Mechanics and Materials

For the past few decades, experimentally developed and calibrated forming limit diagrams (FLDs) have been used to predict the onset of necking or uncontrolled fracture in sheet metal forming. While FLDs have served a useful purpose when other alternatives were not available, the development and use of new alloys and the increased role of manufacturing process simulation have warranted the need for fundamental models that can accurately predict the onset of fracture in sheet metal forming operations. Such models can significantly accelerate the insertion of newly developed materials and can reduce material waste due to uncontrolled failure. A few models for developing failure criteria are reported in the literature; however, these models are for rate independent materials, and most have ignored the effects of crystallographic texture evolution and the effect of texture on flow strength, ductility and dynamic recovery. Therefore, the goal of this study is to develop a coupled plasticity/damage model with associated laws for microstructure evolution and anisotropic plasticity to predict temperature and rate-sensitive damage accumulation at the low stress triaxialities encountered in metal forming processes. This model will be developed to predict failure in wrought and ultra-fine grained magnesium alloys. The project also aims at identifying grain refinement approaches to improve the room temperature formability of the investigated magnesium alloys.

The ever increasing cost of energy coupled with environmental concerns, have lead the automotive industry to consider various energy saving measures. Among them, reduction of the vehicle weight as one of the most effective, provided that stringent safety regulations are maintained. Accordingly, the industry world-wide has been adopting various types of advanced high strength steels (AHSS) which, when properly designed, can have both high strength and ductility. AHSS achieve their strength by a combination of factors: grain refinement, solid solution strengthening and precipitation hardening (PH), transformation strengthening and grain boundary strengthening. Although recent advances have demonstrated the feasibility of using AHSS, there is a lack of fundamental understanding of the driving mechanisms for ductility/formability, strength and fracture/crash-worthiness and how they relate to the underlying microstructure, as well as lack of material models that relate properties to the microstructure. The objectives of this proposed work are:

1) to investigate AHSS steel (with emphasis on DP and PH) by an integrated multiscale experimental and modeling approach to understand the local deformation mechanisms,

 2) to identify the appropriate mechanical and microstructural properties that have significant influence on the local deformations, and

3) to develop fundamental understandings on key mechanical properties and microstructure features influencing the local formability.

Texas A&M University at Qatar in partnership with surgeons from Cornell Weill Medical School at Qatar is proposing a research program aimed at creating a physics-based software that will predict the deformation of surgical threads when subjected to conditions commonly encountered during surgery. Of particular interest is be the study of thread tangling, a non-linear and dynamical process detrimental to surgeons during knot formation. The software will use the Cosserat theory of elasticity, a theory particularly suited to describe long and thin flexible structures which take spiral-type configurations in addition to bend and twist. The uniqueness of the proposed work is the method of solution: a discrete optimization-based dynamic programming technique originally developed for information theory problems of text strings which will potentially reduce the computing time. We also plan an experimental phase on bending and twisting deformations of threads to validate the data with the simulations. The proposed research is interdisciplinary in nature with experts drawn from mechanical and electrical engineering, computer graphics and the medical fields. The outcomes of this research will help fill the gap in the area of medical simulations which lag far behind simulations in other fields. The software will train a new generation of medical school students and will diversify Qatar’s economy.

It is well-established that pavement subgrade soil stabilization has a major influence on pavement construction and durability and that failure to chemically alter certain subgrades in the state of Qatar has resulted in early pavement failures. In previous work sponsored by QNRF, we explored synthesizing defined polymers as candidate binders for Qatar subgrades, with encouraging practical results, which, in some cases, demonstrated quantifiable engineering advantages over traditional stabilizers including Portland cement and lime. The intended proposal will expand on this investigation. The objectives are to: better understand how the structure of the polymer relates to its efficiency as a stabilizer, particularly for Qatari subgrade soil; tailor a polymer to be compatible with a subgrade soil of defined material characteristics; to carry out mechanical testing in both the laboratory and in the field under realistic conditions (curing conditions, temperature and humidity) with the variants of the polymer binders; explore the utility of the polymer modified systems in various pavement structures compared to structures without stabilization and also with traditional stabilization alternatives using state-of-the-art models that predict pavement performance; carry out a comparative and commercial assessment of a possible candidate judged against standard alternatives, such as cement and lime.