CAREER: Glass/Polymeric Material Systems in Civil Infrastructure

Cornell University, Ithaca NY

Investigators

Abstract

Glass windows are important for quality of life of a building's occupants, but windows can pose a hazard for the occupants when a blast load shatters them. This is a matter of increasing significance for building security. In addition, glass is an attractive structural material in settings other than windows because of its unique aesthetic appeal. This research project deals with the development of innovative models for fracture and damage to inorganic (silicate) and organic (Polymeric) glass, and to laminated windows composed of alternating layers of glass and elastomer. Chief concerns are rate dependence and accurate prediction of fragment size and velocity. The models will also account for practical issues like framing and mounting systems and realistic loads. The main scientific hurdles to be resolved are better models for rate-dependent viscoelasticity and plasticity, more efficient and accurate use of cohesive interface models for explicit modeling of dynamic crack growth, and new homogenization procedures that will capture the results of a very fine-grid cohesive finite element simulation on a coarser more computationally feasible mesh. Each of these hurdles poses interesting technical questions; for example, in the case of cohesive interface models, even the basic matter of valid ranges for the size of the elements is currently incompletely understood and will be elucidated in this research effort. The computational models will be verified using laboratory experiments by industrial and academic collaborators. An important theme in the research is bridging the various time scales: the fastest phenomenon under consideration, namely the propagation of a dynamic cracks through one process-zone length, takes place over an interval that is about 18 orders of magnitude shorter than the interval required for surface damage to accumulate. Therefore, special attention will be paid to models that are able to make accurate predictions for many different time-scales and frequencies, and to homogenization techniques that can obviate the need for very small steps. The educational aspect of the proposed CAREER plan involves the development of industrial experience for undergraduates, restructuring of an undergraduate and graduate course to include more modern coverage of strength of materials especially inelasticity, creation of a new undergraduate course on advanced structural systems to cover nonlinear material modeling, and creation of a graduate seminar on computational solid mechanics with direct links to the proposed research. For most of these courses, new case studies based on industrial practice and also new computer codes tailored for classroom use will be developed. Outcomes of the proposed research plan include computational models and methods better able to efficiently predict the safety of windows in a secure building, better models for assessing durability under naturally occurring loads like wind gusts and damage from small particles, and new insight into fracture mechanics and the effect of loading rate. Outcomes of tthe educational plan will be students with a better appreciation for the purposes and methods of modeling of materials (particularly inelastic and nonlinear) at different length and time scales, new educationally oriented finite element codes useful in a variety of classroom settings, and new instructional modules for outreach to K-12 students.