Papers by Keyword: Cone Crack

Abstract: The presence of surface compressive residual stress in a laminated material enhance the resistance of the component by reducing the stress intensity factors acting on the cracks -either natural or artificial- existing in the surface. Fissures in the form of cone crack are often generated by blunt contact in service, that can affect the functionality as well as the strength of the material. In this work, a two-steps analysis of the effect of residual stresses on the geometry of cone crack and how this change in geometry influences the far-field strength of the material was performed by means of a Finite Elements model and of experimental observations. In the first part, an automatic incremental model was formulated, which allowed to establish the crack shapes that were used in the second part for simple four-points test models. It was observed that residual stresses change considerably the crack shape, with important implications in the design of contact-damage tolerance, and that this reflects on corresponding changes in the strength.

Abstract: In order to investigate the effect of a confinement condition on the damage induced by a spherical impact, an experimental setup that can impact contact pressure to the specimen through a pressing die was composed. The steel and the WC balls in 3mm diameter impacted to the soda-lime glass specimen with dimension of 33×33×8m in the impact velocity range of 30m/s to 200m/s. Three different conditions are given for the impact damage investigation, which are the case without a pressing die and the cases of p=0MPa and p=200MPa with a pressing die. The stress distribution in the glass specimen by impacting the particle was also evaluated using MARC s/w system. The particle impact produced various kinds of the damage such as the ring and the cone cracks, the radial cracks and the craters. The contact pressure applied to the specimen changed stress fields in the specimen. The damage zones of the specimen without a pressing die increased as the impact velocity increased. The damage extents in the specimen with the contact pressure of 200MPa were reduced as compared with the case of those without a pressing die.

Abstract: In order to investigate the possibility of punching process of brittle material by ball impact, effects of impact angle on cone crack formation in impact-loaded soda-lime glass were evaluated experimentally. Evaluated were also contact area between specimen and sealing, and the optimal condition for cone crack formation in glass plates by impact with small steel balls. It has been found that lateral and radial cracks gradually developed asymmetrically. However, the perfect cone cracks were found to develop almost symmetrically. As the impact angle increased, the growth rate of cone cracks decreased. Regardless of the impact angle, the PMMA sealing was more effective for perfect cone formation than Aluminum and Polyurethane sealing. Thus, the application for industrial technology for hole (or nozzle) punching process of the brittle materials is expected to be feasible, based upon proper selection of sealing materials.