Advancement in FRP composites using three-dimensional stitched fabrics and enhancement in FRP bridge deck component properties.

Use of FRP composites in construction industry has been growing rapidly. However, currently all composite products are manufactured with one and/or two dimensional fibers and fabrics (1-D or 2-D). A shortcoming thick composite (\u3e 0.75 in.) made of 1-D or 2-D fabrics is its dramatic reduction in strength, i.e., up to 50% of thin (\u3c0.5 in.) composites. This can be attributed to shear lag leading to ply-by-ply failure; in addition, premature failure of matrix and fibers or the interface failure is very common in thick composites. Therefore, the motivation of the present work is to fabricate and test composites with 3-D stitched fabrics, which overcome the limitations in composites made of 1-D or 2-D fabrics. In this study, composites were fabricated using 3-D stitched fabrics with different: (1) fiber architecture; (2) stitch density; (3) stitch material; and (4) manufacturing process. Strength and stiffness of composites with 3-D stitched fabrics (at coupon level) under tension, bending and shear loads were experimentally established and theoretically evaluated. Structural properties of composites made of 3-D stitched fabrics were compared with the structural properties of composites made of unidirectional fibers and 2-D stitched fabrics. Composites made of 3-D stitched fabrics were found to have enhanced strength and stiffness (about 30%). The existing FRP bridge deck component (first generation) was modified with respect to weight, fiber architecture and manufacturing process leading to the development of the second generation FRP bridge deck component. In the second generation FRP bridge deck component, the self-weight was reduced by about 11% without sacrificing strength and stiffness. The global stiffness of second generation FRP bridge deck component was evaluated experimentally (3 point bending test) and theoretically by Approximate Classical Lamination Theory. The ultimate stress of second generation FRP bridge deck component (30.8 ksi) was three times more than that of first generation FRP bridge deck component (10.3 ksi). The stiffness of second generation FRP bridge deck component was found to be 8.28E+08 lbs-in2/foot width while the stiffness of first generation FRP bridge deck component was found to be 8.44E+08 lbs- in2/foot. Trail second generation FRP bridge deck module has to be tested under fatigue loads

Effect of fiber architecture on properties of pultruded composites

The orientation of reinforcements in a composite system has major influence on both the elastic and inelastic properties, including failure modes. Manufacturing a polymer composite structural member can be simplified by using certain types of fiber/fabric architecture. The structural performance of a finished composite part does vary with the manufacturing process and constituent materials including fiber and resin type, fiber architecture and Fiber Volume Fraction (FVF).;In this research, the structural behavior of pultruded composite plates having different fiber architecture (uni-, bi-, tri and quadri-) manufactured by the pultrusion process is investigated. Further the mechanical properties of pultruded composites are compared with performance of composites made from compression mold. The strain energy density values of composites manufactured through compression molding and pultrusion are compared with each other so as to create a database to predict the strength and stiffness of composites. In addition, the response of pultruded composites with two different resin systems namely polyurethane and vinyl ester having same fiber architecture are evaluated.;Bi-linear stress-strain response under tension was observed for all composites except for tri-directional composites, which showed tri-linear stress-strain response up to the maximum stress. Under bending, the stress-strain response for uni- and quadri-directional reinforcements are tri-linear, while that for bi- and tri-directional reinforcements, the stress-strain curve has four linear slopes. It is observed that under tension, change in first slope took place at 29% ∼ 40% for composites with various fiber architectures (uni-, bi-, tri- and quadri-directional). In bending, it was observed that for composites with uni-directional fabrics, the change of first slope takes place at about 50% of maximum stress, in case of bi-directional the change of first slope is at 22%, and for all other fabrics i.e., tri- and quadri-directional fabrics, the change of first slope is at about 31%--34%.;The maximum tensile stress and strain in pultruded composites were mostly driven by the fiber orientation, while the maximum bending stress and strain were controlled by interface bonding of resin, fiber architecture and the process type. The ratio of bending strength to tensile strength in pultruded composites varies anywhere from 1.09 to 2.62. For a given fiber architecture, the tensile stress for compression molded plates is always higher than pultruded plates while the bending stress in pultruded composite plates is always higher than the values from compression molded plates. These anomalies are attributed to types of failure modes. With regards to resin system in pultruded composites, vinyl ester resin had more ductility and toughness compared to polyurethane resin, which is contrary to research finding of some researchers. It is likely that the vinyl ester resin is toughened or urethane modified.;The strain energy density of pultruded composites under tension is found to be the lowest value in quadri-directional fabrics compared to other fiber/fabric architecture because of the presence of off-axis plies. The off-axis plies reduce the capability of straining without failure due to stress concentration which in turn reduces the strain energy density. In bending, the strain energy density which is normalized with reference to FVF in the bending direction is within 20% difference regardless of fiber/fabric architecture

Experimental evaluation and field implementation of FRP bridge deck modules

Construction of highway bridge decks using fiber reinforced polymer (FRP) composite deck and superstructuremodules in lieu of concrete decks has proven to be feasible. However, FRPs are not widely accepted yet despite theirbenefits such as non-corrosiveness, higher strength to weight ratio, and better fatigue resistance than conventional materials.Lack of wider usage of FRP material is mainly attributed to the absence of: 1) standardized test procedures, 2) designspecifications, and 3) construction procedures. The higher initial cost is also inhibiting bridge engineers in selecting FRPmodules as highway bridge super structural systems.Implementation of FRP composites technology for highway bridge decks leads to higher safety and lower life cyclecosts. Significant ongoing research and development of FRP deck modules as illustrated herein, has proven to enhancedeck module properties in developing FRP modules with enhanced structural performance.Prodeck 4 is one such multicellular deck that was recently developed, and extensively evaluated for static and fatigueloads, and its response results are presented herein. From rigorous testing, it was concluded that Prodeck 4 could resistAASHTO HS 25 loading with maximum stringer spacing of 48 inches. This led to construction of two bridges (one in Ohioand other in West Virginia) using Prodeck 4 as decking

Teacher Motivation in India

This paper is based on a recent study on teacher motivation in India, which is part of an international research project on this topic covering 12 countries in South Asia and Africa. This study is based on review of government data, policy documents and published material on India and interviews with stakeholders in the state of Rajasthan and rapid survey in ten schools of Tonk District of Rajasthan. This report therefore draws upon national trends and explores them in the context of Rajasthan.The key issues pertaining to the motivation of primary school teachers can be summarised as follows: First, the education system has expanded rapidly and enrolment rates have shot up. But growth rate in the number of teachers has not kept pace with the rise in enrolment.Second, the social distance between the teachers and the children is wide in government schools (which cater to the very poor). Third, teachers lack the skills to manage so much diversity in the classroom. Fourth, systemic issues dealing with corruption have vitiated the larger teaching environment in the country. Fifth, teachers’ unions and block and district-level administrators claim they are asked to do a range of non-teaching taskswhich them away from the classroom. Sixth, teacher training has picked up since 1994 with almost all teachers expected to attend a range of training programmes every year. Seventh, teachers and administrators are continuously embroiled in court cases to do with promotions and placements, claiming arrears due to them and disciplinary action-related issues.teacheres, school education, teaching environment, teacher motivation, teacher training, coruption,Rajasthan, Education, Sociology, Psychology