The Frank W. Otto Distinguished Lecture Series: Topics in Mechanical Engineering next lecture will be held on Friday, November 4, at 2:00 pm in the Simons Center for Geometry and Physics, Room 102. Emmanuel E. Gdoutos, Professor and Director of the Laboratory of Applied Mechanics at Democritus University of Thrace, Greece, will present “Failure of Sandwich and Cellular Materials.” This lecture is sponsored by the Department of Mechanical Engineering.
Abstract: Sandwich structures consisting of strong and stiff facings and light-weight cores offer improved stiffness and strength to weight ratios compared to monolithic materials. Under flexural loading the facings carry almost all of the bending, while the core takes the shear loading and helps to stabilize the facings. Facing materials include metals and fiber reinforced composites. The latter are being used in advanced applications due to the large strength-to-weight ratio. The core materials mainly include honeycombs, cellular foams and wood. In the present seminar the failure behavior of composite sandwich beams subjected to three- and four-point bending will be presented. The beams were made of unidirectional carbon/epoxy facings and various core materials including PVC closed-cell foams, a polyurethane foam and an aluminum honeycomb. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. It was established that the initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions. The crack growth behavior of polymeric foams under mixed-mode loading conditions will also be presented. Polymeric foams are anisotropic materials and crack kinking occurs even though the applied load is perpendicular to the crack plane. The stress analysis of the plate was performed by finite elements. Crack trajectories for various angles of the orientation of the axes of orthotropy of the material with respect to the applied load were obtained.