Volume 48, Issue 10

Two flat glass/epoxy test pieces were adhesively bonded to varying degree along the common width face starting from either ends to yield a set of samples i.e., sparsely bonded, moderately bonded and fully bonded ones. The samples thus prepared were subjected to low velocity impacts. Impact data show total energy and peak load registering low values for the sparsely bonded case and the value increasing as the bond area increases. Further, the stiffness parameter also showed a gradual increasing value with an enhancement in the level of interfacially introduced bond area. However, as regards the deflection, a discernible trend reversal was noticed in that it was high for the sparsely bonded case and low for fully bonded ones. Fractographic analysis showed that fully bonded ones displayed the through thickness crack propagation, tensile outward fiber failure and protrusion feature on one face while the sparsely bonded ones displayed debonding of the end region, a split and a wide opening of one of the two debonded end region with hardly any tensile outward fiber fracture features. Moderately bonded, on the other hand, showed hybrid characteristics encompassing both the outward protrusions of fibers on the tension side as well as the debonding, a feature also corroborated by the scanning electron microscopic (SEM) observations. These fracture features were analyzed and an effort made to correlate them with the impact test data.

Details of surface finish affect significantly the surface quality of ceramic specimens (e.g. surface roughness, residual stress). To analyse the influence of surface quality on strength five samples of silicon nitride specimens were machined applying different surface finishing procedures. Then they were strength tested using the biaxial Ball-on-three Balls (B3B) test. The test results were compared to those of conventional bending tests. A fractographic analysis was performed on selected specimens to identify the fracture origins. It could be shown that a better surface quality leads to an increased strength but increases the scatter of strength data too.

Although some publications have claimed that mechanical specimen preparation is inadequate for producing damage-free specimens for EBSD, this is certainly not true. Our methods have concentrated upon producing the best possible surfaces using an automated grinder-polisher with standard consumable products in a reasonable amount of time and at low cost. Furthermore, these methods are highly reproducible as demonstrated by extensive tests on many metals and alloys from aluminum to zirconium. Success depends first, and foremost, upon limiting cutting damage by using the proper blade and cutter. Next, commence grinding with the finest abrasive that will remove the cutting damage in a reasonable time and make all of the specimens in the holder co-planar. Polishing is done in counter rotation with a low holder rotational speed to keep the cloth as uniformly covered with abrasive and lubricant as possible. The grinding and polishing steps must keep the surface perfectly flat for best results. After the final polish, a general purpose etch can be applied, with the specimens in the holder, to evaluate the success of the preparation and determine what the structure is. Then, remove the etched surface by repeating the final step but with about half the required time. Preparation procedures are influenced by the crystal structure of the specimen. Face-centered cubic specimens will always exhibit more damage from each step than less ductile HCP and BCC metals and alloys.