface energy as well as the total surface energy of the polymer. Therefore, the maximum increase in surface energy results in stronger adhesion of the polymer when the polymer is exposed under a stainless-steel electrode rather than nickel and copper electrodes.

Transverse Compressibility of a Commingled Roving

The transverse compressibility of a commingled roving composed of continuous glass and polymer fibers was measured and compared with the respective transverse compressibility of a homogeneous polymer roving and of a homogeneous glass roving. The transverse compressibility of each homogeneous roving was fitted with an existing model developed for aligned fibers. The model parameters for each of the two homogenous roving were then applied in parallel and in series to reproduce the transverse compressibility of the commingled roving. The configuration applying the homogeneous polymer and glass roving in series reproduced best the transverse compressibility of the studied commingled roving.